;■ :;;: HB Isi ■:■. ' ■■-■■ ''....'■' • ' PESTS OF PEAR IN CALIFORNIA HAROLD F. MADSEN MARTIN M. BARNES CALIFORNIA AGRICULTI Pest control in pears requires There are some thirty insect and mite pests which attack pears in California. Proper identification is the key to intelligent control in pear orchards. The ten most important ones that attack pears over a wide area, are the European red mite, the two spotted mite, pear psylla, pear leaf blister mite, orange tortrix, codling moth, consperse stink bug, Baker's mealybug, pear thrips, and San Jose scale. To facilitate field identification, pear pests described in this cir- cular are classified into several groups according to the parts of the tree which they attack. But such a classification is only a convenient means of separating the pests, and may not always reflect their com- plete effects upon the crop. A foliage feeder, for example, can cause severe leaf damage or defoliation and, as a result, the fruit may fail to mature. A knowledge of the life history and habits of the species involved is necessary in order to obtain effective control of most of the pests which attack pear. Proper timing of spray applications is extremely important, because most of the control practices are preventive in nature. In producing a crop of pears, it is not possible to wait to see if infestations of certain pests will develop, since by that time, the damage will be done. For example, a grower must protect his fruit from codling moth damage by applying chemicals before the larvae hatch from the eggs and enter the fruit. Once the larvae have entered the fruit it is no longer possible to prevent damage. Certainly no grower wishes to apply chemicals continuously for pest control. In many instances, haphazard and too frequent appli- JUNE, 1959 L2] year round program cations can bring about increased populations of some pests. A sound control program should be based not only on the use of the proper chemical, but also on a thorough understanding of the biology and habits of the particular pest species involved. Without such infor- mation, many control practices would be hit and miss, with erratic results and a waste of materials and money. Cultural practices should not be overlooked, as it is often possible to reduce pest populations by their use. Natural enemies, parasites, and predators, play an important role in holding populations of destructive pests under control. Though it is not always possible to wait for parasites and predators to reduce pest populations, in many cases they can keep pests below economic levels. Parasites which attack the European fruit lecanium are an example of this, for they may often hold this scale species under con- trol. An unnecessary application of insecticides would not only be without profit in itself, but might well destroy the parasites and bring about an outbreak of the scale. In this circular, each pest will be discussed from the standpoint of its appearance, seasonal development, and the injury it causes. Specific suggestions for chemical control will not be given. These change constantly and can be found in the spray, dust, and fumiga- tion programs which are issued each year and are available at the local University of California Farm Advisor office. It is hoped, how- ever, that a better understanding of the pests attacking pear will lead to a sounder program of control. THE AUTHORS: Harold F. Madsen is Lecturer in Entomology and Associate Entomologist in the Experiment Station, Berkeley; Martin M. Barnes is Associate Entomologist in the Citrus Experiment Station, Riverside. [3] Pests that attack . . . The fruit Codling moth 5 Consperse stink bug 9 The foliage European red mite 11 Two-spotted mite 12 Brown mite 14 Bean thrips 15 Pear psylla 16 Aphids 18 Tentiform leaf miner 19 Pear sawfly 21 Pear-slug 22 Foliage and fruit Pear leaf rust mite 23 Pear leaf blister mite 24 Grape mealybug 25 Fruit tree leaf roller 27 Orange tortrix 28 Cankerworms 29 Flowers and fruit Pear thrips 30 Twigs and limbs European fruit lecanium 31 Calico scale 33 San Jose scale 34 Italian pear scale 35 Buffalo tree hopper 36 American plum borer 37 Shot-hole borer , 37 Pacific flatheaded borer 38 The roots Woolly pear aphid 40 [4] PESTS of PEAR in CALIFORNIA HAROLD F. MADSEN MARTIN M. BARNES PESTS THAT ATTACK THE FRUIT CODLING MOTH There can be no doubt that the cod- ling moth, Carpocapsa pomonella Linn., is the principal insect pest of pears both historically and at the present time. It is distributed over the state wherever pears are grown, and with the exception of some of the high mountain areas, it is a major pest in all districts. Prior to 1945, the codling moth was difficult to control even with five to seven sprays per season, but following the introduc- tion of DDT, codling moth damage has been greatly reduced. This insect is a constant threat, and a regular seasonal spray program must be directed against it. Appearance The adult has a wing expanse of about % to % inch. The forewings are brown- ish with several gray cross lines and near the tip of each is a coppery spot. The hind wings are pale gray with fringed borders. The presence of this coppery spot at the tip of each forewing serves to distinguish the codling moth from other moths associated with pears. The eggs are small and disklike, opaquely white when first laid, and are deposited on the leaves and fruit. As they mature, the eggs develop a red ring, and just before hatching the black head of the larva may be seen. The newly hatched larvae are white with a black head. When mature, the larvae attain a length of % to % inch, and are pinkish white in color with a mottled brown head. Injury The damage done by the codling moth is restricted to the fruit. Larvae bore through the skin and usually penetrate to the core, where they consume the seeds and other tissues in this general area. The presence of one or more holes in the fruit, which are plugged with frass, is a characteristic sign of codling moth attack. The larvae may enter through (Continued on page 8) Adult codling moth. [5] Pear psylla nymph, showing red eyes, yellow body with dark brown markings. This coloring distinguishes the pear psylla from immature aphids or whiteflies. For better identification the color photos shown here will help to identify several important pests of pears and/or the damage they do. These par- ticular pests are often distinguishable from other similar pests only by the color pat- terns they make on fruit, leaves, or twigs. San Jose scale is distinguished by red spots on the fruit associ- ated with depressions in the skin. Pear rust mite damage is iden- tified by completely russeted brown fruit, as compared with the normal green pear in the center. [6] Italian pear scale's red body is always asso- ciated with green moss and lichens. This is its one distinguishing feature. Pear psylla eggs. Note the yellow color and beadlike appearance of the eggs against the dark pear bark. Brown mite eggs may be identified by their red coloring and roundness. They are usually found in conjunction with old, white hatched eggs. [7] Wm,, Left, fruit cut open to show codling moth larvae. Right, young fruit showing codling moth entries. the sides, stem end, or calyx end of the pear. Entries through the calyx end are hard to see and are often referred to as "invisible worms." Larvae often pene- trate a short distance into the fruit, where they may die either from insecti- cides or natural causes. These shallow entries are called stings. Fruits attacked by the codling moth are classed as culls and cannot be used for either fresh shipment or by the can- nery. Tonnage of fruit may be reduced to a significant extent by the codling moth, and this may mean the difference between profit and loss on the season's crop. Seasonal development The codling moth winters as mature larvae in cocoons beneath the bark scales of the trunk and main limbs of the tree. They may also overwinter in such pro- tected places as wounds, crotches, or in the litter on the ground. Pupation takes place in the spring, and the first adults emerge in April about the time that the trees have passed the blossom stage. The first brood of moths emerge over a con- siderable period, extending to early June. After emergence is well underway, codling moth flight activity is highest during periods with quiet evenings and when the temperature is favorable. At least three flights occur during a normal season, and the peak of each flight may be detected with the aid of bait pans. The moths are most active at dusk and mating as well as egg laying takes place during the twilight hours. More eggs are laid in the upper half of the tree than in the lower half. The eggs are laid singly on fruit and leaves, and on hatching, the larvae wander for a period before they enter the fruit. When mature, they leave the fruit and pupate in any convenient sheltered spot on the tree. A second gen- eration is produced during July, and on late pear varieties, such as Winter Nelis, a partial third brood may emerge in Sep- tember. About 50 days are required to complete a life cycle, and this period will vary in length with the temperature. Control program Before the introduction of DDT, cod- ling moth sprays were timed by means of bait pen catches. The first spray ap- plication is now made during petal fall, or even by calendar date in April. Later sprays are spaced 25 to 30 days apart. On most varieties, three applications have been sufficient to obtain seasonal [8] control. The timing of sprays is adjusted so that active spray residues cover the fruit at the time the larvae are active and by concentrating on the first brood, there is sometimes no need to protect against a second brood. In the last few years, there has been an increasing number of reports from grow- ers about difficulty in controlling the codling moth. A few of these cases have been related to a change in the flight pattern of the moths. In some cases it is possible that the pest has acquired a resistance to DDT. In the first case, the use of bait pans may be necessary to re- adjust the timing of treatments, and in the latter case, it is necessary to use some pesticide other than DDT. Correct timing and thorough coverage are essential in a well planned and suc- cessful seasonal spray program directed against the codling moth. CONSPERSE STINK BUG The consperse stink bug, Euschistus conspersus Uhler, is a relatively new pest of pears, as it was first recognized as a problem in 1950. The distribution of this stink bug is statewide, but it occurs in damaging numbers on pears principally in the foothill districts of northern Cali- fornia. The bug is associated with cover crop and uncultivated areas, therefore it is rarely a pest where pears are clean cultivated and surrounded by well-culti- vated land. Appearance The adult stink bug is approximately V2 inch long, shield-shaped, gray brown in color, with the legs and antennae yel- low, and covered with small black dots. The underside of its body varies from gray to green. The nymphal stages vary in color from black and white in the early instars to various combinations of yellow and brown in the late instars. The eggs are barrel shaped and are laid in clusters of 7 to 20. When first laid they are pearly white in color with Adult consperse stink bug. a ring of dark spines at the top, and then turn pink before they hatch. Injury The feeding of the bugs on the ma- turing pears produces white corky areas under the skin of the fruit. When peeled, these spots turn brown on exposure to the air. The spots are too deep to be re- moved by ordinary peeling practices. If the pears are punctured when they are almost mature, there will be little evi- dence of attack other than the presence of excrement spots on the fruit surface. If the damage is done earlier, dimples, or irregular depressed areas, will be evi- dent. The bugs feed near the stem end of the pears, therefore most of the corky spots will be located from the middle of the pear to the stem. A single bug moves from tree to tree and punctures a large number of fruits. If the bugs are migrating into the or- chards, the outside rows will show most of the damage. The attack of the con- sperse stink bug can be very serious, and in heavy infestations an entire crop can be lost for both shipping and canning outlets. [9] Left, depressed areas are the result of stink bug attack. Right, peeled pear showing corky spots the result of stink bug feeding. Seasonal development Stink bugs overwinter as adults be- neath leaves and trash on the orchard floor, or in protected places near the or- chards. They are usually inactive during the winter months but may fly on warm days. In early spring, about March or April, the bugs become active, feeding on the broad-leaved weeds in the or- chard, and moving to nearby open fields where suitable host plants are present. They prefer such weeds as dock, plan- tain, mustard, and mullein. Eggs are laid in clusters on the undersides of the leaves of these weeds or occasionally on pear leaves. The eggs hatch after one to three weeks, depending upon temperature, and the nymphs feed on the broad-leaved host plants. First generation adults ma- ture in June, by which time the weeds in the uncultivated areas have begun to dry. Adults of this generation move into the orchards, where irrigation has kept the weeds green. It is this generation which attacks the maturing fruit. A sec- ond generation is produced on the cover crop within the orchard during July and August, and adults of the second genera- tion overwinter in or near the orchards. There is an overlapping of the first and second generations during the period of June through July, and some of the first generation adults may survive through the winter. Control program The entire program for stink bug con- trol is based on a combination of chemi- cal control and weed eradication, and the two must be carefully integrated. Since this bug is so dependent upon weed hosts, chemical control is not effective without a corresponding program of weed eradication. Clean cultivation within the orchards is important and the removal of blackberry patches and weedy areas near the orchards is also necessary. Since most of the bugs overwinter in ground cover within or near the or- chards, chemical control consists of ground applications when the bug starts activity in early spring. Careful observa- tion of populations on the weeds outside of the orchards is of paramount impor- tance, for these bugs are the ones which will migrate to the pears in midsummer. Spot treatment of these weedy areas with a suitable insecticide will aid in reduc- ing the populations. In early spring, if the bugs are located in the orchards, cultivating before spray applications are made may drive the bugs to the adjoining uncultivated areas, and thus they may escape treatment. [10] PESTS THAT ATTACK THE FOLIAGE EUROPEAN RED MITE The European red mite, Panonychus ulmi (Koch), is one of the most impor- tant pests of pears in northern California but does not occur on this crop in south- ern California. The mite is capable of rapid build up and can cause consider- able damage in the summer months. It is of equal importance in the coastal dis- tricts, interior valleys, and the foothill areas. Predators and parasites seem to play a minor role in the suppression of this pest and, as a result, chemical con- trol measures must be applied on a sea- sonal basis. Appearance The adult European red mite is globu- lar in shape, red in color, with conspicu- ous white spots from which dorsal setae arise. The immature forms are usually bright red in color, but some may have a greenish appearance. The eggs are bright red, striated, slightly flattened on top and with a fine spike on the dorsal surface. The mite is very distinctive in appearance and would not be confused with the other spider mites occurring on pear in California. Injury The feeding of the mites on the leaves gives a bronzed appearance to the foli- age. If high temperatures follow a Euro- pean red mite attack, the leaves will turn brown and dry. Frequently, severe dam- age to the foliage appears after the mite populations are destroyed. If the mites are allowed to build up to a point where there is bronzing of the foliage, a few days of hot weather will cause the leaves to dry, even though the mites may have been controlled before the high tempera- tures occurred. Complete defoliation can occur when populations are high. Through the damage to the leaves, the mites have an indirect effect on the fruit. If the foliage is damaged so that leaf function is slowed or stopped, the fruit will fail to develop properly and will not reach normal size. On occasion, the mites lay eggs in the calyx end of pears, and this presents a problem to the canning industry, for contamination of the finished product can occur. Left, overwintering eggs of the European red mite on a pear twig. Right, close-up of the mite. Injury to pear leaf caused by European red mite. Seasonal development Overwintering takes place as an egg on the limbs and twigs of the tree. The eggs are usually found in roughened places on the bark, and a favorite site for winter egg deposition is the juncture of the two-year-old and current season's wood. The eggs are often piled one on the other and, with heavy infestations, the twigs have the appearance of being painted red. The mites hatch in April, soon after the trees have bloomed. They attack the foliage and in the early season are mostly found on the undersides of the leaves. Many generations are produced each year, and the period of time necessary to complete a generation is shorlened as the temperature increases. In the sum- mer months the mites are more abundant on the upper leaf surfaces, and the sum- mer eggs are laid near the midribs of the leaf. As long as foliage is available, the mites will continue to increase in numbers, but populations will drop if leaf damage is extensive. In late August, the mites begin to lay overwintering eggs and this continues through September and even October. In most cases the win- ter egg deposition is completed in Sep- tember, and the adult population de- clines rapidly thereafter. Control program Since this mite overwinters as an egg on the tree, it is possible to apply con- trol measures during the dormant or prebloom period. However, because the eggs are sometimes well hidden or piled one on the other, it is not always possible to obtain the desired control. In addi- tion, European red mite has developed a resistance to a number of chemicals in California, and this complicates the con- trol picture. Since predators and para- sites play such a minor role in reducing European red mite populations, it is best to begin control measures before popu- lations build up to a high level. When conditions become unfavorable for mite development because heavy leaf injury has taken place, the mites may deposit overwintering eggs as early as June or July. This leaves a potential mite problem for the next season, even though the mites do not cause further trouble during the current season. If there is a heavy carry over of winter eggs, the mites can often cause considerable dam- age during the early spring when the new foliage is being produced. Usually the European red mite does not become a problem until the warm summer months, but by applying control measures during the early season, it is often possible to avoid a midseason buildup. TWO-SPOTTED MITE Another very important mite pest of pears in California is the two-spotted mite, Tetranychus telarius (Linn.). Al- though capable of causing more damage to the foliage than the European red mite, [12] Left, overwintering colony of two-spotted mite beneath bark. Right, blackening of leaves caused by feeding of this mite. it does not occur in heavy populations each season. Generally, the two-spotted mite is more severe in the interior valleys and foothill districts, although on occa- sion it can be very numerous in the coastal areas. Bartlett pears are very sensitive to the attack of this mite and can tolerate only low populations. For this reason, it is necessary to observe or- chards carefully, so that the mites will not cause damage before treatments can be applied. The Winter Nelis variety ap- pears to be immune to infestation by this mite. Appearance The adult females are larger than the European red mite, globular in shape, greenish to yellow in color with a con- spicuous dark spot on each side near the middle of the body. On occasion, the spots are so enlarged as to cover most of the body, giving the mite a black ap- pearance. The overwintering form of the two-spotted mite is bright orange in color without the side spots. Immature forms resemble the adults except they [13] are smaller in size. The eggs are spheri- cal and almost translucent, without a fine spike on the dorsal surface. This mite produces a moderate amount of webbing and is usually found on the un- derside of the leaves. Injury The feeding of the two-spotted mite on pear leaves produces a characteristic blackening of the foliage. It is not un- common to have a colony of 2 to 3 mites near the midrib of a leaf, and as a result of their feeding, a large section of leaf will turn black from the midrib to the margin. Because of this, more damage can be done with a lower mite popula- tion than is the case with the European red mite. Blackening of the foliage may appear after the mites have been controlled. A period of hot dry weather shortly after an effective spray has been applied, may result in blackening of the foliage and even defoliation if mite populations were high. Heavy mite populations which cause defoliation will result in the failure of the fruit to size properly. Also, severe midsummer defoliation may cause the trees to bloom in the fall, reducing the next year's crop. Seasonal development In most areas, the two-spotted mite overwinters as an inactive adult, either beneath bark scales or under the trash on the ground. On occasion, however, if temperatures are warm enough, the mites will remain active during the winter, maintaining a low population on orchard cover crop plants. Because this mite spends the winter in protected areas, it is not susceptible to control during this period. Rather, it is necessary to rely on foliage treatments to obtain control. In the spring, the mites begin activity and are usually found at this time on the weed hosts beneath the orchard trees. It is rare that the two-spotted mite will be found on pear foliage during the early season. As summer approaches and tem- peratures rise, the mites increase in pop- ulation and begin to move up the trunks of the trees to the foliage. Characteristi- cally, the lower portions and centers of the trees are attacked first, and the mites spread to the outside as populations in- crease. Many generations are produced during the summer, and under optimum conditions, the mites can complete their life cycle in ten days. In the fall, feeding slows down, and by October, the orange overwintering forms begin to appear. These mites move down to protected places to spend the winter. Control program Because populations may develop rapidly, it is necessary to check orchards frequently, paying special attention to the foliage on the lower inside of the tree, to be sure that populations do not increase to damaging numbers before they are noticed. Since the mites feed on the cover crop in the spring and can produce large num- bers on the weeds, a degree of control can be obtained by directing sprays on the ground. If high mite populations are present, and the weed hosts are allowed to dry because of infrequent irrigation, the mites can move to the trees in large numbers, creating a severe problem al- most overnight. On the other hand, it has been observed that the mites will tend to remain on a permanent ground cover, such as clover, if the orchard is frequently irrigated and the cover crop remains green. The mites colonize on the undersides of the leaves, and they are frequently attacked by predators such as the lady beetle Stethorus, the green lacewing Chrysopus, and predatory thrips. On oc- casion, the predators are numerous enough to keep the mite populations be- low treatment levels. BROWN MITE The brown mite, Bryobia arborea (Morg. & Ander.), previously known as the clover mite, occurs on pears in cer- tain localities. In northern California, it is usually found in the Sierra foothill counties and is rarely present in the in- terior valleys and coastal districts. It is frequently encountered as a pest of pears in southern California. The damage caused by this mite is not so severe as that caused by the European red mite or the two-spotted mite, and in addition, it is rarely found in high populations on pears. It is a very important mite on peaches and plums and frequently will be present in large numbers on these trees although only a minor pest on pears in the same locality. Appearance The mite is easy to distinguish in the adult stage from the two preceding species. The adult female has a brown to dull green body, flattened above, and the front legs are very long, extending forward when the mite is at rest. The immature stages are bright red in color and can be confused with larvae of the [14] European red mite. The egg is spherical, smooth, red in color, and it lacks the dorsal spike which is characteristic of the eggs of the European red mite. Injury The feeding of brown mites on the leaves produces a stippled appearance of the foliage. In most cases, the leaves do not dry and turn brown nor does de- foliation take place. If populations are heavy, the leaves will take on a very pale look as the stippling becomes general. Since the mites spend much of the day on the wood, the leaves closest to the twigs and spurs are most heavily at- tacked, and the new growth is usually free of mite damage unless populations are extremely high. It is rare that damage is severe enough to affect the growth of the fruit, although on occasion, the leaves can be badly damaged. Seasonal development The brown mite overwinters in the egg stage on fruit trees. The eggs are laid around leaf buds and in roughened places in the bark, as is the case with the European red mite. They are often piled one on another and are frequently most numerous in the juncture of 2-year- old wood and the current season's growth. The eggs hatch in early spring, often prior to the bloom period. The mites do not spend their time on the leaves as is true for other spider mites, but stay back on the wood during parts of the day. Feeding takes place on the leaves at night or when the light inten- sity is low. The mites feed both on the upper and lower leaf surfaces but are more frequently found on the upper sur- face. Most of the summer eggs are laid on the twigs, but they will also be found along the midrib of the leaves. On al- monds, the mites go through three dis- tinct generations and lay overwintering A color photo identifying brown mite eggs appears on page 7. eggs by June. On pears, however, they continue to develop throughout the spring and summer but tend to slow down during hot weather. The mites continue to be active until September, at which time the overwintering eggs are laid. Control program Since the brown mite overwinters as an egg, control measures can be used during the dormant or pre-bloom stage of the trees. Control of the winter eggs is usually the most satisfactory way to reduce populations for the next season. During the foliage period, treatments must be directed to the twigs, for this area is where the mites spend most of their time. A superficial coverage of the leaves will not suffice where the brown mite is concerned. In most cases, control measures are directed against the two-spotted or Eu- ropean red mite rather than brown mite on pears, and these measures are usually sufficient to prevent brown mite damage. BEAN THRIPS In the Sacramento Valley of Califor- nia, the bean thrips, Hercothrips fascia- tus (Perg.), is occasionally a pest of pears. The chemicals currently in use control this thrips although they are not directly applied for this insect, and it is rare that an infestation is encountered. Appearance The adult thrips is about 1/25 of an inch long, and the body color is dark brown to black. The forewings have two white dots which give the appearance of bands across the wings. The antennae and legs have light colored bands as well. The eggs are very small and white and are placed within the leaf tissue. The nymphs vary in color from yellow to pink, but generally they tend to be more pink in color than nymphs of most thrips species. [15] Injury The thrips is principally a foliage feeder but may also attack the fruit. The feeding of the thrips produces a silvery appearance of both foliage and fruit, with the presence of characteristic black spots of excrement. Severe infestations may cause the leaves to dry and turn a brown to reddish color. If this condition occurs, the fruit will be indirectly af- fected and may fail to reach proper size and maturity. Seasonal development The thrips overwinter as adults in sheltered places and begin activity as soon as the weather turns warm. They may become active during the winter on sunny days, but populations do not build up until spring. Eggs are laid in the leaf tissue of the host plants. Usually two or more generations will be produced in spring on weed hosts which, in pear or- chards, will usually be prickly lettuce or common sow thistle. During the early summer, the thrips may fly to the foliage of pears and insert eggs into the leaves. Three or more generations may be pro- duced on pears during the summer months. There are possibly six or more overlapping generations per year, de- pending upon summer temperatures. Control program Ordinarily sprays applied for other insect pests of pears will adequately con- trol the bean thrips. The insect can also be controlled by orchard sanitation. Re- moval of the host plants, prickly lettuce and common sow thistle, from the or- chard and from areas bordering the or- chard is usually sufficient to prevent bean thrips from attacking the pears. The adults are not strong fliers, so there is little chance of infestation resulting from weed hosts located outside the or- chard. PEAR PSYLLA The pear psylla, Psylla pyricola Foerst., has long been a major pest of pears in the eastern United States. Cali- fornia, however, considers the pear psylla as a new pest, for it did not invade the state until recently. Since the original infestation in 1953, it has spread to most of the pear grow- ing areas with the exception of southern California. It primarily attacks pear, seeming to prefer the Bartlett and D'Anjou varieties, and will occasionally attack quince. Appearance The adults resemble miniature cicadas and are about 1/10 inch long. The color Pear fruit with honeydew produced by pear psylla. [16] An adult pear psylla. varies from dark to reddish brown, with either reddish or green markings. The wings are transparent and are held roof- like over the body. The young nymphs are very tiny and yellow in color. As they mature they be- come flat and broad, with color varying from yellowish green to reddish brown. The eyes are bright red, and each nymph is immersed in a droplet of honeydew. The last instar is called the "hardshell" stage. This stage is dark in color with prominent wing pads and no longer lives within a drop of honeydew. The eggs are pear-shaped and are usu- ally orange yellow in color. They are found on the twigs and buds in the early spring, and on the leaf petioles and near the leaf midribs in summer. Injury The damage caused by this pest is of two general types. One type results from the production of large amounts of honeydew which drips onto the foliage and fruit. In addition to the sticky con- dition which results, a black fungus grows in the honeydew, causing a sooty appearance of both leaves and fruit. Fruit so affected is not suitable for fresh shipment. In addition, the feeding of Color photos of the pear psylla and the damage it does appear on pages 6 and 7. the nymphs has a toxic effect upon the leaves causing them to turn yellow. If infestations are unchecked, it is possible that complete defoliation could occur, with adverse effects upon fruit size. In most cases, however, the principal cause of damage to the fruit is the pro- duction of large amounts of honeydew by moderate populations. Young trees can be severely stunted by pear psylla. Although the fruit is not directly at- tacked, it can fail to reach full size if the psylla infestation seriously impairs the function of the leaves. Seasonal development The pear psylla overwinters as an adult in sheltered places in the bark or under trash on the ground. In early spring, prior to the bloom stage of the trees, the adults become active and de- posit eggs on the twigs. Most of the eggs are laid on or near the fruit spurs. Hatch- ing takes place by the time the first leaves appear, and the young nymphs feed on the foliage. As previously noted, each nymph is enclosed in a drop of honeydew and remains within the drop until the final instar or "hardshell" stage is formed. In this stage, the nearly ma- ture insect is active and may wander over the leaf surface or back to the twigs. , Newly emerged adults are very light in color but soon turn dark brown. The adults are very active and tend to fly about from tree to tree. For this reason this pest is capable of very rapid spread. Each generation requires about 30 days and there are three to five generations per season. The growing insect passes through 5 instars or nymphal stages. The overwintering adults are formed in the fall and they tend to fly for considerable distances. For this reason, a few scat- tered infestations of pear psylla can be- come general in a very short time. Control program Control of this pest is almost entirely dependent upon application of insecti- [17] cides. Very few parasites have been re- corded from pear psylla, and predators do not seem to play an important role in reducing populations. Timing of sprays is of extreme importance, because the "hardshell" and adult stages are dif- ficult to control. If materials are applied when most of the population is in either of these stages, satisfactory control will not be obtained. The chance of reinfes- tation is very great because adults are able to fly long distances. Winter sprays at the delayed dormant stage of tree development are useful means of reducing populations. The treatment should be made in late Febru- ary, when both adults and eggs are pres- ent. Full dormant sprays during January are too early for pear psylla control, since the insect is hidden and inactive at that time. The presence of backyard trees and marginal or abandoned orchards plays an important role in pear psylla control. If these trees are not treated, they can support a population of pear psylla which can rapidly reinfest commercial plantings. With the development of hous- ing projects in or near many of our pear districts, backyard pear trees can become a real factor in pear psylla reinfestation if the psylla is not controlled on these trees. APHIDS Aphids are frequent pests of pear trees in both the coastal districts and the in- terior valley, but they are seldom of im- portance in the foothill districts or in southern California. There are several species of these insects which may attack the new shoots and foliage of pear trees. The three most commonly encountered are the green peach aphid, Myzus per- sicae (Sulz.), the melon aphid, Aphis gossypii Glover, and the bean aphid, Aphis fabae Scop. Since all three do the same general type of damage and are often found associated, they will be dis- cussed as a group. Appearance The aphids found on pears are all similar in appearance, and accurate iden- tification of the species involved requires laboratory examination. The green peach aphid, as the name implies, is a light green in color. The melon aphid is gen- erally dark green, and the bean aphid is a black species. The bean aphid seems to prefer the sucker shoots in the center of the tree, but both the melon and green peach aphid will attack the new growth all over the tree. Injury Feeding of the aphids on the foliage will cause it to curl, and the growth of shoots will be stunted. In general, how- ever, this type of damage is of minor importance. Most of the injury caused by aphids is from the production of honeydew which falls to the fruit. The presence of the honeydew causes the Left, russet spots on a pear fruit caused by aphid honeydew, and right, general russet from the same cause. . , ; ,v"".;. ' \, ; ..»■ lenticels to turn dark, giving the pear a russeted appearance. The russet may be localized or there may be a general surface russet, depending upon the de- gree of aphid infestation. The presence of honeydew also makes the fruit sticky, and a black fungus often grows in the honeydew. The black fungus gives the fruit a sooty appearance. Seasonal development All of these aphids thrive on a wide range of host plants and they occur on other crops or on weeds in or near the orchards. The aphids do not spend the winter on the trees. Instead, they are found on various weeds as well as com- mercial truck crops. In the spring, usu- ally after bloom when the trees are grow- ing rapidly, the aphids appear on the foliage and shoots. Here they establish colonies and may pass through several generations while the weather remains cool. With the onset of warm summer weather, the aphids leave the pear trees for other hosts. Even though the pear trees may send out a flush of growth in the fall, and though the weather is rela- tively cool, the aphids do not return to the trees. In most seasons, aphids will be present only for about a month dur- ing the early season, but if cool weather persists, they will remain on the trees until midsummer. Control program There is little that can be done to re- duce aphid populations other than to treat when infestations appear. Although the aphids are associated with weed hosts, there seems to be little difference in infestation between orchards which are clean cultivated and those which have cover crops. Apparently, weeds border- ing the orchard or in nearby open areas are quite important as a source of aphids. In most cases, due to the early spring attack and the migration from other hosts, predators and parasites seldom play a role in the suppression of aphids on pears. If an aphid infestation is pres- ent, however, and a period of warm weather comes, it may not be necessary to treat. In most cases, the aphid popu- lations decline rapidly after periods of hot weather. TENTIFORM LEAF MINER This insect, Lithocolletis sp., a moth, was not considered a pest of pears until 1952, when a heavy outbreak occurred in the foothill districts of northern Cali- fornia. Since that time, it has become a general pest in the pear growing districts of northern California. The species has not been determined, and there is a pos- sibility that more than one species is in- volved. There are scattered observations in the literature concerning the presence of a leaf miner in pears prior to 1952, but the infestations were not serious enough to warrant studies on the pest and no injury was reported. Appearance The adult moth is very small, being % inch in length. The forewings are golden brown in color with silvery streaks mar- gined in black. The hind wings are gray with long hairs on the margins. When at rest, the wings are held roof-like over the body. Adult tentiform leaf miner. Pear leaves injured by tentiform leaf. Leaf miner larva within a mine. Freshly laid eggs are opaque and faintly yellow, becoming translucent as they mature, so that the developing larva can be seen. In its first three instars, the larva is flattened with a wedge-shaped head, and is legless. The body is white in color with a brown head. The fourth and fifth in- stars have rounded bodies with true legs and prolegs present. The body color varies from white to yellowish. Pupae are dark brown in color, very slender, and are enclosed in light, silken cocoons. Injury Leaf miner damage is restricted to the foliage and in a heavy infestation over 60 per cent of the leaf tissue can be destroyed. The larvae feed irregularly on the cells beneath the upper epidermis of the leaf and consume all the tissue be- tween these cells and the lower leaf epidermis. Only a thin epidermal layer remains on the underside of the leaf, and the upper side of the blotch presents a spotted appearance. Although the trees are not defoliated, leaf function is im- paired, and the fruit may fail to attain proper size. It is possible that a con- tinued attack over a period of several sea- sons may weaken the tree, producing other adverse effects, but this has not been observed in the field. It is often the case that leaf miner dam- age alone is not serious enough to affect the trees, but a combination of mite at- tack and leaf miner injury may have serious results. Seasonal Development The leaf miner overwinters as a pupa within the tissue of fallen leaves on the ground. The adults emerge very early in the spring, usually during the month of February. They rest on the tree trunk, limbs, and cover crop until the first pear leaves unfold. Eggs are laid on the un- derside of the leaf as soon as the new leaf flattens out. On hatching, the young larva mines through the underside of the egg directly into the leaf tissue. A linear or serpentine mine is formed first and, as the larva develops, a blotch type mine is produced. The more mature larvae tie the sides of the mine together with silk, forming a pleated or tentiform mine. Pupation takes place within the mine. As the adult emerges, the old pupal case is left protruding from the mine. There are four generations per year, and the later generations overlap in the late summer. In general the first generation is from March to May, the second from May to July, the third from July to September, and the fourth is the overwintering gen- eration which develops from September until the leaves drop. Control program Since this insect has four generations per season, control with chemicals be- comes difficult if treatments are delayed until there is considerable overlapping of developmental stages. It is best to time a treatment against the first generation larvae at the petal fall stage of pears be- fore the second generation moths emerge. It is also possible to direct control measures in spring against the moths. The pupae are within the leaves on the ground and by spraying these with a residual type chemical the adults will be killed as they emerge. Parasites play an important role in re- ducing numbers of this pest. There are at least three species of parasites which attack the larvae, but they usually do not become effective until late summer. It is best not to apply chemicals for con- trol of this insect in the late season, for natural control factors may hold the leaf miner in check for the following season. Cultural control measures, such as disking under the leaves in the winter or raking and burning the leaves may reduce the numbers of leaf miners. How- ever, active infestations cannot be con- trolled in this way. Larva of pear sawfly on pear leaf. CALIFORNIA PEAR SAWFLY The California pear sawfly, Pristo- phora californicus (Marlatt), is a minor pest of pears since it is usually well con- trolled by the spray program applied for other insects. It is encountered in back- yard plantings and is occasionally a problem in orchards where the first cover spray has not been applied. It is gener- ally distributed over the state wherever pears are grown. Appearance The adults are small sawflies about !/4 inch long, black in color, with yellow markings on the prothorax. The eggs are white in color and are inserted in the leaf tissue. The larvae resemble caterpil- lars in appearance, having both true legs and prolegs. They are bright green, closely matching the leaf color, and rest along the edges of the feeding area, which makes them difficult to see. Injury The damage caused by the pear sawfly is the destruction of leaf tissue by the feeding of the larvae. Circular holes are cut along the leaf margins and within the leaves. If infestations are heavy, the entire leaf is consumed, leaving only the midrib. The larvae do not feed on the fruit, but restrict their attack to the foliage. Seasonal development The California pear sawfly overwin- ters as a pupa in the soil. The adults emerge in early spring, mate, and insert their eggs into the leaf tissue, commonly at the leaf margins. The young larva on hatching, begins to consume the leaf tis- sue, feeding in a characteristic circular pattern. The larvae remain on the leaves during April and May, and as maturity is reached, they drop to the ground and enter the soil. There is one generation per year, and the insect is present on the trees only during the early spring months. Larva of pear-slug, showing characteristic feeding damage Control program Since this pest is so well controlled by the standard spray program on pears, there is no need for special measures directed against it. In backyard plant- ings, considerable damage can be done if the infestation is not noticed. Control can easily be obtained if treatments are applied as soon as the first circular holes appear in the leaves. PEAR-SLUG Another pest of minor importance is the pear- or cherry-slug, Caliroa cerasi (Linn.). The standard spray program on pears controls this pest so that it is seldom encountered in commercial pear orchards. It is generally distributed over the areas where pears are grown, but is a problem only in backyard trees or in untreated orchards. Appearance The adult pear-slug is a small sawfly which is shiny black in color. The eggs are oval, white in color, and are inserted in the leaf tissue. The larvae are slug-like, being coated with a slimy exudate which is olive green in color. The anterior end is wider than the rest of the body, and a fully matured larva may be % i ncn m length. An in- festation by this insect may also be iden- tified by the characteristic way the leaves are skeletonized by the feeding of the larvae. Injury Pear-slugs restrict their feeding to the foliage, and the degree of damage de- pends upon the severity of the infesta- tion. On backyard trees most of the leaves may be skeletonized, resulting in serious damage to the tree. In such cases, the fruit may fail to reach proper size and maturity. Seasonal development The pear-slug overwinters as a pupa in the soil, and adults emerge in the [22] early spring months, usually in April or May. The eggs are inserted into the leaf tissue, and on hatching, the larvae feed on the upper side of the leaves. They may remove all of the tissue with the excep- tion of a fine network of veins. When the larva matures, it drops to the soil where it pupates. A second generation will appear in July and August, and this brood is usually the most conspicuous. Control program In commercial orchards there is little need to apply special control measures for this insect, since the standard spray program for other pests will control it. In backyard plantings, if the first gener- ation of pear-slug is overlooked, the second brood can then cause consider- able leaf damage. Trees should be in- spected frequently so that control meas- ures may be applied before this occurs. The larvae are easy to control with al- most any insecticide or dust, and even washing the foliage with water from a garden hose will remove them. PESTS THAT ATTACK FOLIAGE AND FRUIT PEAR LEAF RUST MITE Very little is known about the pear leaf rust mite, Epitrimerus pyri (Nal.), other than it can be a serious pest of pears in some seasons. It has been re- ported as occurring in damaging num- bers in limited localities and in certain seasons. It is not known what factors contribute to these localized outbreaks. In general, most of the pear leaf rust mite attacks of recent years have oc- curred in the Sierra foothill districts of northern California, but reports of dam- age have been received from other areas as well. Appearance The adult mite is very small, and cannot be clearly seen without the aid of a hand lens. The overwintering stage is brown in color, and the summer form is pale white to cream. Both stages have the middle of the back arched, giving them a wedge-shaped appearance. The immature forms are wedged-shaped like the adults and are pale white in color. The eggs are spherical and transluscent. Injury The feeding of the mites on the leaves causes them to turn brown or reddish. This injury, however, is of minor impor- [23 tance when compared with the effects of their feeding on the fruit. An extreme russetting of the fruit surface can occur, and the entire pear surface can be rough and brown. This type of damage is seri- ous on fruit shipped to the fresh market, for a smooth-skinned pear is desired. Depending upon the severity of the in- festation, the fruit damage can vary from complete russet to a slight roughening of the areas around the stem and calyx ends. Seasonal development Very little is known about the biology of pear leaf rust mites. They overwinter as non-feeding mites behind leaf buds of one year old wood or in roughened areas between the two-year-old wood and cur- rent seasons growth. They will often be located around the blind buds at the base of an old leaf scar. As the new growth starts in the spring, the mites become active and feed upon leaves and fruit. They apparently prefer tender new foliage, for the populations become inactive as the leaves harden. It is suspected, however, that they may be able to remain active on the developing fruit. A color photo of pear leaf rust mite damage is shown on page 6. ] After harvest, pear trees will often send out a new flush of growth, and the mites are found actively feeding on the new leaves during the fall. Control program Since so little is known about the biol- ogy of this mite, there is no clear-cut method of control. The mite spends the winter in a partially exposed condition. Therefore post harvest, winter, and spring sprays applied for other pests may give relief. Since attacks of this mite are so sporadic, it is either kept under con- trol by natural factors or by the spray program applied to pears. Frequently, only a single limb on a tree is affected, which may indicate a spray miss, or that the mite does not rapidly spread from the original point of infestation. PEAR LEAF BLISTER MITE The pear leaf blister mite, Eriophyes pyri (Pgst.) is a major pest of pears in all of the important pear districts of Cali- fornia. The mite is capable of causing considerable injury and in most areas must be controlled each season. Although the pest has been known for many years, there are aspects of its biology which are not well understood. It is one of the few pests capable of producing injury during the winter, spring, and summer months, attacking the buds, leaves, and fruit. Although the distribution of this pest is very wide, it is more frequently encountered in damaging numbers in the Sierra foothill districts of northern California. Appearance The adult mites are very small and cannot be seen clearly without the aid of a hand lens. The body is white in color, long and slender, striated, with a few long hairs. The immature forms resemble the adults except for the smaller size. The eggs are spherical and pearly white in color. Injury The damage caused by this mite can be separated into three distinct types. During the winter, the feeding of the mites under the bud scales is believed to cause the bud to dry and fail to de- velop. This type of damage, however, is similar to the bud injury caused by in- sufficient chilling and the two causes of bud failure may be confused. Consist- Pear fruit injured by pear leaf blister mite. [24] ently heavy populations of mites within injured buds usually implicate the blister mite. This injury is not predictable, since pear buds often have extremely high mite numbers and yet show no sign of damage next spring. Early feeding of the mites on the de- veloping fruit causes depressed russet spots which can be the most serious aspect of blister mite attack. The fruit is often deformed and misshapen as well. The presence of these oval russet spots, usually depressed, with a halo of clear tissue surrounding the spot, is a char- acteristic symptom of blister mite attack. The Bartlett pear is most susceptible to fruit damage by blister mite but other smooth-skinned varieties such as Cornice and D'Anjou are similarly affected. Pears with a naturally russeted surface such as Bosc, Hardy, and Winter Nelis do not show the effects of blister mite attack. The third type of injury is the blister- ing of the leaves. Although defoliation does not occur, the leaf function can be seriously impaired by a heavy infesta- tion. Seasonal development Although there are details of the biol- ogy of pear leaf blister mite as yet unex- plained, the general life history is well known. The mite overwinters as an adult beneath the bud scales on fruit buds and leaf buds. The fruit buds are preferred and in most cases the terminal bud of a twig carries the heaviest population. The mites are able to reproduce during the winter, and all of its growth stages can be found under the bud scales. At the time the buds open in the spring, the mites begin to attack the developing flowers and fruit, producing reddish blisters. When the new leaves develop, they also develop blisters from the effects of the mites feeding on the foliage. The mites develop colonies within the leaf blisters, feeding on the leaf tissue within this protection. They can move in or out Pear leaves showing characteristic blisters caused by pear leaf blister mite. of the blister through a small hole located at the center of the raised area. The mites pass through several generations on the leaves but slow down in activity during the warm summer months. Fresh blisters are often produced again in the fall, when the tree may produce a flush of new growth. As cool fall weather ap- proaches, the mites leave the blisters and migrate to the buds to spend the winter. Control Program Most of the overwintering mites are found beneath the first bud scales in the fall, and for this reason a post-harvest treatment is preferred for control. As the season progresses, however, they move deeper into the buds, and if treatments are delayed until winter, the mites are more difficult to reach. Spring treatments are less satisfactory, for the mites form protective blisters as soon as the buds open. GRAPE MEALYBUG The grape mealybug, also called Baker's mealybug, Pseudococcus mari- timus (Ehr.), is distributed over a wide [25] J A pear fruit with a colony of mealbug in the calyx end. area and is one of the more important pests of pears in California. Infestations of mealybug can be serious because of the fruit damage which results, and also because these insects seek sheltered places where they are difficult to reach with insecticides. The severity of this pest tends to vary. It may be abundant in some seasons and of minor importance in others. Appearance The adult mealybugs are about % inch long, dark purple in color, and covered with a uniformly distributed, white, waxy powder. Filaments of wax extend from the margin of the body and from the posterior end. These posterior fila- ments are longer than those on the sides and may extend backwards by half a body length. The eggs are yellow to or- ange in color and are laid in cottony egg sacs. The crawlers are yellow to brown and quite active. Injury Most of the obvious damage caused by mealybug is that which results from the honeydew which drips to the foliage, twigs, and fruit. A black fungus grows [26 in the honeydew, thus giving the foliage and fruit a sooty appearance. The feed- ing of mealybugs within the calyx end of the fruit causes a break down of the tissues, and the end of the fruit may be- come soft when the pear begins to ripen. In addition, it is not possible to remove the insects from the calyx ends of the pears with the present washing practices, and the mealybugs remain on the fruit after it is packed. A severe mealybug at- tack, therefore, causes the fruit to be rejected for fresh shipment because of the sooty appearance and creates a prob- lem of insect contamination for the can- ning industry. Seasonal development Mealybugs spend the winter as eggs or as crawlers within the white cottony egg sacs, although the majority of the individuals winter in the crawler stage. Their egg sacs are usually found in the cracks of the bark or under loose bark scales. In the spring months, the young mealybugs move to the bases of the shoots or other tender growth in order to feed. They mature by early June and the females then move back to the trunk and limbs to lay eggs. The eggs hatch in June, and the crawlers again move to tender growth. On pears, the crawlers also enter the calyx end of the fruit, form colonies within this protected area, and feed on the fruit tissue. They may also congregate around the stem end of the fruit. The adults of this generation move back to the bark in the late summer, usu- ally from August to September, and lay eggs in protected areas on the limbs and trunks. They may then overwinter as eggs, or the eggs hatch to produce crawl- ers which overwinter within the old egg sac. Control program Parasites and predators play an im- portant role in reducing mealybug popu- lations, and an outbreak can be caused by unnecessary use of insecticides. The presence of wax on their bodies, and the tendency of the mealybugs to seek pro- tected places, makes chemical control difficult. Use of a sufficient gallonage of spray to wet the wood thoroughly is es- sential for mealybug control. ALhough the overwintering eggs and crawlers are susceptible to insecticides, they are so well protected in the bark crevices that they are difficult to contact. Treatment during the winter, however, partly disinfests trees so that there are fewer mealybugs at the beginning of the next season. Spring and summer treat- ments must be timed to coincide with the appearance of crawlers, otherwise the control obtained will not be satisfactory. FRUIT TREE LEAF ROLLER Akhough a pest of long standing to deciduous fruits, the fruit tree leaf roller, Ar chips argyrospila (Walker), is rarely encountered as an injurious insect on pears. It is so well controlled by sprays applied for codling moth that many growers do not know of its existence. At the present time, it occurs in damaging numbers only in backyard plantings or in abandoned orchards. Appearance Adults of the fruit tree leaf roller are inch long and the forewings are brown mottled with gold and white. The moth, when at rest, presents a bell-shaped appearance. The mature larva is dark green in color, with a black prothorax and head. The immature larvae may be lighter in color, but they do not vary from a distinct green. When disturbed the larvae will wriggle backwards and often drop on a silken thread. The eggs are laid in masses of 30 to 100 and are cemented over with a secretion so that they appear as irregular gray patches on the twigs. Injury The fruit tree leaf roller is principally a leaf feeder, but it also will attack the fruit. Larvae bite deeply into the surface of the fruits and, since they are active so early in the season, the injury heals over by harvest time. Fruit injured by the leaf roller presents characteristic deep irregular holes with rough or scabby scar tissue present. Young fruits may be so severely injured that they remain small and misshapen. If infesta- tions are heavy, the leaves can be badly injured, but in most cases, the leaf dam- age is of minor importance when com- pared with the scarring of the fruit. Seasonal development Fruit tree leaf rollers overwinter as eggs in masses on the twigs and limbs. Left, overwintering egg masses of fruit tree leaf roller. Right, a pear leaf attacked by this pest The eggs hatch in early spring, during the bloom period of pears. The young larvae feed on leaves, tying them together or folding over an edge of a single leaf and tying it down with silk. They pupate within the leaf rolls, and adults emerge in May and June. The adults fly during twilight hours, otherwise they remain quietly resting on the foliage or limbs during the day. There is one generation per year, and the overwintering eggs are laid in June. Control program The commercial pear grower has not been concerned with fruit tree leaf roller in recent years so long as an adequate codling moth spray schedule has been carried out. The practice of applying the first treatment at the petal fall stage co- incides with the activity of fruit tree leaf roller and readily controls the pest be- fore damage is done. The presence of this insect in large numbers in aban- doned orchards does point out, however, that the insect is still a potential pest which could become important if there were a shift from the standard spray program. ORANGE TORTRIX As a general feeder on both citrus and deciduous fruits, the orange tortrix, Argyrotaenia citrana (Fern.), is of con- siderable importance. It occurs on pears in limited localities, being more fre- quently encountered in the coastal dis- tricts than in other areas. It is present in the Sacramento Valley and foothill districts, but is more scattered in occur- rence. Populations of this pest tend to fluctuate, the severity of its attack vary- ing from season to season. The orange tortrix is not susceptible to DDT, the standard insecticide used for codling moth control. Therefore when economic populations occur, a change of chemicals is necessary to provide control of both species. Appearance The adult moth varies in size from ^4 to V2 i ncn l° n g> an d when it is at rest, the wings are in the shape of a bell. The forewings are light brown to reddish brown in color with a diagonal black bar across each forewing. When the moth is at rest, the bars form a V-shaped band. The hindwings are uniformly light brown in color. The mature larva varies from light green to straw colored, and the prothorax and head are brown. The larva will wriggle backwards when disturbed and often drops on a silken thread, like the fruit tree leaf roller. The eggs are cream A pear fruit showing injury by orange tortrix, and right, eggs of this same pest. colored to translucent, and laid in over- lapping masses of 10 to 40. Injury The orange tortrix is principally a leaf feeder but will also attack the fruit. If the infestation is serious, considerable leaf damage can result, but in most cases, the leaf destruction is of minor impor- tance when compared with the damage caused by feeding on the fruit. The lar- vae are surface feeders rarely penetrat- ing deeply into the tissue. They feed in an irregular pattern, producing shallow, serpentine markings on the surface of the fruit. These feeding areas are com- monly found in the calyx end or on the sides of fruits which are touching. Dam- aged fruit is rejected both for fresh shipment and for canning. Seasonal development The orange tortrix overwinters in sev- eral stages, but the larval stage is most commonly found. Larvae spend the win- ter in shelters constructed of dry leaves on the twigs, where they feed to a limited extent on the bark. They will also con- struct silken shelters on mummified fruit left on the trees and will do some feeding on this fruit. It is possible to find pupae, adults and eggs during the winter, but the majority of the individuals are in the larval stage. Since they do not overwinter in a uni- form stage of development, the spring and summer generations overlap con- siderably. There may be two to four gen- erations per season depending upon the locality involved, and all stages can gen- erally be found at any time. The adults lay their egg masses on the smooth bark of the main limbs, and the young larvae move to the foliage after hatching. They fasten leaves together with silk and feed within this protected area. They may also tie a leaf to a fruit or live in the calyx end of the fruit under a net of webbing. They are commonly found between two fruits which are touching or within clusters of fruit. Pu- pation takes place within the tied leaf clusters or in protected areas on the fruit. Control program Parasites play a role in limiting the numbers of orange tortrix, and the at- tacks of this pest tend to fluctuate. Since the insect is not susceptible to DDT, it cannot be controlled by the codling moth program unless substitute materials are used. It has been found, however, that the timing of treatments for codling moth control will serve for orange tortrix and there is no need for additional applica- tions. If infestations are high, it is usu- ally necessary to use a substitute ma- terial in the entire codling moth schedule, but for minor infestations the use of a substitute material in the second or third spray is usually sufficient. The removal of mummified fruit may help to reduce overwintering sites for the orange tortrix. Since it is capable of spending the winter in other places on the tree, this procedure may not be eco- nomically worthwhile. SPRING AND FALL CANKERWORMS These two pests, the spring canker- worm, Paleacrita vernata (Peck), and the fall cankerworm, Alsophila pome- taria (Harris), will be discussed to- gether, for they are similar in their at- tack on pears. They differ in life history, but the larvae are present on the trees at the same time of year. Before DDT became generally used for codling moth control, these pests were of major im- portance on pears. They are so well con- trolled by the codling moth program at present, that they are seldom encoun- tered in commercial orchards. Appearance The adults of both species are much alike in external appearance. The females are wingless, gray insects about % inch long. The males are winged and are gray [29] to brown in color with a wingspread of about 1 inch. The larvae of both species are typical of the family Geometridae, commonly called measuring worms. When mature, they are almost 1 inch long, green to olive green in color, with stripes of a different shade of green along the sides below the spiracles. The main difference between the two species is the presence of a third pair of prolegs on the fifth ab- dominal segment of the fall cankerworm. The spring cankerworm has two pairs of prolegs, lacking the third pair. Injury The larvae are primarily leaf feeders and tend to skeletonize the leaves. A heavy infestation can cause considerable foliage damage. In addition, they will feed on the young fruit, often biting deep holes. Since feeding takes place early in the spring, these areas heal over by har- vest, and the injured fruit will show de- pressions, with scar tissue present. The fruit damage is similar to that caused by the fruit tree leaf roller, except that the cankerworms usually cause more exten- sive injury to the fruits. Seasonal development The fall cankerworm overwinters as an egg on the twigs and small limbs. The eggs are laid in regular rows and are quite conspicuous. The larvae hatch in spring and feed on the leaves. When ma- ture, the larvae drop to the ground and pupate in the soil. Moths emerge in the fall, mate, and lay the overwintering The spring cankerworms overwinter as pupae in the soil, and the moths emerge in early spring. They mate and lay their eggs in masses on the twigs and limbs. The larvae hatch about the same time as the fall cankerworm, so that both species are active as larvae at the same time. When maturity is reached the larvae drop to the ground, where they enter the soil and pupate. There is only one complete generation per year with both species, although in some seasons there may be a partial sec- ond brood. PESTS THAT ATTACK FLOWERS AND FRUIT PEAR THRIPS Prior to 1946, the pear thrips, Taenio- thrips inconsequens (Uzel), was rated as one of the most important insect pests of pears. At the present time, it is held under control by the current spray pro- gram and is a pest only in a few locali- ties. It is an insect that is capable of in- juring pears severely, therefore it should not be disregarded. Appearance The adults are about % 5 of an inch long, and are dark brown to black in color. The wings are lighter in color, especially at their bases, and the eyes are dark red. Larvae are white, and possess a ring of dark spines on the underside toward the posterior end. The eggs are microscopic and are inserted under the epidermis of leaf and blossom tissue. Injury The damage caused to pears by the pear thrips is of two general types. The adults feed on the opening fruit buds, causing them to dry out and fail to blos- som. As soon as the buds are attacked, they produce gum, and this condition is referred to as bleeding buds. This char- acteristic bleeding is a diagnostic symp- tom of the presence of pear thrips. The larvae, or white thrips, feed on the developing fruit, and this type of feeding results in russet or scabbing of the fruit surface. These scars on pears are usually corky and the fruit may be- come misshapen. Fruits so injured are [30] not acceptable for the fresh fruit market. A less conspicuous form of injury may result from the insertion of eggs into the blossom stems. These egg punctures may cause the flowers to drop. However, high populations are necessary before this type of injury becomes significant. Seasonal development The pear thrips spend the winter as pupae within cells constructed in the soil. The cells are usually deep enough to escape normal cultivation. The adult thrips emerge in March or April, as soon as the soil warms up. The adults feed on the partially open buds, and lay their eggs in the flower parts. The eggs hatch in seven days or more, depending upon temperature, and are known as "white thrips." They feed on the developing fruit and, when mature, drop to the ground. The larvae enter the soil, con- struct cells, and remain quiescent until they pupate during September or Oc- tober. Control program DDT as applied for codling moth con- trol destroys the thrips larvae before they enter the soil. In this way, orchardists prevent thrips problems for the corre- sponding season of the next year. The pear thrips persist in a few localities, and in such areas it may be necessary to treat at the crack bud stage in March. Treat- ments must be applied early if bud dam- age is to be prevented. There are a number of factors which tend to hold thrips in check, such as high soil temperatures during the larval stage in the soil and heavy spring rains prior to emergence of the adults. A common practice among pear grow- ers when this pest was of major impor- tance was to delay disking of the cover crop. This would keep soil temperatures lower, and thus delay the emergence of adults until the trees were past the bloom stage. PESTS THAT ATTACK TWIGS AND LIMBS EUROPEAN FRUIT LECANIUM Most of the scale insects which attack pears, such as the European fruit le- canium, Lecanium corni Bouche, are not restricted to one host, but may attack many deciduous fruit trees. The Euro- pean fruit lecanium, also known as the brown apricot scale, is more common as a pest of stone fruits, but it does occur on pears, sometimes in damaging num- bers. This scale is distributed over all of the fruit-growing areas of the state but is a more important pest in the foot- hill districts of northern California and in southern California. Appearance The mature scale is hemispherical in shape and is a little longer than broad. The color is usually shiny brown. They may be from % to % inch long. The form of the adult scale varies consid- erably. They may be rounded, elongate, humped, or flattened, depending upon the size and shape of the limb or twig that is infested. The color also varies, from yellowish brown to a very dark brown. Immature forms are oval, flat- tened, and yellow brown to pale brown in color. The eggs are oval and pearly white and are laid beneath the mature female scale. Injury The feeding of the scale insects on the tree causes a general weakening effect, but this damage is usually not noticeable. The production of large amounts of [31] Immature and (right) mature European fruit lecanium. honeydew which drips to the foliage and fruit, with the subsequent growth of a sooty black fungus, constitutes the prin- cipal damage caused by this pest. Honey- dew is produced in large amounts by the maturing scales in the early spring, and at this time much damage may occur. The crawlers produce a fine spray of honeydew during summer, which often covers the fruit and leaves with a thin but sticky film. In some instances, the population of adult scales is too low to produce significant amounts of honey- dew in early season and the trees seem free of trouble. The crawlers produced in late spring, however, may be numer- ous enough to cause a sticky condition on the fruit by harvest. Seasonal development The scales pass the winter as imma- ture forms on the twigs. In early spring, they begin to increase in size and to pro- duce honeydew. By March and April, the scales have grown considerably and are [32 near maturity. Maturity is reached by April and May, and eggs are laid in large numbers beneath the body of the mature female. Hatching takes place in June and early July, and the crawlers move to the leaves, where they settle and begin feed- ing. In October and November, before the leaves start to fall, the immature scales move back to the twigs where they spend the winter. Only one generation a year occurs. There is a heavy natural mortality of immature stages on the leaves during the summer months, and only a small percentage survives. The young are produced in such large num- bers, however, that this low survival rate may result in a considerable number of scales. Control program The overwintering stages of the Euro- pean fruit lecanium are very susceptible to sprays applied during the dormant season. It is important, however, not to delay spraying beyond the full dormant period. Once the scales have begun to grow in early spring, beginning with the first swelling of the buds, they become very resistant to most insecticides. When this stage is reached, and until the scales mature and crawlers are again produced, there is no way to control this insect. In summer, the crawlers and early instars are susceptible to sprays, but timing again is an important factor. It is neces- sary to wait until emergence of the crawl- ers is complete, for those beneath the old scale will not be affected. Parasites usually play an important role in reducing populations of this scale. A parasitized scale can be recognized, for it usually turns black in color. In many cases, the parasites are capable of holding the scales in check, and treat- ment is not necessary. Present spray practices for other pests, and drift of insecticides from adjoining areas may, on the other hand, destroy the parasites and bring about an outbreak of the scale insects. CALICO SCALE Although the calico scale, Lecanium cerasorum Cockerell, is more common as a pest of stone fruits and walnuts, it is occasionally found on pears. In rare instances, the scale may be abundant enough on pears to require control meas- ures, but in most cases, infestations are limited to very few scales. The size and coloration of the scale make it very con- spicuous. Therefore, when present, it is noticed even though populations are low. Appearance The adult calico scale is globular in shape, about % inch in diameter, and dark brown with irregular white marks on the dorsum. The brown and white pat- tern and the shiny surface of the scale make it very conspicuous. Immature forms are oval, flattened, light to dark brown in color, and have a waxy cover- ing. Injury The damage caused by this insect is similar to that produced by infestations of the European fruit lecanium. If the scales are quite numerous, their feeding upon the twigs can result in a reduced vigor of the tree. Of more immediate concern to the grower is the production of honeydew which drips to the foliage and fruit. As is so often the case with such honeydew, the growth upon it of a black fungus results in a black or sooty appearance of affected leaves or fruit. In the same way as the European fruit le- canium, honeydew is produced both by the maturing females in spring and by the immature forms in summer. Seasonal development The calico scale overwinters as a par- tially grown scale on the twigs. In early spring, prior to the blooming of the trees, the scale begins to grow and reaches ma- turity by April or early May. Eggs are laid in great abundance under the female scale, and crawlers emerge in late May . Calico scale on a pear twig. or early June. The crawlers move to the leaves, where they settle and feed. In the fall, the immature scales move back to the twigs to spend the winter. There is only one generation each year. Control program The scale spends the winter in an im- mature stage which is susceptible to treatment. If treatments are delayed be- yond the full dormant period, however, the scales may start to grow before sprays are applied. After growth begins in early spring, the scales are very re- sistant to most chemicals. Summer treat- ments, applied after all the eggs have hatched, are also effective. In most cases, parasites keep the scale population below economic levels and treatments are not necessary. At times, however, the sea- sonal spray program, or drift of insecti- cides from adjoining areas, may destroy [33] the parasites and cause an outbreak of the scales. SAN JOSE SCALE Pears, as well as other deciduous fruits, are often attacked by the San Jose scale, Aspidiotus perniciosus (Corn- stock) . It can be an important pest, for its attack is not limited to the twigs and limbs, but also involves the fruit. It is distributed over most of the areas where pears are grown and has a wide host range, occurring on many ornamental trees and shrubs as well as fruit trees. Appearance The mature female scales are about 1/12 inch in diameter, circular in shape, somewhat convex, and gray in color. The hardened covers have centrally located exuviae which are yellow in color. The insects beneath the scale covering are bright yellow with two pairs of lobes. The yellow body color serves to distin- guish this scale from the Italian pear scale, which has a purple body. The covers of immature forms of the San Jose scale are black in color and when present are referred to as black cap stages. Injury The concentration of scales on the twigs or limbs, and their consequent feeding, may cause the death of tissues, and in many cases, the entire limb or twig can be killed. The scales tend to congregate around the buds or nodes of the twigs and can be found in concen- trations so dense that their covers over- lap. A diagnostic feature of the effects of San Jose scale is the red discoloration of plant tissue around the place of at- tachment. On the fruit, the presence of the scale produces a sunken spot, surrounded by a circular red area. If the scale attack is heavy, the fruit can be stunted and misshapen. On a green fruit, such as pears, these red spots are very conspicu- A color photo showing damage by San Jose scale is shown on page 6. ous, and fruits so affected are classed as culls. Unlike the unarmored scales, such as European fruit lecanium, no honey- dew is produced by the San Jose scale. This scale is often a pest on young trees, and frequently escapes notice. In such cases, the scales can become so nu- merous that the young trees will be seri- ously damaged or killed. Seasonal development San Jose scale overwinters on the twigs and limbs in several stages, but mostly as the first nymphs or black caps. They remain inactive until late January or early February at which time the nymphs start to grow and transform into second nymphs. At this stage the black color is lost, and the scales become gray. Dur- ing March and April, the scales develop to mature males and females. From May on, crawlers are produced almost con- tinuously until late fall. In contrast with most species of scales, the young of the San Jose scale are born alive. There is a considerable overlapping of generations during the summer and fall, and it is San Jose scale on pear twigs. [34] principally in winter that the majority of the scales are in the immature stages. The crawlers wander about before set- tling on the twigs, limbs, or fruit. Since they are produced almost continuously during summer and fall, they may be spread by various means, such as wind or birds. Control program Since the scale occurs in overlapping generations during the spring, summer, and early fall, control measures applied during these times are only partially ef- fective. During the winter months, when the scales are mostly in the first stage nymphs, they are more susceptible to treatment, and sprays applied during the dormant season are usually effective. The problem of coverage is most important in San Jose scale control, since the scales are located on the twigs and limbs, and are often piled one on the other. It is often noted that the fruit from the tops of the trees are attacked by San Jose scale, indicating that coverage in that area of the tree was not adequate. With this scale species, a thorough drenching spray is most important, and if proper winter controls are used, the scales can be held below injurious levels. Some of the immature individuals, especially those which settle on leaves or actively growing twigs, perish before attaining maturity. Older nymphs and adults are attacked by parasites. Serious infestations occur from time to time, pre- sumably when for unknown reasons the natural control factors fail. ITALIAN PEAR SCALE Although distributed rather widely over most of the pear growing areas, the Italian pear scale, Epidiaspis piricola (Del Guer.), is seldom considered to be a major pest. It is associated with moss or lichens, hidden under bark folds, and is generally not noticed until infes- tations become severe. In most cases, the spray program used for other scale in- sects holds this pest in check. The scale is more commonly encountered on back- yard trees and in abandoned rather than in well-kept orchards. Appearance The cover of the adult female is a light to dark gray circular scale with dark brown exuviae. The covering of the male scale is slender, white in color, and has yellow exuviae. Beneath the scale covering, the body of the mature female is reddish purple in color, and this serves to distinguish it from San Jose scale. The covers of the immature forms are also gray in color but tend to be lighter than the adults. This insect is usually found hidden under moss and lichens and is seen only if this protective plant cover is scraped away. Injury The damage caused by this scale is difficult to assess, since this species sel- dom occurs in large numbers. If numer- ous, it may adversely affect the vigor of infested limbs with a consequent reduc- tion in fruit size. It has been observed that pitting of the limbs can result from a concentration of scales in one area, and on nursery stock they are capable of pro- ducing pits on the small twigs. The scale is restricted to the wood of the tree and does not attack the fruit. Seasonal development The biology of this scale is incom- pletely known. It overwinters mostly as a mature scale, but immature stages can also be found in winter. Crawlers seem to be produced more abundantly in the spring but are also present in early summer. There may be more than one generation per year. At any rate, obser- vations indicate that adults and imma- ture forms occur together during the summer. A color photo showing Italian pear scale appears on page 7. [35] Control program Dormant sprays for other pests will hold the Italian pear scale in check unless the trees are too heavily covered with moss and lichens. In this case the use of ma- terials during the dormant season which destroy moss and lichens, will expose the scales, and they apparently will not sur- vive when the plant growth is removed. The effect of parasites and predators on these scales is not known, but a num- ber of natural factors apparently hold the scale in check. BUFFALO TREE HOPPER In the foothill districts of northern California, the buffalo tree hopper, Stictocephala bubalus (Fab.), is often encountered as a pest of pears. It breeds in areas of natural wild growth, and pears grown close to this native cover Buffalo tree hopper damage on a pear twig. are subject to attack. Since the adults and nymphs also feed on a variety of native shrubs and trees, uncultivated or- chards are more apt to be infested. In areas where cultivation is generally prac- ticed, the buffalo tree hopper is seldom observed. Appearance The adult treehoppers are about % inch long, bright green in color, with yellow pigmentation on the underside of the body. As is common with this group of insects, they possess horns on the pronotum. These horns are short, stout, and project laterally. The eggs are white, cylindrical, and are rounded on one end and tapered on the other. They are inserted in slits within the bark of the host plants and are deposited in rows. The immature forms are green in color and have large spiny structures on the dorsal surface. Injury The damage caused by the buffalo tree hopper is restricted to the twigs and small branches. The egg punctures can often be so numerous as to impair growth and cause the bark to split. In some cases the twig will be girdled and killed out- right. These splits in the bark are also avenues of infection for certain diseases. The egg punctures are usually found in two- and three-year-old wood rather than in new growth. On older trees, the dam- age is minor unless egg infestation is un- usually high, but young fruit trees and nursery stock may be killed. Seasonal development The treehopper overwinters in the egg stage in the twigs of fruit trees or other host plants, and the eggs hatch in the spring, usually in May or early June. The nymphs feed on the succulent foliage of trees or weed hosts and reach maturity in midsummer. In September and Oc- tober, the adults insert their eggs under the bark of host trees in crescent shaped [36] slits. They are usually laid two to a slit, opposite each other, and the series of two slits form an oval area on the twig. Control program The only known way to control this insect is by clean cultivation or removal of native hosts. In some foothill areas, this is not practical and the trees suffer damage as a result. There is no chemical at present that will serve to prevent egg deposition, and as long as native host plants are abundant, there is no practical means of control. AMERICAN PLUM BORER The American plum borer, Euzophera semijuneralis (Walker), is occasionally encountered on pear trees, although it is not restricted to this host. Very little is known about the biology of this pest, and it is seldom damaging enough on pears to be noticed. Appearance The adult moth has a wing spread of about % inch, with the forewings gray in color with brown and black markings. The mature caterpillars resemble codling moth larvae, for they are white to pinkish in color with brown heads. Injury Apparently the American plum borers attack areas on the trees which are al- ready injured and thus contribute to a general weakening of the host. They do not seem to be primary pests except in the case of graft unions, where they will invade callous tissue. The larvae feed within the bark, and therefore can de- stroy considerable tissue. The factors which bring about an attack of the borer are not known, as they are not frequently encountered. Most of their attacks are restricted to the trunk and main limbs of the trees. They are often found feeding in large numbers in gall tissue. This type of feeding does no harm to the tree as far as is known. Seasonal development Larvae can be found at most periods of the year, indicating that there may be either several overlapping generations or a single brood which has a long breed- ing span. They are found only in wounds, gall tissue, graft unions, or in sunburned areas on the trunks and main limbs. They are usually not encountered in healthy tissue. Control program If pear trees are kept in a healthy con- dition and graft unions well covered until they have healed, there is appar- ently little need for growers to be con- cerned with this borer. Graft wounds may be protected from infestation by local application of insecticides to the vunerable areas. SHOT-HOLE BORER The shot-hole borer, Scolytus rugu- losus (Ratz.) , is a general pest of decidu- ous fruit trees and is widely distributed over the fruit growing areas of Califor- nia. It is attracted to orchards which are neglected or in poor condition and is more often encountered in stone fruit trees than in pear trees. Appearance The adult beetles are about 1/10 inch long, and are cylindrical in shape. The body color is black or dark brown with the legs a lighter brown. Mature larvae are white with small brown heads. They are legless, and the bodies are usually curved. Injury The damage to fruit trees caused by the shot-hole borer is from the feeding of both the adults and larvae. The adults frequently attack the base of the buds, where they bore short holes. A healthy tree responds by profuse gumming. The adults will also attempt to enter the twigs and main limbs. If the tree is in a healthy condition, the borers will not be able to [37] establish colonies because of gumming, but a continued attack of this kind will eventually weaken the trees. On weak trees, the adults are able to penetrate to the cambium layer and con- struct their tunnels. The larvae, which feed at right angles to the main tunnel, can girdle the twig or limb and thus kill it. Even though the twig or limb is not immediately killed, it becomes suscepti- ble to further beetle attack, and eventu- ally becomes so riddled with mines that it cannot continue to function. Seasonal development The shot-hole borers spend the winter as larvae within the inner bark of the infested trees. They continue to feed dur- ing the winter months. Some pupation takes place in winter, but the majority of the larvae pupate early in spring. Adults emerge through small round holes in the bark in late April or early May. The females cut circular holes in the bark and construct radial tunnels through the cambium layer. As soon as a short length of tunnel is completed, eggs are laid along its walls. Newly hatched larvae feed in side channels which are usually at right angles to the main tunnel. By June, the adults of this generation develop, and thereafter the broods overlap greatly. Eggs, larvae, pupae, as well as adults occur together in the completed burrows. Beetle activity continues through October, and there are probably three or four generations per season. Control program Since the beetles do not propagate in healthy, vigorous trees, the control of this pest is mostly a cultural one. If the trees are kept in good condition by proper fertilization and irrigation, the beetles will not be able to enter the bark and establish colonies. A program of orchard sanitation is also very important in shot-hole borer control. Any limbs which are infested should be removed and destroyed, either by burning in winter or by shredding. If infested wood is left in the orchard or piled nearby, the borers will complete their development, providing a source of beetles which will again attack the orchard trees. Weakened or dying trees or limbs in an orchard serve to attract the borers, and infestations are apt to develop in these trees. Later, beetles emerging from these trees will attack healthy trees and <>' Left, entrance holes of ot-hole borer. Right, bark peeled back to show a pear limb attacked by shot-hole borers. [38] eventually weaken them until they too are susceptible to shot-hole borer attack. PACIFIC FLATHEADED BORER One of the worst pests of newly planted trees is the Pacific flatheaded borer, Chrysobothris mali Horn. The borer will attack trees while they are in the nur- series and after they have been planted in the orchard. These borers are dis- tributed over most of California and are usually more abundant in orchards lo- cated near wooded areas which may pro- vide a source of the beetles. They have a wide host range and will attack many native and introduced trees and shrubs. Appearance The adult beetles are % to % m ch long and dark reddish bronze in color. There are coppery spots on the wing covers and the entire wing cover has a coppery sheen. The mature larvae have the typical appearance of this family of borers, having large and flattened leg bearing segments, with a relatively slen- der and segmented abdomen. The larvae are pale yellow in color and when fully grown may be V2 inch in length. Injury The damage caused by the Pacific flat- headed borer results from the mining of the cambium layer by the larvae. They form a shallow winding mine in the inner bark which may extend into the outer wood. A symptom of injury is the flow of sap in the affected areas which appears as a wet spot on the bark. Later, these areas may crack and expose the borings. The feeding of the larvae may result in the death of a portion of the bark, or, if the infestation is extensive, the tree may be girdled and killed. The beetles may attack any portion of a tree, but on young trees their attack is usually confined to the main trunk. Development The borers spend the winter beneath the bark of the infested host plants as larvae or prepupae. Pupation begins in March and continues until June or later. Beetles begin to emerge in April and continue to emerge through July, with a few continuing into August. The eggs are laid on the bark, usually in some crevice or depression. There is a single generation per year, but the presence of the various stages of development over- laps considerably during the spring and summer. Control program All of the circumstances which dispose a tree to attack by the Pacific flatheaded borer are not known, but it seems to be attracted primarily to weakened trees or to those with injuries or sunburned areas. Young trees are much more sus- ceptible to attack, and it is rare that a well established tree will become in- fested. Control measures are mostly cultural and involve the protection of the young trees after planting. Whitewashing the trunks up to where the main limbs arise will usually prevent attack, if the white- wash is properly applied and repeated when necessary. Paper or cloth trunk protectors will also help to prevent at- tack. The above practices are based on preventing injury or sunburn on the bark, for these areas seem to be attractive to the borers. If infested limbs or wood are left in or near the orchards, this will provide a source of beetles which may attack or- chard trees. Any such wood should be burned or shredded, including infested wood from native trees or shrubs. [39] PESTS THAT ATTACK ROOTS WOOLLY PEAR APHID The only well known insect pest occur- ring on pear roots is the woolly pear aphid, Eriosoma pyricola Baker. Very little is known concerning either the biology or the injurious effects of this pest under California conditions, al- though it has been reported from several pear growing areas. It has been found attacking both young and established trees under a variety of growing condi- tions and in areas with different soil types. In the eastern states, the biology of this insect is well known, but under Cali- fornia conditions it does not follow the same pattern. Appearance The aphids are dull green to blue in color and covered with a flocculent white wax. They are found exclusively on the roots of the trees, both main and feeder roots. Injury The damage caused by the woolly pear aphid is not clearly defined. On estab- lished trees, there seems to be a lack of vigor, poor growth, and lowered pro- duction. However, this may be compli- cated by other factors since some of the affected orchards are planted on shallow soil. In some areas, trees with woolly pear aphid present on the roots show little difference in growth habits from uninfested trees. It has been reported that infestations of pear root aphids on young trees can stunt them severely and in some instances can cause the death of the trees. In most cases, however, the attack of pear root aphid on young trees is not severe enough to do more than temporarily slow their growth. Seasonal development In the eastern states, the aphids winter in the egg stage on European elm where they produce a cockscomb gall forma- tion on leaves in the spring. During the summer, they migrate to the pear roots and return to the elms in late fall. There are also wingless forms which remain on the pear roots the entire year. In California, the migration from pear to elm has not been observed, and ap- parently the aphids confine their activi- ties entirely to pear roots. It has been noted that nymphs and adults are present during the summer, which indicates that reproduction takes place during this period. Control program Control measures for the aphids in established orchards have not been de- veloped. Since they are below ground, a soil fumigant or a systemic insecticide which moves through the vascular sys- tem to the roots would be required. To destroy aphids on young trees infested in the nursery, the roots may be dipped in an insecticide suspension before plant- ing. It has been noted that the aphids are less injurious to young trees if the soil is kept moist. If trees are properly cared for they are better able to with- stand root aphid attack. Co-operative Extension work in Agriculture and Home Economics, College of Agriculture, University of California, and United States Department of Agriculture co-operating. Distributed in furtherance of the Acts of Congress of May 8, and June 30, 1914. George B. Alcorn, Director, California Agricultural Extension Service [40] 20m-6,'59(9820)WP