UNIVERSITY OF CALIFORNIA PUBLICATIONS. 
 
 COLLEGE OF AGRICULTURE. 
 
 AGRICULTURAL EXPERIMENT STATION. 
 
 THE 
 
 CALIFORNIA PEACH-TREE BORER. 
 
 By C. W. WOODWORTH. 
 
 
 "1 
 
 The Old Practice of Digging Out the Borers. 
 
 BULLETIN No. 143 
 
 (Berkeley, September, 1902.) 
 
 SACRAMENTO: 
 a. j. johnston, : : : : : superintendent state printing. 
 
 1902. 
 
BENJAMIN IDE WHEELER, Ph.D., LL.D., President of the University. 
 
 EXPERIMENT STATION STAFF. 
 
 E. W. HILGARD, Ph.D., LL.D., Director and Chemist. 
 
 E. J. WICKSON, M.A., Horticulturist, and Superintendent of Central Station Grounds. 
 
 W. A. SETCHELL, Ph.D., Botanist. 
 
 R. H. LOUGHRIDGE, Ph.D., Agricultural Geologist and Soil Physicist. (Soils and Alkali.) 
 
 0. W. WOODWORTH, M.S., Entomologist. 
 
 *M. E. JAFFA, M.S., Assistant Chemist. (Foods, Fertilizers.) 
 
 G. W. SHAW, M.A., Ph.D., Assistant Chemist. (Soils, Beet-Sugar.) 
 
 GEORGE E. COLBY, M.S., Assistant Chemist. (Fruits, Waters, Insecticides.) 
 
 LEROY ANDERSON, M.S.A., Animal Industries. San Luis Obispo. 
 
 A. R. WARD, B.S.A., D.V.M., Veterinarian, Bacteriologist. 
 
 E. H. TWIGHT, B.Sc, Diploma E. A.M., Viticulturist. 
 
 E. W. MAJOR, B.Agr., Dairy Husbandry. 
 
 A. V. STLTBENRAUCH, M.S., Assistant Horticulturist and Superintendent of Substations. 
 
 *J. BURTT DAVY, Assistant Botanist. 
 
 H. M. HALL, M..S., Assistant Botanist. 
 
 W. T. CLARKE, Assistant Entomologist. 
 
 C. A. COLMORE, B.S., Clerk to the Director. 
 
 EMIL KELLNER, Foreman of Central Station Grounds. 
 JOHN TUOHY, Patron, 
 
 ,\ 
 
 . Tulare Substation, Tulare. 
 JULIUS FORRER, Foreman, 
 
 R. C. RUST, Patron, ) 
 
 > Foothill Substation, Jackson. 
 JOHN H. BARBER, Foreman, ) 
 
 S. D. ME RK, Patron, ) 
 
 V Coast Range Substation, Paso Robles. 
 J. H. OOLEY, Workman in charge, ) 
 
 S. N. ANDROUS, Patron, ) I Pomona. 
 
 >- Southern California Substation, •< 
 J. W. MTLLS, Foreman, ) /Ontario. 
 
 V. C. RICHARDS, Patron, ) 
 
 )■ Forestry Station, Chico. 
 T. L. BO H LENDER, in charge, ) 
 
 ROY JONES, Patron, 
 
 WM. SHUTT, Foreman 
 
 * Absent on leave. 
 
 [■ Forestry Station, Santa Monica. 
 
 The Station publications (Reports and Bulletins) will be sent to any 
 citizen of the State on application, so long as available. 
 
CALIFORNIA PEACH-TREE BORER. 
 
 The most injurious insect in the Santa Clara Valley is generally con- 
 ceded to be the California peach-tree borer. This insect is most abun- 
 dant on peach and apricot trees, or on prune trees growing on peach 
 and plum roots. It bores into the bark just beneath the surface of the 
 ground, and is most easily recognized by the very characteristic masses 
 of gum that exude from the tree at the point of attack. These borers 
 often become so abundant as to entirely girdle large trees, causing their 
 death; and even when not so deadly their attack seriously cripples the 
 tree. The labor necessary to dig out or otherwise destroy these insects 
 amounts to a great deal. This Station has been repeatedly called upon 
 to advise in the matter of the repression of this pest, and to assist in 
 determining the facts involved in its treatment. Experimental work 
 undertaken in response to these inquiries has resulted in establishing 
 some important facts, and this bulletin is designed to furnish these data 
 and to give a general account of the history of this insect, in order that 
 growers may more intelligently direct their operations for the suppression 
 of the pest. 
 
 The Insect Peculiar to Santa Clara Valley. — Very diligent inquiry has 
 failed to discover that the peach-tree borer does any serious injury in 
 any part of the State other than the Santa Clara Valley. This is partic- 
 ularly remarkable from the fact that the Eastern species is so widespread 
 and so generally injurious, and from the further fact that the region 
 about San Jose has been a distributing point for nursery stock. It is 
 from this district, most probably, that the San Jose scale was distributed 
 over the State. The insect is one readily carried in nursery stock, and 
 so we must suppose that the conditions in other parts of the State must 
 be in some particular unfavorable to it, thus preventing its undue 
 increase. It is difficult, however, to conceive how the conditions in 
 this valley can be so strikingly different from those elsewhere as to make 
 this difference in the ability of the insect to maintain itself. 
 
 Significance Elsewhere. — While at the present time the insect is thus 
 extremely local in its distribution, there is every reason to expect that 
 in time it may suddenly become injurious elsewhere. The moth has 
 been collected in many localities by entomologists, and probably occurs 
 sparingly all over the State, only awaiting the advent of the peculiar 
 conditions which have made it successful in the struggle for existence in 
 
4 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. 
 
 the Santa Clara Valley. It is quite possible that the insect has occurred 
 and has done injury in other regions, and that orchardists have supposed 
 the death of the affected trees to be produced by other causes. 
 
 Relatives of this Insect in California. — The California peach-tree borer 
 belongs to the family Sesiidae, a small family of slender-bodied moths, 
 mostly day-flying in their habits, and often ornamented in a manner to 
 suggest a wasp in color and shape. The species known as occurring in 
 this State may be distinguished by the following synopsis : 
 
 SESI.ID.E. 
 
 Tongue long, (a); -rudimentary. Tibiae tufted, Paranthene ; -hairy, Mgeria. —(a) Pos- 
 terior independent vein of hind wing arising from posterior vein, (6); -from center of 
 cross vein, Melittia; -from end of cross vein. Palpi with long hairs, Memythrus ; -short 
 hairs, Albuna. —(b) Tibiae hairy, Vespamima; -slightly tufted. $ abdominal tufts 
 narrowing, 9 abdomen with lateral tufts, Sanninoidea ; - $ fanlike, 9 none lateral. 
 Sesia. 
 
 Melittia gloriosa feeds on sumac. 
 
 Memythrus robinix quite injurious to poplars and locusts. 
 
 Mgeria. Abdomen except base yellow, pacifica; -banded, tibialis. These insects 
 attack poplars and willows. 
 
 Vespamima sequoix attacks pines and redwoods. 
 
 Sanninoidea opalescens on peach, cherry, apricot, and prune. The most injurious 
 species of the group and the one treated of in this bulletin. 
 
 Albuna pyramidalis. 
 
 Sesia. Abdomen all blue, achillx; -all black, albicornis; -sides, or all of last two 
 segments red, animosa; -last three or four red, behrensii; -fourth and last two red, 
 polygoni; -all banded white, candescens; -all banded yellow, novaroensis ; -two white, 
 prosopis; -two yellow, neglecta; -$ with two or three, 9 with four yellow, rutilans; 
 - $ with four, 9 with three, tipuliformis ; - $ with six, 9 with five yellow. Fringe 
 red, rileyana; -orange, arizonise. 
 
 The food of only a few of these species has heen determined. The albicornis preys 
 on willows ; tipuliformis on currants and gooseberries ; rutilans on strawberries ; and 
 prosopis in the galls on mesquit. 
 
 Paranthene palmii, the food of which is unknown. 
 
 LIFE HISTORY. 
 
 A good deal yet remains to be learned in regard to the life history of 
 this insect. No one has thus far made very careful breeding experiments, 
 nor has there been sufficient continuous observation of field conditions, 
 to answer all the questions that might be raised in regard to it. The 
 life history is known to be very different from that of the Eastern 
 peach-tree borer, as occurring in the Northeastern States. It is possible, 
 however, that the history of that insect in the southern limit of its 
 range might be more like that of our species, but the knowledge which 
 we have of it in the Southern States is quite as meagre as of this species 
 in California. 
 
 Winter Condition. — This insect is best known in its winter quarters, 
 because it is during the winter that practically all of the work for its 
 repression is done. In striking contrast with the Eastern borer, our 
 insect is more or less active all through the winter season, and the 
 
PEACH-TREE BORER: LIFE HISTORY. O 
 
 young worms grow and feed during all the warmer weather. It 
 appears that pupation never occurs until well into the spring, even 
 though the worm is quite large in the fall. This produces a tendency 
 toward the production of a large spring brood of moths; but a great 
 many of the worms that are on the tree in the winter do not transform 
 until quite late in the summer. 
 
 The larvae are found of all sizes during the winter. Farmers very 
 commonly suppose that this difference in size represents distinct broods, 
 
 Fig. 1. A nearly full-grown larva of the Peach-tree Borer. Magnified four diameters. 
 
 Fig. 2. The head from below. Still 
 more enlarged. 
 
 Fig. 3. The same from above. 
 
 and they commonly recognize three of these sizes, which they designate 
 as the small, medium, and large sized worms. In fact, however, this 
 classification is not sound, since every intergrade exists from the 
 smallest to the largest. During the course of their development these 
 insects molt like other larvae, each stage possessing a very much larger 
 head than the one immediately preceding it. The different stages can 
 usually be quite clearly distinguished by the size of the head; but there 
 is considerable variation in the size of two insects in the same stage, so 
 that we have not been able to satisfy ourselves as to the exact number 
 
6 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. 
 
 of molts. This will have to be determined by careful breeding experi- 
 ments. It is not likely, however, that this information will have any 
 very significant economic bearing upon the problem of suppression. 
 There is a great deal of difference between the burrow produced by a 
 young worm as contrasted with that of one of the older individuals, the 
 former being always very shallow and usually quite devoid of gumming 
 material, whereas the burrows of the large borers extend through the 
 bark and into the solid wood, and are almost invariably indicated by 
 the mass of gum on the outside. The time when the burrow becomes 
 gummy, or when the insect penetrates deeply into the bark, seems to be 
 wholly a matter of chance, or of individual peculiarity. 
 
 The Gum. — The most evident sign that the worm is working in the bark 
 of the tree is the exudation of a greater or less mass of gum from the 
 burrow. This gum mass is so uniformly present that most orchardists 
 consider it an unfailing and only sign of the work of the insect. Our 
 observations have shown that this is far from being the case. A great 
 many larvae were found by careful search, especially younger larvae, in 
 which there was no evidence whatever of gumming; and on the other 
 hand, conspicuous masses of gum occurred very commonly where there 
 was no evident sign of insect work. 
 
 It appears to be probable that the gum has no necessary relationship 
 to the insect at all, but represents rather the evidence of the work of 
 some decay-producing organism which has gained entrance to the tree 
 at the point where it was injured by the feeding of the borer. Indeed, 
 the presence of the gum seems to be distasteful to the borers, sometimes 
 it even apparently causes them to abandon a burrow and start another. 
 Gumming also occurs not uncommonly along the edges of wounds made 
 from other causes, and almost always accompanies the attack of toad- 
 stool fungi where it occurs along the line separating the dead from the 
 living bark. Gumming may occur where the insect attacks the tree 
 above the ground, but is always more copious in the moist situations 
 below the surface. 
 
 The fact that those attempting to cut out the insect depend almost 
 wholly upon the presence of the gum for the discovery of the burrows 
 of the larva, results in worms being overlooked in case the gumming 
 has not yet occurred; or sometimes the tree may be very seriously 
 mutilated in endeavoring to find a worm corresponding to a mass of gum 
 which has been produced by other causes. 
 
 The Burrow. — Ordinarily, there seems to be a great deal of variation 
 in the shape and direction of the burrow — about as many burrowing up 
 as down. The general direction of the burrow is usually more nearly 
 vertical than horizontal, though a few may go directly around the tree. 
 Very careful study fails to reveal any decided preference as to the side 
 
PEACH-TREE BORER: LIFE HISTORY. I 
 
 of the tree affected, so it would seem that in all these matters the location 
 or direction of the burrow is simply an accident. 
 
 Some have supposed that there is a certain definite arrangement that 
 would have to be taken into consideration in the matter of treatment. 
 The habits of the worms within the burrow are subject far no recog- 
 nized rule. They appear to move about the burrow, according as the 
 needs of feeding or cleaning-out compel them, with very little regard 
 to temperature or time of day. The burrow appears to be always kept 
 open by the worm, and the gum that gathers on the sides is pushed out 
 with the excremental matter that accumulates in the burrow. Some- 
 times the gum hardens into a tube-like extension of the burrow, which 
 may become as much as an inch long. 
 
 This gum tube is not to be confused with the silken tube almost devoid 
 of gum, which is made by the insect as its transformation period 
 approaches. The winter tube made by the Eastern species seems to 
 resemble rather the transformation chamber than the gum tube. In 
 many cases the transformation chamber contains more or less gum also, 
 and indeed sometimes the tube is chiefly gum and excrement at one end, 
 and silk and excrement at the other. Our species does not appear to 
 have the habit of making winter tubes, but continues to feed through 
 the cold season. 
 
 Spring Conditions. — With the commencement of the flow of the sap 
 in the spring, the older larvae proceed to the formation of their trans- 
 formation tubes. These are sometimes, indeed quite commonly, formed 
 within the burrows, especially if the amount of gum has not been 
 excessive. In other cases they will be upon the surface of the bark at, 
 or near, the mouth of the burrow. At no time of the year can a larger 
 number of worms, preparing for transformation, be found than in the 
 spring, due to the fact evidently that many of the wintering worms 
 which had for a long while been full grown and were only deterred from 
 transformation on account of the season, now suddenly find conditions 
 favorable and proceed to prepare for their transformation. After the 
 tube is formed and the insect ceases to feed, it still remains for some 
 time in the larval condition, and if disturbed will wake up at once; 
 indeed, it seems to be able to reproduce a new tube, if removed from the 
 old one, without any particular loss to itself. Finally, however, activity 
 ceases, the insect somewhat shrinks in size, and after a short period of 
 complete rest, during which it is unable to walk if removed, the skin 
 breaks and discloses the pupa which has been formed within. The life 
 of the insect within the pupa does not last very long, exactly how long 
 we can not state, and upon its conclusion the pupa becomes suddenly 
 active, pushes itself out of the transformation tube and almost immedi- 
 ately gives forth the moth form. In Fig. 4, showing the pupa of this 
 insect, will be seen the structures which aid them in this work of 
 
8 
 
 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 
 
 forcing the body out of the burrow. The sharp edge appearing on the head 
 end of the pupa, seen best in the side view, enables the insect to break 
 the structures ahead of it, and the spines which bound the back side of 
 most of the abdominal segments hold the insect in place, or give it a 
 point of leverage, so that it can, by bending its body back and forth, 
 gradually force its way forward. After it has gotten into the open, the 
 widely spreading spines, shown at the posterior end of the body, pre- 
 vent further progress and hold the pupa case to the end of the burrow 
 during the progress of the hatching of the moth. The line of splitting 
 
 Fig. 4. Pupa of the Peach-tree Borer. Magnified about four times. 
 
 along the back, through which the moth emerges, can be seen in the 
 right-hand figure. 
 
 The moth is not very commonly seen flying. Like the other mem- 
 bers of the family, it flies in the daytime and not at night, as is the 
 case with most moths. It produces a great many eggs, which are 
 laid upon the trunks of the trees scattered about, apparently with no 
 attempt at order. The egg is beautifully sculptured, slightly flattish, 
 but oval in outline. The insect is quite prolific, laying some hundreds 
 of eggs, and as they are, as a rule, laid singly, one moth can injure an 
 immense number of trees.' Young worms on hatching from these eggs 
 enter some crack or crevice of the bark, where they lie concealed, eating 
 into the substance of the bark, migrating about if the situation is not 
 to their liking, and usually travel downward. As a rule, they are not sat- 
 isfied until they get beneath the surface of the ground, where they find 
 
PEACH-TREE BORER: LIFE HISTORY. 9 
 
 the bark still moist. If there should be a small amount of earth in the 
 crotch of the tree they will very often select this place, and may come to 
 full development in the bark there. After attaining some size, usually 
 before reaching a quarter of an inch in length, the migratory habit 
 seems to be almost wholly lost, and the insect will thereafter ordinarily 
 complete its existence in one burrow. Throughout its life it is active, 
 however, in keeping its burrow clean, sometimes going quite out on the 
 surface of the bark in case the earth is loose, and if removed from 
 the burrow will have no trouble in establishing a new one. 
 
 Summer Conditions. — Throughout the summer there is a continuous 
 production of moths and laying of eggs, so that at any season of the 
 year worms can be found of nearly every size. The spring brood of 
 moths, however, which is, as already explained, unusually numerous, 
 results in there being a size of worm fairly uniform and more abundant 
 in numbers than those of any other size. These worms become full 
 grown, or nearly full grown, by autumn, but do not transform until the 
 following spring. Those individuals that are somewhat belated may 
 not be half grown at the time of the dropping of the leaves, but they 
 will generally be ready for pupation by the approach of spring. 
 Sometimes the summer moths may in some regions become more 
 abundant than usual, so as to produce a fairly distinct lot of worms of 
 considerably smaller size than these spring larvae. Occasionally, also, 
 there may be a similar abundance in the fall. These peculiarities have 
 given rise to the idea of three broods; but it appears that while there 
 may be three times in the year in which the moth is more abundant 
 than in others, and three fairly distinct sizes of larvae, still each lot 
 requires a full year for its complete transformation. The summer and 
 fall broods do not by any means remain distinct from the spring brood, 
 on account of the precociousness of some individuals and the belated 
 development of others, the latter thus becoming a part of the preceding 
 or succeeding brood. Commonly, the summer and fall broods can not be 
 as clearly distinguished as the spring crop of moths. 
 
 The really significant part of the outline of the life history here given 
 is that there is no time during the summer when eggs may not be laid, 
 and that usually the largest growth of young worms occurs early in the 
 season, but that occasionally equally abundant layings may occur at 
 any time in the summer. It will not be possible under our conditions, 
 therefore, to mark out any plan of annual treatment which will be 
 equally effective in different years. 
 
10 
 
 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. 
 
 REMEDIES. 
 
 The remedy, upon which the most dependence is placed in fighting 
 the Eastern peach-tree borer, is that of digging out the worms. The 
 conclusion of the very elaborate investigation by the Cornell Experi- 
 ment Station was that this process must form the essential part of any 
 plan for the control of this insect. In addition to it, the use of tar, 
 tobacco stems, tarred paper, or mounding with earth, must be resorted 
 to. The first of these was found to be the most effective, but possibly 
 dangerous to the tree under some conditions. 
 
 In California all of these methods and many others have been used 
 quite extensively and with more or less satisfactory results, but they all 
 certainly leave much to be desired, since they do not avoid the necessity 
 of also digging-out. The digging-out process so mutilates the tree, even 
 
 Fig. 5. Two forms of tools used in the "digging-out" method. 
 
 when the greatest care is exercised, that many growers are of the opinion 
 that more injury is done than when the worms are left alone. When 
 the digging is left to careless help, the tree is often very badly mutilated. 
 Fortunately, the peach root heals over a wound very readily and is very 
 tenacious of life, often keeping the top alive when there is but a narrow 
 strip of bark left intact. 
 
 Digging-Out. — The tools used in digging-out are a shovel, and a pick 
 if the ground is hard, together with a hoe or trowel for removing the 
 earth, and a chisel, gouge, knife, or home-made tool for cutting out the 
 insect. Several forms of these special tools are on the market in San 
 Jose, two of which are here figured. Some growers prefer a blacksmith's 
 hoof-knife instead of the form of gouge characteristic of these tools. 
 
PEACH-TREE BORER: REMEDIES. 11 
 
 The time of the digging-out is almost always made a matter of con- 
 venience, and the facts we have so far learned in regard to the life 
 history do not, as yet, prove that better results would follow a different 
 practice. An important feature of the digging-out method is that it is 
 extremely difficult to find all, or even the larger worms, in a tree; and 
 if the worms are small their discovery is almost or quite impossible. A 
 single going-over of the trees is thus only partially effective, and many 
 orchardists have found that three times during the winter will not 
 exhaust the supply, even though it is quite certain that no moths were 
 flying during the intervals. The rush of other work usually prevents a 
 summer digging-out of the worms, though it would seem that just as 
 good or better results might follow from work at that season. We do 
 not have sufficient data to decide accurately the relative value of the 
 supplementary means used in connection with the digging-out process. 
 
 CARBON BISULFID. 
 
 A method that has given exceedingly satisfactory results under favor- 
 able conditions is the use of carbon bisulfid. The fact that under other 
 conditions less thorough work was done, and that in some cases it has 
 undoubtedly resulted in the death of the trees, does not signify that it 
 is unavailable for the destruction of this pest. This substance has been 
 used on a commercial scale only in California, though the suggestion 
 was originally made for the Eastern borer by Prof. A. J. Cook, Con- 
 ductor of Farmers' Institutes for southern California, then residing in 
 Michigan. In Slingerland's experiments in New York it proved an 
 entire failure, and was condemned by him as being too expensive, too 
 dangerous to the tree, and entirely ineffectual against the insect. We 
 have no record of the temperature or the condition of the soil in these 
 experiments, and can only conjecture why the results were so unsatis- 
 factory. Certainly, as used in the orchards about San Jose there is 
 nothing as cheap as this method. When properly handled the danger 
 to the tree is none; and in effectiveness, when conditions are right, it 
 leaves nothing to be desired. 
 
 Danger to the Tree. — Carbon bisulfid has been used for so long a time as 
 an insecticide for the control of phylloxera that we may be very confident 
 as to its uniformity of action and efficiency against insects, and also 
 of the extent of the danger to the plant. 
 
 As used against the borer the danger from this substance is wholly 
 that of the action of the gas, since so little liquid is applied to each tree 
 that it all evaporates before it would be possible for it to penetrate 
 through the bark to the living tissue beneath. Some growers even make 
 it their regular practice to pour the liquid on the bark, and without bad 
 results. If enough material was used, or the soil was very wet so as to 
 prevent evaporation, injury might come from the action of the liquid. 
 
12 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. 
 
 The effect of the gas is dependent upon its density and the length of 
 time it is acting. Even the most delicate growing parts of the plant 
 are tolerant of a weak dose of gas continued almost indefinitely. The 
 point at which injury to root hairs occurs is very little beyond the 
 point where it begins to be effective against insects. 
 
 With the more easily killed insects it might be possible to use the 
 substance for the complete eradication of a subterranean insect, if we 
 could obtain an even distribution of the gas in the soil. 
 
 In actual practice it is found that in the case of phylloxera the use of 
 a strength that will be safe to the plant, almost always leaves some- 
 where a little colony of these creatures which are able in a short time 
 to repopulate the vine and require another treatment. This repetition, 
 every season or two, is very expensive in field work, so that it pays only 
 in unusually valuable vineyards. The chief uses of this chemical have 
 become, therefore: first, the stronger " death treatment,'' with which 
 both vines and insects are destroyed together; and, second, for disinfect- 
 ing cuttings or vines removed from the soil. In the latter case they are 
 given a still stronger dose, but for a shorter period, and even though the 
 smaller rootlets may be killed, the plant does not die, because being 
 planted in new soil it can replace any dead parts at once. The bark- 
 covered parts of the plant are many times more resistant to carbon 
 bisulfid vapor than are the growing rootlets and root hairs, and these 
 latter are quite as resistant as most insects. 
 
 In treating a peach tree, should there be any root hairs immediately 
 about the crown they 'might be killed by the carbon bisulfid at the 
 strength used, but this would not amount to anything to the tree. The 
 danger to the tree would only come from a strength of gas and a length 
 of time of treatment sufficient to injure the most resistant part of the 
 root-system. 
 
 The amount used in any case should not be sufficient to cause the 
 death even of root hairs very far away from the trunk; and the real 
 danger to the tree is not from too great destruction of root hairs, but 
 from the danger that the gas be retained about the crown in a concen- 
 trated condition long enough to cause the death of the more resistant 
 parts of the tree. 
 
 The only thing that could cause this retention of the gas about the 
 crown is the presence of water in the soil, which closes up the spaces 
 between the soil particles, through which the gas gradually diffuses 
 itself. The danger is greatest in heavy soils. In a very light, sandy 
 or gravelly soil the difficulty would more likely be that the soil might 
 be so dry that the gas would diffuse so rapidly as to fail to kill the 
 insect; in that case, of course, being also perfectly harmless to every 
 part of the tree. Practice has shown that there is a wide margin 
 between effectiveness against the insect and danger to the bark of the 
 
PEACH-TREE BORER: REMEDIES. 13 
 
 tree. Intelligently applied, there is no reason why it might not always 
 be entirely safe and effective. 
 
 Condition of the Soil. — The character and condition of the soil is the 
 most important consideration in the use of carbon bisulfid. The same 
 soil varies most greatly near the surface in the amount of moisture it 
 contains, and unlike the phylloxera work, it is here in this variable 
 surface soil that this treatment is to be made. 
 
 Extreme conditions should certainly be avoided, and uniform results 
 require uniform conditions. The best results have usually been obtained 
 in the orchards where the soil was rather light and in the best condition 
 of tilth. Under these circumstances, the method of procedure is the 
 simplest. All that is necessary is to pour the carbon bisulfid upon the 
 ground around the tree close to the trunk and immediately mound up 
 the earth a few inches against the base of the tree. In most soils it will 
 be necessary, in order to secure the best results, to remove the soil that 
 immediately surrounds the tree, as this is somewhat hard and packed, and 
 to replace it with loose soil taken from the surface stirred by the culti- 
 
 Hard earth removed. Filled with surface soil. Mounded after treatment. 
 
 Fig. 6. Method of treatment in medium and heavy soils. 
 
 vator. This is made level and the carbon bisulfid applied as before, and 
 more loose soil used in mounding. If the soil is rather wet or heavy it 
 will be necessary to remove this soil impregnated with the chemical, so 
 as to give the gas an opportunity to dissipate itself after a day or two, 
 and thus prevent too long an exposure of the root crown to the gas. 
 
 Except on the lightest soils the earth should always be removed if a 
 rain should intervene, as it will effectually seal up the gas and prevent 
 its escape into the air. 
 
 In some orchards sufficiently dry soil may not be found for filling the 
 excavations at the time it is desired to make the treatment, in which 
 case chaff or straw may be used instead, covering it well with earth - after 
 pouring on the carbon bisulfid. This should, of course, also be removed 
 after a day or two. 
 
 In very dry, light soils, if the carbon bisulfid dissipates itself too 
 rapidly to accomplish the desired destruction of the borer, the use of 
 water will make it effective. For this purpose, excavate around the 
 trunk, then wet the soil, put back the earth, making all level, apply the 
 carbon bisulfid, bank up the earth, and sprinkle the top slightly. In a 
 day or two the extra earth may be removed, if it has not dried out 
 enough to permit the escape of the gas. 
 
14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 
 
 The Dose. — In the matter of the quantity to be applied to a tree, there 
 is a great deal of difference in the practice of different orchardists. 
 Economy would favor as small a dose as will be sufficient, but if too 
 small, nothing will be accomplished by the treatment, so orchardists 
 generally feel that it is better to give too much than too little. It will 
 not be possible to recommend a dose that will do for all conditions. 
 Probably a larger number try to make their average dose about one 
 ounce than any other amount; and this may be taken as a tentative 
 dose to experiment with. Each orchardist must determine for himself 
 that which will be best under his conditions. The most important 
 factor in this matter is the degree of looseness of the soil. The heavy, 
 compact, moist soils require the smallest dose; and the lighter, looser, 
 and drier soils a larger quantity of the carbon bisulfid. 
 
 The common practice is to vary the dose 
 according to the size of the tree, putting 
 often several times as much around a large 
 tree as a small one. Some little variation 
 of this kind should occur, but not as much 
 as is the practice. In an orchard with fairly 
 uniform trees the best practice would be to 
 make the dose uniform, without regard to 
 the small variation in the size of the tree. 
 A little change in the character of the soil in 
 different parts of the orchard is a very much 
 more significant matter. 
 
 The method of applying carbon bisulfid 
 
 Fig. 7. Can for measuring dose of USUally adopted is the USe of a COmmOD 
 carbon bisulfid. . 
 
 machine oil-can. This has the advantage 
 of convenience, but makes it difficult to apply a uniform dose. The 
 deposition of sulfur in the spout decreases the rate of flow, and often 
 gives trouble and makes the judging of the size of the amount dis- 
 charged very difficult. We have planned a can by which a uniform 
 dose can be rapidly measured and applied. It is shown in Fig. 6. It 
 consists of an ordinary kerosene can, or a machine oiler could be 
 used instead. A bottle (a) with a doubly perforated cork and discharge 
 tube (b) is attached to the spout (c). The can is reversed until the 
 bottle-measure is filled, when by righting it the liquid will pour out of 
 the discharge tube. A bottle of any required size, fitted with perforated 
 cork, can be had at any drug store. 
 
 Summer Treatment. — So far the use of the carbon bisulfid, like the 
 digging-out process, has been almost wholly confined to the winter 
 season. This has been chiefly because this season is the least busy, 
 and partly because of the fear that there would be more danger to 
 the tree if the chemical were applied when the tree was not dormant. 
 
PEACH-TREE BORER: SUMMARY OF CONCLUSIONS. 15 
 
 The danger to the tree at this season is not at all greater than when 
 the tree is dormant, when the treatment is made in the manner 
 employed for this insect. The drier average condition of the soil, which 
 favors the rapid diffusion of the gas, may cause some trouble, on account 
 of the difficulty of keeping the dose strong long enough to kill the 
 insect. 
 
 Quite as much, or more, of the injury to the trees is done by the 
 worms during the summer than during the winter, and it would seem 
 desirable to make one or more applications to prevent this summer 
 injury. As so many of the worms are small in summer, digging-out 
 would be very difficult to do in a thorough manner; but carbon bisulfid 
 finds no more difficulty in discovering a small worm than a large one, 
 and the injury is stopped before it is hardly begun. 
 
 If but a single application is to be made, the best time to do it is early 
 in the winter, after all the eggs have hatched and no more moths are 
 flying. The earlier worms will have already done considerable injury 
 by this time, which might be prevented by a midsummer treatment. 
 Whether more treatments than these two will be profitable in most 
 seasons it is not possible now to say, but careful observation of the con- 
 dition of the trees in an orchard ought to enable any grower to come to 
 satisfactory conclusions on this subject. 
 
 SUMMARY. 
 
 While the peach-tree borer is at present injurious only in the Santa 
 Clara Valley, a watch should be kept for it elsewhere. 
 
 As far as known we have but one brood a year, but worms in all con- 
 ditions can be found at almost any season, and moths fly and lay eggs 
 all summer. 
 
 The presence of the gum can not be depended upon as an indication 
 of the young worm, so that it is difficult to get all when digging them 
 out. 
 
 Carbon bisulfid has proven a most efficient method of killing the 
 worms. 
 
 The use of carbon bisulfid is not without danger to the tree, but with 
 proper caution is safe. 
 
 The condition of the soil is the most important item to consider in 
 the use of carbon bisulfid. 
 
 The soil next to the tree must be loose enough to allow the gas to 
 reach every part of the crown, in order to kill all the worms. 
 
 Uniform treatment as to dose should be attended to. The time for 
 the most important treatment is in the early winter. Probably, in 
 addition, a midsummer treatment would be nearly as useful.