Division of Agricultural Sciences UNIVERSITY OF CALIFORNly cr *,CKS %. l"-«r*-\ *LS**i i I university or cAurpn^A. JUN 7-1977 SER. REC. L%RARY i ,4 >V NEMATODES and their Control in VINEYARDS Mr If ■*''♦ . H. HART ; N. KASIM 1CULTURAL Station e r v i c e CIRCULAR 533 Revised CAECAG 533 1-20 (1973) Nematodes and Their Control in Vineyards THIS CIRCULAR provides information on nematodes in vineyards for growers, chemical company representatives, and others interested in grape production. Specifically, it deals with the following: • General description of nematodes • How they injure plants • What species are found in California vineyard soils • Brief life histories of prevalent species • Control measures, including preplant and postplanting soil fumigation, and use of resistant rootstock varieties November 1973 THE AUTHORS D. J. Raski is Professor of Nematology and Nematologist in the Experiment Station, Davis; W. H. Hart is Extension Nematologist, Davis; and A. N. Kasimatis is Exten- sion Viticulturist, Davis. THE COVER PHOTO shows the application of fumigant under continuou prior to planting a vineyard. While the University does not yet recommend tl fairly common practice in the coastal areas. Scope of the Problem All grape varieties grown on their own roots and most common grape rootstocks used for commercial propagation may be attacked by several kinds of plant-para- sitic nematodes which are widely distri- buted in California. These nematodes also attack many other agricultural crops and ornamentals and have been spread by transplants and plant divisions of many crops in soil on plants or agricultural ma- chinery and in irrigation water. Studies of nematodes and the experience of growers indicate that nematodes on grape can be a problem in any area of the state where grapes can be grown successfully. The importance of the root knot nematode in grape production has been recognized for many years. However, we now know that these nematodes, as well as other less obvious species, do much more harm than was realized. We have more complere knowledge about the wide distribution of plant-parasitic species in vineyard soils. At the same time, growers increasingly have been replanting grapes in old vine- yard sites that have reached a stage of declining productivity or on old agricul- tural lands formerly used for tree crops or for nematode-susceptible vegetables and field crops. Vines may produce satisfactory yields for long periods, even though nematode populations are increasing, if other fac- tors such as soil, water, and cultural practices are favorable. Even old and heavily infested vines may remain pro- ductive under optimum cultural condi- tions. However, the high nematode popu- lations will attack, stunt, or kill young vines when such soils are replanted. Studies under controlled greenhouse conditions have demonstrated that many nematode species injure grapes (table 1) . Field experiments with established nema- tode populations have provided additional evidence and have demonstrated the bene- fits of proper soil treatment before re- planting. Studies have shown that certain nema- todes formerly not known to be damaging to grapes may cause serious injury. These include species which do not enter root tissues but feed on roots while remaining in the soil. One such species also carries and transmits certain virus diseases of grape and is an important factor in the persistence of these diseases in vineyard soils. What Nematodes Are Nematodes are slender, active, worm-like organisms. Like insects, nematodes differ greatly in habits, size, and appearance. The smallest plant-parasitic forms are about Y25o inch long, while the adults of certain animal parasites can grow to be several feet long. The typical, or basic, body form of nematodes is long and cylindrical, with the body tapering at both ends to the head and tail. In a number of plant-parasitic forms, the adult female becomes a swollen pouch-like organism, lemon-, pear-, kid- ney-, or irregularly-shaped, depending on species, while the male remains slender and worm-like. Plant-parasitic species are very small, averaging only about % 4 inch in length; and structural features, even body shape, can be observed only with a microscope. These species vary not only in the appear- ance of the adults but in the way they live and feed. Feeding is accomplished by means of a hollow needle-like mouth part (the spear or stylet), which is used to puncture the cells of plant tissues and ex- tract the contents. [3] All plant-parasitic forms begin life as eggs, deposited by females in plant tissue or in the soil, singly, or in egg masses held together by a jelly-like material each of which may contain more than 500 eggs. Larvae form within the eggs, hatch, and go in search of suitable plant tissues on which to feed. Larvae undergo several moults, increasing in size until the adult stage is reached. In some species the larva which hatches from the egg is the only stage that can move and is the infective stage. In other species, all stages from young larvae to adults can move freely and are equally infective. Nematodes that attack grape represent virtually all types of plant-parasitic species. Some are endoparasites; that is, they live most or all of their lives inside the roots. There, they are protected by layers of root tissues against adverse soil conditions and chemical soil treatments. Others are ectoparasites — feeding on ten- der root tissues, while most or all of their bodies remain in the soil outside the roots. These species are more vulnerable to soil treatment of established plants, since their bodies are not protected by root tissues. Migratory nematodes are those whose adults and larvae move freely through soil and root tissue. Sedentary nematodes have larvae that move freely, but the adult females are swollen organisms that cannot move. Listed here are the nema- todes infecting grape, grouped according to their types: Type Endoparasites Ectoparasites Migratory Root lesion nematodes (Pratylenchus spp.) Dagger nematodes {Xiphinema spp.) Ring nematodes (Criconemoides spp.) Pin nematodes (Paratylcnchus spp.) Spiral nematodes (HeUocotylenchus spp.) Sedentary Root knot nematodes (Meloidogyne spp.) Citrus nematodes (Tylenchulus semipenetrans ) How Nematodes Injure Plants Nematode infestations destroy plant roots which result in weak top growth and re- duced yields. When young plants are placed in heavily infested soil, root growth may be completely prevented and the plants may never become established. This injury may take place in a number of direct and indirect ways. The most obvious means by which nematodes injure plants is the mechanical penetration and feeding on roots by large numbers of nematodes. As many as 2,000 to 10,000 root lesion nematodes may be present in one gram of root. A single gall induced by root knot nematodes may con- tain more than a dozen females, each cap- able of producing 600 eggs, and these galls may be so close together on young roots that they resemble a string of beads. The impact of sheer numbers of nema- todes, therefore, has a significant effect on plant growth. Nematodes play an important part in allowing entry for secondary decay or- ganisms into roots. The wounds made in roots by the entry and feeding of endo- parasites. together with the weakened con- dition of such roots, enable other soil or- ganisms, fungi, and bacteria to enter the roots, which they may not have done otherwise. In feeding in or on roots, nematodes [4] puncture cells of the root and withdraw part or all of the cell contents. During this process the nematodes inject salivary fluids into the cell. The function of these secretions is not understood completely, but the effects can be seen readily in some cases. The growth of cells, even those some distance from the cell actually fed upon, often is changed radically. Cells may be killed, stop normal growth, or begin to enlarge or divide abnormally. The conductive tissue which supplies water and soil nutrients to the plant tops often is blocked, and both root and top growth is suppressed. Certain ectoparasitic nematodes trans- mit specific virus diseases during feed- ing on grape roots. These nematodes now are known to be responsible for the per- sistence of certain viruses in soil for sev- eral years even after diseased host plants have been removed. Only a few nema- todes are required to transmit the disease to new plants, and the virus persists in the nematodes for considerable periods. Above-ground symptoms of nematode injury to established plants, except for symptoms of nematode-transmitted virus diseases, usually are similar both to the effects of other root-destroying organisms and to any adverse soil or cultural condi- tion which results in reduced growth and productivity. Root symptoms of nematode infestation are more characteristic than those seen above ground, but they vary with dif- ferent nematodes, degree of infection and the response of the host plant. Root knot nematodes Meloidogyne spp. produce swellings or galls on roots. Infection occurs in young rootlets, but galls may persist on older roots. Heavy infections may completely destroy the root systems of young plants. Galling of roots blocks the flow of water and food, thus starving the plant. Those parts of the roots beyond the point of at- tack often die. Root knot nematodes occur throughout California but cause more se- vere injury in light coarse-textured soils than in loam and clay soils. The root knot nematodes have been known since about 1850 and have been described under a variety of popular and scientific names. The most common of the former have been root knot or garden nematodes or eelworms. About a dozen species and varieties of root knot nema- todes are now known to exist. At least five are known in California; three have been found on grape. (See table 1.) Table 1 NEMATODES OF IMPORTANCE ON GRAPE IN CALIFORNIA Name of Nematode Common Scientific Distribution Root Knot: Cotton Meloidogyne incognita Common Mostly in warm soils of the San Joaquin Valley and in southern California Uncommon on grape but not on other crops Common Pratylenchus vulnus Dagger: American (none) Citrus Xiphenema americanum Common Tylenchulus semi- Tulare, and Riverside counties. transmits the fanleaf virus disease complex. [5] Root knot nematodes are sedentary endoparasites. Females within root galls deposit a large number of eggs in a jelly- like material referred to as an egg mass. Larvae form within the eggs and hatch when soil conditions are suitable. When soil conditions are unfavorable, many larvae remain within the eggs and can survive for several years. Free larvae in soil, in the absence of a suitable host plant, can survive for at least a year under normal soil conditions. After hatching, the young infective larvae move through the soil or root tissue to a suitable root or to new areas of the root. Movement of individual larvae is limited to a few inches. In general, roots grow to the nematodes, since their move- ment is limited. Infective larvae penetrate young rootlets near the growing point. Some penetration also occurs in areas where roots have been injured. Once within the root, larvae establish themselves and begin to feed. At this point they are incapable of further move- ment except for the head in feeding. Dur- ing development, larvae swell, first be- come flask-shaped and finally, after sev- eral moults, become adults. Adult females are soft-bodied and pear-shaped and are pearly-white at maturity. These are the so-called "pearls" which growers and home gardeners often see in cut sections of galls from fleshy-rooted plants. Adult males develop within the bodies of flask- shaped late larval stages; at maturity they are once again elongate worm-like bodies able to move about. Males are not necessary to continued reproduction of the nematode. Development of males ap- pears to be associated with vitality of the host plant. More males are produced on declining or heavily infested plants than on lightly infested ones. The number of generations per year of root knot nematodes is governed by soil temperature in the presence of suitable hosts. Generations may develop almost continuously in warm areas under favor- able conditions. In temperate regions, the number of generations varies from one to two per season in the north to as many as five to eight in the south. In hot desert areas, reproduction may be reduced by lack of moisture, even though favorable temperatures may be present for a longer period. In general, root knot nematodes can grow and reproduce at any tempera- ture suitable for growth of susceptible host plants. Growth of young rootlets may be corn- Root knot nematode: infectious larva (top) finds young feeder roots and enters them. Inside the roots it swells (center) and, on maturity, deposits eggs in masses either inside or outside the root (bottom). The eggs hatch to become infectious larvae. Actual length about 1 /60th inch. 6] pletely stopped when larvae enter. In the root area where a larva is feeding, cells enlarge and cell walls eventually collapse leaving large abnormal "giant cells" on which the nematode continues to feed. Several such "giant cells" may be formed around the head of each nematode. As infection continues, changes occur in other nearby cells, including conductive tissues, which result in partial or com- plete blocking of the flow of water and nutrients. Depending on the root knot species involved, the root below the site of infection may die, and new rootlets will be produced just above the infection site which, in turn, will become infected. The latter effect will eventually produce an abnormally branched "hairy root" condition. Root lesion nematodes Pratylenchiis spp. cause decaying areas (lesions) on the large roots of some plants that may become large enough to be seen with the naked eye. On other plants, including grape, they invade the young rootlets injuring and often girdling them. The system of small rootlets, which is the plant's most important mech- anism for the absorption of water and soil elements, may be completely destroyed. Root lesion nematodes occur on grape throughout the state. Damage usually is more severe on heavier, fine-textured soils but also occurs in coarse-textured soils. At least nine root lesion nematode spe- cies are known in California, and are among our most important nematode pests on agricultural crops. (See table 1.) One species, Pratylenchus vulnus, is known in many areas of the state on grape as well as on other important tree and vine crops. Infested plants lose their vigor, and production is reduced. Young plants placed in infested soil fail to pro- duce satisfactory root systems and will remain weak or die. Another species, Pratylenchus neglec- tus, is frequently found in soil samples from grapevines. This species also has The root lesion nematode spends its life cycle feeding while moving through the root and deposit- ing eggs singly. Actual length varies from about l/30th to l/50th inch. been found in a few declining vineyards heavily parasitizing the roots of vines and appears to be a serious pathogen in these cases. A third species, P. thornei, also is commonly found in soils with vineyard potential, but this species has not been found in grape roots and is not believed to be of importance in vineyards. Root lesion nematodes are endopara- sitic and migratory. Adults as well as larvae are worm-like in shape and are able to move through the roots or soil. Eggs are laid singly in root tissue while females move through the roots feeding on first one cell, then another. [7] Dagger nematodes Xiphinema spp. are large nematodes of the ectoparasitic migratory type. They do not enter the roots but remain in the soil feeding on the suceulcnt tissue of young root tips with their long needle-like mouth parts (spears). Growth of young rootlets is suppressed, and root tips often become slightly swollen and somewhat curved or sickle-shaped. Branching may occur above the place of feeding, and re- peated feeding by large numbers of dagger nematodes may form a dense mass of abnormally branched, swollen and darkened rootlets. Two species of dagger nematodes occur on grape and other crops in California (table 1.). Both are distributed widely in California and have similar direct ef- The dagger nematode lives outside the roots and feeds on them by inserting its long dagger-like spear. Actual length about 1 10th inch. fects on vines. One species, Xiphinema index, also transmits the fanleaf-yellow mosaic-vein banding virus disease com- plex of grape. This nematode is respon- sible for the reinfection with these viruses of new grape plantings on old grape land, even though several years may have passed since the removal of old virus- infected vines. The roots of such plants which remain in the soil after old plants are removed may remain alive for several years providing food and a source of virus inoculum for dagger nematodes year after year. Xiphinema index is found most commonly in coastal areas but is also known in the San Joaquin Valley as far south as Visalia and Delano. Another, Xiphinema americanum, is the most widely distributed dagger nema- tode in California. In grape it is often present only in small numbers and usually in association with other nematode spe- cies such as root knot, lesion, and ring nematodes. Assessment of damage caused by this species is difficult because of these coincident infestations and because X. americanum is difficult to rear under greenhouse and laboratory conditions. Field evidence indicates it is a serious pathogen reducing plant vigor and pro- ductivity. In some vineyards it builds up to very high populations causing extreme damage to and decline of vines. Citrus nematode Tylenchus semipenetrans was first dis- covered in California in 1912 and subse- quently has been found on commercial citrus in most areas of the world where the crop is grown. Other hosts include olive, persimmon, and the grape, Vitis vinijera. While most of California's citrus ap- pears to be already infested with the citrus nematode, it has been found on grape in only a few localities. Root symp- toms on grape resemble those on citrus, although its effect on vine growth or pro- duction has not been evaluated com- pletely. [8] Citrus nematode sometimes is referred to as an exposed sedentary endoparasite but is treated in this paper as an ectopara- site, because the body is never completely covered by root tissue. Young larvae feed on outer cortical layers of young roots and begin to develop. As the females de- velop through successive larval stages, the head penetrates deep into the rootlet, while the body outside the root enlarges and becomes a variably-shaped curved swollen structure on the surface of the root. At maturity females deposit numer- ous eggs in a jelly-like egg mass. Females often occur in large numbers on infected roots, and, since soil particles cling to the jelly-like material containing the eggs, in- fected roots appear crusted with soil which does not shake off and can be washed off only with difficulty. Males of the citrus nematode remain small and worm-like throughout life. Adult males are only slightly larger than the larvae that are to become females. Males do not feed and are not necessary for reproduc- tion. Ring nematodes Criconemoides spp. (ring) and pin ne- matodes, Paratylenchus spp. (pin) nema- todes are both migratory ectoparasites which occur widely in grape and many other crops and native plants in Califor- nia. Ring nematodes are small but robust and distinguishable from other nematodes by their prominent cuticular rings. Pin nematodes, in contrast, are very small with delicate obscure rings. Both groups have very long heavy spears in propor- tion to the size of the body. Spear length The citrus nematode, in its immature stages (center) lives outside the root. When it becomes an adult (top) it penetrates the root with its head, leaving the tail end outside where it swells and produces eggs (bottom). Actual length is about l/60th inch. [9] Table 2 NEMATODES OP SUSPECTED IMPORTANCE ON GRAPE IN CALIFORNIA Name of Nematode Common Scientific Distribution Root lesion Ring: ( none) (none) Pin: (none) (none) Spiral: (none) (none) Pratylenchus neglectus Criconemoide8 xenoplax Common Common Paratylenchus hamatus Common Helicotylenchus dihystera Limited, according to present records Limited, according to present records in some species may be nearly half the length of the entire body. The life histories and habits of these nematodes have not been completely in- vestigated. Although they occur on roots and in the soil around roots in large num- bers, their effects on most plants are still obscure. That they cause diseases has been demonstrated in only a few cases. On grape they may produce injury by their feeding in large numbers, and they may play a role in transmitting soil-borne dis- eases or in weakening a plant so that it becomes more susceptible to other disease. Spiral nematodes Helicotylenchus spp. (table 2) occur in many areas of the state around the roots of many agricultural and native plants. Normally they have been con- sidered migratory ectoparasites but often enter part way into the roots of some hosts. In grape they recently have been found entirely within roots and must be considered at least partially endopara- sitic. Recent laboratory studies have shown that these two species multiply readily in grape roots, but pathogenic effects have not been determined. How to Recognize Nematode Injury Root symptoms of nematode injury may be distinct as with root knot nematodes but injury caused by other nematodes is often obscure. Heavy infection often is followed rapidly by secondary soil or- ganisms which produce extensive decay. The roots of young plants placed among large populations of root knot nematodes may die before producing characteristic symptoms. Root lesion nematodes move from decaying root areas to new sites. When lesions produced by these nema- todes have been invaded by secondary decay organisms, the nematodes often can be found only in the soil. A field examination of vineyards or other crops gives only superficial and un- reliable evidence that nematodes may or may not be a factor in the growth of that crop or future crops. Root galls may be found indicating the presence of root knot nematodes, but other nematodes also may be present which do not produce obvious root symptoms. Laboratorv examination of both roots and soil usually is necessary to make 10 sure of the presence of injurious species. Both types of examination are required to detect the presence of the wide variety of nematode types known to attack grape. Identification of both the nematode group and species present is required. An ex- amination which shows only the total number of nematodes per acre is of little value unless injurious species are identi- fied from the mass of harmless or bene- ficial species usually present in all soils. Samples should be collected from sev- eral areas within the vineyard or other planting. Roots and soil from around the roots should be taken from a depth where moisture is uniform, usually at least 8 to 12 inches below the surface. Avoid sur- face soil and roots near the surface, where fluctuating temperature and moisture may reduce nematode numbers to low levels. Samples should be taken and source identified; vigor of the planting should be noted. If growth is satisfactory or uni- form over large areas, a number of sub- Above: healthy grapevine roots. Below, left: roots injured by dagger nema- todes, with distortions mostly on the tips of the rootlets. Below, right: roots at- tacked by root knot nematodes; note absence of feeder roots and characteristic swellings on the large as well as the feeder roots. samples may be combined to make a single sample of a large area. In areas of poor or questionable growth, however, samples should be identified separately. After collection, samples should be pro- tected so that nematodes remain alive until the sample is examined. Place soil and roots in containers such as plastic bags to prevent drying and do not allow these containers to overheat in the sun in the field, the hack of a car or truck, or during storage. In shipment or transport, samples can be protected in cardboard boxes, insulated with newspapers, or in inexpensive plastic foam chests. Make sure that labels are complete giving (1) name and address of grower, (2) name, variety, and location of crop, (3) portion or block which sample represents, and (4) pertinent history of crop vigor and previous crops. Samples should be sent only to com- mercial laboratories which have agreed to perform the complete soil and root examinations and species determinations required. The University of California performs a limited number of examina- tions in conducting its own experimental work and as an aid to farm advisors. Limited examinations also are performed by the California Department of Agri- culture as an aid to county agricultural commissioners. Neither the University nor Department of Agriculture can pro- vide laboratory services for normal agri- cultural operations. How Vineyards Are Affected The ultimate result of heavy nematode progressively weaker each year. Attempts infection on established grapes is weak- to provide increased or more frequent ened vines and reduced yields. In a typi- water, more fertilizer and to lessen the cal nematode situation, a few vines or crop load on affected plants by changed areas of vines in a vineyard block become pruning practices may improve the plants If your vineyard shows weak areas like the one pictured below, nematodes may be suspected. temporarily. Infected vines eventually be- come weakened and less productive, are removed, and new vines are set out. With- out soil treatment these young plants usually fail to grow satisfactorily or are killed. Infested areas enlarge further and eventually spread throughout most of the vineyard. Fanleaf virus further compounds the problem. Vines are damaged both by nematodes inhibiting good root develop- ment and by systemic infection of a virus disease. Control also is more difficult, be- cause both the virus reservoir (the vine) and the vector (the dagger nematode) should be eliminated. Many plant-parasitic nematodes are widely distributed in grape and other agricultural soils. Eradication from field soils is impossible with present tech- niques and may never be practical. The problem thus becomes how best to live with injurious species and reduce popula- tions below damaging levels. Control Nematode control practices presently in use are directed toward either providing clean soil in which new vines may be placed or restoring vigor and produc- tivity to established vines. Preplant treat- ments with various nematicides such as the 1,3-dichloropropene (1,3-D) soil fu- migants are well established, although rates to be used and depth of application still are being studied and modified. Treatment of existing vines with di- bromochloropropene (DBCP) soil fu- migants is widely used, although research suggests that vine improvement and in- creased production can be expected only when ectoparasitic nematode vulnerable to this treatment are the principal species present. Currently there is considerable interest in systemic chemicals which would be picked up by the plant from foliage or soil applications, then moved through the plant to the roots. A few such candidate chemicals now are being tested for effective systemic activitv, but Effect of preplant fumigation on two-year-old Thompson Seedless grapevines: The plant on the left was planted in fumigated soil, the one on the right was planted at the same time in untreated soil. [13] results suggest poor and erratic control. Neither the use of DBCP or systemic nematicides have shown promise for con- trol of the dagger nematode-fanleaf virus disease complex in grape. An overall program A well-planned control program based on careful analyses should include the use of nematode- resistant rootstocks, virus- and nematode-free planting material, and the selection of the most effective soil treat- ment for the particular type of nematode infestation. Cultural controls such as crop rotation and fallowing of the land are not sufficient in themselves, but may be used to obtain better chemical control. Overall preplanting soil treatment of large areas or blocks is advisable where many vines are in a declining condition or where previous replanting attempts have resulted in a high percentage of failures or weak vines. Such treatment also may be advisable where other crops such as orchard trees have been removed or where transplants of susceptible an- nual crops have been introduced and have provided means of introduction and build-up of nematode pests. Spot preplanting treatment of single vine replant sites, or of small areas, is sometimes desirable. However, reinfesta- tion of small areas from adjacent in- fested vines will readily occur. Chemical control The use of chemicals in soil is restricted by factors not encountered in the applica- tion of chemicals to the tops of plants. Ne- matode control materials move through the soil as gases or as solutions or emul- sions in water. The soil itself restricts dif- fusion of these materials depending on various physical and chemical factors such as the amount of clay and organic matter, soil temperature, and the amount of soil moisture present. Agricultural soils vary widely from area to area and within a single field. Thus the amount of chem- ical necessary per acre is difficult to ascer- tain with accuracy and usually is decided on the basis of the particular soil present that is the most difficult to treat. The depth to which effective treatment is de- sired also influences application rates and methods. While low rates and shallow application can be used for shallow-rooted annual crops, high to very high rates and deep applications are necessary where long-lived perennial plants, such as grape, are to be grown. Preplant soil treatments Soil fumigants with 1,3-dichloropropene ( 1,3-D) as the principal active ingredient are the most widely accepted preplant soil fumigants for field conditions. These are available as D-D® (Shell Chemical Co.), Telone® (Dow Chemical Co.), and Vidden-D® (Dow), a formulation simi- lar to D-D®. Current recommendations (published in the Pest and Disease Control Program for Grapes, University of California Ex- periment Station and Extension Service) for the use of D-D®, Vidden-D® and Telone® suggest the use of D-D® or Vid- den-D® at 60-170 gallons per acre or Telone® at 60-137.5 gallons per acre in old vineyard and orchard soils. In land previously used only for annual crops these recommendations suggest D-D®, Vidden-D® and Telone® at 40 to 60 gal- lons per acre. These treatments have produced re- markably stronger vine growth in treated soil as compared to untreated soil. How- ever, a significant population of nema- todes invariably survives these treatments and often increases again within a few years to damaging numbers so that much of the advantage of treatment is lost. Recent experiments on control of dag- ger nematode and fanleaf virus have shown excellent results using high dosages of 1,3-D (250 gallon per acre) in a split application (200 gallons at 30 inches * depth on 2-foot spacing plus 50 gallons at 8 to 10 inches depth on 1-foot spacing) . These results have been successful enough to warrant recommendation of this treat- [ 14 merit (Pest and Disease Control Program for Grapes, University of California Ex- periment Station and Extension Service) . Experiments now are underway to test this treatment on root knot and other nematode prohlems in the lighter sandy soils of the interior valley. There is a need to know if this treatment will protect vines for a significantly longer time, es- pecially during the early critical years when the plants are becoming established. The success of such an expensive treat- ment can only be determined by several years of yield records comparing various dosage levels of the fumigants. In any soil fumigation, it is important to seal the soil immediately after treat- ment with a ring roller, springtooth har- row, or heavy drag. Then leave the soil undisturbed until shortly before planting. A waiting period between treatment and planting of at least one week for every 10 gallons of fumigant is necessary in light soils. Heavier soils require longer intervals before planting. Longer periods also are required if soil temperature drops significantly or if rains saturate the soil following treatment. Tilling treated soils or digging planting holes a few days be- fore planting hastens aeration in these areas. Methyl bromide (CH 3 Br) is a liquid 1 under pressure which becomes a gas at normal pressures. It has been used for many years for soil treatment in straw- berry fields and plant nurseries for con- trol of many kinds of organisms, includ- ing weeds, fungi, and nematodes. When methyl bromide is applied, the soil must be covered at time of treatment with a gas-proof tarpaulin such as polyethylene. Rates of 250 to 400 pounds per acre of methyl bromide have been used, usually mixed with chloropicrin. In recent years CH 3 Br has been used for control of oak root fungus before planting grapes and is being tested for control of the dagger nematode-fanleaf virus complex. This material is being tested currently for control of root knot and other nematodes along with the 1,3-D trials as described above. As with the 1,3-D treatments, recent research with methyl bromide indicates that deeper ap- plication must be used to obtain satisfac- tory nematode control. Application depths of 2 to 3 feet have been promising. Until further information is developed the use of methyl bromide for nematode control must be considered experimental. Treatment of established vines Many vineyards suffer decline and re- duced productivity but nevertheless pro- duce sufficiently so that replanting is not considered economic. A treatment of such established vines would be the most prac- tical solution. A chemical for use in side- dressing treatment of growing vines should be nematicidal at economically practical rates and low in phytotoxicity at those rates. DBCP meets these requirements at least in part. It is highly nematicidal at rates as low as % gallon per acre. Also it can be used safely around many kinds of plants, particularly woody perennial types, at rates as high as 5 gallons per acre without plant injury. DBCP can be applied either by soil in- jection or in irrigation water. Soil injec- tion or "side-dressing" usually is made with a formulation of 50 to 75 per cent (by volume) active ingredient diluted with "paint thinner" or other similar ma- terials. Applications in irrigation water are made with emulsifiable concentrates. University of California field trials (in grape) have given most consistent production increases when DBCP was ap- plied in water in flood treatments (basins) wetting the soil to 4 to 6 feet. Results of soil injection (chisel) trials have been inconsistent and have given increased yields only in a few cases. Chisel applications also produce (1) root damage, (2) difficulty in treating closer than 15 to 18 inches of the vine row, thus leaving an untreated strip of l 1 /? to 3 feet down the row, and (3) dam- [15 age to cane growth during application. ( lanes also may be a hazard to the opera- tor, unless treatment is made either after pruning or before vine growth begins. Sprinkler applications of DBCP are at- tractive t<> growers and have resulted in improved growth and yields in a few cases; however, much of the chemical is lost to the atmosphere during application. The amount of loss apparently depends on atmospheric factors such as temperature and movement of air. These losses cannot be accurately predicted to permit recom- mendations for this method of applica- tion. I se of DBCP in flood irrigation treat- ments of grapes has given the most con- sistent results when ectoparasitic nema- todes such as the dagger nematodes were the principal problem. Only a few trials for control of endoparasitic nematodes, such as the root knot nematodes, have been successful. Growers are urged to include untreated areas for comparison with treated areas and to make careful comparison of yields between these areas to determine the economic value of treat- ment. DBCP should be used at the rate of 2 gallons active ingredient (i.e., 4 gallons 50 per cent emulsifiable formulation con- taining 8.6 pounds DBCP per gallon) per acre applied in irrigation water as a post- harvest treatment. Sufficient water should be used to penetrate 4 to 6 feet in depth and the material metered into the water throughout the irrigation. The flooding method, however, is lim- ited by the following requirements: 1. Leveled land. 2. Equipment to develop borders. 3. Labor to manage water and main- tain borders during applications. Offsetting these limitations are the ad- vantages of treatment of all of the soil area and more 1 uniform distribution of DBCP. Some questions about the use of DBCP in vineyards remain to be clarified: (1) Since the most favorable yield responses have followed treatments of vines grow- ing in sandy soils, can similar responses be obtained in heavier loam or clay type soils? (2) What is the most favorable timing and rate of application: single ap- plications up to 2V2 gallons per acre of DBCP. repeated lower rates up to 1 gal- lon per acre annuallly, or up to V12 gallon per acre applied three or four times in one season? (3) What is the amount of material lost to the atmosphere during application in water either by flooding or by sprinkler? (4) Can responses be pre- dicted on the basis of nematode species involved? Of population levels? Cultural practices and soil preparation The roots of woody plants including grape may remain alive in the soil for a long time after such plants have been removed. These roots provide food for plant-para- sitic nematodes and protect endoparasitic types against chemical treatment. Allow at least two years after removal of a vineyard or orchard before treating the soil and setting out new plants. When old vines are removed, cut them deeply enough to remove all crowns and prevent suckering. During the two-year rotation period, avoid deep-rooted crops, such as cotton, and highly susceptible crops, such as tomato and potato, which could present a problem of removing crop debris be- fore treatment or would maintain or build up nematode populations. Always allow sufficient time, even after removal of an- nual crops, to permit roots to decay so nematodes are exposed to the action of soil fumigants. Cotton presents a particu- lar problem because this crop is removed late in the fall and its roots do not decay as rapidly as those of fleshy-rooted plants removed earlier in the season. If you have doubt that roots have decayed sufficiently, delay treatment, or use rates of materials suggested following the removal of trees and vines. Shortly before treatment the soil should be subsoiled to a depth of 3 feet in at least [16 two directions to break up any plow sole or shallow hard pan. Then disc and har- row the soil until tilth approximates a seedbed condition. Soil temperature at the time of treatment should be 50 to 85°F at a 6-inch depth. When 1,3-D is used, soil moisture gen- erally should be near field capacity in sandy soils and 50 to 75 per cent of field capacity in heavy soils. (However, some trials with 1,3-D at high rates have given excellent control in dry sandy soils.) The use of methyl bromide requires that soil moisture be as low as possible. Sudan grass or safflower should be grown dur- ing the summer preceding a late summer or fall treatment to dry the soil out as completely as possible. Following this, the soil should be ripped and tilled as for 1,3-D treatment. Geographical influence on control: In the San Joaquin Valley and Southern California interior valleys, endoparastic nematodes are the most important nema- tode parasites of grape. Root knot nema- todes predominate, but root lesion nema- todes also are common in the San Joaquin Valley and may occur in the same vine- yards. Adequate crop rotation before treatment and replanting is particularly important in these areas, because the nematodes most commonly found are en- doparasitic, and the woody roots of vines or trees may persist and harbor and pro- tect nematodes for a long time. Soils of the interior valleys are often light-textured sandy types, and irrigation water is generally available, even though not always adequate. Moisture necessary for good land preparation and treatment usually can be provided during the favor- able fall period. In the central and northern California coastal valleys, endoparasitic nematodes ordinarily are a minor problem in the non-irrigated areaswherethe heavier min- eral-type soils have a high water-holding capacity. In these areas the most common nematodes found on grape are ectopara- sites, especially dagger nematodes, al- though ring nematodes and pin nema- todes also are found. Irrigation water is not generally avail- able, and proper land preparation may be dependent on rainfall, limiting the period when soil treatment can be made. When land preparation and treatment cannot be made until spring, cooler soil temperature and the heavier soil types may delay planting beyond a desirable planting date. Management practices New vines require special attention to attain maximum vigor and growth in the early years after planting. Adequate water and fertilization, careful pest con- trol, and pruning to the vigor of indivi- dual vines all will contribute to the basic strength of the vines. Clean nematode-free stock should be insured by planting cuttings taken from canes, the desired portion of which were not in contact with the soil. To establish a vineyard with cuttings, considerable ex- perience is needed to care for vines planted over a relatively large area. In general, we would recommend the plant- ing of strong rootings to best insure a good stand of vines. Hot water treaments for nematode con- trol (or phylloxera) are necessary if root- ings did not come from a fumigated nur- sery site, if there is any doubt about the cleanliness of the rootings, or if they are lightly infested with nematodes but other- wise have made strong growth. Hot water treatment should be given only to strong rootings which are com- pletely dormant. Following washing, trim- ming and bundling, submerge the vines in water heated to 125°F and hold there for exactly five minutes. Accurate timing and uniform temperature are important for good control and vine safety. Cool the rootings immediately following treatment and protect them from drying out. They may be planted directly or heeled-in in a nematode-free medium such as wood shavings. A more complete discussion of [17] these procedures is available from your local farm advisor in the U.C. Extension sheet OSA #48, "Hot water dip for nem- atode control on grape rootings." Care of young vines often determines the success of a commercial vineyard. Good cultural practices include: 1. Care- ful pruning of vines as they come into bearing. Overcropping, an imbalance of fruit with vine capacity, can easily re- sult from leaving too many canes at the second and third winter's pruning of the Thompson Seedless variety, for example. Wine grape varieties that are trained to a bilateral cordon are readily overcropped when too many spurs are left on the quickly established framework. In both cases, early removal of the excess number of bunches by thinning effectively pre- vents fruit overload. 2. Irrigation practice designed to main- tain a supply of available moisture in the root zone during the growing season. Do not, however, stimulate late growth which deters good wood maturity. 3. Pests and disease control, such as for Pacific mites and powdery mildew, which can materially damage leaves and hence their ability to function and elaborate the carbohydrate materials needed for vine growth and fruit development. 4. Fertilization of sandy soils in which root knot nematodes are generally a prob- lem. Nitrogen, the element usually needed, should be applied in the dormant season. 5. The date of proper timing for harvest. Since the major storage of carbohydrate reserves in the vine does not occur until after the fruit is picked, the harvest date should not be delayed. An inadequate storage of reserves results in weakened vines. The preplant fumigation gives the vine an opportunity to become estab- lished. Good growing practices, however, are essential to maintain healthy, vigor- ous vines that can bear good crops of good-quality fruit each year. Nematode-resistant rootstocks Several species of grapes native to the [18 central southern part of the United States have inherent resistance or tolerance to nematodes. Field trials in California with hybrids or varieties of these species have demonstrated their value as rootstocks in commercial vineyards. The proper choice of the stock best suited for a given variety and vineyard situation is very important. Nematode-re- sistant stocks differ considerably in vigor and in their effects on fruit quality and vine behavior. The most vigorous stocks. Dogridge and Salt Creek, are recom- mended only for very sandy soils with a low fertility and water-holding capacity. The less vigorous stocks should be planted in the more favored vineyard soils. Wine and raisin grape varieties have been more readily adapted to the use of nematode-rCsistant rootstocks than those of table grapes, since appearance of the mature fruit is of minor importance. Re- sults with table varieties have been vari- able, even though many successful table grape vineyards on rootstocks may be found. Without careful vineyard manage- ment, the color of red table varieties, for example, may be duller and darker and the bunches may have a poorer set, re- sulting in a straggly appearance. These undesirable results may be minimized by careful management, including pruning, water and fertilizer management, and the use of zinc applications. A brief summary of some of the char- acteristics and behavior of the rootstocks currently recommended for use in Cali- fornia vineyards is given in table 3. The first four stocks have resistance or toler- ance to nematodes and are recommended for use in the San Joaquin Valley and in the interior valleys of southern California. The remaining stocks, St. George and A x R 1, while they do not possess nema- tode resistance, are resistant to phylloxera and are the stocks of choice for the coastal valley counties. Rootstocks with dual re- sistance to these two pests are urgently needed. Cultural practices where rootstocks are ] Table 3 SUMMARY OF THE CHARACTERISTICS OF GRAPE ROOTSTOCKS CURRENTLY RECOMMENDED FOR CALIFORNIA Rating Rootstock Nematode susceptibility* Phylloxera suscepti- bility* Performance! Remarks Root knot Lesion Dagger Table Wine, raisin Dogridge, Vitis champini 1 1 2 2 V G Very vigorous. For heavy pro- ducing wine or raisin varieties grown on very sandy soils of low fertility where nematode damage is usually severe. Salt Creek (Ramsey), V. champini 1 1 2 2 V G Very vigorous. Excessive growth more easily controlled by cultural practice than with Dogridge. Use in same situations as Dogridge. Harmony (1613 sdlg. X Dogridge sdlg.) n 2 1 1 V-G G More vigorous than 1613, but not as vigorous as Dogridge or Salt Creek. Well suited to all but very sandy soils, and particularly suited for raisin or wine grape production. 1613, Solonis X Othello it 3 1 2 V-G G§ Vigorous. Well adapted to fertile loamy sand to sandy loam soils of the San Joaquin Valley. St. George, V. rupestris 3 3 3 1 V G§ Vigorous. Susceptible to nema- todes. Well adapted to shallow or nonirrigated soils in the coastal valley areas. AXR#1 (Aramon X Rupestris, Ganzin No. 1) 3 3 3 1 V G§ Vigorous. Susceptible to nema- todes. Best performance on the fertile valley soils in coastal counties. * 1 = low; 2 = intermediate; 3 = high. t V = variable; G = good. t Some strains in local areas may be damaging. § Wine varieties only. used will probably have to be adjusted for growth will tend to in- owth becomes overly ■ ■ o leave more fruiting duce or even eliminate Dn, and reduce irriga- te summer. Such vines zinc deficiency, which clusters and lighter ;ncy can be remedied ieties by daubing the id with a zinc sulfate rootstock vines care- worn from virus dis- 19 eases. Rootstock mother vines may be symptomless carriers of virus diseases, which have little effect on the growth and development of the rootstocks but which may drastically affect the crop and vigor of the scion variety after budding or grafting. Certified planting stock is the most reliable source of clean rootstock vines and is obtainable from participants in the Grapevine Registration and Cer- tification Program administered by the California Department of Agriculture. Additional costs are encountered where rootstocks are used — for rootstock vines, in disbudding, in budding or grafting ] and U nv-up, and in suckering. These costs Ti y be easily offset by the develop- ment of a vineyard with "built-in" pro- tection, one that will have a normal eco- nomic life without further investment. In very sandy s >. re nematode i' tions are heavy, it may be imposs grow grapevines without the use ol tode-resistant rootstocks. To simplify this information, it is sometimes necessary to use trade namt. products or equipment. No endorsement of named products is intended nor is i cism implied of similar products not mentioned. r 12%m-ll,'73(R1649L,)PAD