Building the 1PM continuum

Frank G. Zalom, Director UC Statewide IPM Project

his year marks the 20th anniversary of the UC Statewide The process of building the IPM continuum identifies the 1 Integrated Pest Management (IPM) Program, which has state of the art, as well as gaps in research and available pest been dedicated to furthering development and practice of IPM control technologies. Conceptualizing IPM as a continuum en- in California by facilitating UC research and extension activi- ables individuals or organizations to evaluate how their cur- ties. Its mission remains relevant today in addressing the envi- rent pest management practices relate to what is possible in a ronmental, social and economic challenges associated with a nonjudgmental way, while acknowledging the degree to pest management system in transition. which IPM-compatible practices are being used. While a sustainable, ecologically based IPM approach has California can be proud of the individual growers, organi- long been a desired goal of IPM zations and in some cases whole in- developers and practitioners, the Ammo, dustries that have successfully current 1PM reality varies with IPM defined moved forward along the IPM con- the system itself and changes in Integrated Pest Management (IPM) is an tinuum, yet we have only begun to response to external factors. fulfill IPM's potential. Researchers in Variables defining an IPM sys- ecologically based strategy that focuses on the public and private sectors have tem include location-specific en- long-term prevention of pests or their damage developed a remarkable number of vironmental conditions, the pest through a combination of techniques such as practical, IPM-compatible tools. complex, resident natural en- biological control, habitat manipulation, These include new applications of emies or antagonists, economic modification of agronomic or horticultural host-plant resistance and biological and sociological structures, and practices, and use of resistant varieties. Em- controls; "reduced-risk" pesticides available research. The availabil- bracing a single tactic to control a specific or- including microbial agents and mat- ity of IPM-compatible tactics, pri- ganism does not in itself constitute IPM, even ing disruption; new classes of pesti- vate and public infrastructure, if the tactic is an essential element of an IPM cides which are more selective and economic and other incentives, system. Pesticides may be used to remove the less disruptive to nontarget species; and community support also in- monitoring approaches like phero- fluence its potential for adop- target organism, but only when monitoring mone trapping, degree-day models tion. IPM as a paradigm is uni- indicates that they are needed to prevent eco- and immunoassays; precision applica- versal; IPM in practice becomes nomic damage. Pest-control tactics, including tion techniques for pesticides; and re- specific to the intended crop, site pesticides, are selected and applied to mini- finements of cultural controls such as or situation. mize risks to human health, beneficial and canopy management, mulches and The concept of IPM as a con- nontarget organisms, and the environment. sanitation. tinuum has been embraced as a Some of these tools have become method for defining IPM systems widely used, while most have not. in a manner that maintains the ecologically based goal while Many need further adaptations to achieve effective and eco- acknowledging the limitations of current knowledge. In the nomical on-farm results. Others need to be more widely dem- IPM continuum, professional scouting and use of available onstrated. IPM-compatible tools for managing several key pest action thresholds are the minimum activities. Monitoring problems remain elusive, and will require innovative research increases knowledge of crop status, pests and beneficial or- to be managed without conventional pesticides. ganisms, supporting better-informed pesticide use, and We have a long way to go before a majority of growers and more importantly, decisions not to apply chemicals. pest managers can and do practice IPM at the highest levels of Further along the continuum, IPM systems incorporate the continuum. Reaching that level will require growers, con- preventative, nonchemical horticultural or agronomic prac- sultants, scientists, government agencies and associated indus- tices and biologically based tactics such as host-plant resis- tries to work together, moving forward a step at a time. tance, pheromone mating disruption, microbial controls and Today IPM is an accepted and unifying paradigm. It is the biological controls. "Reduced-risk" pesticides, which legacy of the visionaries who proposed the radical idea for present less risk to human health and the environment, such a program, and the people whose support in the legisla- would be used sparingly and only when other options are ture and within the University allowed it to begin and then not possible. At the highest level of the continuum, IPM as- flourish. It remains the strongest framework under which the sures that pest and crop management decisions are inte- biological, environmental and regulatory challenges facing grated and ecologically based. pest management can be addressed.

2 CALIFORNIA AGRICULTURE, VOLUME 54, NUMBER 6 N)0\J DEC "),_000 LiA

Grape Damage Symptoms and Causes

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i de CAUSE - i i a 2: Y n' t t i I . Mildew k t Nit. deficiency Thrips IIII fa Hail 11 Air pollution II Phos. deficienc Boron deficiency 2 . 3 Bud mites NW Zn deficienc Moisture stress Springy frost ■ Scion/rootstock interaction Mites W. Grape Leaf Skeletonizer Leafhopper Sulfur burn Botrytis bunch rot High temperatures Leaf roll Erineum mites

'early spring 2numerous sp ing latera s amid-summer cok) -1APTIO1J7) 6-POLoe& ~G g/Mf4L ■ 5- Grape Damage Symptoms and Causes

5 2 8 6 t 0 IMPROPER USE OF a I 12 a S CHEMICALSPRAYS

e g ; =moms= =moms= o ; = CAUSE RESIDUAL HERBICIDES Napropamide (Devrinol) Oryzalin (SurfIan) Trifluralin (Tref Ian) Dichlobenil (Casoron) Diuron (Karmex, Aceto) ti U Simazine (Princep) Dinoseb (Preemerge) Oxyfluorfen (Goal) FOLIAR HERBICIDES Dinoseb (dinitro) Oxyfluorfen (Goal) Paraquat (Paraquat CL) ■ I Weed Oil Glyphosate (Roundup) N Dalapon ti

e £ a ..t. 2i s 1 1 3 ? . !, , 2,,,,, r SYMPTOMS IN a i 1 yF g W I DEFINED AREAS z g ':2° '! E 143 r! ! 1 ° OG 0 O a t g = 2 Ff RI" CAUSE S Phylloxera • • Thrips Phytophthora Root Rot Nematodes P deficiency Zn deficiency Fanleaf' Boron deficiency Pierce's disease K deficiency Variable soil problems Oak Root fungus Root competition (oaks) Mites ■ Gophers • Spring frost, low temp. • • Leaf folder 0.L.R. Mg deficiency I Grasshoppers Deer damage Rabbit damage Botrytis bunch rot Branch & twig borer Cutworms White fly Salt toxicity Boron toxicity

'Leaves with bands may not have wide basal sinus Near ground, petioles not eaten Insects are members of the phylum Arthro- pods and the class Insects. Members of the class Insects are all subclassified into one of about 20 orders. Examples of common Insect Classification orders are: Scientists who classify living things divide Common name Order Name animals into a number of groupings, going from the largest generally•related categor- Bristletails Thysanura ies and moving to the more specific dif- Chewing lice Mallophaga ferentiations. Every animal is a member of Sucking lice a: Anoplura WITHOUT METAMORPHOSIS Phylum Thrips Thysanoptera Class Termites Isoptera Order EX AMPLE"; (HIDERS Grasshoppers Orthoptera Family Genus TH YSA NUR True bugs SILVERFISH Hemiptera S 'ecies SPRI NGTA I LS COLLEMROLA Aphids. leafhoppers. Homoptera I scale insects EGG YOUNG ADULT Moths, butterflies Lepidoptera Insects without metamorphosis emerge from the egg looking - exactly Beetles Coleoptera like they will when grown, except they are much smaller. Flies Diptera Wasps, bees, ants. Hymenoptera EXAMPLES (HIDERS GRADUAL METAMORPHOSIS sawfiies GRASSHOPPERS ORTHOPTERA Fleas TERMITES IS< /PTERA I1410KLICE CI IRK( IDENTIA TH RIPS TI I YSANOPTERA LYGUS.STINRRUGS II EM IPTERA APHIDS III IMOPTERA EARWIGS HERM APTEK A EGG NYMPHS ADULT BITING LII:E M A LLOPII AGA ■ SI -CKING LICE A NOPLAIRA !meets with gradual metamorphosis change shape gradually. Wings develop externally and as growth takes place, the nymph looks more like the adult. ANTENNA• /// % clnly, A* INCOMPLETE METAMORPHOSIS EXAMPLES ORDERS i MAYFLIES EPI I F:M ERI D A DR AGoNFLIES FIR IN ATA \IMOUTH STUN EFLIES PUG( /PIER% EGG NAIADS ADULT

\ / shape gradually. In incomplete metamorphosis, the insect changes They do not look like adults until shedding their last skin. Then there is a quick change. EX AM PLES ORDERS COMPLETE METAMORPHOSIS

LACEWINGS NEUROPTERA BEETLES COLE( 'ITER A SCORPHINFLIES M ECOPTERA CA DDISFLIES TRICHOPTERA BUTTERFLIES, MOTHS LEPIDOPTERA Mother Goose & Grimm FLIES. MOSQUITOES DIPTER A FLEAS SIPII0NA PTER A BEES. WASPS HYMENOPTERA EGG LARVAE PUPA ADULT

!‘ AO NOW MY In complete metamorphosi the insect goes through four stages of LOVELY ASSISTANT growth. The young do not resemble the adult. There is a great change Kt, ENTER THE in shape when the adult emerges from the pupal stage.

COCOON . 1! NOTICE SHE HAS NO WINGS,

5 - 59 INSECT TRICKS - - -

Grape Pests

'1. Grape leafhopper, Erythroneura elegantula Osborne and E. variabilis Bea. - Cicadellidae Anagrus epos Girault mymarid wasp Dikrella californica (Lawson). blackberry leafhopper Aphelopus comesi - dryinid wasp Anystis agilis(Banks) - anystid mite 2. Pacific spider mite, Tetranychus pacificus McG. - Tetranychidae Metaseiulus occidentalis Nesbitt, predatory mite - Phytoseiidae Tydeid mites, Pronematus ubiquitus (McGregor) and Pronematus anconae Baker -Tydeidae 3. Willamette mite, Eotetranychus willametti Ewing - Tetranychidae 4. Twospotted spider mite, Tetranychus urticae Koch - Tetranychidae 5. Grape leaffolder, Desmia funeralis (Hubner) - Pyralidae Microbracon cushmani Mues. - braconid wasp Nemorilla pyste (Walker) - tachinid fly Erynnia tortricis (Coq.) - tachinid fly 6. Omnivorous leafroller, Platynota stultana'Walshingham - Tortricidae Goniozus platynotae Ashmead - bethylid wasp Apanteles sp. - braconid wasp Cremastus platynotae Cush. Elachertus proteoteratus (Howard) - eulophid wasp Spilochalis sp. - chalcid wasp Nemorilla pyste (Walker) - tachinid fly Erynnia tortricis (Coq.) - tachinid fly 7. Raisin moth, Cadra figulilella (Gregson) Pyralidae 8. Navel orangeworm, Amyelois transitella (Walker) - Pyralidae 9. Dried fruit beetle, Carpophilus hemipterus (Linn.) - Nitidulidae 10. Vinegar or pomace fly, Drosophila melanogaster Meigen - Drosphilidae 11. Orange tortrix, Argyrotaenia citrana (Fernald) - Tortricidae Exochus nigripalpus subobscurus Tow. - ichneumonid wasp Apanteles aristoteliae Vier. - braconid wasp Nemorilla pyste (Walker - tachinid wasp Dibrachys cavus Walker - chalcid wasp 12. Pierce's disease Cicadellidae Grass sharpshooter or green sharpshooter, Draeculacephala minerva Ball Redheaded sharpshooter, Carneocephala fulgida Nott. Blue-green sharpshooter, Grazhocephala atropunctata 13. Western grapeleaf skeletonizer, Harrisinalarillians Sturmia harrisinae Coq. - tachinid fly Apanteles harrisinae Mues. - braconid wasp Virus disease 14. Grape phylloxera, Daktulosphaira vitifoliae (Fitch) - Phylloxeridae 15. Grape mealybug, Pseudococcus maritimus (Ehrhorn) - Pseudococcidae Acerphagus notativentris (Girault) - encyrtid wasp Zarhopalus corvinus (Girault)- encyrtid wasp 16. Thrips Thripidae Western flower thrips, Frankliniella occidentalis (Pergande) Grape thrips, Drepanothrips reuteri Uzel Grass thrips, Frankliniella minuta Moulton Citrus thrips, Scirtothrips citri (Moulton) Bean thrips, Caliothrips fasciatus (Pergande) Six-spotted thrips, Scolothrips sexmaculatus(Pergande) and S. pallidus (Beach) 17. Cutworms Noctuidae Variegated cutworm, Peridroma saucia (Hubner) Black cutworm, Agrotis ipsilon (Hufnagel) Brassy cutworm, Orthodes rufula (Grote) Spotted cutworm, Amathes C-nigrum (Linn.) Euxoa spp. 18. Grape bud beetle, Glyptoscelis squamulata Crotch - Chrysomelidae 19. Click beetle, Pacific coast wireworm, Limonius canus Le Conte - Elateridae 20. Achemon sphinx moth, Eumorpha achemon (Drury) - Sphingidae 21. Whitelined sphinx moth, Hyles lineata (Fabr.) - Sphingidae 22. Grape erineum mite and grape bud mite, Colomerus vitis (Fagenstecher) -Eriophyidae 23. Grape rust mite, Calepitrimerus vitis (Nalepa) Eriophyidae 24. Saltmarsh caterpillar, Estigmene acrea (Drury) - Arctiidae 25. Yellow woollybear, Diacrisia virginica (Fabr.) - Arctiidae 26. Branch and twig borer, Polycaon confertus Le Conte - Bostrichidae 27. Grasshoppers Acrididae Schistocera shoshone (Thomas) - green valley grasshopper S. vaga (Scudder) - vagrant grasshopper Melanoplus devastatorScudder - devastating grasshopper 28. Scale insects Coccidae Brown apricot scale or European fruit scale, Lecanium corni Bouche Cottony maple scale, Pulvinaria innumerabilis (Rathyon) Soft brown scale, Coccus hesperidum L. Frosted scale, Lecanium pruinosum Coq. Black scale, Saissetia oleae (Olivier) Diaspididae Oystershell scale, Lepidosaphes ulmi (Linn.) Oleander scale, Aspidiotus nerii Bouche Olive scale, Parlatoria oleae (Colvee) California red scale, Aonidiella aurantii (Maskell) Florida red scale, Chrysomphalus aonidum (Latreille) Greedy scale, Hemiberlesia rapax (Comstock) Grape scale, Diaspidiotus uvae (Comstock) San Jose scale, Quadrasidiotus perniciosus (Comstock) Walnut scale, Quadraspidiotus juglansregiae (Comstock) Margarodidae Cottony cushion scale, Icerya purchasi Maskell Ground pearls, Margarodes meridionalis Morrison 29. Consperse stinkbug, Euschistus conspersus Uhler Pentatomidae 30. False chinch bug, Nysius raphanus Howard - Lygaeidae 31. Grape whitefly, Trialeurodes vittata (Quaintance) - Aleyrodidae 32. Ground mealybug, Rhizoecus falcifer Kunchel d'Herculais - Pseudococcidae 33. Flea beetles Steel blue grapevine flea beetle, Altica torquata Le Conte - Chrysomelidae 35. Little bear beetle, Pocalta ursina (Horn) - Scarabaeidae 36. Darkling ground beetles, Blapstinus spp. - Tenebrionidae 37. Minor cicada, Platypedia minor Uhler - Cicadidae 38. Hoplia beetle, Hoplia callipyse Le Conte and H. pubicollis Le Conte - Scarabaeidae 39. Amphicerus beetles, Amphicerus bicaudatus (Say) and A. cornutus (Pallus) 40. Termites Western subteranean termites, Reticulitermes hesperus Bank - Rhinotermitidae Western drywood termite, Itcisitermes minor (Hagen) - Kalotermitidae 41. Lead cable borer, Scobicia declivis (Le Conte) - Bostrichidae 42. Sawtoothed grain beetle, Oryzaephilus surinamensis (Linn.) - Cucujidae 43. Indian meal moth, Plodia interpunctella (Hubner) - Pyralidae 44. Beet armyworm, Spodoptera exigua (Hubner) Noctuidae 45. European earwig;, Forficula auricularia Linn. -Forficulidae 46. Western grape rootworm, Bromills obscuruq, L. - Chrysomelidae RNAL:00 AGOG LTURALISCIk.NCE,V 00 ,1: 1 SHE 0 0 ,vi•"; rR4t a C11LtFORN 1A =ION! ANIII • - • .14.1`.:•':,:" : ; ■.3i f.$ NNW All Marc " '''Volume 52 .-I rsisc;nbes;' •

,4"' • • ;■ :. ) :•4 ;

• J. . I ,Ecology Of a Blackberry L' - Sy-stem .- and its Relevance to , CaliforniaGrape Agroecdsystems D.`W. Williams

Fig. 20. Phenological relationships of wild grape, blackberry, the grape leafhopper (GLH), the black- berry leafhopper (BLH), and Anagrus epos in the riparian habitat. The stippled area for grape is the period during which the vine has leaves, while that for blackberry represents the time of active leaf production, Roman numerals represent generations of the respective insect species. Both leafhopper species overwinter as diapausing adults, while Anagrus hibernates in its immature stages in BLH eggs in overwintering blackberry leaves. Note that Anagrus develops its first generation on BLH eggs before GLH eggs are available for attack.

,s • . •, • J

1. • • r• ■. • r . • :Natural ecosystems are often sources of pest arthropods and their natural ,

enemies for nearby agroecosystems. This study treats the ecology of the , j, native California blackberry, Rubus ursinus Cham, and Schlecht, and an imported blackberry, Rubus procerus P.J.- Mueller, the blackberry leaf- \-- - hopper (BLH), Dikrella californica (Lawson), and its egg parasite, A nagrui epos Gii-ault;-in two riparian habitats and a vineyard site. Anagrus is also an effective natural enemy of the grape leafhopper (GLH), Erytbroneura elegantula Osborn, which evolved on wild grape in the riparian habitat _ and became a serious pest after the introduction of commercial varieties. The parasite overwinters in immature stages in the eggs of BLH in blackberry: In the early spring, growth of the native blackberry and BLH oviposition precede grape growth and GLH oviposition by the length of one parasite generation. Since Anagrus becomes active when BLH ovi- position begins,,this synchrony allows the parasite to increase its popula- tions in the riparian refuge before entering the vineyard. The two blackberry species differ in their preferred habitats: the native blackberry is limited to moist shady habitats, while the imported species grows in open sunlit areas. In phenology the imported blackberry appears less synchronized with and less constrained by the California climate. The blackberry leafhopper produces three generations per year and overwinters as a diapausing adult.,The leafhopper is well adapted to the phenology of the native blackberry, but less so to that of the imported species, which breaks dormancy in the spring long after BLH terminates diapause. Leaf- hopper females oviposit primarily in. the lower half of the leaf canopy of the native blackberry throughout the season, while in the imported species they, shift oviposition from the top of the canopy in early spring to the bottom by late summer. - A time-varying life table analysis shows that BLH immature mortality due 'to Anagrus, nymphal parasites, and general predators is positively density dependent. Age-specific life table analyses in the laboratory estimate that Anagrus' intrinsic rate of increase (r m ) is 2.2 times those of BLH and GLH. Although r m is a questionable index of parasite effectiveness, the difference probably allows A nagrus to respond rapidly to changes in GLH populations. Suggestions for the further augmentation of Anagrus pop- ulations in artificial refuges includes the management of blackberry and the monitoring and maintenance of BLH populations.

1. THE AUTHOR:

D. W. Williams is Systems Analyst/Modeler, University of California State- / J. wide Integrated Pest Management Project.

3(-1 Grape Leafhopper ...7ontrol Studies Hiroshi Kizio Department of Entomology

The grape leafhopper, Ervthroneura elegantula Osb., is the most common leafhopper found in northern California. Other leafhoppers which infest grapes are the variegated leafhopper,Erythroneura variabilis Beamer, and Dikrella cockerelli (Gillett).

Seasonal development

Seasonal development of the grape leafhopper is shown on the following page.

Monitoring grape leafhopper infestation

Monitoring leafhopper infestations consists of examining nymphal popu- lations. The method is as follows:

1. Examine one vine in every 5th row. Avoid the border rows. 2. Select one leaf from the vine which is located between the 5th and 10th vine in the row. 3. Select a leaf which appears to have the highest number of nymphs. 4. Average the nymphal counts from at least 15 leaves. 5. Evaluate the infestation. Economic levels may vary with variety and vigor of the vines. Ex: Thompson Seedless for wine 20 nymphs per leaf for first brood 10 to 15 nymphs per leaf for subsequent broods.

Biological Control

Blackberry refuges

A small mymarid wasp, Anagrus epos (Girault), is a leafhopper egg parasite and is highly effective in reducing the grape leafhopper populations in vineyards. One of the primary host of the wasp is the blackberry leafhopper living on wild blackberry plants. The seasonal development of the wasp and leafhopper is shown on the following page. Generally, there are two blackberry species involved in the natural blackberry plants, one an escaped cultivated Himalaya blackberry and the other, the native California wild blackberry. The leafhoppers sustained themselves better on the California wild blackberry. Blackberry planted by growers near vineyards as parasite r fuges have not been too successful. The reasons for failure appeared to be: 1 extensive plantings of Himalaya blackberry, 2. insufficient size of the plantings, and 3. lack of maintenance of the refuges.

Prune leafhopper

Eggs of the prune leafhopper, Edwardsiana prunicola Edw., are also parasitized by the Anagrus wasp. Seasonal development of the leafhopper is shown on the follow- ing page. The Anagrus wasp parasitizes the eggs in the leaves and twigs. The wasp overwinters in the immature stage in the parasitized eggs in the twigs. In April, the adult wasp emerges from the eggs in Fhe twigs, migrate3to nearby vineyards, and parasitizes the eggs of the grape leafhopper which has begun to lay eggs. Grape Leafhopper

Fall Winter Adults in weeds - trash

August - egg laying stops Summer Spring April - Eggs t animus wasp i 1/2 - 3 147,0.4 Akeelata wasPI generations / Nmwstis mite depends on temperature General predators Minute pirate bug Green lacewing larva Damsel bug [ Big eyed June - May - dults but

Fall Winter

Adults are laying eggs Prune Leafhopper continuously Ana ru wasp Summer Spring paras tizes the ggs

Eggs in twigs Eggs in twigs Fall Winter )1 September Adults (3) April - hatch Blackberry Leafhopper Summer Spring Adults (1) Eggs in leaves Eggs in leaves July (2) Adults PACIFIC MITE & WILLAMETTE MITE in the Southern San Joaquin Valley

The authors are Donald L. Flaherty, Farm Advisor, Tulare County; Frederik L. Jensen, Extension Viticulturist, Parlier; and Curtis D. Lynn, Farm Advisor, Tulare County.

Figure 1. Pacific mites on underside of leaf. Actual Figure 2. Predatory mites, Metaseiulus occidental Is size of largest mite in photo is about inch. (Photo (Nesbitt). Actual size is slightly larger than the Pacific by Frank E. Skinner, Staff Research Associate, UC Di- mite. vision of Biological Control.)

Figure 3. Leaf damage and burned shoot tip caused by Figure 4. Leaf damage caused by Willamette mites. Pacific mites.

The Pacific mite (Tetranychus pacificus McGregor) damage adversely affects fruit quality and:or ma- is second to the grape leafhopper as a pest of turity. Pacific mite damage sometimes affects the grapes. Where present, it can be a more serious following year's vine growth and crop, and very problem than the leafhopper, but it does not infest heavy infestations may even kill grapevines. This so large an acreage. Since the Willamette mite does not mean that only very low Pacific mite popu- (Eotetranychus willamettei Ewing) seldom causes lations can be tolerated in a vineyard. Based on economic damage, control measures are only in- past experience and on vineyard vigor, the grower frequently required in the southern San Joaquin should determine whether or not a particular popula- Valley. tion level is tolerable.

Large populations of Pacific mites cause extensive The following characteristics help to distinguish leaf damage by their feeding, which results in between these two spider mite species on grape- burned foliage and distorted shoot growth. The vines. AGRICULTURAL EXTENSION UNIVERSITY OF CALIFORNIA AXT-394 10 73 • Adult Pacific mites are slightly greenish to red- Both species produce many generations each year. dish in color, and Willamette mites are usually Large Pacific mite populations quickly develop pale yellow. Mature females of both species have during favorable periods. This is because the fe- spots along their sides; these spots are minute male can lay five eggs per day, and it takes less on Willamette mites. Mature Pacific mite females than 10 days for more egg-laying females to develop also have two posterior spots. It is necessary to from the eggs. use a hand lens and it also takes practice to Pacific mites usually become troublesome with the identify these characteristics. hot weather in early June. Populations remain high • Pacific mites prefer the exposed parts of a grape- until mid-August when reproduction slows and pred- vine, particularly the top and the side that faces ators take their toll. the afternoon sun. Willamette mites seek the less A predatory mite, Metaseiulus occidentali s (Nesbitt), exposed, shady areas. gives good control of spider mites if not disturbed • High Pacific mite populations often produce ex- by pesticides and if well distributed in the vineyard. tensive webbing and cause burning of the vertical The grower can estimate the potential effectiveness shoot tips on the tops of vines. Older leaves are of the predators by monitoring predator and spider also burned, but this must be distinguished from mite populations and by learning to recognize toler- sunburn or sulfur burn. able spider mite levels.

• Willamette mites produce very little webbing and With practice, the predator can be easily identified show little preference for vertical shoot tips on by using a hand lens. The female predator mite is the top. Their damage to vines is characterized usually found along leaf veins or wedged in vein by yellowed or bronzed foliage. They do not angles, where it prefers to lay its eggs. When carry- usually cause foliage burning unless the vines ing eggs, it is pear shaped and slightly larger than are weak. female spider mite adults. The predator's color varies, depending on how recently and on what prey • Pacific mites favor the weaker vines and their it has fed. It is often slightly reddish when it has damage to a vineyard is often spotty. Willamette fed on Pacific mites and yellowish when it has mites generally prefer healthy, vigorously grow- preyed on Willamette mites. If not carrying eggs, ing vines. the unfed predatory mite is colorless and flattened. The eggs are somewhat football shaped in contrast to the round eggs of spider mites. Pacific and Willamette mite females overwinter under the bark. Large numbers of these mites are Six-spotted thrips, Scolothrips sexmacuiatus (Per- sometimes found when the bark is peeled away. In gande), also plays a significant role in the natural the spring, the females move to growing vine shoots control of spider mites. This minute predator is to lay eggs. voracious and can rapidly reduce a Pacific mite in- festation. Unfortunately, its distribution is spotty When Pacific mites overwinter in large numbers and and it does not usually appear in vineyards until move to young shoots in the spring, they are a about mid- season. serious problem. These early Pacific mite infesta- Good pest management necessitates maximum use tions usually result from heavy pesticide treatment of natural enemies of spider mites. the previous year.

Willamette mites that have overwintered in large This is one of a series of six bulletins on grape numbers may damage young shoots in the spring, pests in the southern San Joaquin Valley. The but this is rare. Their yellowing or bronzing of the other five are: AXT-392, Grape. Leafhopper; foliage in the spring and summer seldom produces AXT-393, Grape Leafhopper Parasite; AXT-395, Roller; AXT-396, Grape Leaf severe injury. But it may occasionally be necessary Omnivorous Leaf Folder; and AXT-397, Grape Mealybug. The to control these mites in less vigorous table grape price is 200 per bulletin or $1.00 for the series vineyards to prevent excessive exposure to sun- of six. light, which would yellow the fruit.

Financial assistance in publishing provided by Raisin Bargaining Association.

The University of California's Agricultural Extension Programs are available to all, without regard to race, color, or national origin.

Co-operative Extension work in Agriculture and Home Economics, Division of Agricultural Sciences, 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. va V4'k 14' 7,

`0-7

:6't;-Z.'")-<(\<%` Biological Control of Pacified\lite_- Willamette Mites in San Joaquin Valley Vineyards

A JOURNAL OF AGRICULTURAL SCIENCE PUBLISHED BY THE CALIFORNIA AGRICULTURAL EXPERIMENT STATION I. Role of Metaseiulus occidentalis II. Influence of Dispersion Patterns of Volume 40, Number 10 • December, 1:970, Metaseiulus occidentalis

D. L. Flaherty and C. B. Huffaker I. Role of Metaseiulus occidentalis Population studies in southern San Joaquin Valley vineyards showed that the distributional patterns of Willamette mite, Eote- II. Influence of Dispersion Patterns of tranychus willamettei Ewing, and Pacific mite, Tetranychus Metaseiulus occidentalis pacificus, differ in the Valley, in the vineyard, and on the vine This study revealed that prey population attributes, not indi- itself. Pacific mite generally does best under hot and dry condi- vidual attributes, dictate the efficiency with which Metaseiulus tions while Willamette mite prefers cooler and more humid occidentalis (Nesbitt) (Acarina: Phytoseiidae) - responds to and conditions, although there is considerable overlapping of the controls populations of given spider mite species (Eotetranycbus two species. willamettei Ewing and Tetranychus pacificus McGregor) on grape- Detailed populations studies showed that untreated vineyards vines. with no histories of pesticide treatment often exhibit more effi- The study also showed that under vineyard conditions, M. occi- cient levels of predation than do vineyards which have been dentalis has the ability to respond numerically to low or high prey treated. Also, contrary to the views of Some investigators, these densities. Using individual vines as study units, the length of the studies indicate that Metaseiulus occidentalis (Nesbitt) has no lag in predator response to low or high prey densitiei was shown self-limiting aspects in its response to low or high prey densities. to be mainly a function of absence or poor distribution of the In undisturbed vineyards, a mild predator-prey interaction ap- predator relative to its prey. pears to help perpetuate effective control of low prey densities Individual vine studies may delineate not only the importance by M. occidentalis. In disturbed vineyards, widely fluctuating of predation (delayed density-dependent action) but the impor- predator and prey populations may lead to population crashes tance of abiotic factors (density-independent actions), as well. and continuation of imbalance. Moreover, when regulating low, Lumping of sampling data from large groups of vines precludes but potentially serious, Pacific mite densities in undisturbed vine- the appraisal and separation of these two equally important facets yards, Al. occidentalis appears to benefit from the presence of the of natural control. less seasonally restricted Willamette mite. Finally, the studies indicate that chemical treatments may disrupt Tonnage and fruit-quality data showed that Willamette mite predator and prey distributional patterns, either directly by anni- is often not a significant pest. Little differentiation has been made hilating the predators or indirectly by annihilating their prey, or in the past between Pacific mite and Willamette mite, and treat- a combination of the two. ments have been applied as if both were serious pests. BIOLOGICAL CONTROL OF THE PACIFIC SPIDER MITE Tetranychus pacificus McGregor Dr. Stephen J. Krebs

BIOLOGY AND ECOLOGY CONSIDERATIONS

The Pacific Spider Mite, Tetranychus pacificus McGregor, is a plant-feeding mite that can be a very serious pest of several crop plants including grapes, cotton, almonds and walnuts. Leaf tissue is damaged by the feeding of the mites, reducing photosynthesis and other leaf physiological functions. Severe economic losses may result. The most important predator of the Pacific Spider Mite in California is the predaceous mite, Metaseiulus occidentalis Nesbitt. It is widely distributed and is usually present in sites containing the Pacific Spider Mite. Metaseiulus occidentalis is capable of very rapid and large increases in population under favorable conditions of abundant prey and suitable temperatures. It overwinters as a mated female and prey is needed in the fall to enhance survival entering diapause. Fall prey may include other mites such as eriophyids, tydeids and tarsonemids. Tydeids are especially important, since they are usually present late into the fall. During the growing season of the crop, there may be a large number of generations of M. occidentalis and population levels are dependent on food supply. The presence of alternate hosts prior to the beginning of Pacific Spider Mite activity in the spring helps maintain the predator popplation.

Several other predaceous mites closely related to M. occidentalis have been reported to feed on the Pacific Spider Mite while it is active. In addition, 'the predatory mite Bdella longicornis may feed on the overwintering hibernant form of the Pacific Spider Mite under field conditions in California, reducing populations at the beginning of the growing season. Some general predatory insects and spiders also feed on the Pacific Spider Mite. The most important of these predaceous insects are the six-spotted thrips, Scolothrips sexmaculatus Pergande, and the minute pirate bug, Orius tristicolor White. At times, these predators can be quite active, especially when the Pacific Spider Mite is at high populations levels. They may be most important in limiting the spread of the pest from areas of high population densities into uninfested areas of the field. A few disease organisms attacking Pacific Spider Mite have been reported. They include the fl - exotoxin of Bacillus thurengiensis Berliner, which also kills the predaceous mite M. occidentalis; the non-occluded virus of the Citrus Red Mite; and a virus-like substance found in several Tetranychus species.

Environmental conditions strongly affect population levels of the Pacific Spider Mite. High populations are correlated with dusty conditions, low leaf water potentials (dry soil conditions) and generally-weak plants. Outbreaks often occur when pesticides have reduced the populations of beneficial species. The Pacific Spider Mite prefers full sun, high temperatures and low humidity.

CONTROL STRATEGIES

A comprehensive biological control program for the Pacific Spider Mite should achieve as many of the following goals as possible in order to be successful in maintaining populations levels of the pest that are below the economic threshold of crop damage:

1. Maintain sufficient moisture in the soil to avoid extreme water stress in the plant. 2. Maintain the proper level an balance of plant nutrients, with special attention to nitrogen. Avoid high levels of this nutrient. 3. Avoid dusty conditions on the leaves of the crop plant. 4. Implement a non-chemical integrated control program for other pests of the crop to avoid harming the beneficials populations; or, where treatment is necessary, use the least-toxic materials available. 5. Monitor relative levels of the pest and its natural enemies, including alternate prey of the natural enemies. 6. Determine the economic threshold level at all points in the crop production cycle. 7. Use cultivars that are relatively resistant to the Pacific Spider Mite. 8. Introduce M. occidentalis into'fields that have a history of Pacific Spider Mite infestations; or, where any of the preceding goals cannot be achieved.

bTamite .sic 9/96 SPIDER MITE STUDIES IN THE INTEGRATED CONTROL PROJECT

Don Flaherty

The last two seasons in the integrated control project has seen an increased emphasis on the problems of spider mites in vineyards. The following summarizes some of the work.

Predator studies.

(a) Work the past two seasons indicates that Typhlodromus mites can be of significant value under certain conditions in suppressing and controlling both species of mites, although less effectively against Willamette mite. Other predators such as Orlus, lacewings, ladybird beetles and six-spotted thrips appear erratic in general; however, six-spotted thrips at times can be quite effective in reducing heavy populations of Pacific mite.

Damage by spider mites to vines.

(a) Pacific mite is more than likely an insecticide induced pest and has become a very serious problem in many areas. It can cause severe damage to vines and lower the quality of the fruit in a very short time. The numbers of mites which cause economic damage are small relative to the numbers of Willamette mite. Insecticides increase the abundance of this pest by reducing the effective ness of its natural enemies and possibly by chemically stimulating its repro- ductive potential. The insecticide, Sevin, is a real culprit in causing heavy flare-ups of this mite. Thiodan, on the other hand, does not appear to have this effect.

(b) Willamette mite Is not a pest of grapes in general and much higher numbers of this mite can be tolerated. We would recommend not treating light to moderate populations even on table grapes. Each individual has to determine In this respect how much he will tolerate. Trying to maintain Willamette free vines will only lead to more serious problems such as low predator-prey ratios, resistance, and aggravation of the Pacific mite problem.

(c) Two-spotted mite is not a pest of grapes, but because it is present on vines, it may have such a potential.

Introduction of predators.

(a) We have made some initial studies, but much work will have to be done because of the many problems involved in trying to establish predators under the present cultural conditions.

Cultural control.

(a) Work is being initiated to Increase the effectiveness of native predators by growing summer grasses in vineyards. We would like to see the effects of holding down dust and improving the habitats of predators.

(b) Work also will be initiated to determine why certain areas are mite free while others are plagued by these pests. We hope to determine whether it is a climatic or soil property. We suspect the latter because of dust and/or its effect on mite populations through plant physiology. Chemical control.

(a) We hope in the future to be able to recommend chemicals which are the least deleterious to natural controls and which do not stimulate mites into abundance. At present, we warn against the use of Sevin In areas where mites are a problem, treating sub-economic levels of leafhoppers, using combinations of insecticides and miticides--unless absolutely necessary, and applying pesti- cides at regularly fixed schedules.

General surveys of the San Joaquin Valley.

(a) Areas differ in their problems with respect to the amount of damage caused by spider mites, and also with regard to which species is the pre- dominant pest. For example;

(1) In the east Tulare area (Woodlake and Exeter) and parts of east Fresno County, Pacific mite Is not found on vines. Willamette mite is present but not normally a pest of any consequence. Treatments are not needed for mites in these areas. Even where heavy applications of insecticides are applied, mites do not become a problem.

(2) In west Fresno County, however, Pacific mite is the most serious pest of vines. It normally is not a pest in vineyards which have not had regular treatments for grape leafhopper. Willamette mite is an occasional pest, but less so In untreated vineyards.

(3) In the southern Tulare County area (Delano), both mites are a problem, especially on table grapes where a lower economic lever has to be maintained. Both species in this area are aggravated by the excessive insecticide and miticide applications. Neither species would be a general pest If certain contact insecticides had not been applied at regular intervals.

(4) In the southern Kern County area (Arvin) ; the problems in general are similar to those in the Delano area; however, Willamette mite appears to be more of a problem.

Predaceous mite - Metassiulus occidentalis Nesbitt

Pacific spider mite - Tetran,chus na- 4 ' 4 -us McG. and Willamette mite - Eoecracvchus willametti Ewing

Hibernation

Preys in fall: Adult females rydelds under bud scales Adult females hibernate Willamette Hibernation under grape bark Fall Winter Tarsonemids Fall Winter Eriophyids Depends on: Day length Temperature Foliage maturity

Eggs Spring Active at bud break Summer Spring

5 day life cycle

Mite reproduction Mite reproduct 5 eggs per day Less than 10 dal,&,11ftgycle Plant Pathology George N. Agrios Proteins synthesized Professor and Chairman Department of Plant Pathology University of Florida, Gainesville Vitamins and hormones formed Third Edition Shoot blight Leaf blight Reproduction and ACADEMIC PRESS, INC. storage of starch, KO/Cavri a..• JOVIMOvick PVIAhaters San Diego New York Berke4ey Boston proteins,and fats London Syaney Tokyo Toronto

Transpiration Fruit spot /

Fruit rot

Leaf spot

Carbon Canker Light dioxide 11 " Translocation of water and minerals

Wilt Food translocation Vascular wilt Photosynthesis (Food manufocture) Crown gall

Sugars and nitrogen form amino acids Root rot

//111 Uptake of water and minerals Protein synthesized

FIGURE 1 - 1 Schematic representation of the basic functions in a plant (left) and of the interference with these functions (right) caused by some common types of plant diseases. Protozoon

Beet Yellows Virus - Tobacco Mosaic Virus • Wheat Striate Mosaic Virus Fungus II • Cucumber Mosaic Virus (mycelium) • Tobacco Necrosis Satellite Virus • Hemoglobin Molecule

Viroids

Mycoplasmas

1 \ 1 Nucleus I \... il tl. Bacterium F:- I. ....:. Nucleolus „,'"---.,., -, ri, ) 5. I

FIGURE 1.2 Schematic diagram of the shapes and sizes of certain plant pathogens in relation to a plant cell.

F.nqi

i .

Bacteria ...- • , . Morphology and flagellation Fission Streptomyces

Mycoplasmos

Morphology Multiplication Spiroplasma

4,■ ..,,. 4: .te,4, .::: N Parasitic . *;,,,?- Higher !4% ..• ... "NMI 1 Plants tL i ) . my I, II IPP4r1 \. .gsgmatgehl.i Dodder Witchweed Dwarf Mistletoe Broomrapes

...--,::--..:-••-:.; :in: /J.. •., .. •,., . .•-• • , 468,0 ,..?'...... ---, ...... --.•. kifiliii(tMffi, Viruses •,j,i .,., ■ .- .- faMt-..• , Morphology Viroids _____.------

Nematodes "..;‘N. '''t'',1,*•\.

N.------..! Larva

FIGURE 1-3 Morphology and multiplication of some of the groups of plant pathogens.

FIGURE 2 - 9 Forms and locations of survival of fungi and bacteria between crops.

In buds....'"

Fruiting bodies In xylem dead vessels fruit Bacteria \ Sclerotia Spore I In cankers Bacteria Plant debris-. In conks

0 ° Bacteria Mycelium Spores In infected roots On or in soil On perennial plants

Sclerotia,myceliurn or bacteria Spores or Mycelium or bacteria bacteria /

On or in seed On or in vegetative propagative On or in insects organs 3 1, 0 Superficial Germ tube Spore mycelium Spore Subcuticular mycelium Spore *Am 4E114 IM

PP 114741101. Direct with haustorio Direct, subcuticulor only

Direct Direct with appressorium (A), penetration penetration peg (PP),and intracellular mycelium (IM)

Direct, intercellular mycelium Direct, intercellular mycelium with haustoria Guttation water droplet Penetration through natural openings

Through lenticel Through stoma Through hydathodes

Penetration through wounds

Through natural cracks between Through wounds Fungus kills and macerates cells main and lateral roots ahead of its advance

FIGURE 2-2 Methods of penetration and invasion by fungi.

Scanning electron micrographs of appressorium formation and penetration through a stoma by the bean rust fungus Uromyces phaseoli. (A) Uredospore, short germ tube, and large. flattened appressorium forming on a membrane. (B) Uredospore, germ tube, and appressorium formed after 6-hour germination over closed stoma on bean leaf. (C) Young appressorium over open

stoma of bean leaf. (Photos courtesy W. K. Wynn, from Phytopathology 66, 136 - 146).

FIGURE 2-3 Methods of penetration and invasion by bacteria. elks"

. • ://p • ( Nectarthode

Through stoma Through wound • 4 • Bacteria in nectar and Through hydathode through nectarthode 3(31 Formation of sheath around hypha penetrating a cell wall. CW = cell wall; H = hypha; A a appressorium; AH = advancing hypha still enclosed in sheath; HC hypha in cytoplasm: S = sheath.

B

Development of tyloses in xylem vessels. Longitudinal (A) and cross-section (B) views of healthy vessels (left), and of vessels with tyloses. Vessels on right are completely clogged with tyloses. PP = perforation plate; V = xylem vessel; XP = xylem parenchyma cell; T = tylosis.

N F

M

Gum barrier in apple twig infected with Physalospora cydontae M = mycelium in vessels; XV = xylem vessel: WF = wood fiber: Abscess on layer WP = wood parenchyma. After Hesler ( IQ [ 6 ) ('on 'nation of abscission layer around a diseased spot of a Prunus leaf. After Samuel (1927). 3 6 Z FIGURE 5-1 Formation of cork layer between infected and healthy areas of leaf. CL = cork layer; H = healthy leaf area; I = infected: P = phellogen. After Cunningham (1928).

Rhizocronia After G. E. FIGURE 5-2 Formation of cork layer on potato tuber following infection with Ramsey, I. .4gric. Res. 9, 421-426 (1917). Napa Valley College 2277 Napa-Vallejo Highway, Napa, CA. 94558

Dr. StephenKrebs,ProgramCoordinator Viticulture and Winery Technology

PHONE: (707) 253 - 3259 FAX: (707) 259 - 8058

ENVIRONMENTAL FACTORS INFLUENCING THE DEVELOPMENT OF GRAPEVINE DISEASES

Stephen J. Krebs April 23, 1998

Environmental factors that influence the development of grapevine diseases include temperature, sunlight, humidity, wind, soil moisture, mineral nutrition and the condition and stage of growth of the grapevine tissue affected by the disease. Like other organisms, grapevine diseases interact with their environment. Particular conditions are required for growth and development of these organisms. In addition, since many diseases and pests are specific to the grapevine, they often thrive under the same conditions that promote growth of their host plant. An understanding of both the biology and the environmental requirements of grapevine diseases is essential in the formulation of an effective and sensible control strategy.

DISEASES OF THE GRAPEVINE

POWDERY MILDEW (Uncinula necator)

Powdery mildew is the most important worldwide disease of the grapevine. The causal organism Uncinula necator is the only species of powdery mildew that attacks the grapevine, and it is only capable of living on Vitis species. Prevention by the application of sulfur or other materials during the period between budbreak and veraison is required for Vitis vinifera cultivars. Most cultivars selected from American Vitis species are resistant to Uncinula necator. 2 Temperature Temperature is the most important environmental factor influencing the development of powdery mildew. • Optimal temperature for infection and development is 20-27 ° C (68-81° F), with a range of 6-32° C (42-90° F). • Above 35° C (95° F), germination of conidia is inhibited • Above 40° C (104 ° F), conidia are killed. • In laboratory studies, conidia germinated in about five hours at 25° C (77 ° F). • In the field, three consecutive days with temperatures between 21-30 ° C(70-85 ° F) for at least six hours each day are required for conidia germination. (See attached table: "Duration of temperatures...by Dr. Gubler.) • At 23-30° C (73-85° F), time from the establishment of a new powdery mildew colony until that colony begins to sporulate is five to six days. • At 7° C (45° F), time from the establishment of a new powdery mildew colony until that colony begins to sporulate is thirty- two days or more. • At 36° C (97° F) for ten hours, or 39° C (102° F) for six hours, powdery mildew colonies are killed. • Ascospore release from cleistothecia occurs between 10-27 ° C (50-80° F), with an optimum of 15 ° C (59° F).

Humidity and Moisture Humidity and free moisture are less important that temperature. However, there are some interactive effects. • Relative humidity of 40-100% is very conducive to germination of conidia and ascospores. • Spore germination may occur even at very low relative humidity. • Sporulation is more sensitive to humidity than is spore germination, with increasing sporulation at higher humidity. • Rainfall of at least 0.1" and tissue wetness of 12-15 hours is required for release of ascospores. • Free moisture may damage both conidia spores and mycelium.

Other Environmental Factors • Low light intensity favors the development of powdery mildew. • Bright sunlight damages conidia spores or inhibits their germination. • Wind has little or no effect on the development of powdery mildew. However, it may hamper the application of control materials. 3 • Excessively high nitrogen status in the vine may make the tissue more susceptible to powdery mildew infection.

Susceptibility of Grapevine Tissue All green tissue of the grapevine is susceptible to infection by powdery mildew, including the shoot, the leaf, the cluster rachis and the berry. • Vitis vinifera cultivars vary in susceptibility to powdery mildew. Chardonnay is especially sensitive, and since it is frequently grown in climates that are conducive to the development of powdery mildew, intensive control practices are often necessary. When more resistant cultivars are grown in warm climates, lower-intensity control practices will usually be successful. Close attention to the timing of fungicide applications is essential for effective control of powdery mildew. • Young, succulent tissue is most susceptible to infection. The berry between bloom and "green pea" stage is especially susceptible, and fungicide applications must be applied during this stage of growth. As grapevine tissue ages, it becomes quite resistant to new infection. • After veraison, (over +10° Brix), berries are resistant to new infection. In vineyards free of mildew approaching veraison, it may be possible to skip the last scheduled control application. Normally, the last several control applications are made during warmer weather which inhibits powdery mildew. The grapevine tissue has become more resistant by this time as well. • Powdery mildew colonies often develop in the fall on leaves, when temperatures are cool. A post-harvest application of a wettable form of sulfur is desirable when mildew is seen at this time. The application should be made as soon as possible after harvest, and a high volume of water per acre should be used to thoroughly wet the vines. This practice will reduce the amount of inoculum that overwinters on the vines. In the following spring season, one or more early-season wettable sulfur applications should also be applied.

BOTRYTIS BUNCH ROT (Botrytis cinerea)

The rot organism Botrytis cinerea is found in all grape growing regions. It is second in importance to powdery mildew only because many cultivars are resistant to this disease. However, it can be the principle disease problem in particular vineyards. 4 Temperature • Spore germination may take place between 1-30°C (33-86° F), with an optimum of 18 ° C (64 ° F). • High temperatures may arrest the development of bunch rot and prevent sporulation.

Humidity and Moisture • In the absence of free water, germination occurs only when relative humidity is 90% or h igher. • Infection under the favorable temperature range of 15-20° C (59-69° F) with free water or 90% minimum humidity occurs after just a few hours. More time is required at cooler temperatures. • Rain at bloom permits flower style infection, and may result in infection of all cluster tissue under temperature and moisture duration conditions favorable to the disease.

Other Environmental Factors • Botrytis cinerea is very sensitive to air movement. An air flow rate of 0.3 m/sec (1 ft/sec) or more greatly reduces the incidence of the disease.

Susceptibility of Grapevine Tissue All succulent green tissue of the grapevine is susceptible to infection. The most common damage is to the ripening clusters, but under certain conditions the shoot, leaf and flower tissue, and immature clusters may become infected. • All of the flower caps and anthers become infected every year at bloom. Some of these dried flower parts trapped in the growing clusters, but disease only develops if environmental conditions favorable to the disease occur. This condition is known as a latent infection, and supplies the inoculum that initiates the growth of bunch rot in the clusters. • Warm spring rains may cause a variation of the disease known as "Shoot Blight". Warm rains at bloom may cause complete destruction of flower parts, especially when wet conditions persist for several days. • Styles of individual flowers may become infected at bloom. In midsummer, these berries often rot. Adjacent berries in the cluster then become infected. These infections may supply additional inoculum if sporulation occurs. • Cultivars with tight clusters are more susceptible to the disease than are cultivars with loose clusters. High soil moisture may contribute to excessive cluster tightness in certain cultivars. • Excessive nitrogen fertilization may cause disease infection indirectly, by stimulating vegetative growth and thus 3L1- 5 creating high humidity conditions around the clusters that favor disease development.

EUTYPA DIEBACK (Eutypa lata)

Eutypa Dieback is a fungal disease of the xylem tissue of the grapevine. The organism enters the xylem when air-borne spores land and germinate on pruning wounds. The disease grows into the xylem tissue over a period of several years, eventually killing the vine.

Temperature Temperature does not appear to be a strong controlling factor in the development of Eutypa lata However, there is an important indirect effect related to the rate at which pruning wounds heal. • Ascospore germination and the growth of mycelium is most rapid at temperatures of 20-25 ° C (68-77 ° F). • Healing of pruning wounds, which prevents infection, is accelerated by warm air temperatures.

Humidity and Moisture Rainfall is the most important environmental condition influencing the development of the disease. • The disease is unlikely to occur in areas that receive less than 10" of average annual rainfall. • The disease can be very common in areas that receive 24" or more average annual rainfall. • Spores are forcibly released from the fruiting bodies found in cankers on dead vine wood during periods of winter rainfall. • Wet conditions slow down the healing of pruning wounds, thereby extending the susceptibility of those wounds.

Other Environmental Factors • Wind increases the rate of healing of pruning wounds. The most favorable weather immediately after pruning consists of warm and windy conditions. • Pruning late in the dormant period reduces the incidence of infection. This is probably the result of a complex of factors including warmer, windier conditions and longer daylength, and changes in spore release patterns. • Spore concentration is related to the proximity of sporulating cankers. Cankers within the vineyard should be removed and destroyed by burning, burial or transporation away from the 6 vineyard. Adjacent infected vineyards are also an important inoculum source. • Eutypa lata attacks some members of the genus Prunus. Apricot trees are especially susceptible, and diseased trees near the vineyard are a source of inoculum. Several wild Prunus species that live in California are also hosts.

Susceptibility of Grapevine Tissue • Cultivars vary in susceptibility to Eutypa lata. Cabernet Sauvignon and Chenin blanc are highly susceptible. Disease incidence is slight in Zinfandel vineyards. • Freshly-made pruning wounds are most susceptible to infection. The cut surfaces of the grapevine heal by dessication, sealing off interior tissue. • The number of wounds created during pruning is directly related to disease incidence. Training and pruning systems which limit wounding to the vine are very effective at reducing disease incidence. Eutypa lata is primarily a disease of cordon trained, spur pruned vines. When appropriate for a particular cultivar, head training and cane pruning should be used. This is especially effective for the control of the disease in the cultivar Cabernet Sauvignon.

PIERCE'S DISEASE (Xylella fastiodosa)

Pierce's Disease is a bacterial disease which attacks the xylem of host plants. Both Vitis vinifera and V. labrusca cultivars are susceptible. The disease is found where a particular combination of biotic factors occur, including the bacterium, susceptible hosts, alternate host reservoirs of the bacterium, and insect vectors that transmit the bacterium from alternate to susceptible hosts. The disease also occurs in almonds (Leaf Scorch) and alfalfa (Alfalfa Dwarf), but these plants are not sources of inoculum for grapevines. The disease is not spread from infected to . healthy grapevines.

Temperature The effect of temperature on disease incidence appears to be indirect. It has a greater effect on the growth and development of the host plants and the vectors than on the bacterium itself. • The disease is transmitted by sharpshooters and spittlebugs in California. These are xylem-feeding insects that are active during the warm part of the year. • Transmission of the bacterium occurs when an infective insect feeds on an actively-growing grapevine leaf. Active growth of the vine is necessary for infection to occur. 7 Humidty and Moisture The disease is found where riparian conditions occur. Locations with year-round water promote disease incidence. • The most important alternate hosts of the disease are riparian species. • Some common horticultural plants also serve as alternate hosts. Irrigated landscaping near vineyards may be an important source of inoculum. • The insect vectors of the disease are abundant in riparian habitats.

Other Environmental Factors The relative proximity of the alternate host and insect vector habitat appears to have a strong influence on disease incidence. • The occurrence of Pierce's Disease is strongly correlated with distance from the riparian or landscape habitat. Beyond about 100 yards from the habitat, disease incidence is negligible. • There are apparently certain "hot spots" in the North Coast where disease incidence is especially serious. • Removal of selected alternate host plants may be somewhat effective in reducing the occurrence of the disease. • Various vegetative barriers, fallow zones and set-backs may help reduce disease incidence. • Planting of high-value crops other than grapevines in the worst locations may prove to be the most favorable economic solution.

Susceptibility of Grapevine Tissue • All Vitis vinifera and V. labrusca cultivars are at least somewhat susceptible to Pierce's Disease. Most commercially- desirable cultivars are highly susceptible. • Injection of antibiotics into the grapevine trunks has been ineffective. • Removal of tissue with visual symptoms does not prevent the death of the infected vine. • Early season feeding by infective vectors results in the death of those grapevines. Late season infection may result in visual symptoms, but eventual recovery by the grapevine.

PHOMOPSIS CANE AND LEAF SPOT (Phomopsis viticola)

Phomopsis Cane and Leaf Spot is a fungal disease of the grapevine that occurs in vineyards of the San Joaquin and Sacramento Valleys, where particular cultivars are especially susceptible. This disease is almost never found in the coastal wine grape districts. In spring in the North Coast, certain 8 foliage symptoms are often mistaken for Phomopsis infection. A biological assay at a competent laboratory is essential for the diagnosis of this disease. Such assays in the North Coast almost always fail to show that Phomopsis is the causal organism of the disorder.

CROWN GALL (Agrobacterium tumefaciens)

Crown Gall is a soil-borne bacterium that causes disease in the woody tissue of the grapevine. The bacterium enters the vine through wounds that are in close proximity with soil This problem can be especially serious during propagation in the nursery. Clean planting stock is essential for the control of the disease. Where vineyards are propagation by field budding, special care should be taken to avoid contamination of the cuts made during the budding operation. The bacterium can be spread from vine to vine if pruning tools are used to cut into a gall. When galls are removed, a bleach solution should be used to sterilize the shears before cutting into other vine tissue. Gall removal is normally not recommended, as it results in a larger wound in the trunk tissue. Instead, the following practices should be employed.

In the field, drip emitters should be positioned so that irrigation water never flows over the vine trunk and graft union.

Galls on the trunk near ground level should be exposed to the air by carefully removing soil from around the base of the vine.

No satisfactory biological controls are available for Agrobacterium tumefaciens Biovar 3, the form of Crown Gall that infects grapevines.

31-1

58 Section 2 • Powdery Mildew

Powdery Mildew Cycle

ASCUS CONTAINING ASCOSPORES

OVERWINTERS IN BARK ...... )

ASCOSPORES ARE RELEASED DURING SPRING RAINS 0 0 CLEISTOTHECIA ARE PRODUCED ON LEAVES, SHOOTS, AND BERRIES BUD SCALE INFECTIONS IN LATE SUMMER GIVE RISE TO OCCASIONAL INFECTIONS ON NEW FUNGUS OVERWINTERS SHOOTS IN SPRING UNDER BUD SCALES

A MILDEWED GRAPE WOOD SHOWS REDDISH BROWN FUNGUS STRANDS BLOTCHES DURING GROW ON OUTSIDE DORMANCY OF TISSUE ID 1110111111 o 0 FRUITS BECOME irr INFECTED IN LATE SPRING SPORES INFECT YOUNG GRAPE TISSUE DURING SPRING, POWDERY WHITE PATCHES APPEAR ON LEAVES

SECONDARY INFECTIONS ON YOUNG LEAVES, SHOOTS, AND BERRIES

University of California Division of Agriculture and Natural Resources 1992

GRAPE PEST MANAGEMENT Second Edition POWDERY MILDEW OP THE GRAPEVINE (Uncinula necator) Stephen Krebs

Disease Cycle fungus overwinters as mycelium in dormant buds fungus overwinters as cleistothecia, produced on leaves, shoots and fruit in fall mycelium grows on new shoots in the spring cleistothecia leads to ascus which releases ascospores in spring, producing mycelium on any green tissue

mycelium produces conidia during the growing season, causing secondary disease cycle on any green tissue

in fall cleistothcecia are produced and developing buds become infected

Damage to the Vine young tissue is most susceptible to infection

FRUIT: infection early in the season destroys fruit completely, is a source for inoculum infection later in the season causes presence of mycelium and sporagium on the surface of the berry at harvest time for winegrapes, an undesireable musty character is produced in both aroma and flavor for table grapes, cosmetic damage and off-flavors occur for raisin grapes, a reduced quality grade results

LEAVES: infection in the early stage of leaf development causes distorted tissue or complete failure to function; reduced photosynthesis; early leaf fall; secondary inoculum

infection in the later stage of leaf development causes reduced photosynthesis infection late in the season can produce overwintering mycelium and cleistothecia SHOOTS: infection causes damage to conductive tissue; provides inoculum 3•1- Resistance to Infection cultivars differ in susceptibility to the disease older leaves develop resistance to new infection after veraison (fruit softening and color change), fruit becomes resistant to new infection (over 10-12 ° Brix)

Environmental Factors temperature is the primary factor in disease development 20-27° C. optimal for infection and development, with a range of 6-32° C.

above 35° C. germination of conidia is inhibited above 40° C. conidia are killed at 25° C. conidia germinate in about 5 hours at 23-30° C. time to sporulation is 5-6 days at 7° C. time to sporulation is 32 days or more at 36° C. for 10 hours or 39° C. for 6 hours, colonies are killed

free moisture may damage conidia, mycelium 40-100% relative humidity allows germination of conidia germination may occur at 20% relative humidity humidity affects sporulation more than germination increased humidity increases spore formation

low diffuse light favors development of disease bright sunlight inhibits conidia germination

Control Methods--Prevention Using Fungicides 1) dusting sulfur only -- 10#/acre at 6", 12", 18" and 24", and then every two weeks until veraison 2) wettable sulfur only (with wetting agent) -- as above 3) wettable sulfur (with wetting agent) and dusting sulfur -- wettable sulfur at budbreak-2" stage, then as with sulfur dust 4) sterol inhibitors only (with wetting agent) -- treat every 17 days after budbreak until veraison 5) dusting sulfur and sterol inhibitors (with wetting agent) -- as with sulfur dust until fruit set, then 2-3 applications of sterol inhibitors 6) wettable sulfur (with wetting agent) dusting sulfur and sterol inhibitors (with wetting agent) -- as with wettable sulfur and dusting sulfur until fruit set, then 2-3 applications of sterol inhibitors

-27 control Methods—Eradication 1) wettable sulfur (with wetting agent) -- applied directly to infected fruit, continue prevention program 2) plain water and wetting agent --applied directly to infected fruit, continue prevention program 3) sterol inhibitors (with wetting agent) -- applied directly to infected fruit, continue prevention program 4) post-harvest wettable sulfur (with wetting agent) -- when heavy infection has occurred that season 5) NOTE: wettable sulfur application at budbreak is actually an eradication method aimed at overwintering mycelium

Control Methods--Cultural Practices these reduce disease incidence, but do not give economic control canopy management -- improved aeration allows penetration of control materials, and brighter light conditions discourage fungus development

vineyard location -- hot growing regions have less disease pressure; some difference may occur in micro-climates within a region

cultivar choice -- resistance level varies within Vitis vinifera

Control Methods—other Considerations environmental factors -- sulfur pollution, chemical pollution development of fungus strains resistant to sterol inhibitors

sulfur residue on fruit -- H2S in wine (other sources of H2 S are yeast strain, yeast strain-cultivar combination, nitrogen- deficienct must)

Choice of Control_ Strategy plant growth stage -- by far the most common method used by growers temperature-based treatment scheduling -- like degree-day models for insect prediction temperature-minimum for sporulation -- cold temperatures inhibit

inoculum level -- heavy infection the previous year indicates that wettable sulfur at budbreak-2" stage should be applied

rose bushes -- common misconception that mildew on roses can be used to determine treatment requirement (control in grapes must be based on prevention) POWDERY MILDEW OF THE GRAPE CALIFORNIA AGRICULTURAL EXTENSION SERVICE

AND ITS CONTROL IN CALIFORNIA 12. For vines of average size, and with good niachinery, from 5 to 15 pounds of sulfur per acre per application are usually used. Very large vines may occasionally require slightly more. SUMMARY 13. Too much sulfur on the vines will cause 'burning' of the 1. Powdery mildew is the most serious fungous disease of the vine vines in hot weather. This damage may occur at any time the tem- that is present in California, and in most vineyard regions of the perature goes above 100° F if enough sulfur is present. state is dangerous every year. 14. High winds, wet vines, and very hot weather should be avoided 2. It attacks all green parts of the vine including stems, leaves, in sulfuring vines, otherwise weather conditions and time of day need have no influence on the time of application. and berries. 3. The disease is caused by a fungus that grows on the outside 15. It is better to sulfur the vines just before than just after surfaces of the vine, and obtains its nourishment by means of minute irrigation. organs (haustoria) which penetrate the outer tissues of the vine. 16. When suckering is needed it should be done before dusting 4. During the summer the fungus spreads principally by means with sulfur. of delicate summer spores. It passes the winter in a resting stage', 17. Knapsack dusting machines of the bellows type are most co ► - chiefly winter spores which are enclosed in very tough spore cases. monly used for vineyard dusting and are to be recommended for 5. The fungus grows best during warm, moderately moist weather. small vineyards. It grows rapidly at temperatures between 75° and 95° F and does 18. Modern engine-driven power dusting machines are capable of not grow below 50° nor above 100° F. doing excellent work and can be recommended for large vineyards 6. It is much easier to prevent the fungus from becoming estab- where the quantity of work to be done justifies the high initial cost. lished than to kill it after it has well started. 19. To be most effective, dusting sulfur should be extremely fine, 7. The fungous body (mycelium) is quickly killed by a suitable easy to work, and free from adulterants. liquid fungicide when brought in contact with it, but it is difficult 20. A liquid spray of potassium permanganate (1 pound to 75 or impossible to kill all of the fungus by this means. gallons of water with sodium silicate and baking soda spreader) will 8. The germination of the spores and the growth of the fungus is kill all of the fungus with which it comes in contact and will not prevented by the close proximity. of sulfur, and it is possible to cover injure the vines nor badly stain the fruit. This spray should be I be green parts of a vine so completely with sulfur dust before the followed with a dusting of sulfur soon after the vines are dry. spores reach them that infection is impossible. 21. Winter spraying is ineffective in controlling mildew and is 9. It is usually necessary to repeat the application of sulfur sev- not recommended for this purpose. eral times to cover new parts that develop after the earlier applica- CALIFORNIA tions. All green areas must be protected with sulfur so long as the weather conditions favor the development of mildew. AGRICULTURAL EXTENSION SERVICE 10. Usually from 3 to 5 applications are reco ► ended. First when the new shoots are 6 or 8 inches long; second when they are 15 to 18 CIRCULAR 31 ....17.) inches long; third when they are 2 to 3 feet long, which will be at or MARCH, 1929 near blooming time; fourth, when the berries are well set; and fifth, when the berries are about half grown. • • 11. In the interior valleys, the first three sulfurings are usually sufficient for early-maturing varieties. For late-maturing varieties, a fourth application is advisable. In the coast regions the full schedule of five applications is usually necessary every year. POWDERY MILDEW OF THE GRAPE AND ITS CONTROL IN CALIFORNIA

H. E. JACOB

FACTS ON WHICH CONTROL IS BASED 1. The fungus grows only on the outside surfaces of the vine. 2. It grows only on the green parts of the vine. 3. During the growing season of the vine, mildew spreads by deli- cate summer spores. 4. In the winter the fungus is chiefly in the form of very resistant resting spores, principally on and in the soil. 5. No practical method is known by which all the winter spores in a vineyard can be destroyed. 6. The germinating summer spores are easily and quickly killed by contact with sulfur or by its close proximity. 7. The mycelium or vegetative body of the fungus is more resistant than the summer spores to the effect of sulfur; hence it is destroyed more slowly by sulfur and a higher temperature is necessary. 8. Sulfur remains active and effective so long as it remains on the green parts of the vine. 9. It is possible, without injury to the vine, if the kind of sulfur and method of application are correct, to cover the green parts so completely with sulfur dust before the spores reach them that there is no possibility of infection. 10. The mycelium is killed quickly at any temperature by a suitable liquid fungicide. 11. It is not practicable to destroy completely all the mycelium by means of liquid spraying. 12. Mildew will not grow in hot, dry weather on leaves exposed to the sun. CALIFORNIA AGRICULTURAL EXTENSION SERVICE CIRCULAR 31 • MARCH, 1929 Ine Relationship between Vineyard Sulfur (5,) on Wine Grapes and Hydrogen Sulfide (H,S)Production During Wine Fermentation Summary of Presentation of March 9, 1993 at Napa Valley College by Dr. Doug Gubler and Dr. Roger Boulton University of California, Davis (Notes by Stephen Krebs) Dr. Gubler, Vineyard Sulfur Residues on Wine Grapes Grapes contain small amounts of sulfur, even in vineyards that have not received sulfur applications for the control of powdery mildew. The level is approximately 1-2 micrograms/gram of berry weight.

At residues of 2 micrograms S 2/gram of berry weight or less at harvest, no H2S will be detectable in the finished wine in sensory analysis. At residues of 4 micrograms S2 /gram of berry weight or more at harvest, there is an increasing likelihood that H2S will be detectable in the finished wine in sensory analysis.

There is a rapid decline in S2 residue concentration following a normal dusting sulfur application, returning to the base level of 1-2 micrograms of S2 /gram of berry weight Micronized sulfur and wettable sulfur residues persist slightly longer than the residue from dusting sulfur, but also return to the baseline value.

Dr. Boulton, Hydrogen Sulfide Production During Fermentation

In past studies where very high (unrealistically high) S2 was added to must, H2S was produced in'the wine. In the current study, realistic levels of S 2 were added to must (1-5 micrograms/gram of berry weight). The threshold in sensory evaluation for the detection of hydrogen sulfide is 2 ppm. Sulfur dust, micronized sulfur, wettable sulfur and sterol inhibitors (non-sulfur chemical treatments) all produce less than the threshold. 1) Elemental sulfur is most important in the production of residues. 2) The type of sulfur does not matter. 3) Date of final application has little effect on levels at harvest under normal commercial practices. 4) Low levels of nitrogen for yeast nutrition result in increased levels of hydrogen sulfide. Residue Thresholds 1) 0-2 micrograms/grams berry weight --- no H2S 2) 2-4 --- low 3) over .4 --- definite problems

BOTRYTIS BUNCH ROT DISEASE CYCLE

WINTER ROTTEN BUNCHES LEFT ON VINE SPORE MASSES PRODUCED b. ON MUMMIFIED FRUITS • N. .1.

t

• k, F... It 'I.

"SHOOT BLIGHT" IN WARM. WET SPRINGS

LATE SUMMER

to. r-Ak SPRING Mt Or IP; PRE-HARVEST ROT • - OF RIPENING FRUIT (f.')

vett- e- MIDSUMMER S. BLOSSOMS COLONIZED

LATE-SEASON RAIN OR SPRINKLER IRRIGATION

INSECT AND MECHANICAL EARLY- DAMAGE SEASON ROT

University of California ` Division of Agriculture and Natural Resources 1992

_ GRAPE PEST MANAGEMENT:. Second,Eciltion o „I) v v- 02_ 0 L w

Bunch Rots of Grape There are many different species of microorganisms which may infect grape berries. These organisms include mainly fungi and bacteria with several genera of these being the most important in causing bunch rot of grapes. Often several of these are present in a rotted cluster making it difficult to determine which one was present first. Some of these organisms may directly penetrate and infect healthy berries while others require wounds or previously infected berries in order to infect the fruit. Economic losses result from the direct reduction in yield as the rotted fruit is culled and the increased harvest costs associated with this practice. Table and raisin grape quality and storage potential plus wine quality are all negatively affected by bunch rots. Losses can be extremely high in some years and in some locations where conditions for the specific organism are extremely favorable.

BOTRYTIS BUNCH ROT The most important fungal plant pathogen responsible for bunch rot of grape berries is Botrytis cinerea Pers. This fungus can grow on any plant material which is succulent (young shoots or flower parts), stressed (damaged or ripened fruit), or dead (yellow leaves). The chemical enzymes produced by the fungus can destroy the integrity of a grape berry within a few days. Secondary organisms such as Acetobacter bacteria and other fungi can then become established on the diseased berry. Botrytis bunch rot can be a severe disease in tight clustered, thin skinned varieties, especially under heavy canopies or during wet growing seasons. Syaptois The bunch rot begins with individually infected berries within the cluster that turn brown due to enzymes produced by the fungus. Often this stage is known as "slipskin" because the enzymes breakdown the cutin in the epidermal cells walls and they slip easily off the berry. If moisture is high and wind is low cracks will form in which the mycelium the spores will produce the characteristic gray mold. If the fungus has green spores it is probably Penicillium, if it has black spores it is most likely Aspergillus. DISEASE CYCLE Overwintering Botrytis survives the winter by forming dormant structures called sclerotia 'either on the surface or within colonized plant tissue. A common source of sclerotia in vineyards is grape mummy clusters from the previous season. The sclerotia are hard, black structures about 1/8 inch in diameter. Because these sclerotia are so hard, it is difficult to get fungicides to penetrate them, which decreases the effectiveness of dormant sprays. After rains or irrigation in the spring the sclerotia germinate and produce gray spores (conidia) which are spread by air currents. The production of spores by Botrytis cinerea results in the characteristic gray fluffy appearance of the fungus and is commonly referred to as gray mold. Germination The spores of B. cinerea require free water and nutrients for germination. In the past it was believed that high relative humidity was sufficient for germination of B. cinerea spores, however recent research indicates that this is incorrect. The spores require continuous free water for germination and growth. The free water can be from dew, fog, irrigation, or rain. Periods as short as 15 minutes with no available water are sufficient to stop the germination of the spores. However, even when water is present, germination is not optimum unless nutrients are also available. The nutrients required for germination can come from many sources, even from the surface of a healthy grape berry. The main nutrient required for germination of the spores is a simple sugar such as fructose or glucose. When water is on a mature grape berry for as little as 2 hours enough sugars can accumulate in the water to stimulate the rate of spore germination and growth. The water and nutrient dependency of the spores can be an important factor in disease control. Often Botrytis bunch rot begins in the cluster where the berries have been damaged. Birds, insects, or mechanical damage of grape berries can cause the juice to be released. This provides the spores with the nutrients and free water they require for germination. The ambient air temperature is also very important for germination. Warmer temperatures usually hasten the rate of drying of the berries and directly reduce the rate of germination. Under field conditions both the temperature and duration of free moisture are important for infection. Laboratory studies have shown that at optimum temperatures (72 F), germination and infection can occur with 15 hours of free moisture. At higher or lower temperatures, the duration of free moisture required for the spores to germinate and infect the berries may be considerably longer. At 90 F and above the fungus does not grow, but it will grow slowly even at 34 F, which allows it to cause severe disease during the storage of table grapes. Infection Under moist conditions early in the spring, the spores can infect the grape flowers, succulent young stems (shoot blight), or young leaves. These infections can lead to further spore production later in the season. When the sugar content of the berries increases and the skins begin to soften during maturation, the berries themselves become more susceptible to infection by the spores. The fungus can penetrate grape berries through wounds or directly penetrate even undamaged berries. The berry skin is the main protection from infection by Botrytis. Any chemicals or cultural practices which alter the skin of the berry will change the susceptibility of the berry to infection. It has been shown that the application of some types of spray adjuvants, or growth in contact with surrounding berries can make the berry more susceptible to infection by Botrytis. When berries are infected, cracks quickly appear in the skin. The spores develop first in the cracks and then spread over the entire berry. The infection of other berries by the rapidly growing fungus and airborne spores contribute to the extremely rapid increase in disease observed after rains late in the season. Under optimum conditions, Botrytis can infect a berry, destroy it, and begin to produce spores in only 3 days. After infection the berry may dry up if high temperatures and low relative humidities prevail (ie the "Noble rot"). However, the fungus is still alive and can continue to grow if conditions for growth become favorable again. 38( MANAGEMENT OF THE DISEASE

Disease control of Botrytis bunch rot is best achieved through an integrated pest management approach. The success of an individual control measure is dependent upon the overall management of the disease. For example the efficacy of a fungicide is dependent upon the ability to get good coverage, and coverage is affected by the canopy management and stage of growth. By cultural control methods, the proper application of fungicides, and resistant varieties the disease can be managed except under the most favorable environmental conditions for the fungus. CULTURAL CONTROL METHODS Sanitation Sanitation is the cornerstone for all effective disease control programs. Clusters left on the vines or on the vineyard floor from the previous season can be an important source of inoculum in the spring of the next season. After the overwintering sclerotia have produced spores, the subsequent infection and disease development on the berries can be managed by maintaining less than optimum conditions for germination and growth of the fungus within the canopy.

Canopy Management Since Botrytis spores have rigid environmental requirements for germination and growth, a level of disease control can be obtained by creating a canopy microclimate less conducive to disease development. The objective is to increase exposure of the grape clusters to air and light so they dry out more quickly after becoming wet. Canopy management can involve direct measures to the canopy or indirect measures which affect the overall growth of the vine. Direct measures can include trellis systems, pruning methods, shoot positioning, shoot thinning, hedging or leaf removal. The goal of all of these practices is to increase air and light penetration to the clusters. Indirect measures may involve irrigation/fertilizer strategies, rootstock selection, clonal selection, or planting density. These indirect practices affect the canopy density by altering the number of shoots, shoot length, lateral growth and the number of leaf layers. These practices may also affect cluster tightness by altering the cluster length, number of berries set, and berry size. Direct measures can be applied to vineyards after establishment and still achieve disease control. For example, hedging is often used in vineyards in California to maintain an upright pattern of shoot growth which enhances air movement directly to the clusters. However, careful timing of this practice is needed to achieve satisfactory results. If the hedging is done too early, lateral regrowth often makes the canopy more dense than non-hedged vines. In some cases these hedged vines have more bunch rot at harvest. Also, severe hedging removes a very large portion of the most photosynthetically active leaf area on the vine. This can result in delays of fruit maturity up to three weeks, thus offsetting any advantages of the open canopy for Botrytis control. S Recent research has shown that the removal of leaves and laterals around the clusters creates a microclimate within the canopy which is less conducive to the development of Botrytis bunch rot. In many cases, the level of disease control was superior to three applications of fungicide in the same vineyard. However, indirectly reducing the total canopy growth may also contribute to disease control. Many indirect practices that affect the canopy are implemented when the vineyard is establis<46hed. The planting density, soil type, rootstock, etc. all affect canopy density and are not changed for the life of the vineyard. Other indirect practices, such as irrigation and fertilization can be altered on a yearly basis. All of these practices can influence canopy density. In general, the more dense the canopy, that is the more layers of leaves surrounding the clusters, the more optimum the conditions will be for development of Botrytis bunch rot. By carefully monitoring these vineyard management practices it is often possible to reduce the density of the canopy which in turn helps to alleviate disease pressure. The microclimatic conditions within the canopy that affect the development of Botrytis the most are those that affect the duration of free water on the berries. The evaporation rate of water is affected by the temperature, vapor pressure deficit and wind speed of the ambient air. When the leaves around the clusters are removed, the wind speed around the clusters is increased, and berry surface temperatures are increased. These two factors contribute to help dry the clusters after they have become wet. If it is an unusually wet year, the benefits of microclimate modifications will be reduced due to the impact of the macroclimate. When this occurs, it may be necessary to increase the application of fungicides. If fungicides are required, however, proper canopy management will continue to benefit the grower due to an increase in deposition of the fungicides on the more exposed clusters.

Irrigation

The choice of type, timing or level of irrigation can all be methods of controlling bunch rots. For example, overhead sprinkler irrigations near harvest can increase the levels of Botrytis. If this is the only type of irrigation available, then the time of day or length of application may be varied to speed the rate of drying of the clusters. For example, in cool, coastal valley vineyards, many growers irrigate at night to take advantage of the warmer, drier daytime conditions to aid in drying. The length of free moisture on the clusters should not be greater than 15 hours, including the time it takes to dry the clusters completely. Other types of irrigation should also be used judiciously. High levels of drip or furrow irrigation will encourage dense canopy growth and provide moist conditions favorable to sporulation. Growers should try to determine optimum levels of irrigation at each vineyard site which result in desirable yields without excessive shoot or lateral growth.

Chemical

There are several different fungicides registered for controlling Botrytis bunch rot, most of which are contact materials. Only one, benomyl, has systemic properties in grape tissues. The mode of action of the fungicides differ. By using combinations of fungicides with different modes of action, it is often possible to delay the development of resistance of a fungus to any specific fungicide. Resistance of B. cinerea to benomyl has been observed in several vineyards and present registration in California requires it be used in combination with captan. The development of resistance of B. cinerea to benomyl is often very rapid, and resistant populations can become dominant quickly, reducing the effectiveness of the fungicide. Resistance to the dicarboximide fungicides (iprodione and vinclozolin) has also been reported, but the resistant strains have reduced sporulation and do not seem to become established as quickly. Spray programs may consist of sprays at bloom, or multiple applications applied at bloom, pre-close, veraison, and at least two weeks before harvest. This should depend upon the history of Botrytis bunch rot in a particular vineyard and variety. Data collected over many years has shown a direct relationship between the number of fungicide applications and the level of Botrytis bunch rot control. The greater the number of spray applications, the higher the level of disease control. Studies to determine the optimum timing of a single application have yielded variable results. A single application at bloom has rarely proven to be significantly more effective than a single application at any other times during the season. The exception being at vineyard sites where there was rain during bloom. At these sites bloomtime fungicide applications were slightly more effective than at other times during the season. The timing of sprays by the growth stage of the plant is usually not very effective, a better method would be to apply sprays only after environmental conditions conducive to the growth of the fungus had occurred. Research in France has shown that better disease control is achieved when the fungicides were applied during wet periods conducive to growth of the fungus. This is logical, for actively growing fungi are more susceptible to fungicides and the protection afforded by the fungicide is going to be present when the berries are most likely to be attacked. In the United States, fungicide applications before or after rain have been reported to reduce Botrytis bunch rot To obtain optimum coverage of pesticides spray adjuvants (most commonly surfactants) are often added to the tank mix. The purpose of these surfactants is to reduce the surface tension of the water droplets thus allowing better dispersion over the surface of the plant. The nonwettability of a plant part is due mainly to the layer of wax on its surface. Some adjuvants actually alter the structure of the plant waxes. However, plant waxes are an important barrier to invasion of fungi. Thus, although the use of an adjuvant may result in an increase in the efficacy of a fungicide due to better coverage and penetration, it may actually make the plant more susceptible to disease. Although specific situations will benefit from the use of spray adjuvants, one must consider that some chemicals already contain them in their formulation, and that the addition of any more adjuvants should be justified only by data which positively demonstrates a significant increase in the efficacy. Biological Control

Biological control of Botrytis bunch rot has been achieved in France with the beneficial fungus Trichoderma viride. Apparently, the effectiveness of the fungus is dependent upon matching particular strains with the growing conditions. For example, an isolate may work well in cool growing areas but another isolate may work best in warm growing areas. 3 (3 Resistance

Several factors are involved in the grape berry being able to resist infection by B. cinerea. Many red varieties contain compounds which inhibit the fungus. The berry skin provides a mechanical barrier to infection. The grape wax also provides an important barrier to infection. Wax formation is inhibited when berries grow in contact with other berries. These contact areas have been shown to be more susceptible to infection by B. cinerea. In general, the tight, thin-skinned white grape berries are the most susceptible to Botrytis bunch rot. However, the thin-skinned red variety Zinfandel is also highly susceptible. Although it is unlikely that grape varieties will ever be developed solely for resistance to Botrytis a wide range of resistance is already available. Below is the relative susceptibility of the major grape varieties in the western United States: Very Susceptible Susceptible Moderately Resistant Highly Resistant

Chenin blanc Barbera French Colombard Cabernet Sauvignon Carignane Gray Riesling Sylvaner Emperor Petite Sirah Grenache Semillon lmEEEr Pinot blanc Sauvignon blanc pAe ript Muscat of Alexandria White Riesling Pinot Noir Rubired Zinfandel GC/ 4 v-401400-y Ruby Cabernet Thompson Seedless An area of research that appears promising is to select within the major varieties clones which have looser clusters. Unfortunately very little of this information is available. only 52 ml. The normal must had 18.24 per cent sugar compared to 30.26 per cent in the molded fruit, and the total acidity was 0.89 per cent com- H I LGARDIA pared to 0.79. These acid values mean that Botrytis cinerea had reduced not only the total amount of acidity but also the relative amount. This is a very A Journal of Agricultural Science Published by valuable and unique characteristic of this mold, which is not a property of f-wi the California Agricultural Experiment Station the other common fungi that attack grapes. In addition, botrytised grapes are always high in glycerin, which is formed in the fruit during themg -MY". VOL. 26 MAY, 1957 NO. 12 bolism of some of the sugars or acids by the mold. Another noteworthy effect- - is that this mold does not impart a foreign or moldy odor to the must ; in THE USE OF BOTRYTIS CINEREA PERS. IN THE fact, wines of properly botrytised grapes have a special odor, which is one of their most attractive features. PRODUCTION OF SWEET TABLE WINES' The viticultural industry of California has not been able to produce a KLAYTON E. NELSON' and MAYNARD A. AMERINE' Sauternes-type wine, largely because climatic conditions prevent the mold from developing in the manner found so desirable in Europe. If such de- INTRODUCTION velopment could be induced under California conditions, the wine industry of this state might be able to add a distinct and valuable wine type to those THE GREY MOLD Botrytis cinerea Pers. is found on grapes wherever they now produced. The present study was therefore undertaken—first, to deter- are grown, though it is seldom noted in hot, dry regions. If the relative mine the most satisfactory techniques for inoculating grapes with Botrytis humidity is too low, little or no infection occurs. In Central European coun- cinerea; and second, to establish the most favorable conditions for its de- tries where the relative humidity is generally high, it is a common parasite velopment. Pilot-plant experiments based on these results could be under- on mature or nearly mature grapes. taken. Since it is an expensive operation consumer-acceptance studies should Miiller-Thurgau (1888) noted that growth of the fungus loosens the skin also be made. of the berry. After infection, depending on the climatic conditions, two different effects on the fruit are noted. In rainy weather the infected grapes HISTORY do not lose water, and the percentage of sugar remains the same or may even France. According to Laborde (1908), the use of botrytised grapes was decrease. Secondary infections by other organisms may follow. According to general in the Sauternes region of Bordeaux as early as 1845. Redding Laborde (1908), cold, wet conditions lead to excessive botrytis growth with- (1861) correctly describes the use of botrytised grapes in Sauternes, out drying, called pourriture grise in France. Such conditions are favorable Bergerac, and Anjou. Shaw (1863) visited Sauternes, probably during the for the growth of Penicillium sp., Aspergillus sp., and members of the vintage of 1862, and described the multiple harvesting of botrytised fruit mucoraceous fungi, which may displace the botrytis. This results in the rapid to produce sweet table wines. Thudichum and Dupre (1872) described the consumption of the sugar and the production of gluconic and glucuronic practice in that region in 1867, and what they reported is essentially the acids. It is then called pourriture vulgaire in France. Under moist conditions, present French procedure. Limited amounts of similar sweet types are berries punctured by insects frequently develop undesirable rots (pourriture produced in Bergerac, Montbazillac, and other Gironde districts. Gaillac, acide). Juice that has exuded from such injuries does not dry, and yeasts east of Bordeaux and north of Toulouse, also produces sweet table wines transform the sugars to alcohol. Acetobacter sp. in turn transforms the from botrytised grapes and has done so since at least 1860 according to Shand alcohol to acetic acid. In contrast, if warm, sunny weather follows infection, (1928). Shand also notes wines from botrytised grapes in Beam in southern the berries lose moisture by evaporation, shriveling occurs, and the per- France. (") centage of sugar in the juice increases (pourriture noble). It is this latter The practice in Sauternes became so famous that the name Sauternes has result that has led to the commercial use of Botrytis cinerea in the produc- become almost a type name for sweet white table wines, although the annual t tion of sweet white table wines in certain areas of Europe, the high-sugar production there is less than a million gallons. The only other French region must being very desirable for the production of high-quality wines of this where this procedure is regularly followed on a large scale in favorable years •-.,type. is in the Anjou-Saumur-Tours district of the Loire Valley, and here only a q The general effect of the mold is to reduce the total amount of sugar portion of the wines, even in favorable years, is sweet. slightly but to increase markedly the percentage of sugar per unit of volume. The general practice in Sauternes is to harvest the botrytised fruit when Midler-Thurgau (1888) noted that 100 sound White Riesling berries yielded it reaches the desired stage of shriveling. This involves picking off portions 100 ml of must. The same number of berries attacked by the mold yielded of the cluster in successive harvests (tries), since not all the berries are Received for publication March 16, 1956. infected equally or shriveled sufficiently at the same time. Seven or more I Lecturer in Viticulture and Assistant Viticulturalist in the Experiment Station, Davis. pickings have been made in some Sauternes vineyards. However, the number " Professor of Enology and En4ogist in the Experiment Station, Davis. varies from vineyard to vineyard depending on the degree of sugar desired Auslese wines are not produced every year in Germany but only when the and on how much volume the proprietor can sacrifice, because the attack of climatic conditions are favorable. Even in the most favorable years the botrytis and the subsequent shriveling always markedly reduce the yield. production is small. However, these sweeter, highly aromatic types help In the warmer years, such as 1904, musts with a sugar content as high as 50 establish the reputation of German wines for quality. per cent have been reported, according to Laborde (1908). The more usual Botrytis also attacks red grapes, but the wines have a brownish-red color result is about 30 to 40 per cent sugar, which yields wines of approximately and the sweet German wines produced from Pinot noir are not of high 13 per cent alcohol and 4 to 14 per cent sugar. quality. Rentschler and Tanner (1955) have also reported on botrytised red Because of the great reduction in volume, sweet table wines produced from grapes in Switzerland where botrytis attack is considered wholly undesirable. botrytised grapes are always expensive. They have, however, attained en- Hungary. Tokay wine is produced in a small district in northeast Hungary. viable consumer acceptance because of their luscious sweet taste and per- Not all the wine is sweet. Muller (1930) reported an annual production of fumed odor. The French name pourriture noble reflects the desirable quality sweet types of 21,000 to 80,000 gallons. of the mold. The most famous vineyard, Château d'Yquem, has become Greger (1881) reports that the Tokay wines of Hungary have had a reputa- synonymous with the finest quality in French wines. Laborde (1908) gave tion since the thirteenth century. The Tokay essenz is made from grapes that the following analyses of Sauternes wines: have shriveled and nearly become raisins. These produce very sweet musts Alcohol Sugar Glycerine which are used to sweeten other less sweet musts or are fermented slowly to per cent per cent per cent only about 8 per cent alcohol and a high sugar content. This latter wine is Minimum 6.4 1.34 0.70 their prized Tokay essence. Szabo and Rakcsanyi (1937) report the following Maximum 17.5 44.5 2.40 analyses in various types of Tokay: Average 12.9 11.1 1.62

Germany. According to Thudichum and Dupre (1872), the advantage of Alcohol Total Sugar Dextrose Levulose D/L* harvesting grapes very late in the Rheingau district originated accidentally % bV vol. % % in 1775 when the owner of Schloss Johannisberg, the Bishop of Fulda, forgot TokajerSzaroorodni 13.5 1.6 0.5 1.1 0.45 to send permission to start the harvest. Miiller (1930) dates the beginning of Mbrer Gutedel 13.8 4.8 1.1 3.5 0.31 Tokajer Amu 13.2 8.7 2.7 4.0 0.67 the practice at 1773 but notes that late harvesting in Germany was described Tokajer Amu 12.0 9.5 3.8 5.9 0.81 in Roman writings. At Steinberg the practice is reported to date from 1822. Tokajer Amu 11.2 18.8 8.3 10.5 0.79 The problem of when the late-picking of botrytised grapes originated in Tokajer Amu 9.0 25.2 11.9 13.3 0.89 Paeans, 1888 23.3 16.6 8.7 2.52 Germany is exhaustively treated by Basserman-Jordan (1923). He recognizes Essen, 1890 7.9 35.1 21.7 13.4 1.62 the Roman procedures of harvesting dried (raisined) grapes as distinct from Fawns, 1906 4.9 42.6 27.4 15.2 1.80 the selection of botrytised fruit, but acknowledges the difficulty of exactly • Dextrose-kwaloe* ratio. dating the latter practice. He dates the practice of multiple pickings in Germany from 1581 at the latest (and perhaps from 1520 at Geisenheim and The prices paid for a bottle of the true Tokay essenz were very high- 1579 at Mainz). The first use of the verb auslesen ("to select from") he dates Gregor reports 3 to 4 pounds in 1881 (and the Tokay bottle holds only about from 1650. The original text in this case, however,' simply indicates that 500 ml) ! Berry Brothers and Company (1933) listed a Tokay essence for green and moldy grapes should be harvested separately from the sound fruit. 79 shillings for sale in London and this was during the depression. The noun Auslese did not appear in this connection until the nineteenth From the description given by Thudichum and Dupre (1872) it is not century. He considers it certain that the practice in its modern form was certain that the Furmint grape of Tokay is attacked by botrytis. They speak established by the first decade of the nineteenth century, and gives evidence of the fruit "cracking" and the juice drying up to form a lump of sugar. from labels of the vintage of 1811. This appears reasonable because practical They further indicate that not all the fruits crack and dry up, for they note ....t.\ hydrometers did not come into use in Germany until the last half of the that the pickers separate the plump from the dried berries during harvesting. eighteenth century. Miller (1930) specifically says that the climate of the Tokay region is too The current practice there is to separate the botrytised clusters. The wines dry, but he then reports that both raisining and botrytis action are respon- produced are called Auslese. Wines produced from such grapes are usually sible' for the sweet types ! From observations on the Furmint variety grown sweet. If small, heavily botrytised portions of the clusters, or only affected in the University of California vineyard at Oakville it would seem that crack- berries, are selected, the wines are called Beerenauslese and are always sweet. ing and drying are likely to be more important than botrytis. However, If the berries are quite shriveled a Trockenbeerenauslese wine may be pro- Blaha (1952) believes that botrytis does contribute. duced. These latter berries sometimes drop to the ground and have to be Russia. Maltabar (1951) reported that botrytis did not infect the grapes laboriously picked up. The wines are very sweet and very expensive. of the Crimea regularly enough to be used in the production of sweet table wines. Khovrenko (1910) reported one case of natural botrytis infection of showed that if grapes were only slightly infected with the mold, the quality Semillon grapes in the Crimea, which led to the production of a sweet table of the dry table wines produced did not suffer. If, however, the grapes were wine in 1899. badly infected, he concluded that it would be better to convert them to dis- Popova and Puchkova (1947) have studied the use of enzyme preparations tilling material. This latter condition probably corresponded to the pourri- of Botrytis cinerea in producing table wines (there called chateau-ikem ture grise stage—that is, infection but no shriveling. The disadvantage of this type). They found the enzyme preparation to contain a variety of enzymes, type of infection is that oxidizing enzymes may be derived from the mold and when added to musts it increased the yield of juice and gave a golden and lead to undesirable darkening in color of dry white table wines. Hilgard wine (dry ?) with an odor unlike that of the wine of untreated grapes. also produced at least one wine from botrytised grapes from St. Helena, Similar fungal enzyme preparations are widely used in California. It is true which remained sweet for about a year—the first instance that we have been that the yield is increased, but specifically beneficial effects on the odor have able to find of the production of such a wine in California. not been reported here. Amerine and Winkler (1944) produced 90 wines from Semillon grapes Preobrazhanskii (1947) reported on the direct inoculation of grapes with from 1935 to 1941. They did not recommend this variety for region I because the fungus. Because of the importance of his work it will be described in of its susceptibility to mold. One sample (vintage of 1940) was noted on their some detail. He inoculated clusters with spore suspensions or infected ber- cellar records as being heavily infected with botrytis. ries. In some cases the fruit was sterilized by dipping it into a bactericidal Botrytis rot is a serious problem to growers of table grapes in California. solution and then rinsing it with distilled water. A temperature of 20° C Fall rains frequently result in severe outbreaks of the disease, particularly (68 ° F) and a relative humidity of 92 to 94 per cent were found to be op- in the Emperor and Flame Tokay districts, according to Nelson (1951). In timum for the development of infection. In inoculation studies in chambers the early stages of infection the skin slips easily from the pulp when pressed the relative humidity was maintained in this range for four or five days, lightly, hence the name "slipskin." This disease is the most troublesome until considerable infection had taken place, and then the relative humidity problem in stored table grapes, being the primary reason for periodically was reduced to 72 to 80 per cent. In Semillon grapes left for 18 days a weight fumigating stored fruit. reduction of 33 per cent occurred and the sugar content increased from In general, however, botrytis infections are not widespread in California 22.7 to 31.1 per cent. vineyards because of the low relative humidity of our viticultural districts Preobrazhanskii (1947) also performed a field experiment with Semillon during the period grapes ripen. This fact is supported by results obtained grapes. Infected berries were placed in the clusters and 50 per cent infection by Nelson (1951), who found that in the absence of free moisture appreciable occurred in nine days. He did not find the sugar/acid ratio to change much infection occurred on Emperor and Flame Tokay grapes at 12° C (54° F) during drying. The pectin content increased. The analyses of his wines show only when the relative humidity remained above 90 per cent. Furthermore, alcohol contents of 3.9 to 14.1 per cent, sugar contents of 5.0 to 13.2 per in some regions and seasons, the temperature may be high enough to inhibit cent, volatile acidities of 0.122 to 0.222 per cent, and total acidities of 0.69 the growth of this fungus. Nelson (1951) obtained practically no infection to 0.88 per cent. These high volatile acidities are very interesting, as we have of Emperor grapes held at 35° C (95° F), and even at 30° C (86 ° F) infec- had the same problem. It was not stated whether the volatile acidities had tion was considerably less than at 25° C (77° F). Vineyard temperatures are been corrected for sulfur dioxide, but this correction would not markedly often in the range of 30 ° to 35 ° C or higher. reduce the volatile acidities reported. It thus appears difficult to produce sweet table wines from botrytised Italy. Garino-Canina et al. (1951) have described' the production of a fruit under California climatic conditions. To do this it will probably be sweet white table wine in the Caluso region of northern Italy. The practice necessary to control or modify the environment around the fruit by artificial there is to harvest the grapes (Erbaluce variety) in September and store means. Conditions of high humidity would have to be provided for the them until March. During this period general botrytis infection and shrivel- fungus to become established on the grapes, followed by a dry environment ing occur. It is quite certain that botrytis is primarily responsible for the to reduce the moisture content of the fruit. The temperature during the increased glycerin and pectin contents of the musts, but much of the increase incubation period would also have to be controlled. If the temperature is too in sugar content is probably due simply to shriveling of the grapes during high, botrytis will not grow well, and thermophilic fungi such as RIticopus storage. nigricans and Aspergillus sp. will predominate, causing unwanted rots and Portugal. Everett (1954) states that the sweet white wines of Grandjo in resulting in off-flavors in the wine. If the temperature is too low, the fungus northern Portugal owe their sweetness to the action of Botrytis cinerea. may grow too slowly, and, in addition, the drying rate will be drastically They are not,- however, always sweet, and the fungus is probably of only reduced because of the lower vapor-pressure deficit. limited importance. California. In California botrytis is seldom observed except very late in the season. Ililgard (1896) reported that it was prevalent in the Napa Valley in 1893 and caused many loads of grapes to be rejected. His experiments Eutypa Dieback Cycle

DIEBACK-INFECTED GRAPEVINE

DEAD INFECTED WOOD

FUNGUS FRUITS (PERITHECIA) PRODUCED IN OLD, DEAD WOOD

SPORES GERMINATE IN WOOD CELLS

SPORES PRODUCED IN SPRING, SUMMER, AUTUMN 1

SPORES DISCHARGED IN WET WEATHER

FRESH PRUNING WOUND

University of California Division of Agriculture and Natural Resources 1992

GRAPE PEST MANAGEMENT: Second Edition

Asci are borne on pedicels (60-130 pm long) and measure The eight Eutypa Dieback 30-60 X 5-7.5 pm, with an apical pore (Fig. 25). ascospores are pale yellow and allantoid and measure 6.5- 11 x 1.8-2 pm. media Eutypa dieback, known also as "dying arm " and formerly as E. Iota may be readily cultured on common laboratory the margin of "dead arm," is one of the mostdestructive diseases.of the woody from small chips taken aseptically from discolored sapwood in diseased arms or trunks. White tissues of commercially grown grapes. The known distribution four of the disease coincides with that of the grapevine throughout mycelium grows from infected wood chips after three to culture, but most countries of both hemispheres; its frequency in any region 'days' at 20-25 ° C. 'Perithecia are not produced in is limited only by. the incidence of rainfall. In' general, the' after six to eight : weeks, conidiomata may develop, often disease occurs abundantly where mean annual rainfall exceeds exuding the dharadteristic conidia (18-45 X 0.8-1.5 600 mm but is unlikely to be found where annual rainfall is Am) (Fig. 26) in orange cirri. Exposing the culture plates to a below 250 mm. It is equally prevalent in regions where winters 12-hr light-dark regime or to near-ultraviolet radiation are severe, such as central Europe and the eastern United States, promotes sporulation. and in more temperate. regions, such as coastal California, Not all isolates sporulate, and isolates vary considerably in southeastern Australia, southern France,and the Cape the amount of dark pigment produced in the medium after one Province of South Africa. ' • , to two weeks. For these reasons, preliminary diagnosis is most The causal fungus has a wide host range including 'approxi- readily acuppliOted by comparing the gross morphology of

mately 80 species distributed in at least 27 botanical families. colonies ,five or , six days old with that of reliable reference Most of its hosts are 'tree species;' including' some 'that are cultures transferred at the same time. components of natural' foresti.'J.The 'most 'seVerelYVficted . .The anamorph may be found on the inner bark covering horticultural hosts are 'grapevine,.apricot;:and black currant. infected wood. Orange cirri containing conidia may ooze from :7J 10 4311,f1 !?:: LIO 04, _1110 this tissue following incubation in a moist chamber. The spores Symptoms e, , of the anamorph do not normally germinate on laboratory Eutypa dieback is seldom seen in grapevines less than eight media, and there is no evidence that they function as years old, and in areas where incidence of the disease is high, propagules. It is possible that they function as spermatia. diseased vines become more numerous" each year thereafter. The most readily recognized symptoms,' most evident during Disease Cycle and Epidemiology - the first two months of the annual growth cycle and especially In regions where winters are temperate, perithecia of E. Iota when the new season's shoots are 25-50 cm long, are reach maturity early in spring, and ascospores are disseminated deformation and discoloration of the shoots.,The young leaves with each rainfall of more than about 1 mm. By late autumn the are smaller than normal, :cupped, and .chlorotic; ,they : often perithecia are almost exhausted, but nevertheless, sufficient develop small necrotic spots, and tatterf d 'margins, sometimes ascospores are available to infect vines pruned during the with larger areas of necrosis, itsthek,*..4 {narked dwarfing,of following winter. In regions where temperatures below 0°C the internodes (Plate 53) accompaniestlie development of theSe prevail in winter, dissemination of ascospores is greatest in late leaf symptoms. Clusters on affected shoots may hive a mixture winter, and they are therefore in abundant supply at the time of large and small berries.`" ' ' • ' when grapevines are usually pruned: Studies in the Central The symptoms arc, readily seen , until late . spring; when Valley of California suggest that viable ascospores may travel affected shoots become obscured from view by 'adjacent healthy up to 100 km. growth. Nevertheless, 'symptoms - on foliage -of diseased arms Infections are initiated when ascospores enter freshly made become more extensive in each successive year until, finally, wounds. Rain is a requisite for the release of ascospores• and, part or all of the arm fails to produce shoots in' spring.'' after aerial transport and deposition, for their entry into the The pathogen does not normally enter the green shoots of the open ends of vessels exposed by pruning. The susceptibility of current season's growth, and therefore it- cannot be cultured wounds, diminishes:markedly during the two weeks following from these tissues. The foliar: symptoms. are believed to be pruning, and after four weeks the wounds are unlikely to be induced by translocation of a toxin generated in the olderwood infected. invaded by the mycelium, Ascospores germinate in 11-12 hr at the optimal temperature of 20-25°C. Germination occurs within the vessels, usually 2 Close examination'of an arm, cordon, or trunk with vascular mm or more beneath the wound surface. The mycelia connection to shoots bearing foliar symptoms usually reveals a proliferate slowly, at first within the vessels and later through canker surrounding a 'pruning wound made 'several years associated elements of the functional wood. previously. Removal of the loose bark is necessary to show the extent of the canker (Plate 54). In cross section, a wedge-shaped The disease develops slowly on grapes, and no symptoms are zone of necrotic sapwood may be found extending from the seen during the first one or two growing seasons after infection. point of origin of the canker (Plate 55). The dead wood is By the third or fourth season, a canker is usually apparent, often brown, hard, and brittle. accompanied by the foliage manifestations previously • 40 described. Several more years may elapse before the affected Causal Organism arm or trunk is killed. Because of the slow progress of the Eutypa lata (Pers.:Fr.) Tul. & C. Tul. • (syn. E. armeniacae disease; its full economic impact is not likely to be felt until a Hansf. & Carter, anamorph Libertella blepharis A. L. Smith vineyard rathes maturity. Perhaps the greatest threat to vine [syn. Cytosporina sp.]) is the causal organism. It produces productivity posed by Eutypa dieback is the possibility of perithecial stromata (Fig. 25) on diseased grapevine wood, at infection of the many large wounds made when mature vines are first in small patches surrounding the original site of infection, reworked to Change the cultivar or to adapt the growth pattern •or sometimes on the wound stub that formed the point of entry, for mechanical harvesting. several years after the initial infection. Later, as the vine is more extensively invaded, larger areas 'of stromatic tissue may form an. the surface of the dead wood -after the loose bark has fallen away. Infected vine wood that has been allowed to remain on Compendiumof Grape Diseases the soil is an especially favorable substrate for development of i II stromata. The stromata are black and • continuous, and Edited by ' ' perithecia are revealed when a shallow slice is cut from the Roger C. Pearson and Austin Ce:Croheen surface with a sharp blade (Plate 56). APS PRESS A The American Phytopathological Socie

rqr Control In regions where inoculum is produced abundantly on many alternative hosts, it is impossible to manage Eutypa dieback effectively by sanitation methods alone. However, in regions with vast plantings of grapes and few alternative, hosts, sanitation may be beneficial. Unfortunately, the ("cultural requirement for regular pruning provides a multitude of entry points for the pathogen each year. No grape cultivars are known to be immune; but where differences in cultivar tolerance are known, it is advisable to prune the least tolerant cultivars when inoculum levels are low. Because of the high incidence of the disease in the eastern United 'States,' many 'growers 'have adopted a' multiple trunk- training system or are practicing a program of trunk renewal from latent buds every 10-15 years. None of the chemicals used routinely to control other fungal diseases of the grapevine provides protection against E. lata, nor indeed is the timing of their application suitable for preventing infection. Furthermore, the slow growth of the pathogen and the delayed manifestation• of symptoms make recognition of the disease difficult until extensive invasion has occurred, by which time it. is usually too late for effective remedial surgery. Hence, the disease has remained essentially uncontrolled. Fortunately, the fungicide benomyl provides a highly effective barrier against the invasion of pruning wounds by mycelia from germinating ascospores if sufficient chemical is

present in , the tissue below the pruning wounds before the spores arrive. To accomplish this, each wound must be flooded to saturation to ensure that the chemical is carried well into the exposed vessels at the wound surfaces; a sparse application of spray fluid cannot be compensated for by increasing the concentration of the chemical in the spray. mixture. Because of these exacting conditions, applications of benomyl by conventional spraying machines have not been successful. Manual, treatment of individual wounds at the time of prung,ni or the use of spraying secateurs, which facilitate the treatment of any selected wound with a saturating deposit of spray fluid, are effective means of application. Because E. kilo seldom invades annual wood, treatment of the wounds on spurs or stubs left from pruning seasonal growth may safely, be omitted, but it is essential to treat all.woundS in wood two,years Or age 'or Older, especially the large wounds made in trunks during renovation or change of cultivar.

•

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Fig. 25. Vertical section of perithecial stroma (left) and asci and ascospores (right) of•Eutypa lata. (Reprinted, by permission, from Carter and Talbot, 1974) • Pierce's Disease The causal agent is a small, nutritionally fastidious, gram- negative bacterium with a convoluted cell wall of several layers and extracellular fibrous strands. It has recently been named Pierce's disease is a principal factor limiting production of Xylella fastidiosa Wells et al. both V. labrusca and V. vinifera grapes in the Gulf Coastal Plains of the United States. In California it kills V. vinifera Disease Cycle and Epidemiology grapevines in isolated, discrete areas, which are. called X. fastidiosa is widely distributed in native plants throughout "hotspots" in that state its natural range in the Americas. Natural hosts occur among The disease was first described in 1892 from the Santa Anna River Valley near Anaheim in southern California. Several both monocotyledonous and dicotyledonous plant families. In decades later, the disease was found in Florida and other areas ; California, wild grasses, sedges, and lilies are frequent hosts in of the southeastern Uniteri Stats. , It was • subsequently hotspot areas, but native forbs, bushes, and trees are also often identified in Mexico, Costa Rica, and Venezuela, and it likely infected. The bacterium also causes diseases in almonds and alfalfa in California and in macadamia nuts in Costa Rica. In occurs in most areas of Central America and southward into the northern parts of South America, where the causal bacteria are wild host plants as well as in grapevines and other cultivated present and potential insect vectors are abundant. It has never hosts, the bacterium survives and proliferates in xylem tissues. In the Americas, many genera of sharpshooter been confirmed to occur in countries outside the Americas. leafhoppers (Cicadellidae) and spittlebugs (Cercopidae) can serve as vectors of the bacterium as they feed on the xylem tissues of host plants. Symptoms Such insects typically suck up large quantities of xylem fluids ' Symptoms vary with the species and cultivar that is affected. during feeding and may ingest bacteria when feeding on either Symptoms in muscadine and other native American grapes an infected grapevine or an alternative host of the bacterium. from the southeastern United States are. milder than those in Bacteria attach to the foregut ("mouth") of the insect. V. vinifera. Symptoms are usually more pronounced in vines Infective vector insects egest fluid, while feeding on xylem that are stressed by high temperatures and droughty conditions. 'tissues of healthy plants, and bacteria are probably transmitted Chloro'tic spots develop on leaf blades near the point of initial with this fluid. The frequency of transmission of the bacterium infection—The "discoloration -intensifies, and . the ,Surrounding during the feeding process is high for some of the vector species. tissues begin to. wither, and dry. The spots gradually. enlarge. Disease symptoms appear as the bacteria increase into dense Starting 'near the , margin of the leaf blade, tissues become aggregates in the xylem vessels. These bacterial aggregates, completely desiccated and die. In late summer drying spreads along with tyloses and gums produced by the grapevine, plug inward in concentric zones until the entire blade may be affected the plant's vascular elements, restricting water conduction to (Plate 79). Leaves'therioften drop from the vine at the point of tissues. The bacteria also produce a phytotoxin that may atta4ment to the petiole, leaving the petiole still attached to the contribute to symptom development. sh?ot (Plate 80). Symptoms develop in adjaccnt leaves along In Florida the disease spreads mostly from vine to vine in the , ail hoot both above and below the point of initial infection. vineyard. Sharpshooter leafhoppers on wild host plants Floer clusters' on infected vines .may set berries,' but these apparently are rarely infective. In California the disease spreads tisua ly dry up. mostly from weedy host plants near the margin of the vineyard '. T Lae in the seasem, wood on affected canes fails to mature and thus is common among plants growing within the first 100 m normally, leaving green "islands" of tissue surrounded by dark from a hotspot location.. - brown, mature wood (Plate 80)..Theseislands persist into,the dormant season and, can , be seen on` canes throughout the Control winter, or until the cane is pruned or dies from frost. Tips of Within the natural range of X. fastidiosa and its insect shoots often die the first year the vine is infected. Initially, only vectors, V. vinifera and V. labrusca grapes become infected and one or a few canes on a vine show foliar and wood symptoms. die quickly. Only muscadine and Euvitis grape cultivars that are In chronically affected vines, budbreak in spring is delayed by developed from grapes that occur naturally within the normal as much as two weeks. The new shoots grow slowly and are range of the bacterium will survive. The use of resistant stunted. The first four to six leaves that form on new shoots are; cultivars is the only effective control for Pierce's disease in the small, and the tissues immediately along major veins appear Gulf •Coastal. Plains states, as well as along the east coast of dark green against a 'chlorotic background (Plate 81). Subse- Mexico•and in the American tropics. Quarantine procedures quent leaves are nailnal.in color but small, Internodes of such for excluding the disease are irrelevant within the native range shoots are muchshorter than normal,': of the causal bacterium. Pierce's disease is a case where sensitive Suckers growing from the base. of chronically affected vines crop plants may be introduced to locations within the natural frequently.appear,th develop normally: Such recovery range of the pathogen rather than vice versa. may persist until".'the ,,middIt or end , of.-....summer; 'then' the • In California and many areas in states north and west of the characteristic leaf -'and wood:osyinptoms "reappear' on most Gulf of Mexico, X. fastidiosa occurs only in isolated hotspots, leaves, shoots,it nd. cafies.t''*:i ' • '' ;'. - ,:-.1-4—.'3, ' ,; ." ' .1;... " and delimitation of these hotspots and site selection away from An affected vine may die the first - year after infection (Plate such areas are effective in controlling the disease. The range of 82), or it may continue to live for five or more years, depending the bacterium in wild vegetation extends from northern on the species and Cultivar, the age of the vine when infected, California southward in the western United States. The disease and local cliinatic conditions. In the American tropics, infected extends southward from about the latitude of Tiennessee in the V. vinifera cultivars usually die within 12 months of planting. eastern states. Pierce's disease is .. __ not a problem where the Causal Organism bacterium is not established in the wild. When Pierce's disease vvii... first scientifically investigated Insect trapping on sticky boards, the capture and identifica- during the late i-930i'and for a considerable time thereafter, a tion of potential vector insects in sweep nets, and serological virus: was believed-:to be the . causal agent. Experiments detection of the bacteria in wild host plants and in macerated conducted during the _early 1970s, however, showed that insects have helped to delimit hotspots. Insecticidal treatments antibiotic treatments suppressed the Symptoms and that to control vectors in hotspot areas have not been effective in immersing ' vines. in hot water eliminated the causal agent. eliminating the disease. Subsequent studies with electron microscopy demonstrated the Quarantine measures for preventing disease spread to areas presence of rickettsialike bacteria in xylem elements of diseased outside the natural range of the bacterium are probably vines in both Florida and California: In 1978 a bacterium was unnecessary. Cuttings or propagation buds from affected vines cultured from infected vines and Koch's postulates were do not survive long enough to establish the disease in a new completed, proving that this bacterium was the cause of the area. To ensure the health of plants taken to new areas, disease. however, propagating wood can be immersed in water at 45° C for 3 hr. Dormant grape cuttings readily survive this treatment, Cov-hp24,J...„ 6- Ile 1) 44,1-e-/ which kills any Pierce's disease bacteria that are present in the wood. Grape Leafroll A. C. Goheen Other Common Names. White Emperor dis- dark-colored fruit, the leaves turn red in the area ease; Rollkrankheit; Blattrollkrankheit; enroulement between the main veins (B). Leaf symptoms are foliaire; accartocciamento; enrollamiento de la hoja; conspicuous in inoculated vines of the Mission va- zavij anj e listov. riety, which is therefore a good indicator for leafroll History and Geographical Distribution. (C). On varieties with light-colored fruit, the symp- References to leaf roll-like diseases of grapevines ap- toms are less conspicuous, but downward rolling, pear in German and French literature from the accompanied by interveinal chlorosis, is usually evi- middle of the nineteenth century. Scheu (1936) dem- dent. On a few varieties, such as Thompson Seedless onstrated the virus nature of the disease. Ten years and Perlette, rolling is very slight, but late in the later, Harmon and Snyder (1946) showed that White summer, burned areas appear between the main Emperor disease, which had been recognized in veins. California for many years, was caused by a virus. The bunch grape hybrid Baco Blanc (Baco 22A) Goheen et al. (1958) correlated leafroll and White is used extensively at the University of California Emperor, and accepted the earlier name, "leafroll." (Davis) for indexing other varieties because it is The disease occurs in the United States, Europe, extremely sensitive to leafroll. If small plants growing South Africa, Australia, New Zealand, Mexico, South in pots in the greenhouse are inoculated by chip-bud America, and wherever rootstocks from western I, grafting in the spring, they develop severe symptoms Europe have been planted. It affects the hybrid and within 6 weeks after being transplanted to the field bunch grape varieties of the northern and eastern nursery. Infected Baco Blanc indicator plants are United States and of Canada, as well as the vinifera severely stunted, the leaves are small, and the blade varieties of California and Arizona. forms an acute angle with the petiole at the point of Economic Importance. The disease reduces attachment; the young leaves at the tips of the canes yield and quality. It gradually decreases the size of or lateral shoots frequently show interveinal chlorosis the vine while decreasing the size of the clusters and (D and E). the number of clusters per vine. Fruit from affected As the crop matures, fruit symptoms become evi- vines contains less sugar than fruit from healthy ones. dent. Affected vines of all varieties have smaller clus- The lowered sugar content delays harvest, which re- ters, fewer clusters per vine, and the sugar content duces the value of the varieties harvested for ship- is decreased. The color of black-fruited varieties is ment to fresh-fruit markets. Delayed harvest also little affected by the disease. but red-fruited varie- causes problems in producing field-dried raisins, as ties, such as Cardinal, Emperor, Mission, Queen, Red well as wines. In many cases, the final sugar levels are Malaga, and Tokay, develop fruit lacking the normal still inadequate, and the fruit must be abandoned. The red color at harvest - time (F). This lack of color in high incidence of leafroll is probably one of the fac- the EmpelkAvariety led to the name "White Em- tors that contribute to the frequent lack of vintage peror." The fruit from infected vines of white varie- years in the wine harvests of western Europe. ties, such as Melon, Riesling, Sylvaner, and Thomp- The disease also reduces the intensity of pigmenta- son Seedless (Sultana), is yellowish white at harvest tion in the fruit of red grape varieties. Where the time, not the greenish white of normal fruit. marketing of a red table grape depends upon bright Internal differences also occur. The principal in- color, a poor color reduces the value of fruit from ternal symptom of leafroll is degeneration of the diseased vines. The color in red wines is also reduced phloem in the canes, petioles, leaves, cluster stems, in intensity. and fruit pedicels. The sieve tube elements, com- Scheu (1936) reported that reduced frost tolerance panion cells, and phloem parenchyma are killed and of infected vines contributes to yield losses. These can obliterated. Phloem degeneration starts early, and be considerable in seasons of late spring frosts. may be found before foliar symptoms appear ex- In California, it is estimated that the disease causes ternally. Trabeculae are also found in stem and leaf an annual loss of about 5 per cent of the total grape tissues, and tyloses occur in petioles of infected vines. crop. Calcium and potassium in the leaf blades are signifi- Host Range. The disorder may occur in all vari- cantly less in affected vines than in healthy ones, eties and species of Vitis. Most rootstock varieties whereas potassium appears to accumulate in the peti- produce no symptoms, but the virus can be easily oles of affected plants (Chapman, 1966) . Starch detected in infected vines by indexing. accumulates in the leaf blades of affected vines. Symptoms. Leafroll symptoms vary, depending Symptoms in labrusca varieties and bunch grape upon the variety, environment, and time of year. hybrids differ somewhat from those in the vinifera Spring symptoms on vinifera vines are obscure, but group. With labrusca and its hybrids, the diseased diseased vines are generally smaller than healthy vines are more reduced in growth compared with ones, and leaf out later. Foliar symptoms first appear healthy ones. The leaves of affected vines are only in early June in nonirrigated vineyards, but not until slightly rolled, and in late summer they burn around August if the vines are irrigated. The leaves roll down- O. margins and between the main veins. Sugar in ward and turn red progressively toward the tips of the fruit is low, and in the red-fruited hybrid Bronx the canes, but the veins remain green throughout the fruit remains colorless, as it does with Emperor. the season (figure 122, A). The leaves at the bases Rootstock varieties derived mainly from species of the canes roll downward, and on varieties with of Vitis other than V. vinifera or V. labrusca do not show leafroll symptoms, although they often carry the virus. c)2 Cause. Leaf roll is caused by a virus. but it has not The disease does not produce s Ymptoms in grape been isolated from grape tissues. rootstock varieties which may carry it. Until 1955. Transmission. The virus has not been trans- there was no seiection against leairoil by LI-- grape- mitted to hosts other than grapevines. It cannot be •o!rowinr industry. even though Scheu 1936( recom- transmitted mechanically from grape to grape by mended rejection of leafroll-infected stocks. and pressed-sap inoculation. It is easily transmitted to indicated that leafroll-free stocks would increase Mission and Baco Blanc by chip-bud grafting. In Mis- grape production to a considerable extent. sion. characteristic leaf symptoms may appear during Failure to avoid leafroll virus is evident, even in the first growing season. but mild strains of the virus the development of new varieties. Several such new do not show until approximately 18 months after varieties released during the past 30 years were inoculation. Mild strains generally do not produce initially grafted onto leafroll-infected rootstocks; symptoms in Baco Blanc, but moderate or severe consequently. all propagating stocks had the disease strains produce symptoms approximately 2 to 3 when released. The true performance of these varie- months after inoculation. ties is still to be evaluated. Clean stocks have been Natural Spread. There is no evidence for natural obtained recently through heat therapy. Breeders spread of leafroll in California. Controlled tests have I must be careful to use only known virus-free root- not vet demonstrated that a vector for leafroll is pres- j stock clones for propagating new selections and ent. The disease is not soil-retained; thus, there is no varieties. reason to think that the vector is a soil organism. Before the middle of the nineteenth century. leaf- The fact that some rootstock varieties are symptom- roll was probably of minor importance in western less carriers of leafroll has led to-wide dissemination European vineyards, if it was present at all. How- of the disease. Many vineyards in California and ever. after phylloxera had made resistant rootstocks other parts of the world have a high incidence. In the necessary. some of these were inadvertently infected propagation of new vineyards. the disease is increased with leafroll: from these plants. the disease has in- when scions and rootstocks are used at random with- creased to the point where it is now a major problem out selection of healthy mother vines. in grape production. The industry must insist on certified planting stocks (especially rootstocks) for Control Measures. The use of disease-free plant- future vineyard plantings. ing stocks eliminates leafroll from new or replanted Detection and Identification. Indexing tests vineyards. If certified grape plants are not available. on the Mission variety are necessary for proving the selection of stocks requires very careful inspection freedom from leaf roll. Infected rootstock varieties of mother vines before propagating wood is taken. show no symptoms, and scion varieties may or may With many varieties in which symptoms are obscure not show -symptoms, or may display confusing ones. or lacking, only an indexing program will assure dis- Agents other than leafroll virus may cause reddish, ease-free planting stocks. yellowish, rolled, or "burned" leaves. as well as re- Through a program of selection, heat therapy. and duced vigor in vines. Indexing tests on Baco Blanc indexing in a joint project at Davis. California. the will indicate the presence of moderate or severe U. S. Department of Agriculture and the University strains of leafroll in 2 to 3 months. but mild strains of California have established a foundation planting are detected only by using the 18-month test on the of grape varieties and rootstocks free from leafroll Mission variety. and other known grape viruses. Stocks from this vine- The most consistent symptom of leafroll in dark- yard have been made available to nurserymen for fruited vinif era varieties is downward rolling and the produCtion of certified grape planting stocks. The reddening of the leaf blade; the major veins remain Nursery Service of the California Department of Ag- green. The symptom develops about midsummer on riculture oversees the production of clean stocks by the basal leaves of the canes. It is most conspicuous nurserymen and the certification of such stocks. just before frost, when many leaves on each vine are Therapy. Heat therapy is used to develop leafroll- affected (figure 122, A) . free clones from affected mother vines. Infected vines In the vineyard, leafroll is often confused with held in a chamber at 100° F. (38° C.) with supple. potassium deficiency; however, this shows earlier mental light continue to grow and produce shoots. in the season than leafroll, and the symptoms develop The tips of such shoots up to 5 cm long may be freed initially at about the tenth node on the cane, whereas from leafroll virus by holding the plants at this tem- leafroll symptoms develop first on the leaves at the perature for 56 days or more. Tip cuttings 2 to 5 cm basal nodes (Ulrich and Ohki, 1966). long from these shoots can be propagated under mist culture and grown into new plants. Indexing tests show that 86 per cent of the vines developed by this method from affected mother vines are free from leafroll virus. Remarks. Although no efficient natural vector is known for leaf roll; this disease is the most wide- spread of all grape virus diseases in California. There are 2 reasons: (1) The virus does not inter- fere appreciably with propagation, so there is no natural elimination of leafroll-infected stocks. (2) A

B E

fi. C F

Fig. 122. Typical aspects of grape leafroll. A: Infected vine of Gamay in late October. B: Leaves of Camay. (Healthy at left; infected, top view, in center; infected, bottom view, at right.) C: Leaves of a Mission in- dicator. (Same relative data as for Gamay.) D: Baco Blanc indicator vines. (Healthy at left; positive leafroll reaction at right.) E: Tip leaves of Baco Blanc. (Healthy at left; diseased at right.) F: Clusters from adjacent Emperor vines. (With leafroll at left; color is affected. Healthy at right.) VIRUS DISEASES OF SMALL FRUITS AND GRAPEVINES

(A HANDBOOK)

EDITORIAL COMMITTEE

N .WW. FRAZIER, Editor, University of California, Berkeley J. P. FULTON, University of Arkansas, Fayetteville J. M. THRESH, East Mailing Research Station, Maidstone, Kent R. H. CONVERSE, Oregon State University, Corvallis E. H. VARNEY, Rutgers University, New Br,u2swick, New Jersey WM. B. HEWITT, University of CalifoNs, Davis UNIVERSITY OF CALIFORNIA DIVISION OF AGRICULTURAL SCIENCES BERKELEY, CALIFORNIA, U.S.A. 1970 Fanleaf of Grapevine A. Vuittenez Other Common Names. Grape infectious de- Host Range. a) Woody Hosts. All V. vinifera generation (Alghisi, 1954; Anon., 1962) ; degineres- varieties are susceptible; no resistant or tolerant cence infectieuse; court-noue; arricciamento; Reisig- variety is known, though some varieties are affected krankheit; Gabler; Krautern; curto infeccioso; urti- more severely than others. cado. Particular strains of fanleaf virus produce All American species introduced into Europe, and symptoms of chlorophyll deficiency designated by derived hybrids of V. labrusca, V. riparia, V . rupes- specific names: green or "true"' mosaic; yellow mo- tris, V. berlandieri, V. aestivalis, and V. candicans, saic; chrome-yellowing; vein banding; mosaique; were found to be susceptible to fanleaf by natural panachure; giallume; Mosaik; Gelbmosaik; .Pana, infection (cultivation in nematode-infested soil) schiire; mosaico amarelo. (Branas et al., 1938) and by experimental inocula- History and Geographical Distribution. tion by grafting - (Vuittenez, 1957a). Symptoms related to fanleaf of grapevine had al- Ornamental. Asiatic species, V. davidi, V. coig- ready been mentioned in French, Italian, German, netiae, V. piasezkii," ishikari, and the fruiting and Austrian literature many years ago (Rozier, varieties of V. amurensis were readily infected by 1800). grafting (Vuittenez, 1957a). The occurrence of patches of the virus, together Ampelopsis and Parthenocissus species have been with the nematode vector of the virus, Xiphinema infected experimentally by fanleaf and yellow mosaic index Thorne and Allen, in indigenous vineyards of in Portugal (Dias, 1957-58). In France, mosaic and eastern Mediterranean countries (Greeee: Terlidou, yellow variegation observed on an ornamental Cissus 1964) and western Asia (Turkey, Iran: Vuittenez, species and Virginia creeper (Parthenocissus quin- 1962; Boubals and Nazemille, 1966) suggests that quefolia) have not been correlated with fanleaf virus. the disease may have existed in those areas from the (Attempti at igraft inoculation to Vitis species were earliest ages of grape culture. From Europe, vege- unsuccessful, as were mechanical inoculation trials tatively propagated planting material has introduced with several herbaceous hosts.) the fanleaf disease, and probably also its nematode Some workers indicate that many woody peren- vector, to practically every part of the world where nials (trees and ornamental shrubs, such as Ligus- the grapevine is now cultivated: California, Central etc.) are pos- and South America, South Africa, and Australia. In trum, Prunus, Juglans., Ulmus, Acer, al., 1960, 1961; Ciferri and. the reverse direction, introduction of grape-,,phyl- sible hosts (Baldacci at 1959), but evidence is loxera into most European vineyards has been indi- Corte, 1960; Corte et a1., needed of•fanleaf virus reisolation from these inocu- rectly responsible for considerable extension of fan- lated species back to grapevine or to herbaceous leaf as well as other virus diseases of grape, as a hosts. result of changes of cultural practices (grafting onto hybrid stocks, increasing exchanges of planting ma- b) Herbaceous Hosts. Several herbaceous plants terial, and repeated replanting of vineyards, espe- may be experimentally infected by mechanical in- cially in the most famous vine-growing countries). oculation of fanleaf virus but, in contrast with In American areas of cultivation of Vitis lab rusca experience with other soil-borne ringspot viruses, (northeastern United States ,and adjacent parts of none has ever been found to be naturally infected in Canada), though symptoms of mosaic and leaf mal- the field. Some very susceptible species, such as formation are, commonly,found ,in some varieties, the Chenopodium quinoa, C. amaranticolor, C. polysper- virus of fanleaf has ,never been isolated from them mum, and to a less extent, Gomphrena globosa and (Dias, personal communication, 1965) . certain Amaranthus species, may be readily in- Fanleaf virus has not been recorded in wild popu- fected by mechanical inoculation from grape. Fan- leaf virus may be subsequently retransmitted me- lations of North American. Vitis: species. No informa- chanically from these to a wide range of species tion is available for Vitis in ,northern and , eastern (Dias, 1963a) ; some are difficult to infect, depend. Economic Importance. ,Under severe. conditions , ing on individual strains of the virus and seasonal of environment (shallow soils, hot and sunny cli- conditions of environment, or may be infected on mate), fanleaf and related diseases may kill the inoculated leaves only. (In the list that follows, these latter species are enclosed in parentheses.) vines. However, affected vines , usually remain alive for a long time, becoming less and less fruitful, until the jnfested vineyards , are abanaoned for economic VIRUS DISEASES OF reasons. The production of fanleaf-diseased vines is reduced to a degree deermined by the weather at SMALL FRUITS AND GRAPEVINES flowering time, but a 50 per cent reduction in weight (A HANDBOOK) ,is an average estimate in European countries for the most susceptible Vitis vinifera varieties; Char- donnay, Muscat, and Traminer. In addition, the 11:01TOLIAL COMMITTII N.A. Ftuit0. WSW'. University of California. Berkeley commercial value of table grape varieties is greatly Fatten, University of Arkensaa, Fayetteville depreciated by the appearance of clusters (dropping I. M. T111113/1. East Malting Research Station, Maidstone. Kent R. H. Conway Oregon State University, Corvallis off and "millerandage") of affected vines. In nur- E. H. Vsancv, Rattan University, N.. Bie.k. New Jersey series, cuttings or grafted plants produced with fan- Wai. R. Hawn, Univenity of CalifoNin Davi. leaf-infected wood have a weaker growth, reduced UNIVERSITY OF CALIFORNIA DIVISION OF AGRICULTURAL SCIENCES ability to form roots, and grafting success is lower. BERKELEY, CALIFORNIA, U.S.A. 1970