JANUARY/FEBRUARY 2005

BY W. D. Gubler, P. E. Rolshausen, F. P. Trouillase, J. R. Urbez, T. Voegel Dept. of Plant Pathology, University of California, Davis, CAG. M. Leavitt, University of CaliforniaCooperative Extension, Madera, CAE. A. Weber, University of CaliforniaCooperative Extension, Napa, CA

Grapevine trunk diseases areresponsible for significant eco-nomic losses to the wine industryworldwide. Symptoms of these

diseases include dead spurs, arms, andcordons and eventual vine death dueto canker formation in the vascular tis-sue. In Eutypa dieback, deformedleaves and shoots occur as thepathogen invades spur positions. Ascankers develop, yield reductionsoccur due to the loss of productivewood. The impact of grapevine wooddiseases can be significant in oldervineyards, and usually becomes moresevere as vineyards become older.

Eutypa dieback, caused by Eutypa latawas originally thought to be responsible

for most canker development in Californiavineyards. However, recent findings havehighlighted the importance of other fungiinvolved in the death and decline ofgrapevines in California. In this regard,

Botryosphaeria species have also beenrecovered from cankers, and weredetermined to be the main cause of cankerdiseases in some California vineyards.

Recent research has also indicated theoccurrence of several new fungal trunkdisease pathogens of grapevine belong-ing to the family Diatrypaceae (the samefamily as Eutypa). These include Eutypaleptoplaca, Cryptovalsa ampelina, Diatrypespecies, and Diatrypella species. We willpresent current information on the epi-demiology and control strategies of fun-gal organisms responsible for grapevinespur, cordon, and trunk dieback inCalifornia.

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RESEARCH UPDATE

Grapevine trunk diseasesin California

Figure I: Fruiting bodies (perithecia) of E.lata on a grapevine previously grafted forvariety change. The large pruning woundfavored formation of E. lata perithecia onthe dead trunk of the old variety.

Figure II: Black stroma bearing perithecia (fruiting bodies) of E. leptoplaca on dead trunk ofbig leaf maple collected in St. Helena, Napa County, CA.

JANUARY/FEBRUARY 2005

Eutypa diebackEutypa dieback was responsible for

a loss in net income for California winegrapes estimated to be over $260 mil-lion in 1999. Many growers considerEutypa to be the most significant dis-ease of grapevines.

Typical symptoms of E. lata includeformation of a wedge-shaped cankerand stunted shoots with cupped, tat-tered, chlorotic, and necrotic leavesthat are best seen in spring time. Foliarsymptoms are due to toxins producedby E. lata. Differences in susceptibilityof grapevine cultivars to infection havebeen reported, although no cultivarsare immune. Cankers develop down-ward at a faster rate than toward theend of cordons and also increase indiameter over time. Extended infectionof grapevines by E. lata leads to vinedeath.

Eutypa lata spreads to new pruningwounds by wind-driven and water-splashed ascospores released duringrain events. Ascospores developinside perithecia (fungal fruiting bod-ies) that form when the fungus entersits sexual stage. The sexual stagedevelops on dead wood, wheremasses of perithecia are produced in ablack substrate referred to as stroma(Figure II). The sexual stage developsin regions that receive over 16 inchesof rain. It is common to find stroma andperithecia on old grapevines and othertypes of wood in the North Coast andDelta production areas.

Ascospores infect grapevines throughfresh pruning wounds during the dor-mant season. They germinate, invade

xylem vessels, weaken the plant by pro-ducing toxins and cause wood decay byexcreting cell wall degrading enzymes.

Eutypa lata also produces asexualspores called conidia. These are formedinside pycnidia (another type of fruitingbody) that develop on wood, but theseconidial spores do not play a role in dis-ease epidemiology.

In California, ascospore dischargeof E. lata occurs from the first rain ofthe early fall until the last rains of thespring (Figure III). Ascospore dis-charge decreases significantly in lateFebruary and remains low to nil byearly March (Figure IX).

However, ascospore release mayoccur during rains in March and Aprilif they are preceded by several weeksof no rain and sunny, warm weather.Such releases may occur becauseperithecia are able to recover in pro-ductivity during the dry period, orbecause spores that would have beenreleased in the winter months arereleased in the spring simply becausethey were not released in the winter.This scenario more often occurs inyears when there is little rainfall dur-ing the winter months.

Ascospore release from individualperithecia may occur continuously forapproximately 24 hours during peri-

ods of rainfall, starting a few hoursafter the onset of a rain (Figure IX).

Over 80 plant species around theworld have been reported to be poten-tial hosts for E. lata. In California,many of these species were found tobe infected with Eutypa lata and boreperithecia producing ascospores inthe vicinity of vineyards. We nowknow that these species serve as nat-ural reservoirs of E. lata inoculum.

In the 1970s, grapevine, apricot,and Ceanothus were found to be nat-ural hosts of E. lata. More recently wehave identified kiwifruit, blueberry,and cherry to be hosts in Californiaand they were shown to bear the fruit-ing bodies (perithecia) of E. lata.

Additionally, a recent survey iden-tified almond, crab apple, and peartrees as new fruit crop hosts for E.lata, and showed the presence of

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Figure III: Ascospore release curve of E. lata during a period of rainfall recorded in December2001 in Davis using a Burkard spore trap placed around dead grapevine trunk bearingperithecia.

Figure IV: Typical wedge shape cankerformed by Botryosphaeria in the cordon ofgrapevine.

Figure V: Mature Botryosphaeria obtusaconidia.

JANUARY/FEBRUARY 2005

perithecia of E. lata on several othernew hosts in California includingCalifornia buckeye, big leaf maple,willows, and oleander (Figure X).

Perithecia of E. lata were found tobe particularly well established ondead branches of various willowspecies occurring along natural creeksand irrigation waterways.

It appears likely that the flora sur-rounding vineyards is potentially akey factor in disease epidemiologyand surely acts as an inoculum reser-voir. Sanitation of the dead wood ofpotential hosts of E. lata in areas sur-rounding vineyards is advised inorder to decrease the inoculum level.Sanitation can be accomplished byremoving the infected tissues onplants that show disease. Generallyspeaking, this disease can be identi-fied on other hosts by the blackstroma that is produced (Figure II). Byremoving the stroma-infected woodand burning it, the number of sporesreleased in winter can be reduced.

Surveys inside vineyards and apri-cot and cherry orchards have revealedan abundance of inoculum in planti-ngs of approximately 20 years andolder. Only a few perithecia havebeen found in almond orchards.

Perithecia of E. lata were found tobe prevalent in vineyards or sur-rounds in the counties of Napa,Sonoma, Yolo, Sacramento, ContraCosta, San Benito, El Dorado,Mendocino, San Joaquin, Stanislaus,and Merced. Perithecia of E. lata werenot found in Madera, Fresno, Kings,Tulare, and Kern counties.

Large amounts of viable inoculumwere found in several old vineyards nearHealdsburg, Sonoma County. Peritheciawere particularly well-developed onvines that had been previously top-worked for variety change. Stroma onthose vines had developed on old woodbelow the grafting wound down to theunion with the rootstock (Figure I).

While E. lata appears to be the pri-mary Eutypa species involved in diebackin California, we have identified a secondEutypa species that can also causedieback in grapevines (Figure XIII). Thisspecies is E. leptoplaca, a slower growingfungus in culture but with the capabilityto do the same kind of damage as E. lata.This new fungus occurs in the NorthCoast but seems to be more limited inits distribution.

It is our opinion after this studythat even though E. lata and E. lepto-placa ascospores can travel over con-siderable distances and cause dis-ease, Eutypa dieback is primarily adisease of local origin, developing inthe vicinity where the ascospores arereleased.

ControlDisease management should include

removal of the dead parts of grapevinesand other host plants because of the poten-tial risk of increased inoculum. We cur-rently have no proof that sanitation willreduce the disease level in vineyards, but itseems appropriate if local production ofinoculum is considered to be a key todisease development.

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Figure VI: Mature Botryosphaeriatheobromae conidia.

Figure VII: Botryosphaeria obtusa pycnidiafound under the bark on the arm of aninfected grapevine. Figure VIII: Botryodiplodia theobromae

pycnidia found on old grapevine pruningwood left on the vineyard.

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Figure IX: Ascospore release of E. lata recorded on the 12th, 13th and 14th of April 2000 in avineyard in Healdsburg, Sonoma County, CA, with rainfall and temperature data. Ascosporerelease occurred for 24 hours during the rainfall period.

JANUARY/FEBRUARY 2005

Grapevine pruning wounds can besusceptible to infection by E. lata for aslong as seven weeks, but the length ofthis period varies with the time of prun-ing, size of the wound, and age of thewood pruned. Wound susceptibility toE. lata declined faster under higher (70ºto 90ºF) temperatures.

Wound healing occurs by depositionof polymerized phenolic compounds inthe opened wood vessels, and concomi-tantly, natural establishment of a micro-bial population on the wound surfaceprovide a natural “bio-barrier” to infec-tion. These natural organisms (epi-phytes), including Cladosporiumherbarum and Fusarium lateritium, growover the surface of a pruning wound andprevent infection by E. lata spores.

In a previous study, more than 1300species of fungi and bacteria were foundto colonize grapevine wounds in springconditions.

Wound healing and colonization byepiphytic fungi and bacteria have beenshown to occur more readily in thewarmer spring months. Ascosporerelease, germination, and infection arealso decreased during this time.Therefore, significant wound protectioncan be readily achieved simply by latepruning of vineyards.

Our work, and other research(Moller and Kasimatis), has shown thatpruning wounds made in March healmore rapidly when compared to mid-winter. In our trials, late season prun-ing wounds that were artificially inoc-ulated showed only approximately10% of the infection rate of pruningwounds inoculated in mid-winter.

However, the large acreage of indi-vidual vineyards in California makeslate pruning impractical for manygrowers who need to schedule theirlabor force throughout the wintermonths. One way to allow for moreefficient late season pruning is to dou-ble-prune a vineyard. This involvesgoing through the vineyard twice dur-ing the pruning season.

The first “pre-pruning” pass ismade early in the season at which timethe canes are simply trimmed back to aset length, usually 12 to 18 inches. Thisstep can be performed mechanically orby a hand crew. “Final” pruning tospurs would take place late in the sea-son (March) when the chances forinfection are reduced.

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Table I. Field trials in evaluating control of E. lata in San Joaquin and Yolo Counties in 2001 to 2002 and in Napa and San Joaquin Counties

in 2002 to 2003. Pruning wounds were inoculated with 1000 ascopores of E. lata one and 10 days after application of test material.

First timing of inoculation Second timing of inoculationMean percent Mean percent Mean percent Mean percent

Treatments infection disease control infection disease control

Non-inoculated control 3 — 3 —Inoculated control 64 — 32 —Boron-free paste 61 4.7 19 40.6 C. herbarum 32 50 17 46.9 Boric acid 2 96.9 9 71.9 Bioshield 4 93.8 7 78.1 Biopaste 1 98.4 2 93.8

Figure X: Geographical area and new hosts of the pathogen E. lata in California. Survey wasconducted in 2002. Areas represented in gray correspond to the areas that were surveyed.

JANUARY/FEBRUARY 2005

By eliminating most of the brushearly in the winter, final pruning shouldgo more quickly, thereby allowing thefinal cuts to be made late in the season.Double-pruning is not appropriate forcane-pruned vineyards where longcanes are retained each year.

Double-pruning creates an opportu-nity for wood pathogens such as E. latato colonize wounds made early in thedormant season during pre-pruning.However, these infections will be elimi-nated during the final pruning step. Weinoculated pre-pruning cuts throughoutthe winter months and showed that byMarch, E. lata had not grown downwardmore than four to five cm, which waswell above the point where final prun-ing cuts were made.

Late pruning, either in a single stepor as the final pass in double-prunedvineyards, is not a guarantee thatEutypa infections will not occur. Latespring rains can trigger ascosporereleases and increase the risk of infec-tion of newly pruned vineyards. How-ever, late pruning certainly reduces theoverall chances for infection and is astandard recommendation for diseasecontrol.

Disease management was histori-cally achieved by treating pruningwounds with fungicides. Benlate®

(DuPont de Nemours & Co., U.S.) wasregistered for E. lata for 30 years, andfield trials showed good efficacy inpreventing Eutypa dieback. However,long-term protection of pruning

wounds was not achievable becausethe product did not persist in woodytissue for a sufficient time period.Therefore, multiple applications ofBenlate would have been required toprovide protection until pruningwounds were completely healed.

Benlate was withdrawn from themarket in 2001 leaving growers with-out an efficacious chemical treatmentto control E. lata. Topsin M was regis-tered in 2003 under section 18 (emer-gency exemption) in California, butthis product also belongs to the sameclass of fungicides as Benlate, a benz-imidazole, and therefore has the samedrawback (short-term protection) asBenlate.

Biocontrol agents have been testedas an alternative method for control ofE. lata. Bacillus subtilis, Fusarium lateri-tium, and Cladosporium herbarum allshowed some potential activity in lim-iting the establishment of thepathogen.

However, unlike chemical applica-tions, which have an immediate pro-tective effect, maximum protectionfrom biocontrol agents requires colo-nization of the surface of the wound.Thus, there is a window of suscepti-bility after treatment, until the biocon-trol agent is established well enoughto prevent development of E. lata inthe wounded tissue.

Biocontrols tested as alternatives tofungicides showed mixed success, butboth F. lateritium and C. herbarum

worked well when they were appliedtwo to three weeks before infectionoccurred.

Boron was tested as an alternativecontrol method because this elementwas proven to be effective at control-ling other wood decay fungi. It is alsoused by growers as a fertilizer spray toimprove fruit set. The application ofboron as a fungicide may not yet belegal to control Eutypa dieback ofgrapevines, however, boron can beapplied to correct nutritional problems.

We evaluated boric acid solutionsand two boric acid-based products aspruning wound treatments. Theseincluded biopaste (5% boric acid[wt/wt] in a polyvinyl paste) andbioshield (5% liquid boric acid[wt/vol] plus a spore suspension ofCladosporium herbarum).

Boric acid reduced ascospore germi-nation and mycelial growth of E. lataunder controlled conditions in the lab-oratory, and the boron-based productsyielded excellent disease control onartificially inoculated grapevines inboth field trials and lab studies in com-parison to C. herbarum and boron-freepaste treatments (Table I).

However, in one observation, the budlocated at the first node below the prun-ing wound failed to push following treat-ment with liquid boric acid. This effectwas also reported in peach and nec-tarine orchards sprayed with toxicamounts of boron-based fertilizers.

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Figure XI: Relative occurrence of Eutypa spp. and Botryosphaeria spp. in California grapevineproduction regions.

Figure XII: Comparison betweenpercentages of cankers infected byBotryosphaeria spp. and other fungi inrelation with grapevine dieback inCalifornia grapevines.

JANUARY/FEBRUARY 2005

Mechanisms involved in bud failureare not understood, and the economicimpact has not been assessed.However, we do not recommend liquidboric acid for Eutypa dieback control.

Treatment of pruning wounds withboron-based products offers an effec-tive, economical, and environmentally-safe management strategy to controlEutypa dieback in vineyards. However,formulations have to be optimized inorder to increase control over longertime periods on the surface of pruningwounds, and to limit possible effects onbud failure of grapevines.

We believe strongly that if boron isused, it should be put in a paste so thatit stays where it is placed.

In earlier studies, soaps also pro-vided good protection of pruningwounds against E. lata. However, mostsoaps, including dishwashing deter-gents, were phytotoxic. One laundrydetergent, Dreft, not only providedexcellent control of E. lata, but hasnever shown any phytotoxicity. Thisdetergent, when used at 30% aqueoussuspension (wt/vol), provided excel-lent disease control.

Further fungicide testing is under-way, and we are trying to convince thechemical industry that Eutypa controlproducts are worth registering forCalifornia viticulture.

BOTRYOSPHAERIA cankerdiseases

“Botryosphaeria canker disease” ofgrapevine is a wood disease caused byas many as four different Botryosphaeriaspecies in California. Although it is wellaccepted that some Botryosphaeriaspecies have been shown to be thecausal agent of canker diseases of vari-ous crops and woody plants inCalifornia, the importance of thesefungi as pathogens of grapevines hasbeen largely ignored throughout thestate.

Various species of Botryosphaeria,causing different symptoms, have beenreported in the last decade aspathogens on grapevines in the U.S.,South Africa, Australia, France, Italy,Portugal, Egypt, India, Mexico, Chile,

and Brazil. In California, wedge-shaped cankers caused by Botryo-sphaeria can be found on vines 10years old and older, especially wherelarge pruning wounds have beenmade in retraining vines.

For several years, Botryosphaeria rho-dina has been known to cause wedge-shaped canker symptoms in California.This species was previously known asBotryodiplodia theobromae, and the dis-

ease it causes was referred to as “Botcanker.”

Fungi often produce both an asex-ual (imperfect) stage and a sexual (per-fect) stage, and they may have differentnames. Botrysphaeria rhodina is thename for the sexual stage of this fun-gus; Botryodiplodia theobromae is thename of the asexual stage.

We prefer to use the name Botryo-sphaeria instead of Botryodiplodia. Thedisease is still known as Bot Canker.

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Figure XIII: Fungal colonies of Eutypa lata (a) and E. leptoplaca (b) growing on PDA-tet dishesincubated at 24ºC under intermittent fluorescent lighting (12 h) for 22 d. Scanning electronmicroscope images of perithecial ostiola showing the roundish ostiole of E. lata (c) and the 3 to 4 sulcate ostioles of E. leptoplaca (d) (Bars = 100µm). Compound microscope images ofthe ascospores of E. lata (e) and smaller ascopores of E. leptoplaca (f) at same magnification(Bars = 10 µm).

JANUARY/FEBRUARY 2005

The fungus is now considered to be anendemic species in many vineyards inwarm and hot climate areas inCalifornia.

Typical symptoms caused by Botryo-sphaeria on grapevines in California arewedge-shaped cankers in the trunk

and cordons (Figure IV) and dead spurpositions. No foliar symptoms associ-ated with Botryosphaeria-inducedcanker diseases have been observed inCalifornia grapevines. This is in con-trast to other areas in the world wherefoliar symptoms have been observed

on grapevines infected by differentspecies of Botryosphaeria (B. stevensii, B.obtusa and B. dothidea).

The wedge-shape cankers caused byBotryosphaeria are visually indistinguish-able from those formed by Eutypa lata orE. leptoplaca. All three fungi can causecankers and can be detected in the vineat the same time. The best distinguishingcharacteristic is the presence of cankersand the absence of the stunted orchlorotic spring growth which is typicalof infections by Eutypa lata.

Botryosphaeria spp. are woundpathogens entering the vine throughfresh pruning wounds. Large numbersof Botryosphaeria conidia are exudedfrom black fruiting bodies (pycnidia)found on diseased vine parts, underthe bark of cordons, trunks, and spurs(Figure VII) or on the residual pruningwood left in the vineyards.

In addition, we also know thatmany of these species cause disease ondifferent hosts around the vineyards.The formation of numerous fruitingbodies provides an excellent source ofspores for further infections in thevineyard. Conidia may be easily dis-tributed over the vineyard due towind, or they may be waterborne insplashed drops from rain or sprinklerirrigation, but very little information isavailable concerning the Botryosphaeriadisease cycle.

Like Eutypa lata and E. leptoplaca, thecanker formed by Botryosphaeria spp.grows more rapidly basipetaly (ortoward the root from the point of infec-tion). The canker develops for severalyears in the trunks and cordons depend-ing on where the infection was located.Death of the infected vine part occurswhen the last live wedge of tissue iskilled by the growth of the fungus.

Eutypa dieback and “Bot cankerdisease” decrease the life of the vine-yard, reduce yields and increase pro-duction costs due to the applicationof control treatments, cultural prac-tices to prevent infections, pruning out

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Figure XIV: % of cankers infected by Botryosphaeria in wine and table grape varieties inCalifornia.

Figure XV: Geographical distribution ofBotryosphaeria species found in thegrapevine production areas in Californiaduring 2003 and 2004.

of diseased tissue, and training newcordons and spur positions to replacethose killed by the disease.

Field survey of BotryosphaeriaIn a recent field survey (2003–2004),

over 1,100 samples showing the typi-cal wedge-shaped cankers were col-lected from 110 vineyards in 12 coun-ties (Mendocino, Napa, Sonoma,Monterey, San Luis Obispo, Madera,Stanislaus, San Joaquin, Fresno, Kern,Tulare, and Riverside County).Botryosphaeria species were found inevery grape growing area surveyed(Figure XV), showing that Botryo-sphaeria species are prevalent incankered cordons and spurs ingrapevines in California.

Botryosphaeria was the main fungusrecovered from cankers in five coun-ties: Mendocino, Sonoma, Monterey,San Luis Obispo, and Riverside.Botryosphaeria was also isolated in ahigher percentage than Eutypa inMadera, Fresno, and Tulare counties(Figure XI). Eutypa lata was the mainfungus isolated from cankers in Napa,San Joaquin, and Stanislaus County. InMendocino, Sonoma, Napa, Monterey,San Luis Obispo, Stanislaus, and SanJoaquin counties both fungi were occa-sionally isolated from the same canker.

It is important to note thatPhomopsis viticola was the principalfungus found in cankers from Fresnoand Tulare counties. We have yet toinitiate a project there to evaluate thesignificance of this finding but plan todo so.

The fungi that cause Esca or blackmeasles (Phaeomoniella chlamydosporaand Phaeoacremonium aleophilum) werealso isolated in a low percentage inthis study. These pathogens producedifferent types of internal symptomsand were not a target of this work, butthey reside in the same vascular tissueas the canker pathogens and thus willbe isolated from time to time.

Four different Botryosphaeria speciesare associated with the wedge-shapecanker symptom in California; Botryo-

sphaeria obtusa, B. rhodina (Botryodiplodiatheobromae), Botryosphaeria dothidea andan as yet unidentified Botryosphaeriaspecies called Botryosphaeria sp1 (FigureXV).

It is also important to emphasizethat only Botryosphaeria rhodina(Botryodiplodia theobromea) was recov-ered from cankers in the desert area ofCoachella Valley. No otherBotryosphaeria species or other woodinvading, canker-causing fungi wereisolated from the wedge shape cankersin this region. Only Botryosphaeria rho-dina has been proven to cause adieback disease causing a wedge-shape canker. The precise role of theother species isolated from cankers isstill not clearly understood.

In the 2003–2004 survey, (FigureXIV), Botryosphaeria was isolated mostoften from Sauvignon Blanc (63.6%recovery from cankers tested) fol-lowed by Chardonnay (54.5%).Cabernet Sauvignon had the mostcankers with Eutypa (57.7%).

Botryosphaeria was isolated in thesame percentage from cankers ofPerlette and Flame seedless (26%).Fewer cankers with Botryosphaeriawere found in Thompson seedless(12.2%). Thompson Seedless appearshighly susceptible to Phomopsis viticolaand the pathogen was isolated from29% of Thompson Seedless cankerstested.

Botryosphaeria was found in vine-yards of all ages sampled (Figure XVI),but was isolated most frequently fromcankers in 21 to 30-year-oldgrapevines (36.5%), followed by thosegrapevines that were 10 to 20 years old(33.4%).

The main fungi isolated from allwedge-shaped cankers collected inCalifornia have been Botryosphaeria(25.5%), followed by Eutypa (20%),Phomopsis viticola (8.7%), Phaeomoniellachlamydospora (5.2%) and Phaeoacre-monium aleophilum (4.3%) (Figure XII).However, the latter two pathogens donot cause cankers and were picked upin these studies as hitchhikers onwood showing symptoms of othercankers. In a parallel study, Eutypa lep-toplaca was also isolated from vines inthe North Coast but was not part ofthis survey.

Other wood decay fungiBesides Eutypa lata and Botryo-

sphaeria species, several other fungiwere recovered from cankers of grape-vines. These include Phomopsis viticola,Phaeomoniella chlamydospora, andPhaeoacremonium aleophilum. Others,such as Diatrypella sp., Diatrype sp.,Crytovalsa ampelina and E. leptoplacawere also isolated from the margins ofinfected tissue.

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Figure XVI: Effect of vineyard age on the occurrence and incidence of Botryosphaeria spp.

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Recently, another Eutypa species (E.leptoplaca) and Cryptovalsa ampelinawere found to be pathogenic ongrapevines as were species of Dia-trypella and Diatrype. These fungalspecies all belong to the same family asE. lata and closely resemble E. lata intheir spore shape, size, and by theirappearance in culture (Figure XIII).These fungi also have been foundcommonly on various host plants inthe vicinity of vineyards.

Eutypa lata and the other diatrypa-ceous fungi have the same morpholog-ical characteristics in culture includingspore shape and color. It is apparentthat over the last several years, E. latawas not the only pathogen being iso-lated from cankers. Not until thisstudy did we realize that more thanone pathogen was capable of causingthe same type of disease.

Given these results, it is evidentthat Eutypa lata is not the only cause ofgrapevine canker diseases in Califor-

nia vineyards. More studies should beconducted to elucidate the impact ofthe different species of Botryosphaeria,and other fungi detected in cankers.The virulence of many of these speciesremains to be determined.

These recent discoveries have led tothe conclusion that grapevine trunkdiseases are more complicated thaninitially thought, and that a complex offungi may be involved. Developmentof information regarding the biology,epidemiology and control of each ofthese fungi and diseases is underway.Nevertheless, we know that vineyardsanitation through the removal ofinfected parts of vines is highlyadvised, and where possible, sanita-tion of surrounding areas where otherpotential hosts of these pathogenicfungi reside. ■

Acknowledgements: We wish tothank the American Vineyard Foundationand the USDA Viticulture Consortium forpartial funding of this work.

ReferencesIrelan, Nancy, W. D. Gubler, and

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