1 JANUARY/FEBRUARY 2005 GRAPEGROWING RESEARCH UPDATE Grapevine trunk diseases in California BY W. D. Gubler, P.E. Rolshausen, F. P. Trouillase, J. R. Urbez, T. Voegel Dept. of Plant Pathology, University of California, Davis, CA G. M. Leavitt, University of California Cooperative Extension, Madera, CA E. A. Weber, University of California Cooperative Extension, Napa, CA rapevine trunk diseases are responsible for significant eco- nomic losses to the wine industry Gworldwide. Symptoms of these diseases include dead spurs, arms, and cordons and eventual vine death due to canker formation in the vascular tis- sue. In Eutypa dieback, deformed leaves and shoots occur as the pathogen invades spur positions. As cankers develop, yield reductions occur due to the loss of productive wood. The impact of grapevine wood diseases can be significant in older for most canker development in California Figure I: Fruiting bodies (perithecia) of E. vineyards, and usually becomes more vineyards. However, recent findings have lata on a grapevine previously grafted for variety change. The large pruning wound severe as vineyards become older. highlighted the importance of other fungi favored formation of E. lata perithecia on Eutypa dieback, caused by Eutypa lata involved in the death and decline of the dead trunk of the old variety. was originally thought to be responsible grapevines in California. In this regard, Botryosphaeria species have also been recovered from cankers, and were determined to be the main cause of canker diseases in some California vineyards. Recent research has also indicated the occurrence of several new fungal trunk disease pathogens of grapevine belong- ing to the family Diatrypaceae (the same family as Eutypa). These include Eutypa leptoplaca, Cryptovalsa ampelina, Diatrype species, and Diatrypella species. We will present current information on the epi- demiology and control strategies of fun- gal organisms responsible for grapevine Figure II: Black stroma bearing perithecia (fruiting bodies) of E. leptoplaca on dead trunk of spur, cordon, and trunk dieback in big leaf maple collected in St. Helena, Napa County, CA. California. JANUARY/FEBRUARY 2005 2 GRAPEGROWING Eutypa dieback # Ascospores Rain (mm) Eutypa dieback was responsible for 60 4.5 a loss in net income for California wine Temp (…F) grapes estimated to be over $260 mil- 4 50 lion in 1999. Many growers consider 3.5 Eutypa to be the most significant dis- ease of grapevines. 40 Series1 3 Typical symptoms of E. lata include Rain Temp 2.5 formation of a wedge-shaped canker 30 and stunted shoots with cupped, tat- 2 tered, chlorotic, and necrotic leaves that are best seen in spring time. Foliar 20 1.5 symptoms are due to toxins produced 1 by E. lata. Differences in susceptibility 10 of grapevine cultivars to infection have 0.5 been reported, although no cultivars are immune. Cankers develop down- 0 0 ward at a faster rate than toward the 10:0012:0014:0016:0018:0020:0022:00 0:00 2:00 4:00 6:00 8:0010:0012:0014:0016:0018:0020:0022:00 0:00 2:00 4:00 6:00 8:0010:00 end of cordons and also increase in diameter over time. Extended infection Figure III: Ascospore release curve of E. lata during a period of rainfall recorded in December of grapevines by E. lata leads to vine 2001 in Davis using a Burkard spore trap placed around dead grapevine trunk bearing perithecia. death. Eutypa lata spreads to new pruning xylem vessels, weaken the plant by pro- ods of rainfall, starting a few hours wounds by wind-driven and water- ducing toxins and cause wood decay by after the onset of a rain (Figure IX). splashed ascospores released during excreting cell wall degrading enzymes. Over 80 plant species around the rain events. Ascospores develop Eutypa lata also produces asexual world have been reported to be poten- inside perithecia (fungal fruiting bod- spores called conidia. These are formed tial hosts for E. lata. In California, ies) that form when the fungus enters inside pycnidia (another type of fruiting many of these species were found to its sexual stage. The sexual stage body) that develop on wood, but these be infected with Eutypa lata and bore develops on dead wood, where conidial spores do not play a role in dis- perithecia producing ascospores in masses of perithecia are produced in a ease epidemiology. the vicinity of vineyards. We now black substrate referred to as stroma In California, ascospore discharge know that these species serve as nat- (Figure II). The sexual stage develops of E. lata occurs from the first rain of ural reservoirs of E. lata inoculum. in regions that receive over 16 inches the early fall until the last rains of the In the 1970s, grapevine, apricot, of rain. It is common to find stroma and spring (Figure III). Ascospore dis- and Ceanothus were found to be nat- perithecia on old grapevines and other charge decreases significantly in late ural hosts of E. lata. More recently we types of wood in the North Coast and February and remains low to nil by have identified kiwifruit, blueberry, Delta production areas. early March (Figure IX). and cherry to be hosts in California Ascospores infect grapevines through However, ascospore release may and they were shown to bear the fruit- fresh pruning wounds during the dor- occur during rains in March and April ing bodies (perithecia) of E. lata. mant season. They germinate, invade if they are preceded by several weeks Additionally, a recent survey iden- of no rain and sunny, warm weather. tified almond, crab apple, and pear Such releases may occur because trees as new fruit crop hosts for E. perithecia are able to recover in pro- lata, and showed the presence of ductivity during the dry period, or because spores that would have been released in the winter months are released in the spring simply because they were not released in the winter. This scenario more often occurs in years when there is little rainfall dur- ing the winter months. Ascospore release from individual Figure IV: Typical wedge shape canker perithecia may occur continuously for formed by Botryosphaeria in the cordon of Figure V: Mature Botryosphaeria obtusa grapevine. approximately 24 hours during peri- conidia. 3 JANUARY/FEBRUARY 2005 GRAPEGROWING Figure VII: Botryosphaeria obtusa pycnidia Figure VI: Mature Botryosphaeria found under the bark on the arm of an infected grapevine. theobromae conidia. Figure VIII: Botryodiplodia theobromae pycnidia found on old grapevine pruning perithecia of E. lata on several other Large amounts of viable inoculum wood left on the vineyard. new hosts in California including were found in several old vineyards near It is our opinion after this study California buckeye, big leaf maple, Healdsburg, Sonoma County. Perithecia that even though E. lata and E. lepto- willows, and oleander (Figure X). were particularly well-developed on placa ascospores can travel over con- Perithecia of E. lata were found to vines that had been previously top- siderable distances and cause dis- be particularly well established on worked for variety change. Stroma on ease, Eutypa dieback is primarily a dead branches of various willow those vines had developed on old wood disease of local origin, developing in species occurring along natural creeks below the grafting wound down to the the vicinity where the ascospores are union with the rootstock (Figure I). and irrigation waterways. released. While E. lata appears to be the pri- It appears likely that the flora sur- mary Eutypa species involved in dieback rounding vineyards is potentially a Control in California, we have identified a second Disease management should include key factor in disease epidemiology Eutypa species that can also cause removal of the dead parts of grapevines and surely acts as an inoculum reser- dieback in grapevines (Figure XIII). This and other host plants because of the poten- voir. Sanitation of the dead wood of species is E. leptoplaca, a slower growing tial risk of increased inoculum. We cur- potential hosts of E. lata in areas sur- fungus in culture but with the capability rently have no proof that sanitation will rounding vineyards is advised in to do the same kind of damage as E. lata. reduce the disease level in vineyards, but it order to decrease the inoculum level. This new fungus occurs in the North seems appropriate if local production of Sanitation can be accomplished by Coast but seems to be more limited in inoculum is considered to be a key to removing the infected tissues on its distribution. disease development. plants that show disease. Generally speaking, this disease can be identi- fied on other hosts by the black # Ascospores Rain (mm) stroma that is produced (Figure II). By 160 6 removing the stroma-infected wood Temp (…F) and burning it, the number of spores 140 5 released in winter can be reduced. Surveys inside vineyards and apri- 120 cot and cherry orchards have revealed 4 100 Spores an abundance of inoculum in planti- Rain Temp ngs of approximately 20 years and 80 3 older. Only a few perithecia have been found in almond orchards. 60 Perithecia of E. lata were found to 2 be prevalent in vineyards or sur- 40 rounds in the counties of Napa, 1 Sonoma, Yolo, Sacramento, Contra 20 Costa, San Benito, El Dorado, 0 0 Mendocino, San Joaquin, Stanislaus, and Merced. Perithecia of E. lata were 14:0016:0018:0020:0022:00 0:00 2:00 4:00 6:00 8:0010:0012:0014:0016:0018:0020:0022:00 0:00 2:00 4:00 6:00 8:0010:0012:00 not found in Madera, Fresno, Kings, Figure IX: Ascospore release of E. lata recorded on the 12th, 13th and 14th of April 2000 in a Tulare, and Kern counties.