Final Research Report to the Michigan Grape & Wine Industry Council

Transcription

1 Final Research Report to the Michigan Grape & Wine Industry Council Proposal Title: Timing of powdery mildew cleistothecium production in the fall and ascospore release in the spring under Michigan conditions. Principal Investigator: Co-Investigator: Name: Annemiek Schilder Name: Nikki Rothwell Mail Address: 105 CIPS, MSU Mail Address: NWMHRS, 6686 S Center Hwy Telephone: Traverse City, MI Fax: Telephone: ; Fax: Original goals and objectives for the project The objectives for this project were: 1) Determine the timing of powdery mildew cleistothecium production on grape tissues and wash-off in the fall in relation to temperature and rainfall 2) Determine the timing of ascospore release in the spring in relation to temperature and rainfall. 3) Determine if fall eradicant and spring dormant sprays can be used to reduce inoculum quantity and survival. Literature Review Powdery mildew, caused by the fungus Erysiphe necator, affects many grape varieties. Severe infections reduce vine growth, yield, fruit quality, and winter hardiness (Pearson and Goheen, 1998). In 2006, an outbreak of powdery mildew occurred on fruit clusters in NW Michigan and resulted in total crop loss in some vineyards, leading to individual grower losses in the tens of thousands of dollars (Charles Edson, personal communication). Powdery mildew-infected grapes are unsuitable for winemaking as they impart off flavors and other negative sensory characteristics to wine. In late summer and early fall, the fungus produces small golden-brown to black fruiting bodies (called cleistothecia or chasmothecia) on infected plant parts (Pearson and Goheen, 1998). The cleistothecia overwinter in bark crevices of the vine and release winddisseminated ascospores in the spring (Cortesi et al., 1995). In Italy, cleistothecia were formed in autumn in both 1994 and 1995, and their dispersal started in late September to mid-october, with the highest number of cleistothecia trapped in funnels during the second half of October (Cortesi et al., 1997). In Australia, but not in New York, the pathogen also overwinters as cleistothecia on fallen leaves. In Eastern Washington, cleistothecia are the only known source of primary inoculum in the grape-production region (Grove, 2004). Ascospores were trapped as late as 70 days after bud burst during rain events of 3.9 to 9.6 mm. Cleistothecium production can be prevented by good disease control. However, even in years with reasonably good disease control, cleistothecia may be produced in copious amounts at the end of the growing season. A previous study on the effects of eradicant fungicides on powdery mildew (Schilder et al., 2008) showed that a number of contact fungicides can kill existing powdery mildew colonies and limit the production of overwintering cleistothecia, particularly JMS Stylet Oil, Sulforix, and Kaligreen. What is not clear, however, is when the best time to apply these products is in terms of reduction of overwintering inoculum. The number of overwintering cleistothecia is known to be correlated with disease pressure the following year. In the spring, powdery mildew primary infections are 1

2 initiated when more than 0.1 inch rainfall occurs and the temperature is at least 50ºF (Pearson and Goheen, 1988). This simple rule can be used to predict infection risk due to primary (ascosporic) infection and improve timing of sprays during the early season, however, this has not been validated under Michigan conditions. Results and Conclusions Grape powdery mildew cleistothecia were already produced in August in both locations but were only dispersed when were mature. Peak cleistothecium production and dispersal occurred in the third week of September in Clarksville and fourth week of September in Traverse City and was correlated with rainfall. This means that applications of eradicant fungicides (e.g., JMS Stylet Oil, Sulforix) to prevent cleistothecium formation should be made at least several weeks before that time period. Ascospore release occurred from bud break until fruit set in both locations in 2009 and While rain events boosted spore release, spores were also released during dry days. However, there were frequent morning dews under cool conditions, which may have also contributed to spore release. Ascospores may have also been released before bud break, which means that these spores were lost in the absence of susceptible host tissue. Ascospore release could be described as a function of degree days and was mostly completed after 300 ggd (from base 50F, from April 1). While activity of the powdery mildew fungus was observed both by spore trapping and use of trap plants, field infections were not observed until late July in Clarksville and late August in Traverse City. This suggests that adverse weather conditions (cool temperatures, rain) limited the success of ascosporic infection. Therefore, it seems that infection success of ascospores is more critical than predicting timing of ascospore availability in determining epidemic development. In a small plot experiment, a fall or spring application (or both) of eradicant fungicides was as effective as a season-long preventative fungicide program. This suggests that inoculum management can improve control of powdery mildew in Michigan. Time line This project was conducted from January 1, 2009 until December 31, 2010 and represents a 2- year project. Work accomplished during period including methods: 1) Determine the timing of powdery mildew cleistothecium production on grape tissues and dehiscence in the fall in relation to temperature and rainfall Unsprayed grapevines in two wine grape vineyards were chosen to study the timing of cleistothecium production. In late summer and fall of 2009 and 2010, random leaf samples were taken on a weekly basis to determine quantity and developmental stage of cleistothecia. Funnel traps were placed below infected vines to determine the number of cleistothecia washed off during rain events. Weather data were collected with Enviroweather stations at each 2

3 location. Data were analyzed with ANOVA and regression analysis. In general, cleistothecium production peaked in mid to late September (a bit later in northern than in central Michigan) in both years and continued until leaf drop (Fig. 1). The ratio of mature to immature cleistothecia increased over that period. Higher numbers of cleistothecia were found on the lower leaf surface, which may be related to lower exposure to wash-off by rain and UV light as well as higher humidity. Numbers in rain water traps tended to be correlated with the amount of rainwater caught in the traps. The data suggest that the best timing for eradicant sprays to diminish cleistothecium formation would be late August to early September. 2) Determine the timing of ascospore release in the spring in relation to temperature and rainfall. The same vineyards as described above were chosen to study powdery mildew ascospore (primary inoculum) release in the spring. Ascospores were captured with a Burkard volumetric spore trap placed next to vines and quantified microscopically. In addition, young potted vines (replaced weekly) served as baits for powdery mildew infection in Clarksville. Field-grown vines were also inspected for infection. Weather data were collected at each location though the Enviroweather network. Data were analyzed with ANOVA and regression analysis. Ascospores were generally low in number and were released almost continuously from (before) bud break until fruit set (Fig. 2). This shows that precipitation is not needed for ascospore release even though it stimulated ascospore release. Moisture in the form of dew may have provided sufficient wetting of cleistothecia in the bark on dry days. However, powdery mildew was seen much later in the season, indicating that infections were not always successful, which is likely due to low (night-time) temperatures inhibiting infections. 3

4 3) Determine if fall eradicant and spring dormant sprays can be used to reduce inoculum quantity and primary infection. In a replicated small-plot trial in cv. Chancellor at the TNRC in Fennville, eradicant fungicide sprays were applied on the foliage of vines infected with powdery mildew in the fall to reduce Treatment Rate/acre Timing JMS Stylet Oil 1 gal 2 September, 2009 JMS Stylet Oil Sulforix 1 gal 2 qt 2 September, April, 2010 JMS Stylet Oil Cuprofix Ultra 1 gal 3 lb 2 September, April, 2010 Sulforix 2 qt 5 April, 2010 Cuprofix Ultra 3 lb 5 April, 2010 Dithane Rainshield 3 lb inch shoot, imm. prebloom Pristine 12 oz 1 st postbloom, 3 rd postbloom Vintage + Ziram 4 fl oz + 3 lb 2 nd postbloom 4 th postbloom cleistothecium production. In addition, some plots received spring dormant sprays in the spring to inactivate overwintering inoculum. Control vines were left untreated. Results showed that all treatments significantly reduced powdery mildew severity during the growing season and were statistically similar (Fig. 3). This indicates that fall and/or spring eradicant fungicide sprays can be effective tools for reducing powdery mildew severity. Communications Activities, Accomplishments and Impacts This project has provided new information on the biology of grape powdery mildew in Michigan and improved recommendations for the management of overwintering inoculum by fall eradicative sprays and spring dormant sprays, which are being adopted by growers. The results of this research were shared at numerous meetings: Great Lakes Expo, Dec. 2009, 2010; Northwest Orchard and Vineyard Show, Jan. 2010, 2011; Southwest Horticulture Days, Feb. 2010, 2011; Viticulture Day, July 2010, 2011; and the Northwest Michigan Horticultural Research Center Open House in August, 2011; Wine grape Integrated Pest Management Kick-off, NWMHRS, April 2010, 2011; 6th International Grapevine Downy and Powdery Mildew Workshop (France), July 2010; and various grape IPM grower meetings in Michigan during the 2010 and 2011 growing seasons. In addition, the data were presented at the American Phytopathological Society meetings in North Carolina (2010). Research and extension publications resulting from this project: 1. Avila, L. L The Epidemiology of Grapevine Powdery Mildew in Michigan and the Effects of Powdery and Downy Mildew on Vine Physiology. MS Thesis, Michigan State University, East Lansing, Michigan. 4

5 2. Avila, L. L., Powers, K.L., and Schilder, A. C Late-season cleistothecium production by Uncinula necator on grape leaves in Michigan. Phytopathology 99:S6. 3. Avila, L. L., Sullenger, A. R., Kroll, J., and Rothwell, N. L Validating environmental parameters for primary infection of grapes by Erysiphe necator ascospores under Michigan conditions). Phytopathology 100:S9. 4. Avila, L. L., Nagendran, S., Rothwell, N. L., and Schilder, A. M. C Production and eradication of overwintering inoculum of Erysiphe necator in Michigan vineyards. Proceedings of the 6th International Grapevine Downy and Powdery Mildew Workshop, 4-9 July 2010, Bordeaux, France. 5. Wise, J. C., Gut, L. J., Isaacs, R., Schilder, A. M. C., Sundin, G. W., Zandstra, B., Hanson, E., and Shane, B Michigan Fruit Management Guide Extension Bulletin E-154. Michigan State University, East Lansing, MI. 6. Wise, J. C., Gut, L. J., Isaacs, R., Schilder, A. M. C., Sundin, G. W., Zandstra, B., Hanson, E., and Shane, B Michigan Fruit Management Guide Extension Bulletin E-154. Michigan State University, East Lansing, MI. Two publications will be submitted to the scientific journal Plant Disease in September, Funding Partnerships Funding for this project from the Michigan Grape and Wine Industry Council was used to leverage additional funding from MSU Project GREEEN (17,000) and the Viticulture Consortium East ($16,000). References Cortesi, P., Gadoury, D., Seem, R. C., and Pearson, R Distribution and retention of cleistothecia of Uncinula necator on the bark of grapevines. Plant Disease 79: Cortesi, P., Bisiach, M., Ricciolini, M., and Gadoury, D Cleistothecia of Uncinula necator - an additional source of inoculum in Italian vineyards. Plant Disease, 81: Gadoury, D.M, Seem, R. C., Ficke, A., and Wilcox, W. R. 2001a. The epidemiology of powdery mildew on Concord grapes. Plant Disease 85: Gadoury, D.M, Seem, R. C., Pearson, R. C., and Wilcox, W. R. 2001b. Effects of powdery mildew on vine growth, yield, and quality of Concord grapes. Phytopathology 91: Gadoury, D.M., Pearson, R.C., Riegel, D.G., Seem, R.C., Becker, C.M., and Pscheidt, J.W Reduction of powdery mildew and other diseases by over-the-trellis applications of lime sulfur to dormant grapevines. Plant Disease 78: Grove, G Perennation of Uncinula necator in vineyards of Eastern Washington. Plant Disease 88: Pearson, R.C., and Goheen, A.C. (eds.) Compendium of Grape Diseases. APS Press, St Paul, MN. Schilder, A. C., Rothwell, N. L., Powers, K. L., and Anderson, M. D Fungicide efficacy in eradicating powdery mildew and reducing cleistothecium formation on grape leaves (abstract). Phytopathology 98:S140 (poster). Thomas, C. S., Gubler, W. D., and Leavitt, G Field testing of a powdery mildew disease forecast model on grapes in California. Phytopathology 84:1070 (abstr.). Willocquet, L., Colombet, D., Rougier, M., Fargues, J., and Clerjeau, M Effects of radiation, especially ultraviolet B, on conidial germination and mycelial growth of grape powdery mildew. European Journal of Plant Pathology 102: