2009 Research Report to the Michigan Grape & Wine Industry Council

Transcription

1 2009 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 not suitable for winemaking as they impart off flavors and other negative sensory characteristics to wine. These may be detectable even at low levels of infection. In late summer and early fall, the fungus produces small golden-brown to black fruiting bodies (cleistothecia) on infected plant parts (Pearson and Goheen, 1998). The cleistothecia overwinter in bark crevices of the vine and release wind-disseminated 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 1

2 overwintering cleistothecia is known to be correlated with disease pressure the following year. In the spring, powdery mildew primary infections are 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; however, early on, cleistothecia were immature. Peak cleistothecium production was apparent in the third week of September in Clarksville and fourth week of September in Traverse City. This means that applications of eradicant fungicides (e.g., Stylet Oil, Sulforix) to prevent cleistothecium formation should be made in late August/early September, and maybe again in Mid September. Ascospore release occurred from bud break until fruit set in both locations in While rain events triggered 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. 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, knowing conditions suitable to ascospore release can help growers understand the risk of disease development but are not sufficient to predict primary infection and are likely to overpredict infection risk. Time line This project was conducted from January 1 until December 31, 2009 and represents year 1 of 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 Using two methods, we assessed cleistothecium production on leaves of Vitis interspecific hybrid Chardonel and V. vinifera L. Pinot Noir in Clarksville (central Michigan) and Traverse City (northwest Michigan) in An 18-cmdiameter collection funnel connected to a 3-L plastic bottle was placed below the canopy of untreated grapevines. Four replicates were used per site. Rainwater samples were collected weekly, filtered, and cleistothecia were counted using a dissecting microscope. In addition, 20 leaf samples were collected weekly from four unsprayed locations in each vineyard to study cleistothecium development on the leaves. Cleistothecia were counted in five 1-cm 2 areas on both surfaces of the leaves, and considered immature if they were yellow or light-brown and mature if they were dark-brown. Campbell weather stations of the Michigan Automated Figure 1. Number of cleistothecia collected in rainwater samples in grape cv. Chardonel in Clarksville, MI, in Precipitation (mm) and temperatures ( C) were averaged for each collection period. 2

3 Weather Network were used to monitor environmental conditions at both sites. In 2009, we sampled two unsprayed Chardonnay vines at the Northwest Michigan Horticultural Research Station, Traverse City, and a Marechal Foch vineyard in Suttons Bay, MI. Ten leaves were randomly collected every week for quantification of cleistothecia in these vineyards. Cleistothecia were already observed in rainwater samples when collection started on Aug 21 and continued until October 1, after which leaves were killed by frost. The highest number of cleistothecia was observed during the third week of September after 20 days without precipitation in Clarksville (Fig. 1), and in the first week of October in Traverse City (data not shown). No cleistothecia were collected during dry periods since no rainwater was in the traps. Low cleistothecium numbers in October may have been due to a drop in temperature, which limit cleistothecium formation. Cleistothecium counts on leaves were variable (Fig. 2). The proportion of mature vs. immature cleistothecia increased as time progressed, although immature cleistothecia were present even up to the first killing frost. A peak in cleistothecium production was observed in late September/early October in Traverse City as well as in Clarksville, where another peak occurred in the second week of September. We found much higher numbers of cleistothecia on lower leaf surfaces than upper leaf surfaces, presumably because the latter are more exposed to rain events. Cleistothecia produced on lower leaf surfaces are less likely to be washed off with rainwater. They may therefore fall to the ground with senescent leaves. Gadoury and Pearson (1988) showed that cleistothecia that remained attached to leaf tissues had not completed the maturation process, hence they were unable to survive the winter Av. No. of chasmothecia (in 10 sq cm) Aug 25-Aug 27-Aug 29-Aug 31-Aug 2-Sep 4-Sep 6-Sep 8-Sep 10-Sep 12-Sep 14-Sep Immature 16-Sep 18-Sep 20-Sep 22-Sep Sampling period Mature 24-Sep 26-Sep 28-Sep 30-Sep 2-Oct 4-Oct 6-Oct 8-Oct 10-Oct 12-Oct 14-Oct 16-Oct Figure 2. Grape powdery mildew cleistothecium formation on grape leaves in Traverse City, MI, in in New York. However, in other locations (Australia, Italy, and Washington), cleistothecia seem capable of surviving on senescent leaves on the soil surface (Grove, 2004). Further studies are needed to investigate the viability of leaf-borne cleistothecia and their epidemiological significance in Michigan. 2) Determine the timing of ascospore release in the spring in relation to temperature and rainfall. To improve disease development predictions, ascospore release and primary infection were monitored in unsprayed areas of research vineyards in Clarksville and Traverse City, MI. Enviroweather stations were used to monitor environmental conditions at the sites. Burkard spore traps (both vineyards) and potted cv. Chardonnay bait plants (Clarksville only) were placed between vines from before bud break until fruit set. Burkard reels and plants were changed weekly and ascospores and powdery mildew colonies counted. Ascospores were detected in the air for more than a week after rain events from May until the end of June. Peak ascospore release occurred in Clarksville on May and in Traverse City on June 9, The presence of powdery mildew colonies on bait plants also indicated ascospore activity since early May. However, infections of 3

4 field-grown vines did not become evident until late June in Clarksville and late August in Traverse City, indicating a discrepancy between the presence of primary inoculum and disease development. This may be related to the exceptionally cool and rainy 2009 growing season, which can reduce infection. Further investigation is needed to better predict powdery mildew development under Michigan weather conditions. Figure 3. Ascospore release of Erysiphe necator in a vineyard in Traverse City, MI, in Precipitation (mm) and average temperature ( C) are also shown. 3) Determine if fall eradicant and spring dormant sprays can be used to drastically reduce inoculum quantity survival. In a replicated small-plot trial in cv. Chancellor in Fennville, MI, the following treatments were applied in en effort to reduce cleistothecium production and reduce viability of cleistothecia. Treatment Rate/acre Timing Untreated - - JMS Stylet Oil 1 gal September 2009 JMS Stylet Oil Sulforix 1 gal 2 qt September 2009 Spring 2010 JMS Stylet Oil Cuprofix Ultra 1 gal 3 lb Sulforix 2 qt Spring 2010 Cuprofix Ultra 3 lb Spring 2010 Standard seasonal program: Dithane Rainshield Pristine Vintage + Ziram 3 lb 12 oz 4 fl oz + 3 lb September 2009 Spring inch shoot, imm prebloom 1 st postbloom, 3 rd postbloom 2 nd postbloom 4 th postbloom All plots were treated with Ridomil MZ twice to reduce downy mildew infestation which was destroying clusters and leaf area. Data collection on powdery mildew incidence and severity is still in progress as the trial has not yet been completed. Communications Activities, Accomplishments and Impacts The results of this research were shared with grape growers at the following meetings: Great Lakes Expo, Dec. 2009; Northwest Orchard and Vineyard Show, Jan. 2010; Southwest Horticulture Days, Feb. 2010; Viticulture Day, July 2009 and 2010; Winegrape Integrated Pest Management Kick-off, NWMHRS, April 2010; 6th International Grapevine Downy and Powdery Mildew Workshop (France), July 2010; and various grape IPM grower meetings in Michigan during the 2009 and 2010 growing seasons. Articles utilizing the results of this project were also 4

5 written for the Grape IPM newsletter and Fruit Crop Advisory Team Newsletter in 2009 and In addition, the data were presented at the American Phytopathological Society meetings in Portland, OR (2009) and Charlotte, NC (2010). This project provides practical information on the utility and optimal timing of fall eradicative sprays and spring dormant sprays, which can be readily adopted by growers. Research publications resulting from this project: 1. Avila, L. L., Powers, K.L., and Schilder, A. C Late-season chasmothecium production by Uncinula necator on grape leaves in Michigan (abstract). Phytopathology 99:S6. 2. 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) (abstract). Phytopathology 100:S9. 3. 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. 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. 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.). 5