Download Timing of powdery mildew cleistothecium

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:
Name: Annemiek Schilder
E-mail: [email protected]
Mail Address: 105 CIPS, MSU
Telephone: 517-355-0483
Fax: 517-353-5598
Co-Investigator:
Name: Nikki Rothwell
E-mail: [email protected]
Mail Address: NWMHRS, 6686 S Center Hwy
Traverse City, MI 49684
Telephone: 231-946-1510; Fax: 231-946-1404
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
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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
2009. 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 2year 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 2009. 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-cm2 areas
Figure 1. Number of cleistothecia collected in
on both surfaces of the leaves, and considered
rainwater samples in grape cv. Chardonel in Clarksimmature if they were yellow or light-brown
ville, MI, in 2009. Precipitation (mm) and temperand mature if they were dark-brown. Campbell
atures (°C) were averaged for each collection period.
weather stations of the Michigan Automated
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2 9Au
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3 1Au
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8 -S
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1 0Se p
1 2Se p
1 4Se p
1 6Se p
1 8Se p
2 0Se p
2 2Se p
2 4Se p
2 6Se p
2 8Se p
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6 -O
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1 0Oc
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1 2Oc
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A v. N o. of chasmothecia (in 1 0 sq cm)
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.
Immature
Mature
We found much higher numbers of
cleistothecia on lower leaf surfaces
350
than upper leaf surfaces,
300
presumably because the latter are
250
more exposed to rain events.
200
Cleistothecia produced on lower
150
leaf surfaces are less likely to be
100
washed off with rainwater. They
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may therefore fall to the ground
with senescent leaves. Gadoury and
0
Pearson (1988) showed that
cleistothecia that remained attached
Sampling period
to leaf tissues had not completed
Figure 2. Grape powdery mildew cleistothecium formation on grape
the maturation process, hence they
leaves in Traverse City, MI, in 2009.
were unable to survive the winter
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 22-26 and in Traverse City on June 9, 2009. The presence of powdery mildew
colonies on bait plants also indicated ascospore activity since early May. However, infections of
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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 2009. 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
Untreated
JMS Stylet Oil
JMS Stylet Oil
Sulforix
Rate/acre
1 gal
1 gal
2 qt
Timing
September 2009
September 2009
Spring 2010
JMS Stylet Oil
Cuprofix Ultra
Sulforix
Cuprofix Ultra
Standard seasonal program:
Dithane Rainshield
Pristine
Vintage + Ziram
1 gal
3 lb
2 qt
3 lb
September 2009
Spring 2010
Spring 2010
Spring 2010
3 lb
12 oz
4 fl oz + 3 lb
10-12 inch shoot, imm prebloom
1st postbloom,
3rd postbloom
nd
2 postbloom
4th 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
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written for the Grape IPM newsletter and Fruit Crop Advisory Team Newsletter in 2009 and
2010. 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. 2009. 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. 2010. 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. 2009. Michigan Fruit Management Guide 2010. Extension Bulletin E-154.
Michigan State University, East Lansing, MI.
4. Avila. L. L., Nagendran, S., Rothwell, N. L., and Schilder, A. M. C. 2010. 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. 1995. Distribution and retention of
cleistothecia of Uncinula necator on the bark of grapevines. Plant Disease 79:15-19.
Cortesi, P., Bisiach, M., Ricciolini, M., and Gadoury, D. 1997. Cleistothecia of Uncinula necator
- an additional source of inoculum in Italian vineyards. Plant Disease, 81: 922-926.
Gadoury, D.M, Seem, R. C., Ficke, A., and Wilcox, W. R. 2001a. The epidemiology of powdery
mildew on Concord grapes. Plant Disease 85: 137-140.
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: 948-955.
Gadoury, D.M., Pearson, R.C., Riegel, D.G., Seem, R.C., Becker, C.M., and Pscheidt,
J.W. 1994. Reduction of powdery mildew and other diseases by over-the-trellis
applications of lime sulfur to dormant grapevines. Plant Disease 78: 83-87.
Grove, G. 2004. Perennation of Uncinula necator in vineyards of Eastern Washington. Plant
Disease 88: 242-247.
Pearson, R.C., and Goheen, A.C. (eds.).1988. Compendium of Grape Diseases. APS Press, St
Paul, MN.
Schilder, A. C., Rothwell, N. L., Powers, K. L., and Anderson, M. D. 2008. 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. 1994. Field testing of a powdery mildew disease
forecast model on grapes in California. Phytopathology 84:1070 (abstr.).
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