Download July 22, 2011

Grape IPM Update
Lorraine P. Berkett
July 22, 2011
Mark your Calendars -- August 19, 2011 -- UVM Vineyard & Orchard “Open House” from
2:00 - 5:00 p.m. at the Horticulture Research Center (HRC) in South Burlington. The UVM
Vineyard has 8 winegrape varieties and 8 table grape varieties. The HRC is also the site of a
USDA-funded Organic Apple Research Project. More details will be available soon but please
mark your calendars… hope to see you there !
Disease Management -- The results of your disease management program so far this season
should start to be evident in your vineyard now. Hopefully, you are not seeing disease
symptoms -- which would be great! But, the following pictures were taken this past week and
show what can occur.
Phomopsis
These Phomopsis disease symptoms are on St. Croix vines. The disease is most likely a problem
when the fungus is allowed to build up on dead canes or pruning stubs (see picture below of
stub with small black dots=fruiting bodies from which fungal spores are released in the spring).
Fruit symptoms only become apparent just before harvest although infections occur from when
the fruit are first exposed until about four weeks after bloom. The critical time to manage this
disease is over. However, it is important to examine your vines to see if you have symptoms on
the shoots and leaves now, and on the fruit at harvest. Infected fruit will look similar to what
Black Rot-infected berries appear like now -- but Phomopsis fruit symptoms only appear near
harvest. If you do have significant infection, please note for next year that protective sprays
may need to be started as early as the 1-inch growth stage and continue through the period of
susceptibility. Also, it is important that diseased canes be removed during winter pruning to
reduce fungal inoculum.
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Gray area on stub has Phomopsis fruiting bodies from which spores are released in the spring to start the disease.
Black Rot
Black rot lesions on Frontenac leaf. Infected fruit are rotting, shriveling, and turning into ‘mummies’.
Regarding Black Rot, the fruit is most susceptible 2-3 weeks following bloom and becomes
highly resistant 5-8 weeks after bloom depending on the variety.
If you have disease
symptoms in your vineyard, it would be wise to keep the fruit protected from infection through
at least the end of July. Please note that symptoms appear only weeks after infection -- so if
you are seeing Black Rot now -- the infection took place weeks ago. And, infections that take
place in July will only become evident in August. Table 3.2.2 in the 2011 New York and
Pennsylvania Pest Management Guidelines for Grapes lists various fungicides and their
effectiveness against this disease and other diseases.
Please note that for resistance
management, the total number of applications from the group of fungicides known as the
Sterol-Inhibiting fungicides (which includes Rally, Elite, Procure, etc., and any combination
fungicide that includes a Sterol-Inhibiting fungicide as a component) should be limited to a
grand total of three applications per year. The total number of applications from the group of
fungicides known as the Strobilurin fungicides (which includes Abound, Flint, Sovran, etc., and
any combination fungicide that includes a Strobilurin fungicide such as Pristine, etc. ) should be
limited to two applications per year.
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Anthracnose
Anthracnose infections can continue to occur. All succulent parts of the vine can be infected
but lesions on shoots and berries are most common and distinctive. The lesions above are on
Marquette. Clusters are susceptible to infection until veraison. In an article in the July 15,
2011 issue of the Michigan Grape and Wine Newsletter, Dr. Annemiek Schilder, a plant
pathologist at MSU, includes a table of fungicides and their effectiveness against Anthracnose -please see this list on page 8 of the newsletter for potential options keeping in mind preharvest intervals, resistance management restrictions, and phytoxicity issues.
Downy Mildew
Berries should be mostly resistant to downy mildew infection at this point in the growing
season (i.e., they lose their susceptibility to infection by midsummer). However, on susceptible
varieties, young leaves remain highly susceptible to infection and even older leaves can
become diseased under high-inoculum conditions. Severe infections can cause defoliation
which impacts fruit ripening and vine winter hardiness. Any practice that improves air
circulation and speeds drying within the vine canopies will help to manage downy mildew.
Fortunately, hot, dry weather can cause the downy mildew organism to become ‘inactive’
during midsummer --- but, if wet weather returns, there can be ‘explosive’ spread of this
disease.
Powdery Mildew -- I have not seen any powdery mildew lesions yet this season so I do not
have current pictures. Pictures of the disease can be seen on the web at:
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http://www.nysipm.cornell.edu/factsheets/grapes/diseases/grape_pm.pdf
Please note that berries remain highly susceptible to infection until about two to three weeks
after fruit set. Again, any practice that opens up the canopy can help to manage powdery
mildew by letting in more sunlight (i.e., powdery mildew is more severe in canopies with
shaded centers). Continued management of foliar mildew is advised on highly susceptible
varieties to avoid poor ripening, premature defoliation, and reduced winter hardiness. Also,
managing foliar infections will reduce disease pressure next year by limiting the number of
cleistothecia (overwintering fruiting bodies) that will form and be the source of infection next
spring.
Insect Management
Grape Berry Moth (GBM) -- I did see berries damaged by GBM larvae this past week.
Webbing between berries damaged by GBM larva
As I had mentioned in the last Update, research at Michigan State University has been
conducted to identify the most effective time to apply insecticides in July/ August to manage
the later generations of this insect. The result of this research is a Growing Degree-Day (GDD)
Model developed by Dr. Rufus Isaacs of MSU which predicts the start of egglaying of the second
and third generations. Dr. Isaacs found that the insect took 810 GDD (base 47F) to complete a
generation and that egglaying starts to increase around 810 and 1620 GDD from the biofix
(=the date when approximately 50% of the flowers are open on approximately 50% of wild
grape clusters).
This information has been incorporated into NEWA - Network for
Environmental & Weather Applications. At the UVM Vineyard at South Burlington, we have
kept a few wild grape vines at the site for the purpose of determining the biofix for the GBM
model -- it was on June 6, 2011. As of today, 1038 GDD have accumulated at this site. Note
that based on this GDD, the output of the model predicts that current larvae are protected in
the berries and to scout when GDD reach 1440-1610.
To see the estimate of the GBM model at a site closest to your vineyard, go to
http://newa.cornell.edu/ , click on a site nearest to you, then click on Grape Berry Moth. In
cooler areas of the state, there is still time to scout and determine if the 6% damage threshold
for treatment has been reached.
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Other resources:
•"How to Use NEWA - An Instructional Video" and "How to Use NEWA - Printable Handout"
•2011 Vine Phenology of the UVM Vineyard is being posted at:
http://pss.uvm.edu/grape/UVMvineyard/2011UVMphenology.html
•2011 UVM Vineyard ‘Blog’ is being posted at:
http://pss.uvm.edu/grape/UVMvineyard/UVM2011Blog/UVM2011Blog.html
•The 2011 New York and Pennsylvania Guidelines for Grapes is on the web at:
http://ipmguidelines.org/grapes/
•Cornell’s Production Guide for Organic Grapes (2010) is on the web at:
http://nysipm.cornell.edu/organic_guide/grapes.pdf
----------------------------------------------------------------------------------------------------------------------------------------------------Where trade names or commercial products are used for identification, no discrimination is intended and no
endorsement is implied. Always read the label before using any pesticide. The label is the legal document for the
product use. Disregard any information in this newsletter if it is in conflict with the label.
The UVM Cold Climate Winegrape Program is supported by the University of Vermont Agriculture Experiment
Station, a USDA NIFA E-IPM Grant, a Vermont Agency of Agriculture Specialty Crop Block Grant, and USDA Risk
Management Agency Funds.
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