Grape berry moth spray timing window is approaching

Checking the Enviro-weather grape berry moth model can help growers improve timing of sprays to protect clusters before harvest.

The growing degree day (GDD) model for predicting grape berry moth phenology during the season is available at the Enviro-weather website. Go to www.enviro-weather.msu.edu, click on Fruit at the top (circle in image below), then Grape over in the left-hand column (square in image below), then Grape Berry Moth (arrow in image below), and it will open the model for the nearest weather station. You can select the preferred weather station from the drop-down menu in the top of the page. This will show you the current estimated growing degree days from various dates in the spring listed across the top of the table that should be around the timing of your biofix date, when 50 percent of the clusters of wild grape were at 50 percent bloom. If you didn’t record wild grape bloom date, use the middle of the table as an estimate.

Enviroweather
Scottdale Enviro-weather station page showing how to get to the grape
berry moth model.

For the Scottdale Enviro-weather station in Berrien County, the model is predicting the start of the third generation of grape berry moth around Aug. 6. The image below clipped from the Assist Chart is what you will see when running the model. Assuming that wild grape bloom was set on May 27, this shows for today, July 30, that the site is 1,479 GDD from biofix. Enviro-weather predicts that the third generation of grape berry moth will begin egglaying at 1,620, and this is predicted to occur at 1,620 GDD after biofix, as indicted by when the cells turn red on the Assist Chart. That level of heat accumulation is expected on Aug. 6 this season for this site. For later sites, these target dates will be later into August. Keep checking the Enviro-weather website to see the predicted timing for the start of this third generation’s egglaying.

Enviroweather
Screen shot of the grape berry moth model on Enviro-weather for the
Scottdale station on July 30, 2013.

The predicted start of egglaying is the optimal timing for application of insecticides that are active on eggs and young larvae, such as Intrepid, Altacor or Belt. For these products, excellent cluster coverage is essential, but once it is on the clusters, long residual control of grape berry moth (two to three weeks) and rainfastness are achieved. For products that are broad-spectrum such as the pyrethroid, organophosphate and carbamate insecticides that are best timed for when the larvae hatch from the eggs, applications should be delayed to be timed 100 growing degree days later at 1,720 growing degree days from wild grape bloom. For the locations in far southwest Michigan, this will be four to five days later based on the predicted temperatures for the coming week.

In our recent research trials, spray programs that timed applications for berry moth control based on the growing degree day model outperformed those that used a calendar approach. This was the case for broad spectrum insecticides, and even better control was achieved when we tested growing degree day timed sprays using some of the new insecticides that are highly active and long-lasting for berry moth control. For example, a program using Intrepid at 8 ounces per acre applied at 810 GDD followed by Altacor at 3 to 4 ounces per acre applied at 1,620 GDD provided similar or slightly better control than a Sevin and Imidan program in the mid- and late season timings.

Altacor also has activity against Japanese beetles, which were first seen this week in scouting across southern Michigan, making it a useful tool for mid-season control when both pests are present. Belt has a similar mode of action to Altacor and is less expensive, but it is more selective and does not provide the Japanese beetle control. Other pest insects may be important in your vineyards, but if you are focusing on berry moth control, growing degree day-timed applications of long-lasting and active insecticides applied with excellent coverage provides an effective program to reduce pressure from this pest.

With harvest approaching, Michigan State University Extension warns growers to beware of products with long pre-harvest intervals and make sure that there are enough days before picking if using one of those. For example, Intrepid 2F has a 30-day waiting period before harvest.

Dr. Isaacs’ work is funded in part by MSU‘s AgBioResearch.

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