Mid-season grape berry moth management

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.        

With bloom behind us, we approach the time of the season when the second generation of grape berry moth begins. Recent vineyard monitoring and scouting in southwest Michigan showed that moth flight had declined and there was little egglaying last week. Larvae that were not controlled around bloom-time are already inside berries or are starting to pupate. This indicates a lull in the activity of grape berry moth before the second generation starts. Growers should now consider the optimal time to protect berries from grape berry moth in vineyards, as the second generation of this pest is expected to start laying eggs this week in southwest Michigan.

If you recorded the date of wild grape bloom in late May-early June, that can now be used to predict the start of second generation egglaying using the MSU grape berry moth degree day model (online at www.enviroweather.msu.edu, look for grape berry moth model in the fruit section). For example, wild grape bloomed on May 24 at SWMREC in Benton Harbor, and using that start date, or biofix, the model predicts egglaying will start 810 degree days later, which is predicted to be June 30 in that region. For other parts of the state, the dates may be different based on the date of wild grape bloom and the accumulated degree days for 2010 in other regions. For example, we would expect a later start to egglaying of the second generation in Fennville, and especially in the Traverse City region.

This season provides a good example of why a degree day model might help growers time applications better than a calendar approach. Last year, we made applications at 810 degree days on July 14, and we are two weeks earlier using the model this year.

The predicted start of egglaying is the optimal timing for application of insecticides that are most active on eggs and young larvae, such as Intrepid. For this product, excellent cluster coverage is essential, but once it is on the clusters, long residual control of grape berry moth (two to three weeks) and rain-fastness is achieved. For products that are broad-spectrum that are best timed for egg hatch, applications should be delayed to be timed 100 degree days after 810, i.e. at 910 degree days. For the example at SWMREC described above, the predicted daily highs and lows indicate that 910 degree days will be reached just after Independence Day (July 4).

In our recent research trials, spray programs that timed applications for berry moth control based on the 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 degree-day timed sprays using some of the new insecticides that are highly active and long-lasting for berry moth control. For example, in 2009 a program using Intrepid at 8 oz/acre applied at 810 degree days (mid-July) followed by Altacor at 3 oz/acre applied at 1620 degree days (mid-August) provided similar or slightly better control than a Sevin and Imidan program in the mid- and late season timings. The earlier season would move timings of these applications up for this year. Other pest insects may be important in your vineyards, but if you are focusing on berry moth control, degree day-timed applications of long-lasting and effective insecticides applied with excellent coverage provides an effective program to reduce pressure from this pest.

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