Aug 12, 2015
Grape berry moth update: Late-season pressure lower in 2015

Recent sampling of southwest Michigan vineyards indicates a lower pressure of grape berry moth than last season, but there are still regions in southwest Michigan with locally high infestations that should be controlled to prevent harvest-time fruit contamination. This is a good time to scout vineyards to determine where those host spots are and take action to prevent further increases.

The growing degree day model for grape berry moth indicates that southwest Michigan vineyards are at the start of the third generation for this pest. Check your local Michigan State University Enviro-weather station to determine the approximate time of the start of egglaying by generation three. The accuracy of this can be improved if you have a record of when wild grape bloomed in the spring, so if you didn’t record it this year, make a note to record it next spring. Application of an effective insecticide with excellent coverage is needed to reduce the number of berry moth larvae entering the berries. There are a large number of chemical options available that are listed in the Michigan State University Extension Bulletin E0154, “2015 Michigan Fruit Management Guide.”

In the past few years, we have been exploring ways to reduce the costs of control programs in vineyards. This includes treating only the vineyard borders with insecticide for the second and third generation of berry moth, so the sprays are focused in regions where this pest is the greatest threat. In many vineyards, this pest is most abundant at wooded borders or borders with tree lines. It can also have hot spots near single trees. The key point is that insect control may not be needed across the whole vineyard. This is in contrast to fungicides that tend to be applied as cover sprays across the whole vineyard when they are needed. If vineyard borders run parallel to the woods, you could spray with fungicide until nearing the woods and then add insecticide to the spray tank. However, this is an added complication and many vineyards have rows that run perpendicular to the woods. This means we need a way to deliver insecticide specifically to the areas where it is needed.

With support from the U.S. Department of Agriculture, National Grape Coop. and Project GREEEN, the MSU Grape Entomology Lab teamed up with the Cronenwett and Gregory farms and Mark Ledebuhr as the engineer to develop a cost-effective way to deliver insecticide only to areas where it is needed. The unit can mount onto existing sprayers and is built from standard equipment. This feeds concentrated insecticide solution into the delivery line near the spray nozzle opening. This approach has been tested for three seasons to apply insecticides against grape berry moth using only border application of insecticides in early July and August.

Eight vineyards in Lawton, Michigan, have been used in this trial, and all have received a post-bloom pyrethroid insecticide. The applications for generations two and three of grape berry moth have been applied in early July and August, respectively, using the precision sprayer that applied these insecticides only to the vineyard borders (10 rows or about five posts). The “standard” vineyards received full covers of insecticides for each berry moth generation.

Overall, our results confirm results from our earlier trials showing that Intrepid and Belt for generations two and three can provide excellent control of grape berry moth. The precision application approach can also help make this cost-effective since we found that the cost of the system to deliver insecticide only when needed would be repaid within about 200-300 sprayed acres. Even if adding this type of system to the sprayer is not worth the expense, border treatments for berry moth can help keep pest management costs under control.

The sprayer units developed for use on an AgTec tower sprayer and for an airblast sprayer will be demonstrated at the upcoming MSUExtension meeting at the Cronenwett farm, 70121 28th St., Lawnton, MI 49065, held Aug. 18, from 2:30-4:30 p.m.

— By Rufus Isaacs, Michigan State University Extension, Department of Entomology

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