About Enviro-weather's Grape Berry Moth Predictive Model Report
By Rufus Isaacs
Grape berry moth typically has 3 generations per season in southern Michigan, and predicting when these occur can help growers target management at the right time to reduce infestation by this pest. The first generation is usually at a low level but many growers target this generation with a 10-day post bloom insecticide which is a good timing to control this first generation. In vineyards with this pest, populations build through each generation and can reach high abundance immediately before harvest causing yield loss, disease, and the risk of crop contamination. Prevention of this mid-late season infestation is most important, and accurate timing of controls is an essential aspect of effective management of grape berry moth.
The MSU degree day model for grape berry moth has been developed to predict the start of egglaying in the second and third generations in southwest Michigan vineyards. It uses growing degree days (GDD) accumulated after wild grape bloom, so it is important to record the date of wild grape bloom near vineyards to run this model. This insect takes 810 GDD (base 47F) to complete a generation, and we have found that egglaying starts to increase at around 810 and 1620 GDD after wild grape bloom for the second and third generations, respectively.
If vineyard pest history and cluster scouting indicate that protection from berry moth is needed, this model can be used to predict when egglaying by the second and third generation are starting. For insecticides that work best when applied just before egg-hatch such as insect growth regulators, application at 810 and 1620 GDD are expected to provide good control of this pest. For example, MSU research trials in high pressure vineyards during 2008 found excellent control of berry moth using Intrepid (8 oz/acre) applied at these GDD timings. For insecticides with shorter residual control such as most broad-spectrum contact insecticides, another application will likely be needed after the 810 GDD timing to provide sufficient coverage of the mid-season generation.
Running the grape berry moth model:
Step 1. Record when wild grape blooms near your vineyard, typically in early June. The date to record is when approximately 50% of the flowers are open on approximately 50% of the wild grape clusters.
Step 2. Go to www.enviroweather.msu.edu and select the nearest weather station to your farm. Select the Fruit Pages and then select Grape Berry Moth model in the Insects section. A new page will appear with a table that has dates and daily degree day totals on the left, and wild grape bloom date across the top.
Step 3. Look across the top of the table for the date(s) when wild grape bloomed on your farm. Look down the table for the row where the table cell turns red, indicating 810 (and later 1620) degree days after wild grape bloom (base 47F). These red shaded boxes indicate the timing of the start of egglaying by the second and third generations of grape berry moth.
In this example, if wild grape bloom was recorded on 6/10, more than 810 degree days have passed as of 7/20. The red cell indicates that egglaying of the second generation has begun. If wild grape bloom was recorded on 6/16, however, less than 700 degree days have passed since wild grape bloom, and egglaying of the second generation has likely not yet started.
Step 4. Make management decisions. The model provides information on timing for the start of mid- and late-season berry moth generations, but not on the need for treatment. Based on pest scouting and vineyard history, make decisions about the need for an insecticide application.