MSU Extension

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.

Grape berry moths have been trapped in vineyards across southwest Michigan over the past three weeks. These male moths in traps indicate that the overwintering generation of this pest has started to emerge, but no egglaying has been detected yet and eggs are not expected until the primary buds begin blooming. This year, as growers aim to trim costs, it will be important to focus insecticides where they are needed most. As part of our research to improve control of this pest, we are working with researchers in New York and Pennsylvania to develop a degree day model to predict important events in the life cycle of grape berry moth. The model is being tested this growing season, but from previous years results, we can see that berry moth development seems to be closely tied to the development of the vine, perhaps because they use similar base temperatures for development.

Our research has tracked the dates of important development stages in the first generation of grape berry moth in commercial vineyards over recent years, and the results are presented in Table 1. One important thing to note is that there is a long time (typically about 4 weeks) between the first moth and the first eggs laid or the peak eggs laid. Looking across the table, it is clear that the start of egglaying in this pest coincides with bloom in juice grapes, and peak egglaying coincides with the 10-day post bloom timing used by many juice grape growers for their first insecticide targeting grape berry moth. This emphasizes that an immediate post-bloom insecticide is generally the most effective timing for controlling the young larvae of this pest.

Table 1. Timing of grape berry moth development in Michigan
vineyards (2002-5). These dates are averages, and the exact
dates will vary from year to year.

Treatments applied earlier than the post-bloom timing can be washed off or degrade before most of the egglaying and are unlikely to protect the clusters from feeding by berry moth larvae. Because of this, insecticides to control the first generation of berry moth are typically timed for the 10-day post-bloom timing. If growers are aiming to reduce costs in vineyards where a crop is expected, scouting clusters just after bloom can be used to determine the level of infestation by this pest and whether an insecticide is warranted at the post-bloom timing. Although there is no formal threshold developed for first generation berry moth, if only a small proportion of clusters have larvae or if the level of feeding is low, there will be minimal effect on yield. Since clusters set only about a third of the potential berries produced, clusters can withstand some feeding and this is worth considering when weighing up the cost of a spray.

If a spray is required, an insecticide targeting the first generation can help reduce pest pressure later in the year. When selecting an insecticide, there are many options for berry moth control. Some of these are selective for this pest, while others will also provide control of leafhoppers, rose chafer and other insects that can occur at bloom. The organophosphate Imidan, carbamates Sevin and Lannate, and pyrethroids Danitol and Capture are all highly effective against grape berry moth. Some regions of southwest Michigan have leafhopper populations with resistance to carbamates, so Sevin and Lannate should be avoided in those regions if leafhopper control is needed. Capture is a relatively new insecticide with an annual limit of 6.4 oz/acre. MSU research trials have found excellent activity of this product at 3.2 oz, leaving the option of a later-season use of this product if a 3.2 oz rate is used after bloom.

In the selective insecticide group, Intrepid 2F is an effective insecticide for control of grape berry moth. This works on the molting system of the larvae, disrupting normal development, and trials at 8 and 12 oz/acre have provided control of first generation berry moth. Another selective insecticide to consider is B.t. (Dipel, Javelin, Deliver etc.), which only targets the larvae of berry moth. Both of these selective insecticides need to be eaten to be effective, so their activity is greatest when temperatures are above 70°F. Intrepid is highly rain-resistant providing 10-14 days of activity, whereas B.t. formulations degrade under ultraviolet light, providing 3 to 5 days of activity. When applying any insecticides to control grape berry moth, target sprays at the clusters to maximize control.

The take-home message for berry moth management is to scout clusters regularly from just before bloom onwards to understand where the pest pressure is greatest, so sprays can be targeted only where they are needed. This will also provide information on when the pest is developing, and will allow management costs to be focused at times when it makes the most economic sense.

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