Managing grape berry moth – timing, activity and coverage
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.
Effective control of grape berry moth with the currently available insecticides leaves less room for error in both timing and coverage than was possible in the past. This is because the remaining products either have shorter duration of residual control, or they are specific to fewer life stages of the pest than the broad-spectrum insecticides that had vapor action. Maintaining control of grape berry moth requires a combination of good timing, high insecticide activity and excellent cluster coverage. Our ongoing research addresses each of these components of berry moth IPM, and this update will cover them in turn.
To time sprays for this pest, monitoring traps and weekly scouting of vineyards can be used to know when moths and larvae are active. This can be focused on vineyard hot spots, but it is useful to spread scouting across your farm to know where grape berry moth activity is greatest. Most growers know hotspots on their farm, but this monitoring can also tell you when the pest is active in different blocks.
Moths emerge in late April or early May, usually around 200-250 growing degree days (GDD base 50) from March 1. This year, we saw the first moths in traps on April 22 in Lawton and April 27 in Scottdale. In recent years in a trial in Paw Paw, we have found the first eggs on clusters around 650 GDD, which typically occurs when the number of moths peaks in traps and when the vines are at trace bloom. This year is no exception, as the first few grape berry moth eggs have been detected in a farm in Berrien County where the warm weather has brought the vines and the insect activity forward.
Egg-laying by the spring generation moths increases during bloom, and so if using a broad spectrum insecticide, the 10 days post bloom spray will be an effective way to control the larvae and eggs present at this time. Treatments applied earlier than the post-bloom timing can be washed off or degrade before most of the egg-laying and are unlikely to protect the clusters from feeding by berry moth larvae. 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 (Photo). 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.
Generations 2 and 3
These generations are harder to time sprays for because there is less likely to be a distinct increase in moths in traps and the generations overlap. From our detailed sampling for eggs in borders of high risk vineyards for grape berry moth, we see some egg-laying during the first half of July and a period of more intense egg-laying that starts around berry-touch in early August and continues through until harvest. This may be partly from moths moving into vineyards from the woods, and partly from the offspring of the earlier generations.
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 during bloom.
The selective insecticide Intrepid has shown good effectiveness against berry moth, and we have tested it in the mid-season timings in July and August at the 12 oz rate. Although this is more expensive than many standard insecticides, the product lasts a long time (two to three weeks depending on the rate) and is resistant to wash-off. This helps make it an effective tool to use against the high pressure of egg-laying seen late in the season, when maintaining control would otherwise require multiple sprays. This works on the molting system of the larvae, disrupting normal development and because it is selective, Intrepid will not control leafhoppers or beetles. It also has a 30-day PHI. 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 70ºF. Intrepid is quite stable and resistant to wash-off once sprayed providing good residual control, whereas B.t. formulations degrade under ultraviolet light, providing three to five days of activity.
Most pyrethroids are inexpensive insecticides with broad insect activity. They have relatively short residual control in the hotter summer weather when growers might be spraying for the second or third generation of grape berry moth. In our 2006 trials with Danitol, Baythroid and Capture, the lower rates of these products declined in activity against grape berry moth after nine days. If using a pyrethroid to control grape berry moth along with Japanese beetle in the hot sunny conditions of July or August, using the full rate will provide the best residual control. Despite the temptation to look only at the price per acre when making decisions, be sure to rotate this class with other chemical classes to avoid resistance developing.
Excellent control of grape berry moth has consistently been seen in our spray trials using either Danitol at 10.6 oz/acre or Imidan at 2 lb/acre (and buffered to pH 6). Venom provided good control of the lower, early season populations and is now registered for this use. We also have tested programs containing the new pyrethroid Capture in the first half of the growing season, and this has performed as well as the standard insecticides.
Getting cluster coverage with your spray material is essential for berry moth control. As the canopy becomes denser after bloom, increase the water volume and slow down to ensure the pesticide has a chance to contact the pest. If the spray doesn’t hit the cluster, a significant investment of time and money is being wasted. To illustrate this, our research in a mature Niagara vineyard found that an airblast sprayer operated at 20 gallons of water per acre gave only half the control of grape berry moth compared with one running at 50 GPA. These results emphasize the need to make sure your sprayer is getting good coverage of the clusters, because it can make a big difference for control.