Late harvest insect problems
By: Jody Timer, Entomology Research Technologist, Erie County
The grape berry moth (GBM): The most destructive grape insect pest in the Eastern US is the native Grape Berry Moth, Paralobesia viteana. This insect is becoming increasingly harder to control as result of shorter residual time of insecticides, resistance to insecticides, and abandoned vineyards. GBM larval burrow into the grape berry soon after hatching, making precise timing of spray applications a critical component of control. This insect has four generations per year. Each generation increases in number exponentially if control measures are not applied to the early generations. Although in early season this insect pest has distinct peaks in generational emergence, by August the peaks have overlapped making complete control almost impossible. Growing areas with large populations require a second generational spray in July and/or August. If these sprays have not been applied and there are GBM problems in your vineyard, it is a good idea to spray for this fourth generation in September. Spray timings can be calculated by following the NEWA model recommendations. Although much of the damage may have already occurred, this spray will help prevent the generations from starting the season next year farther into your vineyard. If you are dropping your crop from the end rows because of the excessive berry moth damage, collecting the dropped grapes as opposed to dropping them under the trellis will greatly reduce overwintering populations from remaining in your vineyard. More GBM information can be found on extension pages and on the LERGP Podcasts.
Spotted wing drosophila (SWD): Spotted wing drosophila, Drosophila suzukii,(SWD)is an invasive vinegar fly of East Asian origin that was recently introduced into the United States. It was first found in Pennsylvania in 2010. The potential infestation rate of spotted wing drosophila differs from other vinegar flies because the female possesses a serrated ovipositor that cuts into healthy fruit to lay eggs. Consequently, spotted wing drosophila (SWD) larvae can be found in fruit that is just ripening. During egg-laying, it is believed that sour rot and fungal disease can also be introduced, further affecting the fruit quality. All fruit flies carry yeast which can affect the quality of wine if these flies are present during winemaking. During peak temperatures, a female can lay more than 100 eggs a day. Such a high reproduction rate indicates the SWDs’ high potential for fruit infestation and their potential for spreading rapidly through a vineyard, with multiple generations occurring each year. Spotted wing drosophila is now one of the most serious pests of thin-skinned fruits including grapes. At this time, no action threshold is available for SWD, so the common recommendation is to increase monitoring when one fly is captured on a farm and began a spray regiment continuing through harvest, making sure to protect fruit through to harvest using registered insecticides. Female SWD are able to lay eggs into fruit from the time of first coloring through to harvest, so this period is the window of susceptibility to SWD. Because SWD populations tend to increase in the later part of the summer, we expect late-harvested fruit, such as grapes, to experience higher pressure from SWD than those that are harvested earlier in the summer such as strawberries and summer red raspberries. A number of registered insecticides have been very effective against SWD in laboratory trials, the most effective chemicals are organophosphate, pyrethroid, and spinosyn class insecticides. Under field conditions, insecticides with fast knockdown activity have performed well at protecting fruit immediately after application. When SWD are detected it is recommended that the spray intervals be tightened to prevent crop infestation before and during harvest.
Spotted Lanternfly (SLF): This newest invasive insect has the potential to be devastating to the grape growing industry. Its preferred host is the Tree of Heaven (Ailanthus altissima) and grapevines. SLF aggregate feeds on vines by piercing the vines and feeding on the phloem and xylem. This feeding causes intracellular damage as the insects siphon vast amounts of phloem which reduces the vine’s health and vigor. The insects excrete honeydew and the feeding sites leak sap, which causes sooty mold to form on the leaves reducing the photosynthesis. The sap also attracts secondary pests such as wasps and bees. The wounds make the hosts more susceptible to disease. Systemic chemicals are preferable and highly effective, but insect feeding is still damaging as there is a constant influx of insects from forest margins. Eggs are laid at the end of the season and the adult insects die. If discovered, egg masses should be removed immediately. Thirteen counties in southeastern PA are now under quarantine for this insect.
Multicolored Asian ladybird beetles (MALB): Although these insects cannot be effectively sprayed at harvest, vineyards should be scouted prior to harvesting to see if they are present. MALB feeds on damaged fruit and causes taint to wine and juice in very small numbers if harvested with the grapes.