Late Season Insect Management
By: Michael Saunders
Well, the grapevines are primed for harvest and the main summer pests are hopefully a distant memory. However, there are still a few insect pests that can bedevil vineyards right up until harvest. Some of the more problematic insects in vineyards at this time of year are wasps and hornets. Typically, they will not feed on grapes until late in the season when these sugar seeking foragers find that the grape crop has become palatably sweetened. Unlike honey bees, which rely on pollen as their protein source, wasps acquire their protein by hunting other insects, many of which are agricultural pests. So, for the majority of the growing season, yellow jackets, paper wasps, bald faced hornets and other Hymenopterans (collectively called wasps) have been quietly and beneficially reducing the populations of other pest insects.
As we approach harvest, wasps are particularly drawn to easily acquired sources of carbohydrates, and the juice of a ripe grape is exactly what they are looking for. There was an excellent presentation on wasp and bee management in grapes by Jody Gangloff-Kauffman at a grape grower meeting in Lancaster in 2013. This presentation is available online at:
Dr. Kauffman’s presentation emphasizes vineyard sanitation as a key factor in minimizing damage due to wasps and bees. She describes a number of procedures for destroying the nests of wasps that are in the vicinity of vineyards as well as traps that can be deployed during the season to reduce their numbers. It is important to bear in mind that these insects in general are beneficial and important regulators of pest insect populations. The best defense is to protect your crop from berry damaging pests, especially birds, as these damaged berries are the main attractant for wasps and bees. Often a grower will blame wasps for berry damage when, in fact, the wasp is merely taking advantage of berries that have been damaged by birds. There is no viable chemical control for wasps in the vineyard.
Perhaps we should not be focused so much on controlling populations of wasps in vineyards given the ecology of the ambient yeasts. It appears that some species of wasps carry Saccharomyces cerevisiae (brewers yeast) in their stomachs and can pass it along to their offspring. Some researchers believe this yeast is ubiquitous in some vineyards because of the wasps, although the connection between the wasp, its associated yeast, and yeasts in the vineyard will need further study. For more on this phenomenon visit: http://www.winespectator.com/webfeature/show/id/47188
Other insects that may be found in late season vineyards include a collection of relatively new invasive species. These include the brown marmorated stink bug, the spotted wing drosophila, and the multicolored Asian Lady Beetle. The brown marmorated stink bug (BMSB) was initially found in Allentown, PA after it was introduced from Asia. This insect has spread across several states and currently is a very serious pest in tree fruits and vegetables, and can be a household nuisance in that BMSB often enter homes in order to overwinter as adults. There is a very large consortium of institutions researching BMSB life history traits, population dynamics, and assessment of damage thresholds in multiple cropping systems. Although the damage potential of BMSB in vineyards appears to be significantly less than what is found in other types of crops, there was serious initial concern that the odor (taint) of this insect would adversely affect wine quality. Work done by Joe Fiola has indicated that BMSB taint is unlikely to persist in finished wine.
The spotted wing drosophila (SWD) is an invasive fruit fly (native to Asia) that differs from most of our native fruit flies in that the female SWD has a serrated ovipositor that allows her to directly pierce the skin of fruit in order to lay eggs. Native fruit flies lay eggs only into previously damaged fruit. SWD can have many generations per year leading to great concern for fruit crops as this insect becomes widely established. Although raspberries, blackberries, and blueberries are the fruit crops most seriously affected by SWD, careful monitoring of any soft skinned fruits (including grapes) is warranted. There is excellent information on identification, monitoring, trapping, and damage detection by SWD at: http://extension.psu.edu/pests/ipm/agriculture/fruits/spotted-wing-drosophila
The multicolored Asian Lady Beetle (MALB) has been somewhat of an enigma in recent years. Like all lady beetles, MALB are voracious predators of other insects, and are considered a valuable biological control agent in many agroecosystems. This insect (again a recent invasive from Asia) protects itself via a process known as reflex bleeding in which it extrudes bodily fluids out of its joints. These bodily fluids contain alkaloids that can taint the flavor of wines should the insect be processed with the harvested grapes. Since MALB tend to seek sources of carbohydrates before overwintering, it is possible that this insect will be present in grapes during harvest. As recently as 6 years ago, it appeared as if MALB was going to be a major problem with massive populations developing in the late summer. Since that time, MALB populations have not been as numerous and the concerns over this insect and its impact on wine production have lessened.
As you approach harvest, be sure to take the time to check your vineyard for the presence of these pests. If you plan to use any insecticides, be very mindful of the preharvest restrictions and be sure to use all appropriate safety equipment.