What’s Bugging Your Vines?
By: Jody Timer
Insect problems in the vineyards do not stop after bloom when Rose Chafer, Flea Beetle, Banded Grape Bug and other early season insects cease to create problems. This blog will briefly describe other important insect pest to be aware of during the ensuing months of the grape growing season.
The grape berry moth remains the most important grape insect pest. Their numbers exponentially increase during the growing season with each subsequent generation. GBM larvae feed directly on berries causing yield loss as a result of loss of berries and crop rejection. In addition, feeding injury provides entry points for fungi and bacteria which can cause cluster rots. This year the Erie County grape growing region has experience extremely high infestation rates during the first generation. Scouting each of your vineyards, paying close attention to wooded edges, is critical to GBM management and will divulge if this pest is present in your vineyard. Infestation can be determined by looking for any of the following signs; holes in berries, webbing in clusters, splits or dark tunneling underneath berry skin, reddish or brown discoloration of berries, and frass in injured berries. A scouting protocol and assigning a GBM risk rating is outlined in “Bulletin 138, Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper”. Scouting can also help growers decide if spraying the entire vineyard is necessary or, if the injury is confined to the wooded edges, just applying a spray to that portion of the vineyard. Spraying just the edges as opposed to forgoing a spray completely will help prevent GBM from moving further into the center of the vineyard with each generation. It is important to time the sprays for GBM to coincide with the generational peaks. Once the GBM larvae are inside the berries, the sprays become ineffective. There are NEWA weather stations throughout the state which can be accessed through Cornell’s NEWA website http://newa.cornell.edu this has been described in previous blogs. When choosing a spray material to apply to GBM infections unfortunately, you get what you pay for. With some minor exceptions, the quality of GBM materials relate closely to the price of those materials. GBM materials seemed to be priced relative to their effectiveness. Anecdotal observation shows crop losses have the potential to exceed 90% if inexpensive materials are used.
We have received many inquiries regarding Japanese beetle damage; questioning how much damage is acceptable before spraying becomes necessary. The simple answer to this is: “It depends on what type of grapes you are growing.” Managing adult Japanese beetles is challenging because of the large numbers that can occur throughout the summer. The hard bodies of the Japanese beetles make them relatively unattractive to many predators. During the latter part of the growing season, several growth processes take place within the vine which requires carbohydrate supplies. Under favorable environmental conditions, the leaves supply the needs of all these carbohydrate sinks. However, premature defoliation or a reduction in effective photosynthetic area within the vine canopies caused by Japanese beetles can adversely affect vine health. Japanese beetles show strong preference for susceptible vines. They prefer Vitis vinifera, followed closely by hybrids, and then juice grapes. Scouting for Japanese beetle is relatively easy. They feed primarily on the top portions of the vines, and are easy to spot especially between 12 p.m. and 2 p.m. Monitoring traps baited with floral lure (for female) and sex pheromone (for male) are very effective at attracting beetles, however, they must be used sparingly because they attract beetles to your vineyard and do not trap and kill all of the beetles. Like most insects they are more abundant at the vineyard borders. When making spray decisions for Japanese Beetles an important factor to consider is: how much damage are they actually causing. Concord vines can stand up to about 30% damage to leaves without suffering damage to the vine. It is essential to remember this percentage is all the leaves not just the top leaves. Also, a percentage of leaf damage is usually lower than growers estimate by just observing the leaves. In a study by Rufus Isaacs of Michigan [http://www.isaacslab.ent.msu.edu/Images/talks/Isaacs%20Viticulture%202010%20JB%20for%20web.pdf] he discovered that in Seyval vines, natural levels of Japanese beetle feeding (6.5% leaf area loss) had no effect on vine growth or fruit quality. Intensive feeding after verasion inside cages (11% leaf area loss) reduced fruit quality. Newly planted and younger vines cannot tolerate Japanese beetle damage as well as established vines.
The spotted wing drosophila (SWD) has become widely established in Pennsylvania over the last couple of years. This insect has many generations per year which leads to their abundance late in the grape growing season. This fruit fly is of importance because it possesses a serrated ovipositor which allows the females to lay their eggs directly into undamaged fruit. These eggs hatch in the fruit and the larvae will then consume the fruit from the inside out. Their microscopic holes also establish pathways for fungi and bacteria to enter the grape berries. Although raspberries, blackberries, and blueberries are the fruit crops most seriously affected by SWD, our research has shown that they will attack all varieties of grapes. The easiest way to monitor for SWD is by simple plastic cup traps containing apple cider vinegar. To determine if they are infesting your grapes it is recommend that you place undamaged grapes in a salt solution and observe if larva float to the top. 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 brown marmorated stink bug (BMSB) is currently a very serious pest in tree fruits and vegetables, and can be a household nuisance. Although BMSB prefer other fruits and vegetables to grapes, they do feed on grapes. Their damage can cause ugly scars on table grapes and grapes grown for sale at fruit stands. This type of damage is not important to juice growers, however, the holes open pathways for fungal and bacteria late season infections. They may also be easily harvest with the grapes. The insects tend to move to the interior of the cluster when disturbed and are hard to see. When killed they give off a foul odor which is how they got their name. Our research has shown that this odor and resulting taste do not survive the pasteurization of juice grapes. There is conflicting research on whether this taint transfers to wine, more research is ongoing. BMSB can be most easily found by putting a cloth under a grapevine and shaking the grapevine. These insect will then, in most cases, drop to the cloth. There are traps commercially available to trap these insect, but their efficacy is very low.
Asian Lady Beetle (MALB) has not been seen in abundant numbers in the past four years. MALB are predators to many insects and are considered a valuable biological control agent in many agroecosystems. When there is a larger than average population of MALB as there was 5 and 6 years ago, they become a problem late in the season. When injured or alarmed they secrete bodily fluids containing alkaloids which 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, they will congregate on ripened grape injuring the grapes and possibly being harvested with the grapes. 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
Life cycle information for the majority of the important grape pests can be found at: http://www.nysipm.cornell.edu/factsheets/grapes/ ; NY IPM Program; Grapes.msu.edu; Mid-Atlantic Vineyards Grape IPM; and Ontario GrapeIPM.