Description and Life Cycle
This is the major insect pest of grape berries in the eastern United States and Canada. When vineyards are left unmanaged up to 90 percent of the fruit often is destroyed by the larvae and the diseases facilitated by the damage inflicted upon the fruit. Infestations vary greatly from vineyard to vineyard, from year to year, and within a vineyard. However, vineyards bordering wooded areas are most vulnerable.
The adult is a mottled-brown-colored moth with some bluish-gray on the inner halves of the front wings. The larvae of this small moth are active, greenish to purplish caterpillars about 3/8 inch long when fully grown. Grape berry moths overwinter in cocoons within folded leaves in debris on the vineyard floor and within adjacent woodlots. After emerging in the spring, the adults mate, and females lay eggs on or near flowers or berry clusters. Newly hatched larvae feed upon the flowers and young fruit clusters. Larvae that hatch in June make up the first generation of grape berry moth and will mature from mid to late-July or August. After mating, females lay eggs on developing berries, and this second generation matures in August or September. Larvae of the second generation, after completing their development, form cocoons in which they overwinter. A third generation occurs commonly in the southern range of the pest and occasionally in the northern tier of states.
First-generation larvae web small flower buds or berries together in early June and feed externally on them or on tender stems. Larvae that attack grape bunches during this time are difficult to see.
Second generation larvae tunnel directly into the green berries and feed internally. Conspicuous reddish spots develop on the berries at the point of larval entry. Berries affected in this manner are known as "stung" berries. The second generation is potentially more damaging than the first. A single larva may destroy 2 to 6 berries in a cluster, depending on berry size, and several larvae frequently inhabit a single cluster.
At harvest, severely infected bunches may contain several larvae, and many of the berries may be completely hollowed. In many cases, bunches are covered with bunch rot fungi and infested with Drosophila spp. fruitflies, and often having an unhealthy appearance.
Management (How to survey vineyard to determine percentage of clusters damaged.)
A protectant insecticide may be needed to prevent damage in areas heavily infested by grape berry moth. The number of spray applications depends on the amount of infested berries the grower is willing to accept. Table grapes require more attention than grapes grown for juice. Corrective measures are usually suggested if more than 5% of the clusters are injured. To determine the percentage of clusters damaged you should randomly inspect 100 clusters along the perimeter of the vineyard and 100 clusters toward the center of the vineyard. This method will tell you if treatment of the entire vineyard is necessary. Treatment of perimeter rows maybe all that is necessary to control this pest. Control of maturing larvae in mid-to late-July is particularly important.
Cultural controls can be used to kill the overwintering pupae in leaves. Leaves can be gathered and destroyed in the fall, or leaves can be buried within the soil in the spring, 2 weeks before bloom, by rototilling or cultivating.
An alternate method of control using pheromone rope ties to disrupt the males of the grape berry moth was approved by the EPA in 1990. This method prevents mating, thus reducing the number of fertile grape berry moth females in a treated vineyard. This method is most effective in vineyards at least 5 acres in size. Ties are dispensed manually at a rate of 400 ties per acre. When a vineyard is under heavy pressure from berry moth, it may require spot treatment with an effective insecticide at the source of the infestation. Studies indicate that vineyards in close proximity to external berry moth sources such as woodlots, may require an application of insecticide in addition to the ties for control of this pest. Vineyards utilizing these ties should continue to scout their plantings in the same manner as previously mentioned. If thresholds are reached the decision to apply an insecticide should be considered.
Monitoring Male Moths
Pheromone traps are available to monitor the emergence of male grape berry moths during the season. This information may be useful for optimal spray timing; sprays should target egg hatch and young larval activity, which occurs several weeks after the first moths are trapped. A minimum of 3 traps for monitoring a single block of approximately 10 to 15 acres is recommended. Traps hung from the top wire of the trellis should be placed around the perimeter of the vineyard before bloom and should be at least 100 feet apart. Sticky trap bottoms should be checked weekly for moths, and pheromone caps should be changed monthly to obtain accurate flight information. Every vineyard location is unique, and growers should not rely on pheromone trap data from other vineyards for timing insecticide sprays.
Pheromone traps should be utilized in vineyards with a history of grape berry moth problems. Trapping of adult male moths indicates the beginning of flight activity. Mating and egg laying will occur over a 2 to 3 week period following the first detection of flight activity. A protective cover spray may be required during this period to prevent egg laying and hatch. Early season control of this pest may prevent it from becoming well established within the vineyard, and may eliminate the need for control later in the season. It should be noted that the second flight activity period occurring in late July and August is the most important. These adult moths in late summer produce the eggs which hatch into larvae capable of causing major damage to the maturing fruit. One should not solely depend upon a pheromone trap for detecting this late season threat. Scouting should be implemented on a weekly basis after bloom. If berry cluster damage reaches 6% in grapes used for processing or 3% in those grown for fresh market, a protective cover spray should be applied.
Current pesticide recommendations may be found HERE