Tederson Galvan, Suzanne Wold-Burkness, and E.C. Burkness, Department of Entomology, University of Minnesota
The grape berry moth (GBM), Endopiza vitana Clemens (Lepidoptera: Tortricidae), is a major pest of grapes in the Eastern U.S., and is capable of causing serious economic loss to commercial vineyards in the Midwest. It is native to the eastern United States, and can be found as far west as the Rockies. The grape berry moth feeds only on grapes and has two to three generations per year in Minnesota. Damage is caused by larvae feeding on flower clusters and fruit.
The adult grape berry moth is an inconspicuous, mottled brown-colored moth with a bluish-gray band on the inner halves of the front wings. It is approximately 1.2 cm long, with a wingspan of 0.8 to 1.3 cm. The newly hatched larva is creamy white with a dark brown head and thoracic shield. Later instars are green to purple in color, and are 0.8 cm in length when fully grown.
Biology & Life Cycle
Grape berry moths overwinter as pupae within curled grape leaves and in the leaf litter along the edges of woods and under vines. Adult moths emerge in mid to late May, and mate. Females lay eggs on or near grape flower clusters. Larvae hatch from eggs in 4-8 days, depending on temperature. Emergence of the overwintering generation peaks in mid-June and continues to mid-July. Larvae that hatch in June make up the first generation. Larvae feed on stems, blossom buds, and berries. Often they feed inside webbing which can cover the entire cluster. Larvae will burrow into berries that are 0.3 cm in diameter, and will successively feed on 2-3 berries. When the first generation is mature, larvae either move to a leaf where they cut out a circular flap to construct a pupation chamber or pupate in the fruit cluster where they fed.
First generation adults begin to fly in late July, and the flight peaks in early August, however, adult moths continue to emerge until early September. Second generation larvae usually burrow into berries where they touch or where the berry is connected to the stem. Conspicuous red spots develop on the berries at the point of larval entry, and are referred to as “stung” berries. Larvae of the second generation complete their development in late September and pupate in fallen leaves and debris on the ground. Typically this is the 2nd and last generation of the year but with high summer temperatures a 3rd generation may be possible.
The larvae cause economic injury in three ways: 1) contamination of fruit, 2) reduction in yield, and 3) entry points for diseases.
Late-instar first generation larvae, and all larval instars of the second generation feed only on the berries. Injured berries ripen prematurely, split open and shrivel. Webbing produced by larvae prevents the berries from dropping. Feeding by GBM larvae not only reduces yield and contaminates the crop, but their feeding creates infection sites for fruit rots and feeding by fruit flies. At harvest, severely infested clusters may contain several larvae. Wine made from this fruit may be poor quality.
Most vineyards have either consistently high or low damage from GBM each year. Because of this, researchers at Cornell have come up with a relatively simple risk assessment that growers can use to assess the potential threat of GBM damage in their vineyard. Three major factors that predict GBM damage severity in a vineyard are 1) whether vineyards are bordered by wooded areas or hedgerows, 2) winter temperature and snow cover in the vineyard and 3) GBM infestation history in the vineyard. See the 1991 publication, Risk Assessment of Grape Berry Moth and Guidelines for Management of the Eastern Grape Leafhopper, for more information http://nysipm.cornell.edu/publications/grapeman/files/risk.pdf
Grape Berry Moth pheromone trap (E.C. Burkness & T.L. Galvan, U of MN)
Sticky traps with a pheromone lure can be used to monitor GBM emergence. Traps should be placed in the vineyard in the early spring, prior to bloom (see picture, left). A minimum of 3 traps/10 acre vineyard block should be used. Traps should be hung from the top wire of the trellis, and placed around the perimeter of the vineyard. Check the traps twice a week for the presence of GBM and record the date of the first moth capture.
Visually examining grape clusters is necessary to determine the severity of grape berry moth damage. As a part of the Cornell IPM program, the following sampling protocol is recommended: select four areas in the vineyard to be sampled (two in the center of the vineyard, and two on the edge of the vineyard). Visually inspect, at random, 10 clusters on each of five vines (a total of 50) in each of the four areas. Record the number of GBM-damaged clusters in each area. Compute separate totals for the center areas and the edge areas to determine the percentage of damaged clusters. For the July sampling date, treatment should be applied if the percentage of the clusters with damage exceeds six percent.
Cultural & Physical Control
Destroying dead leaves may reduce grape berry moth emergence in the spring. In addition, burying leaf litter covering leaves with one inch (2.5 cm) of compacted soil will prevent emergence. Both of these actions must be completed three weeks prior to bloom.
In light infestations, injured berries can be removed by hand; however this may not be a feasible option for larger vineyards.
Trichogramma spp. (Hymenoptera: Trichogrammatidae), an egg parasitoid, can provide some control of GBM. However, since grape berry moth is not a preferred host, relying solely on the resident population of Tichogramma spp. is unrealistic. Instead, augmenting the population with releases of Trichogramma sp. may be necessary to provide noticeable control. In New York, Cornell researchers made inundative releases of T. minutum and found significantly lower levels of berry injury from GBM in plots where releases were made, compared to control plots and plots treated with conventional insecticides
Where grape berry moth is an annual problem, post bloom sprays of insecticides may be necessary, and mid to late summer may be needed to control the second generation. The number of spray applications depends on the amount of infested berries a grower is willing to accept. Several insecticides provide good control of GBM, and can be found in the Midwest Small Fruit Pest Management Handbook.
Mating disruption is based on the principle that when a specific pheromone is released in the air in sufficiently high quantity, the males are unable to orient to the natural source of pheromone, and fail to locate the calling female which prevents reproduction. The strategy is implemented by installing pheromone dispensers (Isomate GBM Plus, http://www.pacificbiocontrol.com/Labels%20&%20MSDS_files/GBMPlus-1PP(2004,Dec).pdf) prior to moth emergence at a rate of 200-400 dispensers per acre (higher rates for high-risk vineyards). The dispensers are easily attached to the upper training wire of the trellis. This strategy has proven effective in both Eastern and Midwestern states.
Bordelon, B., M. Ellis, and R. Foster [eds.]. 2007. Midwest Commercial Small Fruit & Grape Spray Guide. http://hort.agriculture.purdue.edu/pdfs/07SprayGuide.pdf
Ellis, M. D. Doohan, B. Bordelon, C. Welty, R. Williams, R. Funt, and M. Brown. 2004. Midwest Small Fruit Pest Management Handbook. The Ohio State University Extension. pp. 125-129. http://ohioline.osu.edu/b861/
Martinson, T. E. C. J. Hoffman, T. J. Dennehy, J. S. Kamas, and T. Weigle. 1991. Risk Assessment of grape berry moth and guidelines for management of the Eastern grape leafhopper. New York’s Life Sciences Bulletin. 138: 1-9.
Weigle, T. H., and A. J. Muza [eds.]. 2007. New York and Pennsylvania pest management guidelines for grapes. Cornell and Penn State Cooperative Extension. http://ipmguidelines.org/grapes/.