Grape berry moth (Endopiza viteana) is becoming a major insect pest of grapes in Texas and can cause serious economic loss to commercial vineyards. Damage results from larvae feeding on flower clusters and fruit, and from an increased incidence of bunch rot and sour rot that can readily establish on insect-damaged berries. The insect is native to eastern North America where it coevolved with wild grapes; its range has now extended west to the Rocky Mountains wherever wild or cultivated grapes occur. Grape berry moth feeds only on grapes and produces multiple generations per year.
Biology and Behavior
Grape berry moth (GBM) over-winters as pupae in leaf litter on the ground. Because fallen leaves are commonly blown to the periphery of the vineyard or adjacent woodlands during the winter, emergence of GBM adults in the spring tends to be localized in these areas and initial feeding damage to grapes often occurs in proximity to these areas of emergence. Adult moths begin to emerge from pupae prior to the grapevine blooming period, but emergence continues for a month or longer. The small (1/4 inch long), inconspicuous brown and gray moths soon mate and fly to nearby grapevines to lay eggs on flower clusters or newly-formed berries. Later-emerging adults deposit eggs directly on grape berries.
First Generation. The newly hatched larvae represent the first generation of the year and the earliest to hatch feed on tender flower clusters and newly formed berries. Larvae are initially extremely small and creamy white in color. As they grow, they change to green or gray-green and eventually are nearly purple when mature. They often spin a web around several flowers or berries on which they feed. Early larvae feed on flowers and externally on young fruit. They begin to burrow into fruit when berries reach about 1/8 inch in diameter. Feeding initially is just below the skin, creating dark tunnels that are readily apparent. Later the inside of the berry is consumed and usually several berries are damaged and eventually appear shriveled within the fine webbing. Mature, first generation larvae often move to the edge of a leaf where they cut and fold over a flap of leaf to form a pupation chamber. Other larvae will pupate within the fruit cluster where they have fed.
Second and subsequent generations. Adults emerge from the first generation pupae and repeat the reproductive cycle to produce a second generation and more crop damage: mating, egg-laying and larval feeding on berries. Larvae of second and subsequent generations burrow into berries and feed internally. They usually enter where the berry joins the stem or where adjacent berries touch. Larvae often feed successively on 2 to 3 berries and sometimes as many as 7 berries as they grow to a size of about 3/8 inch prior to entering the pupal stage. Mature larvae usually spin down to the ground to construct pupal cells in fallen leaves.
See photos of Signs and Symptoms
It is likely that three or perhaps four generations of GBM are produced each year in Texas. The first two generations are distinctly separated in time, but the third and later generations typically overlap and are difficult to distinguish.
Some degree of GBM control is possible by burning or burying the leaves in which the pupae are over-wintering. Leaves should be covered with 1 inch of compact soil at least 3 weeks prior to grapevine bloom to prevent moth emergence.
Light infestations of GBM can be managed by simply removing injured berries by hand. Moderate to severe infestations of GBM require a management program that may include the use of insecticides.
Insect Monitoring. Infestations of GBM can vary greatly from year to year and within a vineyard so insect monitoring and scouting for damage provides guidance on the need for control measures and their timing. Damage to grape flower clusters from GBM feeding can first be observed by scouting during the early bloom period. Emergence of new adults in the spring and the beginning of egg-laying is closely related to grapevine phenology. Research in Arkansas indicates the first emergence of moths occurs there when growing degree-day accumulations (50oF base) reach between 450 and 700 gdd (Johnson, et al., 2003).
Pheromone traps can be used to monitor the timing of the first adult berry moth emergence. Traps should be installed when shoot growth reaches about 12 inches on the most advanced variety. Strategically place three GBM pheromone traps in vineyard border rows near suspected over-wintering areas (where old leaves have blown or near adjacent woodland). Check the traps twice a week for the presence of GBM and record the date of the first moth capture. A large population of GBM in traps and significant damage to flower clusters or very young fruit indicates the need for early insecticide application. If an insecticide spray is warranted, the first application should be made five days after the first moth was captured. Target this spray application to treat only the grapevine rows experiencing damage, usually the perimeter rows near the GBM over-wintering area.
Emergence of the second generation is fairly predictable by growing degree-days, occurring between 1200-1700 gdd (Johnson, et al., 2003). Scouting the vineyard for GBM feeding damage to berries can be used to monitor the degree of damage from second and later generations. Feeding damage can be identified by an entry hole on the berry that is often surrounded by a conspicuous red or purple spot that may eventually cause discoloration of as much as half the berry. Berry-to-berry tunneling within a cluster may also be observed. Infested berries undergo premature fruit ripening (including coloration on red cultivars) that leads to berry splitting and shrivel. Bunch rot or sour rot diseases often begin in berries damaged by GBM feeding.
Pheromone traps should be moved to the middle of the vineyard about mid-May to monitor second and subsequent generations. Replace the pheromone ampules within the traps every 30 days to maintain freshness. Monitor these traps twice a week and record the date that the first moth is captured. Large numbers of GBM in traps and significant damage to developing fruit indicates the need for an insecticide application. If an insecticide spray is warranted, apply five days after the first moth was captured. Second and subsequent generations of GBM are typically dispersed throughout the vineyard so the entire vineyard should be treated. Insecticide applications may have to be repeated because moth emergence of second and later generations is spread out over time.
Insecticides. Several insecticides (Table 1.) provide good control of GBM, but these should only be used when and where GBM populations have reached significant damaging levels. Follow all pesticide label instructions with care.
|Table 1. Recommended insecticides for grape berry moth control.|
|Material||Rate Per Acre|
|Sevin 50% WP||4 lbs|
|Sevin 80% WP||2.5 lbs|
|Sevin 4F||2 quarts|
|Imidan 70%WP||1.3-2.2 lbs|
|Danitol 2.4 EC||10.6 fl. ozs.|
Mating Disruption Strategy. An alternative to conventional insecticide control for vineyards of at least 5-10 acres is disruption of GBM mating by the use of pheromones. This approach permeates the vineyard atmosphere with GBM pheromone, disrupting the ability of male moths to locate females for mating. Mating disruption is recommended by Virginia Tech University, but has not been tested in Texas. The strategy is implemented by installing pheromone dispensers (Isomate GBM Plus) prior to moth emergence at a rate of 200-400 dispensers per acre (high rate for high-risk vineyards). The dispensers are rope-style and are easily attached to the upper training wire of the trellis.
It should be noted that the level of control may be significantly reduced if mated females are present in adjacent vineyards or on nearby wild grapevines. Some disadvantages of this method are that it controls only one insect and the strategy is likely to fail in smaller vineyards. The per-acre cost of Isomate GBM Plus is higher than insecticide sprays, but the advantages are that it provides season-long control, does not affect beneficial insects, and is completely non-toxic to mammalian life.
Under circumstances of frequent high populations of GBM some producers choose not to employ the IPM monitoring methods of trapping and scouting. Instead, it is assumed that high GBM populations are present and an insecticide application will be needed. The insecticide is applied seven days after full bloom (90% caps off) to control the first generation.
Grape Berry Moth. New York State Integrated Pest Management Program.
Johnson, D., R.K. Striegler, B.A. Lewis, and C. Lake. 2003.Crop Profile for Grapes in Arkansas. University of Arkansas.
Longstroth, Mark. Grape Berry Moth Fruit IPM Fact Sheet. Michigan State University Extension.
Pfeiffer, D.G. 2003. Mating Disruption for Grape Berry Moth in Virginia Vineyards. Virginia Tech University.