Fruit IPM Fact Sheet
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Grape Berry Moth

Mark Longstroth, District Extension Fruit Educator

The grape berry moth (Endopiza vitana Clemens) is a major pest of grapes in Michigan. It is native to the eastern United States where it originally occurred on wild grapes. The grape berry moth feeds only on grapes and usually has two or three  generations a year in Michigan. When vineyard are left unsprayed, up to 90% of the berries may be destroyed

Life History

Grape berry moth pupae overwinter in cocoons within folded leaves and debris on the vineyard floor. Adult moths begin to emerge from overwintering pupae in mid to late May before blossom in Concord. After emerging the adults mate, and the females lay eggs on or near grape flower clusters. Emergence of the overwintering generation peaks in mid-June and continues to mid-July. Larvae that hatch in June make up the first generation. First generation adults begin to fly in late July and flight peaks in early August. But adults continue to emerge until early September. Larvae of the second generation complete their development in late September and build cocoons in which they overwinter. In years with hot long summers there may even be a third generations of larvae. This occurred in Michigan in 1995 and 1998.
The adult grape berry moth is a small inconspicuous brownish moth with a slate gray saddle in the middle of its back when it is resting. When resting it is about 3/8 inch (6 mm) long. Its wingspan is 1/3 to 1/2 inch (9 to 12 mm). During most of the day the moths rest on the vines. Around mid- to late afternoon they become active and their rapid, zigzag flight can be observed until after dusk.
In early spring, eggs are laid singly on buds, stems, or newly forming berries. Later most eggs are laid directly on the berries. Depending on the temperature, eggs hatch in 4 to 8 days. The opaque white eggs are oval, scale-like and measure only 0.7mm. They can usually be seen only with a hand lens.

The newly hatched larva is creamy white with a dark brown head and thoracic shield. As they grow the body becomes greenish and eventually turns purple. The head of the mature larvae is light brown but the thoracic shield remains dark brown. Mature larvae are 1/3 inch (10 mm) long.
In early Spring, larvae feed on tender stems, blossom buds and berries. Often they feed inside webbing which can involve the whole cluster. Larvae that attack grape clusters at this time are difficult to see. Growers need to examine flower or berry clusters for webbing before and after bloom. A protective insecticide may be needed to prevent damage in heavily invested areas. When the berries reach 3 mm in diameter, larvae begin to burrow into them. Often larvae feed successively on 2 to 3 berries. Mature first generation larvae move to a leaf where they cut out a circular flap to construct a pupation chamber. Some larvae pupate in the fruit cluster where they have fed. It is not unusual in Michigan to have both first and second generation larvae in the vineyard.

Second generation larvae tunnel directly into the fruit and feed internally. Conspicuous red or purple spots develop on "stung" berries at the point of entry. Second generation larvae usually enter where the berries touch each other or where the berry joins the stem. The larvae feed just below the skin, but eventually the inside of the berry is attacked. Larvae feed on berries in succession and up to 7 berries may be destroyed. Most second generation larvae spin down to the ground where they construct pupal cells in fallen leaves and debris. Infestations by grape berry moth can vary greatly from year to year and are often uneven in a vineyard.

Damage

The damage by first generation larvae can be serious since a single larvae can destroy a dozen or more potential berries by feeding on buds and flowers. Late first and all second generation larvae feed only on the berries. The second generation is potentially more damaging than the first. A single larvae can destroy a half dozen berries in a cluster, and several larvae may inhabit a single cluster. Injured berries ripen prematurely, split open and shrivel. Webbing produced by larvae prevent the berries from dropping. Larvae feeding directly reduces yield and contaminates the crop. More importantly, feeding by larvae creates infection sites for fruit rots and feeding by fruit flies. At harvest, severely infested bunches may contain several larvae, and many berries which are completely hollowed out. In many cases, the bunch is covered with bunch rot fungi, infested with fruit flies and appears unhealthy.

Monitoring and Control

In light infestations, injured berries can be removed by hand. Several cultural methods have been used in the past to reduce the overwintering generation. Some control can be achieved by removing and destroying leaves with pupal cells in the fall. Covering leaves with cocoons under the trellis with one inch (2.5 cm) of compacted soil will prevent emergence. This operation must be completed 3 weeks ahead of bloom.
Where grape berry moth is an annual problem, post bloom sprays of insecticides may be necessary and mid- and late summer may be needed to control the second generation. The number of spray applications depends on the amount of invested berries a grower is willing to accept. Table grapes require more attention that grapes grown for juice.
Sex pheromone traps may be used to monitor the emergence and flight of male moths to determine the emergence of generations and improve the timing of sprays. In general, pheromone trap catches are not a reliable method for determining pest populations in the vineyard, but the information is useful in timing insecticide sprays. Because of the spotty nature of grape berry moth infestations, a minimum of 3 traps for monitoring is recommended. Traps should be placed around the perimeter of the vineyard and should be at least 100 feet apart. Traps should be checked weekly for moths and the pheromone caps replaced monthly to obtain accurate trap information. Each vineyard location is unique and growers should not rely on trap data from other vineyards to time insecticide sprays.
Scouting vineyards is necessary to determine grape berry moth activity. Scouting for eggs is not productive. Adults are unlikely to be seen unless caught in pheromone traps. A trained eye can recognize them flying in the late afternoon. Signs of larval feeding are the easiest to find. Examine fruit clusters after bloom for evidence of webbing in the clusters. This will give an indication of Initial numbers of overwintering moths. Later examine fruit clusters for stings indicating larvae entry. This is not effective for white grape varieties.

See the MSU Grapes Website for more information on Grape berry moth and grape scouting reports.

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Created: March 21, 1997
Last modified: May 31, 2007