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What is it?
Grape berry moths are of the endopiza species and grape berry moths are the most serious insect pest of grapes in the United Staes. Grape berry moths can cause damage from their larval to their adult stage and can cause severe damage to the grape harvest.
What does it look like?
Endopiza species grape berry moths are usually dark green or purplish worms when seen on the grape plants themselves. These worms are typically approximately 3/8 inch long and have dark brown heads. More often than not, you will see the body of the worm sticking out of the grape fruits, but will not see the dark brown heads of endopiza species, because they bury them deep in the fruit of the grape where they feed. Your grapes will have the fruits clustered together by webs that are whitish and look similar to very thin cotton balls or strands of cotton stretched between the grapes. Often the webs of grape berry moths will stretch between a close knit cluster of grapes to a surrounding leaf, or leave cluster. In between the leaves there may be white cottony coccons hanging or nestled amongst the leaves. The webs are formed as the larvae feed on the inner pulp and seeds of the fruit of the grape plant. As they feed, the worms create silken threads which bind the fruit of the grape plant into clusters in their wake. Just one green or purple worm can damage several berries on it’s own. An infestation of grape berry moths can affect an entire harvest. Full grown moths tend to be a purplish or brownish color and are often seen flying around trellised areas of grape vines, or those which grow wild.
How does it manifest?
The purplish brown adult grape berry moths of endopiza species, emerge in the late months of spring and lay eggs on grape blossom ends as well as small grape fruits. Larvae then hatch from the eggs and begin feeding on the surrounding fruits of the grape plant. These green and purple wormlike larvae will also feed on the buds and blossoms of grape plants. Typically the grape berry moth larvae feed for a period of three to four weeks at which time they cut a small section of a leaf, bend it over or in on itself and form a coccoon. The larvae then pupate inside the cocoon and emerge again in a few weeks as mature adult grape berry moths. These purplish brown adult grape berry moths then go on to repeat the cycle of feeding and reproduction again, but this time they will lay eggs on ripening fruit, rather than primarily buds and blossoms. The second generation of grape berry moths produced during the growing season will pupate and overwinter to emerge the following spring and begin the process once again on new grape plant growth.
What can you do about it?
When you notice the tell-tale webbing and cocoons of grape berry moths and their larval worms, remove and destroy all infested grapes and surrounding leaves which may have silken threads attached to them. Stop cultivation for the rest of the summer. This insures that the grape berry moth cocoons will remain on top the soil and can easily be removed with any fallen plant debris or grapes at the end of the growing and harvest season. Additionally, the following year when you plant your grape plants, treat the plants with a diazinon containing insecticide spray at the first sign of bloom. Apply a second application of the insecticide one week later. This should control the first generation of grape berry moths which have overwintered. However, you may need to do a two time application again in mid-summer to handle and second generation which may have erupted from any grape berry moths which survived the first two diazinon treatments.
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