Grape Grower's Tips: Information On Grape Leaf Skeletonizers

Clusters of yellow striped caterpillars feeding on your grape leaves are grape leaf skeletonizers. Instruction on how to deal with the pest.

What is it?

Grape leaf skeletonizers are of the harrisina species and frequently attack grapes in home gardens as well as plants in abandoned vineyards. Grape leaf skeletonizers are troublesome not only due to the damage they do the the grape plants, but also because if touched by human or animal body parts these insects have black spines which may cause welting and pain.

What does it look like?

Harrisina species grape leaf skeletonizers are yellow caterpillars which have black stripes on their bodies. Often these stripes may also appear to be purple if they are slightly lighter. These pesky caterpillars are covered in black spines along their colored stripes. Damage from grape leaf skeletonizers can be severe as these harrisina species insects feed on the grape leaves, consuming absolutely everything except the actual leaf veins. The caterpillars ususally begin feeding on the topside or underside of the grape leaves and will feed in rows. If you have one grape leaf skeletonizer, you have many and they are usually seen in clumps or groups feeding on a single leaf.

How does it manifest?

Grape leaf skeletonizers over winter in cocoons either on leaves or plant debris that has fallen to the ground. In late spring the adult form, which is a smoky black or metallic green moth, emerges and takes flight. The adult female grape leaf skeletonizers then lay their eggs on the undersides of the grape leaves. Later, the striped yellow caterpillars emerge from under the leaves and begin to feed on the leaf they hatched from. Usually they chew the surface layer on the topside of the leaf, then repeat the process on the bottom of the leaf. Once the leaf is thus weakened and as these insects mature they begin to feed on the actual leaf tissue between the veins of the leaf. Grape leaf skeletonizers are healthy eaters and can easily defoliate a grape plant vine in a matter of several days. Two or three generations of grape leaf skeletonizers are viable every year so the damage continues from mid-May when the moths first emerge to late August.

What can you do about it?

Grape leaf skeletonizers can be controlled by the application of a carbaryl containing insecticide. You must be sure to spray both the topsides and the undersides of the grape leaves. One treatment typically will take care of the infestation if you are diligent about application of the insecticide. However, treatment with carbaryl can be repeated if you wait at least ten days. Additionally, be sure to clear away all plant debris and fallen leaves in the area after your harvest to prevent grape leaf skeletonizers from overwintering there. You should also be very careful not to touch grape leaf skeletonizers with your bare hands as the black spines they are covered with will prick you and can cause serious, painful welts.

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