Common Insect and Mite Pests of Grapes in Iowa

Common Insect and Mite Pests of Grapes in Iowa

Prepared by Donald R. Lewis
Department of Entomology, Iowa State University February, 2001

Buds:

Foliage:

Roots and Stems:

Buds

Symptoms	Comments	Controls
At bud swell: holes in ends and sides of buds. Severe bud damage prevents berry production. At 10-inch shoot: Irregular holes in leaves; skeletonization	Look for dark metallic blue or green beetle 3/16 inch long. Damage is not significant after buds exceed ½ inch in length. Look for gray-brown elongate larvae up to ¼ inch long	- Establish vineyard away from grape-infested woodlands. - Monitor for beetles at bud break. Spray if more than 4% of buds are damaged. - Treatment for larvae is rarely justified.

Flower Clusters / Berries

Grape Berry Moth

Symptoms	Comments	Controls
June: flower buds and berries webbed together, with hard-to-see caterpillars feeding on surface. August to Harvest: Red spots on “stung” berries; hollow or caterpillar-infested berries; bunches covered with bunch rot fungus.	Small caterpillars up to 3/8 inch long. Caterpillars cut flaps and pupate inside grape leaves.	- Monitor and spot treat heavily infested areas (especially borders). - Gather or rototill leaves 2 weeks prior to bloom. - Pheromone traps for monitoring male moths. - Pheromone rope ties for mating disruption.

Yellowjackets and Paper Wasps

Symptoms	Comments	Controls
Wasps and “bees” feeding on ripe grapes.	Wasps are beneficial predators early in the season, and scavengers on sweets late in the summer.	- Destroy nearby nests if found. - Prevent nesting with spring baiting. - Harvest frequently and thoroughly.

Foliage

Rose Chafer

Symptoms	Comments	Controls
Large irregular holes in foliage; blossom buds completely consumed	Light brown, slender “June beetles” 5/8” long appear at time of bloom and stay for only 5 to 10 days.	- Handpicking. - Mass trap with commercial attractant. - Spray when more than 2 beetles per vine are present.

Grape Phylloxera

Symptoms	Comments	Controls
Galls on roots and underside of leaves. Root galls may cause vines to wilt and die. Leaf galls cause leaf stunting / deformation.	Susceptible cultivars grafted onto resistant rootstocks will have leaf galls but not the more serious root galls.	- Plant resistant varieties or susceptible European varieties that are grafted onto resistant native roots.

Japanese Beetle

Symptoms	Comments	Controls
Skeltonization of foliage in late June – August. Beetles feeding in clusters.	Limited distribution in Iowa. One-half inch metallic green/copper-red beetle. Thin-leafed French hybrids are more heavily damaged than thick-leafed, pubescent varieties such as Concord.	- Visual monitoring is easy; traps are not necessary. - Spot treat with insecticide if more than 15% of leaves on susceptible varieties are damaged.

Leafhoppers

Symptoms	Comments	Controls
Pale stippling on upper leaf surface may turn turn brown. Look for small white cast skins and dark varnish spots on leaf undersides.	At least 3 different species are common. Adults are 1/8 inch long, pale yellow with yellow, red or blue markings or zigzag stripes; or dark with orange markings.	- Moderate infestations do not significantly affect yield or quality. - Healthy vines can tolerate up to 15 leafhoppers per leaf. - Late-producing varieties are more prone to damage.

Spider Mites

Symptoms	Comments	Controls
Tiny yellowish stippling to bronzing on upper leaf surfaces. Fine webbing on leaf undersides.	European red mite is dark red and about 1/50^th inch long.	- Predatory mites usually keep populations low and prevent severe damage. - Use miticides to prevent bronzing.

Grape Mealybug

Symptoms	Comments	Controls
Sticky honeydew on fruit clusters later turns to black sooty mold. White, wooly insects on stems.	Easily detected melaybugs are difficult to control.	- Midseason sprays can be used if damage occurred previous year.

Roots and Stems

Grape Cane Girdler

Symptoms	Comments	Controls
Wilted or broken, hollowed canes (pencil-sized);	Weevil chews a row of holes that circles the cane. Small white larva lives in pith	- Damage beyond fruit clusters does not reduce yield. - Prune and discard wilted canes in July – Aug.

Grape Root Borer

Symptoms	Comments	Controls
Stunted growth and production. Weakened plants may wilt or die	1.5 inch long white larvae burrow in the crown just below the soil surface.	- Control weeds. - Pheromone traps for monitoring male moths; spray in July – August to prevent new infestation. - Pheromone rope ties for mating disruption.

Grape Cane Gallmaker

Symptoms	Comments	Controls
Red swellings of new shoots just above the nodes.	Weevil larvae live inside the swollen stems. More common along wooded borders.	- Galls beyond the fruit clusters cause no serious yield loss. - Prune and discard.

Grape Tumid Gall

Symptoms	Comments	Controls
Small round red succulent galls on leaves or flowers in early season		- Conserve biological controls. - Spray in May if serious problem has developed.