Grape-Thrips

Thrips in high populations can cause significant scarring on leaves that may lead to leaf necrosis and abscission. Here is a severely infested Pinot noir leaf in mid-summer in western Oregon.

Photo courtesy of Patty Skinkis, OSU

Thrips cause brown lesions or scars on the leaf surfaces during summer.

Photo courtesy of Patty Skinkis, OSU

Berry scarring is evident in vineyards with high thrips populations. Here scarring is visible at véraison for Pinot noir. However, the scarring is of less importance for berry quality in wine grapes than table grapes.

Photo courtesy of Patty Skinkis, OSU.

Includes

Grape thrips (Drepanothrips reuteri)
Western flower thrips (Frankliniella occidentalis)

Pest description and crop damage Thrips commonly found on grapes are approximately 0.04 to 0.6 inch in size. Adult thrips have feather-shaped wings. Nymphs are wingless and usually yellow-orange. They usually appear at bloom as they feed on pollen and tender tissues. However, thrips have been found in early spring in Oregon vineyards, much earlier than bloom. Thrips may scar very young berries as early as fruit set. Later, the scars can restrict berry growth, producing oddly shaped or scarred berries. Occasionally, large populations of thrips may damage shoots and leaves in spring, particularly when cool conditions restrict plant growth. Damage caused by thrips during this period has been reported to be similar to that of rust and bud mites (leaf deformation and shoot scarring). High thrips populations have been observed in western Oregon vineyards and have led to strange growth patterns; however, economic damage was not reported. Damage is usually minor and cosmetic on wine and juice grapes in the Pacific Northwest. These are of cosmetic concern for table grape production. Extremely high populations that cause greater damage are usually found in vineyards located near alternative wild hosts.

Biology and life history Western flower thrips appear to be the most important species on grapes in the Pacific Northwest. This species has up to five or six generations per year. Populations usually peak during spring, which may be a result of migration into vineyards from surrounding host plants that are beginning to senesce. Thrips overwinter as adults or nymphs.

Reproduction may be sexual or asexual. The minute eggs are laid in soft tissue, particularly in flowers. Each female lays about 20 eggs that hatch in about 5 days. The two nymph stages can feed on the host over a period ranging from 7 to 12 days. Pupation occurs in soil debris. Adult thrips feed on pollen as well as plant tissues. Scarring has been observed on stem, leaf and berry tissue in Oregon.

Grape thrips overwinter as virgin females in the soil; populations usually reach a peak in midsummer. This species may be mostly responsible for young leaf and new growth damage during summer.

Sampling and thresholds Thrips populations can be determined by counting nymphs and adults that have been knocked out of flowers or fruit clusters onto a board or into a container. Reliable thresholds have not been developed, although numbers in the range of 5 to 30 thrips per cluster are unlikely to be damaging. Populations on leaves can be identified using leaf washes in spring and summer using the alcohol wash as described for rust mites.