![]() Red onions are particularly susceptible, while Spanish onions tend to be somewhat resistant. Heavy thrips buildup may cause the cabbage head to become distorted. Thrips are often found several layers deep within developing cabbage heads. ![]() Since thrips prefer tight spaces, cabbage varieties with extremely dense heads are most susceptible to damage. Both adults and larvae can cause silvery streaking on leaves, which becomes dry and yellow. Recall that feeding damage causes whitish blotches and dry, yellow areas on leaves, decreased pollen set, and, under heavy infestations, brown leaf tips and distorted or undersized bulbs. Management thresholds are most often based upon numbers of immature (nymphs) per leaf, and are not based upon levels of visual damage. ![]() Forecast rain in the coming week across southern Wisconsin may slow this development.Ĭontinue scouting susceptible crops, however, to determine whether established thresholds have been met or exceeded. Throughout portions of Wisconsin, ‘abnormally dry’ conditions are developing in portions of the state, and these conditions also favor the development and survival of onion thrips populations. Second cutting alfalfa is also a significant risk factor for the movement of adult onion thrips. Mass immigration of adult thrips to onion fields can occur any time throughout the summer but is likely coincident with harvest of infested legume and grain fields that are nearby. nymphs) somewhat resemble adults except they are smaller and are often yellow in color. Their wings have no veins and are fringed with long hairs. Adult onion thrips are about 1/12” long, thin, and pale yellow to brown in color. They may attack nearly all garden crops, but serious damage is generally limited to onions, cabbage, cucumber, and tomatoes (hoop/hot house). Onion thrips ( Thrips tabaci) are an important annual pest of onion. Groves, Professor and Department Chair, UW-Madison, Department of Entomology, (608) 698-2434 (mobile), e-mail Entomology Webpage: New resource: 2022 Potato Late Blight Fungicides
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