Co. 1995. High water volumes (30 gal/A) is recommended in the Midwest Systemics activity helps. Davis, M., E. Grafius, W. Crenshaw and T. Royer. Madison, Wisconsin 53706 Feeding causes whitish blotches that may appear as silvery streaking on leaves. The adults can range from a pale yellow to dark brown and are usually smaller than 1/16 of an inch. This site is maintained by Center for Agriculture, Food and the Environment in the College of Natural Sciences. If you find three thrips per onion leaf, consider chemical treatments. Chemical: Apply insecticides each year as soon as thresholds (see above) have been exceeded to target the insects before they can reach protected areas (e.g., the insides cabbage heads and onion necks) where insecticides cannot easily penetrate. Immature onion thrips are small and milky white at first and after molting turn to green or lemon-yellow with red eyes. An EEO/Affirmative Action employer, University of Wisconsin-Madison Division of Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This damage can provide entry points for bacteria that cause bacterial soft rot (see University of Wisconsin Garden Facts HXT1224, Bacterial Soft Rot, for details). Adult – Pale yellow to dark brown in color, the onion thrips adult is slightly less than 2 mm long. Appearance: Adult onion thrips are about 1/12 inch long, thin and pale yellow to brown in color. If possible, avoid planting cabbage, cauliflower or onions close to and immediately downwind of small grains or alfalfa. As feeding continues, affected tissue may turn dry and yellow, and may eventually brown and die. Young thrips lack wings, but adult thrips have four wings that are very narrow and fringed with hairs. Adults and nymphs pass the winter in small grains, clover and alfalfa fields concealed in grass or other plant remnants. Onions that have a more circular leaf structure and that have glossier foliage tend to be less prone to damage. Sprays need to be applied based on high populations but before feeding damage is readily apparent. Thrips have rasping mouth parts which they use to tear open plant cells to feed on plant juices. Eastman et al. Occasionally a few plague thrips (Thrips imaginis) are also found, especially early in the crop season. 1 Both species have fairly wide host ranges, feeding on both broadleaf and grass plants, including alfalfa, common bean, grains, grasses, and various weed species. Pp. Adults lay eggs singly in the epidermis, nymphs feed on … Onion thrips are tiny insects that range in color from yellow to black and are only 1/16” in length. Thrips are some of the most damaging insect pests to the leaves of onions world-wide. Practice good field sanitation at the end of the season. Immature onion thrips are small and milky white at first and after molting turn to green or lemon-yellow with red eyes. (1995) reports that all varieties can tolerate populations of 25 thrips per plant. Scouting: Thrips populations can develop very rapidly. Be sure to routinely and carefully monitor crops for thrips during the periods indicated in the table below. Thanks to Julie Hill, Bryan Jensen and Carol Shirk for reviewing this document. The females deposit eggs in tender plant tissues. Onion thrips, Thrips tabaci, are cosmopolitan insects, feeding on a wide variety of vegetable plants, small grains, field crops and weeds. LEARN HOW TO STOP THE INVASIVE SPOTTED LANTERNFLY, Coronavirus: Information and resources for the Extension Community, Whitney Cranshaw, Colorado State University, Bugwood.org. Growth from egg to adult can be completed in two weeks when temperatures are warm. Onion thrips (Thrips tabaci) are an important annual pest of onion. They spend the winter as adults in crop remnants, alfalfa, wheat, greenhouses and weeds along the border of crop fields. See All Pest, Disease and Weed Identification, See All Beer, Hard Cider, and Distilled Spirits, See All Community Planning and Engagement. Cultural: Remove plant debris from gardens (and commercial fields) as well as any areas surrounding a location where you will be growing onions or other susceptible vegetables. Thrips feeding can also lead to distorted and undersized bulbs. Red onions are particularly susceptible to thrips damage, while Spanish onions tend to be somewhat more tolerant. Thrips can produce five to eight generations per year, and outbreaks are most likely to occur in the summer during hot, dry periods. Eggs hatch after five to 10 days. Symptoms and Effects: In general, onion thrips prefer tight spaces and cause severe damage on plants that produce tightly packed leaves. Thrips damage can increase occurrence of purple blotch (Alternaria porri), as fungus can penetrate the plant through wounds caused by feeding. Activity may continue throughout the year in warmer parts of the state. Use the lower threshold during this period, or if expected efficacy of the insecticide to be used is low, water availability is limited, or other conditions reduce the overall health of the plants. Entering your postal code will help us provide news or event updates for your area. Onions. Flood. Development of an infestation is influenced by seasonal conditions. The Commercial Vegetable Guide list current labeled options. Why do we need this? Treat if thrips reach 1 to 3 per leaf. Its two pairs of narrow wings are fringed with long hairs. For current information on chemical control of onion thrips and pesticides labeled for this pest, please see the New England Vegetable Management Guide website. When using foliar sprays, direct the sprays down into the center of the plants to maximize penetration into protected areas. See UW-Extension Publication A3422, Commercial Vegetable Production in Wisconsin, for a list of registered insecticides. Feeding occurs on the interior of the onion neck, on developing leaves. Also, use sufficient water, as well as a spray additive, to help the insecticide penetrate. They can attack many garden crops, but most commonly cause serious damage to onions, leeks and garlic. If feeding on cabbage, the cabbage is blistered, scarred, and bronzed by thrips feeding on leaves; and heads are unmarketable with thrips present and evident. UMass Research and Education Center Farms, Conservation Assessment Prioritization System (CAPS), Extension Risk Management/Crop Insurance Education, North American Aquatic Connectivity Collaborative, Civil Rights and Non-Discrimination Information. Heavy rain or overhead irrigation can lower populations. Follow the package directions. In the midwest, development from egg to adult is estimated to take 20 to 40 days, with 5 to 8 generations per year. Evaluate thrips numbers in a field by randomly sampling entire onion plants (see Identifying … Young thrips lack wings, but adult thrips have four wings that are very narrow and fringed with hairs. Nymphs mature into adults after 15 to 30 days, and adults return to plants to feed. The pest breeds most rapidly when a mild, dry winter is followed by a hot, dry spring. Although there are many species of thrips, the western flower and onion thrips are the most common species in North America. Onion thrips damage to onion leaves (left) and numerous onion thrips adults and nymphs on an onion leaf (right). They can attack many garden crops, but most commonly cause serious damage to onions, leeks and garlic. (1995, see reference below) lists tolerant, moderately tolerant, and susceptible varieties. Cabbage, broccoli, and cauliflower. X-number: XHT1134 Onion thrips (Thrips tabaci) are an important annual pest of onion. The irregular and blotchy whitening of the plants is known as 'blast'. Resistance to thrips infestation occurs in some varieties of sweet Spanish onions. A couple of treatments with insecticidal soap kills them. Where many thrips have fed, the discolored areas coalesce to form large brownish, blister-like areas. On onions with continuing leaf growth, these feeding points elongate to give the typical onion thrips symptoms: whitish spots and streaks on the leaves. The females deposit eggs in tender plant tissues. Adults lay eggs singly in the epidermis, nymphs feed on leaves, and pupation occurs in the soil. Scallions are particularly sensitive because the whole plant is marketed. 608-262-2863, University of Wisconsin Garden Fact Sheets.
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