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Onion Thrips



P_onionthrips

Onion Thrips

Usually appear in

Spring to Autumn.


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Caused By:-     The insect Thrips tabaci

Description

Onion thrips (Thrips tabaci) is a world wide pest of onions, other Allium species and several crops, such as cabbage, cotton, celery, tomatoes, beans, cucumber and pineapple. Thrips are easily detected by visual inspection of the onion plant as their feeding activities produce silver or whitish streaks on leaves. The damaged young, expanding leaves become distorted and the onion bulb growth is smaller. Severely damaged leaves and plants may turn brown and die. Thrip damage is most severe during hot, dry seasons.
Adult Thrips are small, 2 mm in length, slender and fast-moving. They are pale yellow to brown in colour and pointed at both ends. The male of the species is wingless and is rarely found. The females have four very slender wings edged with long hairs. When at rest, the wings are laid over the abdomen and extend slightly over it. They lay their eggs in the tissues of the onion or plant. The young nymphs are similar in shape but smaller in size.
At first they are small and milky white turning to green or yellow with red eyes. Young thrips
Adults and nymphs pass the winter in small grains, clover and alfalfa fields concealed in grass or other plant remnants. Activity may continue throughout the year in warmer climates. Growth from egg to adult can be completed in 15 to thirty days depending on temperature and the adults may live up to 20 days with each female producing up to 80 eggs. therefore the infection can explode in a short time.
Thrips feed by piercing or rasping the surface tissues and sucking up the sap. As the plant leaf continues to grow their feeding damage elongate to give the typical thrips symptoms of whitish spots and streaks on the leaves.
Red onions tend to be more susceptible than white onions and resistance to thrips occurs in some varieties of sweet Spanish onions. Picture by Whitney Cranshaw, Colorado State University, Bugwood.org.
See also PEA THRIPS, GLADIOLUS THRIPS, PRIVET, THRIPS, WESTERN FLOWER THRIPS.


Control

There are several natural enemies that help in the control of thrips, but none of them alone can reduce the thrips populations to a low enough density. The intensive use of pesticides also limits their natural enemies as well and there is a chance of pesticide resistance developing. Therefore care must be exercised in pesticide use and rotating different pesticides may be useful.
At the end of the hot dry season, thrips populations are at their maximum and in some places it is better not to plant under these conditions because thrips control is almost impossible. As rainfall washes off the Thrips overhead irrigation is one method of controlling them.
Thrips are not good flyers, but they move long distances on the wind. Younger plots should be planted upwind of older plots, relative to prevailing winds, to make it harder for the thrips to find the new plantings.
Mixed cropping of carrots and onions also may reduce thrips population.



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