Tuesday, August 10, 2010

Onion Thrips

Damaged foliage with silver grey flecks and twisted bent growth indicate onion thrip.
Onion thrips, Thrips tabaci are important because they carry the disease spotted wilt which affects a wide range of plants including tomatoes and ornamental such as dahlias. This insect is found in all onion/leek/garlic growing areas of the world and is mainly a problem during warm dry weather and less of a worry during cool rainy periods. Thrips can be hard to detect at first as the young wingless creatures, which are pale yellow, congregate in the throat or 'chit' of the plant feeding on the newly unfolding leaves. The adults spend their time on the exposed upper surface of the leaf where they feed by piercing the the tissues and sucking on sap.The clever female thrips are able to reproduce without mating resulting in many generations being produced within a season. The female is a tiny light or dark brown insect about 1.3mm long with two pairs of narrow wings fringed around the margins with fine hairs. The male is smaller. Both are strong fliers and are easily carried by wind to infect a large area. Control can be achieved by inspecting the throats of young plants for early signs of infestation and spraying appropriately. Removing broad leaf weeds where thrips may lurk and providing good irrigation during dry weather helps keep this pest at bay.

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