The objectives of this work to determine the economic injury level of Thrips tabaci Lind, on onion. Two experiments were carried out at EPAGRI S.A., Ituporanga, Santa Catarina State, Brazil, between August and December, 1993 and 1995. In 1993, sprays with lambdacyhalothrin, 5 g a.i/ha, were used throught the cycle whenever the number of nymphs of onion thrips reached the following levels per plant: 5, 7, 10 and 15, during the whole cycle; 5, and 7 by bulb development and 10,15, 20 after; 10 by bulb development and 20, 30 after; and untreated control. In 1995, spray with lambdacyhalothrin, 30 g a.i/ha, was used when the levels of nymphs per plant were observed during the whole cycle: 1, 3, 5, 7, 10, 15, 20, 25, 30, 40, 50, 60 and untreated control. In 1993, the number of sprays was reduced from eight (using chemical control when the number of 5 nymphs per plant was reached) to four (treatments with 10 nymphs before and 30 after the bulb development). In 1995, the untreated control gave a similar yield to chemical control treatments. Hence the plants tolerated the onion thrips damage. This difference was due to soil management (in 1995, in addition to the chemical fertilizer, green manuring with Stilozobium sp was also used) and to regular distribution of precipitation. Therefore the economic injury level of onion thrips is related to rational soil management and distribution of precipitation.
Allium cepa, Thrips tabaci; insect; onion thrips; cultural control; damage.