Impact and Economic Threshold of Thrips tabaci on Onions
Heavy onion thrips, Thrips tabaci, infestations resulted in onion yield losses of 43 and 34.5% in 1988 and 1989, respectively. No impact on yield was observed in 1990, a season with low thrips densities. The relationship between damage and yield was best described by non-linear models. Differences in the onion plant response to thrips damage were observed between 1988 and 1989, which were linked with the duration and intensity of the seasonal water deficit. Economic thresholds of 2.2 and 0.9 thrips per leaf were estimated for 1988 and 1989, respectively. These thresholds can be used for onions sold at harvest or stored because costs associated with storage are compensated by a higher return price. The use in 1990 of the 0.9 thrips per leaf economic threshold would have resulted in unnecessary pesticide treatment making this threshold suitable only for severe drought situations.
KeywordsHydrazin Cypermethrin Cumi Cymbush
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