Onion thrips insecticide trial results

The weather conditions this year were favorable for onion thrips development; therefore many commercial onion farms experienced unusually high numbers of onion thrips in Michigan. The vegetable entomology laboratory at MSU conducted an onion thrips insecticide trial this summer on a commercial farm in mid-Michigan. This year we had nine insecticide treatment combinations (see graph with seasonal averages and table) with multiple types of insecticides in rotation in each treatment.

Starting in mid-June, 2010, we visually counted thrips on onion leaves, and nymph numbers were recorded weekly. We started applying our insecticide treatments once we reached the 1 thrips nymph per leaf threshold in our experimental plot (June 18, 2010). Thereafter, weekly visual counts were made and insecticides were applied to those treatment plots that exceeded the 1 thrips nymph per leaf threshold. Because of the high thrips abundance this year, only one of our treatment combinations (“treatment code number 6,” see the graph and table for details) suppressed thrips nymph numbers below threshold after week 3.

Unfortunately, numbers climbed back up in “treatment 6” plots at week 5, and so we continued applying insecticides. Our best performing product combination was alternating use of Lannate and Radiant. Although this treatment combination suppressed thrips nymph numbers to the numerically lowest average value, it was not significantly different from other treatments that had also Lannate and Radiant in combination with an experimental product (HGW86). The Movento, Lannate, Radiant combination was also not statistically significant from the lowest average values. Our plan for next year is to include some products that were not tested this year, but may be of interest to commercial onion growers in Michigan.

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