Insecticides for onion thrips management

Section 18 exemption for Movento and results of the 2011 onion thrips insecticide trial.

The Section 18 exemption for Movento (spirotetramat) is available and onion growers can use this product for onion thrips management in Michigan in the 2012 growing season. The minimum interval between applications is seven days, the pre-harvest interval is also seven days and the maximum amount of Movento that can be applied in a single season is 10 fl oz/acre with 5 fl oz/acre as the only approved rate of application. This means two applications of Movento can be made to onions within a growing season, and these should be done consecutively, 7 to 10 days apart, for insecticide resistance management purposes. Movento has to be tank-mixed with a non-ionic (penetrating) surfactant to maximize leaf uptake since this product moves systemically in the plants. Movento is more effective at suppressing larval onion thrips, therefore it is recommended that it’s used in the early part of the growing season before thrips population pressure peaks.

The graph below shows the results of the 2011 onion thrips insecticide trial conducted by the MSU Vegetable Entomology lab. Our goal was to compare the performance of insecticide rotations, so we applied them weekly, regardless of thrips threshold. Each insecticide within a sequence was applied twice in a row (sprayed two consecutive weeks) for resistance management purposes. There were eight different treatment combinations with the following insecticides: Agri-Mek, Lannate, Movento, Radiant, Tolfenpyrad (an experimental product), and Vydate. Treatment sequences are shown in the table under the figure.

Results of the 2012 onion thrips insecticide trial conducted by
the MSU Vegetable Entomology lab. Click here for a larger image.

Results of the 2012 onion thrips insecticide trial

All of our insecticide treatments decreased onion thrips numbers significantly relative to the untreated control. Treatments 7 and 8 suppressed thrips the best when comparing seasonal averages, but this was not statistically significantly different from treatments 3, 5 and 6. The common feature of these treatments is that they all had Radiant in the rotation either at weeks 3-4 or 5-6, applied at a time when thrips population pressure was the highest during the summer.

The results of this insecticide trial indicate that there are multiple insecticide rotations that can achieve good thrips suppression in the field (for example, treatments 5 and 7-8), but since not all products have the same efficacy, the sequence has to be carefully adjusted to achieve the desired results. Treatments 5, 7 and 8 contain commercially available and currently registered products and performed the best in our trials. Interestingly, there did not seem to be a straightforward correlation between the level of thrips control and onion yield, although treatments 7 and 8 had the highest yields among our treatments.

For more information, please visit the MSU Vegetable Entomology lab website.

Dr. Szendrei’s work is funded in part by MSU’s AgBioResearch.

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