Onion thrips are present in Michigan onion and cabbage fields

Onion thrips have been making an early appearance in Michigan this year. Check your onion and cabbage fields for this insect.

Onion thrips have been commonly found in cabbage and onion fields throughout Michigan during the first week of June, and although numbers are not alarmingly high at this time, early intervention may prevent populations from becoming abundant early in the season. Onion thrips prefer dry, hot weather, as expected for this weekend, and during these conditions their numbers can rapidly increase on plants.

Onion thrip

Management on onions

When populations are still low early in the season, a foliar insecticide called Movento may be an option for commercial onion growers to manage onion thrips. A Section 18 exemption for Movento (spirotetramat) is available; this means that 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, seven 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 below.

Results of the 2012 onion thrips insecticide trial conducted by the
MSU Vegetable Entomology lab. Click here for a larger image.
Figure 1 

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. Please use the E-312 bulletin, 2012 Insect, Disease and Nematode Control for Commercial Vegetables, for guidance on insecticides registered on different vegetable crops.

Michigan State University is not supporting the use of any particular insecticide brand. When using pesticides, always follow the label recommendations.

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

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