Onion thrips management – Part II: Management Options

Marion Paibomesai, Vegetable Crops Specialist, OMAF & MRA, Michael Tesfaendrias, Muck Crops Research Station, University of Guelph and Dr. Mary Ruth McDonald, University of Guelph

Slightly updated…

This is the second part of the Onion Thrips Management article, developed from material presented at the Muck Conference in Bradford, ON in early 2013. See Part I for information on scouting onion thrips at https://onvegetables.com/2013/06/20/onion-thrips-management-part-i-identification-and-monitoring/. Based on the material presented at the Muck Conference, this article will focus on the use of pest control products for the management of thrips.

What works?

A lot of work has been done examining the efficacy of pest control products on onion thrips. In New York (NY), Radiant (known as Delegate in Canada), Entrust (spinosad), Agri-Mek (abamectin) and Movento (spirotetromat) have demonstrated good to excellent control, consistently. Likewise in Ontario, Delegate, Movento and Agri-Mek provided good to excellent control. According to trials in NY, Delegate and Movento are rated the best in terms of relative efficacy, while Agri-mek ranked second. Movento should be used early in the season, as this product is more effective on larvae. Agri-mek should also be used earlier in the season because it has a long pre-harvest interval of 30 days. Delegate was found to be very effective for controlling thrips. Also note, that pyrethroids are registered for thrips control on onions; however, Matador (lambda-cyhalothrin) and Decis (deltamethin) resistance was noted in muck growing regions in Ontario in the early 2000’s. Table 1 lists products that are registered in Ontario on dry bulb onions for onion thrips management. Figure 1 shows the onion thrips efficacy plots from the Muck Crops Research Station in 2012.

Table 1. Pest control products registered for onion thrips on dry bulb onions in Ontario. The information is provided as a guideline only. Refer to labels for rates and directions for use. For resistance management purposes, each product should be used in an integrated pest management program and in rotation with other management strategies. 

Product(active ingredient) Chemical Group Pre-harvest Interval Rate Notes
Movento 240 SC

(spirotetramat)

23 3 days 365 mL/ha Control of onion thrips larvae. Maximum of 2 applications/crop season. Should be used in first half of the season when adult populations are relatively low or building. Reductions in numbers of thrips larvae may take 3 to 4 days after application. 12-hr re-entry interval. Please refer to label for further application instructions.
Agri-mek 1.9% EC

(abamectin)

6 30 days 600 – 1200 mL/ha Applied with non-ionic surfactant at rate of 0.25 to 0.5% v/v of spray mixture. Agri-mek in combination with a non-ionic surfactant has been tested on some varieties of bulb onions. Test a small area before treating entire field to ensure safety. Maximum of 3 applications/season. Do not allow entry until residues have dried.
Delegate WG

(spinetoram)

5 3 days 200-336 g/ha Do not use more than 2 consecutive applications of Group 5 insecticides. Apply with water volume of 300 to 500 L of water/ha with sufficient pressure to ensure spray penetrate leaf axils. Maximum 3 applications/year. 12-hr re-entry interval.
Entrust 80 W

(spinosad)

5 3 days 131-158 g/ha Suppression only. Do not use more than 2 consecutive applications of Group 5 insecticides. Apply with water volume of 300 to 500 L of water/ha with sufficient pressure to ensure spray penetrate leaf axils. Maximum of 3 applications/year. Do not allow entry until residues have dried.
Success 480 SC

(spinosad)

5 3 days 218 – 262 mL/ha
Matador 120EC/ Silencer 120 EC

(lambda-cyhalothrin)

3A1 14 days 188 mL/ha Maximum of 3 applications/year. 10 day re-entry interval for hand harvest and thinning. 24-hr re-entry interval for all other activities.
Ripcord 400 EC/UP-Cyde 2.5 EC

(cypermethrin)

3A1 3 days 175 mL/ha – Ripcord280 mL/ha – UP-Cyde Maximum of 3 applications/season. 12-hr re-entry interval as per UP-Cyde label.
Decis 5 EC

(deltamethrin)

3A1 5 days 200 mL/ha – maximum of 1 application/season Maximum of 1 application/season.
Dibrom

(naled)

1B 4 days 0.55 L/ha 48-hr re-entry interval. Maximum 2 applications/season.
1 Resistance to these insecticides has been observed in Ontario muck soils.
Figure 1. Onion thrips efficacy trial at the Muck Crops Research Station, 2012. The orange lines indicate one set of replicates for the treatments indicated (i.e. Sylgard, Movento followed by Delegate, Concept and Delegate) with 2 beds of 4 rows per treatment. The black box (check) indicates a plot where no insecticides were applied. Note the silvery light coloured foliage of the onions in the untreated plot, which is indicative of onions thrips feeding damage. Photo by L. Riches, Muck Crops Research Station.
Figure 1. Onion thrips efficacy trial on dry bulb onions at the Muck Crops Research Station, 2012. The orange lines indicate one set of replicates for the treatments indicated (i.e. Sylgard, Movento followed by Delegate, Concept and Delegate) with 2 beds of 4 onion rows per treatment. The black box (check) indicates a plot where no insecticides were applied. Note the silvery light coloured foliage of the onions in the untreated plot, which is indicative of onions thrips feeding damage. Photo by L. Riches, Muck Crops Research Station.

Careful when mixing

Use surfactants as per insecticide and surfactant label directions. Be sure to calculate your surfactants rates properly! There is new work going on to investigate how using improper rates of surfactants affects the wax layer of onions. From work done in NY State by Cornell, avoid tank mixing Delegate, Agri-Mek or Movento with Bravo (chlorothalonil) as the spreader-sticker qualities of this fungicide reduces thrips control by 25-48%. In some cases, they found that including a surfactant helped “restore” efficacy of the insecticides on thrips, but this wasn’t always consistent. Dr. Mary Ruth McDonald is also investigating at the Muck Crops Research Station the efficacy of adjuvants on thrips control and if damage to leaf waxes possibly caused by adjuvants could expose the plants to foliar diseases.

Order of applications

For seeded onions, Cornell is suggesting two applications of Movento, followed by two applications of Agri-Mek, followed by two applications of Lannate (Lannate is not registered on onions in Canada. Do not use on dry bulb onions grown in Ontario), followed by two applications of Delegate or even switching the Lannate and Delegate applications depending on the thrips pressure.  For example, if thrips pressure is high after the Agri-Mek applications, they suggest using Delegate to knock down populations. The consecutive applications (i.e. between the first Movento spray and the second) are timed 7 to 10 days apart, based on thresholds. Scouting for onion thrips is important when using this strategy, since applications are typically based on action thresholds and thus on weekly counts of thrips in the field.

Similar research has been done in Ontario.  The most effective combinations for thrips control were two applications of Movento followed by two applications of either Delegate or Agri-Mek.  These products are all from different chemical classes, so these spray programs also help to prevent insecticide resistance in the thrips.  The timing of applications is based on the action threshold of 1 thrips/leaf.

Why use two applications in a row?

Resistance to insecticides is a major concern when dealing with thrips. Using two applications of the same product (or chemical class) in a row in the same field with no more than 2 weeks between the applications should target the same generation of thrips, which is a good resistance management strategy. After the two applications of the same chemical class, switch to two applications of a different chemical class. Keep in mind that if the action threshold is not reached (or close to being approached) within 2.5 to 3 weeks, it is important to use an insecticide from a different chemical class for resistance management purposes.

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