Onion Thrips Control in Onion, 2021

The objective of this study was to compare the efficacy of two commonly used insecticides, spinetoram and cyantraniliprole, with a novel one, isocycloseram, for control of onion thrips on onion. Onion seed ‘Safrane’ was planted in a commercial onion field near Elba, NY (GPS coordinates: 43°08′25.6′N 78°06′17.7′W) on 10 April 2021. Onion seeds were treated with FarMore FI500 to primarily control onion maggot (Delia antiqua) and with EverGol Prime to control onion smut. Foliar pathogens were managed throughout the season with commonly used foliar-applied fungicides. Seeds were planted 1.3 inches apart within row and rows were spaced 15 inches apart. Plots were 5-ft wide and consisted of four 15-ft rows. There were a total of four treatments evaluated (including an untreated control; Table 1). Four replications of each treatment were arranged in an RCB design. Insecticides were applied using a CO₂-pressurized backpack sprayer and boom equipped with four, twin flat-fan nozzles (TJ-60 8003VS) calibrated to deliver 39 gallons per acre at 40 psi. Sprays were initiated on 19 July when onion thrips reached a density of 17 thrips/leaf (152 thrips larvae per onion plant), which was well above the action threshold of 1 thrips/leaf. Plots were sprayed a second time on 26 July.

Plots were assessed one week after each application to evaluate efficacy of treatments by randomly selecting 15 plants from each plot and recording the number of larvae. Data were analyzed using regression analysis for mixed models in SAS (v. 9.4; PROC MIXED) with treatment as a fixed effect and replication a random factor in the model. Data were transformed using a log₁₀ (x + 1) function to stabilize variances before analysis. Treatment means were compared using Tukey’s studentized range (HSD) test at P < 0.05.

The growing season began hot and dry, causing onion thrips populations to increase earlier than usual. In July, conditions became cool and wet, which attenuated the typical exponential increase in densities often observed in July and August. On 26 July, all treatments had similar and significantly fewer thrips than the untreated control (Table 1). On 2 August, all insecticide treatments significantly reduced thrips densities compared with those in the untreated control, but the best control was provided by Exirel and PLINAZOLIN technology (Table 1). Overall, these results indicated that all three insecticides were effective in reducing an economically damaging infestation of onion thrips.¹

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