Onion Maggot Control Using Insecticide Transplant Treatments for Onion, 2019

Onion maggot (Delia antiqua Meigen) control using insecticide treatments to protect transplanted onion was evaluated on muck soil in a commercial onion field south of Oswego, New York (GPS: 43°27′04.3″N 76°23′58.6″W) in 2019. Onion ‘bare-root’ plants (cv. ‘Bradley’, Sunbelt Transplants, Inc., Buckeye, AZ), were established on 22 May. Onions were grown from raw seeds. Each plot consisted of two 15-ft long rows, separated by 15 inches. Plots were separated from each other within rows by a 3 ft alley of bare soil. There were no guard rows. Plants were transplanted at a density of 3 per ft (90 plants/plot). There were four treatments, including the untreated check that were arranged in an RCB design with six replicates (Table 1).

The amount of insecticide needed to prepare the treatment solutions were partially determined by the amount of water that adhered to a single, average-sized onion transplant (0.02 fl oz, determined from previous experiments), and the maximum plant density in transplanted onion fields (125,000 plants/acre). Plants were dipped in the treatment solution for 30 s and allowed to dry prior to transplanting.

Efficacy of treatments was evaluated one or two times per week from 24 Jun through 22 Jul. Sampling began as soon as maggots were found until the end of the first generation in late-Jul. Plants containing maggots or those obviously dying from maggot feeding (but larva not present) were recorded as dead and then removed from the plot. A final plant stand count was recorded on the last day of the evaluation, 22 Jul. In each plot, the percentage of plants killed by maggots was calculated by taking the sum of the number of maggot-killed plants divided by the sum of all maggot-killed plants plus the final plant stand count and then multiplying this quotient by 100. These data were analyzed using a mixed model procedure in SAS (PROC MIXED, v. 9.4) with treatment as the fixed effect and replicate as the random effect. Percentage data were transformed using a square root (x + 0.001) function before analysis, but untransformed means are presented. Treatment means were compared using the Tukey-Kramer Pairwise Comparison Test at P < 0.05.

Conditions were wet at planting and during the entirety of the trial. Onion maggot pressure was considered very high for a New York onion field. The percentage of plants killed in the untreated check was very high and significantly greater than the percentages in all treatments (Table 1). Levels of onion maggot damage were low and similar among the Entrust and Radiant treatments, despite high maggot pressure in the field (<6% damage) (Table 1).¹

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