Onion Maggot Control Using Insecticide Transplant Treatments for Onion, 2018 Open Access

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°26′58.5″N 76°23′56.2″W) in 2018. Onion ‘bare-root’ plants, cultivar ‘Bradley’ (Bejo Seeds, Geneva, NY), were transplanted on 16 May. Each plot consisted of two 10-ft-long rows, separated by 15 inches. Plots were separated from each other by a 3-ft alley of bare soil. There were no guard rows. Plants were transplanted at a density of 3 per ft (60 plants/plot). There were four treatments, including the untreated check that were arranged in an RCBD with six replicates.

The amount of insecticide needed to prepare the treatment solution was 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 5 Jun through 12 Jul. Sampling began as soon as maggots were found until the end of the first generation in mid-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, 12 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 multiplied this quotient by 100. These data were analyzed using a mixed model procedure of SAS (PROC MIXED, v. 9.4) with treatment as the fixed effect and replicate as the random effect. Proportion data were transformed using a square root (x + 0.001) function before analysis, but untransformed means are presented. Treatment means were compared using Tukey’s Studentized Range (HSD) Test at P < 0.05.

Conditions were hot and dry during the entire trial. Onion maggot pressure was considered very high for a New York onion field. Onion maggots killed nearly 6 of 10 onion plants in the untreated control (Table 1). Despite high maggot pressure, both rates of Entrust SC and Radiant SC provided equivalent and commercially acceptable levels of maggot control (<15% damage) (Table 1).¹

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