Onion Maggot Control in Onion, 2019

Abstract

Onion maggot (Delia antiqua Meigen) control using seed treatments was evaluated on muck soil in a commercial onion field south of Oswego, New York (GPS: 43°25′04.4″N 76°27′11.4″W) in 2019. On 15 May, dry bulb onion seeds, cultivar ‘Highlander’, were planted with a hand-pushed vacuum seeder. Each plot consisted of two 30-ft rows spaced 10 inches apart. Plots were separated from each other by a 3-ft alley of bare soil. There were four treatments including the fungicide-only check. Treatments were arranged in a RCBD, replicated five times. All treatments, including the fungicide-only control, were commercially treated with Apron XL (10 g a.i./100 kg of seed), Maxim 4 FS (5 g a.i./100 kg of seed), and Dynasty (2.4 g a.i./100 kg of seed) for seedling disease control. Additionally, all plots were treated with an at-planting in-furrow drench of Dithane F-45 Rainshield, applied at 5.6 liters/ha using a gravity fed system, to control onion smut. Efficacy of treatments was evaluated one to two times per week beginning 24 Jun, when maggot damage was first detected, and ending 22 Jul, corresponding to the end of the first generation of onion maggot. At each evaluation, seedlings containing maggot larvae or those obviously dying from maggot feeding (but larva not present) were recorded as dead and then removed from each plot. A final plant stand count was recorded the last day of evaluation, 22 Jul. Because seedling loss from factors such as excessive rainfall, wind, and disease can be confounded with damage from maggot feeding, data were analyzed by taking the sum of all maggot-killed plants and divided by the sum of maggot-killed plants plus the final stand count for each replication. This quotient was the final proportion of plants killed by onion maggot. These data were analyzed using a linear mixed model in SAS (v. 9.4; PROC MIXED) with treatment as the fixed effect and replication as the random effect. Proportion data were transformed using an arcsine 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 considerably wet and cool during the entirely of the trial, resulting in low plant stands. However, onion maggot pressure remained very high; onion maggots killed nearly two-thirds of the plants in the fungicide-only control (Table 1). The percentage of plants killed in the Cruiser 70WS treatment was also very high and similar to the fungicide-only control. In contrast, the seed treatment combinations (Cruiser + Regard and Cruiser + Trigard) significantly reduced the percentage of plants killed by onion maggot compared with levels in the fungicide-only control and the Cruiser 70WS treatment. The Cruiser + Regard and Cruiser + Trigard treatments did not differ in their control of the pest. No phytotoxicity symptoms were observed following any of the insecticide treatment applications.1 Means (± standard error) followed by the same letter are not significantly different (P > 0.05; Tukey’s studentized range [HSD] test; n = 5). Data were arcsine square root (x + 0.001) function for analysis, but untransformed data are shown.

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