Graduate Thesis Or Dissertation
 

Determining novel control methods for cabbage maggot (Delia radicum) in the Pacific Northwest

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/z603r633c

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  • Cabbage maggot, Delia radicum (Diptera: Anthomyiidae) impacts the production of Brassicaceae crops worldwide. The larva feed on the roots of crops causing reductions in yields due to impaired root function and unmarketability of crops. Chemical and cultural management programs are commonly used to control cabbage maggot with varying rates of success. Chemical control options are dwindling due to restrictions placed on current chemistries and have varying levels of efficacy due to inaccurate application timing and placement. Cultural control options have high costs, labor requirements, and inconsistent effectiveness which dissuades many growers from relying on cultural controls. The lack of effectiveness of currently used control methods highlights the urgency to determine novel methods to control cabbage maggot. We conducted three laboratory bioassays in 2021 and 2022 to determine the efficacy of organic and conventional insecticides after ingestion by cabbage maggot adults. We wanted to identify insecticides with the potential to be integrated into baits or lures in a field setting. After exposure to the insecticides, flies were observed for fixed sample times to determine when they died. Conventional insecticides generally induced death quicker than the organic insecticides. Zeta-cypermethrin and bifenthrin were highly effective with the greatest mean number of dead flies 1.75 hours after exposure compared to spinetoram and cyantraniliprole (P<0.001 for all comparisons). However, spinetoram performed similarly to zeta-cypermethrin and bifenthrin from hour 2 until the end of the run, so it also had high efficacy. The organic insecticide spinosad was highly effective since it had the greatest mean number of dead flies compared to the other organic insecticides erythritol, pyrethrins + azadirachtin, and V-10433 until 4 hours after exposure (P<0.001 for all comparisons). Pyrethrins + azadirachtin had moderate efficacy and had similar mortality to spinosad 18 hours after exposure. From the bioassays, we identified promising insecticides that we hope to test with bait stations in the field. We conducted a two-year on-farm field trial in 2021 and 2022 to determine the effectiveness of utilizing trap cropping to control cabbage maggot. Our goal was to determine if a turnip trap crop could effectively pull cabbage maggot away from a rutabaga cash crop. We also wanted to observe any differences in attractiveness between different varieties of turnip trap crop. There was not strong evidence that the flies were more attracted to the trap crop than the cash crop based on fly presence. There were not significant differences at the α=0.05 significance level in fly count numbers on sticky traps across distance from the trap crop (P=0.06) or variety of trap crop (P=0.33). In 2022, there was a very weak correlation between trap crop leaf area and visual feeding damage for all sample dates. The lack of relationship between leaf area and damage may indicate host finding cues other than plant size are more important for cabbage maggot. From these trials, we hope to further investigate what plant characteristics are most attractive to CM and establish better population monitoring techniques.
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