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Canola Seed Treatments Waning While Flea Beetles Peaking

Posted: Jun 17 2022

Extension Entomology and county Extension Agents have received many complaints of economic flea beetle feeding damage in canola and even replanting of fields (see Around the State – Northeast and North Central). Insecticidal seed treatments are waning, and growers have made rescue foliar insecticide applications to stop further feeding damage. It is imperative to scout your canola fields daily for seed treatment failure and economic flea beetle damage. Foliar insecticide application is warranted when 20-25% defoliation has occurred on seedlings through the 6- 8 leaf stage. Please see last week’s Crop & Pest Report article on flea beetles, and for more information on flea beetles and foliar control, please consult NDSU Extension Publication E1234 (revised) - Integrated Pest Management of Flea Beetles in Canola and E1143-22 - North Dakota Field Crop Insect Management Guide for a list of insecticides for flea beetle control registered for use in canola.

Q: What does insecticide seed treatment failure look like? A: Increase feeding damage and flea beetles actively feeding on previously unscathed seedlings. The photos below tell the story. The first photo was taken in our insecticide seed treatment trial at seven days after emergence, and shows 1-2 leaf seedlings with only minor pitting on the cotyledons and no actively feeding flea beetles. The second photo shows the same treatment only three days later! The cotyledons and true leaves are severely pitted, and there are flea beetles actively feeding. Note that there are several crucifer flea beetles in the photo. This is another indication that seed treatment efficacy is failing, because crucifer flea beetles are controlled more effectively by seed treatments than striped flea beetles.

Q: How long will an insecticide seed treatment last, and will I have to make a foliar rescue treatment? A: It depends on several factors. Time from planting to emergence, plant growth, and flea beetle pressure all affect how well a seed treatment performs. In our trial, we saw seed treatments no longer controlling flea beetles at 10 days after canola emergence, and time from planting to complete seedling emergence was another 10 days. Keep in mind that our trial experienced heavy feeding in a very small area, and had a fairly long emergence period, so what you see for seed treatment efficacy in your fields may be different. However, based on the complaints we’ve received, what we saw in our trial matches closely to what growers are experiencing.

Q: Does the addition of Lumiderm or Buteo Start to the neonicotinoid in the seed treatment provide additional protection against flea beetles, and if so, for how long? A: Yes, but probably not for long. In our trial, all insecticidal seed treatments had the same level of economic feeding injury at 10 days after emergence. However, neonics combined with Lumiderm (cyantraniliprole) or Buteo Start (flupyradifurone) did exhibit less feeding injury and more advanced growth at seven days after emergence compared to the neonics alone. We’ll be taking growth stage notes and yield data, so our final results will be shared over the winter meeting season. Adding Lumiderm or Buteo Start might well buy you more time to make a foliar rescue application - flea beetles can do a great deal of damage in a short amount of time. Also, if flea beetle pressure is light, the addition of Lumiderm or Buteo Start to the neonic might allow the canola to outgrow flea beetle feeding and a rescue treatment might then not be necessary. That’s speculation of course, and more research needs to be done on that front.

Q: What good did a seed treatment do for me if I still have to make a foliar insecticide application? A: Seedlings were protected in the early plant growth stages, resulting in more advanced plant growth. Seedling damage caused by flea beetles will delay growth, flowering, and maturity - the more severe the damage, the more growth stages are delayed. If you’ve got protection early, this potentially translates to flowering and seed development prior to high heat in late summer, which could then translate to increased yield potential. Severe flea beetle feeding can also cause stand loss, which can result in yield loss if the plants can’t compensate for stand loss.

Patrick Beauzay - Research Specialist, Extension Entomology, State IPM Coordinator

Janet J. Knodel - Extension Entomologist

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