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Canola Flea Beetle Scouting Critical

Posted: May 22 2024

Canola planting is in full swing with about 21% planted, ahead 7% from last year and 2% was emerged (Source: USDA News Release NASS - May 13, 2024). Flea beetles continue to be observed in most major canola production areas – Minot, Langdon, Devils Lake and Dickinson. Scouting 2-3 times a week will be important to ensure that your canola insecticide seed treatment is working and protecting the seedling to the 6-8 leaf stage. Warm, sunny weather will increase flea beetle feeding pressures and larger populations will move into canola fields. Whereas cool, wet weather will reduce flea beetle feeding pressures and slow beetle’s movement into canola fields, mainly field edges. If more than 20-25% defoliation is observed in canola fields, a foliar insecticide spray is warranted to prevent yield loss. Pyrethroids (IRAC 3A) are the only class of insecticide labeled for foliar control of flea beetles in canola (active ingredients - bifenthrin, deltamethrin, lambda-cyhalothrin, zeta-cypermethrin). One premix is labeled as Besiege (chlorantraniliprole + lambda-cyhalothrin). For insecticides registered for control of flea beetles for canola, please refer to the 2024 North Dakota Field Crop Insect Management Guide.

What is the best foliar insecticide to apply for control against both striped and crucifer flea beetles in canola? Foliar insecticide treatment efficacy was examined for control of crucifer and striped flea beetles in spring canola. Plots were rated for flea beetle feeding injury using the 0-6 scale developed by Dr. Janet Knodel, with 0 = no feeding and 6 = dead plant. Within each plot, 10 randomly selected seedlings were rated. For analysis, the 10 ratings were averaged for a single rating value per plot. Feeding injury was rated at pre-spray, 7, 10 and 14 days after emergence (DAE). 2023 Foliar Insecticide trials for control of flea beetles in spring canola (Table 1): In general, all pyrethroids with the exception of Delta Gold gave good protection against flea beetle injury. Brigade applied twice gave the best protection among pyrethroids, but it may not be necessary or advisable to do this in one field season due to an increased risk of flea beetle populations developing resistance to bifenthrin (IRAC 3A, pyrethroid). If a single foliar application can provide protection through the 4-6 leaf crop stage, canola can tolerate additional flea beetle feeding pressure without a significant decrease in yield. If a second foliar application is needed based on the established economic threshold of 20-25% defoliation, we recommend either using a different pyrethroid (although cross-resistance within the pyrethroid class could develop), or an entirely different mode of action. Among the IRAC 28 diamides (Vantacor and Exirel), Exirel showed excellent performance against flea beetles. Exirel (cyantraniliprole) has good translaminar and systemic activity, while Vantacor does not. Exirel would be a good choice for a first foliar application, although recent research has shown that striped flea beetles are not controlled as well as crucifer flea beetles with cyantraniliprole. Another concern is when applying Exirel after using Lumiderm (also cyantraniliprole) as an insecticidal seed treatment, which would give greater potential for flea beetles to develop resistance to cyantraniliprole because it would be essentially making back-to-back cyantraniliprole applications in one field season (high risk for insecticide resistance development)

There were no significant differences among treatments for plant stand. For test weight at Fargo, the fungicide check had significantly lower test weight than all other treatments. The same trends observed for feeding injury were observed for yield, with a fairly strong relationship between feeding injury and yield. Treatments ranked with the highest to lowest yield were Brigade applied twice, Brigade applied once, Ridgeback, Exirel, Warrior II, Mustang Maxx, Delta Gold, Vantacor, Helix Vibrance seed treatment and Fungicide check. Thanks for support from the Northern Canola Growers Association. Disclaimer: Mention of insecticides does not imply any discrimination against any product not tested by the authors or the university.

Story by: Janet J. Knodel - Extension Entomologist

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