BackgroundAlfalfa weevils are a pest in seed alfalfa production because the larvae eat the flower buds off the plants. High population of Alfalfa weevil can substantially decrease yield. In the last few years, Alfalfa Weevil larvae have become more resistant to common insecticides used control them, especially in Rosemary Alberta and surrounding area. Therefore, alfalfa seed growers of this region are experiencing higher populations that are more difficult to control. This study focuses on testing several insecticide options for farmers, aiming to help them protect their crops from this formidable pest. Farming Smarter applied multiple insecticides to seed alfalfa when alfalfa weevils were infesting the crop. Researchers evaluated the efficacy of the insecticides by sweeping each plot (10 sweeps) and counting the larvae of the Alfalfa weevil. Assail and Entrust on average over the 4 weevil count periods show lower weevil populations, with Assail 1x and 2x, and Entrust 2x showing lower weevil counts, especially at 4 days after application (DAA). Confident yield benefits were not found for any of the treatments.
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Project Objectives
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Methods |
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Farming Smarter staff applied the insecticides at 40 L/acre water volume at half, normal, and double label rates of each insecticide, using CO2 propelled hand booms. The middle 2 meters were sprayed, leaving a 2-meter buffer on either side of the plots. Spraying occurred when the larvae were actively hatching. Farming Smarter closely collaborated with Alfalfa Seed Commission to time the pesticide application appropriately. Plots were swept right before spraying and larvae were counted. This was repeated at 4, 7, and 11 days after application (DAA). Yield and dockage were gathered from the middle 2-meters of each plot (treated area). Statistical analysis was completed using a linear model with ANOVA statistics, using 95% confidence, to assess treatment effects. Table 1 outlines the timeline of each research activity.
Table 1: Research Activities Timeline
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Measurements
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ResultsWeevil ControlResults show Assail at normal and double rate 4 DAA lowered the weevil population and kept it low through the rest of the count timings (Fig. 2). Silencer showed similar results to Entrust at 4 and 7 DAA but had high population counts at 11 DAA, and on average performed more like the UTC (Fig. 2). Coragen did not control weevils any better than the UTC treatment. Statistical analysis showed Entrust at half rate performed better than Coragen and the UTC at 4 DAA (Fig. 3). Numerically, Assail at normal and double rates and Entrust at half rate had lower weevil counts at 4 DAA. Assail half and normal rates numerically perform better than the UTC at 7 DAA. At 11 DAA, Assail normal and double and all Entrust rates numerically showed lower weevil counts than the others, which were similar to the UTC (Fig. 2). Averaging all weevil count timings, Assail at normal and double rates and Entrust at half rate lowered or slowed population growth more than the other treatments (Fig. 4). Looking at the results for each location separately there are some slight treatment differences. At site 1, Assail double rate at 4 DAA, statistically lowered the weevil population more effectively than Coragen at half rate. At site 2, Assail at 1x and double rates 4 DAA, did statistically better than Coragen at normal rate and the Untreated Check (Appendix B). At site 2, Assail at normal 7 DAA, was statistically better than Entrust at quarter rate. At site 1, Entrust one eighth rate at 11 DAA was statistically better than Silencer.
Seed YieldComparing the two locations shows a significant difference in grain yield (P < 0.0001), with site 2 yielding much lower than site 1. However, the treatments affected the weevils similarly at both sites. High variability was observed at each site, especially at site 1, reducing the overall confidence of the results. No statistical difference was found between the treatments (Fig. 5). Numerically, with both sites combined, Entrust all rates, Assail normal rate, and Silencer show higher yield than the UTC. All rates of Coragen are as good or lower yield than the UTC (Fig. 5).
Summary of previous research (2017-2020)In 2017 Entrust was the only chemical to show effective control in the lab experiments. In 2018 Entrust at two higher rates (87.5 and 175 g/ha) showed significantly lower weevil counts than the water control. In 2019 it was concluded that single applications of Assail and Entrust at label rates was effective at controlling alfalfa weevil and a second application approximately 2 weeks after the first application improved the control (better than a single application). In 2020 Entrust, Coragen, and Assail at double and normal rate were affective at controlling Alfalfa weevil, with all treatments being statistically better than the untreated check in all Weevil count timings. In 2020 the Silencer treatment was comparable with the untreated check. |
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RecommendationsResults from the 2021 trials suggest Assail at double and normal rate and Entrust at half rate are the most effective chemicals for reducing alfalfa weevil population compared to untreated check. We see potential in Assail and Entrust at label rate or higher to help to reduce Alfalfa weevil population in seed alfalfa. Numerical results of yield benefits also point to Assail and Entrust at normal rates or higher as benefiting yield. Future research considerations are as follows. The alfalfa weevil has shown high levels of resistance to chemicals, seen in the single application trials that show small decreases of weevils. Where a second application was employed (in 2019) there was a large decrease in weevils. Therefore, it is suggested that further studies include a second application timing to the treatments. In 2021 the chemicals were sprayed at one spray volume (40 L/acre), and it was recognized after the fact that Entrust was sprayed at a lower chemical rate and water volume rate than the previous trials. It still performed well, however may have performed better if sprayed at a higher chemical rate and water volume. A standard water volume of 80 L/acre should be considered in further studies as well because it may provide greater coverage of the plants and weevils which may improve efficacy of some or all the chemicals. Use of different combinations of insecticides could also be considered in future research to provide added control. Research will continue in 2022 to aid the ongoing battle against the Alfalfa Weevil and support the seed alfalfa growers. Project Video
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Article
Right now, we have three separate trials for alfalfa going on at Farming Smarter. We're researching how to best combat alfalfa weevil, the best time & product to desiccate alfalfa, and the effect of plant growth regulators on the crop.