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Latebreaking Poster

Session: Agriculture (Latebreaking)

LB 1-6 - Comparing the impact of early harvest and insecticide use in alfalfa weevil management from ecological and economic perspectives

Thursday, August 10, 2023
5:00 PM – 6:30 PM PDT
Location: ESA Exhibit Hall
The alfalfa weevil (Hypera postica Gyllenhal) is a major concern for producers of alfalfa (Medicago sativa L.) in the Intermountain West. Large densities have the potential to cause significant economic damage via plant defoliation and slowed regrowth after harvest. One commonly recommended method of alfalfa weevil control is early harvest. Early harvest is a widely used mechanical control method which consists of producers timing their initial harvest early in the season to decrease alfalfa weevil damage. but specific impacts of harvest timings are still not fully understood and in surveys Wyoming producer confidence in early harvest efficacy is limited compared to insecticide use. To foster a better understanding of early harvest and increase confidence in it we conducted a manipulative plot-level study for 2-years (2019 and 2021) at a research farm in southeastern Wyoming. Plots were harvested at different times based on alfalfa development and half of each harvest timing replicate was insecticide treated. With this setup we were able to compare the impact of different harvest timings and insecticide use on both alfalfa weevil activity and crop yield and quality. An economic analysis was also conducted which used yield and quality information to determine the average price per ton of our harvested hay. Earlier harvests were found to be an effective method of alfalfa weevil control and were generally comparable in efficacy to insecticide treatment. Higher yield but lower quality was observed in later harvests with insecticide use having relatively little impact. In both 2019 and 2021 the earliest harvest timing resulted in the highest price per ton for hay irrespective of insecticide treatment. When alfalfa weevil densities were increased the price per ton decreased less in later cuttings when insecticides were used. Generally, early harvest can be as effective and economical as insecticide use. In some situations where higher yields are a priority for producers and alfalfa weevil pressure is strong, insecticides may need to be considered to allow for later harvest. Overall, an integrated pest management approach should be employed and determined based on producer goals and crop needs for optimal control of alfalfa weevil. This multidisciplinary work was a collaborative effort conducted by entomologists, forage agronomists, and agricultural economists.