Intermountain Alfalfa Management PDF Download

Alfalfa weevil (Hypera postica Gyllenhal) is a pest of alfalfa (Medicago sativa L.). Insecticides are the primary method of weevil control but with increasing insecticide resistance, alternative non-chemical methods are critical for future management. Multiple studies were conducted to explore two alternative methods: early harvest and biological control. Early harvest is a mechanical method of control where recommendations are vague and previous work is insufficient for improving recommendations. One study based in Wyoming and one spanning multiple states in the Intermountain West was conducted to 1) evaluate how early harvest compares to insecticides and 2) impacts both alfalfa weevil populations and their natural enemies. Biocontrol is another promising alternative method of alfalfa weevil control. Bathyplectes curculionis (Thomson) is an imported European parasitoid that is commonly collected in the Intermountain West but does not adequately manage weevils. It remains largely unknown why B. curculionis is not more successful, but they are documented to host both native and introduced hyperparasitoids. Hyperparasitoids potentially impact B. curculionis survivorship, but this remains largely understudied. Through sampling efforts across the Intermountain West, we quantified hyperparasitoid parasitism in the region within alfalfa-alfalfa weevil systems and explored the interaction between B. curculionis and hyperparasitoids. Through our efforts, we determined early harvest is an effective method of weevil control comparable to insecticide use. Multiple hyperparasitoid species were found consistently across the region but their impact on B. curculionis biocontrol remains unclear. This combined early harvest and biocontrol work will support IPM recommendations to growers and increase alfalfa production sustainability.