On-farm harvest timing effects on alfalfa weevil across the Intermountain West region of the United States

Authors: HERREID, JUDITH - University Of Wyoming; Rand, Tatyana; COCKRELL, DARREN - Colorado State University; PEAIRS, FRANK - Colorado State University; JABBOUR, RANDA - University Of Wyoming

Submitted to: Frontiers in Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2024
Publication Date: 4/23/2024
Citation: Herreid, J., Rand, T.A., Cockrell, D., Peairs, F., Jabbour, R. 2024. On-farm harvest timing effects on alfalfa weevil across the Intermountain West region of the United States. Frontiers in Insect Science. 4. Article 1324044. https://doi.org/10.3389/finsc.2024.1324044.
DOI: https://doi.org/10.3389/finsc.2024.1324044

Interpretive Summary: Alfalfa (Medicago sativa L.) is an economically important commodity worldwide. A major economic concern for alfalfa producers in the intermountain west, is the damage caused by the alfalfa weevil feeding. Recently, this pest has become more problematic as it has developed resistance to insecticides, leading to renewed interest by producers in non-chemical control methods. Harvesting alfalfa early in the season to decrease alfalfa weevil damage is one promising cultural management approach. But specific management recommendations for early harvest are currently lacking do to a lack focused of research on the topic. To better understand how early harvest impacts both alfalfa weevils and their natural enemies and how producers could use this method across the Intermountain Western U.S., a study was conducted in alfalfa production fields in Colorado, Montana, and Wyoming over three growing seasons. Result indicated that the timing of the initial alfalfa harvest spanned more than one month across fields, and alfalfa plant stage at harvest ranged from late vegetative to early bloom. Harvest resulted in greater reductions in alfalfa weevil densities the earlier it was implemented. Results further suggested that removing hay in a timely manner can further decrease alfalfa weevil densities. Cumulatively the results suggest that combing early harvest with bailing as soon as possible following cutting could reduce densities of this economically damaging pest.

Technical Abstract: Alfalfa (Medicago sativa L.) is an economically important commodity in the Intermountain Western United States. A major concern for alfalfa producers in this region is the alfalfa weevil (Hypera postica Gyllenhal). Recently, insecticide resistance development has resulted in this pest being more problematic, resulting in renewed interest by producers in non-chemical control methods. One such cultural control method is early harvest which consists of producers timing their harvests early in the season to decrease alfalfa weevil damage. This method can be difficult to employ because recommendations are often vague. To better understand how early harvest impacts both alfalfa weevils and their natural enemies and how producers are using this method across the Intermountain Western U.S., a study was conducted in alfalfa production fields in Colorado, Montana, and Wyoming over three growing seasons. It was determined that the timing of the initial alfalfa harvest spanned more than one month across fields, and alfalfa plant stage at harvest ranged from late vegetative to early bloom. Harvest was more impactful on reducing alfalfa weevil densities the earlier it was implemented. Removing windrows in a timely manner is likely useful to further decrease alfalfa weevil densities. This work has increased our understanding of early harvest in an on-farm setting and helped us build better recommendations for producers across the Intermountain Western U.S.