Alfalfa Weevil | VegEdge

Degree-day models for alfalfa weevil are used to predict egg hatch and larval development in spring. These maps use a modified sine-wave degree-day calculation of lower (48°F) and with a Jan. 1 biofix date (Peterson & Meyer 1995. Environ. Entomol. 24: 1404-1407).

Alfalfa weevil is a univoltine pest which only has one generation a year in Minnesota. Pupae do not cause damage to alfalfa, and adults enter a summer dormancy until the following year. Therefore, damaging larval stages typically are centered around the first cutting of alfalfa each year, but can occasionally cause damage to early growth of the second cutting. If mowing will occur soon (e.g., more than 50% of plants are at bud stage), insecticide application generally does not have an economic return on investment since mowing and lack of cover will reduce larval populations. Scouting should continue after haying since it is possible for larvae to cause damage on new growth under windrows.

In recent years, growers have been seeing feeding damage up to July 1, usually well after when the models would have us expecting feeding would end. There is a western strain of alfalfa weevil that has an extended development period where their peak feeding is about 1-2 weeks later than the eastern strain we typically see in Minnesota. This western strain may be becoming more predominant the across the state, so if you are in an area that appears to have a history of extended feeding, keep scouting for 1-2 weeks after these models suggest. For recent updates on these changes, an update article is available at MN Crop News.

Current degree-days

Forecast degree-days

The Minn. Extension IPM Program is a collaboration of University of Minnesota Extension & the College of Food, Agriculture, and Natural Resource Sciences (CFANS).