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Alfalfa Weevil Active

Alfalfa weevil reports are starting to come in, particularly in southwestern Ontario. Though the fields may look good from the road, it is important to walk into the fields to see if weevil is getting out of hand. Scout fields twice a week for the next four to six weeks. Larval activity tends to peak at the same time as the bud stage of the first crop.

Cutting early is the recommended management strategy. Insecticides are only recommended when cutting is impractical, i.e. when the alfalfa is in the pre-bud stage. If there is 40 percent leaf tip feeding, with 2 or 3 active weevil per stem, and there is more than 7 to 10 days to preferred harvest date, consider applying an insecticide. Leaf tip feeding refers to the percent of plant tips showing obvious signs of damage, which is not to be confused with the percent defoliation. Less than 1 active larva per stem does not require action, but continue to monitor the situation. If the alfalfa is less than 30 cm (12 in.) high with more than one larva per stem, action is required. Two larvae per stem require action if the alfalfa is less than 40 cm (16 in.) high. If there are more than 3 active larvae, no matter how tall the plant is, immediate action is required.

For more information on alfalfa weevil, refer to the OMAFRA publications,

Publication 811, Agronomy Guide for Field Crops:
http://www.omafra.gov.on.ca/english/crops/pub811/13forage.htm#weevil

Publication 812, Field Crop Protection Guide:
http://www.omafra.gov.on.ca/english/crops/pub812/4weevil.htm