Taking an environmentally sensitive approach to pest management


Integrated Pest & Crop Management



AUTHOR

Wayne C. Bailey
University of Missouri
Division of Plant Sciences
(573) 882-2838
baileyw@missouri.edu

Alfalfa Weevil vs. Clover Leaf Weevil

Wayne C. Bailey
University of Missouri
(573) 882-2838
baileyw@missouri.edu

Published: April 4, 2011

Two different species of weevil larvae can be present in Missouri alfalfa fields. Alfalfa weevil (AW) larvae often cause severe damage to first-cutting alfalfa whereas larvae of the clover leaf weevil are generally heavily parasitized and rarely causes economic damage to alfalfa. Occasionally clover leaf weevil larvae are misidentified as alfalfa weevil and needlessly sprayed with an insecticide. How do we tell them apart in the field so we don't apply unneeded insecticide applications?

The following list compares identifying characteristics of larvae of these two weevils found in alfalfa fields early season.

Clover Leaf Weevil (CLW)

  • Appear in fields in early season, often March and April
  • Larvae look similar to Alfalfa weevil larvae, but are larger in size, have a white stripe running down the back that is often bordered by patches of pink or rosy pink areas or flecks
  • Head capsules are brown in color
  • Larvae feed at night and generally spend the day on the ground near the plant or in the plant crown
  • Larva often roll into tight c-shape when disturbed
  • A large majority of CLW larvae are often infected by a fungal pathogen or parasitized by one to several larvae of a parasitic wasp species
  • Feeding damage is seen as circular holes cut into the alfalfa leaflets
  • Populations of CLW rarely reach economic levels due to fungal pathogen or parasitism, so they rarely require insecticide applications to reduce or prevent damaging populations

Alfalfa Weevil (AW)

  • Larvae appear in fields about two weeks later than CLW (late March, April and May depending on location in state)
  • Larvae have brown to black head capsules (sometimes difficult to distinguish from CLW larvae)
  • AW larvae always feed on the alfalfa plant foliage and are not found on the ground
  • Parasitism rates rarely exceed 15% in most areas of the state
  • Small larvae (1st and 2nd instars) feed inside growing plant terminals that produces shot-hole damage on plant leaflets as they grow out of the terminal. Older larvae (late 2nd, 3rd, and 4th instars) substantially reduce forage yield and quality of the alfalfa by skeletonizing and defoliating plant leaflets
  • Common pest of first cutting alfalfa in Missouri, especially in the southern half of the state.

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REVISED: December 1, 2011