Issue No. 3, Article 3/April 9, 2004
Alfalfa Weevil or Clover Leaf Weevil?
It's the time of year that, when walking through our alfalfa fields, we ask ourselves that age-old question--Is this an alfalfa weevil or a clover leaf weevil? Well, maybe we don't always ask ourselves that very question, but it is one that should be considered this time of year. Kevin Black, with Growmark, has recently received reports of scattered alfalfa weevil activity in southern Illinois. Truth be told, these may not all be alfalfa weevils that are feeding in these alfalfa fields.
The alfalfa weevil and clover leaf weevil can both be found in early spring and can easily be misidentified. Larvae of the alfalfa weevil are green, with a white stripe down the back and a black head capsule. Clover leaf weevil larvae are also green with a white stripe on the back, but the stripe is bordered by reddish pink smudges. The head capsule of cloverleaf larvae is brown.
Alfalfa weevil larva.
Clover leaf weevil larvae. (Photo courtesy of Matt Montgomery, U of I Extension, Sangamon/Menard counties.)
Injury caused by these insects is very similar, though injury caused by the clover leaf weevil occurs just prior to that caused by the alfalfa weevil. Alfalfa weevil larvae remain on the plant most of the time and prefer to feed on the tips of plants; clover leaf weevil larvae feed on the lower leaves of the plant but feed primarily at night. During the day, they can be found in the soil around the crowns of the plant or in debris. Adults of the clover leaf weevil are light brown, with a wide, dark brown stripe on the back. The adult alfalfa weevil is about half the size of the clover leaf weevil and is brown, with a dark, narrow stripe along the center of the wing covers.
Fungal organisms usually keep clover leaf weevil infestations in check, and they generally do not cause economic injury. It is important to distinguish between these two insects to correctly assess the situation and avoid unnecessary insecticide treatments.
Table 1 lists accumulated and projected degree-days (base 48°F) from January 1. Alfalfa weevil larval hatch is expected to occur after the accumulation of 300 degree-days. Alfalfa fields in southern Illinois will soon be experiencing larval hatch. View statewide maps and the most current degree-day accumulations at locations near you with our degree-day calculator.--Kelly Cook