Integrated Crop Management

Alfalfa weevils to hatch soon

We are having a cool spring, but degree-day information indicates that alfalfa weevil larvae will start to hatch in southern Iowa by the end of the third week in April.

Scouting should begin at approximately 200 degree days in fields south of I-80, and at 250 degree days in fields north of I-80. The Iowa map shows the accumulated degree days across the nine crop reporting districts. Proper management of this insect requires timely scouting, correct identification, determination of population levels, and if necessary, cultural or chemical control.

Fields should be scouted for alfalfa weevils because the larvae can be very destructive to first cutting alfalfa. They remove leaf tissue, beginning with the new leaves at the top of the plant and then work down the stem to other leaves. This feeding reduces forage quality and quantity. Begin by scouting on south-facing hillsides because these areas warm up quickly and larvae hatch here first compared with north-facing hillsides.

Next week's issue will be have more specific scouting information and economic thresholds for this pest, or see pages 48-49 [1] in the April 24, 2000, ICM Newsletter for the details.

Below: Accumulated degree days, base 48°F (projected date of first scouting). January 1 through April 15, 2001.

Degree day map for alfalfa weevil

This article originally appeared on page 49 of the IC-486 (6) -- April 23, 2001 issue.


Source URL:
http://www.ipm.iastate.edu/ipm/icm//ipm/icm/2001/4-23-2001/alfsoon.html