Integrated Crop Management

Weevils can delay alfalfa regrowth

Dry soil conditions across parts of Iowa, combined with large populations of adult alfalfa weevils, may delay the regrowth of second-cutting alfalfa.

Kyle Jensen, extension field crops specialist at Lewis, reports that several acres of a 40-acre field near Beebeetown, Harrison County, southwestern Iowa, suffered damage from the weevils. The affected area hadn't been growing for about 10 days, and upon inspection, it was found to have adult weevils "barking" the green stems and chewing on the new buds.

Adult alfalfa weevils. (Marlin E. Rice) [1]Adult alfalfa weevils. (Marlin E. Rice) Field defoliation from adult alfalfa weevils in southwestern Iowa. (Kyle Jensen) [2]Field defoliation from adult alfalfa weevils in southwestern Iowa. (Kyle Jensen) Green alfalfa stems “barked” by adult alfalfa weevils. (Kyle Jensen) [3]Green alfalfa stems “barked” by adult alfalfa weevils. (Kyle Jensen)

Typically, we don't witness this type of problem from alfalfa weevils, but dry soil conditions place an additional stress on the crop that slows down the regrowth. During these environmental conditions, the regrowth should be scouted for the presence of weevils and their injury 4-5 days after the first cutting. If adult weevils are "barking" the green stems and the stubble is not regrowing, then an insecticide should be applied to remove the insect stress from the crop.

Table 1. Insecticides labeled for alfalfa weevil.

Insecticide Rater per Acre
(High and Low Rates)
Harvest Interval
(Days)
Baythroid 2E 1.6-2.8 ounces 7
Furadan 4F 0.5-2 pints 7-28
Lannate LV 3 pints 0
Lorsban 4E 1-2 pints 14-21
Mustang Max 2.24-4.0 ounces 3
Pounce 3.2EC 4-8 ounces 0-14
Sevin XLR+ 3 pints 7
Warrior 2.56-3.84 ounces 7

Marlin E. Rice is a professor of entomology with extension and research responsibilities.

This article originally appeared on page 185 of the IC-498(15) -- June 18, 2007 issue.


Source URL:
http://www.ipm.iastate.edu/ipm/icm//ipm/icm/2007/6-18/alfalfaweevil.html