Pictured: Alfalfa weevil leaf feeding. Photo by K. Hamilton DATCP
The state Department of Agriculture, Trade and Consumer Protection conducted surveys in between rain showers this week for alfalfa pests.
As the first alfalfa harvest ramps up, alfalfa weevil larvae have become common in alfalfa sweep net collections. Feeding pressure has increased in southern Wisconsin fields.
Sampling across Columbia, Dane, Dodge, Green, Iowa, Jefferson, Rock, and Sauk counties found mostly light to moderate leaf feeding (10-30 percent) by weevil larvae. A few fields had heavier feeding at or above the 40 percent economic threshold.
Of the 57 alfalfa fields surveyed May 22-28, four had heavy defoliation affecting 50-60 percent of stems, 18 had moderate feeding on an estimated 20-40 percent of stems, and 35 had light feeding on up to 10 percent of plants.
Alfalfa fields with above-threshold leaf feeding (40-60 percent) were found in Green, Jefferson, and Rock counties. This week’s finding of the heaviest feeding pressure in the south-central region aligns with the UW-Madison Alfalfa Weevil model forecast. It signals that cutting the first crop should be a priority for the next rain-free window.
Check alfalfa regrowth for signs of weevil injury four to five days after harvest. Check until the new growth of the second crop is established. The economic threshold for regrowth is reached if 50 percent of new stems or crown buds show damage, and weevil larvae are still actively feeding in the field.
Learn more: https://www.youtube.com/watch?v=Y8Q0A8ZVZL8
