Alfalfa Weevils Still Active

April 7, 2000
The up-and-down temperatures have caused some starts and stops in alfalfa weevil development, but most people know they're still out there. Numbers of alfalfa weevil larvae in fields in southern Illinois have been relatively high, and small larvae are beginning to show up in central Illinois. Matt Montgomery, Extension Unit Assistant in Sangamon County, reported finding first instars during the week of March 27.

Bob Scott with the Illinois State Water Survey has supplied us with maps of accumulated heat units (above a base temperature of 48°F) from January 1 through March 31, 2000 (Figure 2) and projected heat-unit accumulations from April 1 through April 14, 2000 (Figure 3). Despite the unusually warm temperatures in March, heat-unit accumulations are not that much advanced from what we witnessed last year.

Hatching of overwintering eggs usually occurs when 200 degree-days accumulate beyond January 1, and we suggest that scouting should begin when between 250 and 300 degree-days accumulate. An early peak of third-stage larvae from overwintering eggs occurs after an accumulation of 325 degree-days; a second major peak of third-stage larvae from spring-deposited eggs occurs after an accumulation of 575 degree-days.

Keep scouting, and keep sending us your reports.--Kevin Steffey

Author: Kevin Steffey