D3495: Alfalfa weevil management in South Dakota

Tuesday, November 12, 2024

9:00 AM – 5:00 PM MST

Location: Phoenix Convention Center, Exhibit Hall 6, PCC

Presenting Author(s)

PR

Philip Rozeboom

IPM Coordinator
South Dakota State University
Brookings, South Dakota

Co-Author(s)

BM

Bradley L. McManus

South Dakota State University
Brookings, South Dakota
Adam J. Varenhorst

South Dakota State University
Brookings, South Dakota

The need for alfalfa weevil management within South Dakota alfalfa depends on whether the weevil larvae reach economic thresholds. Alfalfa weevils have a varied economic threshold based on the insecticide application cost per acre, the value of hay per ton, plant height, and the total amount of alfalfa weevil larvae per 30 stems. If an economic threshold is reached, chemical management is recommended. In South Dakota, alfalfa weevils have caused significant defoliation during the last few growing seasons. Also, multiple insect species have shown resistance to insecticides. Because of these two factors, a field, efficacy evaluation was conducted to understand what modes of action may still provide effective chemical management of the alfalfa weevil. The three modes of action tested were an acetylcholinesterase inhibitor (IRAC Group 1B), a sodium channel modulator (3), and a voltage-dependent sodium channel blocker (22A).