By Phillip Glogoza, Extension Educator - Crops
The cool temperatures have delayed alfalfa weevil population development in the region. In west central MN, first cut got underway two weeks ago. As we move northwest, first cut may just be beginning for some. In some cases, cutting alfalfa may have removed significant eggs laid in stems, while in other sites young larvae are feeding in the growing terminals, whether it is regrowth or uncut alfalfa.
Degree day models provide some guidelines for where the weevil population development should be and an indication of when feeding injury is most pronounced. The NDAWN map for DD through June 17 and the table 1 insert will help you determine where your fields are at this time. Table 2 summarizes treatment decisions for both pre- and post-cut treatment thresholds.