Alfalfa Weevil Update - 04/18/25

Insecticide Applications – and Weevil Numbers On The Rise…

While sampling tailed off this week as previously scouted stands were sprayed – weevil numbers in untreated fields continued to climb as indicated below:

If you have not yet treated, evaluate fields soon! If you have treated, make preparations to resume scouting following appropriate re-entry intervals (REI).

What About Treated Fields?

A couple of observations from previously treated fields:

• Products worked! Any re-sampled (sweep – not stem – sampling) field showed few larvae. Pictured below (Treated – Left; Untreated – Right) are results from a field with an untreated check strip. While difficult to see, most of the green in the pictures are alfalfa weevil larvae. While the application didn’t kill every weevil larvae, it did kill most.

• Labels differ in how they affect other present insects as well. In some fields, weevil pressure has been reduced by the insecticide application – but aphid pressure is still prevalent. Some of it can be explained by products being labeled for one pest but not another. Some may be due to applications reducing beneficial insects while after our target pest.
• Alfalfa is growing well! If you applied/are planning to apply an insecticide, be aware of pre-harvest intervals (PHI) associated with any used product to insure you aren’t trying to harvest before appropriate harvest intervals have been honored.

Have a great weekend!

David G. Hallauer, Meadowlark District Agent, Crops & Soils