Alfalfa Weevil Controls

Listen to the article

If you listened under "Alfalfa Weevils", you heard how to decide if you need weevil control.

In an early season infestation, alfalfa only 3 to 7 inches tall:    Treat when worm feeding becomes evident, this usually requires 1 to 2 larvae per stem.

In a mid-season infestation, alfalfa 8 to 14 inches tall:   Treat when worm feeding is occurring on 30 to 50 % of the terminals & there are 4 or more larvae per stem. This feeding level can cause severe foliage loss in only 3 or 4 days.

In a late season infestation, early cutting may be advised if the weevil feeding damage is within 10 to 14 days of the normal time to cut the alfalfa. Weather should be such that windrows will be rapidly removed from the field to expose the weevil larvae to sunlight & drying winds.

If harvest must be postponed, or something may restrict rapid regrowth, then spraying before cutting may be advised.  After harvest spraying may be necessary to protect new regrowth if there are 8 or more larvae per square foot of stubble present.   Alfalfa weevil insecticides recommended for this area are:

• Carbofuran* (Furadan 4F)
• Chlorpyrifos (Lorsban 4E)
• Cyfluthrin (Baythroid 2)
• Microecapsulated Methyl Parathion
• Methyl Parathion*
• Phosmet* (Imidan)
• Malathion
• Permethrin (Pounce 3.2EC, Ambush 2E)
• Lambda-cyhalothrin (Warrior T)

Be sure to read the label for rates & restrictions.

Also see: MU XPLOR Guidesheets: Crop Publications (Forages)

Leon Stites, HLStites@oznet.ksu.edu
County Extension Agent, Agriculture
Leavenworth County, Kansas
Kansas State University Research and Extension