Pest managers, in southern Indiana, should now be scouting their alfalfa for leaf feeding from weevil larva. Higher risk fields are those that have been in alfalfa for over three years. Most vulnerable areas of the field are southern facing slopes that heat up first in the season. This pest is often overlooked during the early spring planting season.
Alfalfa weevil damage to upper foliage of stems.
Producers can manage this pest most effectively by utilizing heat unit accumulations data (base 48°F) to determine when sampling should begin and when an action should be taken. The management guidelines listed below should be used to determine when alfalfa weevil should be controlled in southern Indiana. Refer to the following map for alfalfa weevil development in your area.
Alfalfa Weevil Management Guidelines Southern Indiana
| Heat Units | % Tip Feeding | Advisory |
|---|---|---|
| 200 | Begin sampling. South facing sandy soils should be monitored earlier. | |
| 300 | 25 | Re-evaluate in 7-10 days using the appropriate HU or treat immediately with a residual insecticide if 3 or more larvae are noted per stem and % tip feeding is above 50% |
| 400 | 50 | Treat immediately with a residual insecticide. |
| 500 | 75 | Treat immediately. |
| 600 | 75+ | If cutting delayed more than 5 days, treat immediately. |
| 750 | If harvested or harvesting shortly, return to the field in 4-5 days after cutting and spray if 1) there is no regrowth and weevil larvae are present OR 2) feeding damage is apparent on 50% of the stubble and weevil larvae are present. |
Alfalfa Weevil Management Guidelines, Southern Indiana.
Amanda Mosiman, Warrick County CES ANR Educator, reported significant alfalfa weevil damage to a poorly seeded alfalfa field. Though this field is only two years old, it has been seeded twice, with plenty of sparse areas to allow weeds to flourish…alfalfa weevil too!
Plenty of weeds and weevil damage in this alfalfa field. (Photo Credit: Amanda Mosiman)
Foliage damage from alfalfa weevil. (Photo Credit: Amanda Mosiman)
