—by Dr. Jeff Whitworth and Dr. Holly Schwarting
Alfalfa weevils continue to be very active in north central Kansas. The recent cooler weather has slowed down development a little but they are still feeding. We determined development from larvae collected on 20 and 22 April. Here is what the population breakdown looks like:
| 20 AprilNo. larvae | 23 April No. larvae | |
| 12 | 1st Instars | 4 |
| 25 | 2nd Instars | 16 |
| 15 | 3rd Instars | 30 |
| numerous | Pupae | numerous |
So what does this mean? Alfalfa weevil larval feeding will continue for another 7-10 days, depending on the weather. Egg hatch and consequent larval feeding has been going on since 13 March in north central KS. Insecticides applied since that time have provided adequate protection, for the most part.
This photo shows KSU chemical efficacy trials with many different products being tested, and the obvious untreated plots plus the border around the plots. The rest of the field was treated with Stallion® by MKC in Abilene, KS and, as illustrated here seemed to work relatively well with 1 application. Remember, feeding will continue for at least another week and therefore treatment (or re-treatment) may still be appropriate.
Alfalfa aphids, mainly pea aphids, are becoming more numerous throughout north central Kansas. Treating for alfalfa weevils probably pretty much decimated the natural enemies/beneficials and they will not repopulate as quickly as the aphids migrate in to infest fields.