–by Dr. Jeff Whitworth, Professor, Field Crops
Alfalfa weevil larvae have been hatching throughout south central and north central Kansas for the last couple of weeks. First larvae/feeding reported from south central Ks. on 15 March and on 21 March from north central parts of the state. The easiest way to find new larvae is to note small, pinprick sized holes in leaves and/or brooming feeding damage on the tips of new terminals (see figure 1). Larval hatching and subsequent feeding will only increase as temperatures increase. It takes temperatures in the mid to low 20’s(F) for a couple hours to actually adversely affect young larvae (remember 2018- and last year, 2020, in mid-April). Also, please remember– utilize whatever treatment threshold that has been successful for you in the past (hopefully-not just spray because your neighbor is–we use a 33-50% infestation level using the “stem count bucket “sampling method). In addition, it is really important to spray with an adequate amount of carrier, i. e. water, to achieve good coverage. After application, and the reentry interval (REI) for the product used, continue monitoring as eggs may continue to hatch for another few weeks, or until swathing. Also, always check the preharvest interval (PHI) for your product of choice.
Figure 1: Leaf feeding plus 1 day old larva (photo by Cody Wyckoff)