–by Jeff Whitworth, Field Crops Entomology
Alfalfa weevils (see fig 1) have been hatching from eggs over about the last two weeks. However, they have not been developing very quickly, nor has the alfalfa, at least throughout north central Kansas. There will be more larvae. This is always a problem for producers, to treat early or not, especially with less foliage to accept the insecticide. If your treatment threshold is reached, irregardless of time it’s probably prudent to make an insecticide application as soon as possible. Less foliage may mean better coverage and therefore kill. But, it also probably means less foliage to accept the spray and thus there may be a little less residual control. But this is always part of alfalfa weevil management.
Figure 1 Alfalfa weevil larvae and leaf damage
We also see conspicuous aphid populations all around the state—both pea (see fig 2) and cowpea (see fig 3). These aphids are causing concern, especially in areas where moisture is lacking. However, these aphids usually do not buildup to the density to actually reduce yield but more often provide a food source for many beneficials if left untreated.
Figure 2 Pea aphids
Figure 3 Cowpea aphids (received from Ed Beason)