— by Dr. Jeff Whitworth and Dr. Holly Davis
Recently mowed alfalfa around north central Kansas still seems to have relatively robust populations of pea aphids. These aphids tend to be more problematic during the cooler weather of spring and fall, but with the cloudy, cooler temperatures so far this spring, they are still doing quite well. Also, most fields treated for alfalfa weevils have few beneficials yet, although they do appear to be coming back. Warmer temperatures and resurgent densities of beneficials should help control these pea aphid populations without the need of an insecticide application. However, if summer temperatures are lower than usual, pea aphid populations may persist and thus monitoring should continue.
Potato leafhoppers are increasing in north central Kansas. Populations sampled were all adults, which means they have recently migrated into the area. These adults will be depositing eggs in alfalfa stems and the nymphs will emerge to begin sucking plant fluids from the alfalfa. If potato leafhopper populations are at, or exceed, treatment thresholds and the alfalfa has recently been swathed, so that it is a few weeks prior to the next cutting, an insecticide application may be justified.
Keep in mind that potato leafhopper and pea aphid populations can be greatly impacted by weather so they should continue to be monitored. For more information regarding these and other alfalfa pests, please see the KSU Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf