— by Dr. Jeff Whitworth and Dr. Holly Davis
Alfalfa is really living up to its reputation as a ‘sink’ right now for many different insect species, including many beneficials such as lady beetles and green lacewings. The one and only potentially serious pest that we are still seeing is potato leafhoppers, and they are in densities that exceed treatment threshold in all fields sampled. These very small, lime green, wedge-shaped insects that move in a herky-jerky manner remove fluid from the alfalfa leaves. This feeding may also introduce a toxin which initially causes the tips of leaves to turn yellow (hopper burn), but may impact the entire stem, and eventually the whole plant. This can be especially problematic this time of year when the plants need to utilize the foliage to transfer nutrients to the roots before winter. The potato leafhopper populations will hopefully be diminishing as they don’t overwinter in Kansas and thus should be heading to the southern U.S. soon. Swathing should also help diminish populations.
This time of year fall armyworms may move into alfalfa where they can add to the defoliation caused by other chewing insects already present. Fall armyworms are more commonly thought of as a pest of corn and sorghum. This time of year those crops are too mature to support the larvae and therefore the adult moths may oviposit in alfalfa.
We also noticed several green cloverworms along with one larva infected with an entomopathogenic fungus.
For more information relative to insect pest management in alfalfa, please see the KSU 2018 Insect Pest Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf