–by Dr. Jeff Whitworth and Dr. Holly Davis
Alfalfa fields sampled this week in north central Kansas had not really changed a great deal with stems anywhere from 2.5 to 9.5 inches tall. Sampling the taller stems (8 – 9.5”) resulted in a composite infestation of 10%. Sampling only the smaller stems (2.5 – 4.5”) resulted in a composite infestation of 27%. The lowest overall infestation level detected from any field was 10% and the highest infestation level was 30%. Smaller stems had smaller larvae with no, or very little damage or defoliation, while larger stems often had evidence of feeding, but no larvae. Thus, it seems the earlier hatching larvae may have been killed by the recent cold weather, or at least populations were reduced. However, we did find 3rd instar larvae and even a pupa. There are also quite a few small 1st instar larvae. This probably means eggs are still hatching with more larvae to come, so at least 1 more week of monitoring would be prudent.
Pea aphids are still present in all alfalfa fields sampled but not yet in numbers to be concerned about. However, there were no beneficials, (lady beetles, lacewings, or parasitic wasps) noted either.
For more information relative to alfalfa insect management, please see the Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf