— by Dr. Jeff Whitworth and Dr. Holly Davis
Most alfalfa monitored in north central Kanas in the last week has started flowering and swathing seems to be well underway. Alfalfa weevil infestations, which we sampled throughout NC KS, never did exceed an overall 30% infestation level (using the cut stem bucket shake method). This year, any time larval numbers started increasing, a sub-freezing cold spell came through and killed many newly hatched larvae.
Since alfalfa fields were not treated for alfalfa weevils they are currently a great place for many beneficials. Uncut fields sampled in the last week had healthy populations of pea aphids as well as a few spotted alfalfa aphids.
However, as beneficial populations increase, these aphid populations are rapidly declining. Presently there are many lady beetles, both larvae and adults, and more adults will be active very soon as there are also many pupae. There are also significant numbers of parasitic wasps parasitizing these aphids as indicated by many mummies.
Additionally, there are a few green lacewings present. All this beneficial insect activity results in aphid populations declining significantly in the fields we sampled. On 11 May, pea aphid populations averaged 50-60/stem, dropping to 6-7/stem on 16 May. Hopefully, after swathing, the beneficials will still be present in sufficient numbers to continue providing aphid control but fields should still be monitored. For more information relative to alfalfa insect management, please refer to the 2018 Alfalfa Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/mf809.pdf