I had a timely email today from Brian Welton in Parma (near Jackson). He has a soy field planted after alfalfa with K deficiency symptoms, testing low on K.

The field has over-threshold populations of soybean aphid. Research by one of my former students showed that SBA survives longer and reproduces better on K-deficient plants. K deficient soybeans = aphid candy.

K deficiency is common in beans planted after alfalfa and on sandier ground. Those of you in areas prone to deficiency (especially SW Michigan – Cass, St Joe, Calhoun, etc) might want to stop by bright-yellowing fields and take a look. I attached a picture showing K deficiency/ aphid infestation in 2000 (Bruce Mackellar, MSUE).

My field crew and several reps report aphid numbers slowly increasing this week. Don’t count aphids out just yet.

Dr. Christina DiFonzo
Field Crops Entomology Program
Michigan State University