Alfalfa has a tremendous ability to survive and grow under dry conditions, but summer 2016 was one of the wettest on record for much of Kentucky. As a result, the University of Kentucky (UK) Plant Diagnostic Laboratory received a number of samples of diseased alfalfa, especially from seedling stands, from producers.

The lab reported cases of water mold, root rot, and seedling blight (caused by Aphanomyces, Phytophthora, and other fungi) early this growing season. Normally, fungicides on coated alfalfa seed prevent most seedling diseases, but it appears this year’s wet and humid conditions overwhelmed the seed treatments in many fields.

Additionally, there was a tremendous amount of summer black stem in the past few months. This disease is not uncommon in Kentucky, but this year it showed up early and continued throughout summer.

The lab also identified cases of Rhizoctonia web blight, which is unusual and indicates very wet and humid conditions. Alfalfa has no genetic resistance to either summer black stem or Rhizoctonia, but good management normally allows the plant to survive these diseases. Some stands were so severely affected that they had to be replanted or will have to be taken out of production