For several decades, farmers have experienced a common stand-establishment disease syndrome when spring-seeded alfalfa was followed by extended periods of wet weather. Seedlings affected by this syndrome exhibit severe stunting as well as yellowing and reddening of seed leaves (cotyledons), but they do not wilt or collapse, as they might from a damping-off disease. Commonly, the problem affects most or all of the field.

Based on research that began in the 1980's, we suspected that a fungus called Aphanomyces euteiches (hereafter simply called Aphanomyces) was responsible. This root-rot fungus can be found in the majority of alfalfa fields we have sampled in central and western Kentucky. However, for many years we lacked conclusive proof that Aphanomyces was, in fact, the cause of this common problem in spring-seeded alfalfa. We also did not have rigorous proof that the syndrome could be avoided by sowing Aphanomyces-resistant alfalfa varieties, which started becoming commercially available in the early 1990's. In this report, we provide a brief summary of research to support our new recommendation: that spring-seeded alfalfa should be sown only with varieties having an R or HR rating to Aphanomyces root rot (ARR).

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