Aphanomyces in Alfalfa? Symptoms and Management Tips.

Aphanomyces root rot is a pathogen that infects annual and perennial species in the legume family. It is often misidentified due to similarities with other legume diseases and nutrient deficiencies. In alfalfa, the disease may infect plants from early emergence to maturity. New seedlings often appear to be stunted with yellow cotyledons and very poor root development with few lateral roots. Established plants that become infected have very poor root development and have less nodulation (Figure 1). Yield losses result from reduced seedling stands and poor producing plants. Infected plants are slower growing in the spring and slower to recover after cutting. Currently, two races of Aphanomyces have been identified, Race 1 and a more virulent Race 2.

Figure 1. Aphanomyces root rot. Picture courtesy of Dr. Craig Grau, University of Wisconsin-Madison. Permission to use granted by Dr. Damon Smith, University of Wisconsin-Madison. Figure 1. Aphanomyces root rot. Picture courtesy of Dr. Craig Grau, University of Wisconsin-Madison. Permission to use granted by Dr. Damon Smith, University of Wisconsin-Madison.

Steps in Managing Aphanomyces in Alfalfa Fields.

  • Improve drainage to prevent areas with standing water. Not only will it help with Aphanomyces, but with other threats to alfalfa including Phytophthora, drowning out, and ice sheeting. 
  • Test soil for the presence and race of Aphanomyces. This is important to know when making cropping or product purchasing decisions.
  • Plant resistant alfalfa varieties. Many alfalfa varieties have resistance to Race 1 and Race 2 Aphanomyces. In most cases, an alfalfa variety that is listed as Race 2 resistant is also resistant to Race 1. 
  • For more information about Aphanomyces and other alfalfa management decisions, go to www.channel.com for alfalfa management articles or visit with your local Seedsman.

Doug Gloystein

Technical Agronomist

Legal Statement

ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields.

Channel® and the Arrow Design® and Seedsmanship At Work® are registered trademarks of Channel Bio, LLC. All other trademarks are the property of their respective owners. ©2021 Bayer Group. All rights reserved.

This browser is no longer supported. Please switch to a supported browser: Chrome, Edge, Firefox, Safari.