Field Crops Plant Pathology

Alfalfa disease management – prevention is the key

• Select high-yielding, winter-hardy varieties with resistance to Phytophthora root rot, anthracnose, Verticillium wilt and Aphanomyces root rot.

• Select well-drained fields.

• Plant in a well-prepared seed bed when soil moisture is adequate for quick germination and seedling emergence. For late summer no-till seeding, plant as early in August as possible to avoid seedling losses due to Sclerotinia crown and stem rot.

• Use seed-treatment fungicides specific for Phytophthora and Pythium to reduce losses from damping off. Most high-quality varieties now come pretreated with fungicides.

• 

  Alfalfa seedlings with signs of Aphanomyces infection

  Minimize traffic over the field. Crown damage from heavy equipment provides an entry way for pathogens as well as causing soil compaction which promotes root rots.

• Harvest on time. Proper harvest intervals will ensure adequate storage of reserves in taproots while minimizing the buildup of disease organisms on leaves, stems and crowns.

• Control insects, primarily alfalfa weevil and potato leafhopper, to minimize plant stress.

• Rotate to corn or small grains between alfalfa crops. Do not follow alfalfa with alfalfa.

Adapted from Alfalfa Diseases, Bulletin 631-98, Ohio State University

Aphanomyces Root Rot in Alfalfa – bulletin in pdf format

Alfalfa Diseases in Illinois

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University of Wisconsin- Extension Forage Resources
visit this site for comprehensive alfalfa management information

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Does the Use of a Foliar Fungicide Improve Alfalfa Forage Production?

Recently the fungicide Headline® received a label for use on alfalfa and there are questions from growers and university researchers regarding the benefits using foliar fungicides in alfalfa grown for hay. Additionally, there is interest and justified concern for the use of tank mixing a fungicide with an insecticide to determine if there is a positive synergistic yield response.

The results from two Wisconsin trials in 2011 are reported here.  The results indicated no consistent response to foliar fungicides across second and third crop alfalfa. While there was evidence of reductions in disease severity and defoliation in some of the alfalfa cuttings, overall, there was no strong evidence of differences in terms of yield. Based on this year’s trial, additional trial data are needed before recommendations can be made regarding foliar fungicide use in alfalfa.