Aphanomyces in Alfalfa Survey - Request for Soil Samples!

Aphanomyces root rot is considered a major alfalfa disease. There are many alfalfa fields in Ontario that show visual symptoms similar to aphanomyces, although this has not been confirmed by laboratory analysis. Aphanomyces can be managed by the use of available Race 1 and Race 2 resistant alfalfa varieties.

Aphanomyces distribution and its impact in Ontario is not well understood. A limited 1992 survey in southwestern Ontario indicated infection in 6 (in 5 different counties.) of 83 alfalfa fields surveyed (7%). Based on the rapid spread of Aphanomyces in neighbouring States in the past decade or so, it seems very possible that has also become a significant alfalfa disease in Ontario. For this reason, OMAFRA, supported by the Ontario Forage Council, is conducting a new survey to update the geographic and race distribution of Aphanomyces in the province.

We Need Your Help!

If you have or know of any fields with potential problems, contact us so that we can sample these fields.

What To Look For?

New Seedings

Seedlings appear stunted, yellow and have a under developed root system with very few lateral roots. The roots often are grey and watersoaked, and turn brown as the disease develops. The cotyledons and first true leaves can be yellow in colour.

Established Stands

General symptoms include poor root development with the absence of the fine, fibrous roots and root hairs, along with reduced nodulation. Affected plants appear short, stunted and yellow in characteristic oval-shaped patches. There appears to be a definite separation between affected patches and normal plants. Because of the stunted root system, infected alfalfa stands do very poorly during extended dry weather, when these patches are particularly noticeable. Plants are slow to break winter dormancy, slower to develop in the spring, lack vigour and regrowth following harvest is delayed. (Photos 1 & 2.)

Photo 1 - Aphanomyces Appearance In An Established Stand
(courtesy Of Dr Dan Undersander, University of Wisconsin)

Photo 2 - Aphanomyces Infected Plants (Bottom) Compared To Normal Plants (Top)
(courtesy Of Dr Dan Undersander, University of Wisconsin)

How to Sample

Soil samples are to be collected from the upper 6 inches of soil and from 25 locations. Take a shovel or cup of soil from these locations throughout the field. Since a bio-assay is needed to test for Aphanomyces a large volume of soil is necessary to grow the plants. Therefore, 4 to 8 liters of soil (1-2 gallons) is required. The collected soils must be kept in the cold or frozen if possible until delievered.

Who to Contact

Joel Bagg 705-324-5856 joel.bagg@ontario.ca
Albert Tenuta 519-674-1617 albert.tenuta@ontario.ca