Biology Management of Brown Root Rot of Alfalfa

Biology & Management of Brown Root Rot of Alfalfa F. A. Gray, C. R. Hollingsworth, D. W. Koch R. W. Groose and R. C. Larsen

Fungal Taxonomy Anamorphic (asexual) stage: Phoma sclerotioides (syn. Plenodomus meliloti & Plenodomus sclerotioides) 8 -wk-old culture on PDA Pycnidia (SEM, 110 x) Hyaline, single-celled conidia (400 x)

History 1933 -1 st reported on sweet clover in Canada 1984 – widespread on alfalfa in the Peace River Valley of Alberta 1996 – 1 st reported on alfalfa in the U. S. in Wyoming Host Range (J. G. N Davidson) Alfalfa Red Clover Alsike Clover Sainfoin Bird’s-Foot Trefoil Sweet Clover

Survival & Spread (J. G. N Davidson) - Survival: in plant debris & in soil - Spread: by wind & grazing animals

Diagnosis a. Plant Symptoms Diseased Severe Winterkill Farson, Wyoming Spring of 1996 Dead Close up of dead and dying plants Plants removed showing severe root rot

Diagnosis b. Root isolation on PDA at 500 F. after 8 weeks Note white mycelium, black pycnidia and yellow spore masses c. PCR-based SCAR markers (R. C. Larsen, USDA-ARS, Prosser, WA)

Distribution Indigenous Fungus CANADA USA Currently known distribution in the U. S. (Idaho, Montana, Wisconsin, Wyoming)

Recommended Control Practices in Canada 1. Crop rotation – Grow annual crops such as oats or barley for 3 years between alfalfa crops. Avoid rotation with other forage legume crops especially sweet clover. 2. Harvesting/Grazing Management - Avoid excessive cutting - Avoid late fall cutting - Avoid overgrazing & grazing in the fall before the ground is frozen.

3. Maintain proper soil fertility 4. Plant a resistant variety - The variety Anik (Medicago falcata) is partially resistant. - The variety Peace is the least susceptible of the Farson, Wyoming M. sativa varieties Peace J. G. N Davidson. Anik

Recommended Control Practices in the USA 1. Same as for Canada (items 1, 2, and 3) 2. Reaction of most U. S. varieties to BRR is currently unknown 3. The variety “Peace” performed well in the presence of BRR at Farson, Wyoming but may be susceptible to other major stand decline diseases in the U. S. 4. Other varieties performing well in the presence of BRR at Farson include: Ranger, Avalanche + Z and Spreador 3

Other available information on Brown Root Rot: a. University of Wyoming Bulletin, B-1136, “Brown Root Rot of Alfalfa” b. b. BRR Evaluation Protocol for, “Standard Tests to Characterize Alfalfa Cultivars” (pending final approval) c. Fagray@uwyo. edu