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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.

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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, 110x)

Hyaline, single-celled conidia (400x)


1933-1st reported on sweet clover in Canada

1984 – widespread on alfalfa in the Peace River Valley of Alberta

1996 – 1st reported on alfalfa in the U.S. in Wyoming

Host Range

(J.G.N Davidson)


Alsike Clover

Bird’s-Foot Trefoil

Red Clover


Sweet Clover

Survival & Spread

(J.G.N Davidson)

  • Survival: in plant debris & in soil

- Spread: by wind & grazing animals


a. Plant Symptoms


Severe Winterkill


Close up of dead and dying plants

Farson, Wyoming Spring of 1996

Plants removed showing severe root rot


b. Root isolation

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)


Indigenous Fungus



Currently known distribution in the U.S.

(Idaho, Montana, Wisconsin, Wyoming)

Recommended Control Practices in Canada

  • 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.

  • 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

  • M. sativa varieties

  • J.G.N Davidson.

Farson, Wyoming



Recommended Control

Practices in the USA

  • Same as for Canada (items 1, 2, and 3)

  • Reaction of most U.S. varieties to BRR is currently unknown

  • 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.

  • 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:

  • University of Wyoming Bulletin, B-1136, “Brown Root Rot of Alfalfa”

  • b. BRR Evaluation Protocol for, “Standard Tests to Characterize Alfalfa Cultivars” (pending final approval)

  • [email protected]