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Brown root rot of alfalfa

Since the 1920s, brown root rot (BRR) has been regarded as an important disease of forage legumes, including alfalfa, in the northern regions of North America.

Aboveground symptoms of brown root rot (BRR) consist of plants that are either slow to green up in the spring or die during the winter. In such instances of winterkill, stand losses often are assumed to exclusively be caused by exposure to harsh winter weather conditions.

However, we now know BRR contributes to plant death in Minnesota alfalfa stands in areas where Phoma sclerotioides (P. sclerotioides) – the pathogen that causes the disease – is present.

Disease symptoms

Substantial stand loss can occur if conditions support the disease's development. Losses either happen in a single winter season, or gradually over many years.

Root rot is common on diseased tap, lateral and feeder roots, as well as on the delicate nodule tissues that contain nitrogen-fixing bacteria.

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Understanding BRR

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Managing the disease

There are limited disease management strategies for soil-borne pathogens. Overall, strategies should focus on maintaining good plant health, particularly as the growing season draws to a close.

Like other disease issues, an integrated management approach is the best strategy to minimize the effects of BRR in your stand.

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Chemical control

Fungicide application isn’t considered to be an effective tool for managing BRR because active ingredient activity is needed in the root tissues of mature plants. Seed treatments or foliar applications of fungicides won’t benefit diseased roots.

The pathogen causing BRR of alfalfa is widespread across Minnesota, but disease severity is closely linked with fall to spring weather conditions and stand management.

In a worst case scenario, the disease can kill plants from fall through spring. In less severe cases, diseased plants may survive and even somewhat recover depending on their susceptibility level and overall health. Managing crop stressors will help extend the productive life of your diseased alfalfa stands.

The use of trade, firm or corporation names is for your information and convenience. Its use doesn’t constitute an official endorsement or approval by the U.S. Department of Agriculture or the Agricultural Research Service.

Charla Hollingsworth, former Extension plant pathologist; Deborah Samac, plant pathologist, U.S. Department of Agriculture Agricultural Research Service; Paul Peterson, former Extension agronomist; Doug Holen, former Extension educator and Howard Person, former Extension educator

Reviewed in 2018

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