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Anthracnose stem and crown rot

Anthracnose is a serious stem and crown rot disease of alfalfa that kills individual plants and causes rapid stand decline.

It’s been controlled by plant resistance in the past. However, new pathogen types have been found. The disease may be on the rise in the Midwest.

Symptoms

brown spots on plant stems and a wilted plant with light brown leaves
Anthracnose on alfalfa

Disease symptoms include:

  • Diamond-shaped lesions near the stem’s base.
  • Lesions have a straw-colored center and brown border.
  • Stem wilting and death cause a shepherd's crook to form.
  • Plants that have symptoms are scattered through a field.

Causes

Anthracnose is caused by Colletotrichum trifolii, a fungus that produces masses of tiny spores on infected stems and crowns.

During periods of warm, rainy weather, spores are splashed from infected to healthy plants. Lesions develop on stems, causing stems to wilt and eventually die. The pathogen grows from stem tissue into the plant crown and causes a crown rot that ultimately kills the plant.

Deborah Samac, plant pathologist, U.S. Department of Agriculture

Reviewed in 2018

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