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Agronomy Journal Abstract -

Role of Anthracnose in Stand Thinning of Alfalfa in Delaware1


This article in AJ

  1. Vol. 70 No. 2, p. 351-353
    Received: Feb 22, 1977

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  1. E. R. Jones,
  2. R. B. Carroll,
  3. R. H. Swain and
  4. K. W. Bell2



Anthracnose, caused by Colletotrichum trifolii Bains, is widespread on alfalfa (Medicago sativa L.) in Delaware and thinning of alfalfa stands is believed to be at least partially due to anthracnose. The purpose of this field study was to determine the effect of C. trifolii on winter survival of alfalfa. Alfalfa plants growing on a Typic Haplueults soil, with and without symptoms of anthracnose, were tagged prior to winter dormancy to determine the effects of C. trifolii on winter survival. Other factors affecting winter survival of alfalfa were evaluated by removing another group of plants with and without anthracnose symptoms from the experimental site before winter dormancy. The following parameters were evaluated: root and crown rot, insect feeding on root and crown tissues, presence of new crown buds, root and crown tissue weights, and total nonstructural carbohydrate levels. Soil surrounding the roots of removed plants was analyzed for soil acidity, P, K, Ca, Mg, and B. Colletotrichum trifolii-infected plants had 22 to 85% lower winter survival values when evaluated the following spring. Colletotrichum trifolii-infected plants evaluated prior to winter dormancy had 7% smaller root systems and 29% fewer plants with new crown buds, but did not have significantly different levels of crown and root rot or root insect damage. Soil tests, indicated no relationship between soil parameters measured and anthracnose. It is concluded that anthracnose was the principal factor responsible for stand thinning of alfalfa during the winter dormant period.

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