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black patch (Rhizoctonia leguminicola) - Horses [Skip to Content]
Illinois Livestock Trail by UNIVERSITY OF ILLINOIS EXTENSION


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QUESTION
After 22+ years using the same pasture, I've had a problem with black patch this year. I can't find much information about where this came from (is it dormant in soil until right conditions?) and what, if anything, I should do about it. My horses slobbered so excessively that I had to remove them from the pasture for fear of dehydration. Any information or direction to resources dealing with this would be appreciated. Before I do anything drastic, like killing off all legumes and reseeding, I'd like to get more information.

Thanks for any help you can provide.


ANSWER

Black Patch is a fungal disease caused by Rhizocotonia leguminicola that can be found on clover or alfalfa leaves. The lesions are blackish brown and irregular shaped on the leaf of the clover plant. The rainy conditions and high humidity of this past year were right for the development of Rhizoctonia leguminicola.

The slobbering you mentioned is specifically caused by slaframine which is an indolizidine alkaloid and a metablite of Rhizoctonia leguminicola. After horses eat the fungus-infected clover or alfalfa for several days, they begin to salivate excessively and lose weight. Pregnant mares may abort if they continue to consume the infected clover or alfalfa. Recovery occurs rapidly once horses have been removed from the infected pasture.

Problem pastures can be used for animals if they are mowed, the infected hay is removed, and the regrowth has no brown spotting on the leaves.







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