Southern Blight

 

This fungus pest is very persistent in the soil so a persistent fungicide is recommended, or several applications of a less persistent one. Terrachlor® (if you can get it) works well because it is persistent. A 10% bleach solution also works in quantity as a drench. Try applying the fungicide in anticipation of the problem next year. Treat areas where it appeared this year as soon as the hot dry weather of late June in the South or July in the Midwest begins. Remember it is soil borne (not in the plants) and drench the area well.


Stem Blight, Sclerotium rolfsii

These are characteristic symptoms of Stem Blight, Sclerotium rolfsii, including yellowing of the leaves, starting at the tips, is one of the first signs.  The petioles or leaf stems are usually affected at the base.  Note the disintegration of the petioles with white fungal mycelia (red arrow) and occasional off-white to tan sclerotia, or fruiting bodies (blue arrows).

Also I have seen some correlation between using hardwood bark mulches and the occurrence of this disease in this area. I would think especially mulches that are from ground stumps may be more of a problem.  Spots: Most round or oval brown spots are the result of fungus infections. They are usually secondary fungus infections or areas of dead or stressed tissue that fungus invades. (Healthy hostas that are active growing are not as open to these fungi.) Numerous tiny brown spots, like pin punctures, usually early in the season are the result of aphids. Aphids can be a problem if cool damp weather persists in the spring or on plants grown in hoop houses or under frost cloth. The numerous punctures made by the sucking mouth parts of the aphids can later become infected with fungus. This fungus can then be spread to healthy plants through the sap in their mouths. A systemic pesticide like Orthene® will kill the aphids in one spraying. Insecticidal soaps work also but may need to be applied more than once. Usually warmer weather and good air circulation will limit aphid populations later in the year. Any fungicide like Daconyl® will slow the fungus.

 

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