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Pests: Southern Blight & Spots, by Bob Solberg Southern Blight: This fungus pest is very persistent in the soil so a persistent fungicide is recommended, or several applications of of a less persistent one. Terrachlor if you can get it works well as it is persistent. 10% Bleach works also 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. 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 invade. (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 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. Hostas that are heat dormant or are stressed due to lack of water or nutritional deficiencies in mid-summer may develop red spots. These are a secondary anthracnose infection and are more pronounced on gold hostas especially 'Tokudama' types but are present on green and blue hostas also. Again a systemic fungicide will help control the spread of the fungus but not make the spots go away. Good cultural practices, (regular irrigation, maintaining adequate nitrogen levels throughout the summer, and keeping the plants cool buy overhead watering or shading them), may decrease this pest problem. Unlike Southern Blight, none of these fungus problems are persistent. Good fall garden cleanup of old foliage may reduce the number fungus spores in the area but the susceptibility of certain hostas (i.e. 'tokudama') to infection maybe genetically based.
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AAA Ornamentals,
8S953 Jericho Road, P.O. Box 277 ~ Big Rock ~ Illinois |