Scouting Notes - August 2008

IR-4 releases survey results. The latest IR-4 survey results listed the top five diseases as powdery mildew, leaf spots and anthracnose, Phytophthora, crown and root rot and Botrytis. The top five insects were: mites and spider mites, aphids, thrips, scale and mealybugs and whiteflies. The top weed problems are similar for different regions of the country with a few distinctions. Of the three pest management tools (traditional, IPM and organic) used, about 43 percent chose more than one tool; 17 percent chose all three.

For more: Cristi Palmer, IR-4, (732)-932-9575; http://ir4.rutgers.edu/ornamentals.html.

APHIS withdraws rule change related to rust. In May, Animal and Plant Health Inspection Service withdrew a proposed rule that would have amended the nursery stock regulations to provide an option in which the post-entry quarantine growing period for Chrysanthemum spp., Leucanthemella serotina and Nipponanthemum nipponicum imported from certain locations would have been reduced from six months to two months. The change would have required that the grower of those plants implement a systems approach in the country of origin to prevent the imported articles from being infected with chrysanthemum white rust. The proposed rule would also have amended the definition of from.

For more: Arnold Tschanz, APHIS, (301) 734-5306.

Don’t overlook black root rot. The most common root rots in greenhouse crop are caused by Pythium and Rhizoctonia. However, black root rot caused by the fungus Thielaviopsis is a serious threat to pansies, viola, petunias and vinca and may also infect cyclamen, poinsettia, primula, impatiens, snapdragon, verbena, phlox, begonia and nicotiana. Thielaviopsis-infected plants often show symptoms similar to nutrient deficiencies such as stunting with older leaves shriveling.

Michigan State University plant pathologist Mary Hausbeck said sanitation is the best preventive measure. If the fungus is established, fungicides containing thiophanate-methyl as the primary active ingredient should be used frequently at the high labeled rate.

For more: Mary Hausbeck, Michigan State University, (517) 355-4576; www.ipm.msu.edu/greenhouseAlert.htm.

Humid, cool weather favors downy mildew. High humidity, prolonged leaf wetness and cool weather favor the development of downy mildew diseases caused by Peronospora, Bremia, Plasmopara and Basidiophora. The pathogens selectively infect ornamentals. Symptoms occur as angular, chlorotic to necrotic spots on the upper leaf surface and a purplish, downy growth on undersides.

Control depends on fungicide applications, use of resistant cultivars and cultural practices. Bess Dicklow of University of Massachusetts plant diagnostic lab recommends minimizing periods of leaf wetness by reducing density of the plant canopy and avoiding overhead irrigation.

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For more: Bess Dicklow, University of Massachusetts, (413) 577-1827; mbdicklo@umext.umass.edu.

August 2008