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Disease Control and Pest Management

Botrytis Blight of Exacum affine and Its Control. J. C. Trolinger, Graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650, Present address of senior author: Technical Division, Yoder Brothers, Inc., P.O. Box 68, Alva, FL 33920; D. L. Strider, professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 74:1181-1188. Accepted for publication 16 April 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1181.

Botrytis cinerea caused a severe blight of potted exacum. Girdling stem cankers, wilting, and death were the most severe symptoms. Isolates of B. cinerea from geranium, zinnia, and tomato caused similar and characteristic disease symptoms on exacum. A disease index based on percentage of plant blighted is presented. Crowded spacing significantly increased disease severity. Benomyl at 0.60 g active ingredient (a.i.) per liter did not control the disease in the greenhouse. Tolerance of B. cinerea to benomyl was indicated in vivo and in vitro. Chlorothalonil plus benomyl at 0.56 + 0.15 g a.i./L, respectively, and chlorothalonil at 1.4 g a.i./L, controlled the disease without phytotoxicity. Bitertanol at 0.08 g a.i./L, iprodione at 0.90 g a.i./L, triadimefon at 0.01 g a.i./L, and vinclozolin at 0.30 g a.i./L were phytotoxic. Iprodione and vinclozolin were most toxic to B. cinerea in vitro, followed by chlorothalonil + benomyl and chlorothalonil alone. Triadimefon, mancozeb, bitertanol, and benomyl were less toxic in vitro. Vinclozolin at 100 μg a.i./ml incorporated in synthetic medium was fungicidal and a lower concentration was fungistatic. Mycelial growth occurred at 4- 36 C, but was scant at 30- 36 C on potato-dextrose agar (PDA), acidified PDA, glucose-asparagine (GA) agar, and oat grain medium. After 4 days of growth on liquid GA, optimum temperature for mycelial growth was 16- 28 C; after 14 days of growth, 16- 24 C was optimum.

Additional keywords: benomyl resistance, gray mold.