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Title: RESISTANCE CASE: GUMMY STEM BLIGHT AND BENOMYL

Author
item MILLER, M.E. - TEXAS A&M UNIVERSITY
item ISAKEIT, T.A. - TEXAS A&M UNIVERSITY
item Bruton, Benny

Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: 4/14/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: In south Texas Didymella bryoniae (Auersw.) Rehm commonly causes lesions in the crown and foliage of melons (Cucumis melo L.) but rarely on fruit. Despite routine benomyl applications, a severe gummy stem blight (GSB) epidemic occurred in Spring-1997 resulting in numerous corky-brown lesions (1-3 mm dia.) below the epidermis of cantaloupe fruit. Overall, cantaloup fruit losses were approximately 68% amounting to an estimated $15,000,000 loss. D. bryoniae isolates were obtained from infected fruit and vines at six locations. In vitro tests indicated that the EC(50) for benomyl against mycelial growth was >5.0 ug/ml for 92% of the isolates, indicating insensitivity to benomyl. Most isolates insensitive to benomyl were also insensitive to thiabendazole. Cantaloupe plants treated with azoxystrobin at 224.0 g/ha had significantly less (p=0.05) fruit with GSB lesions, higher marketable yield, lower foliar disease ratings, and fewer stem lesions than plants treated with other fungicides and the control in field studies. Chlorothalonil at 2.5 kg/ha and cyprodinil at 280.0 g/ha also effectively controlled GSB on fruit, stems, and foliage significantly better than most of the other fungicides and the control, but to a lesser degree than azoxystrobin.