Submitted to: South Texas Melon Committee Annual Research Report
Publication Type: Experiment Station
Publication Acceptance Date: 12/1/1997
Publication Date: N/A
Technical Abstract: In the Lower Rio Grande Valley of Texas (LRGV), 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. D. bryoniae isolates (137) were obtained from infected fruit and vines at six locations in the LRGV. 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. Quadris, Nova, Folicur, and Rocket at 5.9 ug/ml effectively suppressed conidial germination and mycelial growth in vitro. These fungicides also prevented development of GSB symptoms on inoculted seedlings in growth chamber studies. However, in field tests, only Quadris, Bravo, and Vangard effectively controlled gummy stem blight.