Evaluation of fungicides and cultivars for control of gummy stem blight of rockmelon caused by Didymella bryoniae

Abstract

Ten fungicides were evaluated in 2 experiments with rockmelons for control of gummy stem blight caused by Didymella bryoniae. The fungicides (g a.i./ha) tebuconazole (100 and 160), fentin hydroxide (226), prochloraz Mn (231 and 370), benomyl (400), benomyl (400, 500) plus white oil (2 L/ha), propiconazole (100), mancozeb (1600), mancozeb plus phosphonic acid (1600 + 1000), myclobutanil (237), and chlorothalonil (1600) significantly (P<0.05) reduced the incidence and severity of gummy stem blight compared with an unsprayed treatment. Total weight of fruit and number and weight of marketable fruit in plots treated with fungicides were increased (P<0.05) by as much as 55% compared with untreated plots. Premature fruit ripening was reduced where there was effective disease control. Tebuconazole was the superior chemical but was phytotoxic when applied at 160 g a.i./ha. Fentin hydroxide caused burn on old foliage. Two accessions of Cucumis melo obtained from the United States Department of Agriculture (PI 266934, PI 266935) and 5 commercial cultivars were evaluated for resistance to gummy stem blight in a field experiment. PI 266934 and PI 266935 were highly resistant and the commercial cultivars were susceptible.