Progress and losses due to gummy stem blight were studied in field plots artificially inoculated with Didymella bryoniae. For the temporal disease progress study, two fields (24 x 32 m) were established in areas free of the disease, without any history of cucurbit cultivation, and no control measures were applied. Data for the disease progress curves were obtained from the mean diseased leaf area in an area of 768 m², at 45; 50; 55; 60; 65; 74; 80 and 87 days after planting (DAP). Disease progressed according to the exponential model, even under marginally favorable environmental conditions. Maximum severity values were observed 87 DAP (12.5-13.6% diseased leaf area). The crop loss experiment was laid out in a randomized completed block design with five disease levels and four replicates. Disease levels were obtained with the application of five fungicide doses (per 100 L of water) of a mixture of active ingredients chlorothalonil and methyl thiophanate, as follows: (a) 0 g a.i. (control); (b) chlorothalonil 25 g + methyl thiophanate 10 g; (c) chlorothalonil 75 g + methyl thiophanate 30 g; (d) chlorothalonil 125 g + methyl thiophanate 50 g; (e) chlorothalonil 250 g + methyl thiophanate 100 g. Disease severity was evaluated once, 78 DAP, with a disease scale ranging from 0 to 9, based on the percentage of diseased leaf area. Maximum disease levels were observed 78 DAP in control plots (26.5% diseased leaf area). There was high negative correlation (r=-0.96) between disease levels and fruit yield. Yield losses due to gummy stem blight reached 19.2% and chemical control reduced disease levels significantly.
Citrullus lanatus; epidemiology; control
