Losses in fresh-market tomato production in Florida due to target spot and bacterial spot and the benefits of protectant fungicides

Three large-scale field tests were conducted under commercial growing conditions in southwestern Florida to quantify yield losses associated with foliar diseases of fresh-market tomatoes, document the benefits of protectant fungicides, and establish a protocol to be used in making yield-loss assessments for fresh-market tomatoes. The benefits of protectant fungicides were amply demonstrated in two of three experiments. Marketable and extra-large fruit yields were reduced 30 and 43% in these tests, respectively, when no fungicides were used. Net returns on investment were $7,800 to $14,800/ha greater in plots treated with chlorothalonil than in control plots. Much of the loss in marketable yield was due to direct damage to fruit by the target spot fungus. As much as two-thirds of the fruit had to be discarded in no-spray plots because of blemishes from target spot. Tank-mix sprays of copper-mancozeb provided good early season control of bacterial spot, but there was no correlation between bacterial spot damage levels and yield or monetary losses. Little return on investment in protectant fungicides was recorded where target spot was not a factor in the third experiment, even though low to moderate levels of bacterial spot were present.