Myrothecium leaf spot can be a minor problem on cantaloupe in Florida. The disease can affect other cucurbits including watermelon, but rarely seen in Florida.
A cantaloupe leaf showing early stages of symptoms including yellow vein limited discoloration and small to large circular or irregular lesions. Wet conditions favor disease development.
The lesions may expand and the center of the lesion breaks out making a shot hole like appearance. Lesions can merge to form large blighted sections on the leaves.
Using a hand lens or under the microscope you could see black, raised fruiting bodies (sporodochia) of the fungus in a circular pattern in the lesions.
Fungal mycelia (white fluffy growth) can be seen growing around sporpdochia on samples collected from field even without incubation in a humid chamber.
Conidia (spores) or fungi can be seen around sporodochia with numerous conidiophores. The pathogen survives in soil and can also cause stem cankers and fruit rot known as crater rot.