Pest Of The Month: Cercospora Leaf Spot

In the state, frogeye leaf spot is most common in North Florida and early plantings in South Florida. Symptoms occur in leaves, stems, and the stalks of both leaves and fruit. Leaf lesions are quite distinctive and allow for quick and relatively easy field diagnosis. Leaf spots are circular to somewhat oval with a light tan center and a distinctive, dark-red border. Spots later become tan with a dark ring and a yellowish halo around the ring, resulting in a “frog-eye” appearance.

Under moist conditions, thin, needle-like spores of the causal fungus may be seen using a hand lens or other magnification in the center of the spots. The affected centers of lesions dry up and often drop out as they age. When numerous spots occur on the foliage, the leaves turn yellow and may drop or wilt. Defoliation is often serious, exposing fruits to sun scald and reducing yields.
Spots also develop on stems and petioles but they are oblong rather than circular. Fruit are unaffected and no symptoms of this disease occur on the pepper fruit themselves.

The fungus survives in or on seed and old affected leaves and plant debris in the soil. Spores will survive in infected debris for at least one season.
Foliar infection occurs by direct penetration of the leaf. The fungus spores require water for germination and penetration of the host. Heavy dew is sufficient for infection to occur. The disease is most severe during periods of warm temperatures and excessive moisture (either from heavy dew, rain, or overhead irrigation).

Fungal growth can occur from temperature is 45°F to 95°F but is most active when temperatures are in the high 70s and low- to mid-80s. The fungus is spread by splashing water, wind-driven rain, wind, on implements, tools, workers, and by leaf-to-leaf contact.

As with all pathogens, an integrated approach is important in controlling the disease. Growers should plant certified seed from disease-free areas. Proper plant spacing in the field is helpful to allow for good air circulation and to reduce extended periods of leaf wetness. Deep incorporation of crop residues and rotating crops using a two-year rotation period will assist in reducing pathogen survival between seasons. Field plantings should be scouted carefully for the first incidence of the disease particularly after extended periods of leaf wetness and warm temperatures. If symptoms appear, apply a protectant fungicide as soon as possible. Varieties differ in their susceptibility to frogeye leaf spot, but the reaction of most varieties is unknown.

If disease is confirmed, a regular fungicide spray program should be initiated. Protectant fungicides, such as copper, are useful in controlling the disease.