Cercospora (Frogeye) Leaf Spot

A fungus (Cercospora Capsici) that is abundant during periods of warm weather coupled with high humidity. As its name suggests, the necrotic spots are circular in shape. Due to the frogeye appearance of these lesions, it is also commonly referred to as “Frogeye Leaf Spot”. Spores of this fungus can come on infected seeds, survive in the soil (infected plant material) and is transferred by water (rain, irrigation – foliar watering), wind and contact (plant to plant or hand to plant). This fungus will spread rapidly in hot, humid environments. The spores can survive in soil and decomposing infected plant material for up to 2 years, if conditions are favourable.

The infection may start at first as tiny yellow spots on the leaf surface. On closer inspection you may find a tiny black spore in the centre. These spots rapidly expand into necrotic spots that are circular in shape. As these circles expand they take the form of a blackish/dark brown ring with a yellow halo. The center of the dark ring will be sunken and have a reddish brown appearance. The centres of these necrotic lesions will eventually turn ashen grey and may drop out, leaving a hole in the centre of this ring. Left untreated, leaves will yellow and fall off the plant.

While Cercospora Leaf Spot does not affect fruit on plants, the lesions it creates on the leaves can give secondary infections an opportunity to infect leaves and fruit. This fungus spreads rapidly and easily and can be tricky to get under control. While not lethal, this is a difficult fungus to get rid of.

Here are suggestions for the control of this fungus:

• Isolate your plant from other healthy plants to avoid any contact.
• Remove infected foliage and dispose of safely in refuse. Do not add infected plant material to the compost pile.
• Wash hands when handling the plant. Clean any tools that have been in contact with infected plants before coming in contact with other healthy plants.
• Treat the plant with a recommended fungicide (Copper based). See your nursery for advice. This can help control the disease on infected plants.
• Use drip irrigation and avoid overhead (foliar) watering and irrigation. The fungal spores can be spread by water droplets.
• Crop rotation is recommended if infection occurs in the field. The spores are known to survive for up to 2 years in moist heavy soils containing infected plant material.
• The safest measure to prevent spread of this disease is to remove infected plants and dispose of safely.