Capsicum & Chilli
During the initial stage of infection, brownish circular spots with light-gray centers and reddish-brown margins appear on leaves. Later on, they develop into large circular tan spots, up to 1.5 cm in size, formed by dark concentric rings growing around a whitish center. A rough dark ring and a yellow halo gives the spots the characteristic 'frog-eye' appearance. As the spots become more numerous, they gradually coalesce to form large leaf lesions. The white center often dries and falls out, leaving a ‘shot-hole’ effect. At later stages of the infection, leaves turn yellow and wilt or drop, exposing fruits to sunscald. In severe cases, spots can also be observed on fruit stalk and calyx, often resulting in stem-end rot.
The symptoms are caused by Cercospora capsici, a fungus that is particularly resilient in the tropics, affecting plants both in seedbeds and fields. It survives from one season to the other in or on seeds, in the soil and also on infected plant residues. It spreads via water, rain, wind and leaf-to-leaf contact and on implements, tools and workers. Foliar infection occurs by direct penetration of the leaf and is favored by prolonged leaf wetness. Optimal conditions for infection are warm temperatures around 23 °C and relative humidity of 77-85%. If these conditions are met, it is very likely to affect yields significantly, particularly if the infection takes place at the beginning of the season.
Seed treatment with hot water at 52°C for 30 minutes is a way to reduce the presence of the fungus on seeds. Note that the treatment may also affect seed germination if not carried out properly (excessive time or temperature). Foliar spray of products containing copper hydroxide can be done, starting when the spots first appear, and continue at 10-14 days intervals until 3-4 weeks before the last harvest. It is important to spray both sides of the leaves.
Always consider an integrated approach with preventive measures together with biological treatments if available. Seed treatment with captan (3g/kg) works fine to fight the disease. Other treatments to control this disease include foliar spray of products containing copper hydroxide, chlorothalonil or mancozeb. Treatment should start when the spots first appear and continue at 10-14 days intervals until 3-4 weeks before the last harvest. It is important to spray both sides of the leaves.