Diseases of Guava

a) Algal leaf spot: Cephaleuros virescens

• Orange, rust-colored, dense, silky tufts on both upper and lower surfaces of leaves which turn reddish-purple in color as they mature; if tufts are scraped away, a thin gray-white or dark-colored necrotic spot remains on the leaf; bark on twigs and branches may be cracked; young stems and fruit may also be attacked.
• Ensure trees receive adequate fertilization, irrigation and and are properly pruned to avoid stress on the plants and promote air circulation through the canopy; periodic applications of a copper based fungicide is usually enough to control the disease.

b) Anthracnose: Colletotrichum gloeosporoides

• Sunken, dark colored lesions on mature fruit which may become covered in pink spores; lesions coalesce to form large necrotic patches on surface of fruit.
• The primary method of controlling the disease is to plant resistant guava cultivars; both systemic and non-systemic fungicides are effective at controlling the disease and are usually applied shortly before flowering and during fruit development.

c) Pseudocercospora leaf spot: Pseudocercospora psidii

• Small irregularly shaped or roughly circular dark brown lesions with darker brown border on upper surface of leaves; lesions may also be present on stems and fruit.
• under humid conditions, fungus may sporulate and gray tufts of mycelium may be visible in the center of lesions; lesions may coalesce to form large necrotic patches.
• In areas where environmental conditions are conducive to the development of the disease, chemical control using appropriate fungicides is necessary to control the disease; copper-containing fungicides are most effective.

d) Rust: Puccinia psidii

• Orange to red pustules appearing on leaves, young shoots, flowers and/or fruit
• leaves distorted; defoliation of tree; reduced growth
• circular lesions on fully expanded leaves with dark borders and yellow halos.
• Primary method of controlling disease is usually the application of appropriate fungicides; cultural practices that may reduce the incidence of the disease include good sanitation practices and adequate fertilization, irrigation and pruning of trees.