Mango Dieback Disease
Infection of mango trees with the fungus Botryosphaeria rhodina manifests itself in dry twigs and can lead to complete defoliation. During the first stage of the disease, the barks become discolored and turn darker. In the following, young twigs start withering at the base, extending outwards until the leaves become affected. As the veins turn brown, leaves curl upwards and eventually fall off the tree. In the final stages of dieback, twigs and branches secrete gum. Initially, small gum droplets become visible, but as the disease progresses the entire branch or trunk may be covered. In severe cases, the tree bark or whole branches die and crack.
Botryosphaeria rhodina survives in plant necrotic tissue for long periods of time. It invades the vascular system of mango trees through wounds in the trunk and branches. The precise mechanism for the infection is not fully understood. Possible entry sites are wounds inflicted by insects (beetles) or mechanical injuries that occured during field work. The primary source of infection might be spores in the dead bark of twigs. They remain on the trees during the growing season and spread during the harvest period. Deficiency in iron, zinc and manganese may favor the outbreak of the disease. Water and freezing stress have also been related to this disease. The disease can occur at any time of the year but it is most conspicuous during late growth stages.
Remove and destroy infected tree parts immediately. Also cut back some of the surrounding healthy branches to ensure a complete eradication of the pathogen.
After pruning, apply copper oxychloride at a concentration of 0.3% on the wounds. Apply Bordeaux mixture twice a year to reduce the infection rate on the trees. Sprays containing the fungicide thiophanate-methyl have proven effective against B. rhodina. Control bark beetles or caterpillar borers by applying bifenthrin or permethrin on the trees.