Charcoal Stalk Rot
· Sorghum · Maize
This soil-borne fungus invades roots at the seedling stage and gradually finds its way to the stems, apparently without symptoms. Later on, mature stems show a black discoloration of their internal tissues that give them a charred appearance, thereby the name. The rot slowly colonizes the vascular tissue, and hard fibrous tissues with black fungal specks are visible between the internodes. The destruction of transport tissues leads to symptoms similar to water deficiency. Plants ripen prematurely and have weak stalks, causing breakage or lodging. Upper leaves first become yellow and then dry out. Brown, water-soaked lesions are present on the roots. In cases of strong infection, more than 50% of plants can break.
This disease is caused by the fungus Macrophomina phaseolina, which thrives in hot and dry environments. It overwinters for periods of up to three years on host crop residues or in the soil. The infection of roots and transport tissue of the stem leads to an impairment of the transport of water and nutrients, thereby the drying of the upper parts of the plant, the premature ripening and the weak stalks. Further favorable conditions for the spreading of the fungus are provided by insects, damaged roots and shoots as well as other plant diseases. Symptoms are are worsened during drought, elevated soil temperatures (over 28°C) and excessive fertilization at later stages of plant growth.
Organic treatments such as farmyard manure, neem oil extracts and mustard cake can be used to control Macrophomina diseases. Soil amendment with pearl millet and weed-based composts can lead to a decrease in soil population of the fungus of 20-40%.
Foliar application of fungicides is not effective, as damage has already occurred when the first symptoms occur. Fungicide-treated seeds may offer protection during seedling growth. The soil can be fumigated with methyl bromide.