Charcoal rot (Macrophomina phaseolina)
Grain sorghum plants affected by the charcoal rot fungus fail to fill grain properly and may lodge in the latter part of the season. Infected stalks show an internal shredding at and above the ground line. This can be observed by splitting the stalk and noting the deteriorated soft pith tissue leaving the tougher vascular strands. Fungal structures (sclerotia) can be observed in the affected tissue, which appears as though it has been dusted with black pepper. Another type of stalk rot (Pythium sp. and Fusarium sp.) may show the shredded condition but the black specks (sclerotia) will be lacking.
Conditions under which charcoal rot is favoured include stressful hot soil temperatures and low soil moisture during the post-flowering period. Host plants are usually in the early-milk to late-dough stage when infection occurs. The fungus is common and widely distributed in nature.
- Avoid moisture stress.
- Manage properly crop residue.
- Rotate crop with non-cereals. Legumes are also susceptible to the disease.
- Avoid excessive plant populations.
- Balance nitrogen and potassium fertility levels.
- Grow drought-tolerant, lodging-resistant hybrids.