Pests and diseases of grain sorghum

Sorghum is attacked by a number of pests and diseases which frequently may be limiting factors in its commercial production. Because it is predominantly a peasant crop, its pests and diseases and the losses they cause have not been as well documented as for other cereal crops.

Grain sorghum is the sixth most important source of dietary calories for the world's population, after rice, wheat, sugar (beet and cane), maize, and Solanum potatoes. It is the fifth most important cereal grain on a world production basis, after wheat, maize, rice and barley. It is the major food grain of many low-income people living in the semi-arid tropical regions of Africa and Asia, and is also used extensively throughout the world as a livestock feed, either as green forage, dry straw, or grain concentrate.

The insect pests which attack sorghum are, in most cases, those which also attack maize. The two main pests are stalk borers and soil pests, principally wireworm. Stalk borers are present wherever sorghum is grown but wireworms occur mainly in the more northern latitudes, especially in the USA.

All the important diseases of sorghum are fungal and they can be classified into (a) those that rot the seed and kill seedlings; (b) those that attack the leaves making the plants less valuable for forage; (c) those that attack and destroy the grain; and (d) those that attack the roots and stalks. The most important of these are smuts which attack the grain. Smut losses vary greatly and although damage as high as 100% has been recorded, the overall figure would appear to be between 5 and 10%. The peasant culture of sorghum makes it difficult to assess the relative importance of the different diseases attacking the crop. A survey of the grain losses in former British Commonwealth countries in Africa gave an overall loss due to disease of at least 9%, of which an estimated 6.6% was due to smut. The overall figure may well be on the low side as diseases such as leaf blight, anthracnoze and bacterial blights are very widely distributed and take a steady annual toll.

Nutritional disorders are a major limitation to high productivity because grain sorghum is grown in areas with impoverished soils and because farmers generally use little fertiliser.