Effective disease management

Downy mildew, smut, rust and ergot are widespread diseases where millet is grown in Africa. In general, effective disease management starts with prevention of attack by ensuring clean planting materials or resistant varieties which should be planted in a clean environment followed by proper field sanitary procedures and good husbandry practices. Normally all cultivation practices that encourage plant vigour will enhance the crop’s ability to reduce the impact of disease attacks.

Downy mildew (Sclerospora graminicola) is the most devastating disease in millet and is important in most parts of Africa. The disease is transmitted through the soil, crop residues, contaminated seeds and tools, and is prevalent during rainy periods. Symptoms often vary. Leaf symptoms begin as chlorosis (yellowing between the veins) on the bottom leaves. White fungus may be observed on the underside of infected leaves. Severely infected plants are generally stunted and do not produce panicles. Inflorescence and glumes can become twisted and transform into leafy structures (green ear symptom). Spreading of the disease can be reduced by destroying prematurely infested tillers and infested crop residues. Some varieties that are resistant to downy mildew have been selected and can be planted, if the risk of downy mildew is high in a particular area. Early sowing is useful also, but is not always feasible due to competition for labour with other crops and the sowing window is often short in rain-fed situations.

Long smut (Tolyposporium penicillariae) attacks the millet plants during flowering by wind-borne spores and rain. Infections are most important when humidity of the air and temperature are high. Green fungal bodies larger than the seed develop on panicles during grain filling. As the crop matures, the fungal bodies change in colour from green to dark brown, containing dark spores. Control of the disease focuses on preventive measures such as the use of tolerant or resistant varieties, timing of planting to avoid flowering during the rainy season, and by applying cultural measures that contribute to crop hygiene. With rainfall variability within and across seasons, timing of planting may be difficult; however, it is important that farmers ensure that they are ready for planting with the first effective rains by having all inputs well before the rainy season starts.

Ergot (Claviceps microcephala) develops after flowering. Pink sticky «honeydew» droplets ooze out of infected florets on the panicles. High humidity and temperatures between 20 to 30 °C favour the development of the disease. Within 10 to 15 days, the droplets dry and harden, and dark brown to black fungal fruiting bodies develop in place of seeds. During threshing they generally get mixed with the grain. The disease can be controlled by rotating millet with non-cereals, preferably pulses, growing resistant varieties, and avoiding planting seeds from infected panicles. For good field sanitation affected panicles should be removed and destroyed.