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Diseases of maize, millet and sorghum          

Symptoms, perpetuation and control

By M. Mithal Jiskani
 Aug  20 - 26 , 2001

Maize is most important cereal crop of the world in terms of its total global production. It ranks second to wheat and equal to rice. Globally, 67 per cent of maize is used for livestock feed, 25 per cent for human consumption and industrial purposes, while 5 per cent is used for seed purpose to sow next crop.

Millet and sorghum are most important cereal crops of the Desert and Mountain (Thar-Cholistan and Kohistan) areas of the world including Pakistan. Millet is the principle cereal crop in the infertile, semi arid zones. Its acreage is dependant on the amount and time of the rain fall, as it is mostly confined in rained areas. Sorghum is heat and drought resistant cereal crop and remain dormant during moisture stress conditions and resumes growth under favourable moisture conditions.

These crops are subjected to a number of diseases, which are responsible for reducing their overall production to a great extent. The plants in all stages of growth and in all natural environments are subject to various mechanical, physiologic and biological stresses, that interfere with their normal growth and development. Weather, toxicants, pollutants, insects, viruses, fungi, nematodes, bacteria and weeds are primary hazards to the production of crops. The actual number of maize, millet and sorghum diseases is unknown, but some of the most common and important diseases are discussed according to Kamal and Moghal (1968), Hafiz (1986), Nyvall (1979) and Jiskani (1999).

Diseases of maize (Makki)

Maize is very efficient water user. It needs large quantities of irrigation water for high yield, because drought conditions lead to lower yields and lower quality grains. Maize requires 6-8 irrigations. First irrigation 3-4 weeks after sowing, remaining may be given at 10-15 days interval. The grain formation is critical growth stage. It is not important grain crop in Sindh, but is grown mostly as fodder crop and very rare as for grain. More than 70 different diseases of maize are reported in the world, which hit the crop and cause considerable damage. Seedling rots reduces stand. Many fungi produce root rot, stalk spotting and early dying due to stalk and root rots. Helminthosporium leaf spots are characterised by small spots with light border or very large light grey spots. Common corn smut, discussed below, is one of the most important than all others.

SMUT (Ustilago maydis)

Symptoms: White to greyish-white galls (soft tumors) develop on any part of the plant. These galls are light coloured in early stages, become blackish on maturity and filled with black powder (spores of disease causing fungus). Large sized galls involving the entire head.

Perpetuation: The disease causing fungi perpetuates through diseased plant debris lying in the field.

Control: (1) Do not sow diseased seed, (2) Follow 2-3 years crop rotation and (3) Do not expose the manure heaps near the field.

Diseases of millet (Bajra)

The area under millet crop is highly variable, because it is dependent on the amount and time of the rainfall. It is mostly confined to the desert and mountain (Thar-Cholistan and Kohistan) area. 3-4 irrigations (30-35, 50-60 and 70-80 days after sowing) are sufficient for better yield. Near about 40 diseases are reported on millet but following are most important because of their considerable losses to over all production.

Green ear or downy mildew (Sclerospora graminicola)

Symptoms: It can be characterised at ear formation stage, when the leaves become distorted, twisted, crinkled and lose their green colour, become white and later turn brown. The ears are transformed in to green leafy structures with enlarged glumes, turning wholly_or partially into loose heads. The affected portions are sterile and they do not produce grains.

Perpetuation: Diseased plant residues help the fungus to survive and oospores present in soil cause primary infection.

Control: (l) Use of resistant varieties, (2) Collection and burning of diseased plants or plant parts, as soon as they appear, (3) Destroy and burn carefully all the diseased plant debris, (4) Use of 2-3 year crop rotation and (5) Avoid cultivation in low lying and drained lands.

Grain smut (Tolyposporium penicillariae)

Symptoms: Infected grains from the smut sori, are thickened, slightly elongated, covered by tough and blakish green membrane filled with fungal spores. These are present singly or in groups, usually a one side of the ear or towards its base, scattered or collected together in patches on the ear.

Perpetuation: Infection is usually through air-borne sporidia released from germinating chlamydospores in soil.

Control: (1) Cultivate resistant varieties, (2) Early collection and burning of diseased ears on appearance and (3) Follow 2-3 years crop rotation.

Diseases of sorghum (Jowar)

The major area of sorghum in Pakistan lies in Punjab, but the yield per hectare is higher in Sindh. The sorghum plants are drought resistant, but 3-4 irrigations (30-35, 50-60 and 70-80 days after sowing) are compulsory for better yield. In case of sorghum, about 50 diseases are recorded world over but following are important.

Grain smut (Sphacelotheca sorghi)

Symptoms: This disease also known as covered or kernel smut. The grains are transformed into white greyish sacs (smut sori), are slightly pointed to oval and filled with black powder (chlamydospores). Most of the grains are found infected.

Perpetuation: Perpetuate through contaminated seed.

Control: (1) Use healthy seed, (2) Sow seed by broadcasting and water the field immediately thereafter, (3) Treat the seed with any one of the organic mercurial or copper seed dressing fungicides and (4) To collect and burn diseased heads.

Long smut (Tolyposporium ehrenbergii)

Symptoms: Individual grains are transformed into large sized smut sori, which are full of solid spores. The diseased grains (smut sori) are found scattered on head. These grains turn into cylindrical and elongated sacs. Mostly upper portions of ear head have higher number of infected grains.

Perpetuation: The disease causing fungus is seed, soil and air-borne.

Control: (1) Use healthy seed, (2) Seed treatment with organic mercurial, (3) Collect and destroy diseased grains, (4) 2-3 years crop rotation and (5) Cultivate disease resistant or tolerant varieties.

Red leaf blight or anthracnose (Colletotrichum graminicolum)

Symptoms: Initially small ovate to irregular red spots appear on leaves. Later on, these increase in number and size to cover larger area of leaf. The infected leaves become reddish brown, show necrosis and become dry. Premature ripening and shrivelling of grains also occur.

Perpetuatlon: Plant debris and seeds may serve as source.

Control: (1) Use of healthy seeds, (2) Destruction of plant debris and (3) Soak the seed in ordinary water for 4 hours and then dip in 55.5°C hot water for one hour.

Red leaf spot (Phyllosticta sorghina)

Symptoms: Small red spots on leaves, stems and grains. These increase in number and size and join up leaves dry 2 write.

Perpetuation: Seed-borne or through diseased plant debris

Control: Same as recommended for red leaf blight.

The author is Assistant Professor (Plant Pathology), Sindh Agriculture University, Tandojam.