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(Sclerophthora macrospora)

Credits: Biovision-Infonet

This fungal disease can be troublesome in low lying areas that become flooded. Infected plants have thick, stiff, twisted, pale green leaves with bumpy surfaces.

The leaves often turn downward, and the plants produce many shoots or suckers giving a bunchy appearance.

Infected plants do not produce heads or produce a proliferation of leafy tissue in place of the head. Wild and cultivated grasses can serve as sources of infection.

What to do:

• Plant resistant varieties.
• Remove diseased plants from the field.
• Rotate with non-cereals.
• Avoid excess soil moisture in the field.

(Helminthosporium turcicum)

Credits: Biovision-Infonet

Leaf blight (Helminthosporium turcicum) Attacks sorghum, Sudan-grass and maize. The causal fungus is carried on the seed and also lives in the soil on dead or decaying plant material.

It may cause seed rot and seedling blight, especially in cool and excessively moist soil.

Seedlings then can become infected readily and may either die or develop into stunted plants. Small reddish-purple or yellowish-brown spots usually develop on the leaves of infected seedlings.

The spots may join to kill large parts of the leaves, which then dry to the extent that severely affected plants look as if they have been burnt.

A greenish, mould-like growth of spores develops in the centre of the leaf spots during warm, humid weather.

The spores are spread by wind or rain and infect other leaves and plants. Under warm, humid conditions the disease may cause serious damage by killing all leaves before plants have matured.

What to do:

• Plant resistant varieties.
• Use certified disease-free seeds.

(Claviceps sorghi)

Credits: Biovision-Infonet

Cream to pink sticky droplets “honeydew” ooze out of infected florets on panicles.

The droplets dry and harden, and dark brown to black sclerotia (fungal fruiting bodies) develop in place of seeds on the panicle.

Sclerotia are larger than seed and irregularly shaped, and generally get mixed with the grain during threshing.

Conditions favouring the disease are relative humidity greater than 80%, and 20-30degC .

The sclerotia falling on the soil or planted with the seed germinate when the plants are flowering.

They produce spores that are wind-borne to the flowers, where they invade the young kernels and replace the kernels with fungal growth.

The fungal growth bears millions of tiny spores in a sticky, sweet, honeydew mass. These spores are carried by insects or splashed by rain to infect other kernels.

What to do:

• Plant resistant varieties, where available.
• Remove affected panicles.
• Avoid planting seeds from infected panicles.
• Plough deep.
• Rotate with non-cereals preferably with pulses.
• Practise good field sanitation

(Puccinia purpurea)

Credits: Biovision-Infonet

Rust appears on leaves as small raised pustules or blisters that rupture and release many reddish-brown spores. These pustules occur on both the upper and lower leaf surfaces.

This disease usually appears when plants near maturity and infection is confined primarily to mature leaves.

Grain yield losses are usually not serious and occurrence of the disease is sporadic. Forage sorghum yields may be affected most.

The rust fungus also attacks Johnson grass and over-seasons on this host.

What to do:

• Use resistant varieties.
• Rotate with non-cereals.
• Control weeds.

(Macrophomina phaseolina)

Credits:Biovision-Infonet

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.

What to do:

• 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.

(Sporisorium reilianum)

Credits: Biovision-Infonet

This disease is characterised by the large, dark-brown smut galls that emerge in place of the panicle. The gall is first covered with a whitish membrane, which soon breaks and allows spores to be scattered by the wind.

Plants become infected while in the seedling stage but evidence of infection is not apparent until heading time. The smut gall produces thousands of spores, which become soil-borne and initiate systemic infection of seedlings in subsequent years.

Different races of the fungus exist which may result in a sorghum hybrid being resistant in one area but not another.

What to do:

• Plant resistant hybrids to avoid losses.
• Use certified disease-free seed.
• Rotate with non-cereals.
• Plough deep.