Economic importance of diseases of plants

Diseases and pest are every farmers worst enemy correct me if am wrong. Which farmer will be bold enough to support the idea that he/she likes diseases of plants and pest attacking their farm at their own expense? If diseases and pest were to be human beings and world riches were to be ranked don’t you think they would have been ruling the world till date and in the future and beyond? Some diseases of economic importance will be looked at and how they attack crops.

READ : Economic Importance Of International Plant Diseases

The amount of cost incurred to countries and farmers by diseases of plants and pest is far greater than what they get after every harvest they make either at the end of a season or year. Some diseases of plants and pest that attack some crops are describe here and into detail.

Maize Smut

Maize smut is caused by ustilago zeae. It occurs wherever maize is grown and is prevalent in warm and moderately dry areas. The disease damages plants and reduces yield. Galls are normally formed on the above ground parts like ears, ears, tassels, stalks and leaves. Losses from maize smut range from a trace up to 10%.


Minute galls form when seedlings are infected. Infection of seedlings could lead to stunting. In older plants, infection occurs on young growing tissues of axillary buds, individual flowers, ear and tassel leaves and stalks. Galls form on infected areas due to stimulation of host cells by fungus. The galls are first covered with a greenish-white membrane. As galls mature, interior darkens and turns into a mass of powdery, dark, olive-brown spores. The silvery gray membrane then ruptures and exposes teliospores into air.


No maize varieties completely resistant to smut are known. Several maize hybrids show some resistance. New races of the pathogen appear constantly making control through resistance difficult. Sanitation measures such as the removal of galls be they open can be applied. Crop rotation involving the growing of maize in small isolated plots can be used. Early detection and burning of diseased plants can be used.

Loose Smut of Cereals

This disease occurs worldwide and is more abundant in humid and sub humid regions. It normally destroys kernels and results in the smearing of and reduction in grain quality of no infected plants. Losses from smut could be up to 10 or 40% in certain localities.


There are usually no discernible symptoms until the plant has headed. Smutted plants sometimes head earlier than healthy plants. Smutted heads are often elevated above those of healthy plants. All heads, spikelets and kernels are transformed into a smut mass consisting of olive-green spores. Smutted kernels are covered with a grayish membrane which soon burst and sets powdery spores free. Spores are blown off by wind and leave the rachis a naked stalk.


Treat infected seeds with carboxin before planting. Carboxin is absorbed and acts systematically within seed or growing plant. Use certified smut-free seed. Seed can also be treated with hot water

Smut of Guinea Corn (Sorghum)

‘Covered smut’ caused by Sphacelotheca sorghi is the most serious in Ghana. The other smuts are ‘loose’ or ‘open smut’ and ‘head smut’ which are caused by S. Cruenta and S. reilina respectively.


The fungus penetrates the coleoptile, then the inner tissues and finally meristematic tissues at the stem apex. During flowering mycelium in meristem enters developing ovaries where it forms chlamydospores. Infected ovaries elongate standing above the floral bracts and also unaffected grains. Spore-bearing ovaries break open allowing wind to carry chlamydospores onto healthy grains


Treat seeds with suitable disinfectant e.g. Copper Sulphate and dieldrin. Early detection coupled with removal and burning of infected plants is also effective.

Maize Rust

Until 1949 Puccinia sorghi was the only rust of maize in West Africa. In 1950, P. polysora appeared in coastal regions and spread throughout the country. It attained epidemic levels and caused severe losses.


The fungus attacks leaves and husks of ear and occasionally stem at nodes. Severe infections of entire plant may assume bright orange appearance and leaf dying quickly thereafter. Uredospores and Teliospores are produced but the latter is rare.

diseases of plants

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