Diseases Affecting Wheat Farming In Kenya

Wheat Farming In Kenya: Wheat (Triticum aestivum L.) is an important cereal and is among the crops that contribute significantly to food security in Kenya. However, wheat diseases are among the biotic factors that affect wheat production. Considerable progress has been made to control wheat diseases through host plant resistance breeding and chemical applications. Frequent changes in the pathogens population still present a major challenge to achieving durable resistance.

This article highlights the prevalence, distribution of wheat diseases, host plant resistance in the key wheat-growing regions of Kenya, and future prospects in Kenya.

Wheat Farming In Kenya

Wheat (Triticum aestivum L) is the second most important cereal crop in Kenya after maize and is produced mainly under rainfed conditions on 0.4% of the arable land. The crop has greater potential in the country where it is grown.

The national demand for wheat and wheat consumption is on the increase, partly due to the high population growth, increased urbanization, and changing diet. The local wheat production has not been able to meet this demand leading to the importation of large quantities to fill the gap between supply and demand. However, this is unlikely to be satisfied partly due to pre-harvest sprouting, lodging, losses caused by re-emerging diseases, insect pests, intermittent droughts, inadequate seed systems, and poor crop practices under resource-constrained small scale farming conditions.

The crop grows in a considerably wide range of altitudes in the country, maturing between 90−145 days depending on the location and cultivars.

Wheat rust diseases in Kenya

Among the wheat diseases, rusts have become the most destructive diseases of wheat in Kenya resulting in yield losses of up to 100% in susceptible cultivars. Breeders have been breeding for wheat rust resistance, since 1908, but up to date, there is no permanent solution to the rust diseases as the pathogens keep on evolving rendering the resistant cultivars ineffective. Since the beginning of the wheat breeding program in Kenya in the 1900s, until early 1980s, stem rust was the most serious disease of the three wheat rusts and therefore was given a high research priority by the breeding program.

Consequently, many resistant wheat cultivars were developed and the disease seemed to have been controlled. It was until between 1985 and 1988 that trace amounts of the disease were observed in the experimental plots in Njoro; in 1996, it was recorded in some commercial cultivars in Mau-Narok and Molo, and in the year 2000 all the cultivars had become susceptible.

According to KARLO, wheat diseases represent a major constraint in almost all wheat growing environments. The most challenging diseases include stem rust, yellow rust and leaf rust. These and other important diseases are described in this section to enable farmers to identify them and use available controls.

Stem Rust

Stem rust is also known as black stem. It infects leaves, stems, leaf sheaths, glumes.

Symptoms
Long red-brown blister-like pustules that tear the upper surface of leaves giving the plant a tattered (torn) appearance. The pustules are longer and larger than those of leaf rust and are also seen on the lower leaf surface

Yellow Rust

Yellow rust is also known as stripe rust. It infects leaves and ears.

Symptoms
Yellow rust spores are orange-yellow in colour. They first appear small and circular and develop into yellow parallel stripes on the upper leaf surface and as yellow powder inside the glumes.

Leaf Rust

Leaf rust is also known as brown rust. It infects leaves only

Symptoms
Leaf rust spores are orange-brown in colour. They appear as circular or oval in shape and are mainly scattered on the upper surface of the leaves. The spores are smaller and rounder than those of stem rust and only appear on the upper leaf surface.

General information for all the three forms of rust

• All the three rusts are mainly wind-borne. They are not seed or soil-borne, so rotation in the Kenyan situation is not a viable control mechanism.
• Avoid planting very susceptible wheat varieties.
• Use resistant varieties wherever possible
• Remove or destroy volunteer wheat plants that will harbour the rusts.
• Monitor the crop for signs of infection from 60 days or two months after planting.
• Apply foliar fungicides when you see the first signs of any of the rusts
• Early fungicide application/protection is important when you plant susceptible wheat varieties. Apply at tillering and flowering growth stages, particularly for stem rust.

Septoria leaf and glume blotch

Septoria leaf and glume blotch, also known as Septoria diseases, attack the leaves and heads.

Symptoms
Brown necrotic lesions with black specks (bearing spores) on the leaves and heads. Severe infection of leaf blotch or glume blotch may result in light shrivelled kernels.

Control

• Plant disease free seed.
• Crop rotation with crops like canola and beans.
• Foliar fungicides recommended for control of rust diseases can also prevent infection if applied early.

Fusarium Head Blight (FHB)

Fusarium head blight is also known as scab. It survives in the soil and on wheat stubble as well as on remains of other grass hosts such as maize.

Symptoms
Symptoms are confined to the head, grain and sometimes on the peduncle (neck)
Bleaching (whitening) of one or more spikelets or whole immature wheat heads. The white heads are sterile or contain shrivelled and or discoloured seeds. White or pink growth is sometimes seen on the bleached heads/spikelets.

Control

• Plant resistant varieties.
• Crop rotation, e.g. Canola between wheat crops.
• Apply a foliar fungicide (Prosaro 250 EC) early to prevent
• infection at flowering.

Take All

Take all is a soil-borne disease. It infects roots, crown and basal part of the stem

Symptoms
Reduced tillering and slight stunting of the plants. Infected plants are in patches, bleached (white) heads, ripen prematurely, die before seed set and can be easily pulled from the soil.

Control

• Crop rotation with, e.g. Canola between wheat crops.

Loose smut

Loose smut is a seed-borne disease.

Symptoms
Easily recognised at heading growth stage by appearance of dusty black heads (black spores) in place of grain.

Control

• Use certified seed.
• Treat seed with recommended seed treatment fungicides such as Vitavax 200FF, Anchor 200FF, Dividend 030 FS.

Barley Yellow Dwarf Virus (BYDV)

Barley yellow dwarf is a virus disease and infects many plant species including barley, maize and other grasses.

Symptoms
Dwarfing and yellow colouring of the leaves from the tip. Infected plants are also associated with upright and stiff leaves

Control

• Control aphids that introduce the virus into the plant
• Treat seed with recommended insecticides such as Gaucho.

Some useful tips to remember when applying fungicides and pesticides

• Adherence to label instructions insures safe use; Follow instructions as outlined on the label.
• Do not stir by putting your hand into the mixture. Use sticks to stir pesticides since some can be absorbed into the body through the skin.
• Apply pesticides at the right time.
• Control the pest, not everything that moves.