Sorghum is Kenya’s 5th most important cereal grain, after wheat, maize, barley and rice. 90% of all cultivated sorghum land is found in developing countries in Africa and Asia. Africa is the largest sorghum producer in the world because of the tropical conditions that favour its growth. Though Africa is a big player, sorghum diseases are affecting productivity.
If sorghum diseases are not controlled on time, there can be a 100% yield loss. The matter is exacerbated further by global warming, which increases drought in sorghum-growing areas, affecting food security in Africa.
This article discusses the different types of sorghum diseases that affect sorghum farmers. Apart from identifying these diseases, we will discuss ways farmers can protect and treat their farms.
Sorghum Production in Kenya
In Kenya, sorghum is mainly grown in semi-arid areas with erratic rains and high temperatures. Despite this, sorghum production has been on an increasing trend.
As of 2014, more than 1.9 million bags of sorghum were produced in the country. The highest-growing regions were Nyanza and Western Kenya, which produced 757,862 and 761,414 bags, respectively. The increase in sorghum production has been attributed to the growth of the sorghum beer market and government strategies implemented to revive Traditional High-Value Crops.
To learn more about sorghum farming, read our Sorghum farming guide. You will learn about the best soil and what to look for to ensure a bumper harvest.
Sorghum farming in Western Kenya thrives because most of these sorghum varieties are tolerant to waterlogging. Sorghum also thrives well in light sandy solids found in the lower eastern regions of Kenya. Most sorghum farmers in Kenya are small-scale farmers who intercrop sorghum with crops such as maize, pigeon peas, beans, and cowpeas.
Use of Sorghum in Kenya
Small-scale sorghum producers in Kenya plants sorghum for home use. However, sorghum is being grown for industrial use due to demand from the beer industry. Other industrial uses of sorghum is to produce edible oils, wax, starch, dextrose agar, and syrup.
Sorghum farmers are encouraged to use the best sorghum fertilizer to increase yields. Fertilisers created explicitly for use by sorghum farmers can increase profits by more than 40% a harvest.
Sorghum Diseases
The first sorghum disease that we will discuss is the sorghum grain mold. Sorghum grain mold disease occurs when it rains during the flowering and grain-filling stage. The most common mold is the Fusarium semi-tectum mould, which causes fluffy white or pinkish discolouration.
The symptoms will depend on the degree of infection and the type of organism involved. Fusarium semi-tectum is mainly spread through air-borne conidia. To prevent this infection, farmers need to create a non-conducive environment.
The fungus thrives best in the following conditions:
- Wet weather conditions
- In long wet periods
- Having compact ear heads.
Other sorghum diseases are:
Sorghum Downy Mildew Disease
The downy mildew disease mostly infects young sorghum plants through conidial infection or the oospore. The best way to detect the infection is to inspect the leaves. When the leaves are unfolding, they will disclosure from green to yellow.
Sorghum downy mildew is a fungal disease caused by the pathogen Peronosclerospora. It primarily affects sorghum crops and can cause significant damage if left unmanaged. Here are some signs and symptoms of sorghum downy mildew disease:
White or grayish-white downy growth: One of the main signs of sorghum downy mildew disease is the presence of a white or grayish-white downy on the leaves, stems, and panicles of infected plants. This downy growth consists of fungal spores and can be observed on the lower surface of leaves, often appearing as patches.
Chlorotic or yellowing of leaves: Infected sorghum plants may develop chlorotic or yellowing on the leaves. The yellowing can start as small spots or streaks and eventually colonise the entire leaf. The affected leaves may also show signs of curling or distortion.
Leaf necrosis: If the disease is not controlled on time, necrotic lesions will develop on the leaves. The lesions are brown or black plants extend from the tips or margins of the leaves toward the midrib or leaf base. The necrotic areas may have a distinct line separating them from healthy tissue.
Stunted growth: Sorghum plants affected by downy mildew often exhibit stunted growth compared to healthy plants. The infected sorghum plants may be smaller, with low biomass.
Panicle malformation: In severe cases, the downy mildew infection will affect the panicles (flowering structures). Infected panicles will be smaller, have a reduced grain set, or show abnormal development, such as distorted or shrunken grain heads.
Premature plant death: In some instances, sorghum plants infected with downy mildew may die prematurely, especially if the infection is severe and occurs early in the plant’s growth stages.
Sorghum mildew disease is transmitted through the presence of oospores in the soil, which cause the initial systemic infection. Another way that the disease spreads is via air-borne sporangia.
The disease thrives best in humid conditions or at night when the temperature is between 21 – 23 degrees Celsius.
Sorghum Charcoal Rot Disease
Charcoal rot diseases mainly affect sorghum grown in dry areas. It impacts the plant when exposed to moisture stress during the pre-flowering stage.
Charcoal rot disease is caused by a fungus known as Macrophomina phaseolina. Macrophomina can be identified by looking out for the following symptoms:
Discolored stems: The stems will discolor if the disease is not treated. At first, the discoloration will appear as dark brown, then black. These lesions may extend up the branch, causing a charcoal-like appearance.
Wilting: The leaves and stems of infected sorghum plants become droopy and lack turgidity. The wilting can be seen on some parts of the plant or affect the entire plant.
Discolored stems: If the disease is not treated promptly, the stems will discolor. At first, the discoloration will appear as dark brown, then black. These lesions may extend up the branch, causing a charcoal-like appearance.
Poor growth: Infected sorghum plants may display stunted growth or exhibit reduced vigor compared to healthy plants. This can manifest as smaller leaves, shorter plant height, and diminished plant size.
Vascular discoloration: Vascular discoloration can be seen when you cut the stems open. When opened, the internal tissues may expose black streaking or discoloration that looks like charcoal.
Root decay: Charcoal rot affects the root system of sorghum plants. Infected roots show signs of decay, such as discoloration. When the seeds are severely affected, it can lead to poor nutrient and water uptake, causing the plant to wilt.
Sorghum charcoal rot diseases thrive best when sorghum is planted during hot and dry weather. It will also thrive when the soil maintains a temperature of 27 – 35 degrees Celsius for over two weeks.
Sorghum Anthracnose
Sorghum anthracnose is a fungal disease that affects sorghum plants. It is caused by the fungus Colletotrichum, a common illness in sorghum-growing regions such as Western Kenya.
Symptoms of sorghum anthracnose include spindle-shaped lesions on the leaves, leaf sheaths, panicles, and other parts of the plant. The lesions are usually tan to light brown and may have a reddish-brown border. As the disease progresses, the lesions willy enlarge, resulting in the death of the affected tissue.
Anthracnose can also cause sorghum seeds to rot and discolor, reducing their quality. In severe cases, anthracnose can result in 100% yield loss.
Sorghum anthracnose can survive in crop residues and plant debris. It can also be spread through contaminated seeds and infected plant material.
Several strategies can be implemented to control sorghum anthracnose. These strategies include:
Use of resistant seeds: Farmers should use sorghum varieties that are resistant or tolerant to anthracnose.
Crop rotation: Avoid planting sorghum or related crops in the same field. Crop rotation will kill the anthracnose fungus.
Sanitation: Remove and destroy infected plant debris to reduce inoculum contamination. This should include crop residues and infected seeds.
Fungicide application: In severe cases, you can use fungicides to control the disease. Consult a local agricultural extension service officer for appropriate fungicide recommendations and application guidelines.
Rust
This is a fungal disease that affects sorghum crops during all growth stages. This sorghum disease is caused by a fungus known as Puccinia Purpurea. When the plant has just been affected by the disease, it will have small dots on the lower leaves, either purple, tan, or red, depending on the sorghum variety planted.
Other signs of Rust are
Rust-colored pustules: The most notable sign of Rust in sorghum is small, raised bumps on the leaves, leaf sheaths, and sometimes on the panicles. These bumps typically have a rust or reddish-brown appearance.
Presence of spores: The rust pustules contain masses of rust-colored spores that can be seen with the naked eye. These spores are responsible for spreading the disease in the plant.
Yellowing and drying of leaves: As the disease progresses, the leaves around the pustules may turn yellow and eventually dry up. The entire leaf may become affected in severe cases, leading to defoliation and 100% yield loss.
Reduced plant vigor: Infected plants may exhibit stunted growth, reduced tillering (formation of side shoots), and overall poor vigor. These symptoms can impact the plant’s ability to produce healthy panicles and yield.
Rust spreads best when the temperature is between 10 – 12 degrees Celsius. It also spreads most during the onset of the long rainy season in Kenya.
Ergot
Ergot is a fungal disease caused by the fungus Claviceps africana. The diseases primarily affect the flowering part of the plant. Symptoms of ergot sorghum diseases are:
Symptoms: A plant infected with sclerotia will have a large and dark head compared to one with healthy seeds. The color can range from black to dark purple or brown. Infected heads may also appear distorted or shriveled.
Development: The ergot fungus infects the ovaries of the sorghum flowers. After infection, the fungus replaces the developing seeds with the sclerotia. The fungus can survive in the soil and plant debris for long.
Disease spread: The condition is primarily spread through contaminated seeds. The condition can also be spread by wind and insects.
Impact: Infected plants suffer from reduced yield because infected seeds reduce quality and quantity. In severe cases, ergot sclerotia may contaminate the harvested grain, reducing marketability.
There are several strategies that farmers can use to control ergot disease. These strategies include::
- Seed selection: Plant-certified, disease-free seed to minimize the introduction of ergot into your fields.
- Crop rotation: Avoid planting sorghum or related grass crops in the same field for consecutive seasons to break the disease cycle.
- Sanitation: Remove and destroy infected plant debris, including ergot-infected heads, to reduce the source of inoculum.
- Field monitoring: Regularly inspect your sorghum crop for symptoms of ergot, particularly during flowering. Early detection allows for timely management actions.
- Chemical control: Fungicides are available for ergot control, but their effectiveness may vary. Consult with local agricultural experts for appropriate fungicide recommendations and application guidelines.
In conclusion, sorghum farmers must be aware of the various sorghum diseases that can affect their farms. This way, identifying these diseases and taking remedial actions will become easy before the disease causes significant losses.
