9 Common Groundnut Diseases and Control Tips

This article covers several diseases that can affect peanut (groundnut) crops, including early and late leaf spots, groundnut rosette disease, peanut smut, peanut mottle virus, and stem rot disease.

The article provides information on the symptoms of each disease, their causes, and their impact on crop yields. It also offers advice on methods of prevention and control, including cultural and chemical control methods, the use of disease-resistant varieties, the application of insecticides, and good sanitation practices.

Farmers can reduce the incidence and severity of these diseases in their crops by taking these preventive measures and ensuring better yields and quality.

1. Early and Late leaf spot disease

Early leaf spot and late leaf spot are two common fungal diseases that affect the leaves of peanut plants. Both disorders can cause significant damage to peanut crops and, if left untreated, can lead to yield losses.

Early leaf spot typically appears on the plant’s lower leaves as small, circular spots that are reddish-brown in color. As the disease progresses, the areas may merge, causing the leaves to turn yellow and eventually die. Late leaf spot, on the other hand, typically appears on the plant’s upper leaves as larger, irregularly-shaped spots that are dark brown in color.

Both diseases can also affect the plant’s roots, particularly in cases of severe infection. The fungal spores can infect the roots, causing a condition known as pod rot, which can result in poor-quality or rotten peanuts.

Farmers can control early and late leaf spots by combining cultural and chemical control methods. Cultural methods include crop rotation, planting resistant cultivars, and practicing good sanitation to minimize the spread of fungal spores.

Chemical control methods involve using fungicides to protect plants from infection. Fungicides can be applied preventatively, before symptoms appear, or curatively after symptoms have already developed. Farmers should work closely with their local agricultural extension service to determine the most effective fungicide treatment for their specific situation and follow label instructions carefully when applying any pesticide.

2. Groundnut Rosette Disease

Groundnut rosette is a viral disease that affects peanut (groundnut) plants, and aphids transmit it. The condition can cause significant yield losses and is a major threat to peanut production in many parts of Africa.

The symptoms of groundnut rosette disease vary depending on the severity of the infection. The disease generally causes the leaves to become yellow and stunted; the plant may produce fewer and smaller leaves. The affected leaves may also develop a characteristic rosette shape, where the leaflets are tightly clustered. The disease can also cause the plant to produce fewer flowers, so the plant’s yield can be significantly reduced.

Groundnut rosette disease can also affect the roots of the plant. In some cases, the roots of infected plants may become stunted and discolored, and the disease can lead to a condition known as root necrosis, where the roots die off.

The severity of the disease depends on various factors, including the viral strain, the age of the plant when it is infected, and environmental conditions. There is currently no cure for groundnut rosette disease, and the best method of control is to prevent the spread of the disease through the use of disease-resistant peanut varieties, the application of insecticides to control aphids, and the removal and destruction of infected plants to prevent the disease from spreading to healthy plants.

3. Peanut Smut

Peanut smut is a fungal disease that affects groundnuts, also known as peanuts. The condition is caused by the fungus Thecaphora frezii, which infects the flowers and developing pods of the plant.

The symptoms of peanut smut include the appearance of black, irregularly-shaped masses on the surface of the developing peanut pod. These masses are clusters of fungal spores and can cause the pods to become deformed or fail to develop correctly. The disease can also cause the plant to produce fewer pods, which can significantly reduce yield.

In addition to affecting the pods, peanut smut can also affect the roots and leaves of the plant. Infected plants may exhibit stunted growth, yellowing or wilting of the leaves, and a reduction in overall plant vigor.

Peanut smut is primarily spread through infected seeds, and the fungus can survive in the soil for several years. The best control method for peanut smut is to use disease-free seed and to rotate peanut crops with non-host crops such as corn or soybeans. Fungicides can also control the disease, but their effectiveness may be limited.

As with any disease, it is vital to monitor peanut crops carefully and to promptly remove and destroy any plants that exhibit symptoms of peanut smut to prevent the disease from spreading.

4. Peanut Mottle Virus

Peanut Mottle Virus (PMV) is a viral disease that can significantly impact groundnut production. It affects groundnut plants by causing mottling and yellowing of the leaves, which can reduce the quality and yield of the crop. The virus is spread by insect vectors, such as thrips and aphids, and can also be transmitted through contaminated seeds.

To prevent the spread of PMV, farmers can take several measures, including:

Planting certified seed tested for the virus to ensure it is free from PMV.
Using insecticides to control insect vectors, such as thrips and aphids, that spread the virus.
Implementing crop rotation and avoiding planting groundnuts in the same field for consecutive seasons.
Removing and destroying infected plants to prevent the spread of the virus.
Practicing good sanitation, such as cleaning equipment and tools between fields, prevents the virus’s spread.
Monitoring the crop regularly for signs of the disease and taking action immediately if the condition is detected.
Using resistant or tolerant varieties of groundnuts that are less susceptible to PMV.
Farmers can reduce the incidence and severity of PMV in their groundnut crops by taking these preventive measures and ensuring better yields and quality.

5. Stem Rot Disease

Stem rot is a fungal disease that affects groundnuts in Kenya. The fungus Sclerotium rolfsii causes it and can significantly impact groundnut production. Stem rot affects the stem of the groundnut plant, causing it to rot and ultimately killing the plant. The disease typically occurs during the crop’s growth and development stages.

The symptoms of stem rot disease in groundnuts include the development of dark, sunken lesions on the stem near the soil line. A white, cottony growth of the fungus usually accompanies the lesions. As the disease progresses, the branch becomes weaker and may break, causing the plant to fall over. In severe cases, entire plants may die before maturity, resulting in significant yield losses.

Stem rot can be difficult to control, but farmers can take several measures to manage the disease, including

Using certified disease-free seed to prevent introducing the fungus to the field.
Practicing crop rotation to avoid planting groundnuts in the same field for consecutive seasons.
Avoiding planting groundnuts in soils with a history of stem rot disease.
Implementing good sanitation practices, such as removing and destroying infected plant debris and equipment between fields, prevents the fungus’s spread.
Using fungicides to control the disease is typically not a cost-effective option.

One fungicide used to manage stem rot disease in groundnuts in Kenya is carbendazim. This systemic fungicide works by inhibiting the growth of the fungus, thereby preventing its spread. Other fungicides that may be effective against stem rot in groundnuts include thiophanate-methyl, flutriafol, propiconazole, and tebuconazole.

6. Pod Rot Groundnut Disease

Pod rot is a fungal disease that can infect groundnuts at any growth stage, leading to significant yield losses and reduced quality. The condition is caused by several fungi, including Aspergillus spp. and Rhizopus spp., and affects the pods of the groundnut plant, causing them to rot and become discolored.

Symptoms of pod rot disease in groundnuts include soft, water-soaked lesions on the pods, which later turn brown or black and become covered with a white or gray mold. The affected pods may also develop a musty or sour odor. In severe cases, the entire pod may rot, and the seeds may become infected, leading to seed discoloration and reduced germination rates.

Farmers can control pod rot disease by using certified disease-free seed to prevent introducing the fungus to the field. Good field sanitation practices, such as removing and destroying infected plant debris, can also help reduce the spread of the disease. Farmers should avoid planting groundnuts in soils with a history of pod rot disease and practice crop rotation to reduce the fungus buildup in the ground.

7.Bacterial Wilt

Bacterial Wilt is a disease is caused by the bacterium Ralstonia solanacearum. The bacterium infects the groundnut plant through the roots and then spreads throughout the plant, causing wilting and eventually killing the plant.

The symptoms of bacterial wilt disease in groundnut roots include wilting and yellowing of the leaves, followed by rapid death of the entire plant. The origins of infected plants may also appear brown and water-soaked, with a foul smell.

As the disease progresses, the leaves of infected plants may turn brown and dry out, and the plant may eventually collapse.

Bacterial Wilt is a highly destructive disease that can spread quickly through the soil and persist in the ground for many years, making it difficult to control. The condition can be spread through contaminated soil, infected plant material, and contaminated water.

To manage bacterial wilt disease, farmers should use disease-free planting material and practice crop rotation to reduce the buildup of bacteria in the soil. They should also avoid planting groundnuts in fields with a history of bacterial wilt disease.

In addition, farmers can use biological control methods, such as soil amendments and biocontrol agents, to suppress the bacteria in the soil.

Chemical control measures for bacterial wilt disease are limited, as no fungicides or bactericides can effectively control the disease. However, some studies have shown that soil fumigation with methyl bromide can reduce the incidence of bacterial wilt disease in groundnuts.

8. Cercospora leaf spot

Cercospora leaf spot is a fungal disease that affects groundnuts in Kenya and is caused by the fungus Cercospora arachidicola. The disease can cause significant damage to the foliage of the groundnut plant and can lead to reduced yields and quality.

The symptoms of the Cercospora leaf spot in groundnuts include the development of small, circular, or irregularly shaped lesions on the leaves. The lesions may start as small, yellow spots, which later turn brown or black and become surrounded by a yellow halo.

In severe cases, the lesions may merge, leading to the death of the affected leaf tissue. The disease can also affect the stems and pods of the groundnut plant, causing dark spots on these parts.

Cercospora leaf spot disease can be managed through a combination of cultural, biological, and chemical control measures. Farmers should use certified disease-free seeds and practice crop rotation to reduce the fungus buildup in the soil.

Good field sanitation practices, such as removing and destroying infected plant debris, can also help reduce the spread of the disease.

Biological control measures, such as using biocontrol agents, can also effectively control the disease. Chemical control measures can include fungicides, although farmers should use them in combination with other control measures to reduce the risk of resistance development.

By implementing these measures, farmers can reduce the incidence and severity of Cercospora leaf spot disease in their groundnut crops and ensure better yields and quality.

9. Rust

Rust is caused by the fungus Puccinia arachidic. The disease can cause significant damage to the groundnut plant’s leaves and stems, leading to reduced yields and quality.

The symptoms of rust disease in groundnuts include the development of small, yellow, or brownish-colored bumps on the leaves and stems of the plant. As the disease progresses, the pustules may become larger, turn reddish-brown or black, and may also merge, leading to the death of the affected tissue.

In severe cases, the disease can cause defoliation and plant death.

Rust disease can be managed through a combination of cultural, biological, and chemical control measures.

Farmers should use certified disease-free seeds and practice crop rotation to reduce the fungus buildup in the soil. Good field sanitation practices, such as removing and destroying infected plant debris, can also help reduce the spread of the disease.

Biological control measures, such as using biocontrol agents, can also effectively control the disease. Chemical control measures can include the use of fungicides. Some of the fungicides to consider are:

Several fungicides can be used to control rust disease in groundnuts, including:

Azoxystrobin: This fungicide is effective against a wide range of fungal diseases, including rust, and can be used as a preventative or curative treatment.
Trifloxystrobin: It should be used as a preventative or curative treatment.
Propiconazole: It can be used to control rust and other fungal diseases in groundnuts.
Tebuconazole: This systemic fungicide is effective against rust and other fungal diseases in groundnuts.