Groundnut Diseases and Management Practices

Groundnut crop is affected by several diseases at different crop growth stages. It is essential that the growers know to recognize the diseases’ symptoms on time and take preventive and control measures to avoid yield reduction.

Foliar fungal diseases of groundnut

Early leaf spot (ELS), Late leaf spot (LLS), and Rust are major foliar fungal diseases reported wherever groundnut is grown worldwide.

Early leaf spot and Late leaf spot in groundnut: These diseases are caused by the fungus Cercospora arachidicola and Phaeoisariopsis personata, respectively. These diseases are also referred to by different names, such as mycosphaerella leaf spots, Cercospora leaf spots, brown leaf spots, peanut Cercospora, viruela, and tikka disease.

Together these diseases can reduce groundnut pod yield by around 50%; in areas where rust disease is also observed, a combined attack of foliar diseases can cause yield losses in excess of 70% [1].

This disease is most common in warm, humid climate regions.

Early leaf spot Symptoms in groundnut

The infection starts about a month after sowing.

• Small chlorotic spots appear on leaflets; with time, they enlarge, turn brown to black, and appear as sub-circular shapes on the upper leaf surface.
• Generally, light brown coloration is seen on the lower surface of leaves.
• Lesions also appear on petioles, stems, and stipules.
• In severe cases, several lesions coalesce and result in premature aging of the groundnut plant.

Late leaf spot symptoms: Infection starts around 55-57 days after sowing in Kharif and 42-46 days after sowing in post rainy (Rabi) season.

• Black & nearly circular spots appear on the lower surface of the leaflets.
• Lesions are rough in appearance. In extreme cases, many lesions coalesce, resulting in premature senescence and shedding of the leaflets.

Rust disease Symptoms and Management Measures in Groundnut

Rust disease is caused by the fungus Puccinia arachidis. This fungus attacks all aerial parts of the plant. This disease is usually observed around 45-50 days after sowing. Small orange-colored rust pustules appear on the lower surface of leaflets; on rupturing, they release masses of reddish-brown spores; along with this rapid defoliation associated with leaf spots, leaves infected with rust become necrotic and dry up but tend to remain attached to the plant; it can cause yield losses over 50%. The rust spores do not survive for a longer time under suitable ambient conditions; its inoculum is mostly airborne and comes from other infected fields [2].

If not properly managed initial stage, the yield losses could be severe. As controlling measures, agronomists advise the following measures:

• Cultivating resistant varieties could be one of the practices where one can escape the disease.
• Intercropping pearl millet or sorghum with groundnut (1 : 3) reduces the intensity of late leaf spot.
• Crop rotation with non-host crops, preferably cereals.
• Removal of debris from the field and volunteer plants in the surrounding.
• Fungicide application is common. Spraying of any one of the following could prevent the disease:

1. Carbendazim 500 g/ha
2. Mancozeb 1000 g/ha
3. Chlorothalonil 1000 g/ha

If the disease persists and based on the severity, carry out the second spray round 15 days later. Combined infection of rust and Leaf spot. Spray any one of the following:

1. Spray 10% Calotropis leaf extract
2. Spray Carbendazim 250 g + Mancozeb 1000g/ha
3. Chlorothalonil 1000g/ha. If necessary, at 15 days later [3].

Soil-borne diseases in groundnut

Groundnut crop is also affected by soil-borne disease. Soil-borne pathogens cause significant yield losses due to the close association of the groundnut pods with the soil [4]. These are challenging to control once they appear; however, maintaining good soil health is of utmost importance for good crop performance.

Collar/Crown rot in groundnut caused by Aspergillus niger. 

This disease is also called seedling blight. The symptoms include, at the preemergence stage, the soil-borne conidia attacking seeds and cotyledons, leading to rotting. The seeds are covered with black masses of conidia spores, and the internal tissues of the seed become soft and watery.

At a postemergence stage, the pathogen attacks the young seedling and causes brown spots on the cotyledons. The symptoms later spread to the hypocotyl and stem regions. Brown discolored spots can be observed on the collar region. The affected region becomes soft and rotten, resulting in seedling death. Therefore, it is called collar rot or seedling blight.

When the pathogen attacks and infects adult plants, crown rot symptoms can be observed. Large lesions develop on the stem below the soil and spread upward along the branches causing drooping of leaves and wilting of the plants.

The favorable conditions for this disease are deep sowing of seeds, high soil temperature (> 35 ° C), and low soil moisture.

Stem rot/White mold in groundnut caused by Sclerotium rolfsii

It is widely distributed in most of groundnut-growing regions worldwide. The pathogen has a wide host range of more than 500 plants, including groundnut, and the disease is gaining importance internationally. The rapidly spreading disease is found in the world’s tropics, subtropics, and warm temperate zones. Severe losses from stem rot disease have also been reported in several countries [5]. The yield loss is recorded from 10-25%.

The pathogen attacks almost all parts of the plant. Initially, it produces sclerotia in soil, germinating under favorable climate conditions to further produce white-colored mycelium. Initial symptoms are chlorosis and wilting of the lateral branches or main stem. Leaves of the affected plants become chloritic and later turn brown as they rapidly dry out. The white mycelium of the pathogen can be seen around the plant stem base region [6].

The best prevention measures are the use of resistant varieties and the use of seeds with fungicidal dressing with Thiram or Captan or Mancozeb @ 3g/kg of seed or carbendazim @ 2g/kg of seed or tebuconazole (Raxil 2% DS) @ 1.25 g/kg seeds or Trichoderma viride or Pseudomonas flurescens 10 g/kg seeds. Soil application of Trichoderma viride or Trichoderma harzianum 2.5 kg/ha to the soil in combination with neem cake or castor cake @300-500 kg/ha. Crop rotation. Removal of infected plants and debris.

Aflatoxin contamination: Aflatoxins are carcinogenic secondary metabolites produced in groundnut seeds using Aspergillus flavus and Aspergillus parasitics, which are harmful to human beings, poultry, and livestock. The fungus attacks the pods and seeds via small cracks or mechanical damage during intercultural operations, harvesting, and post-harvest management. This disease significantly hampers the trade of groundnut between countries and continents.

To prevent aflatoxin contamination in groundnut, similar management practices for soil-borne diseases should be followed. Additionally, application of FYM/ Compost @ 5-10 t/ha, Application of Gypsum @ 400-500kg/ha at flowering, following proper agronomical practices, avoiding mechanical damage to the pods during harvesting, proper drying of pods, storage of groundnut pods at low temperature and low humidity, moisture free conditions [3].

Viral Diseases of groundnut

Field identification of virus diseases of groundnut is very challenging and sometimes misleading. Getting confirmation from the plant protection or agriculture extension officer is crucial.

Peanut Bud Necrosis Disease (PBND) caused by the peanut bud necrosis virus

Thrips Palmi Karny transmits the virus. This disease is predominantly seen in south and southeast Asia. The first disease symptoms are initially seen on young quadrifoliates as mild chlorotic spots, which later develop into necrotic and chlorotic rings and streaks. Further, plants will be stunted and bushy, with the death of the terminal bud being a characteristic symptom. Stunting, axillary shoot proliferation, and leaflet malformation are secondary symptoms. In severe situations, the virus leads to crop loss. And harvested seeds from infected plants will be small, shriveled, discolored, and mottled.

Tomato Spotted Wilt Virus (TSWV): concentric ring spots on a groundnut leaf are the characteristic symptom of the disease. Other symptoms are more or less similar to PBND.

Peanut Strip Virus (PStV): dark green stripes and discontinuous banding along the lateral veins of young leaves or oak leaf symptoms are occasionally caused by PstV [7].

Groundnut Rosette disease (GRD): In this disease, there are two types chlorotic rosette and green rosette. Both variant forms cause severe stunting with shortened internodes, leaf size, and bushy plants. This disease is present in a small proportion every season. However, it is severe in late planting, causing 5-30% yield losses.

As a management precaution for all virus diseases of groundnut, growing of resistant varieties, field sanitation, timely sowing, and proper agronomic practices, removal of infected seedlings, maintaining optimum population, effective control of vectors, and intercropping and border cropping, removal of alternate weed hosts of the virus.

Root-knot disease

Root-knot disease caused by Meloidogyne arenaria and Meloidogyne hapla. The symptoms are stunted plant growth, chlorotic leaves, and a poor root system with a bushy plant appearance. On pods, knots and galls are observed. Similar symptoms are observed for root lesion disease caused by Pratylenchus brachyurus and ‘Kalahasti malady’ caused by Tylenchorhynchus brevilineatus predominantly observed in India, characteristic symptoms of stunted plant growth with foliage greener than normal, brownish yellow lesions are seen on pegs and pods.

Growing nematode-resistant varieties and crop rotation with non-host crops is recommended as a precautionary measure for the nematode.

References:

1. McDonald, P. Subrahmanyam, R.W. Gibbons and D.H. Smith, 1985. Early and late leaf spots of groundnut, ICRISA T Information Bulletin no. 21.
2. N.Nigam, 2015. Groundnut at a glance.
3. http://agritech.tnau.ac.in/crop_protection/groudnut_diseases/groudnut_d2.html.
4. Thiessen, L.D. and Woodward, J.E. 2012. Diseases of peanut caused by soilborne pathogens in the Southwestern United States. International Scholarly Research Notices. 2012.
5. Kasundra, S. and Kamdar, J., Phenotyping Technique For Stem Rot Disease In Groundnut Under Field Conditions (2016).
6. https://images.app.goo.gl/RThaWH4f4zmjMefL7
7. http://eagri.org/eagri50/PATH272/lecture09/008.html

Further reading

Groundnut: Plant Information, History, Uses and Nutrition Value

Principles of selecting the best varieties of Groundnut: A Comprehensive Guide

Groundnut Soil requirement, Soil preparation and Planting

Weed Management in Groundnut Farming

Fertilizer requirement for Groundnut Cultivation

Irrigation Requirement and Methods for Groundnut Cultivation

Groundnut Diseases and Management Practices

Groundnut Insects, Pests, and their Management

Harvesting, Drying, Curing, and Storage of Groundnut