• Diseases are one of the most important factors contributing to low yields in groundnut. Numerous diseases caused by fungi and viruses have been reported in India. Some of them are widely distributed and cause considerable losses while others are restricted to some areas

• TIn India, this disease was first reported from Punjab in 1969. A new disease 'Alternariosis' of groundnut from Tamil Nadu was reported in 1979. The disease was found on plants of all ages but damage was greatest on those nearing maturity. The disease generally occurred in combination with leaf spots and rust.
• Of late, this disease becomes one of the major foliar diseases in some areas like Cuddalore and Villupuram districts. But it is always observed on the post-rainy season irrigated crop.

• Alternaria arachidis Kulk., A. alternata (Fr.) Keissler (A. tenuis Auct.) and A. tenuissima (Kunze ex Pers.) Wilts are the fungi responsible for Alternaria leaf spots.

• The disease is spread by wind- borne conidia.

. Lesions produced by Alternaria arachidis are brown in colour and irregular in shape surrounded by yellowish halos. Symptoms produced by A. tenuissima are characterized by blighting of apical portions of leaflets, which turn light to dark brown in colour. In the later stages of infection blighted leaves curl inward and become brittle.

• * Lesions produced by A. alternata are small, chlorotic, water soaked and they spread over the surface of the leaf. The lesions become necrotic and brown and are found to be irregular in shape.
• Veins and veinlets adjacent to the lesions become necrotic and the symptom is called veinal necrosis. Lesions increase in area and their central portions become pale, rapidly dry out and disintegrate.
• Affected leaves show chlorosis and in severe attacks become prematurely senescent. Lesions can coalesce, give the leaf a ragged and blighted appearance. Profuse sporulation occurs on the upper surface on mature lesions.

• Spray any one of the following fungicides for control of this disease.
• Mancozeb 1 kg/ha.
• Chlorothalonil 1 kg/ha.

• TIt is also called as peanut spotted wilt, Tomato Spotted Wilt Virus (TSWV), ring mosaic, groundnut mosaic, bunchy top, chlorosis, ring mottle and bud blight. It was first reported in India from Punjab.
• Yield reduction depends on the age of the crop, growth habit, cultivar, soil factors and environmental factors. This disease is common on crops grown in the dry (summer) and rainy seasons in India. It is considered to be an important disease in Coimbatore district of Tamil Nadu.

• Tomato Spotted Wilt Virus (TSWV).

• This virus is spread by seven species of thrips. Among them, Frankliniella schultzei is the most efficient vector. Larvae acquire the virus. Adults can not acquire but can transmit the virus. The virus is transmitted in a persistent manner. The virus can be transmitted by mechanical sap inoculations and through grafts. It is not transmitted through groundnut seeds.
• The virus has hosts of more than 200 species in 34 families. In India, tomato, brinjal, blackgram, greengram, Zinnia, Chrysanthemum, Trianthema portulacastrum, Gynandropsis pentaphylla, Ageratum conyzoides, Cassia tora, etc. frequently act as the host plants for this virus.

Plants infected by necrotic strain are killed very rapidly. Necrosis on older plants usually spreads only to the petiole or to the portion of the stem immediately below the necrotic terminal bud. In the late-infected runner type groundnuts, a few branches may show mild ring spots or necrosis of the buds and then the whole plant turns yellow, wilts and sometimes dies. The stunting and proliferation of axillary shoots are common secondary symptoms. Leaflets formed on these axillary shoots show reduction in size, distortion of the lamina, mosaic mottling and general chlorosis.

Very rarely, the lamina is reduced to the midrib, giving the leaflets a 'shoe-string' appearance. These secondary symptoms are most common on early-infected plants.

• This disease is due to a strain of tomato spotted wilt virus. The virus infection is noticed at about 3 weeks after sowing as the young leaves exhibit chlorotic ring spots. As the virus becomes systemic different kinds of malformation of leaves, mosaic patterns and necrosis of terminal buds are seen.

;Seeds from early infected plants are small and shriveled and their testa show red, brown or purple mottling. Late infected plants may produce seeds of normal size, but the testae are often mottled.

Crop loss

• In early infections it may cause up to 100 per cent loss in yield.

• Clean cultivation is essential. All weeds should be thoroughly eliminated to remove all sources of infection.
• Sorghum as intercrop or barrier crop and cumbu as intercrop with groundnut reduces the disease incidence.
• Adopt closer spacing (15x15 cm) and eliminate infected plants up to 6 weeks after sowing.
• Spray monocrotophos 36 WSC (500 ml /ha) 30 days after sowing either alone or in combination with anti-viral principles (AVP) from sorghum or coconut leaves. For the preparation of anti-viral principle (AVP), sorghum or coconut leaves are collected, dried and powdered. To one kg of leaf powder, two litres of water is added and heated to 60°C for an hour. It is then filtered through muslin cloth and diluted to 10 litres before spraying. Five hundred lit of extract is required to cover one hectare. Two sprays at 10 and 20 days after sowing are needed.

• This disease was first reported from Java in 1926. In India, the disease is prevalent in all groundnut tracts and is usually most severe in light sandy soils.

• Aspergillus niger Van Tieghem is the causal agent of crown rot.
• The mycelium is hyaline to sub-hyaline. The condiophores arise directly from the substrate and are septate, smooth and thick-walled and hyaline to olive brown in colour. The vesicles are mostly globose and have two rows of hyaline phialides viz., primary and secondary phialides.
• The conidial heads are dark brown to black. The conidia are produced in long chains and are globose, spinulose and dark brown on maturity.

• The pathogen is carried on the seed surface and in or under the tissues of the testa. The primary sources of inoculum are a) mycelium and spores carried on the seeds. b) plant debris in the soil and c) infected cotyledons or embryos. Seeds become infected during the last days of maturation in the soil and during harvesting, handling and particularly during shelling.
• The disease perpetuates through contaminated soil also. Soil infection spreads to cotyledons or directly to hypocotyl. The seedlings become more susceptible when they are injured.
• The fungus can tolerate low moisture levels and develops well at temperatures between 30° and 35°C. It builds up in soils continuously cropped with groundnut. * Conditions, which are not conducive for quick seed germination such as deep sowing, high soil and air temperatures and chemical toxicity increase the disease incidence. Spreading varieties are more susceptible than bunch varieties.
• The disease is particularly high when the weather during the harvesting period is wet and it increases the seed-borne infection.

In a moist soil, seeds may be attacked immediately after sowing leading to pre-emergence rotting. If the ungerminated seeds are removed from the soil they are found covered with masses of black conidia which give the seed a sooty appearance. Post-emergence infection often culminates in death and rapid decay of seedlings. The first symptom in emerged seedlings is usually rapid drying of the entire plant. Affected tissues are covered by sporulating fungus at the soil surface.

• As the infection spreads, the entire collar region become dark brown and shredded. When the infection occurs at hypocotyl region just below the cotyledons, the plant may wilt temporarily but eventually recover.
• Mature plants are also attacked. Lesions develop on the stem just below the soil surface and spread upward along the branches. Beacause of the woodiness of mature plants, symptoms are not generally observed until permanent wilting of branches on the plant is apparent. The dead and dried branches are easily detached from the disintegrated collar region. The fungus sporulates on the surface of mature pods resulting in patches of black sooty spores.

• Harvested pods should be dried promptly.
• Deep planting of seed should be avoided.
• Avoid mechanical damage to the pods and kernels.
• Destruction of infected plant debris.
• Deep ploughing of field.
• Spanish bunch variety J 11 is found resistant to crown rot
• Seed treatment with carbendazim (2 g/ kg) or thiram (4 g/ kg) minimizes the disease incidence.

• It is known by several names such as wilt, charcoal rot, ashy stem blight and root rot. It was first reported in India in 1927. It is prevalent in almost all the groundnut growing localities in India.

• The disease is caused by Macrophomina phaseolina (Tassi) Goid., the sclerotial stage of the fungus is Rhizoctonia bataticola (Taub.) Butler. The fungus produces hyaline to dull brown mycelium. The sclerotia are thick walled and dark brown in colour.

• The fungus is primarily seed and soil- borne and persists in soil for longer period as actively growing mycelia or dormant sclerotia. The longevity of pycnidiospores in soil and in infected plant debris is dependent on soil moisture and soil temperature.
• Secondary spread occurs through sclerotia carried through irrigation water, implements and farm operations.
• It prefers high temperature and/or low soil moisture for its activity and infection.
• The pathogen has a wide host range including many leguminous crops such as sesame, sunflower, castor, maize, sorghum, blackgram, greengram, redgram, cowpea, soyabean, cotton, etc.

• The disease may appear at any stage of crop development. In the early stages of infection reddish brown, water soaked lesions appear on the stem just above the ground level. Later the lesions darken and the disease spreads upward to the aerial parts and down into the roots.
• If the lesions girdle the stem, wilting occurs. The dead tissue is covered with abundant sclerotia giving the appearance of a light covering of soot. Pycnidia are also formed in some cases.
• Roots are also affected and they rot. The root tissues are found disintegrated.
• Affected plants come off very easily from the soil and the barks peel off while pulling out. The root bark of affected plant shreds and studded with numerous black sclerotia.
• Pegs and pods are also attacked and are covered with fungal spores leading to 'blacknuts' formation. In the pods the shills as well as kernels are affected. Due to infection in the kernel, the fungus grows between the cotyledons. The fungal growth on kernels becomes black and it produces many minute sclerotia.
• The quality grades of affected kernels are reduced. Such affected kernels will have high fatty acid content, which reduces the value of kernels.
• Dry rot affected pods and kernels are prone for infection by secondary parasites such as Aspergillus flavus.

• Non-host crops may be chosen as inter or mixed crops or be included in the rotation to reduce the soil inoculum and subsequently the disease.
• As and when the diseased and dried plants are noticed in the field they should be removed along with the roots and burnt.
• Treat the seeds with carbendazim 2 g/ kg or
• Trichoderma viride 4 g/kg or
• Pseudomonas fluorescens 10 g / kg.
• Spot drenching with carbendazim @ 0.5 g/lit of water as and when the disease is noticed in the field.
• Soil application of Pseudomonas fluorescens @ 2.5 kg /ha after mixing it with 50 kg of well-decomposed FYM or sand on 30 days after sowing minimizes the disease incidence.

• This is also known as chlorotic rosette. It was reported from Tamil Nadu in 1967.

• Groundnut Rosette Virus (GRV) is the major and causal agent of the disease in groundnut but it is dependent on the other Groundnut Rosette Assistor Virus (GRAV) for transmission by aphids.

• Aphis craccivora is the important vector. Virus is acquired by the aphids within 30 minutes of feeding. The virus is also transmitted through graft but not through seed.

• Chlorosis and vein banding are observed on young leaflets. Terminal bud necrosis and concentric chlorotic rings observed in BND are absent. Secondary symptoms are characterized by reduction in the size of leaflets showing general chlorosis, vein banding and dark green patches.
• Field grown plants are slightly stunted with extreme proliferation and rosetting of the secondary shoots. Leaflets are small, cupped, crinkled, malformed and chlorotic.

• Destruction of volunteer groundnut plants.
• Spraying of monocrotophos (500 ml/ha) helps to check the spread of disease.

• Tylenchorhynchus brevilineatus Williams is the causal agent of Kalahasti malady and the disease is prevalent in Coimbatore, Erode and Dindigul districts.

Infected plants appear in patches in the field and are stunted with greener than normal foliage. Small brownish-yellow lesions appear on the pegs and on young developing pods. The margins of the lesions are slightly elevated because of the proliferation of host cells around the lesions. Peg length is reduced and in advanced stages of the disease, the entire pod surface becomes blackened. Discolouration is also observed on roots, but this is less conspicuous than pod discolouration.

• Kernels from diseased pods are apparently healthy, although commonly smaller than normal.
• An avoidable yield loss of 10% was estimated due to this nematode.

• Soil incorporation of either carbofuran 3G @ 33 kg/ha or phorate 10G @ 10 kg/ha reduces the disease incidence.
• Soil application of FYM @ 12.5 t/ha or neem cake @ 500-1000 kg/ha reduces the nematodes in the field.

• Peanut Stripe Virus (PStv)

• The virus is mechanically sap transmissible. The vector, Aphis craccivora transmits the virus in a non-persistent manner. The virus is transmitted through seed. Seed transmission ranges from 2.7 to 28.8 per cent.
• The virus infects clusterbean, cowpea, greengram, sesame and soyabean.

• The characteristic symptoms exhibited by this virus are striping or even banding along the lateral veins of the peanut leaflets.
• Infected plants show oak leaf pattern or mild banding of mid vein of the leaflets. The diseased plants are stunted.
• Symptoms varies with virus isolate and groundnut cultivar. Necrotic and stripe isolates cause severe reduction.

• As the virus is transmitted through seed, certified seeds should be used. The diseased seeds should not be imported from other countries either for research or for commercial purpose. Strict quarantine measures should be followed to avoid the disease.
• Collateral hosts should not be grown in the vicinity of groundnut crop.
• The disease can be reduced by spraying monocrotophos 36 WSC (500 ml /ha), which controls the insect vector.

• Rust is considered economically important in almost all groundnut growing areas. Loss will be heavy if the crop is also affected by leaf spots.

• Puccinia arachidis Speg. is the causal agent of rust disease.
• The fungus produces only uredial and telial satges. The uredial stage is the most predominant and commonly observed stage. Uredia are predominantly hypophyllus, scattered or irregularly grouped, round ellipsoid or oblong, dark cinnamon brown when mature; ruptured epidermis conspicuous; uredospores are pedicellate, unicellular, yellow, oval or round 16 to 22 x 23 to 29 µm and echinulated with 2 or 3 germpores.
• Telia are hypophylus, 0.2 to 0.3 µm in dia, scattered, naked, chestnut brown becoming grey from germination or almost black and the ruptured epidermis prominent. Teliospores are oblong or ovate in shape with rounded to acute and thickened apex, constricted in the middle (2 celled) and dark brown in colour.
• Pycnial and aecial stages have not been recorded.

• The pathogen is known to perpetuate, spread and produce severe outbreaks by means of wind-borne uredospores. Uredospores also spread as contamination of seeds and pods. Rainsplash and implement also help in dissemination.
• No alternate host is found to be involved in the life cycle. The pathogen may survive from season to season on volunteer groundnut plants and collateral hosts like Arachis marginata, A. nambyquarae and A. prostrata.
• High relative humidity (above 85%), heavy rainfall and low temperature (20°-25°C) favour the disease development and spread.

The disease attacks all aerial parts of the plant except flowers and is usually found when the plants are about 6 weeks old. Small brown to orange coloured pustules (uredosori) of 0.5 to 1.4 um dia appear on the lower surface of leaves. The epidermis ruptures and exposes a powdery mass of reddish brown uredospores. Corresponding to the sori, small, necrotic brown spots appear on the upper surface of leaves. Rust pustules on the leaflets cause loss of photosynthetic tissues and it leads to chlorosis and death of the whole leaflet.

Leaflets may dry up to give the plant a burnt appearance. Rust pustules may also be seen on petioles, stem and on shells of developing pods. Late in the season, brown teliosori, as dark pustules appear among the necrotic patches. In contrast with the rapid defoliation associated with leaf spots, leaves infected with rust become necrotic and dry up, but tend to remain attached to the plant. The severe infection leads to production of small and shriveled seeds.

• In India, combined attack of rust and leaf spots lead to 70 per cent loss in pod yield while the loss due to rust alone was 52 per cent. Losses when rust occurred at flowering, pegging, pre-pod forming and pod forming stages were 49, 41, 31 and 18 per cent respectively.

• Volunteer groundnut plants should be eradicated.
• Weeds should be kept under control, because heavy growth of weeds may encourage disease development.
• Avoid monocropping of groundnut in endemic areas.
• Grow moderately resistant varieties like ALR 1, ALR 2, ALR 3 and VRI 4.
• Spray any one of the following fungicides.

• Stem and pod rots are considered as potential threat to groundnut production in many warm and humid areas under irrigated conditions. This disease is commonly known as stem rot, southern blight, Sclerotium blight, white mould, Sclerotium rot, Sclerotium wilt, root rot and foot rot.
• In India, the disease occurs sporadically and yield losses may amount to 27% or more.

• Sclerotium rolfsii Sacc. is the causal agent of this disease.
• The mycelium of the fungus is septate and hyaline with conspicuous branching at acute angles. The young growing mycelial mass is snow white with a silky lusture. * Sclerotia are at first white, becoming light brown to dark brown at maturity with 0.5 to 1.5 mm in dia.

• The primary source of inoculum is the sclerotia. This can remain viable in the soil for 2 to 3 years. The fungus also survives as mycelium in the soil only for short periods (1-2 months).
• The mycelium can be seed-borne.
• Moderate to high temperature (25° to 35°C) and moist conditions enhance the disease development. Frequent rains or irrigation and dense foliage canopy increase or prolong high soil moisture, which favour stem rot.
• Monocropping, soils with high organic content and fertility, mechanical or biological damage to stems or pods may increase disease severity. Calcium deficiency predisposes stem rot incidence.
• This pathogen has a wide host range of nearly 500 plant species. Redgram, blackgram, greengram, cowpea, ragi and betelvine are few important crop hosts.

The pathogen attacks all parts of the plant but stem infection is the most common and serious, hence it is named as stem rot. The first symptom is the sudden wilting of a branch, which is completely or partially in contact with the soil. The junction of the branch with the stem near the soil level is the most favoured point of attack and a white coating of fungus mycelium is formed there. Leaves of affected branch become chlorotic and then turn brown as they rapidly dry out. As the disease advances a white mycelial web spreads over the soil and the basal canopy of the plant.

Management

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Storage disease

Contamination before harvest

After harvest

In storage

Management

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Tikka leaf spots

Introduction

Fungi

Cercospora arachidicola

Phaeoisariopsis personata

Epidemiology

Nature and symptoms of damage

Early leaf spot

Late leaf spot

Crop loss

Management

Management of late leaf spot and rust of groundnut

Botanicals

Biological Control

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Yellow mould or Aflaroot disease

Introduction

Fungus

Nature and symptoms of damage

Crop loss

Management

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Root-Knot Nematode

Stage and symptomss

Management

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