Important diseases of groundnut, symptoms of damage and there management aspects are as follows:
1. Early Leaf Spot (Cercospora arachidicola):
Symptoms:
Infection starts about a month after sowing. Small chlorotic spots appear on leaflets, with time they enlarge and turn brown to black and assume sub circular shape on upper leaf surface. On lower surface of leaves light brown colouration is seen. Lesions also appear on petioles, stems, stipules. In severe cases several lesions coalesce and result in premature senescence.
Management:
Intercropping pearl millet or sorghum with groundnut (1: 3) is useful in reducing the intensity of early leaf spot. Crop rotation with non-host crops preferably cereals. Deep burying of crop residues in the soil, and removal of volunteer groundnut plants are important measures to reduce the primary source of infection. Spray carbendazim 0.1% or mancozeb 0.2% or chlorothalonil 0.2%.
2. Late Leaf Spot (Phaeoisariopsis personatum):
Symptoms:
Infection starts around 55-57 days after sowing in Kharif and 42-46 days after sowing in Rabi. 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.
Management:
Intercropping pearl millet or sorghum with groundnut (1:3) is useful in reducing the intensity of late leaf spot. Crop rotation with non-host crops preferably cereals. Deep burying of crop residues in the soil, removal of volunteer groundnut plants are important measures in reducing the primary source of infection. Spray carbendazim 0.1% or mancozeb 0.2% or chlorothalonil 0.2%.
3. Rust (Puccinia arachidis):
Symptoms:
Pustules appear first on the lower surface and in highly susceptible cultivars the original pustules may be surrounded by colonies of secondary pustules. Pustules may also appear on the upper surface of the leaflet. They may be formed on all aerial plant parts apart from flower and pegs. Severely infected leaves turn necrotic and desiccate but are attached to the plant.
Management:
Early sowing in the first fortnight of June to avoid disease incidence.
Destroy volunteer (self-sown) groundnut plants and crop debris to reduce/limit primary source of inoculum. Spray chlorothalonil 0.2%; or mancozeb 0.25% or hexaconazole/propiconazole to reduce disease incidence.
4. Stem Rot (Sclerotium rolfsii):
Symptoms:
Development of white fungal threads over affected plant tissue particularly on stem. Base of the plant turns yellow and then wilts down. Sheaths of white mycelium develop around the affected areas of the stem near the soil due to this the stem becomes shredded. White sclerotia of mustard seed size are produced in the infected tissues which later turn to brown colour. Seeds in the infected pods show a characteristic bluish-grey discolouration.
Management:
Deep ploughing to bury surface litter, cultivation of groundnut in flat or lightly raised beds. Seed treatment with Trichoderma viride @ 4 g/kg seed and soil application of Trichoderma viride @2.5 kg/ha, mixed with 50 kg FYM or in conjunction with organic amendments such as castor cake or neem cake or mustard cake @ 500 kg/ha. Seed treatment with 3 g thiram + carbendazim is recommended.
5. Bud Necrosis – Peanut Bud Necrosis Virus (PBNV):
Symptoms:
Chlorotic spots appear on young leaflets and necrotic rings and streaks are developed. Terminal bud necrosis occurs when temperature is relatively high. As the plant matures it becomes stunted with short internodes and proliferation of auxiliary shoots. The virus is mainly transmitted by thrips.
Management:
Early sown crop during kharif and rabi/summer seasons is less infected.
Destruct alternate weed hosts like Bidens pilosa, Erigon bonariensis, Tagetes minuta, Trifolium subterraneum. Increase plant density, do early sowing, mixed cropping with pearl millet to restrict vector movement. Groundnut should be intercropped with fast growing cereal crops such as pearl millet in 7:1 ratio. Spray monocrotophos 1.6 ml/l or dimethoate 2 ml/lit to control the vector.
6. Alternaria Leaf Disease (Alternaria arachidis and A. tenuissima):
Symptoms:
Lesions produced by A. 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 colour. In the later stages of infection, blighted leaves curl inward and become brittle. Lesions produced by A. alternata are small, chlorotic, water soaked, that spread over the surface of the leaf.
The lesions become necrotic and brown and are round to irregular in shape. Veins and veinlets adjacent to the lesions become necrotic. 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.
Management:
Foliar application of mancozeb (0.3%) or copper oxychloride (0.3%) or carbendazim (0.1%).