Diseases Of Oilseeds

I . DISEASES OF GROUNDNUT

1. Early leaf spot: Cercopora arachidicola

Late leaf spot: Phaeoisariopsis personata

Symptoms:

a.Early leaf spot: The sports are circular to irregular and reddish brown to dark brown in color. Spots appear on the upper surface, encircled by a bright yellow halo. On the lower surface the lesions are light brown in color.

b. Late leaf spot: Leaves show dark, small, circular spots scattered on the surface and appear in large numbers. The lower surface of the lesionturns to carbonaceous black. Petioles and stem also exhibit blackelongated lesions. Spotted leaves shed prematurely The mycelium is inter and intracellular. Conidiophores are short,olivaceous brown, 1-2 septate and geniculate, arising in clusters.

Favourable Conditions : Prolonged high relative humidity for 3 days Low temperature (20 C) with dew on leaf surface; Heavy doses of nitrogen and phosporus fertilizers ; Deficiency of magesium in soil.

2. Rust :

Causal organism : Puccinia arachidis

Symptoms: The leaflets exhibit large number of small powdery pustuleson the lower surface. Correspondingly the upper surface shows yellow discoloration which later turns brown. Pustules coalesce and severe infection causes drying and shedding of leaves. Pustules are also seen on petiole and stem. The pustules represent the uredosori.

Favourable Conditions

High relative humidity (above 85 per cent);Heavy rainfall.Low temperature (20-25˚C).

3. Collar rot / Seedling blight / Crown rot

Causal organism : Aspergillus niger and A. pulverulentum

Symptoms: The fungus causes pre-emergence and post-emergence rot and crown rot symptoms.

Post-emergence rot: Young seedlings exhibit circular brown spots on cotyledons. Similar spots appear on the collar region. The affectedportionbecomes soft and rots. Profuse growth of the fungus is seen on theaffectedregions.

Crown rot: The adult plants develop large brown lesions on the stem.Leavesdroop and plants wilt.

4. Root rot

Causal organism : Macrophomina phaseolina

Symptoms: The affected plants exhibit reddish brown discoloration on the stem near soil level. Leaves and branches droop and the whole plant wilts. White mycelial growth is observed on the lesions. The bark of the root becomes shredded and large number of sclerotia are formed in the shredded tissues and also on the wood.

Favourable Conditions : Prolonged rainy season at seedling stage and Low lying areas.

5.Disease : Ring mosaic / Bud necrosis / Bud blight

Causal organism : Groundnut bud necrosis virus

Symptoms: The disease is characterized by mottling and ring spotting of leaves, reduction in leaf size and stunting of plants. Leaves are malformed to varying sizes and they become narrow with necroticlesions. Stem also exhibits streaks and necrosis of bud occurs in advanced stages. The virus is transmitted by the thrips, Frankliniellaschultzi and Thrips tabaci

Disease management

1. Seed treatment: Treat the seeds with any one of the followingThiram @ 4g/kg of seed or Mancozeb @ 4g/kg of seed or Carboxin @2g/kg of seed or Carbendazim @ 2g/kg of seed or Talc formulation of T.viride @ 4g/kg of seed or P. fluorescens @10g/kg of seed.

2. Early leaf Spot and Late leaf Spot:

Spray any one of the following: Carbendazim 500 g/ha or Mancozeb 1000 g/ha or Chlorothalonil 1000 g/ha . If necessary give the second round 15 days later.

Combined infection of rust and Leaf spot

Spray any one of the following: Spray 10% Calotropis leaf extract or Spray Carbendazim 250 g + Mancozeb 1000g/ha or Chlorothalonil1000g/ha. If necessary give the second round 15 days later.

3.Rust: Spray any one of the following:

Mancozeb 1000g /ha or Chlorothalonil 1000g /ha or Wettable sulphur2500g /ha or Tridemorph 500 ml/ha or If necessary, repeat the spray 15days later.

4.Collar rot

Crop rotation.Destruction of plant debris.Remove and destroy previous season's infested crop debris in the fieldSeed treatment with Trichoderma viride / T.harzianum @ 4 g/kg of seeds and soil application of Trichoderma viride / T.harzianum at 2.5kg/ha,preferably with organic amendments such as castor cake or neem cake or mustard cake @ 500 kg/ ha.

5.Root rot:

Soil application of P. fluorescens @ 2.5g /ha mixed with 50 kg of well decomposed FYM / sand at 30 DAS. Spot drench with Carbendazim 1 g / l

6.Groundnut Bud Necrosis:

Adopt a close spacing of 15 x 15 cm. Remove infected plants up to 6 weeks after sowing and spray Monocrotophos 36 WSC 500 ml/ha, 30 days after sowing either alone or in combination with antiviral principles.Antiviral principles from sorghum or coconut leaves. AVP are extracted as follows: Sorghum or coconut leaves collected,dried, cut into small bits and powdered to one kg of leaf powder twolitres of water is added and heated to 60°C for one hour. It is then filtered through muslin cloth and diluted to 10 liters and sprayed. To cover one ha 500 liter of fluid will be required. Two sprays at 10 and 20 days after sowing will be needed