Groundnut

Disease Management

Introduction Alternaria Leaf Diseases Anthracnose Collar Rot Or Crown Rot Or Seedling Blight Dry Root Rot Or Dry Wilt Fusarium Diseases Kalahasti Malady Yellow Mould Or Aflaroot Disease Bud Necrosis Or Bud Rot Or Bud Blight Pepper Spot And Leaf Scorch Root Knot Nematodes Rust Rhizopus Seed And Seedling Rot Stem Rot Or Sclerotium Wilt Tikka Leaf Spots Major Diseases Of Groundnut And Their Control

Introduction

  • India is the largest producer of groundnut in the world.
  • But average yields are low at 745 kg/ha.
  • One of the important factor contributing to low yield is disease attack.
  • Groundnut crop is prone to attack by numerous diseases to a much larger extent than many other crops.
  • More than 55 pathogens including viruses have been reported to affect groundnut.
  • Some diseases are widely distributed and cause economic crop losses while others are restricted in distribution and are not considered to be economically important at present.
  • The diseases which are of minor importance today may become major later.
  • Among fungal foliar diseases, only a few are economically important in India such as leaf spots (early and late) and rust which are widely distributed and can cause losses in susceptible genotypes to the extent of 70 per cent when both of them occur together.
  • Of late Alternaria leafspot (A. alternata) is becoming increasingly important in Southern states and Gujarat on rabi/summer crop and in Gujarat also on kharif groundnut crop.
  • Other fungal foliar diseases like anthracnose, pepper spot and leaf scorch, Phomopsis leafspot, Phyllosticta leafspot, Pestalotiopsis leafspot, Phoma leaf diseases, Drechslera leaf blight, Zonate leafspot and Cylindrocladium leaf spot are not economically important diseases at the present time and hence control schedules are not yet developed for these diseases.
  • Of the seed and soil-borne diseases, collar rot, stem rot and dry root rot have been realised as major limitations.
  • These diseases cause severe seedling mortality resulting in 'patchy' crop stand in sandy loam soils and reduce the yields from 25-40 percent.
  • Several virus diseases of groundnut have been reported from India.
  • Economically important virus diseases are few like bud necrosis, peanut mottle and peanut clump.
  • Control measures for other virus diseases are not yet established.
  • Bud necrosis disease of groundnut is wide spread with wide host range.
  • It is a serious disease in Andhra Pradesh and Madhya Pradesh.
  • It has also started assuming importance in the recent years in Haryana and Uttar Pradesh states and on summer crop in Gujarat state.
  • In India, bud necrosis disease can cause serious yield losses ranging upto 50 per cent.
  • Peanut(Groundnut) mottle virus (PMV) has been reported to occur on rabi/summer groundnut mainly in the states of Andhra Pradesh, Maharashtra and Gujarat.
  • Losses have been reported to vary from 5-30 per cent.
  • The PMV has been reported to be seed-brone to the extent of 0.1 to 3.5 per cent.
  • Peanut clump has been reported from Punjab, Gujarat, Andhra Pradesh and Uttar Pradesh on crops grown in sandy soils.
  • Yield losses of upto 60% have been recorded in late infected plants.
  • Reports on diseases caused by nematodes in groundnut are very few in India.
  • The root knot nematodes have been reported to cause damage in various parts of the country.
  • Recently, a nematode induced disease locally known as 'Kalahasti Malady' was observed in Chittoor and Nellore districts of Andhra Pradesh.

Top

Alternaria leaf diseases (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 characterised 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 coalese, give the leaf a ragged and blighted appearance.

Control:

  • Control measures are not yet developed for Alternaria leaf diseases.
  • Fungicides are being evaluated at various research centres in the country for control of Alternaria leafspot of groundnut.

Top

Anthracnose (Colletotrichum dematium and C. capsici)

Symptoms

  • Small water-soaked yellowish spots appear on the lower leaves which later turn into circular brown lesions with yellow margin 1 to 3 mm in diameter.
  • In some cases lesions enlarge rapidly become irregular and cover the entire leaflet, and extend to the stipules and stems.

Control

  • Spraying of copper oxychloride and Mancozeb are effective in controlling the anthracnose disease of groundnut.

Top

Seed and Soil-Borne Diseases

1. Collar rot/Crown rot/Seedling blight : (Aspergillus niger and A. pulverulentus)

Symptoms

  • Pre-emergence rotting of seeds, rotting of the hypocotyl, but the most common cause of loss is early post emergence seedling blight.
  • Hypocotyl tissues become water soaked and light brown.
  • The first symptom in emerged seedling is usually a rapid wilting of the entire plant or its branches
  • At this stage, the hypocotyl and tissiues of the cotyledonary node are particularly rotted.
  • As the infection spreads, the whole collar region becomes shredded and dark brown .

  • Mature plants may also be attacked. Lesions develop on the stem below the soil and spread upwards along the branches.
  • The dead dried branches are easily detached from the disintegrated collar region.

Control

  • Recently a spanish bunch variety J 11 has been reported to be resistant to collar rot. In endemic areas, J II variety could be grown.
  • Deep planting of seed should be avoided as etiolated hypocotyl is prone to infection. Avoiding mechanical damage, destroying plant debris, deep ploughing and rotation of groundnut with gram and wheat are useful in reducing the collar rot disease incidence.
  • Seed treatment with tetramethyl thirum disulphide (thiram, TMTD) 75% WP @ 3-5 g/kg seed or Captan 80% WP 3 g/kg seed or Carbendazim (Bavistin) 50% WP @ 2 g/kg seed will control borne infection.

Top

Dry root rot/Dry wilt : Macrophomina phaseolina and Rhizoctonia bataticola

Symptoms

  • The disease may appear at any stage of the crop growth.
  • Water soaked necrotic spots appear on the stem just above the ground level.
  • The lesions darken as the infection spreads upward to the aerial parts and down into the roots.
  • The entire stem becomes shredded and with the development of sclerotia becomes black and sooty in appearance Roots, pegs and pods also rot and become covered with sclerotia.
  • Roots are commonly attacked in association with stem rots and wilt.
  • Occasionally only the roots are attacked, when the tap root turns black and later becomes rotten and shredded.
  • The kernels turn black with abundant sclerotia internally and externally on the testas and shells.
  • The symptoms of the leaf infection are characterised by marginal zonate and irregular spots.
  • Minute spots are also quite common and expand into bigger wavy spots.

Control

  • Measures which encourage good crop growth such as adequate fertilization, irrigation and pest control, may help in reducing the disease.
  • Seed treatment with spores and mycelial fragments of Trichoderma polysporum has been shown to prevent invasion by M. phaseolina.
  • Seed treatment with carbendazim 2 g/kg seed or Captan 3 g/ kg seed or thiram @ 3-5 g/kg seed is most effective.
  • PCNB (Brassicol 75% WP) 0.5% can also be applied @ 1 litre/ square metre or in the form of soil dust O 25 kg/ha in two split applications, 12.5 kg/ha before sowing and the other 12.5 kg/ha 15 days later.

Top

Fusarium diseases: Fusarium oxysporum and F. solani

Symptoms

  • Germinating seeds are attacked by Fusarium spp. shortly before emergence.
  • There is a general tissue disintegration and the surface of the seedling is covered with sporulating mycelium.
  • Damping off symptoms characterized by brown to dark brown water soaked, sunken lesions on the hypocotyl which later encircle the stem and extend above the soil level.
  • Roots are also attacked, especially the apical portions.
  • The affected seedlings become yellow and wilted.
  • The leaves turn greyish green and the plants dry up and die.
  • The roots and stems show internal vascular browning and discolouration.
  • These fungi are also commonly associated with pod rot.

Control

  • Seed treatment with systemic fungicides like Carbendazim may be useful in controlling pre-emergence rots.

Top

Kalahasti Malady : (Tylenchorhynchus brevilineatus)

Symptoms

  • Small brownish yellow lesions appear on the pegs, pod stalks and on young developing pods.
  • The margins of the lesions are slightly elevated because of the proliferation of host cells around the lesion.

  • Pod stalks are much reduced in length and in advanced stages of the disease the entire pod surface becomes discoloured.
  • Discolouration is also seen on roots.
  • Affected plants are stunted and greener than normal foliage.

Control

  • Soil treatment with aldicarb and carbofuran is effective in reducing soil population.
  • Use Resistant varieties.

Top

Yellow mould or Aflaroot disease : Aspergillus flavus

Symptoms

  • Seed and un-emerged seedlings attacked by the fungus are rapidly reduced to a shrivelled, dried, brown or black mass covered by yellow or greenish spores .
  • Decay is most rapid when infected seeds are planted.
  • In some cases the emerging radicle and hypocotyl are infected which decay rapidly.
  • After seedling emergence cotyledons already infected with the fungus, show necrotic lesions with reddish brown margins.
  • This necrosis terminates at or near the cotyledonary axis.
  • Under field conditions the diseased plants are stunted, and are often chlorotic.
  • The leaflets are reduced in size with pointed tips, widely varied in shape and sometimes with veinal clearing .
  • If affected plants are dug up, the radicle is found to be lacking in secondary root development.

Control

  • Since the fungus is a weak parasite, agronomic practices which favour rapid germination and vigorous growth of seedling will reduce the chance of A. flavus infection.
  • Seed treatment with carbendazim @ 2g/kg seed or Captafol @ 3 g/kg seed or thiram @ 3-5 g/kg seed has given good results.

Top

Bud necrosis/Bud rot/Bud blight : Tomato Spotted Wilt Virus

Symptoms

  • Chlorotic rings are present on leaves of infected plants. A conspicuous symptom is necrosis of terminal bud.
  • Plants infected early in the season are stunted, and shoots bear small leaves that are distorted and mottled .
  • Mature plants show less stunting and Chlorotic rings and mottle on young leaflets often occur about 40 days after planting.
  • Necrosis of the bud may spread to the petioles and stem, sometimes leading to death of the plant.
  • Later formed leaves are smaller than normal and show a wide range of symptoms, including distortion, mosaic mottling and general chlorosis.
  • Pod size and number are greatly reduced. In late infections, pod size is reduced.
  • Seeds are often shrivelled and have mottled and discoloured testa.

Control

  • Early sown crop during kharif and rabi/summer seasons is less infected.
  • The reason is that incidence of the disease is closely correlated with crop infestation by migrant thrips, which are the vector.
  • Insecticides such as Dimethoate, Methyldemeton and Monocrotophos at the rate of 1.5ml per litre of water gives control of thrips effectively.
  • Cultivars like Kadiri 3 and ICGS 11 which are tolerant to this disease should be used.
  • Plant density can be increased to decrease the proportion of infected plants.
  • Groundnut should be intercropped with fast growing cereal crops such as pearl millet.

Top

Pepper Spot And Leaf Scorch (Leptosphaenrulina crassiasca)

Symptoms

  • This disease is characterized by two distinct symptoms and is confined to leaves.
  • Pepper spots are dark brown to black lesions usually less than 1 mm in diameter, irregular to circular in outline and occasionally depressed.
  • Discrete lesions over the leaflet surface are visible from both sides of the leaflet.
  • However, growth of the plant is stunted.
  • Lesions tend to coalese giving the leaflet surface a netted appearance Leaf scorch symptoms frequently develop from the tips of leaflets, forming a wedge-shaped lesion with a bright yellow zone along the pariphery of the advancing margin of the lesion.
  • Ascocarp of the fungus are abundant in the dead tissue.

Control

  • The control programme for early and late leafspots also will hold good against this disease.

Top

Root-knot Nematodes : Meloidogyne arenaria, M. hapla, M.javanica

Symptoms

  • Groundnut plants infected with the groundnut root-knot nematode commonly develop enlarged roots and pegs which develop into galls of various sizes.
  • Pods also become infected and develop knobs, protuberances, or small warts.
  • Development of the root system is commonly much reduced.
  • Plants infected with root-knot nematodes may show various degrees of stunting and chlorosis.

Control

  • Deep ploughing, rotation of groundnut with other crops like cotton and flooding can significantly decrease levels of infestation of root-knot nematodes in soils.
  • Non-fumigant systemic nematicides like aldicarb and phenamiphos (Nemacur) are most effective when applied in furrows at planting, at the rates of 2-3 kg of active ingrediant per hectare.

Top

Rust (Puccinia arachidis)

Symptoms

  • Rust disease can be readily recognized when the orange coloured pustules appear on the lower leaf set surface and rupture to expose messes of reddish brown urediniospores.

  • Pustules appear first on the lower leaflet surface and in highly susceptible cultivars the orginal pustules may be surrounded by colonies of secondary pustules.
  • Pustules may later be formed on the upper leafset surface opposite those on the lower leaflet surface.
  • The pustules are usually circular and range from 0.5 to 1.4 mm in diameter.
  • They may be fromed on all aerial plant parts apart from flowers and pegs.
  • Leaves infected with rust become necrotic but tend to remain attached to the plant.

Control

  • All the control measures of early and late leafspots are also applicable to rust control.
  • Besides these, rust can also be controlled effectively by the following measures.
  • Strict plant quarantine regulations should be enforced to avoid the spread of rust on pods or seeds to disease free areas.
  • Spray application of Tridemorph 0.07 per cent at 14-21 days interval gives good control of rust. Normally 3-4 sprays are required.
  • Spray application of Triadimef on at 100g/acre on 35 and 50 days after sowing.

Top

Rhizopus seed and seedling rot : Rhizopus arrhizus and R. oryzae and R. stolonifer

Symptoms

  • Seed and pre-emerged seedlings attacked by Rhizopus spp decay rapidly.
  • The infected seed and seedlings are reduced to a dark brown or black spongy mass of rottend tissue covered with a mat of mycelium on which masses of grey-black spores are produced.

Control

  • Removal of crop debris by burning or by deep ploughing can help in preventing inoculum being carried over from season to season.
  • Harvesting at normal maturity reduces the chances of infection of pods.
  • Planting of damaged seed should be avoided.
  • Seed should not be planted too deep as etioloated seedlings are very susceptible to the pathogens.
  • Seed treatment with fungicides like thiram, captan or with a mixture of these two is effective.

Top

Stem rot/Sclerotium wilt (Sclerotium rolfsii)

Symptoms

Stem rot symptoms
on twig and seed

  • The first symptom is the sudden wilting of a branch which is completely or partially in contact with the soil.
  • The leaves turn brown and wilt but remain attached to the plant.
  • At the junction of the branch with the stem near soil a white coating of fungus mycelium is formed.
  • As the disease advances a white mycelium web spreads over the soil and the basal canopy of the plant.
  • The sclerotia, the size and colour of mustard seeds, appear on the infected areas as the disease develops and spreads.
  • The entire plant may be killed or only two or three branches may be affected.
  • Infection of pegs can take place independent of stem or together with it. Lesions on the developing pegs can retard pod development. infected pods are usually rotted.
  • A root rot caused by S. rolfsii is also prevalent in some areas.

Control

  • Cultural practices such as deep' covering or burial of organic matter befores planting, non-dirting cultivation by avoiding movement of soil up around the base of plants and preventing accumulation of organic debris are extremely useful in reducing the incidence of Sclerotium wilt. Crop rotation with wheat, corn and soyabean may minimize the incidence of stem rot.
  • Seed treatment with carbendazim / Thirum/ captan @ 2-3 g/kg sed is effective.
  • A mixture of fungicides viz., terrachlor plus terrazole @ 20 kg/ha plus 40 kg/ha at pegging is also effective in controlling stem-rot diseases.

Top

Early And Late Leaf Spots

Early leafspot: Cercospora arachidicola

Symptoms

Early leaf spot symptoms

  • Lesions are sub-circular in shape and from 1 to over 10 mm in diameter.
  • They are dark brown in colour on the upper leaflet surface where most sporulation occurs and a lighter shade of brown on the lower leaflet surface.
  • The early leaf spot usually has a light to dark brown centre and a yellow halo.
  • Distribution of fruiting structures is random on upper leaflet surface.
  • Lesions are also produced on petioles, stems and pegs.
  • These are oval to elongate in shape and have more distinct margins than the leaflet lesions.
  • On severity of the diseases, leaflets become chlorotic, then necrotic, lesions coalese and leaflets are shed.

Late leafspot : Phaeoisariopsis personata

Symptoms

Late leaf spot symptoms

  • Lesions circular to sub-circular in shape with 1 to 6 mm diameter.
  • All lesions are dark brown to black in colour.
  • On the lower leaflet surface where most sporulation occurs the lesions are black in colour and slightly rough in appearance.
  • Fruiting structures are in concentric rings on the lower leaflet surface Lesions on other parts and effects on disease severity are similar to that of early leaf spot.
  • Comparison of early and late leaf spots.
Sl.No.
Characteristics
Early leaf spot
Late leaf spot
(i)
Seasonal development
Early
Late
(ii)
Shape of spot
Circular to irregular
Usually circular
(iii)
Leaf surface where first and most spores produced
Upper
Lower
(iv)
Colour of spot on upper leaf surface
Light brown to black tending toward brown
Brown to black tending toward black
(v)
Colour of spot on lower leaf surface
Brown
Black

Control of early and late leafspots

  • Removal of volunteer groundnut plants and 'ground keepers' and removal or burial of infected crop debris is important in reducing the primary source of infection.
  • Crop rotation is of primary importance in avoiding early season infection.
  • Time of sowing and plant spacing are important considerations. Where possible, there should be a clear break in time between successive groundnut crops.
  • The early and late leafspots are effectively controlled by the spray application of Carbendazim 0.05 per cent plus Mancozeb 0.2 per cent 2-3 weeks interval, 2 or 3 times starting from 4-5 weeks after planting.

Top

Major diseases of groundnut and their control

Sl.No.
Name
Nature
Possible yield loss (%)
Chemical control
Major Fungal Diseases
(1) Early and late leaf spots Soil
and Air-borne
10-50
  • Spray application of Carbendazim (Bavistin) 0.05% plus Mancozeb 0.2% at 2-3 weeks interval, 2 or 3 times starting from 4-5 weeks after planting (CBR 1:14:8 to 24.4)
(2) Rust Air-borne Around
  • Same as above
  • Spray application of Tridemorph 0.7% at 14-21 days interval 3-4 times after initiation of the infection.
  • Triadimefen spray at 100 g/acre on 35 and 50 days after sowing (CBR for 100 f/acre - 1:3.2)
(3) Collar rot Seed
and Soil-borne
25-40
  • Seed treatment with captan 80% WP @ 3g/kg seed or Thiram 75% WP @ 3-5 g/kg seed or Carbendazim 2 g/kg seed.
(4) Stem rot / Sclerotium wilt Seed
and Soil-borne
27 and more
  • Dry seed treatment with Carbendazim/thiram/Captan or Captafol @ 2-3 g
  • Soil application of a mixture of fungicadis viz., terrachlor + terrazole @ 20 kg/ha + 40 kg/ha at pegging.
(5) Dry wilt or Dry root rot Seed
and Soil-borne
-
  • Seed treatment with Captafol 0.2%
  • Drenching with Brassicol 75% WP (0.5%) @ 1 litre/sqaure meter or soil application @ 25 kg/ha in two split, 12.5 kg/ha before sowing and the other 12.5 kg/ha 15 days later.
Major Virus Diseases
(1) Bud necrosis Thrips
trans
mitted (Franklin
iella schulzel)
Upto 50
  • Control vectors (thrips) with Dimethoate @ 400 ml/ha or Methyl demeton @ 360 ml/ha community basis.
(2) Peanut mottle (Peanut Mottle Virus-PMV) Aphid transmi
tted,
seed-borne also
(0.1
to 3.5%)
30-50 As above
(3) Peanut clump (Peanut Clump Virus-PCV) Soil-borne Upto 60
  • Soil application of Nemagon and Temik one week before planting.

Top

Uttar Pradesh