Groundnut Diseases

Root-Lesion
Symptoms
Roots are restricted in length and total volume, and tend to be discolored as the nematodes feed on the tissues of roots, pegs and pods. The pod lesions begin as tiny, tan to brown colored, pin point areas on the shell surface.

Root-Lesion
Symptoms
As the nematodes feed and reproduce, the affected area on pods becomes larger and darker. Older lesions are characterized by a blotchy appearance and indistinct margins (Fig.). Severely attacked plants are stunted and chlorotic with reduced root systems.

Root-Knot
Symptoms
Nematode damage is frequently not suspected until roots and pods are examined.Galls (like swellings) form on roots, pegs, andpods of infected plants. These galls reach a diameter. Root development is commonly reduced.

Symptoms
Pods also become infected and develop knots, or small warts (Figs.). Pegs and pods occasionally begin to deteriorate at maturity. Severely infected plants are stunted and have chlorotic leaves.
Management:

Root-Knot nematode populations are reduced in the absence of a host plant.
Hence, crop rotation with poor or immune host crops like sorghum or pearl millet will reduce its population and thus its effect on groundnut plants.
Similarly, good weed control should be practiced as many weed species act as hosts for root-knot nematodes.
Soil treatment with nematicides before planting will limit the damage caused by these nematodes.
A few nematicides can also be applied after planting.
These chemicals are relatively expensive and require costly equipment for the application.

Groundnut Rosette

General :

The most destructive virus disease on groundnut in sub-Saharan Africa(SSA).
Three casual agents are invoved in GRD such as Groundnut rosette assistor virus (GRAV), Groundnut roselte virus (GRV) and a satellite RNA (satRNA)
Trasmitted by an Aphid, aphis craccivora

Symptoms:

Two symtom variants ,chlorotic rosette and green rosette
Both forms of the diseases cause plants to be severely stunted, with shortened internodes and reduced leaf size , resulting in a bushy appeaerance of plants.
In chlorotic rosette , leaves are usually bright yellow with a few green islands and leaf lamina is curled.
In the green rosette , leaves appear dark green,with light green to dark green mosaic

Management:

Destroy virus sources: Remove infected plants after harvest , volunteer plants or that can harbor vector aphids.
Cultural practices:

Sow early in the rainy season to take advantage of low-aphid population.
Remove and destroy early infected plants and fill the gap.
Maintain optimum plant population in the field, which covers ground thereby discourages landing of vector aphids on the crop.

3. Chemical treatment: Seed treatment with imidaclorprid and followed by regular systemic insecticide spray in the early stages of the crop growth ( from

emergence to 40th day ) will control vector aphids.

4. Cultivate resistant variables : Some resistant cultivators available for cultivation in SSA are ICG 12991 , ICGV-SM 99568 , ICGV 93437 , ICGV-IS 96894 ,

ICGV-SM 99541

General:

Peanut Clump Virus (PCV)

The disease affects groundnut especially in western africa and occurs in groundnut crops in several parts of the Indian subcontinent
The disease is soilborne and is caused by peamt clump virus (PCV) that is trasmitted by a fungus, Polymyxa sp. living in the oil.

Symptoms:
1. As it is soil borne, disease affected patches are seen at the same place as in the previous year if groundnut is sown again in the same field.

2. Early infected plants are conspicuous in the field because they are severely stunted and dark green.

3. Young leaves show mosaic, mottling, and chlorotic ring symptoms.

4. Older leaflets are darker green with faint mottling.

Management:

Rotation of groundnut with cerals should be avoided
Grassy weeds and their roots should be removed regularly from infested field and burned.
Practice soil solariazation for atleast 70 days during summer months.

Peanut stripe virus (PStV)

General:

PStV is seed transmitted as well as trasmitted by aphids (Aphis craccivora, A. gossypii and Myzus persicae)

Symptoms

Symptoms vary, depending on the virus types (isolates) and groundnut cultivar.
Stripes appear in stripe isolate and groundnut cultivar.
Stripe isolates cause severe yield reductions. Mild mottles and blotches appear in the other isolates.

Managenent:

Production and distribution of virus-free seed should be given a high priority.
Selection of large seeds for sowing could reduce the source of prmary inoculum and this decreses the incidence of disease.
Control vectors ( Aphids ) with Dimethoate @1ml/lt of water.

Peanut Mottle Virus (PMV)

General:

Aphid transmitted and seed borne virus

Symptoms
Appear on young leaves as irregular dark green islands (Fig.). Mosaic symptoms are not clear on older leaves. Mild mottle symptoms are visible by keeping the leaves before light. Infected plants produce only a few small pods.

Management
Avoid sowing virus-infected seed as this disease is seed-borne. Remove any infected groundnut plants in the field from the previous crop as the virus is spread through aphids. The yield reduction due to this virus is not very significant. Hence the control methods are not identified for this virus.

General :

Caused by Ralstonia solanacearum
Soil-borne disease
Wilt symptoms can be observed 3 weeks after sowing

Fig.1

Symptoms
Infection of young plants can result in sudden wilting and death, but the leaves remain green. Infection of mature plants results in loss of turgidity, and leaves become light green, chlorotic, and curl at the tips. Eventually leaflets become brown but remain attached to the plant (Fig.1). In some instances only a single branch may wilt and die

Symptoms: To identify the bacterial infection, dip the root in water. Notice masses of bacteria ooze from the cut ends of infected roots and steams as shown in the Figure.2.

Management:
Crop rotation with cereal crops may reduce the incidence of a bacterial wilt.Use the seed produced in unaffected areas. The groundnut variety, Schwarz 21, has a high level of bacterial wilt resistance.Prevent the disease being introduced into new areas by following plant quarantine regulations.

Fig.2

Black Rot

Symptoms
Diseased plants appear in the field in localized patches (Fig.). Early symptoms are chlorosis and wilting of foliage on the main stem. Plants may not wilt but appear chlorotic and stunted. The disease may spread further in subsequent years.

Black Rot

Symptoms Reddish orange fungal bodies are formed in dense clusters on infected branches near the soil surface. Underground plant parts can be affected. In severe cases the disease may destroy pods and kernels.

Charcoal Rot

Symptoms
Older plants are infected near the soil surface. The infection spreads upward within the stems and branches, and downward into the root system killing the plant. Sometimes, the disease is restricted to the roots. When pods are invaded their interior surfaces turn gray (Fig.).

Pod Rot

Symptoms
Pod rots are characterized by brownish black lesions on the shell. The lesions enlarge and the entire pod surface becomes discolored. In advanced stages the kernels decay. This fungus can also affect lower leaves in contact with soil causing a leaf blight.

Pre-emergence Seed and Seedling

Symptoms
Infected seed and seedlings are reduced to a dark brown or black spongy mass of rotted tissue It is seed borne fungi. So, decay is most rapid when infected seeds are sown.

Pre-emergence Seed and Seedling Rots
Management Sow good quality and disease-free seed. Avoid damage to the seed testa. Deep placement of seed at sowing. Treat the seed with Thiram at 3 g/kg seeds or with carbendazim at 2 g/kg seeds. Follow crop rotation, i.e., cereal-cereal-groundnut.

Yellow Mold

Symptoms
Seeds and non-emerged seedlings become shriveled and brownish. The cotyledons are covered with yellow or greenish yellow spores (Fig.).Decay is most rapid when infected seeds are sown.After seedling emergence there might not be any new infection.

Management

Sow good quality and disease-free seed.
Avoid damage to the seed testa.
Deep placement of seed at sowing.
Treat the seed with Thiram at 3 g/kg seeds or with carbendazim at 2 g/kg seeds.
Follow crop rotation, i.e., cereal-cereal-groundnut.

Diplodia Collar Rot

Symptoms
Seedlings or maturing plants are infected at or near the soil surface and the fungus quickly invades the stem. The first field symptom is wilting of lateral branches or the entire plant. Infected plants usually die within a few days. The base of the infected plants and the tap root become slate gray to black.

Rhizoctonia Damping-Off

Symptoms
Seedlings show sunken, elongate, dark brown areas just below the soil surface (Fig.).The lesions enlarge, become black, and girdle the hypocotyls (Fig.). Similar lesions develop on tap roots, and extend to the entire root system leading to dry root rot. Subsequently the plants are killed.

Foliar Diseases
Please note that most of these foliar diseases are not economically important as these diseases may not cause much damage to the crop. Hence, no management practice is normally required for these foliar diseases. The foliar diseases that are economically important are dealt in Module 2 of this course.

Web Blotch

Symptoms
Scattered tan colored specks or streaks appear on the upper surfaces of the lower leaves.The discolored areas expand, forming large, nearly circular, purplish brown to dark brown blotches with inconspicuous margins (Fig.). Blotches often coalesce and cover the entire leaflet.

Scab

Symptoms
Numerous round to irregular lesions appear on both surfaces of leaflets.The lesions on upper leaflet surfaces are light tan with sunken centers and raised margins. Lesions are frequently covered with continuous velvet-like layers of grayish olive green fruiting bodies.

Symptoms The lesions on petioles and branches may develop into cankerous scabs, giving the plants a burnt appearance (Fig.).Lesions cover nearly all of the plant, including pegs.In advanced stages of disease development plants are stunted.

Alternaria Leaf Spot

Symptoms
Small, chlorotic, water soaked lesions appear on both surfaces of the leaflets. These lesions enlarge, become irregular in shape, and are brown with darker brown margins; the central portions later become pale, dry rapidly, and disintegrate.

Alternaria Leaf Spot

Symptoms
Veins and vein-lets adjacent to the lesions die. Affected leaflets are chlorotic (Fig.). In severe attacks they age prematurely age and dry. Adjacent lesions join together, giving the leaf a ragged and blighted appearance.

Phyllosticta Leaf Spot

Symptoms
Infection starts in damaged and dead tissue and subsequently spreads into the living green areas of the leaflets. Lesions are circular to irregular and are light tan in color surrounded by a reddish-brown border (Fig.).

Powdery Mildew

Symptoms
Large whitish spots cover the upper surfaces of leaflets. These spots are covered with fungal growth that gives them a powdery white appearance. The centers of the spots later become brown and necrotic.

Cercospora Leaf Spot

Symptoms
Small necrotic lesions appear on leaflets. These lesions enlarge and become irregular or angular shaped light brown spots (Fig.). When long periods of leaf wetness occur, the spots join together leading to drying of leaves and defoliation.

Myrothecium Leaf Blight

Symptoms
Round to irregular lesions with gray brown colored centers and brown margins surrounded by chlorotic halos occur on both surfaces of leaflets. When lesions join together, give dried appearance on leaves (Fig.).

Zonate Leaf Spot

Symptoms
Small lesions have a light brown center surrounded by a brown ring of dried tissue. Large lesions show a Zonate pattern on both surfaces of leaflets.

Sclerotium Leaf Spot

Symptoms
Appear on mature plants as gray necrotic ring spots which may develop shot holes.During long periods of leaf wetness the spots coalesce leading to a severe blight.

Pepper Spot

Symptoms
Numerous minute, dark brown to black, and irregular to circular spots appear on lower leaves. Such spots appear on both sides of the leaflet; but are more often found on upper surfaces.

Pepper Spot

Symptoms
Leaf scorch, the most common symptom, frequently develops on the tips, and occasionally on the margins, of leaflets. The wedge shaped lesions have a bright yellow zone along the periphery of their advancing margins. The drying tissue becomes dark brown and tends to break along the leaflet margins (Fig.).

Anthracnose

Symptoms
Wedge shaped lesions resembling pepper spot disease appear on the leaflet tips. Lesions may also develop on the leaflet margins leading to marginal blight. The periphery of the advancing margins of the lesion is surrounded by a bright yellow zone (Fig.).

Alternaria Leaf Blight

Symptoms
Light to dark brown irregular spots appear towards the tips or margins of the leaves. These rapidly enlarge and join together to form wedge shaped lesions (Fig.).

Alternaria Leaf Blight

Symptoms
In the later stages of disease development, blighted areas become dark brown and tend to break. The scorch symptoms resemble those caused by Pepper Spot and Anthracnose. It is often difficult to distinguish between these diseases in the field.

Pestalotiopsis Leaf Blight

Symptoms
Dark brown circular spots surrounded by faint yellow haloes appear on infected leaves. These spots enlarge and join together to dry up the leaflets, especially on the margins (Fig.).