MANAGEMENT PRACTICES OF SUNFLOWER

Sunflower

Helianthus annuus

Description

Sunflower, Helianthus annuus, is an herbaceous annual plant in the family Asteraceae, grown for its seeds. The plant has a thick, hairy, erect stem which gives rise to a large flower head. The plant has large, broad lower leaves which are oval and arranged alternately on the stem and smaller, narrower upper leaves which are attached individually to the stem. The flower head is a large disc reaching 10–30 cm (4–12 in) in diameter which is made up of 16–30 individual florets which are yellow-gold in color. The outer florets are sterile and produce the outer petals of the flower head, while the inner florets will mature into the seeds in the central disc. Sunflowers are annual plants, harvested after one growing season and can reach 1–3.5 m (3.3–11.5 ft) in height. Sunflower may also be referred to as girasole and originates from North America.

Sunflower seeds

A field of sunflowers

Field of sunflowers

Developing flower head

Sunflower head close-up

Back of flower

Sunflower foliage

Sunflower close-up

Sunflowers

Uses

Sunflower seeds can be eaten either fresh or cooked or used to extract oil which is widely used in cooking. The seeds are commonly harvested for bird seeds. Sunflowers are often grown as ornamental plants due to their large, attractive flower head.

Propagation

Requirements
Sunflowers are generally very easy to grow and thrive in areas with long hot summers which promote flowering. They grow best at temperatures between 21 and 25.5°C (70–78°F). Sunflowers can be very large and require plenty of space although there are some varieties which have been specially bred to be compact for growing in smaller spaces or for growing in containers. Sunflowers will grow in a variety of soils as long as they are not waterlogged and can be grown successfully at a pH ranging from 6.0 to 7.5. A pH above 6.0 is not recommended. They should be grown in an area that receives full sunlight and it is preferable to provide them with some shelter from wind which can damage the stems e.g. along a fence or wall. Sunflowers originate from the dry prairie regions of North America and are drought resistant once established. Their easy to grow nature makes them ideal plants for growing with children. 

Planting
Sunflowers are most easily grown by direct seeding outdoors. In areas with a long growing season, they should be planted in late Spring after all danger of frost and when the soil has warmed through. However, in areas with short growing seasons, the seeds can be planted a week or two before the last frost date as the plants are tolerant to cold Prepare the soil for planting by digging to loosen the soil and break up any large clumps. Plant seeds 2.5–5.0 cm (1–2 in) deep and space them 10–15 cm (3–4 in) apart. If planting in rows, allow 0.75 m (~30 in) between each one. An application of a balanced fertilizer at planting promotes the development of a strong root system. The seeds should sprout in 7–10 days. When the seedlings are about 15 cm (6 in) tall with two pairs of true leaves, thin the plants to a final within row spacing of 60 cm (2 ft). Sow more seeds every 2–3 weeks for a continuous bloom over the summer. 

General care
Although sunflowers are drought resistant, frequent, deep watering promotes the development of a strong root system. The plants do not require fertilizing, indeed, addition of nitrogen promotes vegetative growth and will delay flowering. The stems of the plants can easily reach in excess of 1.8 m (6 ft) in height and will benefit from some support. Bamboo stakes work well.

Harvesting
Sunflowers are ready to harvest when the back of the flowers begin to turn yellow and the flower head droops. Cut the stem about 5 cm (2 in) below the head and hang up to dry in a warm, well ventilated place for several weeks. When the heads are thoroughly dried, remove the seeds with a brush or by hand. Allow the seeds to dry out for a further few days before storing.

Diseases

Alternaria leaf blight FUNGUSAlternaria helianthi

Alternaria lesions on sunflower leaves

SYMPTOMS

Dark brown lesions on leaves surrounded by a yellow halo; lesions coalesce and become irregularly shaped and cause leaves to become blighted; plant becomes defoliated and dies

COMMENTS

Disease emergence favors hot weather and frequent rainfall; fungus may survive in crop debris or on suitable weed hosts; disease can be transmitted through infested seed

MANAGEMENT

Prune out infected leaves; use adequate plant spacing to reduce humidity around plants and promote good air circulation; disease can be controlled by application of appropriate foliar fungicide

Downy mildew FUNGUSPlasmopara halstedi

Symptoms of downy mildew on sunflower foliage

Downy mildew on sunflower leaf

SYMPTOMS

Death of seedlings leading to reduced stand in field; if seedlings survive they may be chlorotic with thickened leaves; white cottony growth is present on leaf undersides; systemic infection causes stunted plant growth and reduced seed production

COMMENTS

Disease emergence favors high humidity; fungus can survive in soil for up to 10 years

MANAGEMENT

Plant sunflower varieties that are resistant to downy mildew; treat seeds with an appropriate fungicide prior to planting; foliar fungicides are ineffective at controlling systemic infections and are not recommended

Phoma blight FUNGUSPhoma macdonaldii

Symptoms of Phoma blight of sunflower

Symptoms of Phoma blight of sunflower

SYMPTOMS

Symptoms of the disease develop after flowering; large black lesions appear on stem and coalesce to form large blackened areas; dark colored irregularly shaped lesions appear on leaves and flowers; early infections can cause flowers to die; infected plants die prematurely and produce little seed; disease often affects plants in a circular pattern in the field

COMMENTS

Fungus survives in seeds or sunflower debris in the field; disease emergence favors periods of wet weather during flowering

MANAGEMENT

Rotate crop to a non-host (e.g. small grains) a period of 4 years; plant hybrids which are more tolerant of the disease; control stem weevil populations in sunflower fields

Powdery mildew FUNGUSErysiphe cichoracearum

SYMPTOMS

Powdery white patches which appear initially on lower leaves but which may spread to all above-ground parts of plants; white patches turn gray in color and black fungal fruiting bodies are visible; severely infected leaves may turn yellow and dry up

COMMENTS

Conditions which favor the development of the disease mach those that are favorable for the host plant; disease emergence is favored by periods of high humidity where leaves remain dry

MANAGEMENT

Allow adequate spacing between plants to promote good air circulation around foliage; plant sunflowers in an area that receives full sun for most of the day; remove and destroy all sunflower crop debris after harvest; applications of appropriate foliar fungicides can help control the disease but care should be taken as some labels do not allow seeds from treated plants to be used as food or feed

Septoria leaf spot FUNGUSSeptoria helianthi

SYMPTOMS

Water-soaked circular or angular spots on leaves with a greasy, greenish appearance on lower leaves; lesions are usually gray with a darker margin; some lesions may have a narrow yellow border; tiny black fungal fruiting bodies may be present in the lesions

COMMENTS

Little is known about the survival and spread of the pathogen which causes the disease; spores are believed to be spread by splashing water; disease will develop rapidly during periods of moderate to warm weather with high rainfall

MANAGEMENT

Plant high quality seed which is free of diseases; rotate crop away from sunflower for a period of 3 years, especially if overhead irrigation is used; fungicides are rarely required for the treatment of Septoria leaf spot

Verticillium wilt FUNGUSVerticillium dahliae

Verticillium wilt symptoms on sunflower

Sunflowers infected with Verticillium wilt

Sunflowers infected with Verticillium wilt

SYMPTOMS

Lower leaves developing mottled appearance; leaf tissue between veins turns yellow and then brown; infected leaves wilt, dry out and eventually die; stems of plants may become blackened close to the soil line; a cross section of the stem reveals blackened vascular system

COMMENTS

Fungus is soil-borne and enters plants through the roots, invading the vascular system; pathogen can be spread to uninfested fields through contaminated irrigation water or movement of infested soils

MANAGEMENT

Plant high quality, disease-free seed; avoid planting sunflowers in fields known to have been infested with Verticillium previously; plant resistant sunflower hybrids in areas where disease is known to be problematic

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MANAGEMENT PRACTICES OF GROUNDNUT

Peanut (groundnut)

Arachis hypogaea

Description

Peanut, Arachis hypogaea, is an herbaceous annual plant in the family Fabaceae grown for its oil and edible nuts. Peanut plants are small, usually erect, thin stemmed plants with feather-like leaves. The leaves are arranged in alternate pairs and have leaf-like attachments near the stalk. The peanut plant produces yellow, orange, cream or white flowers which produce 'pegs', characteristic floral structures which sink into the ground to grow the pod. The pods can reach up to 10 cm (4 in) in length and can contain between 1 and 5 seeds. The peanut plant can reach 0.6 m (2 ft) in height depending on the variety and as an annual plant, survives only one growing season. Peanut may also be referred to as groundnut, monkeynut or earth nut and originates from South America.

Peanut kernels

Peanut foliage

Peanut foliage

Peanut seedlings

Peanut field

Harvesting peanut

Peanut with flower

Peanut flower and bee

Harvesting peanut

Uses

Most commercially grown peanuts are used for the extraction of their oil which is used in cooking. The by product of oil extraction is a pressed cake which is used as an animal feed and also in the production of peanut flour. Raw kernels are also commonly roasted and eaten as a snack food.

Peanut Processing

Roasted, salted peanuts

Propagation

Basic requirements
Peanuts grow very well in tropical and subtropical climates, requiring warm temperatures and a long growing season. Plants grow optimally at a temperatures between 30 and 34°C (86–93°F) although they will tolerate a range between 15 and 45°C (59–113°F). Temperatures above 34°C may damage flowers. The peanut plant grows best in a light, well draining sandy loam, but may also grow in heavier soils. The optimal pH range for peanut growth is with a pH of 6.0-6.5. Peanuts are resistant to drought and can withstand long periods without water albeit with a reduction in yield. For optimal production, a well distributed rainfall of between 500 and 600 mm of water over the course of the growing season is ideal.

Propagation
Peanut is usually propagated from seed. Seeds should be planted in a well prepared seedbed in soil that is loose and crumbly with no large clumps. The seedbed should be free from weeds which will compete with the peanut seedlings. Weeds may be removed by hand cultivating or through the use of an appropriate herbicide. Peanut seeds should be planted by hand to a depth of 3–5 cm (1–2 in). It is best to ridge the soil or use flat beds as this will make harvesting the peanuts easier. Peanuts can be grown a sole crop or intercropped with other crops such as corn (maize), cassava or soybean. 

General care and maintenance
To achieve maximum yields, peanut fields should be kept as free as possible from competing weeds. Plants should be supplied with additional irrigation if dry conditions coincide with flowering and pod fill. Peanuts do not generally require the addition of supplemental nitrogen as their roots form symbioses bacteria which are capable of fixing atmospheric nitrogen in the soil. Peanuts require calcium in the soil for good pod fill. the calcium in the soil is absorbed directly by the pods in the pegging zone. Calcium deficient soils may result in empty or poorly filled pods. 

Harvesting
Peanuts are ready for harvest between 85 and 130 days after sowing, depending on the variety. Pods can be harvested by hand or by mechanical means. Plants should be pulled from the ground and the pods removed. After harvest, pods are dried in the sun for 2–10 days until their moisture content is about 10%.

Diseases

Armyworms INSECTSpodoptera spp.

Death of armyworm (Spodoptera frugiperda) larva due to ex...

Armyworm (Spodoptera frugiperda) adult

Beet armyworm (Spodoptera exigua) adult

Beet armyworm (Spodoptera exigua) larva

Yellowstriped armyworm (Spodoptera ornithogalli) larva fe...

Armyworm (Spodoptera frugiperda) larva feeding on leaves

Southern armyworm (Spodoptera eridania) larva

Armyworm (Spodoptera frugiperda) eggs

SYMPTOMS

Singular, or closely grouped circular to irregularly shaped holes in foliage; heavy feeding by young larvae leads to skeletonized leaves; shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside.

COMMENTS

Insect can go through 3–5 generations a year.

MANAGEMENT

Organic methods of controlling armyworms include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae.

Botrytis blight FUNGUSBotrytis cinerea

SYMPTOMS

Numerous spots on upper surface of leaflets; entire plant or discrete parts may wilt and die; pods and stems become covered in fungal sclerotia.

COMMENTS

Disease emergence favors high moisture and high temperature; plants damaged by frost or other pathogens are particularly vulnerable to attack.

MANAGEMENT

Avoiding frost damage by planting early peanut varieties can help protect the plant from fungal colonization; application of appropriate foliar fungicides (e.g. benomyl), where available, can help to control the disease.

Charcoal rot FUGNUSMacrophomina phaseolina

SYMPTOMS

Water soaked lesions on stems of seedlings close to soil line; lesions girdle stem and kill seedlings; lesions in similar area may be present in older plants; lesions are initially water-soaked but turn brown; if lesions girdle the stem, plant wilts and branches die; infections beginning in the roots cause leaves to turn yellow and wilt and causes stems to be blighted.

COMMENTS

Fungus survives in crop debris in the soil; disease emergence is favored by high soil temperatures which cause plants to be water stressed and more susceptible to disease; fungus can survive for prolonged periods in dry soils but are killed in wet soil.

MANAGEMENT

Rotating crop with rice for a period of 3-4 years can reduce the level of oioculum in the soil; providing the plants with adequate irrigation and fertilization reduces susceptibility to the disease; there are currently no resistant varieties of peanut; frequent irrigation to wet soil reduces the incidence of the disease.

Cylindrocladium black rot FUNGUSCylindrocladium crotalariae

Blackened and shriveled roots due to black rot infection

Rotting caused by Cylindrocladium black rot on peanut

Clusters of fungal fruiting bodies on peanut stem

Plants yellowing and wilting

SYMPTOMS

Leaves on main stem turning chlorotic and wilting; entire plant wilts very rapidly when there is a period of water stress following high moisture; clusters of red-brown fungal bodies occur on on stems, pegs and pods; roots destroyed; roots blackened and shriveled.

COMMENTS

Crops planted early are more susceptible to the disease as they are often exposed to cooler temperatures and higher soil moisture; disease is seed transmitted and also can spread over long distances by wind.

MANAGEMENT

The most effective method to control the disease is to plant peanut varieties that have some resistance to the disease; rotation of crop with nonhost such as corn , cotton or tobacco may help to reduce inoculum in the soil; application of appropriate soil fumigants in heavily infested fields can help to control the disease.

Early leaf spot FUNGUSCercospora arachidicola

Symptoms of early leaf spot on peanut leaves

Close-up image of an early leaf spot lesion on peanut

SYMPTOMS

Small chlorotic flecks on leaf petioles, stems and pegs which enlarge and turn dark in color; lesions on upper surface of leaves usually possess a yellow halo and are reddish brown on the underside of leaves.

COMMENTS

Disease emergence is favored by high humidity and warm temperatures; spread of the disease is promoted by pronlonged leaf wetness.

MANAGEMENT

If disease is present, a rotation away from peanut for a period of 2-3 years is advised but is insufficient to control the disease completely; peanut crop debris should be plowed into soil after harvest and any volunteers removed from the nonhost crop; fungicides should be applied with caution as they can exacerbate other foliar diseases where they are present.

Late leaf spot FUNGUSCercospora personatum

Cercospora infected peanut leaves

Severe defoliation in peanut field infected with Cercospora

Defoliation due to Cercospora infection

Cercospora lesions on peanut

Peanut plant infected with Cercospora fungus

Peanut plant infected with Cercospora fungus

Peanut plant infected with Cercospora fungus

SYMPTOMS

Small chlorotic flecks on leaf petioles, stems and pegs which enlarge and turn dark in color; symptoms may be very similar or identical to early leaf spot and can only be differentiated by examination of conidia under a microscope.

COMMENTS

Disease emergence is favored by high humidity and warm temperatures; spread of the disease is promoted by pronlonged leaf wetness.

MANAGEMENT

If disease is present, a rotation away from peanut for a period of 2-3 years is advised but is insufficient to control the disease completely; peanut crop depris should be plowed into soil after harvest and any volunteers removed from the nonhost crop; fungicides should be applied with caution as they can exacerbate other foliar diseases where they are present.

Phyllostica leaf spot FUNGUSPhyllostica arachidis-hypogaea

Circular lesions with red-brown margins and light brown o...

Symptoms of Phyllostica leaf spot on peanut leaves

SYMPTOMS

Circular lesions with red-brown margins and light brown or tan centers on leaves; centers of lesions may dry out and drop from leaf resulting in a "shot-hole" appearance.

COMMENTS

Phyllostica leaf spot is known to occur in the U.S., India, China, Argentina, Thailand, the Philippenes, Pakistan, Zimbabwe, Niger and Burkino Faso.

MANAGEMENT

Disease is held in check by fungicides applied to control early or late leaf spot.

Root knot nematode NEMATODEMeloidogyne spp

Galls on peanut roots

Galls on root due to Root-knot nematode, Meloidogyne aren...

Root-knot nematode, Meloidogyne arenaria, on peanut showi...

SYMPTOMS

Galls on roots which can be up to 3.3 cm (1 in) in diameter but are usually smaller; reduction in plant vigor; yellowing plants which wilt in hot weather.

COMMENTS

Galls can appear as quickly as a month prior to planting; nematodes prefer sandy soils and damage in areas of field or garden with this type of soil is most likely.

MANAGEMENT

Plant resistant varieties if nematodes are known to be present in the soil ;check roots of plants mid-season or sooner if symptoms indicate nematodes; solarizing soil can reduce nematode populations in the soil and levels of inoculum of many other pathogens.

Rust FUNGUSPuccinia arachidis

Symptoms of rust on peanut leaves

Symptoms of rust on peanut leaves

Rust symptoms on peanut

Rust symptoms on peanut

Symptoms of rust on peanut leaves

Rust symptoms on peanut

Symptoms of rust on peanut leaves

Rust symptoms on peanut

Symptoms of rust on peanut leaves

Rust symptoms on peanut

SYMPTOMS

Characteristic orange pustules on undersides of leaves which become covered in masses of red-brown spores; pustules may form on pods.

COMMENTS

Peanut rust is highly specific to peanut; disease emergence and spread is favored by warm temperatures followed by leaf wetness.

MANAGEMENT

Allow field to fallow for at least one month between successive peanut plantings; remove any volunteer peanut plants during fallowing to reduce inoculum; sprays of appropriate fungicides such as Bordeaux mixture can effectively control the disease; such fungicides are often also effective at controlling leaf spot.

Sclerotinia blight FUNGUSSclerotinia minor

Severe Sclerotinia blight on peanut

Early infection of Sclerotinia minor on peanut

Sclerotia of Sclerotinia minor inside peanut pod

Hard black sclerotia on infected peanut stems

Stem shredding by Sclerotinia minor on peanut

Sclerotia, stem bleaching and shredding by Sclerotinia mi...

SYMPTOMS

Tips of infected branches wilt or flag rapidly; early signs of infection include the presence of small water-soaked lesions at the base of the stems which turn yellow or bleached; leaves on infected branches turn chlorotic and then wither; fluffy white fungal growth may appear on infected tissues during periods of high humidity.

COMMENTS

Fungus can survive for prolonged periods in the soil, even in the absence of peanut; emergence of the disease in the peanut crop is favored by periods of cool weather, moist soil and high humidity.

MANAGEMENT

Plant seeds which are coated with protectants; avoid injuring plants with tools and/or machinery; application of appropriate fungicides can reduce crop losses when disease is present; avoid excessive irrigation during cool weather.

Southern stem rot FUNGUSSclerotium rolfsii

Dense white mycelial growth and brown sclerotia of Sclero...

Below-ground symptoms of southern stem rot.

White fungal mat developing on the stem close to the soil...

SYMPTOMS

Lateral branches or main stem yellowing and wilting; white fungal mat developing on the stem close to the soil line; white to brown spore containing structures developing from the fungal mats.

COMMENTS

Pathogen has a large host range and attacks many crops including sugar beets; disease favors dry soils which crack deeply, allowing the penetration of oxygen.

MANAGEMENT

Plow crop debris deeply into soil after harvest of crop; crop rotation of 3-4 years are very effective at reducing soil inoculum in the case of severe infestations; applications of appropriate fungicides can help suppress stem rot but care should be taken with selection as some pesticides (e.g. benomyl) are known to increase the severity of the the disease.

Stunt VIRUSPeanut stunt virus (PSV)

Peanut stunt virus infected leaf

Symptoms on leaves

Peanut stunt virus infected plants

Symptoms of peanut stunt virus on peanut leaves

SYMPTOMS

Leaves curled and pale yellow to green; leaf petioles shortened; plants growth severely stunted; plants may produce very few pods if they have been infected early in the growing season.

COMMENTS

PSV is transmitted by aphids; legumes such as white clover are the primary source of inoculum.

MANAGEMENT

Avoid planting peanut in close proximity to legumes such as clover; remove any infected plants from plantation to reduce inoculum.

Thrips (Tobacco thrips) INSECTFrankliniella fusca
Frankliniella occidentalis
Thrips palmi

Thrips damage to peanut

Thrips damage to young peanut plant

SYMPTOMS

If population is high leaves may be distorted; leaves are covered in coarse stippling and may appear silvery; leaves speckled with black feces; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color.

COMMENTS

Thrips transmit viruses to plants, including Tomato spotted wilt virus and Peanut bud necrosis virus.

MANAGEMENT

use adequate plant spacings to avoid overcrowding; provide plants with adequate irrigation and fertilization to encourage the fast establishment of seedlings and growth of a close canopy which is unattractive to thrips vectors.

Tomato spotted wilt virus & Peanut bud necrosis VIRUSTomato spotted wilt virus (TSWV)
Peanut bud necrosis virus (PBNV)

Groundnut bud necrosis disease symptoms:mild chlorotic mo...

Tomato spotted wilt virus symptoms

Symptoms of tomato spotted wilt virus

Twisted terminal with mottled leaflets ue to tomato spot...

Stunted plant with small, darkened pods due to tomato sp...

Tomato spotted wilt virus infected plants

SYMPTOMS

Chlorotic spots or mottled patterns on leaves; drooping leaflets during hot weather; necrosis of terminal buds; stunted growth; new leaflets are reduced in size and may be puckered with mosaic mottling.

COMMENTS

Both viruses have an extremely wide host range and are transmitted by thrips vectors.

MANAGEMENT

Use high quality seed and use adequate plant spacings to avoid overcrowding; provide plants with adequate irrigation and fertilization to encourage the fast establishment of seedlings and growth of a close canopy which is unattractive to thrips vectors; intercropping peanut with sorghum or millet can reduce disease incidence.

Two-spotted spider mite ARACHNIDTetranychus urticae

Spider mite damaged leaves

Spider mites infestation

Spider mite damaged leaves

SYMPTOMS

Leaves stippled with yellow; leaves may appear bronzed; webbing covering leaves; mites may be visible as tiny moving dots on the webs or underside of leaves, best viewed using a hand lens; usually not spotted until there are visible symptoms on the plant; leaves turn yellow and may drop from plant.

COMMENTS

Spider mites thrive in dusty conditions; water-stressed plants are more susceptible to attack.

MANAGEMENT

Spraying plants with a strong jet of water can help reduce buildup of spider mite populations; if mites become problematic apply insecticidal soap to plants; certain chemical insecticides may actually increase mite populations by killing off natural enemies and promoting mite reproduction.

Velvetbean Caterpillar INSECTAnticarsia gemmatalis

Green form of a velvetbean caterpillar feeding on peanut ...

Dark form of velvetbean caterpillar feeding on peanut lea...

Velvetbean caterpillar Adult on peanut plant

Velvetbean caterpillar Adult

Dark form of a velvetbean caterpillar, Anticarsia gemmatalis

SYMPTOMS

The larva causes damage to plant by feeding on leaves. The larva after hatching from egg starts feeding on leaves The first and second stage larva skeletonise the leaves by feeding only on soft parts. The later stage laraves consumes entire leaves. They will stripe the field just in four to seven days. The larvae may also feeds on tender stem, buds and pods.

COMMENTS

Velvetbean caterpillars feeds on legume (like soybean, kudzu, velvetbean, horse beans, cowpea), cotton and several weeds. Generally moths lay eggs in mass under leaf surface.

MANAGEMENT

Encourage natural predators and parasites in the field; early or late planting of crops helps in escaping the insect attack; grow available resistant varieties; spray biocontrol agents like nuclear polyhedrosis virus (NPV) and the bacterium Bacillus thuringiensis (Bt). If the incidence is severe spray suitable insecticide.

Verticillium wilt FUNGIVerticillium spp.

SYMPTOMS

Chlorosis of leaf margins; curling leaves; loss of leaf turgor; plants wilt and become stunted as the disease progresses; plants wilt rapidly during periods of water stress; vascular system becomes dicolored.

COMMENTS

Fungus can survive in the soil for several years; disease is spread to uninfested fields by movement of infested soil or contaminated tools and machinery; there are no peanut varieties known to have resistance to the disease.

MANAGEMENT

Irrigate plants frequently to reduce wilting of infected plants and allow them to reach maturity; eliminate weeds int he plantation which may allow inoculum to build up in the soil; remove and destroy infected crop residue after harvest to reduce inoculum in the field.

Web blotch (Phoma leaf spot) FUNGUSPhoma arachidicola

Web blotch infected leaves

SYMPTOMS

Circular, brown-black lesions on the upper surfaces of the leave; web or net-like brown lesions on leaves may form on leaves during periods of high humidity; as sisease progresses, lesions darken and develop a rough texture; lesions may cover entire leaf surface.

COMMENTS

Disease emergence is favored by cool, moist conditions and periods of prolonged leaf wetness.

MANAGEMENT

Remove and destroy infested crop debris to prevent build up of inoculum in soil; rotate crops away from peanut; foliar fungicide applications are largely ineffective if conditions are favorable for the disease.

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