Important Plant Diseases Caused by Bacteria – Notes

Bacteria:

Important diseases caused by bacteria:

Mycoplasma-like Organism (MLOs):

Japanese workers in 1967 showed that mulberry dwarf disease was incited by a mycoplasma like organism.

Table 2: Plant diseases caused by mycoplasma like organisms (MLO’s):

Rickettsia-like Organisms (RLOs):

These disease causing agent have been recognised in recent years. They have distinct cell walls and belong to the group of bacteria. They are readily seen in the electron microscope and are usually transmitted by leaf hopper. Unlike mycoplasma-like organism, they are susceptible to pencillin. Rickettsia like organisms usually occur in xylem and phloem vessels.

Transmission of Plant Viruses:

The chief methods of transmission of plant viruses are:

1. Seeds and pollen grains transmission:

Certain viruses like bean mosaic and curly top virus of beet sugar are transmitted by seed and pollen grains.

2. Transmission by vegetative propagation:

One of the chief methods of transmission of viral diseases especially of potato, raspberry, turnips, bulb plants, fruit trees and many ornamentals. The diseased vegetative parts such as tubers, bulbs, root, off shoots, buds and scions which are used for propagation will contain the virus present with parent plant. The new plants so raised by above mentioned methods are usually infected.

3. Transmission by mechanical means:

Many viral diseases especially mosaic viruses are mechanically transmitted by the following methods:

(a) By contact of infected leaves with healthy leaves brought about by wind.

(b) By rubbing the juice of the diseased plant over the surface of leaves of healthy plants.

(c) By grafting infected buds to healthy plants.

(d) Knife and other mechanical contaminated implements may spread the disease.

(e) Roots of diseased plant may come in contact of roots of healthy plants and thus spread the disease.

(f) Dodder (Cusutta) may serve as a bridge between the healthy and diseased plants resulting in viral infection.

4. Soil transmission:

Soil borne viruses are potato mosaic virus and oat mosaic etc. they are transmitted through the soil.

5. Insect transmission:

About 150 species of insects are known to transmit from one plant to other. Insects capable of virus transmission are known as insect (carries). Some of them insect vectors which play a major role in dissemination viruses are the aphids, leaf hoppers, beetles, scale insects, thrips and white files the insect vectors are sucking insects.

Table 3 : Some insect vectors of plant virus diseases.

6. Transmission by fungi:

Gorgon (1985) found that the diseased lettuce was infected by Olpidium. He later discovered that the fungus act as a vector of the big vein mosaic. The virus acquired by the fungus remains in oospore. Similarly tobacco mosaic virus has been reported by Teakle (1960) to enter roots of its host by the zoospores of Olpidium brassicae.

7. Nematodes:

Some soil borne viruses are transmitted by nematodes. Examples are tobacco rattle, pea early browning and Colocasia mosaic etc.

Management of Virus Diseases:

1. Elimination of source of viral infection:

(a) Perennial weed hosts, annual weed hosts, unrelated crops, voluntear crops and approach crops.

(b) Plant residue.

(c) Rogueing

2. Avoidance of vectors:

(a) Breaking the life cycle of hosts, vectors and viruses

(b) Creating physical barriers

(c) Early sowing

(d) Crop rotation

(e) Intercropping

3. Use of resistant varieties:

4. Insecticidal sprays or neem oil sprays.

In case of non-persistent viruses such as Potato Virus-Y, use of insecticides to control vectors can reduce the vector population and disease incidence but cannot check the entry of vectors and spread of the disease.

Table 4: Important diseases caused by viruses 

Cereals:

Rice

Blast-pyricularia oryzae

Symptoms:

The typical symptoms appear on leaves, leaf sheath, nodes and even the glumes are also attacked. On the leaves, the lesions start as small water soaked bluish green flecks, soon enlarge and form characteristic spindle shaped spots with grey centre and dark brown margin.

In infected nodes, irregular black areas encircle the nodes can be noticed.

Pathogen:

Mycelium of the fungus, is hyaline to olivaceous, septate and highly branched. Conidia are produced in clusters on long septate, olivaceous slender conidiophores.

Favourable Conditions:

Application of excessive doses of nitrogenous fertilizers, intermittent drizzles, cloudy weather, high relative humidity (93-99 per cent), low night temperature (between 15-20 °C), more number of rainy days, longer duration of dew, cloudy weather, slow wind movement and availability of collateral hosts.

Mode of Spread and Survival:

The disease spreads primarily through airborne conidia since spores of the fungus present throughout the year. Mycelium and conidia in the infected straw and seeds are important sources of inoculum.

Management:

Remove and destroy the weed hosts in the field bunds and channels. Treat the seeds with Captan of Thiram or Carbendazim or Carboxin or Tricyclazole at 2g/kg. Seed treatment with biocontrol agent Trichoderma viride @ 4g/kg.

Brown Spot or Sesame leaf spot:

Helminthosporium oryzae

Symptoms:

The fungus attacks the crop from seedling in nursery to milk stage in main field. Symptoms appear as lesions (spots) on the coleoptile, leaf blade, leaf sheath, and glume, being most prominent on the leaf blade and glumes. The disease appears first as minute brown dots, later becoming cylindrical or oval to circular.

Pathogen:

H. oryzae produces greyish-brown to dark brown septate mycelium. Conidiophores may arise singly or in small groups.

Favourable Conditions:

Temperature of 25-30 °C with relative humidity above 80 per cent are highly favourable. Excess of nitrogen aggravates the disease incidence.

Mode of Spread and Survival:

The infected seeds are the most common source of primary infection. The conidia present on infected grain and mycelium in the infected tissue may viable for 2 to 3 years. The fungus may survive in the soil for 28 months at 30 °C and 5 months at 35 °C. Airborne conidia infect the plants both in nursery and in main field.

Management:

Removal of collateral hosts and infected debris in the field. Crop rotation, adjustment of planting time and proper fertilization are suggested. Use of slow release nitrogenous fertilizers are suggested.

Sheath rot:

Sarocladium oryzae

Symptoms:

Initial symptoms are noticed only on the upper most leaf sheath enclosing young panicles. The flag leaf sheath show oblong or irregular greyish brown spot. They enlarge and develop grey centre and brown margins covering major portions of the leaf sheath.

Pathogen:

The fungus produces whitish, sparsely branched and septate mycelium. Conidiophore is slightly thicker than the vegetative hyphae. Conidia are hyaline, smooth, single celled and cylindrical in shape.

Favourable Conditions:

Closer planting, high doses of nitrogen, high humidity and temperature around 25-30 °C. Injuries made by leaf folder, brown plant hopper and mites increase infection.

Mode of Spread and Survival:

Mainly through air-borne conidia and also seed-borne.

Management:

Apply recommended doses of fertilizers. Adopt optimum spacing. Spray Carbendazim 250 g or Edifenphos 1 lit or mancozeb 1 kg or Chlorothalonil 1 kg/ha at boot leaf stage and 15 days later.

Sheath blight:

Rhizoctonia solani

Symptoms:

The fungus affects the crop from tillering to heading stage. Initial symptoms are noticed on leaf sheaths near water level. On the leaf sheath oval or elliptical or irregular greenish grey spots are formed. As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border.

Pathogen:

The fungus produces usually long cells of septate mycelium which are hyaline when young, yellowish brown when old. It produces large number of globose sclerotia, which are initially white, later turn to brown or purplish brown.

Favourable Conditions:

High relative humidity (96-97 per cent), high temperature (30-32 °C), closer planting and heavy doses of nitrogenous fertilizers.

Mode of Spread and Survival:

The pathogen can survive as sclerotia or mycelium in dry soil for about 20 months but for 5- 8 months in moist soil.

Management:

Avoid excess doses of fertilizers. Adopt optimum spacing. Eliminate weed hosts. Apply organic amendments. Avoid flow of irrigation water from infected fields to healthy fields. Deep ploughing in summer and burning of stubbles.

Stem rot:

Sclerotium oryzae

Symptoms:

Small black lesions are formed on the outer leaf sheath and they enlarge and reach the inner leaf sheath also. The affected tissues rot and abundant sclerotia are seen in the rotting tissues. The culm collapses and plants lodge.

Pathogen:

White to greyish hyphae produce smooth, spherical black and shiny sclerotia, visible to naked eyes as black masses.

Favourable Conditions:

Infestation of leaf hoppers and stem borer and high doses of nitrogenous fertilizers.

Mode of Spread and Survival:

The sclerotia survive in stubbles and straw are carried through irrigation water.

Management:

Use of recommended doses of fertilizer. Deep ploughing in summer and burning of stubbles. Avoid flow of irrigation water from infected fields to healthy fields.

Bacterial leaf blight:

Xanthomonas oryzae p. v. oryzae

Symptoms:

The disease is usually noticed at the time of heading but in severe cases occur earlier also. Seedlings in the nursery show circular, yellow spots in the margin, later enlarge, coalesce and cause drying of foliage.

In grown up plants water soaked, translucent lesions appear usually near the leaf margin. The lesions enlarge both in length and width with a wavy margin and turn straw yellow within a few days, covering the entire leaf.

Pathogen:

The bacterium is strict aerobe, gram negative, non spore forming.

Favourable Conditions:

Clipping of tip of the seedling at the time of transplanting, heavy rain, heavy dew, flooding, deep irrigation water, severe wind, temperature of 25-30 °C and application of excessive nitrogen, especially late top dressing.

Mode of Spread and Survival:

The infected seeds as a source of inoculum may not be important since the bacteria decrease rapidly and die in the course of seed soaking.

Management:

Burn the stubbles. Use optimum dose of fertilizers. Avoid clipping of tip of seedling at the time of transplanting. Avoid flooded conditions. Remove weed hosts. Grow resistant cultivars like IR 20 and TKM 6.

Maize (Zea mays)

Downy mildew/Crazy top:

Peronosclerospora sorghi

Symptoms:

The most characteristic symptom is the development of chlorotic streaks appear on the leaves and the plants exhibit a stunted and bushy appearance due to the shortening of the intemodes.

White downy growth can be seen not only on the lower surface of leaf but also on the chlorotic streaks.

Pathogen:

The fungus grows as white downy growth on both surface of the leaves, consist of sporangiophores and sporangia.

Favourable Conditions:

Low temperature (21-23 °C), high relative humidity (90 per cent), water logging condition and light drizzling. Young plants are highly susceptible.

Mode of Spread and Survival:

The primary source of infection is through the oospores present in the soil and also the dormant mycelium present in the infected maize seeds. Secondary spread is through air-borne conidia. The oospores survive in the soil as well as in the infected plant debris.

Management:

Deep ploughing. Crop rotation with pulses. Adjust the time of sowing. Rogue out infected plants. Treat the seeds with Metalaxyl compound (Apron 35SD) at 6 g/kg.

Leaf blight:

Helminthosporium maydis

Symptoms:

The fungus affects the maize plant at young stage. Small yellowish round to oval spots are seen on the leaves. The spots gradually increase in area into bigger elliptical spots and it is greyish brown colour in the centre with dark brown margins.

Pathogen:

Conidiophores are in group, geniculate, mid dark brown, pale near the apex and smooth. Conidia are distinctly curved, fusiform, pale to mid dark golden brown with 5-11 pseudosepta.

Favourable Conditions:

Optimum temperature for the germination of conidia is 18 to 27 °C. Infection takes place early in the wet season.

Mode of Spread and Survival It is a seed-borne fungus.

Management:

Treat the seeds with Captan or Thiram at 4 g/ kg. Spray Mancozeb 1.25 kg/ha.

Rust:

Puccinia sorghi

Symptoms:

Circular to oval, elongated, brown powdery pustules are scattered over both surface of the leaves. As the plant matures, the pustules become brown to black owing to the replacement of red uredospores by black teliospores.

Pathogen:

Uredospores are globose or elliptical finely echinulate, yellowish brown with 4 germ pores. Teliospores are brownish black, or dark brown, oblong to ellipsoidal, rounded to flattened at the apex.

Favourable Conditions:

Cool temperature and high relative humidity. Management

Remove the alternate hosts. Spray Mancozeb at 1.25 kg/ha.

Head smut:

Sphacelotheca reiliana

Symptoms:

Symptoms are usually noticed on the cob and tassel. Large smut sori replace the tassel and the ear. Sometimes the tassel is partially or wholly converted into smut sorus. Under such conditions the individual spikelets on tassels may form shoot like growths, or the entire tassel may develop into leaf like structures.

Pathogen:

Smut spores (chlamydospores) are produced in large numbers which are reddish brown to black, thick walled, finely spined, spherical or slightly irregular.

Favourable Conditions:

Low temperature favours more infection and this fungus also infects the sorghum crop and vice versa.

Mode of Spread and Survival:

The smut spores retains its viability for two years. The fungus is externally seed-borne and soil-borne. The major source of infection is through soil-borne chlamydospores.

Management:

Field sanitation. Crop rotation with pulses. Treat the seeds with Captan or Thiram at 4 g/kg.

Charcoal rot:

Rhizoctonia bataticola

Symptoms:

The fungus attacks roots of seedlings and young plants. The affected plants first exhibit the wilting symptoms. The stalk of the infected plants can be recognized by grayish streaks and become weak.

Pathogen:

The fungus produces large number of sclerotia which are round and black in colour. Sometimes, it produces pycnidia on the stems or stalks.

Favourable Conditions:

High temperature and low soil moisture.

Mode of Spread and Survival:

The fungus has a wide host range, attacking sorghum, cumbu, ragi and pulses. It survives for more than 16 years in the infected plant debris. The primary source of infection is through soil- borne sclerotia.

Management:

Long crop rotation with crops that are not natural host of the fungus. Irrigate the crops at the time of earhead emergence to maturity. Treat the seeds with Carbendazim or Captan at 2 g/kg.

WHEAT (Triticum aestivum):

SMUTS

Spores

BUNT:

Cotton:

Wilt

Fusarium oxysporum f.sp. vasinfectum

Symptoms:

The disease affects the crop at all stages. The earliest symptoms appear on the seedlings in the cotyledons which turn yellow and then brown. The base of petiole shows brown ring, followed by wilting and drying of the seedlings. In young and grown up plants, the first symptom is yellowing of edges of leaves and area around the veins i.e. discolouration starts from the margin and spreads towards the midrib.

Pathogen:

Macroconidia are 1 to 5 septate, hyaline, thin- walled, falcate with tapering ends.

Favourable Conditions

Soil temperature of 20-30 °C, hot and dry periods followed by rains, heavy black soils with an alkaline reaction.

Mode of Spread and Survival:

The fungus can survive in soil as saprophyte for many years and chlamydospores act as resting spores. The pathogen is both externally and internally seed-borne.

Management:

Remove and burn the infected plant debris in the soil after deep summer ploughing during June- July. Apply increased doses of potash with a balanced dose of nitrogenous and phosphatic fertilizers.

Root rot:

Rhizoctonia bataticola

Symptoms:

The fungus causes three types of symptoms viz., seedling disease, sore-shin and root rot. Germinating seedling and seedlings of one to two weeks old are attacked by the fungus at the hypocotyl and cause black lesions, girdling of stem and death of the seedling, causing large gap in the field. In sore-shin stage (4 to 6 weeks old plants), dark reddish-brown cankers are formed on the stems near the soil surface, later turning dark black and plant breaks at the collar region leading to drying of the leaves and subsequently the entire plant.

Pathogen:

The fungal hyphae are septate and fairly thick and produce black, irregular sclerotia. Favourable Conditions

Dry weather following heavy rains, high soil temperature (35-39 °C), low soil moisture (15-20 %)

Mode of Spread and Survival:

The disease is mainly soil-borne and the pathogen can survive in the soil as sclerotia for several years. The spread is through sclerotia which are disseminated by irrigation water, implements, heavy winds and other cultural operations.

Management:

Apply farm yard manure at 10 t/ha or neem cake at 2.5 t/ha. Adjust the sowing time, early sowing (First week of April) or late sowing (Last week of June) so that crop escapes the high soil temperature conditions. Adopt intercropping with sorghum.

Anthracnose:

Colletotrichum capsici

Symptoms:

The fungus infects the seedlings and produces small reddish circular spots on the cotyledons and primary leaves. The lesions develop on the collar region, stem may be girdled, causing seedling to wilt and die. In mature plants, the fungus attacks the stem, leading to stem splitting and shredding of bark. The most common symptom is boll spotting.

Pathogen:

The pathogen forms large number of acervuli on the infected parts. The conidiophores are slightly curved, short, and club shaped. Favourable Conditions

Prolonged rainfall at the time of boll formation and close planting.

Mode of Spread and Survival:

The pathogen survives as dormant mycelium in the seed or as conidia on the surface of seed for about a year. The pathogen also perpetuates on the rotten bolls and other plant debris in the soil.

Management:

Remove and burn the infected plant debris and bolls in the soil. Rogue out the reservoir weed hosts.

Boll rot

Symptoms:

Initially, the disease appears as small brown or black dots which later enlarge to cover the entire bolls. Infection spreads to inner tissues and rotting of seeds and lint occur. The bolls never burst open and fall off prematurely.

Favourable Conditions:

Heavy rainfall during the square and boll formation stage, punctures caused by the insects, especially red cotton bug Dysdercus cingulatus, close spacing and excessive nitrogen application. Mode of Spread and Survival

The fungi survive in the infected bolls in the soil. The insects mainly help in the spread of the disease. The fungi make their entry only through the insect punctures.

Management:

Adopt optimum spacing. Apply the recommended doses of fertilizers. Carbendazim 1 kg from 45 day at 15 days interval.

Leaf blight:

Alternaria macrospora

Symptoms:

The disease may occur in all stages but more severe when plants are 45-60 days old. Small, pale to brown, irregular or round spots. Each spot has a central necrotic lesion surrounded by concentric rings.

Pathogen:

The fungus produces dark brown, short, 1-8 septate, irregularly bend conidiophores with a single conidium at the apex.

Favourable Conditions:

High humidity, intermittent rains and moderate temperature of 25-28 °C.

Mode of Spread and Survival:

The pathogen survives in the dead leaves as dormant mycelium. The pathogen primarily spreads through irrigation water. The secondary spread is mainly by air-borne conidia.

Management:

Remove and destroy the infected plant residues. Spray Mancozeb or Copper oxychloride at 2 kg/ha at the initiation of the disease.

Bacterial blight:

Xanthomonas campestris p.v. malvacearum

Symptoms:

The bacterium attacks all stages from seed to harvest.

Pathogen:

The bacterium is a short rod with a single polar flagellum. It is gram negative, non-spore forming.

Favourable Conditions:

Optimum soil temperature of 28 °C, high atmospheric temperature of 30-40 °C, relative humidity of 85 per cent, early sowing, delayed thinning, poor tillage, late irrigation and potassium deficiency in soil.

Mode of Spread and Survival:

The bacterium survives on infected, dried plant debris in soil for several years. The bacterium is also seed-borne and remains in the form of slimy mass on the fuzz of seed coat. The primary infection starts mainly from the seed-borne bacterium. The secondary spread of the bacteria may be through wind, wind blown rain splash, irrigation water, insects and other implements.

Management:

Remove and destroy the infected plant debris. Rogue out the volunteer cotton plants and weed hosts. Follow crop rotation with non-host crops. Early thinning and early earthing up with potash.

Sugarcane (Saccharum officinarum):

Red rot:

Colletotrichum falcatum

Symptoms:

Typical symptoms of red rot are observed in the intemodes of a stalk by splitting it longitudinally. These include the reddening of the internal tissues which are usually elongated at right angles to the long axis of the stalk. The presence of cross­wise white patches is the important diagnostic character of the disease. The diseased cane also emits acidic-sour smell.

Pathogen:

The fungus produces thin, hyaline, septate, profusely branched hyphae containing oil droplets. The fungus produces black, minute velvety acervuli with long, bristle-like, septate setae. Monoculturing of sugarcane, successive ratoon cropping, water logged conditions and injuries caused by insects.

Mode of Spread and Survival:

The fungus is sett-borne. The fungus also persists in the soil on the diseased clumps and stubbles as chlamydospores and dormant mycelium. The primary infection is mainly from infected setts. Secondary spread in the field may be through irrigation water and cultivation tools. Management

Adopt crop rotation by including rice and green manure crops. Select the setts from the disease free fields or disease free area. Avoid ratooning of the diseased crop.

Smut:

Ustilago scitaminea

Symptoms:

The affected plants are stunted and the central shoot is converted into a long whip-like, dusty black structure. The length of the whip varies from few inches to several feet. In early stages, this structure is covered by a thin, white papery membrane. The whip may be straight or slightly curved. On maturity it ruptures and millions of tiny black smut spores (teliospores) are liberated and disseminated by the wind. Affected plants are usually thin, stiff and remain at acute angle.

Pathogen:

The fungal hyphae are primarily intercellular and collect as a dense mass between the vascular bundles of host cell and produce tiny black spores.

Favourable Conditions:

Monoculturing of sugarcane, continuous ratooning and dry weather during tillering stage.

Mode of Spread and Survival:

Teliospores may survive in the soil for long periods, upto 10 years. The spores and sporidia are also present in the infected plant materials in the soil. The smut spores and dormant mycelium also present in or on the infected setts. The primary spread of the disease is through diseased. The secondary spread in the field is mainly through the smut spores developed in the whips, aided by air currents.

Management:

Plant healthy setts taken from disease free area. Remove and destroy the smutted clump. Discourage ratooning of the diseased crops having more than 10 per cent infection. Follow crop rotation with green manure crops or dry fallowing.

Sett rot or Pineapple disease:

Ceratocystis paradoxa

The disease primarily affects the setts usually two to three weeks after planting. The fungus is soil-borne and enters through cut ends and proliferates rapidly in the parenchymatous tissues. The affected tissues first develop a reddish colour which turns to brownish black in the later stages.

Pathogen:

The fungus produces both macroconidia and microconidia. Conidiophores are linear, thinwalled with short cells at the base and a long terminal cell.

Favourable Conditions:

Heavy clay soils, temperature of 25-30 °C and prolonged rainfall after planting.

Mode of Spread and Survival:

The fungus survives as conidia and chlamydospores in the soil and in the infected, buried cane tissues. The inoculum moves from field to field through wind-borne conidia or irrigation or rain water.

Management:

Soak the setts in 0.05% Carbendazim or 0.25% Emisan for 15 minutes. Provide adequate drainage during rainy seasons.

Rust:

Puccinia erianthi

Symptoms:

Minute, elongated, yellow spots (uredia). The pustules turn to brown on maturity. Late in the season, dark brown to black telia appear on the lower surface of leaves.

Pathogen:

The mycelium is hyaline, branched and septate.

Favourable Conditions:

Temperature of 30 °C, relative humidity between 70 and 90 per cent, high wind velocity and continuous cloudiness.

Mode of Spread and Survival:

The fungus survives on collateral hosts like Erianthus fulvus and Saccharum spontaneum. The uredospores also survive in the infected stubbles in the soil. The disease is mainly spread through air-borne uredospores.

Management:

Remove the collateral hosts. Spray Tridemorph 1 kg/ha.

Gummosis:

Xanthomonas campestris p.v. vasculorum

Symptoms:

The bacterium produces two distinct types of symptoms. On the mature leaves longitudinal stripes or streaks appear around the affected veins near the tip. Initially these stripes are pale yellow in colour, later turn to brown. The infected canes are stunted with short internodes, giving a bushy appearance.

Pathogen:

The bacterium is a short rod, Gram negative, non spore forming with a single polar flagellum. It is a facultative anaerobe and it produces yellow slimy growth.

Mode of Spread and Survival:

The bacterium remains viable in the soil as well as in infected canes. The primary transmission is through naturally affected diseased setts or through soil-borne contamination. The secondary spread may be through wind splashed rain, harvesting implements, animals and insects.

Management:

Remove and burn the affected clumps and the stubbles in the field. Select setts from disease free areas. Avoid growing collateral hosts like maize, sorghum and cumbu near the sugarcane fields.

Grassy shoot:

Mycoplasma like Organism (MLO)

Symptoms:

The disease symptoms are usually seen two months after planting. The disease is characterised by the production of numerous lanky tillers from the base of the affected shoots. Leaves become pale yellow to completely chlorotic, thin and narrow. The plants appear bushy and ‘grass like’ due to reduction in the length of internodes and premature and continuous tillering.

Pathogen:

MLO is found to present in the sieve cells of infected plants.

Mode of Spread and Survival:

The pathogen is transmitted by aphids viz., Rhopalosiphum maidis, Melanaphis sacchari. In addition, leaf hopper, Proutista moesta also involves in the transmission.

Management:

Select setts from middle of the healthy fields or from the commercial seed nursery. Remove and burn the infected clumps periodically. Treat the setts before planting as follows: Hot Water Treatment (HWT) at 50 °C for 2’Л hr. Hot Air Treatment (HAT) at 54 °C for 8 hr or Aerated Steam Therapy (AST) at 50 °C for 1 hr or Moist Hot Air Treatment (MHAT) at 54 °C for 2 hr.

Oil Seeds:

GROUND NUT (Arachis hypogaea)

Rust (Puccinia arachidis)

Symptoms:

The disease attacks all aerial parts of the plant. The disease is usually found when the plants are about 6 weeks old. Uredosori appear on the lower surface of leaves. The epidermis ruptures and exposes a powdery mass of uredospores. Corresponding to the sori, small, necrotic, brown spots appear on the upper surface of leaves. The rust pustules may be seen on petioles and stem. Favourable Conditions

High relative humidity (above 85 per cent), heavy rainfall and low temperature (20-25 °C).

Mode of Spread and Survival:

The pathogen survives as uredospores on groundnut plant. The fungus also survives in infected plant debris in soil. The spread is mainly through wind-borne inoculum of uredospores.

Management:

Avoid monoculturing of groundnut. Spray Mancozeb 1 kg. or Wettable sulphur 2.5 kg. or Tridemorph 500 ml or Chlorothalonil 1 kg/ha.

Collar rot or seedling blight or crown rot:

Aspergillus niger and A. pulverulentum

Symptoms:

The fungus is both seed-borne and soil-borne. So the infection can be seen at any stage from sowing onwards.

Crown rot:

The infection when occurs in adult plants show crown rot symptoms. Large lesions develop on the stem below the soil and wilting of plant.

Favourable Conditions:

Deep sowing of seeds, high soil temperature (30-35 °C) and low soil moisture.

Mode of Spread and Survival:

The pathogens survive in plant debris in the soil, not necessarily from a groundnut crop. Soil- borne conidia cause disease carry over from season to season. The other primary source is the contaminated seeds. The fungi are carried on the seed surface or under the testa.

Management:

Select good quality seeds. Treat the seeds with Carbendazim 2 g or Thiram 4g/kg. Avoid deep sowing of seeds. Destroy the crop debris by burning. f

Root rot:

Macrophomina phaseolina

Symptoms:

In the early stages of infection reddish brown lession appears on the stem just above the soil level. The leaves and branches show drooping, leading to death of the whole plant. The decaying stems are covered by whitish mycelial growth. The rotten tissues contain large number of black or dark brown, thick walled sclerotia. When infection spreads to underground roots, the sclerotia are formed externally in the rotten tissue. Pod infection leads to blackening of the shells and sclerotia can be seen inside the shells.

Favourable Conditions:

Prolonged rainy season at seedling stage and low lying areas.

Mode of Spread and Survival:

The fungus remains dormant as sclerotia for a long period in the soil and in infected plant debris. The primary infection is through soil-borne and seed-borne sclerotia. The secondary spread of sclerotia is aided by irrigation water, human agency, implements, cattle etc.

Management:

Treat the seeds with thiram 4 g or carbondazim

GINGELLY (Sesamum indicum)

Root rot or stem rot or charcoal rot

Macrophomina phaseolina

Symptoms:

The disease symptom starts as yellowing of lower leaves, followed by drooping and defoliation. The stem portion near the ground level shows dark brown lesions and bark at the collar region shows shredding. The sudden death of plants is seen in patches. In the grow-up plants, the stems portion can be easily pulled out leaving the rotten root portion in the soil. The infection when spreads to pods, they open prematurely and immature seeds become shrivelled and black in colour.

Favourable Condition:

Day temperature of 30 °C and above and prolonged drought followed by copius irrigation.

Mode of Spread and Survival:

The fungus remains dormant as sclerotia in soil as well as in infected plant debris in soil. The infected plant debris also carry pycnidia. The fungus primarily spreads through infected seeds which carry sclerotia and pycnidia. The fungus also spreads through soil-borne sclerotia.

Management:

Apply farm yard manure or green leaf manure at 10 t/ha or neem cake 250 kg/ha.

Powdery mildew:

Erysiphe cichoracearum

Symptoms:

Initially greyish-white powdery growth appears on the upper surface of leaves. When several spots coalesce, the entire leaf surface may be covered with powdery coating. In severe cases, the infection may be seen on the flowers and young capsules, leading to premature shedding. The severely affected leaves may be twisted and malformed.

Favourable Conditions:

Dry humid weather and low relative humidity.

Mode of Spread and Survival:

The fungus is an obligate parasite and disease penetrates through cleistothecia in the infected plant debris in soil. The ascospores from the cleistothecia cause primary infection.

Management:

Remove the infected plant debris and destroy. Spray Wettable sulphur at 2.5 kg/ha or dust Sulphur at 25 kg/ha.

Leaf blight:

Alternaria sesami

Symptoms:

Initially small, circular, reddish brown spots appear on leaves which enlarge later and cover area with concentric rings. The lower surface of the spots are greyish brown in colour. Dark brown lesions can also be seen on petioles, stem and capsules.

Favourable Conditions:

Low temperature (20-25 °C), high relative humidity and cloudy weather.

Mode of Spread and Survival:

The fungus is seed-borne and also soil-borne as it remains dormant in the infected plant debris.

Management:

Treat the seeds with Thiram or Carbendazim at 2 g/kg. Spray Mancozeb at 1 kg/ha.

Wilt:

Fusarium oxysporum fsp. sesami

Symptoms:

The disease appears as yellowing, dropping and withering of leaves. The plants gradually wither, show wilting symptom leading to drying. The infected portions of fungus produces macroconida, microconidia and chlamydospores.

Mode of Spread and Survival:

The fungus survives in the soil in the infected plant debris. It is also seed-borne and primary infection occurs through infected seeds or through chlamydospores in soil. The secondary infection may be caused by conidia disseminated by rain splash and irrigation water.

Management:

Treat the seeds with Thiram or Carbendazim at 2g/kg. Apply heavy doses of green leaf manure or farm yard manure.

Bacterial leaf spot:

Pseudomonas sesami

Symptoms:

The disease appears as water-soaked yellow specks on the upper surface of the leaves. They enlarge and become angular as restricted by veins and veinlets. The colour of spot may be dark brown with shiny oozes of bacterial masses.

Mode of Spread and Survival:

The bacterium remains viable in the infected plant tissues. It is internally seed-borne and secondary spread through rain-splash and storms.

Management:

Keep the field free of infected plant debris. Spray with Streptomycin sulphate.

SUNFLOWER (Helianthus annuus)

Leaf blight

Alternaria helianthi

Symptoms:

The fungus produces brown spots on the leaves, but the spots can also be seen on the stem, sepals and petals. The lesions on the leaves are dark brown with pale margin surrounded by a yellow halo. The spots later enlarge in size with concentric rings and become irregular in shape.

The fungus produces cylindrical conidiophores, which are pale grey-yellow coloured, straight or curved, geniculate, simple or branched, septate and bear single conidium.

Favourable Conditions:

Rainy weather, cool winter climate and late sown crops are highly susceptible.

Mode of Spread and Survival:

The fungus survives in the infected host tissues and weed hosts. The fungus is also seed-borne. The spread is mainly through wind blown conidia. Management

Remove and destroy infected plant debris. Rogue out weeds at periodical intervals. Sow the crop early in the season (June sowing). Treat the seeds with Thiram or Carbendazim at 2g/kg.

Rust:

Puccinia helianthi

Symptoms:

Small, reddish brown pustules (uredia) covered with rusty dust appear on the lower surface of bottom leaves. Infection later spreads to other leaves and even to the green parts of the head. In severe infection, when numerous pustules appear on leaves, they become yellow and dry. The black coloured telia are also seen among uredia on the lower surface.

Mode of Spread and Survival:

The pathogen survives in the sunflower plants and in infected plant debris in the soil as teliospores. The disease spreads by wind-borne uredospores from infected crop.

Management:

Remove and burn the infected plant debris in the field. Remove the volunteer sunflower plants. Spray Mancozeb at 1 kg/ha.

Root rot or charcoal rot:

Rhizoctonia bataticola

Symptoms:

The fungus is seed-borne and primarily causes seedling blight and collar rot in the initial stages. The grown-up plants also show symptoms after flowering stage. The infected plants show dropping of leaves and death occurs in patches. The bark of the lower stem and roots shreds and associated with a large number of sclerotia. Dark coloured, minute pycnidia also develop on the lower portion of the stem.

Mode of Spread and Survival:

The pathogen survives in soil and in infected crop residues as sclerotia and pycnidia. The pathogen is seed-borne and it serves as primary source of infection. Wind-borne conidia cause secondary spread. The soil borne sclerotia also spreads through rain splash, irrigation water and implements.

Management:

Treat the seeds with Carbendazim at 2 g or Thiram at 4g/kg or treat the seeds with Trichoderma viride at 4g/kg.

Head rot:

Rhizopus sp.

Symptoms:

The affected heads show water soaked lesions on the lower surface, which later turns brown. The discolouration may extends to stalk from head. The affected portions of the head become soft and pulpy and insects are also seen associated with the purified tissues. The larvae and insects which attack the head pave way for the entry of the fungus which attacks the inner part of the head and the developing seeds. The seeds are converted into a black powdery mass. The head finally withers and droops down with heavy fungal mycelial nets.

Favourable Conditions:

Prolonged rainy weather at flowering and damages caused by insects and caterpillars. Mode of Spread and Survival

The fungus survives as a saprophyte in host debris and other crop residues. The disease is spread by wind blown spores.

Management:

Treat the seeds with Thiram or Carbendazim at 2g/kg. Control the caterpillars feeding on the heads. Spray the head with Mancozeb at 1 kg/ha during intermittent rainy season and repeat after 10 days, if the humid weather persists.

CASTOR (Ricinus communis)

Seedling blight:

Phytophthora parasitica

Symptoms:

The disease appears as circular, dull green patch on both the surface of the cotyledonary leaves. It later spreads gradually and cause rotting. The infection moves to stem and cause withering and death of seedling. In mature plants, the infection initially appears on the young leaves and spreads to petiole and stem causing black discolouration and severe defoliation.

Favourable Conditions:

Continuous rainy weather, low temperature (20-25°C) and low lying and ill drained soils.

Mode of Spread and Survival:

The fungus remains in the soil as chlamydospores and oospores which act as primary source of infection. The fungus also survives on other hosts like potato, tomato, brinjal, sesamum etc. The secondary spread takes place through wind-borne sporangia.

Management:

Remove and destroy infected plant residues. Avoid low-lying and ill drained fields for sowing. Treat with Thiram or Captan at 4g/kg.

Rust:

Melampsora ricini

Symptoms:

Minute, orange-yellow coloured, raised pustules appear with powdery masses on the lower surface of the leaves and the corresponding areas on the upper surface of the leaves are yellow. Often the pustules are grouped in concentric rings and coalesce together to form drying of leaves.

Pathogen:

The fungus produces only uredosori in castor plants and other stages of the fungus are unknown. Uredospores are of two kinds, one is thick walled and other is thin walled. They are elliptical to round, orange-yellow coloured and finely warty.

Mode of Spread and Survival:

The fungus survives in the self sown castor crops in the off season. It can also survive on other species of Ricinus. The fungus also attacks Euphorbia obtusifolia, E. geniculata, and E. marginata. The infection spreads through air-borne uredospores.

Management:

Rogue out the self-sown castor crops and other weed hosts. Spray Mancozeb at 1 kg/ha or dust Sulphur at 25 kg/ha.

Leaf blight:

Alternaria ricini

Symptoms:

All the aerial parts of plants viz., leaves, stems, inflorescences and capsules are liable to be attached by the fungus. Irregular brown spots with concentric rings form initially on the leaves and covered with fungal growth. When the spots coalesce to form big patches, premature defoliation occurs. The stem inflorescence and capsules are also shown dark brown lesions with concentric rings. On the capsules, initially brown sunken spots appear, enlarge rapidly and cover the whole pod. The capsules crack and seeds are also get infected.

Favourable Conditions:

High atmospheric humidity (85-90 per cent) and low temperature (16-20°C).

Mode of Spread and Survival:

The fungus also survives on hosts like Jatropha pandurifolia and Bridelia hamiltoniana. The pathogen is externally and internally seed-borne and causes primary infection. The secondary infection is through air-borne conidia.

Management:

Treat the seeds with Captan or Thiram at 4g/ kg. Remove the reservoir hosts periodically. Spray Mancozeb at 1 kg/ha.

Horticultural Crops:

BANANA (Musa spp.):

Panama disease/Fusarium wilt/Vascular wilt Fusarium oxysporum fsp. cubense

Symptoms:

The infected plants show characteristic yellowing of leaf blades developing as a band along the margin and spreading towards midrib. The leaf wilts and the petiole buckles. The leaf hangs between the pseudostem while the middle of lamina is still green. All the leaves collapse whereas the petioles join the pseudostem and die.

Mode of Spread and Survival:

The pathogen is soil-borne. It survives in soil as chlamydospores for longer periods. The primary spread of the disease is through infected rhizomes and secondary spread is through irrigation water.

Management:

Infected plants should be removed and destroyed. After removal and destruction of affected plants with the rhizome, the pits have to be treated with lime at 1 to 2 kg/pit.

Anthracnose/Fruit rot:

Gloeosporium musarum

Symptoms:

The fungus attacks the young banana fruits usually at the distal end. The skin of the fruit turns black and shrivels and becomes covered with characteristic pink acervuli. Finally the whole finger is affected. Later the disease spreads and affects the whole bunch. The disease results in premature ripening and shrivelling of the fruits which are covered with pink spore masses.

Mode of Spread and Survival:

The spread of the disease is by air-borne conidia and numerous insects which frequently visit banana flowers also spread the disease.

Management:

In the field the distal bud should be removed when all the hands have opened to prevent infection. Infected materials should be burned.

Black spot or black tip:

Deightoniella torulosa

Symptoms:

The fungus causes three kinds of symptoms vis., black spot on leaves, black tip or black end on fruits and speckle (fruit spot). The earliest symptoms on leaves are round pin point, black spots on the main veins of the lamina, usually close to the leaf margin. These increase in size, become lenticular in the direction of the veins and are usually separated from the normal green leaf tissue by a narrow bright yellow peripheral band.

Mode of Spread and Survival:

The conidia are spread by air.

Management:

Affected leaves and fruits should not be left on the garden and they should be collected and destroyed along with dead and dried sheaths. Removal and destruction of trashes before heavy rain reduces the level of infection.

Bunchy top:

Musa virus

Symptoms:

The affected leaf shows green streaks on the secondary veins on the under side of lamina and on the midrib and petiole. The powdery bloom covers the midrib and petiole. If this is rubbed off the dark green streaks can be clearly seen. The streaks vary from a series of dark green dots to a continuous dark green line with a ragged edge.

Mode of Spread and Survival:

It is not transmitted mechanically. The major vector is banana aphid viz., Pentalonia nigronervosa. It is transmitted in a persistent manner.

Management:

The disease management can be attained by the following ways:

1. Selection of healthy suckers for planting.

2. Removal of affected trees and suckers at periodical intervals.

3. Control of aphid vector by suitable chemical methods.

MANGO (Mangifera indica)

Malformation- Fusarium moniliforme var- Subglutinans

Symptoms:

Three distinct types of symptoms are produced. They are bunchy top of seedlings (BT), vegetative malformation (MV) and floral malformation (MF). Bunchy top phase (BT) appears on young plants in the nursery beds when they are 4 to 5 months old. The characteristic symptoms of the disease is the formation of a bunch of thickened small shootlets bearing small rudimentary leaves or occasionally several bunches arising from a leaf axil at the top or lower down the main shoot. These shootlets are much thicker than main axis from which they arise. The shoot remains short and stunted. The growth of the plant is stopped and it gives an appearance of bunchy top. Vegetative malformation (MV) induces excessive vegetative branches of limited growth in young seedlings. They are swollen and are with very short internodes forming bunches of various sizes. Malformation of inflorescence (MF) shows variation in the panicle formation.

Mode of Spread and Survival:

Diseased propagation materials help in the spread of the disease.

Epidemiology:

The disease is serious in the northwest region where the temperature is between 10°C and 15°C during December-January before flowering.

Management:

The disease incidence is reduced by spraying with NAA at 100 to 200 ppm during October. Pruning of diseased parts along with the basal 15 to 20 cm apparently healthy portions, followed by spraying of carbendazim 0.1 per cent or captafol 0. 2 per cent effectively control the disease.

Powdery mildew:

Oidium mangiferae

Symptoms:

It usually occurs during December-March. A whitish bloom of fungal growth covers the stalks of the panicle, flowers and tender fruits. The affected flowers and fruits drop prematurely reducing the setting of fruits. At higher altitudes, the infection extends to the young leaves and twigs. Many of these are covered by the white powdery fungal growth and may exhibit distorted growth.

Mode of Spread and Survival:

During off season, the pathogen has been reported in intact green malformed panicles mostly hidden under dense foliage. During flowering period (January-March), the conducive environmental conditions activate the dormant mycelium in necrotic leaves. Abundant conidia are produced and blown over to the new flushes through wind on young panicles which provide sufficient spore load for initiating the disease.

Epidemiology:

Rains or heavy mist in the morning accompanied by cool nights during the flowering period favour the disease.

Management:

Three or four dustings with sulphur powder at fortnightly interval controls the disease.

Anthracnose:

Colletotrichum gloeosporioides

Symptoms:

The fungus attacks tender shoots and foliage.

Brown or dark circular or irregular spots are formed on the leaves and such leaves are crinkled. The affected portions dry up and fall off and leave ragged margins. Often these leaves are shed leaving the twigs bare. The infection spreads to the green twigs and forms dark brown lesions on them. Young branches die-back. Older twigs and branches are infected through wounds and are killed.

Mode of Spread and Survival:

Inoculum remains on dried leaves, defoliated branches, mummified flowers and flower brackets and they serve as primary inoculum. Secondary spread is through air-borne conidia. The fungus can enter the pores of green fruits.

Epidemiology:

Under field conditions, the disease can be found on the fallen leaves and the blighted peduncles frequently remain in situ for many weeks. They produce spores under favourable moisture conditions and serve as foci of infection for the succeeding bloom. Even after they had fallen to the ground, they may continue to be the sources of infection for few weeks.

Management:

Diseased twigs, leaves and fruits which fall on the ground in the orchard should be collected and all infected twigs should be pruned and burnt. Spraying of Bordeaux mixture 0.6 per cent in the young plants during February, April and September controls the disease.

Sooty mould:

Capnodium ramosum

Symptoms:

The fungi produce mycelium which is usually superficial and dark. They grow on the flowers, both tender and old leaves, stems and fruits. They grow and thrive on the sugary secretions of the plant hoppers. Black encrustations are formed on the surfaces of different parts of the plant.

Mode of Spread and Survival:

Diseased leaves serve as primary inoculum. Epidemiology

Disease is severe in old and dense orchards where light intensity is low. Trees exposed to eastern side has less incidence while the trees in centre of the orchard has more incidence. High infestation with plant hoppers and the sugary substances secreted by them favour development of sooty mould.

Management:

Both the insects and the sooty moulds are to be simultaneously controlled in the eradication process. The insects are killed by spraying with carbaryl or phosphamidon 0.03 per cent.

Red rust:

Cephaleuros virescens

Symptoms:

The disease is characterised by red rusty spots on the leaves and young twigs. The spots are initially circular, slightly elevated and later coalesce to form irregular spot.

Epidemiology:

The disease is more common on close plantations. The zoospores cause initial infection.

Management:

It is controlled by spraying with Bordeaux mixture 1 per cent or copper oxychloride 0.1 per cent or lime sulphur.

Anthracnose/Wither tip/Die-back:

Colletotrichum gloeosporioides

Symptoms:

The plant is affected at all stages. The weakened or injured twigs and branches are generally affected. The branches begin to wither from the tip downwards. The drying back gradually progresses downwards with the leaves turning yellow, withering and drooping and gum formation on the affected stem.

Mode of Spread and Survival:

The fungus, survives in a dormant condition in the dead twigs and branches.

Epidemiology:

It causes decline of acid lime trees in North India. Deficiency of nitrogen and unfavourable soil conditions make the plant weak and susceptible to the disease.

Management:

Dried twigs should be pruned. The cut ends should be protected by painting with Bordeaux paste or any other copper fungicide. Such trees may be sprayed thrice with carbendazim 0.1 per cent or captafol 0.2 per cent after pruning. The trees should be adequately manured with urea.

Powdery mildew:

Acrosporium tingitaninum

Symptoms:

All the aerial plant parts including young and actively growing leaves and twigs are affected. On the upper surface of the leaves white powdery patches of fungal growth are seen. The patches extend and cover the whole leaf. Petioles and stems are also covered by whitish fungal growth.

Mode of Spread and Survival:

The fungus spreads through wind-borne conidia. The water shoots under the canopy are first infected.

Epidemiology:

The disease appears usually from October to march and in higher elevations. Damp mornings with few hours of sun shine are the most favourable conditions for the onset of disease.

Management:

The affected plant parts should be removed and destroyed carefully. Water shoots should be pruned to reduce infection. Dusting finely powdered sulphur gives effective control.

Scab/Verucosis:

Elisnoe fawcetti

Symptoms:

The disease attacks leaves, twigs and fruits. The lesions on the leaves in early stages consist of small, semi-translucent dots which become sharply defined pustular elevations usually on the under side, flat or somewhat depressed at the centre.

Mode of Spread and Survival:

The pathogen perpetuates and survives in off­season as ascospores. The fungus spreads through conidia. It attacks sour orange, rough lemon and pummelo.

Epidemiology:

The fungus infects tissues only when the surface is wet but prefers 16 to 20 °C temperature.

Management:

The diseased leaves, twigs and fruits should be collected and destroyed. Spraying with Bordeaux mixture 1.0 per cent is quite effective.

GRAPEVINE (Vitis Vinifera)

Powdery mildew-uncinula necator

Symptoms:

The fungus attacks all the stages of the crop growth. The characteristic symptom of this disease is the appearance of white powdery patches on affected parts. On the leaves the disease starts as small, white patches which later become larger in size and powdery in appearance. Sometimes the entire leaf is covered with dusty white fungal growth..

Mode of Spread and Survival:

It survives as dormant mycelium and as cleistothecia on the shoots and buds from season to season. The disease spreads by the air-borne conidia.

Epidemiology:

The disease occurs in severe form during October-November in North India and February- June in South India. Disease is favoured by warm weather and retarded by sunshine.

Management:

Overcrowding and dense growth of the vines should be avoided by proper pruning. Effective control can be achieved by spraying wettable sulphur 0.2 per cent or dinocap 0.7 per cent or carbendazim 0.1 per cent or sulphur dusting at berry development stage with a prophylactic treatment.

Downy mildew:

Plasmopara viticola

Symptoms:

The disease is usually first observed as small translucent, pale yellow spots with indefinite borders on the upper surface of leaves. On the under surface of leaves and directly under the spots, a downy growth of the fungus appears.

Mode of Spread and Survival:

The pathogen survives on the infected leaves and vines as oospores and dormant mycelium. The secondary spread is through wind-borne sporangia and zoospores which are found on the new flush.

Epidemiology:

Disease development is favoured during rainy season when there is a heavy dew, relative humidity is above 80 per cent and temperature is between 23°C and 27°C.

Management:

Sanitation is very important in the management of this disease. Removing and burning of all diseased leaves, shoots, flowers and berries that may contain hibernating oospores help in preventing epidemics. Vines should be planted with proper spacing and should be trained in such a manner that leaves do not remain near the ground surface.

Anthracnose/Bird’s eye spot:

Elsinoe ampelina

Symptoms:

The fungus attacks shoots, tendrils, petioles, leaves, veins and stems. Numerous spots occur on the young shoots. These spots may unite to girdle the stem and cause death of the tips. Spots on petioles and leaves cause them to curl or become distorted.

Mode of Spread and Survival:

The pathogen survives as mycelium in the cankers on the stem and on the infected twigs. Secondary spread is through conidia which are carried by wind and rain water.

Epidemiology:

The disease is severe during July-August and November-December months. Infection in new sprouts takes place during rainy season.

Management:

The diseased leaves and twigs should be pruned and burnt. Spraying pruned the canes and leaves with a mixture of ferrous sulphate 2.5 kg + 0. 5% sulphuric acid in 4.5 litres of water controls the disease.

Bacterial canker:

Xanthomonas campestris pv. viticola

Symptoms:

The disease starts as small water-soaked spots surrounded by yellowish halo at lower surface of the leaf. These spots enlarge in size and become dark brown and angular. Sometimes these spots coalesce to form larger patches. Leaves also show vein infection. Infected leaves after drying remain attached to the stem. Lesions are brown to black, elongated and cankerous on petioles and canes.

Mode of Spread and Survival:

The alternate hosts are neem and mango. The bacterium survives in the infected, dry leaves upto 65 days. Secondary infection takes place through wind splashed rain. Disease spreads to distant places by diseased cuttings.

Epidemiology:

Temperature range of 25 to 30 °C is favourable for the disease development. Free water from dew, irrigation or rain on leaf are more important for pathogenesis.

Management:

Regular inspection of vineyard, destruction of infected plant materials, use of disease-free cuttings and late-October pruning are recommended for its management.

GUAVA (Psidium guajava)

Fusarium wilt:

Fusarium oxysporum

Symptoms:

The disease is characterised by yellowing and browning of leaves, discolouration of the stem and death of the branches along one side. Sometimes the infection girdles the stem and the whole plant may wilt. Leaves die and the twig barks split.

Mode of Spread and Survival:

The fungus first colonises on the surface of the roots and enters the stem tissues at the basal portions near the ground level. It multiplies in vascular region and affects the cortical cells.

Epidemiology:

Higher disease incidence is noticed during the monsoon period. The disease appears in August and increases sharply during September-October.

It is severe in alkaline soils.

Management:

Dry branches should be cut off and wilted plants uprooted. Soil should be treated with lime or gypsum to make the soil pH 6.0 to 6.5. Balanced nutrition of host reduces severity of the disease when organic nitrogen is supplied.

Fruit canker/Scab/Grey blight:

Pestalotiopsis psidii

Symptoms:

Infection generally occurs on green fruits. Minute, brown or rust-coloured, unbroken, circular, scabby lesions of 2 to 4 mm dia, appear on the fruit which later tear the epidermis open in a circinate manner. The margin of the affected area becomes raised.

Mode of Spread and Survival:

Infected leaves and fruits serve as primary inoculum. Secondary spread is through the wind- borne conidia.

Epidemiology:

The fungus is capable of growing at temperature between 20 and 25 °C. Mycelial growth with intensive sporulation takes place at 5.5°C.

Management:

Spread of the disease can be checked by three or four spraying with Bordeaux mixture 1.0 per cent or copper oxychloride 0.2 per cent.

Anthracnose/Die-back/Fruit spot/Twig blight:

Gloeosporium psidii

Smptoms:

Severity of the disease may show die-back of main branches resulting in death of plants. The most characteristic symptoms appear during the rainy season as small pin-head sized spots on the unripe fruits. They gradually enlarge to form sunken and circular, dark brown to black spots.

Mode of Spread and Survival:

The pathogen remains dormant for about three months in the young infected fruits. It becomes active and incites rot when the fruit begins to ripe. In moist weather, acervuli appear as black dots scattered throughout the dead parts of the twigs. From the twigs, the fungus penetrates the petioles and attacks the young leaves, which become distorted with dead areas at margins or tips.

Epidemiology:

The cool season (January-March) and the hot, dry weather (April-June) prevent the spread of infection. In moist weather, acervuli are produced in abundance on dead twigs and pinkish spore masses are seen. Conidia initiate fresh infection.

Management:

Spraying the trees with Bordeaux mixture 0.6 per cent or copper oxychloride 0.2 per cent before the onset of monsoon reduces the disease incidence.

APPLE (Pyrus malus)

Collar rot Phytophthora cactorum

Symptoms:

Important symptoms of collar rot are production of rough patches on the stem around the collar or crown region of the tree at soil level which develop into cankers. Rapid extension of the cankered area, both in lateral and vertical directions, results in girdling of the tree.

Mode of Spread and Survival:

The pathogen survives as oospores in the soil.

Epidemiology:

A soil temperature of 12°C to 20°C with pH of 5 to 6 is found to be the best for the survival of the fungus.

Management:

Grafting of rootstocks 30 cm above the ground level reduces initial infection. The disease can be controlled by painting wounds with copper paints and drenching the area around the trees with fungicides like mancozeb or metalaxyl.

Stem cankers:

a. Black canker sphaeropsis lvalorum

Symptoms:

It is also known as black rot, die-back or smoky blight canker. The disease appears in three phases, i.e., stem canker, leaf spot (frog eye leaf spot) and fruit rot (black rot). Among them the canker phase is the most destructive. In this, reddish brown sunken lesions develop on trunk and branches. The lesions turn smoky with alternate rings. The wood below is stained reddish brown.

Mode of Spread and Survival:

The pathogen survives winter in the form of dormant mycelium and fruiting structure in cankered.

Epidemiology:

High humidity and a temperature range of 20 to 22 °C favour the disease development.

Scab-venturia inequalis

Symptoms:

The most striking symptoms of scab are commonly observed on leaves, fruits and rarely on 1 to 3 years old shoots. In severe cases, petioles and blossoms also exhibit scab symptoms. On leaves, lesions first develop on the lower side. Most of these lesions do not have a definite margin in contrast to those on the upper side of the leaf. Lesions appear as olivaceous spots which turn dark brown to black and become velvety.

Mode of Spread and Survival:

Pseudothecia formed in autumn and winter mature in spring to produce ascospores, the chief inoculum for primary infection. The secondary spread is through conidia.

Management:

Clean cultivation reduces primary infection. Fallen leaves should be collected and destroyed along with pruned materials. Control programmes should have aim of elimination/reduction of pseudothecial formation and secondary infections.

Powdery mildew

Podosphaera leucotrigha

Symptoms:

The disease appears soon after the buds develop into new leaves and shoots. Sometimes buds are so heavily infected in the previous season that they are killed before developing into leaves. The disease may be seen on both surfaces of leaves in severed infections.

Mode of Spread and Survival:

The fungus overwinters in the form of mycelium in diseased vegetative buds and fruits. Secondary spread is through wind-borne conidia.

Epidemiology:

The conidial germination takes place when air is saturated and the temperature is between 10 and 25 °C.

Management:

Pruning after shedding of leaves, thinning out and cutting back of laterals, removal and destruction of all diseased parts are important in the control of powdery mildew.