Tag: viral diseases

• Potato is susceptible to various fungal and viral diseases.
• Major diseases include early blight, late blight, black scurf, leaf roll, and mosaic viruses.
• Effective management requires understanding pathogen biology and disease cycles.

• Small, dark lesions with concentric rings (bull’s eye) on older leaves.
• Yellowing tissue around spots; severe cases cause foliage death.
• Stem lesions may girdle plants near soil line.

Etiology:

• Septate, branched, light brown mycelium; conidia borne in chains, obclavate, muriform.

Disease Cycle:

• Primary infection from mycelium/conidia in plant debris.
• Secondary spread by wind, water, or rain splash.

Management:

• Use disease-free seed and crop rotation.
• Remove and destroy infected debris.
• Fungicide sprays: Mancozeb 0.25%, Chlorothalonil 0.2%, or Zineb 0.25% at intervals.

• Water-soaked, dark lesions on lower leaves, expanding rapidly in cool, moist weather.
• Lesions not limited by veins; entire leaves may die quickly.
• Tubers show irregular, sunken, brown to purplish areas with granular rot beneath skin.

Etiology:

• Coenocytic, hyaline, branched mycelium; sporangia are oval/pear-shaped, germinate by zoospores.

Disease Cycle:

• Primary infection from infected tubers and soil.
• Airborne sporangia cause secondary spread.

Management:

• Protective fungicide sprays (Mancozeb/Zineb 0.2%).
• Use resistant varieties (e.g., Kufri Naveen, Kufri Jeevan).
• Destroy foliage before harvest; avoid tuber injury during harvest.

• Necrosis at sprout tips, sunken lesions on stolons, roots, stems.
• Black sclerotia (scurf) on tuber surface.
• Stunted plants, purplish leaves, deformed tubers.

Etiology:

• Basidiomycete fungus; produces sclerotia, rarely basidiospores.
• Mycelium is septate, branched; sclerotia are dark brown to black, irregular.

Disease Cycle:

• Primary infection from sclerotia in soil.
• Seedlings from infected soil spread disease.

Management:

• Plant only disease-free seed tubers.
• Seed treatment with fungicides (e.g., mercuric chloride; safer alternatives preferred).
• Crop rotation and shallow planting reduce severity.

• Upward rolling of young leaves; leaves become dry, thick, and brittle.
• Plants are stunted, erect, light green; tubers reduced in size and number.
• Net necrosis may develop inside tubers.

Transmission:

• Spread by aphids (Myzus persicae, Aphis gossypii) and infected tubers.

Management:

• Use disease-free, certified seed tubers.
• Rogue and bury diseased plants.
• Control aphids with insecticides (e.g., Phorate 10G, 10 kg/ha).

• Light yellow mottling, slight crinkling, interveinal necrosis, mild stunting.

Severe Mosaic (Potato virus Y – PVY):
Symptoms:

• Chlorotic and necrotic streaks, leaf drop, interveinal and stem necrosis, stunting, leaf rugosity.

Rugose/Common Mosaic (PVX & PVY):
Symptoms:

• Black streaks on veins/stems, shriveled and mottled leaves, dwarfing, reduced tuber size.

Transmission:

• PVX: Mechanical (sap), seed, tools, contact.
• PVY: Aphids (Myzus persicae, Aphis gossypii), infected tubers.

Management:

• Use disease-free, certified seed tubers.
• Grow resistant varieties (e.g., Chippewa, Irish Cobbler).
• Rogue diseased plants; control aphids (Phorate 10G, 10 kg/ha).
• Early harvesting and hygiene reduce spread.

• Use certified, disease-free seed tubers for all plantings.
• Practice crop rotation and field sanitation to reduce inoculum.
• Apply recommended fungicides and insecticides judiciously.
• Grow resistant varieties where available.
• Monitor fields regularly for early detection and management.

• Papaya is susceptible to various fungal, viral, and post-harvest diseases.
• Diseases affect yield, fruit quality, and marketability.
• Effective management requires accurate diagnosis and integrated approaches.

• Powdery Mildew: Oidium indicum, Oidium caricae, Leveillula taurica
• Leaf Blight: Corynespora cassiicola
• Damping-Off: Pythium aphanidermatum, Rhizoctonia solani
• Foot Rot: Pythium aphanidermatum
• Anthracnose: Colletotrichum gloeosporioides

• Speckled, water-soaked spots on leaf underside.
• Powdery patches enlarge, covering leaves.
• Leaves become chlorotic, distorted, and fall prematurely.

Management:

• Clean cultivation and balanced fertilization (increase K, reduce N).
• Dusting sulfur (30 g/10 L water) at symptom onset.
• Spray Triadimefon (0.1%) or systemic fungicides (Bayleton, carbendazim) at intervals.

• Water-soaked patches at stem base, girdling stem.
• Tissues turn brown/black and rot; terminal leaves yellow and wilt.
• Fruits shrivel and drop; plant may topple and die.
• Roots deteriorate; bark appears dry, honeycomb-like.

Management:

• Use well-drained nursery beds; remove and destroy diseased seedlings.
• Apply Trichoderma viride (15 g/plant) with FYM at planting.
• Seed treatment with captan (4 g/kg) or chlorothalonil (2 g/kg).
• Drench stem base with COC (0.25%), metalaxyl (0.1%), or Bordeaux mixture (1.2%).

• Gray to brown spots with dark margins and yellow halo on leaves.
• Necrotic areas form as spots coalesce.
• Fruits develop light spots that enlarge, become dark brown, and may show concentric rings.
• Premature fruit drop common.

Management:

• Remove and destroy affected fruits.
• Harvest fruits at maturity.
• Spray copper oxychloride (0.3%), carbendazim (0.1%), or thiophanate-methyl (0.1%) every 15 days.
• Hot water or fungicidal wax treatment for export fruits.

• Papaya Mosaic Virus (transmitted by Aphis gossypii)
• Papaya Leaf Curl Virus (transmitted by Bemisia tabaci)
• Papaya Ring Spot Virus (PRSV; transmitted by aphids)

• Mild mosaic pattern and deformation in young leaves.
• Dark green blister-like patches on yellowish-green leaves.
• Leaf vein clearing, downward curling, and shortened petioles.

• Severe curling, crinkling, and deformation of young leaves.
• Vein clearing and thickening; twisted petioles.
• Stunted growth, reduced yield, and possible defoliation.

• Prominent mosaic and chlorosis on leaves.
• Oily streaks on petioles and trunk.
• Distorted young leaves; concentric rings and C-shaped markings on fruits.

• Use disease-free seedlings for planting.
• Rogue and destroy infected plants promptly.
• Control vectors with insecticides (monocrotophos 0.05%, dimethoate 0.2%, metasystox 0.1%).

• Macrophomina Rot: Macrophomina phaseolina
• Rhizopus Rot (Soft Rot): Rhizopus stolonifer
• Phomopsis Rot: Phomopsis caricae
• Anthracnose: Colletotrichum gloeosporioides

• Small water-soaked spots on fruit surface.
• Spots deepen, causing internal rot and sclerotia formation.
• Inner tissues turn brownish-black with dark mycelial growth.

• Irregular water-soaked lesions on injured fruits.
• Lesions covered with whitish fungal growth, turning dark brown.
• Fruit becomes watery, emits foul odor, and infection spreads rapidly.

• Initial water-soaked spots become sunken and dark brown to black.
• Spots may be surrounded by white, raised tissue.
• Infected area becomes soft and pulpy.

• Harvest fruits at proper maturity and during cool hours.
• Dipping fruits in TBZ (1000 ppm) or benomyl (20 ppm) reduces storage decay.
• Dusting fruits with benzoic acid (0.1%) in kaolin reduces rotting.

• Adopt clean cultivation and use disease-free planting material.
• Monitor and manage vectors for viral diseases.
• Apply recommended fungicides and biological agents for fungal diseases.
• Practice proper post-harvest handling to minimize losses.

• Cucurbits include cucumber, melon, watermelon, pumpkin, squash, and gourds.
• Major diseases: Downy mildew, Powdery mildew, Fusarium wilt, Angular leaf spot, Cucumber mosaic, and Tospovirus.
• Diseases caused by fungi, bacteria, and viruses.
• Effective management requires accurate diagnosis and integrated control strategies.

• Pathogen: Pseudoperonospora cubensis (oomycete fungus).
• Hosts: All major cucurbits.
• Symptoms: Small yellow, water-soaked lesions on upper leaf surface; lesions turn brown and necrotic.
• Severe infection causes leaf curling, death, and reduced fruit quality.

• Survives on collateral hosts and plant debris.
• Spread by wind-borne sporangia and rain splash.
• Management: Remove weeds, avoid overhead irrigation, use resistant varieties.
• Fungicide sprays: Metalaxyl, chlorothalonil, or zineb at recommended intervals.

• Pathogens: Erysiphe cichoracearum and Sphaerotheca fuliginea.
• Symptoms: White, powdery mycelium on both leaf surfaces, stems, and petioles.
• Leads to leaf yellowing, drying, premature defoliation, and fruit deformation.

• Overwinters as cleistothecia or on collateral hosts.
• Spread by wind-borne conidia.
• Management: Use resistant varieties, ensure good air circulation, apply fungicides (e.g., Calixin, Karathane).

• Pathogen: Fusarium oxysporum f.sp. niveum.
• Symptoms: Seedling damping-off, yellowing and wilting of leaves, vascular discoloration, stem lesions.
• Older plants may collapse suddenly, especially under stress.

• Survives in soil as chlamydospores for years.
• Primary infection from soil; secondary spread by water and wind.
• Management: Seed treatment (Carboxin/Carbendazim), crop rotation, use resistant varieties, balanced fertilization, maintain soil pH 6.5–7.0.

• Pathogen: Pseudomonas syringae pv. lachrymans (bacterium).
• Symptoms: Small, angular, water-soaked leaf spots; milky exudate under moist conditions.
• Lesions dry to form shot-holes; fruit spots cause internal decay and deformation.

• Seed-borne and survives in crop debris.
• Spread by irrigation water and handling wet plants.
• Management: Use pathogen-free seed, crop rotation, avoid overhead irrigation, apply bactericides (e.g., Streptomycin), destroy crop debris.

• Pathogen: Cucumber mosaic virus (CMV).
• Symptoms: Mosaic, leaf distortion, stunting, flower abnormalities, fruit deformation.
• Transmitted by aphids (non-persistent) and cucumber beetles; survives on weeds and alternate hosts.

• Rogue infected plants and eliminate weed hosts.
• Control aphid vectors with insecticides (e.g., monocrotophos, phosphamidon).
• Use resistant varieties where available.

• Pathogen: Tomato spotted wilt virus (TSWV), a tospovirus.
• Symptoms: Leaf bronzing, chlorotic spots, mosaic, die-back, stunting, fruit ring spots and necrosis.
• Transmitted by thrips (e.g., Frankliniella occidentalis, Thrips palmi).

• Use mesh screening and phytosanitary measures in nurseries.
• Avoid planting near thrips reservoirs (ornamentals, older crops).
• Control weeds and volunteer cucurbits.
• Implement early insecticide programs to manage thrips populations.

• Combine cultural, chemical, and biological methods for effective disease control.
• Use resistant varieties and certified seeds.
• Practice crop rotation and field sanitation.
• Monitor regularly for early detection and timely intervention.