| { |
| "schema_version": "1.0.0", |
| "disease_id": "tea.disease_fungal.gray_blight", |
| "aliases": [ |
| "Pestalotiopsis leaf spot", |
| "Grey leaf spot", |
| "Grey blight" |
| ], |
| "crop": { |
| "common_name": "tea", |
| "scientific_name": "Camellia sinensis", |
| "family": "Theaceae" |
| }, |
| "condition": { |
| "common_name": "gray blight", |
| "scientific_name": "Pestalotiopsis theae", |
| "alt_names": [ |
| "Grey leaf blight" |
| ], |
| "pathogen": { |
| "type": "disease_fungal", |
| "taxonomy": { |
| "kingdom": "Fungi", |
| "phylum": "Ascomycota", |
| "class": "Sordariomycetes", |
| "order": "Xylariales", |
| "family": "Amphisphaeriaceae", |
| "genus": "Pestalotiopsis", |
| "species": "theae" |
| } |
| } |
| }, |
| "issue_type": "disease_fungal", |
| "transmission": { |
| "vectors": [ |
| "rain splash", |
| "wind" |
| ], |
| "dispersal": [ |
| "conidia (asexual spores)" |
| ], |
| "overwintering": [ |
| "infected leaves", |
| "plant debris on the ground", |
| "cankers on stems" |
| ] |
| }, |
| "environmental_risk": { |
| "risk_factors": [ |
| "high humidity", |
| "prolonged leaf wetness", |
| "mechanical injury (e.g., hail, pruning wounds)", |
| "sun scorch", |
| "nutrient stress" |
| ], |
| "temp_c_day": [ |
| 20, |
| 30 |
| ], |
| "temp_c_night": [], |
| "relative_humidity_pct": [ |
| 85, |
| 100 |
| ], |
| "leaf_wetness_hours_threshold": 10 |
| }, |
| "severity_rubric": { |
| "unit": "percent_leaf_area", |
| "mild": "1-10% of leaf area is affected. Lesions are small, distinct, and mostly on older leaves.", |
| "moderate": "11-30% of leaf area is affected. Lesions are larger and may begin to coalesce.", |
| "severe": ">30% of leaf area is affected. Lesions have merged into large necrotic patches, potentially leading to defoliation.", |
| "notes": "Severity is assessed on the most affected leaves of a plant to represent the peak disease expression. It measures the direct loss of photosynthetic area." |
| }, |
| "symptoms": { |
| "leaves": [ |
| "Initial spots are small, yellowish-brown, and circular to slightly irregular.", |
| "Mature lesions develop a distinct grayish-white or light brown center.", |
| "A prominent, dark brown to purplish border surrounds the necrotic center.", |
| "Lesions often exhibit concentric rings, giving a 'target' or 'zonate' appearance.", |
| "Tiny, black, pinhead-sized dots (acervuli) are often visible within the gray center.", |
| "The central tissue of the lesion becomes thin and papery.", |
| "Lesions may coalesce to form large, irregular necrotic blotches.", |
| "In some cases, the dead central tissue falls out, creating a 'shot-hole' effect.", |
| "Symptoms are typically more prevalent on older, mature leaves." |
| ], |
| "stems": [ |
| "In severe infections on young shoots, small, sunken, dark lesions or cankers can form." |
| ], |
| "fruit": [], |
| "roots": [], |
| "whole_plant": [ |
| "Reduced plant vigor and overall poor growth in cases of severe infection.", |
| "Premature defoliation can occur when disease pressure is high." |
| ], |
| "signs_microscopic_or_visible": [ |
| "Presence of black, erumpent acervuli (fungal fruiting bodies) in the center of mature lesions, sometimes arranged in concentric rings." |
| ] |
| }, |
| "lookalikes": [ |
| { |
| "condition_name": "leaf blight", |
| "condition_id": "tea.disease_fungal.leaf_blight", |
| "key_differences": [ |
| "Leaf blight lesions are often larger, more irregular, and start from the leaf tip or margin, whereas gray blight spots are more circular and can appear anywhere.", |
| "Gray blight has a more distinct gray/white center and dark border compared to the more uniform brown necrosis of many leaf blights.", |
| "Concentric rings ('target spots') are a classic feature of gray blight, which is less common in leaf blight." |
| ] |
| }, |
| { |
| "condition_name": "algal leaf spot", |
| "condition_id": "tea.disease_other.algal_leaf_spot", |
| "key_differences": [ |
| "Algal spots are raised, superficial, and have a velvety texture, typically appearing orange-red or grayish-green.", |
| "Gray blight lesions are sunken (necrotic), not raised, and are integral to the leaf tissue.", |
| "Algal spots do not have the characteristic gray center with a dark border or concentric rings." |
| ] |
| }, |
| { |
| "condition_name": "helopeltis_damage", |
| "condition_id": "tea.pest_insect.helopeltis_damage", |
| "key_differences": [ |
| "Helopeltis damage (from tea mosquito bug) appears as angular, dark brown to black necrotic spots without a gray center or distinct border.", |
| "Insect damage often causes significant distortion, puckering, or curling of young, tender leaves, which is not a primary symptom of gray blight.", |
| "Helopeltis feeding spots are numerous and clustered, reflecting the insect's probing, while gray blight lesions are typically fewer and more developed." |
| ] |
| } |
| ], |
| "management": { |
| "cultural": [ |
| "Prune bushes to improve air circulation and sunlight penetration, which reduces leaf wetness duration.", |
| "Remove and burn or bury infected leaves and pruned debris to reduce inoculum.", |
| "Maintain balanced soil fertility and pH to ensure plant vigor.", |
| "Avoid mechanical damage to plants during field operations." |
| ], |
| "biological": [ |
| "Application of bio-control agents like *Trichoderma* spp. can help suppress pathogen growth in the soil and on plant surfaces." |
| ], |
| "chemical": [ |
| "Apply protective fungicides (e.g., copper oxychloride, mancozeb) before periods of high risk.", |
| "Use systemic fungicides (e.g., hexaconazole, propiconazole) for curative action, following local regulations and resistance management guidelines." |
| ], |
| "notes": "An integrated pest management (IPM) approach is recommended, combining cultural practices with judicious, need-based fungicide applications timed with weather forecasts." |
| } |
| } |
