Knowledge base
Plant Diseases
Fungal, oomycete, bacterial, and other plant diseases — identification, biology, affected hosts, risk factors, and prevention principles.
50 entries · every entry is sourced and dated
These entries explain identification and prevention principles. They do not provide chemical treatment instructions; any control measures must follow locally authorized guidance and product labels.
- Plant disease
Anthracnose
Colletotrichum spp.
Anthracnose is a group of fungal diseases caused by Colletotrichum species, producing sunken, dark lesions on leaves, stems, pods, and fruit. It affects a wide range of crops, including common bean, mango, banana, and cucurbits, and is a major cause of post-harvest fruit losses.
- Plant disease
Apple Scab
Venturia inaequalis
Apple scab is a widespread fungal disease of apple caused by Venturia inaequalis, producing olive-green to black scabby lesions on leaves and fruit. Wet spring weather during bud break and early leaf growth is the main driver of infection each season.
- Plant disease
Bacterial Leaf Blight of Rice
Xanthomonas oryzae pv. oryzae
Bacterial leaf blight is a major bacterial disease of rice caused by Xanthomonas oryzae pv. oryzae. It produces water-soaked, yellow-margined lesions that spread from leaf tips, and a severe seedling wilt called kresek, particularly in warm, wet conditions.
- Plant disease
Bacterial Leaf Spot
Xanthomonas spp. and Pseudomonas syringae pv. species
Bacterial leaf spot is a disease of tomato and pepper caused mainly by Xanthomonas and Pseudomonas bacteria, producing small, water-soaked leaf and fruit lesions. It spreads readily in wet, warm conditions and through contaminated seed, water, and equipment.
- Plant disease
Bacterial Wilt
Ralstonia solanacearum species complex; related Erwinia and Dickeya species cause similar wilts in some hosts and regions
Bacterial wilt is a soil-borne disease affecting tomato, potato, cassava, and ginger among many other crops, caused mainly by Ralstonia solanacearum. It produces rapid wilting and vascular browning and is favoured by warm, wet soil conditions.
- Plant disease
Black Rot of Crucifers
Xanthomonas campestris pv. campestris
Black rot is a major bacterial disease of brassica crops caused by Xanthomonas campestris pv. campestris. It produces V-shaped yellow lesions at leaf margins with blackened veins and can spread systemically, making seed health and sanitation central to management.
- Plant disease
Black Sigatoka
Pseudocercospora fijiensis (syn. Mycosphaerella fijiensis)
Black Sigatoka, also known as black leaf streak disease, is a major fungal foliar disease of banana caused by Pseudocercospora fijiensis. It progressively destroys leaf tissue, reducing photosynthetic capacity, plant vigour, and bunch yield and quality, and is favoured by warm, humid, rainy conditions.
- Plant disease
Brown Spot of Rice
Bipolaris oryzae (teleomorph Cochliobolus miyabeanus)
Brown spot is a fungal disease of rice caused by Bipolaris oryzae. It produces numerous small, brown, oval leaf spots and is strongly associated with nutrient-poor, stressed soils, making it a classic indicator of poor crop nutrition.
- Plant disease
Cassava Brown Streak Disease
Cassava brown streak virus and Ugandan cassava brown streak virus (genus Ipomovirus)
Cassava brown streak disease is a viral disease of cassava caused by ipomoviruses spread by whiteflies and infected cuttings. It is especially damaging because it causes a dry, corky brown rot inside the storage roots, often with few obvious leaf symptoms.
- Plant disease
Cassava Mosaic Disease
Cassava mosaic geminiviruses (genus Begomovirus)
Cassava mosaic disease is a viral disease of cassava caused by cassava mosaic geminiviruses and spread by whiteflies and infected cuttings. It produces leaf mosaic, distortion, and stunting, and is one of the most damaging constraints on cassava production in Africa.
- Plant disease
Cercospora Leaf Spot
Cercospora beticola
Cercospora leaf spot is a major foliar fungal disease of sugar beet and related Beta crops caused by Cercospora beticola. It produces numerous small, circular spots with tan centres and dark reddish borders that can coalesce and destroy the canopy in warm, humid weather.
- Plant disease
Charcoal Rot
Macrophomina phaseolina
Charcoal rot is a soil-borne disease caused by Macrophomina phaseolina that affects many crops. It is favoured by hot, dry, drought-stressed conditions and produces a grey-black discoloration of the lower stem and roots studded with tiny black microsclerotia.
- Plant disease
Citrus Canker
Xanthomonas citri subsp. citri (syn. Xanthomonas axonopodis pv. citri)
Citrus canker is a bacterial disease causing raised, corky lesions on the leaves, stems, and fruit of orange and other citrus. It is spread mainly by wind-driven rain and readily moved on contaminated plant material, equipment, and clothing.
- Plant disease
Clubroot
Plasmodiophora brassicae
Clubroot is a soil-borne disease of brassica crops caused by the protist Plasmodiophora brassicae, producing swollen, distorted root galls that impair water and nutrient uptake. It is favoured by acidic, moist soils and can persist in soil for many years.
- Plant disease
Coffee Leaf Rust
Hemileia vastatrix
Coffee leaf rust is caused by the fungus Hemileia vastatrix, producing orange-yellow powdery pustules on the underside of coffee leaves that lead to premature leaf drop, reduced photosynthetic capacity, and yield loss, particularly in susceptible arabica coffee.
- Plant disease
Common Scab
Streptomyces scabies and related pathogenic Streptomyces species
Common scab produces rough, corky lesions on potato tubers and can also affect radish and beetroot. It is caused by soil-dwelling Streptomyces bacteria and is favoured by dry soil and elevated soil pH during early tuber or root development.
- Plant disease
Common Smut
Ustilago maydis
Common smut is a fungal disease of maize caused by Ustilago maydis, producing large, greyish-white galls on ears, tassels, and other actively growing tissue. It survives in soil and residue for years and infects mainly through wounds.
- Plant disease
Damping-off
Multiple genera (e.g. Pythium, Rhizoctonia, Fusarium spp.)
Damping-off is a seedling disease complex caused by several soil-borne fungi and oomycetes, mainly Pythium, Rhizoctonia, and Fusarium species. It kills seeds before or shortly after emergence and is one of the most widespread causes of poor stand establishment across many crops.
- Plant disease
Downy Mildew
Multiple genera (e.g. Plasmopara, Peronospora, Pseudoperonospora, Bremia spp.)
Downy mildew is a group of oomycete diseases, not a single pathogen, that produce yellow leaf patches and a characteristic fuzzy sporulation on the underside of leaves. Different host-specialised species affect grapevine, cucurbits, lettuce, sunflower, and many other crops.
- Plant disease
Early Blight
Alternaria solani (and related Alternaria species)
Early blight is a common fungal disease of potato and tomato caused by Alternaria solani. It produces dark leaf lesions with concentric rings resembling a target, usually starting on older foliage, and can also affect stems, fruit, and tubers.
- Plant disease
Ergot
Claviceps purpurea (and related Claviceps species)
Ergot is a fungal disease of open-flowering cereals and grasses, caused by Claviceps purpurea, in which dark sclerotia replace developing grain in infected florets. It is favoured by cool, wet weather during flowering and is a recognised grain-quality and food-safety concern because of the alkaloids sclerotia contain.
- Plant disease
Fire Blight
Erwinia amylovora
Fire blight is a destructive bacterial disease of apple and other pome fruits, caused by Erwinia amylovora. It produces blossom blight and shoot dieback with a characteristic shepherd's-crook shape, and spreads via rain splash, wind, and flower-visiting insects during bloom.
- Plant disease
Fusarium Head Blight
Fusarium graminearum (teleomorph Gibberella zeae) and related Fusarium species
Fusarium head blight is a fungal disease of cereal heads caused chiefly by Fusarium graminearum. It bleaches infected spikelets, shrivels grain, and can lead to mycotoxin contamination, making it a serious food-safety as well as yield concern.
- Plant disease
Fusarium Wilt
Fusarium oxysporum
Fusarium wilt is a soil-borne fungal disease caused by Fusarium oxysporum. The fungus colonizes the water-conducting tissue of host plants, causing wilting and yellowing, and can persist in soil for many years.
- Plant disease
Gray Leaf Spot
Cercospora zeae-maydis
Gray leaf spot is a foliar fungal disease of maize caused by Cercospora zeae-maydis. It produces long, narrow, grey-to-tan lesions bounded by the leaf veins and can sharply reduce grain fill when it develops early in humid, residue-rich systems.
- Plant disease
Gray Mold
Botrytis cinerea
Gray mold is a widespread fungal disease caused by Botrytis cinerea, one of the broadest host-range plant pathogens known. It causes fuzzy grey fungal growth and rapid decay on flowers, fruit, and foliage, and is a major cause of losses both in the field and after harvest.
- Plant disease
Huanglongbing
Candidatus Liberibacter asiaticus (and related Liberibacter species)
Huanglongbing, or citrus greening, is a destructive bacterial disease of citrus caused by Candidatus Liberibacter species and spread by citrus psyllids. It causes blotchy leaf mottling, misshapen bitter fruit, and gradual tree decline, and there is no cure once trees are infected.
- Plant disease
Late Blight
Phytophthora infestans
Late blight is a destructive oomycete disease of potato and tomato that can destroy foliage and tubers within days under cool, wet conditions. It remains one of the most economically significant plant diseases worldwide.
- Plant disease
Maize Lethal Necrosis
Maize chlorotic mottle virus co-infecting with a cereal potyvirus
Maize lethal necrosis is a severe viral disease of maize caused by co-infection of Maize chlorotic mottle virus with a cereal potyvirus. The synergistic infection causes mottling, necrosis, and often plant death, with major impacts where it has emerged.
- Plant disease
Net Blotch
Pyrenophora teres (anamorph Drechslera teres)
Net blotch is a foliar fungal disease of barley caused by Pyrenophora teres. It occurs as a net form producing dark net-like leaf patterns and a spot form producing dark oval spots, both able to reduce grain fill in wet seasons.
- Plant disease
Northern Leaf Blight of Maize
Exserohilum turcicum (teleomorph Setosphaeria turcica)
Northern corn leaf blight is a foliar fungal disease of maize caused by Exserohilum turcicum. It produces large, cigar-shaped grey-green to tan lesions and can cause substantial yield loss when it develops before or during grain fill in humid conditions.
- Plant disease
Panama Disease
Fusarium oxysporum f. sp. cubense
Panama disease is a soil-borne vascular wilt of banana caused by Fusarium oxysporum f. sp. cubense. The fungus invades the roots and vascular system, causing yellowing, wilting, and internal browning, and its Tropical Race 4 strain threatens widely grown banana types.
- Plant disease
Powdery Mildew
Fungi of the order Erysiphales (e.g. Blumeria graminis)
Powdery mildew is a group of common fungal diseases producing white, powdery growth on leaves and stems. Host-specific species affect many crops, and management relies mainly on prevention and monitoring.
- Plant disease
Rice Blast
Magnaporthe oryzae (anamorph Pyricularia oryzae)
Rice blast, caused by the fungus Magnaporthe oryzae, is one of the most destructive diseases of rice worldwide. It can affect leaves, nodes, and the neck of the panicle, with neck blast in particular capable of causing severe yield loss through unfilled or chalky grain.
- Plant disease
Root Rot
Multiple genera (e.g. Pythium, Phytophthora, Rhizoctonia, Fusarium spp.)
Root rot is a general term for root diseases caused by several different soil-borne fungi and oomycetes rather than a single pathogen. It reduces root function and vigor across a wide range of crops, and accurate diagnosis is essential to choosing an effective response.
- Plant disease
Sclerotinia
Sclerotinia sclerotiorum
Sclerotinia is a fungal stem and pod rot caused by Sclerotinia sclerotiorum, affecting a very wide range of broadleaf crops including oilseed rape, soybean, sunflower, and common bean. It is favoured by cool, wet conditions during and after flowering, and typically begins on senescing flower petals.
- Plant disease
Septoria Tritici Blotch
Zymoseptoria tritici (teleomorph Mycosphaerella graminicola)
Septoria tritici blotch is a foliar fungal disease of wheat caused by Zymoseptoria tritici. It produces irregular tan lesions studded with small dark fruiting bodies and is one of the most damaging leaf diseases of wheat in temperate, humid regions.
- Plant disease
Sheath Blight
Rhizoctonia solani (teleomorph Thanatephorus cucumeris)
Sheath blight is a fungal disease of rice caused by Rhizoctonia solani. It produces oval, banded lesions on the leaf sheaths near the waterline that climb the plant in dense, well-fertilised canopies, and related forms affect maize.
- Plant disease
Southern Rust of Maize
Puccinia polysora
Southern corn rust is a foliar rust disease of maize caused by Puccinia polysora. It produces dense, orange, mainly upper-surface pustules and can develop explosively in hot, humid weather, causing rapid loss of green leaf area.
- Plant disease
Soybean Rust
Phakopsora pachyrhizi
Soybean rust is a foliar rust disease of soybean caused by Phakopsora pachyrhizi. It produces small tan to reddish-brown pustules on the underside of leaves and can cause rapid defoliation and yield loss in warm, humid conditions.
- Plant disease
Stem Rust
Puccinia graminis (host-specialised formae speciales, e.g. f. sp. tritici on wheat)
Stem rust is a historically damaging fungal rust disease of wheat, barley, oats, and rye, caused by Puccinia graminis. It produces elongated, reddish-brown pustules mainly on stems and leaf sheaths and can cause severe yield loss when a virulent race meets susceptible varieties under favourable weather.
- Plant disease
Sudden Death Syndrome
Fusarium virguliforme (formerly Fusarium solani f. sp. glycines)
Sudden death syndrome is a soil-borne disease of soybean caused by Fusarium virguliforme. The fungus infects the roots and releases a toxin that moves to the leaves, producing striking interveinal yellowing and browning while the veins stay green.
- Plant disease
Take-all
Gaeumannomyces tritici (formerly Gaeumannomyces graminis var. tritici)
Take-all is a soil-borne root disease of wheat and other cereals caused by Gaeumannomyces tritici. It rots the roots and stem base, producing stunted plants and prematurely white, empty heads, and typically worsens under continuous cereal cropping.
- Plant disease
Tan Spot
Pyrenophora tritici-repentis (anamorph Drechslera tritici-repentis)
Tan spot is a foliar fungal disease of wheat caused by Pyrenophora tritici-repentis. It produces tan lesions with yellow halos, is strongly favoured by cereal residue left on the surface, and can reduce grain fill when it moves onto the upper leaves.
- Plant disease
Tar Spot of Maize
Phyllachora maydis
Tar spot of corn is a foliar fungal disease of maize caused by Phyllachora maydis. It produces distinctive raised, black, tar-like spots on the leaves and, when severe, can reduce grain fill and weaken stalks in cool, humid conditions.
- Plant disease
Tobacco Mosaic Virus
Tobacco mosaic virus (genus Tobamovirus)
Tobacco mosaic virus is one of the most stable and best-studied plant viruses, causing mottled, mosaic-patterned leaves and stunting in tobacco, tomato, pepper, and other plants. Unlike many plant viruses, it spreads mainly through mechanical contact rather than insect vectors.
- Plant disease
Tomato Yellow Leaf Curl Virus
Tomato yellow leaf curl virus (genus Begomovirus)
Tomato yellow leaf curl virus is a whitefly-transmitted begomovirus that causes one of the most damaging virus diseases of tomato. Infected plants show upward leaf curling, yellowing, and severe stunting, with heavy losses when young plants are infected.
- Plant disease
Verticillium Wilt
Verticillium dahliae and Verticillium albo-atrum
Verticillium wilt is a soil-borne fungal vascular disease affecting a very wide range of crops, including cotton, eggplant, olive, and potato. The fungus persists in soil for many years and blocks water movement within the plant, causing wilting and vascular discoloration.
- Plant disease
Wheat Leaf Rust
Puccinia triticina
Wheat leaf rust is one of the most widespread rust diseases of wheat, caused by the fungus Puccinia triticina. It produces orange-brown pustules on leaves and can reduce yield when infection develops early and spreads widely under favourable weather.
- Plant disease
Wheat Stripe Rust
Puccinia striiformis
Wheat stripe rust, also called yellow rust, is caused by the fungus Puccinia striiformis. It produces distinctive yellow-orange pustules arranged in stripes along the leaf veins and, unlike some other wheat rusts, can develop and spread under relatively cool conditions.