Table of Contents
Fungicide
Some of the fungi are responsible for foliar diseases – Downy mildews; Powdery mildews; and White blister are some of the highly prevalent foliar diseases.
Other Fungi
Clubroot; Pythium species; Fusarium species; Rhizoctonia species; Sclerotinia and Sclerotium species – are soilborne diseases.
Some fungal diseases occur on a wide range of vegetables.
These diseases include Anthracnose; Botrytis rots; Downy mildews; Fusarium rots; Powdery mildews; Rusts; Rhizoctonia rots; Sclerotinia rots; Sclerotium rots.
Others are specific to a particular crop group
Clubroot (Plasmodiophora brassicae) in brassicas, Leaf blight (Alternaria dauci) in carrots, and Red root complex in beans.
Other Fungal Diseases of Vegetables include:
- Target spot – Alternaria solani (tomatoes)
- Aphanomyces root rot – Aphanomyces euteiches pv. phaseoli (beans)
- Aschochyta collar rot (peas)
- Gummy stem blight – Didymella bryoniae (cucurbits)
- Alternaria leaf spot – Alternaria cucumerina and A. alternata (cucurbits)
- Black leg – Leptosphaeri maculans (brassicas)
- Ring spot – Mycosphaerella brassicicola (brassicas)
- Late blight – Septoria apiicola (celery)
- Cercospora leaf spot – Cercospora beticola (beets)
- Leaf blight – Septoria petroelini (parsley)
- Septoria spot – Septoria lactucae (lettuce)
- Leaf blight – Stemphylium vesicarium (spring onions)
- Leaf blight – Alternaria dauci (carrots).
Fungal Disease |
Factors conducive to spread |
Crops affected |
Symptoms |
White blister/ White rust (Albugo candida) |
Optimum conditions for disease development are 3-4 hours in mild temperatures (6- 24?C). | Brassicas (including Asian leafy brassicas). |
White blisters and swellings on leaves and heads of affected plants; blisters consist of masses of white dust-like spores; up to 100% losses have been reported.
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Downy mildews (individual species damage particular crop families) |
High humidity, leaf wetness and cool to mild temperatures (10-16 °C). | Wide host range including onions; peas; lettuce; celery; spinach; kale; herbs; cucurbits; brassicas; Asian leafy brassicas. |
Symptoms usually begin with yellowish leaf spots which then turn brown; downy growth appears on underside of leaves.
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Powdery mildews (some species are restricted to particular crops or crop families) |
Moderate temperatures (20-25?C); relatively dry conditions (unlike downy mildews). | Wide host range and very common, especially in greenhouse crops: cucumber; melons; pumpkin; zucchini;parsnip; beetroot; potato; herbs; peas; bitter melon;tomato; capsicum; Brussels sprouts; cabbage; swedes. |
Small, white, powdery patches on most above-ground surfaces; usually observed first on undersides of leaves but eventually cover both surfaces; affected leaves become yellow, then brown and papery and die.
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Clubroot (Plasmodiophora brassicae) |
Warm weather; acidic soil (pH less than 7); high soil moisture. | Brassicas (including Asian leafy brassicas). |
Plants are yellow and stunted and may wilt in hotter parts of the day; large malformed ‘clubbed’ roots which prevent the uptake of water and nutrients, reducing the potential yield of the crop.
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Pythium species |
Cold, wet soil conditions; known as water moulds, they enter untreated water supplies; water supplies for irrigation and hydroponics should be tested regularly.
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Many vegetable crops in including cucurbits; brassicas; lettuce. | May kill seedlings, which die before they emerge or soon after emergence; plant collapse. |
Sclerotinia rots (S. sclerotiorum and S. minor) – a range of common names are used |
Windy, cool, humid weather; wet soil; survival structures known as sclerotia remain viable in soil for long periods (10-15 years).
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Most vegetable crops. | Water-soaked rotting of stems, leaves, and sometimes fruit; followed by a fluffy, white and cottony fungal growth which contain hard black pebble-like sclerotia. |
Sclerotium rots (Sclerotium rolfsii and S. cepivorum) |
S. rolfsii – Warm, moist conditions. S. cepivorum –Development is favoured by cool soil conditions (14-19?C) and low moisture. | S. rolfsii – Wide host range including: beans; beets; carrot; potato; tomato; capsicum; cucurbits. S. cepivorum – only affects onions, garlic and related Alliums (shallots; spring onions; leeks). |
S. rolfsii – Lower stem and root rots; coarse threads of white fungal growth surround the diseased areas; small brown fungal resting bodies. S. cepivorum – Yellowing and wilting; fluffy fungal growth containing black sclerotia forms at the bases of bulbs.
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Fusarium wilts and rots (Various Fusarium species including F. solani and F. oxysporum) |
Warm to hot weather. | Wide host range including: brassicas; carrots; cucurbits;onions; spring onions; potato; tomato; herbs; peas; beans. | Causes severe root and crown rots or wilt diseases by attacking roots and basal stems; cucurbit fruit and potato tubers can be affected in storage. |
Botrytis rots – for example Grey mould (Botrytis cinerea) |
Cool, wet weather. | Celery; lettuce; beans; brassicas; cucumber; capsicum; tomato. | Softening of plant tissues in the presence of grey fungal growth. |
Anthracnose (Colletotrichum spp. except for in lettuce – Microdochium panattonianum) |
Cool, wet conditions. | Wide range of crops including: lettuce; celery; beans; cucurbits; tomato, capsicum; potato; globe artichoke. | Typical symptoms begin with sunken and water-soaked spots appearing on leaves, stems and/or fruit. |
Rhizoctonia rots (Rhizoctonia solani) – range of common names, e.g. Bottom rot (lettuce) and Wire stem Brassicas)
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Warm, humid weather; can survive for long periods in the soil in the absence of a host plant. | Wide host range including: lettuce; potato; brassicas;beans; peas; beets; carrots; capsicum; tomato; cucurbits. | Range of symptoms depending on the crop being grown but can affect roots, leaves, stems, tubers and fruit; plants wilt and may collapse and die. |
Damping-off (Pythium, Rhizoctonia, Phytophthora, Fusarium or Aphanomyces)
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Occurs under cold, wet soil conditions; shore flies and fungus gnats can spread Pythium and Fusarium. |
Many vegetable crops including: leafy vegetables;brassicas; carrots; beetroot; cucurbits, eggplant; tomato;coriander; spring onions; beans | Young seedlings have necrotic stems or roots; seedlings die or show a reduction in growth. |
Cavity spot (Pythium sulcatum) |
Growing carrots after carrots; acidic soil; not harvesting carrots as soon as they reach marketable size. |
Carrots. | Cavity spots are small elliptical lesions often surrounded by a yellow halo. |
Tuber diseases (Various species) |
Potato and sweet potato. |
Potato tubers may be infected with superficial skin diseases, such as common scabs, powdery scab, and Rhizoctonia. Sweetpotatoes may be infected by scurf.
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Rusts (several species, e.g. Puccinia sorghi – sweet corn; Uromyces appendiculatus – beans; Puccinia allii – spring onions). |
Wind can spread spores great distances; favored by low rainfall, 100% relative humidity and cool to mild temperatures. | Sweet corn; beans; onions; spring onions; beets; celery; silverbeet; endive. |
Small, red or reddish-brown pustules that form on the underside of the leaves and sometimes on the pods as well; dusty reddish-brown spores released from pustules (may be black in cold weather).
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Black root rot (Different species on different vegetable crops) |
Cool soil temperatures; high soil moisture. | Lettuce; beans; cucurbits. | Blackening of roots; stunted plants; plants may die. |