Fungal Disease

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.

 

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.

 

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.

 

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.

 

 
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.

 

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).

 

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.

 

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) 
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)    

 

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.

 

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).

 

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.