Disease fungi and bacteria can cause significant damage to plants. This document provides an overview of common bacterial and fungal diseases that affect vegetables. It describes key symptoms, factors that promote spread, and crops affected for diseases such as bacterial leaf spot, bacterial soft rot, downy mildew, powdery mildew, clubroot, fusarium wilt, botrytis gray mold, and rhizoctonia root rot. Management strategies aim to prevent or limit pathogen development through practices like using pathogen-free seeds and crop rotation.

1. Plant Diseases
Disease fungi take their energy from the plants on which they live. They are responsible for a great deal
of damage and are characterized by wilting, scabs, moldy coatings, rusts, blotches and rotted tissue. This
page is designed to help identify some of the more common plant diseases and provides earth-friendly
solutions for combatting them.
Bacterial diseases - an overview:
 Pathogenic bacteria cause many serious diseases of vegetables. They do not penetrate directly into
plant tissue but need to enter through wounds or natural plant openings. Wounds can result from
damage by insects, other pathogens, and tools during operations such as pruning and picking.
Bacteria only become active and cause problems when factors are conducive for them to multiply.
They are able to multiply quickly. Some factors conducive to infection include: high humidity;
crowding; poor air circulation; plant stress caused by over-watering, under-watering, or irregular
watering; poor soil health; and deficient or excess nutrients.
 Bacterial organisms can survive in the soil and crop debris, and in seeds and other plant parts. Weeds
can act as reservoirs for bacterial diseases. Bacteria spread in infected seed, propagating material and
crop residues, through water splash and wind-driven rain, and on contaminated equipment and
workers' hands. Overhead irrigation favours the spread of bacterial diseases.
 Warm, wet weather favours the development of some bacterial diseases, while others are favoured by
cool, wet conditions. Development is often arrested by hot, dry conditions, but may exacerbate
symptoms once the plant is already infected (e.g. Bacterial wilt caused by Ralstonia solanacearum).
Sometimes bacterial ooze may be seen on diseased plant tissue.
 However, symptoms of bacterial diseases may be confused with those caused by fungal diseases. It is
important to have diseased tissue examined in a plant diagnostics laboratory to confirm the type of
pathogen causing the disease.Different strains (pathovars – pv.) of bacterial diseases affect different
types of vegetable crops or cause different diseases in the same crop. For example: Xanthomonas
campestris pv. vitians in lettuce and X. campestris pv. cucurbitae in cucurbits; and in beans
Psuedomonas syringae pv. syringae and P. syringae pv. phaseolicola cause different diseases.
Common bacterial diseases and crops affected:
Disease
Factors
conducive to
spread
Crops affected
Symptoms
1 Black rot
(Xanthomonas
campestris pv.
campestris)
Warm, wet
conditions.
Brassicas.
Light-brown to yellow V-shaped lesions on
the leaf, which become brittle and dry with
age. Vein blackening with the necrotic
area.
2
Bacterial
canker
(Clavibacter
michiganensis
pv.
michiganensis)
Moderate
temperatures
and high
humidity.
Tomato; capsicum;
chilli
Seedlings may die and older plants may
wilt and die eventually. Older plants have
leaves that turn yellow and wilt only on
one side. Cankers on stems and fruit.
Tissue inside stems becomes discoloured.
3 Bacterial soft
rot
Warm, wet
conditions.
Wide range of
vegetables,
Wet, slimy, soft rot that affects any part of
vegetable crops including heads, curds,

2. (Pseudomonas
spp., Erwinia
spp.)
including lettuce;
brassicas; cucurbits;
tomato; capsicum;
potato; sweetpotato;
carrots; herbs.
edible roots, stems and leaves. May have a
disagreeable odour.
4
Bacterial leaf
spot/Bacterial
spot
(Xanthomonas
campestris -
various strains)
Overhead
irrigation and
windy
conditions.
Range of vegetables
including lettuce;
cucurbits; tomato;
capsicum.
Lettuce – Large brown to black circular
areas that start as small translucent spots;
usually on outer leaves. Tomatoes and
capsicums – Greasy spots on leaves and
stems that go from tan to black; fruit may
have circular spots with central scab.
Cucurbits – Begin as small water-
soaked/greasy spots on underside of leaves
with corresponding yellowing on upper
side; fruit may produce light-brown ooze
from water-soaked markings.
5
Bacterial wilt
(Ralstonia
solanacearum)
High
temperatures,
high soil
moisture and
poor drainage.
Once infection
has occurred,
severity of
symptoms is
increased with
hot and dry
conditions,
which facilitate
wilting.
Potato; tomato;
capsicum; eggplant.
Wilting, yellowing and stunting of plants
but they may wilt rapidly and die without
any spotting or yellowing; vascular tissue
appears brown and water-soaked; a white
ooze appears when pressure is applied to
affected tubers or stems.
6
Bacterial leaf
spot/Bacterial
spot/Bacterial
blight
(Pseudomonas
syringae -
various strains)
Long periods of
leaf wetness.
Beet; spring onions;
leeks; rocket;
coriander.
Beet – irregular, round leaf spots with a
grey centre surrounded by a purple margin.
Spring onions/shallots – pale yellow to
light-brown lesions with a water-soaked
appearance around the margins; outer
leaves wither and die and youngest leaf
turns lemon to light-green. Leeks – brown
streaking on the shank.
7
Bacterial blight
(Pseudomonas
syringae pv.
pisi)
Cool, wet,
windy
conditions.
Peas.
Water-soaked spots on leaves and stipules
which become dark-brown and papery in
warm weather or black in cool weather.
Water-soaked spots on pods that become
sunken and dark-brown.

3. 8
Bacterial speck
(Pseudomonas
syringae pv.
tomato)
Humidity and
overhead
irrigation.
Tomato.
Small dark spots surrounded by a yellow
halo on leaves; dark raised specks on fruit.
9
Bacterial
brown spot
(Pseudomonas
syringae pv.
syringae)
Cool, wet,
windy
conditions.
Beans.
Tan to reddish-brown spots on leaves.
Water-soaked spots on pods which enlarge
and become sunken and tan with
distinctive reddish-brown margins.
Other bacterial diseases of vegetables include:
 Peppery leaf spot – Pseudomonas syringae pv. maculicola (brassicas)
 Varnish spot – Pseudomonas spp. (lettuce)
 Corky root – Rhizomonas suberifaciens (lettuce);
 Angular leaf spot – P. syringae pv. lachrymans (cucurbits);
 Bacterial pith necrosis – Pseudomonas corrugata and other bacteria (tomatoes);
 Common bacterial blight – Xanthomonas campestris pv. phaseoli (beans)
 Halo blight – Pseudomonas syringae pv. phaseolicola (beans)
 Black leg – Erwinia carotovora pv. atroseptica (potatoes).
Management:
Disease management strategies aim to favour the host plant’s growth and development while attacking
vulnerable stages in the lifecycle of the pathogen to prevent or restrict its development. The key means of
bacterial disease management include:
 Exclusion or eradication of the pathogen (quarantine and use of pathogen-tested seeds and
propagated materials)
 Use of clean transplants
 Monitor crops regularly and use predictive models
 Reduce the pathogen levels by crop rotation
 Remove weeds and incorporate crop residues that can host the disease
 Protect the host plant by using resistant plant varieties
 Minimise mechanical damage to crops and damage by insect pests
 Avoid working in crops when they are wet
 Spray with a registered bactericide when weather conditions favour disease development to
prevent infection
 Understand chemical resistance and rotation of chemical groups
 If the plants are already infected, isolate and destroy them and prune infected leaves, but avoid
excessive handling of diseased plants; if the disease is systemic and has spread throughout the
plant, the plant cannot recover and should be destroyed (burning or burying)
 Use correct temperatures and packing conditions during transport and storage.

4. Fungal diseases - an overview:
Fungi constitute the largest number of plant pathogens and are responsible for a range of serious plant
diseases. Most vegetable diseases are caused by fungi. They damage plants by killing cells and/or causing
plant stress. Sources of fungal infections are infected seed, soil, crop debris, nearby crops and weeds.
Fungi are spread by wind and water splash, and through the movement of contaminated soil, animals,
workers, machinery, tools, seedlings and other plant material. They enter plants through natural openings
such as stomata and through wounds caused by pruning, harvesting, hail, insects, other diseases, and
mechanical damage.
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, e.g. Clubroot (Plasmodiophora brassicae)
in brassicas, Leaf blight (Alternaria dauci) in carrots, and Red root complex in beans.
Common fungal diseases and crops affected:
Disease
Factors
conducive to
spread
Crops affected
Symptoms
1
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.
2
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.
3
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.

5. 4
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.
5
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.
6
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.
7
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.
8
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.
9 Botrytis rots –
for example
Cool, wet
weather.
Celery; lettuce;
beans; brassicas;
Softening of plant tissues in the
presence of grey fungal growth.

6. Grey mould
(Botrytis
cinerea)
cucumber;
capsicum; tomato.
10 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.
11 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.
12
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.
13
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.
14
Tuber diseases
(Various
species)
Potato and
sweetpotato.
Potato tubers may be infected with
superficial skin diseases, such as
common scabs, powdery scab, and
Rhizoctonia. Sweetpotatoes may be
infected by scurf.
15 Rusts (several
species, e.g.
Puccinia sorghi
– sweet corn;
Uromyces
appendiculatus –
beans; Puccinia
allii – spring
onions).
Wind can
spread spores
great distances;
favoured 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).
16 Black root rot
(Different
species on
Cool soil
temperatures;
high soil
Lettuce; beans;
cucurbits.
Blackening of roots; stunted plants;
plants may die.

7. different
vegetable crops)
moisture.
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 – Leptosphaeria 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).
Management:
Integrated Crop Protection (ICP) or the Integrated Pest Management (IPM) approach has achieved
success in the management of the fungal diseases. ICP considers the production system as a whole,
including all pests and the importance of soil health. It requires a good understanding of the fungi; the
periods during which the crops are susceptible; and the influence of environmental conditions.
Tips for managing fungal diseases include:
 Understand the lifecycles, survival mechanisms, and conducive environmental conditions for
fungi
 Be committed to farm sanitation – clean up your farm and remove all weeds, crop debris, and
volunteer hosts
 Use resistant or tolerant varieties
 Use clean transplants and seed (and seed treatments)
 Monitor weather conditions (particularly temperature, humidity, and leaf wetness)
 Have knowledge of relevant disease prediction models
 Understand the implications for irrigation timing and minimise free moisture and high humidity
periods (e.g. irrigating at around 4 am rather than at dusk, not irrigating during peak periods of
spore release)
 Appropriate crop rotations (long rotations with non-host crops may be necessary)
 Avoid heavily infested blocks by testing soil for soilborne diseases prior to planting
 Monitor crops regularly and be able to detect early symptoms on your crop
 Amend and manage soil to disadvantage the fungi (some fungal diseases can survive in the soil
for 30 years or more)
 Minimise ways in which the disease can spread on-farm – remove and destroy sick plants when
symptoms first show
 Understand the influence of planting time, plant spacing and overlapping crops
 Apply preventative fungicides based on weather conditions
 Understand fungicide resistance and rotation of chemical groups.