blight

A serious disease which affects first the top leaves, with brown blotches in late summer, in warm, wet weather. More often than not, the fungus then spreads down the stems killing the foliage.


Symptoms

  • Brown spots which begin on upper leaves
  • Brown patches on tubers, firm at first but quickly turning to a soft, wet rot
cane spot

This fungal disease can be a serious problem in raspberries, hybrid berries and blackberries. Spots first appear in May and June then travel up the plant. The purple spots grow like fairy rings, leaving dead cells in a depression as they expand. Infections which overwinter on last years' canes will infect the following year's new growth unless checked.


Symptoms

  • Purple spots on lower parts of stems
  • Spots grow and spread upwards, leaving silvery-white depressions with purple margins - typically elliptical on stems and circular on leaves.
  • Leaves and fruit may be distorted and leaves may die back
  • In severe cases, plant may die
chocolate spot

As the name suggests, this fungus (and, less commonly, its relative Botrytis cinerea) causes small red/brown spots on leaves and streaks on stems. The disease progresses rapidly in damp conditions, when the spots enlarge and spores are released, spreading the infection to other plants. In serious cases, the spots merge and darken, and may cause stems to collapse and even kill the plant.


Symptoms

  • Red/brown brown spots, sometimes with a white/grey centre as they expand, on all parts of the plant
  • Shrivelled and dropped leaves and flowers
  • In severe cases, collapsed stems
club root

A serious disease which infects the roots, causing swelling and distortion as it creates a gall from which spores are eventually released. This fungus-like organism, related to powdery scab in potatoes, leads to poor growth and even death.


Symptoms

  • Poor growth
  • Foliage wilts in dry weather, recovering when wet
  • Foliage discoloured - purple tinge
  • Roots swollen and distorted
crown rot

The collective name for a variety of fungi and bacteria which attack the base of the leaves and the crown, where new leaves are formed.


Symptoms

  • Soft brown/black areas around the crown
  • Yellowing leaves
  • Weak/collapsing stalks
cucumber mosaic virus
This serious viral disease affects, and may even kill, a surprising number of different vegetables and flowers. It is usually spread by aphids but can also be spread by contact. It survives between crops in other hosts, usually weeds.

Symptoms

  • Distinctive light green/yellow and dark green mosaic pattern on leaves
  • Leaves may curl downwards
  • Fruit become misshapen, knobbly and pale, even white
  • Growth is stunted and the plant may eventually die
downy mildew
A range of species of fungus, each of which may only have a limited range of hosts, but which manage to infect a very wide range of edible and ornamental plants. The fungus spreads by airborne spores and thrives in conditions when leaves are damp. It is most serious on lettuce, where it can kill whole leaves, and onions, where the leaves die back and the bulbs can rot, preventing storage.

Symptoms

  • Discoloured, often yellow (but also brown, purple or pale green) patches on the surface of leaves. Infections on other parts of plants are less common but pea pods are sometimes affected
  • Corresponding grey (lettuce), white (brassicas) or purple (legumes) mouldy/furry patch on the underside.
  • Weak or stunted growth
  • Leaf die-back or fall
grey mould
This fungus thrives in cool, damp and over-crowded or badly-ventilated conditions. Almost any crop can be affected. The fungus generally enters through existing wounds and healthy plants are less likely to be affected.

Symptoms

  • Generally start with a brown rot followed by the grey fluffy mould which gives it its common name
  • Lettuce commonly show a reddish-brown colour and the leaves may break away from the roots
  • Tomatoes may show spots on the surface
parsnip canker
A number of different species of soil fungus infect damaged or stressed parsnips - damage can be physical, such as hoeing, or as a result of pests such as carrot fly. Stress can result from poor drainage, acidic soil, fresh manure or sowing too early. Bigger roots seem to be more susceptible than smaller ones. The disease normally begins on the shoulders of the root and, although the root is largely still edible, it does prevent storage.

Symptoms

  • Rough orange-brown patches on roots and spots on the leaves and/or just black or purplish rot
powdery mildew
Powdery mildew is a collective name for a group of fungi that infect a very wide variety of plants - a single species only infects a limited number of crops. It tends to occur when the air is damp but the soil is dry. The whole plant is weakened and leaves and flowers may wither and drop, or growth may be distorted.

Symptoms

  • Almost any part can be affected with a white powdery coating which may spread
  • Upper surfaces of leaves are often particularly affected.
  • In gooseberries (American Gooseberry Mildew, Sphaerotheca mors-uvae), the fruit are covered with a brown furry coating, which becomes a bit like felt with age. However, the fruit beneath are still edible if it is scraped off.
rust
This fungus lives within the leaf, developing the slot-shaped, raised pustules that give its name from summer onwards. There tend to be leeks (and other alliums) in the ground for much of the year, so the airborne spores it releases can usually find a living host to spread to. Humid conditions and dry soils seem to encouage infection. Although it does affect vigour, it is not usually too serious in vegetables as it has very little effect on the edible parts of the plant.

Symptoms

  • Rusty (yellow, brown or orange) spots and blotches on leaves
  • In severe infections, leaves can shrivel and die
scab, common

This is a bacterial disease that favours high pH (>5.2) and dry conditions. It overwinters in the soil or in tubers which were missed at harvest, infecting new tubers as they grow. The plant reacts with a corky scab which eventually bursts then regrows, leading to the characteristic raised and layered appearance of the scabs produced. Common scab is usually less serious than powdery scab, the damage being largely cosmetic - tubers are still completely edible - although in severe cases, where the skin cracks, it can affect storage.



Symptoms

  • Raised rough corky brown patches on tubers
scab, powdery
Powdery scab is caused by a single-celled organism related to amoeba. Transmission from tuber to tuber involves a swimming stage so wet conditions favour infection. While unsightly, the potatoes are perfectly edible after peeling. However, secondary infections can enter the lesions and reduce storage life.

Symptoms

  • Initially, small purple/brown marks
  • These develop into irregular depressions with raised edges. These pustules contain the powdery/dusty spores which go on to infect other tubers
sclerotinia fungus (white mould)
This genus of fungi includes Sclerotinia sclerotiorum, Sclerotinia minor, and Sclerotinia trifoliorum which between them can infect most of the crops grown on allotments. They get their common name from the cotton wool-like mould which attacks the above-ground parts of the plant, often killing it. As the fungus grows it may form small (2-5mm by up to 25mm) blackish sclerotia. These hard little irregularly shaped pods are what allows the fungus to survive between crops. When conditions are right, they either produce miniture toadstool-like structures which release millions of spores, or begin sending out new cotton wool-like growth to infect nearby plants. The fungus prefers cool, damp conditions which help the spores to germinate and symptoms generally don't appear until summer.

Symptoms

  • Initially, wet, slimy patches appear on particularly near the base of the stem
  • Plants may suddenly wilt and collapse
  • Lower leaves turn brown and soggy
  • Cotton wool like growth on any aerial part of the plant
  • Affected parts may develop a bleached and/or shredded appearance
violet root rot
This fungal root infection (also known Rhizoctinia spp.) is probably the most serious disease of asparagus but also affects a wide range of other crops. It spreads slowly from plant to plant via its mycelium (mat of filaments). It can survive for years in the soil as irregular black lumps known as sclerotia. It can also survive in a range of weed species, including bindweed, dandelion, dock, shepher's purse and nettle. It tends to affect older plants more severely and is more serious in warmer conditions. Its affects are not usually visible until later in the summer. Affected root crops cannot be stored but may still be edible once peeled as the fungus does not penetrate far.

Symptoms

  • Slowly spreading patches of crop which yellow, wilt and may die
  • Soil clings to the surface of root crops when lifted - they develop a leathery skin texture
  • Only when you lift the root might you see the fine violet/purple mat of threads which gives this disease its name
  • Roots may also develop a brownish rot as secondary infections enter the wounds created by the fungus
white rot
Also known as allium root rot, this is fungal disease which can spread from plant to plant down a row via its mycelium of white filaments. It also forms black sclerotia, or storage structures, which can lie dormant in the soil for years until they detect chemicals exuded from allium species in the the cool, moist conditions that it requires. Leeks are generally less severely affected than onions and garlic. Warm, dry conditions will slow the spread of the disease.

Symptoms

  • Yellow, wilting foliage which then dies
  • White mould is usually visible on the base of the plants but it can spread to cover the whole bulb
  • The mould is sometimes dotted with the poppy seed-sized black sclerotia
wilt
These two fungi both hamper the plant's ability to transport water from roots to leaves by clogging the xylem vessels which transport water or as the plant blocks them itself in an attempt to reduce the spread of the disease.

Symptoms

  • Symptoms generally don't appear until later in the growing season as it takes a while for damage to become apparent
  • It begins with isolated patches of leaves which, at least initially, begin to wilt during the day but may recover at night when they need to suck up less water from the roots.
  • However, eventually leaves may yellow and die
  • Potatoes and tomatoes may survive but with reduced yields, peppers and aubergines tend to collapse as rots sets in at the base of the stem.
  • If you cut through the stem above ground level, escpecially near where the leaves join the stem, you may see light or dark brown staining. Similar staining can be seen in potato tubers