Plant Diseases, Disorders and Viruses

Diseases are the malfunctions of plants caused mainly by four groups of pathogen. Fungi, bacteria, Viruses and fungus-like organisms. Also included in this page are disorders caused by imbalances in the plant and environmental conditions.
It is always helpful to know what is causing the malfunction of the plant as Fungi, bacteria and viruses are contacted, treated and have different effects upon the plant.
There is a great deal of diversity even within the disease itself, for example Rust can occur on roses, beans and many other species but is often specific to its host, e.g. broad bean rust cannot infect roses. In addition rose rust has only one host throughout the year whilst some have alternating hosts meaning treating one plant may be of little benefit.
If you believe you have one of these diseases then clicking the name above the photo will take you to the specific site with instructions and tips of how to cure your specific problem, and don't worry despite the mass of problems that may go wrong with plants, most are treatable or even entirely avoidable with good cultural practise!
A/N: will add a jargon dictionary soon (Soon: Pronounciation: "soo- n" Definition: 10 months)
Warning: This page has not been spell checked yet, you will probably only understand one word in ten
Dispite all effort being made to provide images, many diseases have different expressions on different plants, if you cant identify it then just bring it in and we will do our best. Try searching for what the problem looks like and you have a good chance of finding it.
Armillaria (Honey Fungus)

Armillaria is a name that sends shivers down the spine of many seasoned gardeners, it was declared by the RHS as the most damaging pathogen in 2010. There are 7 species found in the UK and of those only 4 have been found in gardens. Of those 4 only two are likely to cause damage to plants, A. Mellea and A. Solidipes, The second of which mostly attacks softwood conifers.
Even within A. Mellea there is a massive variation of colour and fruiting body however there are a few constant identifiers. Armillaria always has a white spore print, It produces rhizomorphs (bootlace like structures for spreading throughout the soil) and it produces under the bark of an infected tree, creamy white mycelium that turns brown-black after exposure to air and smells strongly of mushrooms.
Armillaria is actually a very weak pathogen and it can often struggle to infect a healthy plant however if the plant is stressed then it can be very dangerous. Plants may begin to flower profusely and decline.
This fungus has the ability to feed off dead wood (as a saprophyte) as well as living wood (as a parasite) meaning after it has killed the plant it can then use it as fuel to reach another underground.
After Armillaria is detected then vulnerable plants should be removed and replaced by resistant plants (there is a list in the specific page). The one upside is that these mushrooms are prized for their taste and health benefits.
(WARNING: Some species can cause sickness if eaten with alcohol and other poisonous mushrooms may be mistaken for Armillaria!)
Plants attacked: Most woody perennials.
Plants that are highly vulnerable:
Acer, Birch, Cedar, Holly, Pear, Apple, Current, Rose, Willow and viburnum
Plants that are strongly resistant:
Box, Juniper, Berberis, Drimys, Erica, Abelia, Abutilon, Kerris, Passion flower.
Even strongly resistant plants CAN be infected if they are stressed or otherwise weakened.

Algae is largely non-pathogenic however it can be unsightly and can potentially cause damage and be a health hazard.
Algal growth may happen on lawns in wet poorly drained areas and paths.
The best way to deal with it is to use a path cleaner or on the lawn a moss killer containing iron sulphate. Avoid walking on compacted ground.
Problem areas: Paving and lawns

Anthracnose is very often confused with other diseases such as bacterial canker, shothole or fungal leaf spot. It affects a wide range of plants with a wide range of lethality however most forms thrive in cool moist conditions so often appear in the autumn.
Most infections start as leaf damage and can be mistaken for shothole or leaf spot whilst damage is minimal. The next visual sign is when lesions (often rust red) develop which sink forming cankers
Plants Attacked: (fruit): Raspberries (esp red), blackberries
Plants Attacked (ornamental): Willow, Rose, Ash, Sycamore, Turf, Others
Bulb rot (narcissus basal rot)

Narcissus basal rot is a very common problem with daffodils and it is important to check before buying and planting that the bulb is solid and firm (Compression with fingers should not leave an indentation). Any infected bulbs must not be stored and should be disposed of immediately. Upon cutting a bulb open there will be a dark grey/black segment of rotted bulb originating from the basal plate.
As with most pathogens this fungi is most prone to attacking weakened plants, such as damaged, cracked or damp bulbs. This fungus is very common in the soil surface. One form of this is called neck rot, It occurs when the bulb, after flowering is attacked through the flower head and thus starts at the top of the bulb. When storing bulbs dusting with sulphur may provide some benefit.
Affected Plants:
Narcissi (daffodils)
Botrytis cinerea (grey mould)

Also known as Grey Mould, Botrytis is very common and many millions of spores are in the air we breathe. It is most often seen as a woolly grey mould often forming on soft fruit such as strawberries or the inside of plants such as cyclamen. It is enhanced by high humidity and poor air flow.
Affected plants:
Many, Cyclamen, pansies, primroses (largely bedding)
Fruit plants: Strawberries, Gooseberries, Raspberries (soft fruit)
Blight (ornamental)

Blight is a very general term for a multitude of diseases both bacterial and fungal. It is commonly seen as blackening of woody tissue and necrosis in leaves leading to high defoliation.
Often the initial sign of blight are lesions forming on the underside of leaves. Blight can also be a gateway infection enabling various Cankers if the plant survives. With any form of blight it is best to remove the plant (and in hedging remove the two closest plants), remove and burn any fallen leaves and preferably plant another similar plant of a different species.
If caught early the plant may be saveable if the infected material is pruned off before the infection reaches the roots.
For Bacterial blights then a copper based chemical may be used.
Affected plants:
Almost anything esp.
Box, roses,
Blight (edible)

Blight also affects many herbaceous edible plants, as with ornamental blight there are a great many causes from both fungal and bacterial sources. The most common blights to a gardener would be tomato and potato blight which are well known for devastating crops, however blights such as apple/pear fireblight may destroy an entire orchard within one season! For tomatoes/potatoes then a copper compound as found  Bordeaux mixture and Bayer fruit + veg control. With annual plants the focus is on reducing the effect rather than completely stopping the disease.
Affected Plants
: Tomatoes, Potatoes, topfruit ext.
See also: Tarspot

Blackspot is a fungus that is renowned for its effects on roses but can be found on many plants. This fungus favours damp warm conditions and requires a certain period of standing water to establish. Left alone it will begin as pale yellow/green spots on the leaf which turn black and spread as the cells are further infected. Interestingly the blackspot is often surrounded by a halo of darker green as it releases auxins in an attempt to keep the leaf alive and prevent dropping. When held up to a light, with mature blackspot then mycelium can be seen as thread like patterns in the dead tissue. A spray of Myclobutanil is effective as a preventative and can be used to control and slowly eradicate it, however plant hygiene will help reduce infections (see specific page for details)
Tarspot by contrast will not produce the green halo.
Affected Plants: Roses (in  particular), Many other plants
Blossom end rot

Blossom end rot is one of the common problems with tomatoes where the end that was formally the blossom turns dark and hard, often in a circle. This can range from a 5p to a 10p size and makes the fruit inedible. It is generally caused by inconsistent watering although any calcium deficiency greatly exacerbates the problem.
Affected Plants: Tomatoes

Bolting is simply the act of a plant flowering and therefore reducing its favourable qualities, for example some herbs become bitter and plant vigour is reduced in strength. For the majority of vegetative plants then removing flowers is important as they weaken and may render the entire plant useless. In an extreme form of bolting, the flowering of some plants such as the Venus fly trap and the century plant actually kills them.
Affected Plants:
Rocket and other salad greens, Certain
Some Root / Bulb plants:
Onions, Garlic, Carrots.
Brown Rot (fruit)

Brown rot is a very common rot often affecting apples where the fruit appears to have shrunk, withered and browned, this starts with small brown spots developing on the fruit in humid conditions. Often white spots may be visible and the fruit appears to have been mummified. The infected fruit is of course not edible and care should be taken to remove the fruit as soon as possible as contact may spread the pathogen.
Affected plants:
Apples, pears, cheries, assorted fruit.

Canker is a very nebulous term when it comes to plant pathology, It is often used to describe a lesion where limited death of plant tissue has occurred however using by using this definition would include many types of rot and Anthracnose. True Cankers occur only on woody plants and are caused by the death of the cambion meristem (responsible for the outward growth of a plant) therefore in most cases creating an area where bark can never be regenerated. The lesions generally increase over the winter months when the plant is dormant and unable to protect itself but reduces over the summer as new cambium is formed.
After the cambium has been destroyed and the effect has extended to girdle the branch then all shoots beyond that point die. This form of dieback is distinct from whole tree dieback which is often a symptom of root rot (Armillaria) or a physiological cause such as severe waterlogging or drought.
If a tree is afflicted with canker the best course of action is to immediately prune the tree to 30cm from the infection and in the case of a fungal canker to treat with a fungicide containing a copper compound. Of utmost importance the blade should be sterilised after every cut!
The majority of cankers apart from Apple, Pear, Cherry and Plum will cause the gradual death of the plant and can be left until their decline is obvious.
Most Affected Plants Fungal:
Apple, Pear, Ash, Beech, Box, Clematis,
Most Affected Plants Bacterial:
Ash, Plum, Cherry,
Horse Chestnut (bleeding)
Coral Spot

Coral Spot is a common and widespread fungus which is interesting as it can feed off both dead and living wood, (saprophytic and parasitic) It is a very poor pathogen often and is most effective when it can attack a plant through dead material and then transfer over to living tissue.
As a saprophyte they produce the namesake coral coloured spots (similar red pustules are sometimes formed in spring). Upon infecting the living tissue it chokes up the water transporting tissue (the xylem) and produces a wilt effect.
Treatment is very difficult and the best method is to observe plants for any signs of the saprophytic assault and immediately prune back infected growth hard and destroy any infected or dead tissue.
Affected Plants: Most Woody plants, Rarely conifers

Clemitis Wilt

Clemitis wilt is one of the boogymen of gardening, whist it is prollific and destructive. It is only common on the large flowering hybrid cultivars and only rarely infects the species clemitis. In reality more infections can be attributed to enviromental control and poor watering practice.

To identify clemitis wilt, look for blackening of foliage and stems split with black inside, wilting and shoots emerging from underground.

It is this last symptom that is most interesting, although there is no cure chemicly for wilt, clemitis are very vigouous plants and they are rarely infected below the ground.

It is ideal when dealing with the succeptable cultivars, to plant them an inch or two deeper than the soil line in a pot and if they become infected cut them to the ground, they should have a reasonable chance of regeneration uninfected.

As with most diseases, reinfection can be greatly reduced by removeing all infected and dead plant material.

Affected Plants: Clemitis (esp. large flowered cultivars)

Clubroot is one of the untreatable diseases in the garden, it attacks the roots of cruciferous plants such as wallflowers, sprouts and broccoli. It is encouraged by an acidic damp soil but a heavily limed soil is inimical to it and it is most prevalent on later growing crops.
With an early infection it may cause the plant to wilt on a hot day and to recover later at night and as the infection takes hold the plant may be stunted and develop a purple tint. As the disease progresses the roots swell and become distorted forming either one or many large galls. These galls are noted to be susceptible to rots and often decay greatly.
There is no chemical treatment for the plant and most infections are caused by contamination either from plant roots or infected soil. If clubroot is detected then immediately dig up the infected plant and as much root material as possible then burn it.
There are several methods of prevention which will be detailed in the specific page
Affected Plants: Crucifers
Resistant: Radishes
Crown Gall

Crown Gall is a bacterial infection that makes tumour like galls form most often on the roots of a plant. These galls reduce the effectiveness of a plants roots but do little damage otherwise, These effects are most often noticed on fruiting plants due to the high requirement for nutrients and water, often causing a reduced yield.
Treatment is almost non-existent however some claims are made that sulphur is effective at control. Best practise would be to minimise wounds on the plant as that is how the plant most commonly becomes inoculated. In herbaceous plants the galls often collapse and are rotted away, In such cases it may be ideal to grow non-susceptible plants for 1-2 years.
Affected plants: Many
Downy Mildew
See also: Powdery Mildew

Downy mildew is a disease with some similarity to powdery mildew in appearance however absolutely no relation to it in treatment and it is only tenuously classed as a fungus.
Downy mildew prefers a moist damp condition and is generaly more destructive than its powdery counterpart.
Affected Plants: Widespread
Damping Off

Damping Off is a disease that targets seedlings and is the biggest killer of plants in the UK according to the RHS. It is mostly prevelent when plants are grown under glass and it is worst when the seedling is growing slowly such as in early spring with little light or warmth.
Cheshunt compound or many other fungicides containing copper make a good preventative drench however most importantly ventilation should be supplied as a high humidity favors this disease greatly.
Affected Plants:
Most Seedlings
Deficiency (Nitrogen)

Nitrogen Deficiancy is a common problem with plants that are not fed, in particular vigourus vegatitive plants. affected plants will be spindely with yellow stems or leaves. Sometimes the entire leaf turns yellow or there may be interveinal patches often tinted with red.
To correct, almost any feed will do and is normaly the best option but for pure nitrogen, Sulphate of Ammonia is incredably concentraited and cost efficiant. To ensure long term nitrogen, useing green manure plants or mulching in nitrogen rich materials (ie paper, grass, manure) helps to provide a constant supplement.
Symptoms normaly expressed on lower leaves
Affected Plants:
All but legumes
Deficiency (Phosphorus)

Phosphorus is used in the plant for respiration, root growth and has been linked to resistance against rust and other vascular diseases. Plants exsibit slow growth, dull yellow or purple leaves and poor root growth.
Deficiancy in Phosphorus is uncommon but it can occure in very heavy soil or if numerous root crop plants have been repeatedly grown in close sucsession.
Superposphate gives an immediate boost and bonemeal can be used for a slow acting long term benifit.
As defficiancy is rare in soil grown plants outside of the most sandy soils, try to increase the warmth of the root zone by covering with black plastic as this can be another cause.
Always be carefull when applying phosphorus as it can have sevear effects on plants includeing toxicity and chlorosis via iron antagonisum.
Affected Plants:
Deficiency (Potassium)

Potassium is used by a plant for its fruiting, flowering and photosynthisis. Affected plants often display a scorched leaf edge and produce few flowers or fruits, they are often much more tender and sussceptable to cold damage.
Deficiancys are most likely on a loose or sandy soil as a clay soil is quite capeable of holding this nutriant.
Although tomato food is not a complete fertilizer it can be used to suplement the potash content of a plant as can sulphate of potash.
Warning: Overfeeding of potassium can cause magnesium deficiancy
Affected Plants:
Espcially Fruiting plants
Deficiency (Iron/Manganease)

Iron and Manganease deficiancys are both very simmilar in symptom and their use in the plant so it is most common to use a remady for both of them. Both of these nutriants are used in photosynthasis and therefore can cause interveinal yellowing (chlorosis) initially at the younger leaves which developes into chlorosis. In the case of manganease deficiancy the leaf may develop a metalic sheen before becoming necrotic. These symptoms are most common among ericacious plants, especily those which are planted in alkaline or limed soil.
Dispite the abundance of Iron in the earth it is often poorly acsessable as it oxidises rapidly into unuseable forms. Treat with Chelated Iron (Sequestrine)
Affected Plants:
Most common on Lime Hateing plants
Deficiency (Magnesium)

Magnesium deficiancys have symptoms very simmilar to Iron and the two are often confused, the key to distinguishing them is the plant and the origin of the chlorosis. As magnesium is a very mobile chemical it tends to migrate to younger leaves meaning chlorosis starts at the lower end of the plant affected leaves sometimes develop a red tint as well as often causeing leaf drop. Like Iron it has an important role in photosynthasis and a minour role in fruit production.
This deficiancy is greatly exacibated by over feeding of potassium as it is taken up in preferance over magnesium.
To treat magnesium deficiany quickly a foliar feed of epsom salts works well but for perenials, especily lime hateing it is important to find the root of the problem. often an incorect pH or an overdose of potassium.
Affected Plants:
Very common on tomatoes, grapes, roses and ericacious plants
Deficiency (Trace Elements)
Deficiancy is less common among the trace elements however it is none the less possable. On plants that show no sign of pest or disease damage and have not been exposed to extreems of cold or heat but are still suffering it is worth giveing a general feed of Vitax or Seaweed to supply some trace elements.
This is most common where the soil is restricted, sandy or plants are highly demanding. Examples of disorders caused or exacibated by this are bitterpip (boron) and blossom end rot (calcium). For more infomation Click Here
Affected Plants:
Dutch Elm Disease

Dutch Elm Disease is the newest epidemic to hit the UK (and mainland Europe) It is a truly devistateing disease that originated in asia and has spread to europe and america, where plants have no resistance to it. Over the last twenty years, this disease has wiped out an estimated 29 million (of 30 million) large Elms. This disease can be recognised by wilting (often patchy as some branches are affected before others) and diaognosed either peeling back the bark and looking for brown streeks or cutting liveing infected tissue and looking for brown rings. The tree should be destroyed upon infection.
Plants Affected:
Numerous forms of elm, especially English
Enviromental damage is more common than many people belive, it can be caused by many factors from too much light to not enough, cold wind and warm air, drought and waterlogging.
The best method to counteract this is to be well aware of the plants favoured conditions and to keep an eye on the weather.
Frost damage: The major problem
Frost damage is often charicterized by floppy foliage and damaged flowers, some plants will go black and others will appear to have wilted. This is exacibated by a windly location and plants in pots are more likely to have root complications as there is less soil to insulate them. Plants can be protected by the use of horticultural fleece or simply by bringing potted plants inside the house. In addition to the physical damage this causes, ice also locks up moisture in the soil meaning potted plants can sometimes become droughted in the winter.
Affected Plants:

Fireblight is the great foe of apples and pears, well known for devistaiting crops (wipeing out 95% of egypt's crop in 1985) If this disease is detected it should immediatly be reported to DEFRA plant health. Whilst it is best known for destroying orchards it is also prevailent on roses, hawthorns and cotoniastas makeing it a prevailent threat. Infection normaly occurs through lenticells, woulds or blossoms, This disease kills quickly and may destroy a plant in months. This is also the reason the Laxton's Superb pear is no longer sold.
Symptoms: Blossoms may wilt and diewhilst flowering, often forming a distincitve shepards hook. A bacterial Ooze may form, this is a very potent source of infection. Any cut wood may have a orange-brown foxy tint to it. May form Cancers.
Treatment: Only treat if this disease is noticed early, a badly infected plant will die and often cause further infection. Cut back the damaged branches/shoots of the plant and be sure to sterilize the blade of the cutting tool with either methalated spirits or Jeyes fluid. There is NO chemical control for this disease.
Defra contact:  planthealth(dot)info(at)defra(dot)gsi(dot)gov(dot)uk or
Affected Plants:
Apples, Pears, Hawthorns, Roses
Flower Breaking

This is most commonly known to effect tulips, however it also affects lillies, pellagoniums and other flowers, it has a truly amazing history, most well known for causeing colour breaking on tulips. Although this virus creates amazing plants it also weakens and eventually destroys the infected bulbs leading to the trajic loss of some of the most remarkable plants in the world, includeing one considered the most beautifull flower in the world, the legendary Semper augustus. As these are virus infections there is no cure for them and they are easily transmitted via cuttings.
Flower breaking viruses are not however restricted to tulips, they are also found on pelagoniums and doubtless many other plants. In effect though not physiologicly these are simmilar to mozaic/mottle viruses
Affected Plants:
Tulips, Pelagoniums, Others
Frost damage

Frost damage is often charicterized by floppy foliage and damaged flowers, some plants will go black and others will appear to have wilted. This is exacibated by a windly location and plants in pots are more likely to have root complications as there is less soil to insulate them.
Plants can be protected by the use of horticultural fleece or simply by bringing potted plants inside the house. In addition to the physical damage this causes, ice also locks up moisture in the soil meaning potted plants can sometimes become droughted in the winter.
Affected Plants:

Fasciation is an interesting disorder as the cause cannot be broken down into any main reason, bacterial infections may be a cause but many affected plants have no contagion, in general it is belived damage to the apical meristem is the root of the problem. Fasciation was named after the roman fasces. The affected plant is characterized by an elongation of the growing point of a plant perpendicular to the angle of growth resulting in a long flat ribbon of tissue sometimes to truly spectacular results.
This is not treatable however many plants are appreciated for their modified appearance and can be quite interesting, On some plants faciated growth can simply be pruned out.
Affected Plants:
Some plants have this natrually and some such as mesembrianthamums are especially prone to it

A Gall is a swelling or abnormality in the tissue of a plant that is caused by an outside organisum, often insect or fungi caused. These galls tend to do very little damage and are often a reaction to certain chemicals released by the source. There are hundreds possably thousands of different variants.
Affected Plants:
Many woody plants
Grey Mould

Grey Mould, also called Botrytis cinerea is a necrotrophic fungus (it first kills its host, then feeds on it) and is well known as a problem on many plants. Interestingly strains of it (noble rot) have been cultivated on grape vines to develoup sweet flavors for desert wines.
It is suppriseingly not over infectious and only becomes a dangerous disease when the plant is stressed or wounded in some way.
Affected Plants:
Most plants, particually cyclemen and other plants with poor air flow
Green Flower disease

Green flower disease is a clemitas specific disease that distorts the flower physicaly whilst leaveing it green. There is no cure, be sure to compare with green petal disorder below.
Affected Plants:
Green Petal Disorder
This is not to be mistaken for green flower disease, it is fairly common and often is more obvious in the first crop of flowers after the winter. The green colouration can be as little as a taint to a solid block of green, the important thing to look for is that the flower itself is not distorted.
Affected Plants:

Helebore Black Death

This disease is fairly recent and is extreamly destructive to helebores. It is characterised by black streaks and rings, stunting and death.

Not much is known about this virus and there are no controls, any infected plants should be dug up and destroyed, however there are few indications the virus is propigated via seed and a particually prized plant may be partially preserved in this way.

Affected Plants:


Honey Fungus
Attacked Plants: Almost all woody perennials
Affected Plants:
See Armillaria
Halo Blight

Halo blight is a blight of broad beans, first noticable as small pale spots on the leaves, these become dark brown sunken spots and in bad infections the tips of the leaves may turn yellow and defoliaton occurs. Sometimes in ideal conditions for infection, a white bacterial ooze may be seen. This can also infect pods causeing them to become unuseable.
This disease can be spread by seed or by water, If this disease is spotted, the plants infected should be destroyed to avoid ground contamination.
Affected Plants:
Peach Leaf Curl

This infection is extremely noticeable, Its namesake curling of the leaves is only the start. Infected leaves form red twisted blisters that look quite raw. These leaves may then produce the resting stage of the spore in white blooms.
Whilst this is happening the leaves will rapidly defoliate causing a reduction of growth and a low fruit count.
This disease only infects the plant at one stage in its life cycle, when buds are starting to burst. This requires a period of 12.5h at below 16* where the leaves are rained on. Therefore it is fairly easy to prevent infection of the leaves with a simple cover.
The spores are also treatable by copper from bourdeux mixture, applied fortnightly through January and february.
Because the disease only infects in the winter/spring, any fresh leaves that appear after defoliation will not be affected.
Affected Plants:
Peach, Necterines, Apricots and Almonds

Lichens are facinateing symbiotic bonds between algae and fungi, they are so closely bound that they often produce spores with both fungal and algae material (diaspores). They do not actually harm the plants however they may cause seeds to not germinate in the soil.
The only point of concern is that they are prone to growing on stable enviroments and this can indicate a lack of vigour.
Affected Plants:
Old trees or stonework
Leaf Roll

Leaf roll can be caused by a number of effects, this section covers enviromental and physiological ones rather than disease related.
Curling  is often caused by Dryness, Overheating and in particular pruneing in these conditions as it causes a great deal of water stress. In addition studies on tomatoes have shown a high nitrogen feed exacerbates this (as nutriants are found predominantly as salts)
To reduce or protect agaisnt curling, make sure that plants are watered and consider shadeing the area slightly if it has been a problem in the past.
Affected Plants:
Many, esp. tomatoes and other fruiting or high stress plants
 Leaf Roll

These diseases (and there are a few) can look very simmilar to physiological leaf curl and therefore care should be taken to diagnose the correct one.
Virus leaf curl generaly has other effects or is localised. Look for patches of yellow, mottleing or thickening on the leaves. If it is viral in nature then the best responce is to destroy the plant as it will rapidly spread to others in the local area.
Affected Plants:
Potatoes, Tomatoes
Grape Leaf Roll


Grape leaf roll is one of the most destructive forms of leaf roll, accounting for up to 60% crop failier. On red grapes the leaves go vivid red and cup as the outer edges curl in. On white grapes, oddly the disease is less apparant and there may only be a little chlorosis and cupping.
This infection causes vines to become weak and it increases the mortality rate over the winter and reduces taste in the grapes (sometimes red grapes can even loose much of their colour)
Although there is no cure, this disease is not hugely contageous and is not often found outside of large scale growers.
Affected Plants:
Downy Mildew

Affected Plants:
Powdery Mildew
Affected Plants:
Mould (Grey)

Affected Plants:
Mould (Slime)

Slime mould is a fasinateing organisum that is only an irritation in the garden. It should be delt with much as algae and indeed it can just disintigrate with a touch.
Although not relevent horticulturally, it is quite biologically inteligent, given it has no brain and has an enviromental memory.
Affected Plants:
Mosaic/Mottle Viruses

There are many mosaic/mottleing viruses, affecting many plants, some of the most noteable are Bean, Cucumber, Tobacco and Tomato mosaic viruses.
Although these are named, Tobacco mosaic virus can for example infect over 350 known species, certain weedkiller products can create simmiler symptoms to the virus but do not make the leaves yellow so much.
In all cases the infected plants should be immediatly pulled as the disease is spread by aphids which may transverse between plants and therefore pass the virus along.
Affected Plants:
Most importantly, Tomatoes
Cucumber Mosaic Virus

Cucumber Mosaic Virus is the most widely rangeing hosted virus known in plant pathology, it can be spread either through sap from working with infected plants or by pests such as aphids. It causes chlorotic mottleing on the leaves and on fruit often stunting them. It infects a huge range of plants.
If infected then destroy the plant and sterilise any used tools!
Affected Plants:
Wide range
Tobacco Mosaic Virus

Tobacco mosaic virus is almost as pernicious as CMV but not quite as destructive, it is extreamly stable and it can suvive quite happily in a greenhouse over winter. One of the tells between TMV and others is it tends to form wave like ripples on leaves along with the regular mosaic chlorosis.
As with all viruses it is best to destroy the plants and sterilise any tools you have used with it
Affected Plants:
Many Plants
Needle Cast

Needle cast is a common group of fungal diseases, and many people have seen it on christmass trees withought realiseing. It causes mass defoliation of conifers, as infected needles do not drop untill the next year however, there may be new needles growing that are already infected and acting as resevours for the disease.
In infected trees, it is generaly not worth applying fungicides as it will firstly only prevent new infections, but also secondly it dose need to be done at the time spores are being produced, which is only detectable when you know the specific strain of disease... which you can only tell from the spore shape!
Affected Plants:

Oedema is a disorder rather than a disease, it is caused when a plant takes up too much water and is comparable in many ways to the human condition with the same name.
This is only realy common in high humidity as the plants are less able to defuse water from the leaves.
Symptoms start off as light spots on leaves that start to swell, becomeing raised to the point they may rupture. At this stage they may become rust coloured and could be mistaken for other diseases, so check the roots on the plant and look for any sign of fungal activity.
On woddy plants this may be expressed through corky protrusions formeing.
If is of vital importance to correct the problem rather than just take damaged leaves off, removeing leaves will simply reduce the ability of the plant to deal with this.
Affected Plants:
All (physiological)
Onion White Rot

Onion white rot is easily the most dangerous disease here, whilst it is restricted to the allium family and leeks, it is highly contagious (to the point if you walk over the soil you risk infecting clean soil) and has a massive mortality rate, to make it worse it can suvive in the soil for up to 15 years and there are no commercial chemicals to treat it.
However as always there is a way to deal with this. White rot activates when it detects certain compounds unique to alliums and therefore it can be tricked by applying ground or crushed onion and garlic. After it has been activated then with no food it will rapidly die. Given the danger of this disease it is recomended you apply the treatment at least twice over sucsessive years.
Use 1 bulb per 5lters or untill you can smell and taste the garlic per meter square. After applying, dig the area and re apply so it penitrates at least a spade spit into the soil. Do this when the ground is between 15-20*c
Affected Plants:
Onions, Garlic, Leeks
Onion Neck Rot

Onion neck rot is a hard to catch disease, it only starts to develop after a number of weeks in storage and other than that it is almost undetectable. Eventually a gray mold will mummify the bulb, starting from the top.
Always check onion sets carefully and make sure there is no decay, never plant or use onions that are soft or badly wrinckled.
Affected Plants:
Onion leaf spot

This is a disease caused by Botrytis squamosa and is encoraged, like many fungal diseases by high humidity and warm weather conditions. It first appears as water-soaked pale ovals on the leaves that develop into sunken lesions and under bad infections the leaf tips turn brown and start to die back.

There is no approved chemical control in the UK and it is best managed by useing a two year crop rotation and increaseing airflow between plants when possable

Affected Plants:



Peony Wilt

Peony wilt is yet another species of Botrytis, in this case Botrytis paeoniae and it carries with it the signiture wilting and brown patches of decay that are followed in humid conditions by a grey fuzzy mould.

Teh symptoms are that leaves collapse and flowerbuds fail, unnopened.

Although control is not perfect due to airbourn spores, removing infected material and any falled debris will markedly reduce damage caused.

Affected Plants:


Powdery Mildew

Powdery mildew is one of the most common diseases gardeners have to cope with, it is prevelent on a number of vegetable crops and is encoraged by a warm dry spell after initial damp weather.
It is not a particually powerfull pathogen and can be controled by a number of chemical products or weakened by simply keeping the plant humid. It dose not aim to kill the host, it just tends to dessicate them.
Affected Plants:

Pythium is very closely related to phytophra and causes the same disease symptoms, namely damping off and root rots. Damping off causes the most plant fatalitys of any disease.
For damping off, do not overwater the seedlings and use fresh compost. This will virtually eradicate any problems. If you use rain water then make sure you cover the water tanks with a mesh or gauze to limit the organic material that enters as it may be a carrier.
When root rot occurs on larger trees, a white wooly rot is often apparant, if you have this, contact a trained tree sergon and he should be able to diagnose it. As pythium is spread by water then in wet years it is particually prevelent. There is no real control for pythium except healthy strong plants.
Affected Plants:

Rust diseasese are an interesting group. There are innumerable variations on the disease and two main forms.
Single species rusts have a simple life cycle and can be treated with comparative ease, roses are a good example, highly prevelent with its charateristic rusty orange spores on the underside of the leaves.
In this case good hygene and potentially chemical control (especialy on roses) will handle the disease well. Remove any infected material and cut it back as far as the plant can suvive. Burn any infected material and a spray of mycrobutinol will stop it returning and starve out any remaining infection with repeated aplications. Do NOT compost any infected material it is likely to suvive!
The other form of rust is harder to control, largely becuse it is heavily reccuring. The second type of rust has two host plants such as pear rust, which overwinters on junipers! In this case the best thing to do is find if your infection has a counterpart that it will also infect, if so be prepaired for a struggle.
Rust is triggered by a duration of sitting water on leaves and cool temprature, this means british summers are ideal for it (but it is less common in warm conditions). Its one saveing grace is that different variations will only infect a very limited range of hosts so it is normaly not transmitable around the garden to other species.
Affected Plants:
Many, esp. Roses
Rot (Soft)

Soft rot is a pernicious problem especially with edibles. It dosent interact much with woody tissue, instead beaking apart soft tissue such as potato tubers or carrots and forming a foul smelling slush.
When soft rot has been found it is imperitive to remove and destroy infected material. To control it keep watering low if you have had it before and space plants out in well ventilated situations to avoid sitting water. With certain plants make sure they do not collect water in cups and dips.
Affected Plants:
Many, Important on fruit
Rot (Brown)
Brown rot is most often seen on apples and other fruit, infected material turns soft and pale brown often with white or pale yellow patches of spores forming, eventually mumifying the fruit.
Control is best achived through removeing infected fruit (it is compostable) and pruning any infected material back but be sure to sterilize between each cut.
Affected Plants:
Apples, Pears, Cherries ext.
Rot (Onion white)

Affected Plants:
Rot (Onion Neck)
Affected Plants:
Rot (Dry Potato)

Dry rot is most prevelent on potato, it initially appears on stored potato often used for seed as a sunken slightly rippled area which remains dry and mostly firm.
When picking seed potatoes then discard any infected. It is not easily transmitted when the stock is dry so others around it will still be plantable.
If you find it has appearaed in harvest then destroy the infected material and do not plant there again for at least five years. Damage is often the cause of infection and watch any damaged potatoes you intend to plant next year closely.
Affected Plants:
Ring Spot

Ring spot is common on a wide range of ornamentals such as nicotiana, it is identifiable by a black necrotic spot in the center that has a yellow/light green halo around it or as mottleing whilst young. It is spread by insects or enters the plant through damage.
Affected Plants:
Wide Range

Biological reversion (as opposed to the disease) occurs mainly on vairagated plants. Most varigations are a result of genetic mutation or damage and this is propagated via cuttings as mutated cells will propagate the mutation but seed will in most cases, not.
Occationally the mutation is unstable and this can cause the variagation to vanish and return to its plain form. A tempory reversion can be caused by putting variagated plants in shade as this encorages more production of chlorophyll, mitigateing the variagation.
It is also responsible for relitively short plants such as euonimous suddenly growing into large trees
Affected Plants:
All (physological)
Blackcurrent Reversion virus

Reversion disease is spread through blackcurrents by the means of mites, in particuallar gall and big bud mite. It causes infected canes to reduce in vigour. It is detectable by a reduction of veins in leaves and colour change, often brighter of flowers. Over time the plant will stop produceing fruit.
There is no method of control except to remove and destroy the plant material.
The change in shape of the leaves is subtle but look for an decreased angle between the front and side lobes, the most relyable way to detect reversion is the reduction of yield.
Affected Plants:

Smuts are closely reltated to rusts and also leave masses of spores, however in this case black like soot (hence the name). These diseases normally affect grasses on which they are only marginally problematic however certain species can affect ornamentals, of particular importance are Alliums.
Due to the genetic divercity of smuts, it is hard to develope a resistant plant and not commercially viable to develop a fungicide for them. Smuts also persist in the soil for many years. Fortunatly the lack of chemical treatments has encoraged other methods to be developed.
Some forms of smut do not produce the black spores and instead produce leaf spots withought the obvious spores. Interestingly the spores can germinate to produce a second form of spore.
Onion Smut only infects via the seed leaves therefore after these have falled, they are effectively immune for transplantation.
Dalias corms are not infected, only the foliage so prune hard in the autaumn before lifting, remove any infected material and they can be overwintered.
Sweetcorn cultivars are available that are less prone to infection.
Affected Plants:
Sooty Mould

Sooty mold is a byproduct of an insect infestation rather than a spontanious problem and is a good example of why pests should be dealt with rapidly. The mold is expressed as a black slightly sticky covering on the top surface of a leaf, very prevelent on the lime trees that line bristols roads.
Whilst it dose no direct damage to the plant, it will indirectly harm it by reduceing photosynthasis and should be delt with quickly. Search the foliage of the plants for any pests as the suger they produce is the basis for the mould. On most ericacious or citrus plants this tends to be scale insect.
Affected Plants:
Any with sap sucking insects.
Scab (Apple/Pear)

Apple and pear scabs are very closely related and treated, so much that many gardeners are not aware they are two diffrent species. In both cases the symptoms are small black/grey patches that appear on the fruits and leaves.

In most cases scab is a minor infection, with one problem, it acts as a gateway to other infections. When there is only a light attack then fruit is perfectly edible and there is next to no deteriation of the quality.

When a plant is infected, keep an eye out for cracks in both the fruit and the bark as this will reduce storage time with fruit and increase infection on both the fruit and the tree itself.

The  disease overwinters on infected material, so the best way to treat an infection is good pruneing and burning of infected leaves. Always collect any infected foliage as it will act as a well for further infections.

Apple scab has been linked with Apple Bacterial Cancer. Mycrobutinol will provide some control however please be aware of harvesting intervals.

Affected Plants:

Potato scab can mean either bacterial of fungal scab, both of them are relitively minor diseases and when infected, the potato creates scabby corky patches along the skin which serve to contain and limit the infection

Common scab is the bacterial form and is much worse when the soil is dry, especially when tubers are forming. It is also more likely to manifest when the soil is alkaline (as most of bristol is) and therefore more common after limeing.

Powdery scab is unfortunately more common when the ground is wet, and has the potential to spread to tomato roots causing damage then.

There is no chemical control, however in most cases it has little relevance to most growers.

Affected Plants:


Spot (Necrosis)

The two most common forms of necrosis spot are Impatians necrosis spot virus (INSV) and Tomato Spotted Wilt virus (TSWV). Both are hard to distinguish and both cover a large range of plants with a vast range of symptoms, so they will be covered togeather here.
These viruses are carried by westen flower thrips which dispite their introduction and lingering menice are poor at overwintering in the UK meaning the most commonly infected plants are those grown in greenhouses or in very warm locations.
The host range is truly immense, spanning over 900 species each! Whilst there are test kits available, they are expencive and must be brought online (
Common symptoms include stunting, distortion, yellow/brown rings or streaks, transparent veins, mottling and wilting.
Affected Plants: Tomato, Impatians, Various
Spot (Black)
Blackspot is a very common disease, especially on roses, it is dangerous but can and should be controlled. It appears as a black/purple spot with the leaf around it starting to pale, normaly it is identiyable as haveing a vivid green halo around it as it tries to trick the rose that the leaf is healthy.
When it infects a plant, it causes heavy leaf drop sometimes total, and it greatly reduces the vigour of a plant. Occationaly it may also infect the shoots of roses.
Interestingly the more modern cultivars are much more badly affected and species roses tend to have more of a resistance to it although this cannot be relyed upon. All leaves should be removed and burnt upon leaf fall as the disease overwinteres in debris.
To avoid resistances being built up (which is common) it is recmedned to always spray preventitivly and to alternate fungicides, notably mycrobutinol (found in most doff products) and tebuconazole found in multirose.
Affected Plants:
Spot (Tar) See: Tar Spot  
Shothole (bacterial)

Shothole is a bacterial infection predominantly on leaves, it is recognised by a purple-gray spot that dries, cracks and drops off the leaf. In some situations it can progress onto buds and fruit of prunus, causeing more serious damage.
Copper can be used to control this disease and infected areas should be pruned out, sterilizeing the blade with each cut.
Affected Plants:
Wide rangeing
Spot (Ghost)

Ghost spot is a failed attempt of Botrytis cinereria to infect tomatoes, the symptoms are small faint white halos on the fruit and rarely a few spots of necrosis. See Gray Mould
Affected Plants:
Slime Mould
Slime Moulds often occur on lawns, they may be unslightly however they cause absolutly no damage to grass as they merely use it as a support. They are easily disperced with water and are extreamly fragile.
Affected Plants:

Stunting can be caused by any number of things,
Deficiancies are the main cause of it although clubroot, shothole, helebore black death and many viruses are more specific possibilitys. When deficiancies are the main culpret, plants tend to recover little worse off, however with many viral or bacterial problems, the plants may never recover.
Affected Plants:
Splitting (of fruit)

Fruit, in particular tomatoes is normaly caused by variations of moisture and temprature. It is exacerbated by heavy watering and rain.
When a plant absorbs moisture, the fruit flesh absorbs it and therefore swells, much like a baloon, however the skin of tomatoes and other fruits is generaly much less flexable or capeable of rapid growth and therefore tears. In addition the skin of fruit often absorbs moisture unevenly and prolonged contact with water causes cracks to form.
To avoid this, water regually but do not drown plants (in any case this reduces taste in many fruit) and avoid watering fruit. Outside then this becomes more difficault and if you have ripe fruit when rain is comeing, it may be wise to harvest a day or so early.
This is entirely normal with some fruit, especially chilli peppers such as the traditional striations on jalapenio chillis
Affected Plants:
Many Fruit when exposed to water after dryness
Silver Leaf

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Silverleaf is one of the big fungle problems, to the extent that susseptable plants are often pruned in the summer rather than autaumn purely to reduce infections. It is most often noticed as a silvering of wilted leaves followed by a death of the branch. If the problem is true silverleaf, there will be a stain of dark wood.
There is no chemical control and infected plants should be pruned back hard, sterilizeing after each cut so as not to pass the infection along. This is one of the few situations that a wound sealent is reccomended.
Avoid pruneing succeptable plants in the autaumn as this disease only infects through wounds and its spores are far more populous in the damp cool weather.
Affected Plants:
Silver Leaf (false)Silver leaf on plum. Image: RHS,
 Horticultural Science

False silverleaf is far less dangerous than its counterpart above, it is not actualy caused by a disease but is a sign of stress to the plant. As this manifests most often when the plant is suffering, wilted leaves are also often common.

The only true way to distinguish the two is that false silver leaf dose not cause a wood stain and generaly is not as destructive to woody material. A minor prune to look for discolouration can be usefull but of course opens wounds in the tree.

Affected Plants:


Tulip Fire

This disease (B. tulipae) related to the more widespread grey mold, fortunatly only infects tulips and a handfull of lillies. It is named tulip fire for its symptoms which warp and distort the leaves with brown patches.
This disease can suvive in the ground for three years and therefore if the ground has been infected, it would be wise to avoid planting in the same location again. Removeing any infected plants will mitigate this greatly and is highly reccomended.

Affected Plants:


Some Lillies

Tar Spot

Tar is simmiler in looks to blackspot, a rapidly spreading black/purple spot although normaly deeper than the above. Unlike blackspot it is purely cosmetic and has nearly no impact on the health of the plant. It overwinters like blackspot on fallen leaves so it can be reduced greatly by good garden hygene.

As it is a biotroph and therefore dose not damage its host, there have been no cures developed.
Affected Plants:
Verticillium Wilt

Verticillium Wilt is an occasionally non-fatal disease that nonetheless can cause significant problems for plants, it has a wide range of hosts includeing a wide range of fruit, woody perennials and vegetables.
It damages plants by invadeing the stem and moveing through the water carring xylem tissue. The infected plant then tries to stop this and blocks up the xylem vessles which causes the plant to start wilting above the infection.
An infection causes dark staining on the woody tissue of perenials and plants may start to recover in humid damp weather as less water is lost through the foliage.
Although the recomended action is to destroy plants and either grass over or replant reistant shrubs, it is often possable to save plants by cutting out damaged infected branches and applying a nitrogen based fertilizer to encorage new vascular growth.
25g/m2 of sulphate of amonia applied 2-3 times over the summer gives most plants a good chance to recover but be aware it may reinfect in time.
Unfortunatly this disease is highly spredable through contaminated soil, be very carfull to clean tools and boots before moveing on.

Affected Plants:



White Blister (also caled white rust)

White Blister is a fungle disease that causes spore filled pustuals to develop, often distorting leaves and stems where they are located. Although the pustules tend to develop on the underside of the leaves there is often a purple halo present on both sides.
Plants infected with this, will have greatly reduced vigour and with severe infections wither and die. Blister is exacerbated in high humidity and therefore reduceing watering and spaceing plants apart will help to reduce incidents of this disease.
This disease infects three different plant family but cannot cross infect between them.
Affected Plants:
Stone Plants
Witches Broom

Witches broom is an interesting disorder that causes mass bundles of twigs to form on woody perennials, it can be caused by a number of things, damage, disease or most interestingly genetic mutation.
This is interesting and indeed relevent to horticulture in that any cuttings taken from a witches broom caused by genetic changes will carry that genetic alteration, therefore produceing extreamly dence strong and often attractive plants which can be propagated into their own cultivar!
A suppriseing number of connifers actually have their roots in proppagation from a genetic abberation!
Affected Plants:
Woody Perenials
Wind damage

Wind damage is fairly common, especially in exposed areas but also behind walls or where the wind is funnled through a small area. Damage includes uprooting but is often manifested as scorching on the edges of leaves and a general lack of vigour.
A wind break can be used but it should not be solid, for best results then a 50% coverage is ideal and provide protection for 10x the hight in distance.
Affected Plants:
Yellowing (Disease)

Yellowing is one of the first indications that a plant is in trouble, with most of the diseases that attack foliage, the plant will attempt to defend itself by dropping the attacked leaf, however before that is done, the plant often quickly draws nutriants and resources from it.
This removes the green mask of the chlorophyll and leaves the more perminant yellow pigmants to shine through.
Affected Plants:
Many diseased plants
Yellowing - Interveinal (Deficiency)

Interveinal yellowing is often a sign of iron, manganease or magnesium deficiancy, especially in acid soil. If there is a defficiancy of iron then it is normally strongest in the new leaves as it is more mobile, however if it is magnesium it is more prone to affect the lower leaves.
A dose of sequestrine will often help to restore greeness, if the cause is belived to be magnesium them epsom salts will also be effective. Be sure to check the packet of sequestrine as some only use iron whilst others use all three nutriants.
Affected Plants:
Especially Ericacious
Yellowing - Whole Leaf (Deficiency)

Whole leaf yellowing is caused predominatly by nitrogen deficiancy, it is especially prevelent in the spring as plants are just starting up new growth and nitrogen is highly soluable, especially in the constant winter drizzle.
A simple feed should clear this up with few problems.
Affected Plants: