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Top Diseases and How to Treat Them

In response to the recent report by the RHS, listing the most common garden diseases in the UK, we have created a comprehensive guide to help you identify and treat the top 10 garden diseases. You can see the symptoms and, where possible, we have given a number of solutions, both chemical and organic. Don't forget to look in the Sun Gardening Shop as many of these products can be found there.

Honey Fungus


Honey fungus is the most destructive fungal disease in UK gardens. It is the common name for 6 related species of fungus with some being more aggressive than others. It spreads underground, attacking and killing the roots of perennial plants and then decaying the dead wood.

Symptoms

Upper parts of the plant gradually dying back over several years or suddenly along with premature autumn leaf colouring. Cracking and bleeding of the bark at the base of the stem, mushrooms are produced in autumn from infected plants (often an indication that the plants is dying). Sheets of white fungus mould between bark and wood, smelling strongly of mushrooms.

Chemical control

There are no chemicals available to control honey fungus. If confirmed, the only effective remedy is to excavate and burn, all of the infected root and stump material.

Non-chemical control

To prevent the spread of honey fungus to unaffected areas, a physical barrier such as a 45cm deep vertical strip of pond lining material or heavy duty plastic sheet buried in the soil will block the underground stems (rhizomorphs). Frequent deep cultivation will also break up rhizomorphs and limit their spread.

Box blight


Box blight is a disease of box leaves and stems caused by fungi and other related plants such as; Pachysandra terminalis and Sarcococca species can also be attacked and killed. The fungi can survive on fallen plant debris for up to 6 years and produce spores when conditions are suitable. The spores are dispersed in water.

Symptoms

Brown leaves which fall from the plant leaving bare stems which may display black streaks and die-back. The fallen, infected leaves may have masses of pibnk or white spores on their underside.

Chemical control

Sprays of Fungus Fighter and Fungus Fighter Plus (both from Bayer) will control this fungus if applied in the early stages of infection.

Biological control

At the present time there are no fully resistant varieties, but forms of Buxus. microphylla appear to be more tolerant than varieties of B. sempervirens. It is suggested that alternative plants with a similar habit are used instead, eg; Ilex crenata and Osmanthus delavayi.

Leaf spots


These leaf spots are mainly caused fungal disease, causing spotting on the leaves followed by defoliation. Severely affected plants can be reduced to bare branches others may have infected leaves hanging on the branches for long periods. Often, affected plants become weakened and vulnerable to attacks from other pests and diseases.

Symptoms

Most commonly seen as purple to black leaf spots, which may be circular or more irregular in shape, as they age these spots often develop a greyish-white centre of dead tissue. In some cases small fungal structures may just be visible within the leaf spot. These are most obvious as tiny black or brown dots in the centre of the spot.

Chemical control

Systhane Fungus Fighter Plus (Bayer), Rosegarde (Vitax), Fungus Clear Ultra (Scotts), Bug & Fungus Killer (Doff), Organic 2in1 Plant invigorator (Vitax), Uncle Tom's Rose Tonic.

Biological control

Remove and destroy all affected leaves promptly, and clear away any dead, infected material from around the plants, as this will be a source of re-infection later in the season. Powdery mildews usually have a narrow host range comprising of just a few related plants. For example, the powdery mildew affecting sweet peas is a different species from the one attacking roses.

Phytophthoras


Over 25 different types of this fungus has been identified in the UK attacking over 80 different plants with Rhododendron, Viburnum and Yew being the most commonly recorded. They are capable of attacking roots, stems and leaves depending on which form of the disease is attacking a particular host plant.

Symptoms

Include wilting, yellow or sparse foliage and branch dieback, often getting progressively worse until the plant dies. With conifers a gradual changing of foliage colour from vibrant to a dull sheen and greying to a brown. The base of the affected plants stem causing a brown or black discoloration below the bark or as bark discoloration and weeping wounds,

Chemical control

There are no chemicals available to gardeners for the control of these root and stem rots.

Biological control

These fungi are often dormant in the soil but the cases of them infecting plants are often associated with wet soil conditions. Improving soil drainage can help to reduce the risk of plants getting these diseases. Infected or suspect plants should always be removed and burned.

Rust


They are amongst the most common fungal diseases, affecting; Trees, shrubs, herbaceous perennials, grasses, bulbs, fruit, vegetables and bedding plants. Most forms of rust diseases are very distinctive and are capable of killing the host plant.

Symptoms

Leaf spots can be orange, yellow, brown, black or white, eventually producing raised structures (pustules) which hold fungal spores, usually on the underside of the leaf. Heavy infections often lead to pale distorted leaves which fall prematurely.

Chemical control

Copper Mixture (Vitax)
Ornamentals only - Systhane Fungus Fighter and Fungus Fighter Plus (Bayer), Multirose Concentrate (Bayer), Fungus Clear Ultra, Roseclear Ultra (both Scotts), Rosegarde (Vitax), Bug & Fungus Killer (Doff).

Biological control

Remove all diseased and dead material at the end of the growing season, and do not compost affected material. Select resistant cultivars when available.

Volutella Box blight


Box blight is a disease of box leaves and stems caused by fungi. The fungi can survive on fallen plant debris for up to 6 years and produce spores when conditions are suitable. The spores are dispersed in water.

Symptoms

Brown leaves which fall from the plant leaving bare stems which may display black streaks and die-back. The fallen, infected leaves may have masses of pibnk or white spores on their underside.

Chemical control

Sprays of Fungus Fighter and Fungus Fighter Plus (both from Bayer) will control this fungus if applied in the early stages of infection.

Biological control

At the present time there are no fully resistant varieties, but forms of Buxus. microphylla appear to be more tolerant than varieties of B. sempervirens. It is suggested that alternative plants with a similar habit are used instead, eg; Ilex crenata and Osmanthus delavayi.

Powdery mildews


A group of related fungal diseases which attack a wide range of plants, causing a white, dusty mould which covers the surface of the plant including leaves, stems, flowers and fruits.

Symptoms

White, powdery patches of fungus spreading on upper or lower leaf surfaces, flowers and fruit. Often causing stunted or distorted leaves.

Chemical control

Edibles - Baking soda applied at 20gm in 1 litre of water, SB Plant Invigorator + 5gm in 1 litre of water.
Ornamentals - Systhane Fungus Fighter Plus (Bayer), Rosegarde (Vitax), Fungus Clear Ultra (Scotts), Bug & Fungus Killer (Doff),

Biological control

Mulching and watering reduces water stress and helps make plants less prone to infection. Select mildew-resistant cultivars where possible.

Root Rots


Caused by soil-borne fungi, which may survive for many years and only become active under specific temperature and moisture conditions when a host plant is preset. Root rot is mainly associated with heavy, poorly drained or waterlogged soils, and the symptoms can be difficult to differentiate from those caused by waterlogging.

Symptoms

These can include wilting, yellow or thinning leaves, shoot tip curling and branch dieback. In many cases the symptoms gradually get worse until the plant dies. A common symptom in conifers is a gradual fading in the colour of the foliage, from a vibrant to a dull green, through to greyish and finally brown.

Chemical control

There are no chemicals available to treat wilts, but sterilising the surrounding soil with Jeyes Fluid after removing affected plants mat help.

Biological control

Improve drainage where possible, remove and dispose of affected plants. Treat replanted specimens with a mycorrhizal preparation prior to planting.

Wilts


Wilts can be caused by soil-borne fungi or as a result of waterlogging they can affect many fruit, vegetables and ornamental plants that enters the plant through the roots. Infection with this fungus causes dieback and the leaves to wilt.

Symptoms

Sudden wilting of plants, especially in hot weather, followed by temporary recovery.Characteristic brown or black markings (staining) in the area under the bark. Dieback is of shoot tips and branches in trees and shrubs, eventually leading to plant death.

Chemical control

There are no chemicals available to treat wilts, but sterilising the surrounding soil with Jeyes Fluid after removing affected plants mat help.

Biological control

Improve drainage where possible, remove and dispose of affected plants. Treat replanted specimens with a mycorrhizal preparation prior to planting.

Viruses

Is one of the most common plant diseases and causes a wide range of symptoms. They are transferred from infected to healthy plants by a carrier (vector) which feeds on plant sap, such as; aphids eelworms. It is rare for a virus to kill its host plant. Often the virus will get its name from the symptoms it causes or the plant on which it was first identified = Cucumber Mosaic Virus.

Symptoms

Yellow mottled leaves (mosaic patterns), yellow blotches, spots or ring markings. Stems, branches and shoot tips often display distortion and stunting.

Chemical control

There are no chemicals available to control virus infections in plants. The use of insecticides to reduce aphid transmission has only a limited effect.

Biological control

Destroy suspect plants as soon as they are spotted will help to reduce the risk of transmission. Good garden hygiene, some weeds act as hosts for viruses eg Groundsel and Shepherds Purse. Where possible choose resistant cultivars.



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