Fungicides are used to treat fungal diseases and can work by a systemic (where the fungicide is drawn into the sap of the plant and transmitted from there to the fungus) and a non-systemic action (where the fungicide remains outside the plant and plays a preventative role). Fungi can build up a tolerance to systemic fungicides and environmental conditions can limit the effectiveness of any fungicide, so trial and error may be needed to find the right one for your problem.
These are a selection of the fungicides available to gardeners. You should always check your local regulations to ensure that the fungicide you wish to use is permitted for that use.
Bordeaux mix/Cheshunt compound/Copper oxychloride
These copper based fungicides (they are a combination of copper sulphate with, respectively, ammonium hydroxide and ammonium carbonate) are used to protect plants against fungal infections. Bordeaux mix is used as a foliar spray against blight on potatoes/tomatoes, celery leaf spot, apple canker, bacterial canker on cherries/plums, peach leaf curl, black currant rust and gooseberry rust. Cheshunt compound can prevent damping-off in seedlings. Both are toxic to mammals and fish and can cause russetting on fruits or scorching of leaves on some plants. Generally speaking, copper compounds are acceptable for organic gardening.
This is a sulphur based fungicide used when taking cuttings to prevent the cutting rotting.
This is used to control damping-off, seedling foot rot, celery leaf spot, peach leaf curl, potato blight, tomato blight, apple/pear canker, bacterial canker of plums/cherries, currant rust, gooseberry rust and cane spot on raspberries and loganberries.
Working as a protectant, this organic chemical is particularly effective against certain foliage blights and rusts.
This organic fungicide both protects plants and can eradicate any present fungal infections through a systemic action. It is used for blackspot, powdery mildew, rusts and apple/pear scab.
Octane acid (iron and sodium salts)/Phenolic formulations
These are both liquid paints used to seal and protect pruning wounds on woody plants.
An organic fungicide used to protect ornamental plants against rusts.
Plant and fish oil blends
These can be used to deal with powdery mildew, blackspot, leaf spots and greasy spot. While they can be used on all plant types, euphorbias may react badly to them. They are also used as insecticides.
This is used to protect plants against foliar fungal diseases such as powdery mildew (often in combination with insecticides), for treating corms, bulbs and tubers to prevent storage rotting and to clean empty greenhouses (plants in leaf can be killed by sulphur) and horticultural equipment such as staging and seed trays (the vapours are an irritant to humans affecting the eyes, nose and throat, plus they can corrode iron, so extra care should be taken when using it). It should not be used on red or white currants, on some gooseberry cultivars or on some of the older apple cultivars. Generally speaking, sulphur treatments are acceptable for organic gardening.
It is used in combination with fatty acids against powdery mildew, though it should not be used near fish, on food crops, young seedlings, ferns or Dianthus spp.
Tar acids and oils
These are derivatives of coal tar and are available as liquids or pastes. They are toxic to fish and an irritant so should be kept away from skin, eyes, food and food containers. They are used in sterilising glasshouse staging, seed trays and pots or as a protective paint for pruning cuts and other wounds on woody plants.
This is a systemic, organic fungicide which is used to both protect against and eradicate clubroot disease on brassicas.
This is used on lawns to protect against fungal infections such as fusarium patch and red thread.
A systemic fungicide used against blackspot, powdery mildew and rusts.