Mould and fungal diseases.

Diseases affect plants of all sizes, from trees to seedlings. A healthy plant given the right conditions should be able to fend off an attack. However damp weather conditions, an old or sickly plant or a closed environment can encourage air or soil-borne diseases to multiply and spread.

A couple of drops of tea tree oil in a sprayer of lukewarm water can be used on plants that are suffering from fungal infection such as rust.

Table: A list of mould and fungal diseases affecting plants.
Disease Symptoms Suggestion
Clematis wilt Leaves turn brown and crispy from the base upwards. Prune back hard in early spring. If it recurs the following year, prune back hard in the spring once again, if it reoccurs in the second or third year then dig out the plant and destroy if you want to replant a clematis in the same place remove the soil and replace with new compost. Try replacing it with a clematis wilt resistant plant. Always plant clematis 6" deeper than it was in the pot.
Brassica ring spot Remove the leaves and burn them.
Canker (Nectria galligena fungus) Affecting apple and pear trees especially. In the spring the bark shrinks and cracks appear, eventually encircling the branch, often killing the branch. Remove damaged branches as soon as you see the problem, cutting back to healthy wood, burn the prunings. If the infection is mid-branch or slight, scrape away the bark to healthy green wood and paint with Arborex. Prune trees well in the winter to create better ventilation through the tree canopy, which should reduce the chance of fungal infection. Bordeaux mixture made up as a spray can also be used.
Mildew Humid, warm weather and usually a lack of rain, encourages mildew on roses, peony and asters. Reduce moisture around the plant, create an open structure to allow better air circulation. Dust the leaves with sulphur as soon as you see the infection or treat with a spray of either bicarbonate of soda (5g to 1 litre of water) or a mix of 1 part milk to 4 parts water.
Fireblight Flowers and shoots wilt, leaves look brown and dry as if caught by a bonfire. Remove bark to reveal a browny-red mark on the bark, remove branch to 60cm (2ft) below this. Wash pruning impliments in disinfectant. Else remove the tree and burn it.
Brown rot (Monilinia laxa fungus) Brown marks on, or the rotting of apples and pears. The fungus thrives in warm wet weather. It enters the fruit from any skin damage and quickly spreads. If the fruit remains on the tree it can spread to ajoining fruit. Remove any fruit that shows any sign of infection. Collect and dispose of any infected fruit that has fallen. Increase air circulation through the tree by pruning well in the winter.
Scab (Ventuia pirina fungus) Brown marks on the fruit and leaves of apple and pear trees. Cracks on the fruit of pears. Occurs in warm, wet weather. Increase air circulation through the tree by pruning well in the winter. Collect and burn any infected leaves and branches. Trees in the shade on heavy soil seem to be affected more than those in full sun on free draining soil. So if your trees are suffering and the tree is too big to move, think about planting anew in a sunnier position, or improving the drainage around the tree with plenty of mulch.
Guignardia aesculi Brown, shrivelled leaves on horse chestnut/conker trees. The fungal disease is specific to the horse chestnut, so won't affect other trees or plants. However, the leaves should be collected and burnt, to prevent the spores reinfecting the horse chestnut trees.
Peach leaf curl As the name suggests the leaves of peaches curl. Cover the tree with plastic sheeting in the winter and spring. If you already have peach leaf curl, spray with Bordeaux mixture.
Botrytis cinerea (grey mould) Furry, grey mould affecting plant shoots, particularly in the greenhouse in autumn and winter. Botrytis (grey mould) is a mould that is naturally present in the air, so it's impossible to eradicate it. It thrives in moist conditions, to reduce its effect on over-wintering plants in an unheated greenhouse, remove any yellowing, dead, dying or already infected leaves and/or flower buds, reduce overcrowding ensuring there is space around the pots to allow a little air to move around the plants, leave compost in the pots to dry out, leaving them just enough water to survive. On milder days open the greenhouse door and vents to allow fresh air to circulate.

If it's occurring in the greenhouse in spring or summer, reduce the amount of watering and try to reduce air moisture by not misting, open vents and windows in the morning and close them in the late afternoon/early evening.

Blossom-end rot Dark or black bottoms on tomatoes, peppers and aubergines. It's caused by a lack of calcium, either in the soil, growbag or container that you're growing in, or that the soil is too dry for the plant to take up any calcium. Check your tomato feed contains calcium, and ensure the soil doesn't dry out, watering twice a day in hot weather. Cherry tomatoes are less prone than larger varieties to blossom-end rot.
Tomato mosaic virus Brown patches on the fruit of tomatoes and brown edges on the leaves is likely to be tomato mosaic virus. This is caused by a lack of potassium in the compost, to resolve, feed the plants weekly with a liquid tomato feed. If the leaves wither before the fruit is affected it's probably blight.

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