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Leaves and sometimes stems are marked by dark blotches caused by a fungus. The spores overwinter on fallen leaves, stem lesions and bud scales, and reinfect the plant the next spring when there's a flush of new foliage. If these leaves are then infected, they too eventually turn ...

Also know as American gooseberry mildew, this greyish-white powdery growth of the fungal disease Sphaerotheca mors-uvae appears on new shoots, which can become distorted and die off. The mildew also affects the upper leaf surfaces and stems

The common, quick-spreading fungal disease Botrytis cinerea strikes in damp, humid weather, and often enters the lettuce through a cut or tear in a leaf. Affected leaves are inedible and should be thrown away but not composted. The worst scenario

Caused by the same fungus responsible for tomato blight, potato blight causes the leaves to develop dark patches, starting at the edges. In humid conditions a white fungus appears around the marks. The infection then travels down the plant to the tubers, which turn a reddish-brow...

Rust is a fungal infection and there are many different types that tend to be specific to particular plants and spreads by means of dust-like spores. The fungus is encouraged by a humid, moist atmosphere and grows on the surface of the leaves

Tomato blight, a fungal infection called Phytophthora infestans, spreads by wind and water-splash. It also attacks potatoes, and is triggered by warm, wet conditions, making outdoor tomatoes more susceptible than those in a greenhouse. The crop

The fungus that causes this problem spreads rapidly in the warm, humid conditions of a greenhouse. It usually becomes apparent on the lowest tomato leaves from early or midsummer, which develop yellow blotches on the upper leaf surface. The leaves eventually turn brown and wither...

Fungal spores attack emerging tulip leaves. They invariably become malformed, with brown spots leading to rotting of both the foliage and flowers, although the buds may well fail to open. If they do open, there will probably be white spots

There are several different viruses that affect tulips, each with slightly different symptoms. Tulip breaking virus causes streaking or marking of purple, pink and red tulips, usually on the late-flowering cultivars. White and yellow tulips aren't affected. The leaves can also be...

The fungus Rhytisma acerinum overwinters on fallen acer leaves, then infects the new spring foliage. The first signs are yellow leaf spots that turn into large shiny black blotches up to 1.5cm across. Severe cases can mean the leaves drop early, but the health of the tree won't s...