Diseases & Disorders

Helpful advice on what to do when problems strike, whether they're diseases, disorders or otherwise - and how to prevent them occurring


Fungal infection

Phytophthora is our second most reported disease. Causing die-back and leaf damage on trees and shrubs and is often fatal.

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  • Narcissus leaf scorch

    Narcissus leaf scorch

    As its name suggests, this fungal disease causes scorch-like symptoms to appear on the leaves. Symptoms start at the leaf tips, when they are sometimes mistaken for frost damage. Flowers can also be spoiled by the appearance of brown blotches.

  • Magnesium deficiency on a tomato. Credit:RHS/The Garden.

    Nutrient deficiencies

    If plants fail to thrive, despite adequate soil preparation, watering and mulching, it may be a sign of a nutrient deficiency. Fruit and vegetables are particularly vulnerable, as are containerised plants and those growing in very acid or alkaline soils. Yellow or reddish coloured leaves, stunted growth and poor flowering are all common symptoms of nitrogen, magnesium or potassium deficiency.

  • Oak decline. Copyright: RHS

    Oak decline

    The phenomenon known as oak decline has been known in the UK for nearly one hundred years. However, in the last few years there has been an alarming increase in the number of trees affected by acute oak decline – a fast-acting problem thought to be caused by bacteria.

  • Oedema


    All plants can be affected by oedema a condition brought on by overwatering or high humidity. It can be particularly troublesome on cacti, camellias, eucalyptus, fuchsias, pelargonium, succulents and vines. However, there are steps you can take to avoid this issue.

  • Onion downy mildew

    Onion downy mildew

    Onion downy mildew is a disease of onions and related crops that damages foliage and bulbs, resulting in loss of yield or even a complete failure of worthwhile bulbs to form.

  • Onion neck rot

    Onion neck rot

    This fungal disease develops during storage, and can cause severe losses of onion and shallot bulbs. Prevention of neck rot depends on the use of appropriate cultural techniques, particularly in relation to conditions at harvest and during storage.

  • Onion white rot. Image: RHS, Horticultural Science

    Onion white rot

    White rot is a serious fungal disease of onions, garlic and leeks causing wilting and yellowing foliage. It may persist in the soil for many years.

  • Pansy downy mildew. Image: RHS, Horticultural Science

    Pansy downy mildew

    Downy mildew of pansies is a disease caused by a fungus-like (Oomycete) organism. It causes pale blotches with fuzzy grey growth on the leaves, leading to the affected patches, and often the whole leaf, dying. It is particularly a problem on winter-flowering pansies in cool, wet weather.

  • Pansy leaf spots

    Pansy leaf spots

    Pansies and violas may be attacked by various leaf spot diseases that disfigure the plants. Plants in containers and those in the ground can be equally affected.

  • Peach leaf curl. Image: RHS, Horticultural Science

    Peach leaf curl

    Peach leaf curl is a fungal disease of peaches, almonds, nectarines and occasionally apricots, which causes severely distorted leaves, making them fall prematurely.

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