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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  • ©RHS SCN0001132

    Impatiens downy mildew

    Impatiens downy mildew is caused by a fungus-like (Oomycete) organism that causes yellowing leaves, leaf loss, and death of bedding Impatiens, commonly called busy Lizzies, during wet weather and damp conditions. Attacks are most likely in summer, or spring in greenhouses.

  • Tomato spotted wilt (Tomato Spotted Wilt Virus) on busy lizzie (Impatiens). Credit: RHS/Pathlogy.

    Impatiens necrotic spot virus and Tomato spotted wilt virus

    These viruses have been a significant problem since the late 1980s, when the western flower thrips, their principal vector, arrived in the UK. Each virus has a huge host range and can produce a bewildering array of symptoms.

  • Iris diseases

    Iris diseases

    Irises can be affected by a number of diseases that reduce the vigour and quality of the plants. Some of these diseases are confined to either the rhizomatous or the bulbous types of iris, but others can affect both types. Problems can be caused by fungi, bacteria and viruses.

  • © RHS_SCN0005429

    Kerria twig and leaf blight

    Kerria, once considered a disease free, spring flowering shrub, is now affected by a fungal infection that causes lesions and defoliation.

  • Laurel: leaf diseases

    Laurel: leaf diseases

    Cherry laurel (Prunus laurocerasus) is generally considered a tough evergreen but its leaves can be affected by diseases such as powdery mildew, leaf spot fungi and bacterial shothole. Affected plants or hedges look unsightly.

  • A brown lawn, caused by drought. Credit:Neil Hepworth/RHS The Garden

    Lawns: dead patches

    Dead patches of grass on lawns are very common. However, it is usually easy to trace and remedy the cause, restoring green and healthy grass.

  • Lawns: dry patch

    Lawns: dry patch

    Dry patch of lawns occurs when the soil in certain areas becomes water-repellent. As a consequence the grass suffers from severe drought, even in wet weather. The result is the appearance of patches of dead grass, with the soil proving very difficult to re-wet.

  • ©RHS PUB0000690

    Leaf damage on houseplants

    Older leaves on healthy houseplants will naturally turn brown and die back over time as the plant matures, which is no cause for concern. But if most of the foliage on the houseplant changes colour in part or whole there may be a cultural problem, often rectified by paying more attention to watering, feeding or moving the plant to a more suitable position indoors. Plants that are unsuited to the conditions are unlikely to survive let alone thrive in the long term. However many house plants are short-lived by nature indoors, poinsettia and cyclamen for example, and will often need to be regularly replaced.

  • Shot hole damage on a prunus. Credit: RHS/Advisory.

    Leaf damage on woody plants

    Abnormal, damaged or falling leaves on a prized climber, shrub or tree can be alarming; however by following these simple steps to pinpoint the cause, gardeners can take effective action to protect their plants.

  • Leafy gall on wallflower. Image: RHS, Horticultural Science

    Leafy gall

    Leafy gall is a bacterial disease of the stems and roots of many herbaceous plants. Infection with this disease causes dense clusters of distorted leafy shoots.

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