Diseases & Disorders

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

phytophthora

Fungal infection

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

Find out more

Sort by:

Filter by:

Filter by:

  • Acer: leaf scorch

    Acer: leaf scorch

    The attractive delicate foliage of Japanese maples (Acer palmatum) is prone to leaf scorch. Cultivars with heavily dissected foliage are particularly prone. Scorch occurs following environmental stresses, such as drying winds, and leads to the foliage turning brown.

  • Algae on rhododendron leaves. Credit: RHS Advisory.

    Algae on leaves

    Evergreen trees and shrubs are vital components of the winter garden, but green, powdery deposits on their leaves can make them dull and unsightly. These are caused by algae, which are harmless to the plant but they do cut out precious light to the leaf surface.

  • Dog lichen, Peltigera canina, on a lawn. Image: RHS

    Algae, lichens and liverworts on lawns

    Lawns in damp or poorly drained conditions can suffer from unsightly problems such as cyanobacteria (an algae-like growth), dog lichen and liverworts. Cyanobacteria in particular can make the lawn very slippery.

  • Lichen growing on tree branches is often a worry to gardeners, but is rarely a problem. Image: Tim Sandall/RHS

    Algae, lichens and moss on trees and shrubs

    Algae, lichens and moss often form green or grey, powdery or mossy, crusty growths on the stems, branches and trunks of trees and shrubs. While this can worry gardeners, these growths are harmless, although may occasionally indicate a lack of vigour in the affected plant.

  • Moss can add character to garden features. Image: John Trentholm/RHS

    Algae, lichens, liverworts and moss

    Algae, lichens, liverworts and moss are often found growing in damp or shady places in the garden on plants, soil and hard surfaces. They do not cause any harm, and can usually be tolerated as they can give a mature look to a garden. But they can make paths and lawns slippery and make ponds and borders unsightly so control is sometimes necessary.

  • Algae on paths can make them slippery. Image: John Trentholm/RHS

    Algae, lichens, liverworts and moss on hard surfaces

    It is common to find growths such as algae, lichens, liverworts and moss growing on hard surfaces. Contrary to popular belief, they do not damage what they are growing on, but can cause patios, drives, paths and steps to become slippery.

  • Liverwort growing on soil in a border. Image: RHS

    Algae, liverworts and moss on borders and containers

    Algae, liverworts and moss will grow on the soil surface of borders, rockeries and containers and are usually associated with compacted soil or poor drainage. Although they don’t harm plants, they can look unsightly, and may inhibit growth of small or young plants.

  • Algae and moss in a greenhouse. Credit: RHS Advisory

    Algae, liverworts and moss on greenhouses

    Green growths such as algae, liverworts and moss can accumulate on the glazing and surfaces of greenhouses, where they are unsightly and cut out light. They can be controlled by improving hygiene and ventilation.

  • Antirrhinum rust. Image: RHS, Horticultural Science

    Antirrhinum rust

    Antirrhinum rust is the most serious disease of antirrhinums (snapdragons). It is a fungal disease that causes dark brown spots on the undersides of leaves. Severely affected leaves shrivel and may die.

  • Apple canker. Image: RHS, Horticultural Science

    Apple canker

    Apple canker is a fungal disease causing disfiguring and sunken patches of dead bark on the branches of apple and some other trees. Infections often begin at wounds or buds.

Advertise here

Get involved

We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.