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  • 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.

  • ©RHS MAR0049977

    Acidifying soil

    Acidifying garden soil will lower its pH so that ericaceous plants such as camellias, blueberries, heathers and rhododendrons can grow. It is usually only required if soil pH is neutral or alkaline. Sulphur is the most common acidifying material. Peat is no longer recommended.

  • ©RHS SCN0005145

    Adelgids

    Adelgids are aphid like insects that suck the sap from conifers. Often covered in a white waxy material some also cause galling on host plants.

  • Agapanthus

    Agapanthus

    Agapanthus (African lily) are summer-flowering perennial plants, grown for their showy flowers, commonly in shades of blue and purple, but also white and pink. They thrive in any well-drained, sunny position in the garden, or grow these beauties in containers.

  • ©RHS SCN0004904

    Agapanthus gall midge

    Agapanthus gall midge is a fly that can cause buds of Agapanthus  to become deformed and discoloured and fail to flower. It was first noticed in the UK in 2014 but may have been present for several years.

  • ©RHS SCN0004669

    Alder leaf beetle

    The metallic blue alder leaf beetle (Agelastica alni) feds on the leaves of alder trees. It has recently become re-established in some parts of England after an absence of more than 60 years.

  • ©RHS SCN0001676

    Alder sucker

    Alder sucker is a common on alder but the damage caused is seldom serious.

  • 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.

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