Plant leaves can sometimes change colour or produce unusual marks, blotches or even weird-looking structures on them. Here are some of the more common leaf problems.
In some cases, you may need to identify pest and disease problems on plant leaves. Click on the links where appropriate to find out even more about prevention and control.
The most common of all pests and almost every plant from the smallest shrub to the tallest oak tree can be infested. They tend to feed on the underside of leaves and you'll often see the white shed skins. Some produce specific leaf problems - such as leaf-curling aphids and blister aphids. Further details on aphids
These insects are about 6mm long with six long legs and antennae. They love the tips of young shoots and have wide tastes - roses, fuchsias, hydrangeas, forsythia, chrysanthemums and currant bushes. They make small holes that get bigger as the leaf grows and expands and often cause the leaf to distort in shape.
Not all of them are particularly harmful. Some will eat through leaves, stems, flower, fruit and even roots. Some curl up the leaves to give them protection from predators
Sometimes, plant leaves change colour during the growing seasons – spring and summer. There are numerous reasons for this, so you'll have to become a plant detective, to see what has caused it.
Downy mildew thrives in moist damp conditions and loves young plants. The upper leaf surfaces develop yellowy discoloured patches that can extend across large areas of the leaf and sometimes a white/grey ‘downy’ coating.
Certain species of the adult flea beetle are fond of cabbages, Brussels sprouts, swede and other brassicas; some like potatoes; others are equally fond of wallflowers, alyssum, aubrieta and nasturtiums. They swarm all over the leaves.
Fungal leaf spots
The spots can be of various colours - grey, brown or black (roses in particular). The spots are in fact dead leaf tissue caused by the fungus that spreads the disease.
Although a trace element, iron can be locked up in the soil so roots of rhododendrons, azaleas, camellias and other ericaceous plants cannot absorb any reserves. Raspberries can also show similar signs of deficiency. Leaves start to turn yellow between the veins.
Yellowish and 2-3mm long. As their name suggests they (the adults) will jump off if the plant is disturbed. The immature nymphs are creamy-white and crawl. Both nymphs and adults feed on the sap of plants. They cause leaf yellowing and the overall weakening of the plant.
Leaf miners produce characteristic pale twisting tunnels (or mines) under the surface of affected leaves.
Potato and tomato blight
Discolouration of the leaves, turning them brown from the edges inwards. The leaves can dry and curl although in moist conditions a white fungal growth can occur around the edges.
Just as the name suggests, a white powdery fungus grows mostly on the upper surface of leaves. It will occasionally spread to the underside and other parts of the plant.
Red spider mites
Perhaps the smallest of the common sap-feeding insects. Leaves first develop a pale mottling, but as the infestation progresses the leaves become increasingly yellowish white.
Rose black spot
The spots can be of various colours - grey, brown or black (roses in particular).
The spores of these diseases need a moist environment in which to prosper. The fungus develops mostly on leaves but also on stems. In appearance, they can develop either as patches or as pustules (like septic spots), usually with a rusty-brown colour – but some are different, such as chrysanthemum white rust.
Slugs and snails
There’s no need to tell you what they look like. And the silvery trails (not always present or visible) will tell you where they came from and where they went on to after lunch.
Sooty moulds are spreading dark brown or black, superficial marks on the top part of the leaves of numerous plants – but particularly glossy-leaved evergreens. they are the result of sap-sucking insects feeding on the leaves above.
Thrips (sometimes called thunder flies or thunder bugs) are yellow-black, very thin and about 2mm long. The typical symptoms are mottled and discoloured leaves, with signs of bleaching.
Vine weevil adults feed on the leaves, making characteristic ‘mouth-shaped’ bites on the edges of the leaves. The grubs are far more destructive, as they eat the roots, causing the leaves and whole plant to wilt.
These little pests set up home and live out their lives on the underside of leaves. As adults, they are about 2mm long with white wings, which give them their name. When disturbed from feeding on the leaves, they produce an almost cloud-like eruption.