Plant leaves can sometimes change colour or produce unusual marks, blotches or even weird-looking structures on them. If you’re worried about your plant leaves, here are some of the more common leaf problems.
In some cases, you may need to identify pest and disease problems on plant leaves. The below list should help you with identification, and you can then click on the links where appropriate to find out even more about prevention and control.
Aphids are 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. You can control aphids with BugClear™ Ultra 2, but head to our guide below for further details about aphid control on specific plants.
Capsid bugs 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. You can protect your roses and other ornamentals with RoseClear® 3 in 1 Action, and visit our helpful guide below to assist with controlling capsid bugs on other plants in your garden.
Not all caterpillars are particularly harmful. Some will eat through leaves, stems, flowers, fruit and even roots. Other caterpillars curl up the leaves to use as protection from predators.
Sometimes, plant leaves change colour during the growing seasons – spring and summer. There are numerous reasons for leaf discolouration, 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. Flea beetles will swarm all over the leaves and will pepper them with holes. In severe cases it can result in wilted or stunted plants.
Fungal leaf 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 iron 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 silvery tunnels (or mines) under the surface of affected leaves.
Potato and tomato blight causes discolouration of the leaves, turning them brown then black from the edges inwards. The leaves can dry and curl, although in moist conditions a white fungal growth can sometimes occur around the edges.
Just as the name powdery mildew suggests, a white powdery fungus grows mostly on the upper surface of leaves. You’ll see white spots on plant leaves – this will occasionally spread to the underside and other parts of the plant. Powdery mildew can be treated with products like FungusClear® Ultra 2.
Red spider mites are 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.
Despite the name, rose black spot, the spots can be of various colours - grey, brown or black (roses in particular).
The spores of rusts 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.
Scale insects are not always easy to see on plants – you’ll likely see brown bumps on plant stems. Occasionally you’ll also see the same brown bumps on the underside of leaves, although this isn’t always as obvious. These are colonies of scale insects clustered together. Infected leaves may turn yellow or become otherwise discoloured.
We all know what slugs and snails look like. The damage they cause is easy to recognise too – they will leave lace-like holes on leaves. The holes are irregular due to their rasping tongues, and you’ll sometimes see them on flower stems too.
The silvery trails (not always present or visible) will tell you where they came from and where they went on to after lunch. SlugClear™ Slug and Snail Barrier is ideal for protecting vegetables, fruit and ornamental plants from slugs and snails. Read our guide below for more tips on how to tackle slugs and snails in your garden.
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.
Whitefly are little pests that 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. Whitefly damage on plants is usually scarcely visible, but when they are disturbed from feeding on the leaves, they produce an almost cloud-like eruption. This can make leaves sticky and a black sooty mould can develop. This can deprive the leaves of light and can eventually kill the plant.
Plenty of pests and insects eat plant leaves in the garden, whether slugs, snails, whitefly or vine weevils. To identify what is eating your plant’s leaves, you can look for the insect itself and evidence of its damage. For example, whitefly are around 2mm long with white wings. We all know what snails and slugs look like and how to identify their presence. When it comes to vine weevil, you can look for their characteristic ‘mouth-shaped’ bites on the edges of leaves.
