These microscopic mites suck sap and cause abnormal growths. These include raised pimples or clumps of matted hairs on leaves, or enlarged buds. Most are harmless and can be tolerated.
The wingless nymphs of box psyllids are covered in a waxy coat, and found inside the ball-shaped shoot tips in spring. Control the pest by cutting off affected growth and discard or burn it.
To avoid maggots in apples, spray emerging caterpillars twice using bifenthrin, starting in midsummer. Also hang pheromone traps in late spring to catch male moths and prevent them from mating.
In spring, the leaves of fruit trees are webbed together and hide green caterpillars inside. Holes are visible when leaves expand. Apply sticky grease bands to the trees and stakes in autumn to trap adult moths.
Tiny blister or shell-like bumps on leaf backs result in poor growth. Other symptoms are sticky excretions and sooty mold on evergreens. Wash off mold, and spray with plant oils, fatty acids, or thiacloprid.
Under glass, hang yellow sticky pads to trap these tiny white flying adults, which suck sap from plants; use a biological control (Encarsia wasp) on larvae, or spray with thiacloprid or organic chemical controls.
Both the adults and larvae eat holes in the leaves, mainly on Viburnum tinus and V. opulus; this can slow growth and looks unsightly. Spray badly affected plants in spring using bifenthrin or thiacloprid.
These tiny black sap-suckers, known as “thunder flies,” cause white patches on the petals and leaves of indoor plants, and also peas, leeks, onions, and gladioli. Spray with bifenthrin or use biological controls.
Small cream grubs with a brown head feed on plant roots, especially those growing in containers or with fleshy roots. This can cause plants to suddenly collapse. The adult beetle is nocturnal, flightless, and makes notches in leaves. Use a biological control (nematodes).
The larvae of butterflies and moths attack many plants. Cabbage white caterpillars decimate brassicas and nasturtiums, while those of the tomato moth damage fruits. Cover plants to keep adults from laying eggs, rub off egg clusters, and pick off any caterpillars you find.
The caterpillar-like larvae devour the foliage on plants such as roses, gooseberries, and Solomon’s seal (Polygonatum). Look out for the first signs of attack, such as leaf rolling (rose leaf-rolling sawfly). Pick caterpillars off by hand or spray with bifenthrin or pyrethrum.
The larvae of various flies, moths, sawflies, and beetles feed within the leaves, creating discolored blotches or linear mines. Most are relatively harmless and can be left untreated. However, if necessary, you can spray leaves with thiacloprid.
Red spider mites
The tiny mites live under leaves and suck sap, causing yellow mottling. Fine webs are sometimes visible. Raise humidity and use a biological control under glass. Otherwise try organic sprays or bifenthrin.
Woolly beech aphid
Seen in early summer, these white fluffy aphids coat shoots and the undersides of leaves. They suck sap, and excrete honeydew that supports black sooty mold. Spray severe infestations with thiacloprid.
Horse chestnut leaf miner
This new but widespread pest attacks mature trees where control is difficult. Leaves show brown marks between the veins, which result in slow growth and early leaf drop.
Mostly beneficial, earwigs are nocturnal and feed on dahlia, chrysanthemum, and clematis flowers. Lure them into upturned flower pots filled with straw and set on stakes; release them elsewhere.