Insects in the garden.

Most insects in the garden are harmless, in fact quite a lot of them are beneficial, pollinating flowers and preying on other damaging insects.

Table: A list of insects, the problems they cause and possible solutions.
Insect Symptoms Suggestion
Leaf cutter bee Near perfect circular / semi circular holes cut in rose leaves. These bees cut the leaf to use in building their hollow cigar shaped nests. It's difficult to catch these bees at work and there is little that you can do to prevent the damage.
Carrot fly (Psila rosae) Small holes in the carrots and general damage to the crop. Carrot flies lay their eggs just below the surface of the soil. When the larvae hatch they burrow into the carrots. The adult flies can be confused into not laying eggs near the carrots by inter-planting your rows with onions or pungent herbs such as sage, chive, rosemary or parsley. Alternatively cover your carrots with thin netting or fleece or create a physical barrier with boards, plastic edging or small box hedge. Growing in a raised bed or barrel can also reduce the incidence of carrot fly.
Leaf miner Erratic lines on the leaves of current bushes and fruit trees. The leaf miner burrows between the layers of leaves, but doesn't do any lasting harm to the plant. Pull off the infected leaves and burn. There is no need to spray with an insecticide. On decidous plants the leaves will fall and it is unlikley that the problem will reoccur.
Scale insect Brown scale on stems and leaves of fruit bushes, left untreated this can kill the plant. Spray with a winter tar wash. Tar wash applied other than in winter will damage foliage and fruit.
Whitefly Damage to the crop. French Marigold (Tagetes) and basil (Ocimum basilicum) discourage whitefly from attacking plants by masking their smell. This is particularly effective in the greenhouse.
Cabbage root fly Cabbage root fly, the eggs are laid at the foot of the plant, when the maggots hatch out, they burrow into the soil and eat the roots. Use collars around the stem of the young brassica plants, to prevent the adult laying eggs near the plant stem.
Millipedes Usually eat dead plant material but can also eat the roots of plants and seedlings. It's not worth chemically treating, although slug pellets will kill them. Clear garden rubbish to reduce hiding places enabling birds to eat them.
Ants Ants collect the sticky substance excreated by aphids, so it might look like they are causing the problem with your plants. If you control the aphids the ants will move on.

Ants do little or no damage to plants, however they can be a nuisance on the lawn. Use a stiff broom on the ant hill and then water the grass with plenty of water, they should move to a different area of the garden.

In the house or greenhose, use an ant powder or Nippon ant killer gel. Instant coffee also seems to repel them, particularly in the kitchen. But using this is probably more expensive than using ant powder.
Woodlice They normally feed on dead plant material but they will also eat seedlings. Dust them with a contact insecticide or use slug pellets.
Mealybug For a biological control in an enclosed space, at the first sign of attack introduce the predator Cryptolaemus montrouzieri.
Root aphid Bugs around the roots of house plants. Use plant pins that contain a systemic insecticide
Red spider mite Small red spider looking insects. Often found on plants in the greenhouse and conservatory, particularly in dry, warm weather, yellowing leaves or shiny silver patches on tomato leaves and fine webs on the leaves and stems. To reduce infestation, mist the plants with water regularly. For a biological control in an enclosed space, at the first sign of attack introduce the predator Phytoseiulus persimilis mite, but they are only useful in a humid greenhouse or conservatory.
Aphids (greenfly/blackfly)

Aphids particularly like to feed on the sap of fresh green shoots of plants and the tender, younger growth at the tips of branches.

The sticky excreta from aphids can encourage the growth of unsightly, black 'soot like' mould.

Hang a nut feeder close to the plants that are affected, and the blue tits that are waiting their turn on the feeder will pick off the aphids.
Aphids will also be cleared up by ladybirds and their larvae as well as the lavae of lacewings and hoverflies (hoverflies are harmless and there are approximately 250 species native to Britain).
If the infestation is serious, pinch back to the closest aphid free bud.
Vine weevil/black vine weevil (Otiorhynchus sulcatus)

Adults eat semicircular holes in leaves, whilst the young grubs eat the roots of plants, in particular containerised plants.

If you plants have been watered but still look droopy, knock it out of its pot and have a look for the maggot looking weevil in amongst the roots. The grubs are white with a brown head about 10mm long. The adults are 8-12 mm long, have black wing cases (although they are flightless) with small orangey patches, they also have a pointed head.

The grubs favourites include chrysanthumum, primula, polyanthus, cyclamen, lilies and strawberry plants.

An adult vine weevil will lay between 500 and 1500 eggs over a couple of months, and this occurs two to three months after they have emerged from the soil.

The adult vine weevil will start to emerge as the soil warms up in April. Put corrugated cardboard or moistened, folded fabric under plants, where the adult weevil will hide during the day, knock out the cardboard in the evening and squash the weevils.

Lift any sorry looking plants and check for the grubs, squashing them as you find them.

Always use fresh compost when planting up hanging baskets, pots and containers, as the eggs are typically too small to see (about 1mm).

Nematodes (small worms that use the vine weevil grubs as their hosts) are available, look for the Heterorhabditis or Steinernema species. These should be applied from mid-March through to May, and again in late summer (Aug - Oct). The roots of plants treated with nematodes have to be kept moist. Bio Provado Vine Weevil Killer 2, will protect plants for up to 4 months.

Earwigs Earwigs love late flowering plants like dahlias, gladiolus and chrysanthemum, they climb up in the morning and eat the flowers during the day. Push in a cane, with a small upturned flowerpot stuffed with loosely fill a flowerpot with straw or hay and leave upturned on the plant stake, in the morning empty the flowerpot, stamping on the escaping earwigs.
Pear midge (Contarinia pyrivora) If the fruit falls whilst still immature this might be due to the 'June drop' where fruit trees shed some fruit to reduce overcrowding. However if the fruit has brown patches at the top and bottom, it's likely that it's the effect of the pear midge (Contarinia pyrivora). The adult lays its eggs in the flower, the larvae (which grow to a couple of mm) hatch and eat the fruit. Check and remove any other browning fruit and collect any windfalls to stop reinfection the following year.
Onion fly Small grubs burrow into the stems and bulbs of onions, leek and garlic. Especially plants grown from seed. As they tend to affect plants grown from seed, purchase young plants directly from garden centres or mail-order companies. Alternatively try planting in a different area of the garden where you haven't planted alliums for 3-5 years.
Codling moth Caterpillers found in the fruit of apples and pears. Codling moth caterpillers hatch in late July/early August and eat the core of the fruit, before burrowing its way out of the fruit. The moth breeds in June and July, so hang codling moth traps in the trees in early June, these use pheromones to attract the male moth, which gets caught on the sticky strip in the trap, so they are unable to fertilise the eggs. Apply glue or grease bands around the trunks of the trees, about 18inches (75cm) above soil level, from early October. These bands trap the flightless females as they climb into the tree. Check every couple of weeks and reapply bands or horticultural tree grease as necessary until April, as some female flightless moths emerge in spring.
Plum fruit moth Caterpillers found in the fruit of plums and damsons. Hang specific plum fruit moth pheromone traps to reduce the infestation.
Eelworm Small holes in potatoes when the potato is cut open there are large brown holes throughout the flesh. Eelworms seem to affect main crop more than early varieties and in particular on newly cultivated ground. Leave a longer period between replanting potatoes or tomatoes in the crop rotation, the longer the better, but at least 4 years. Plant marigolds between rows of potatoes to deter the eelworm also wrap the potato tubers in newspaper when planting them. There are also eelworm resistant cultivars available.

Mould and fungal disease problems in the garden >>

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