Aphids-(various species) are a soft bodied (1-7mm) pest that lives in colonies. Aphids have a needle like mouthparts able to tap into individual sieve tubes. As the contents of these sieve tubes are under positive pressure, their contents surge into the aphid as it feeds on its sugary meal at an average flow rate of 1mm3 per hour. The aphids may have varying colours, notably pale green, grey-pink or black. Heavy infestations develop at the shoot tips, underside of younger leaves, stems and flower buds sometimes causing leaf curling and stunted growth. They size of the colonies quickly reduces plant vigour and can damage delicate shoots. The sugary excretions produced by aphids make the foliage sticky and can allow growth of a black sooty mould, as well as encouraging protective ants which must be removed for biological controls to work. Aphids may also spread viral diseases.
Aphids attack woody perennials first (1o Host), especially in the late spring and early summer. Most species over-winter on trees as eggs, which hatch in the spring as the buds start to open. Aphids infestations normally leave their tree hosts by late June or July when winged aphids develop and migrate to their summer herbaceous hosts (2o Host). When the winged, sexually active adults find a suitable host, the female can often rapidly colonise by asexual (without sex) reproduction giving birth to live young clones. These wingless, young clones can start feeding immediately and produce live young of their own very quickly. Winged forms develop when overcrowding or a deterioration in the host plant induces a need to move to another plant. The egg-laying form of aphids only develops at the end of the aphids’ period of activity, usually autumn, but for some species this is in the summer. Most aphid species overwinter as eggs but some can remain as active aphids, particularly in mild winters or on indoor plants.
Early damage is hard to detect, easily confused with spider-mite, the undersides of leaves develop light-coloured spots, especially near leaf veins. Eventually as colony size increases the tell-tale white skin moults litter the plant, leaves and flowers become deformed and distorted, with heavy infestations completely wilting and possibly killing plants. Surviving plants remain stunted.
Covering plants at the appropriate time of year can stop winged individuals colonising plants. Their natural control predators include ladybirds, and their larvae, hoverfly larvae, lacewing larvae and several parasitic wasps. Damage decreases in hot, dry weather and in the presence of strong, dry winds. Companion planting of coriander, anise, wormwood, or mint to drive away aphids, which are also repelled by nasturtiums, marigolds, chives, onions, and garlic.
Treat with soft soap insecticides, then Aphidius parasite. If severe colonies and open soil present, then it is appropriate to use Aphidoletes predator.