Anyone who has tried to grow vegetables will know that sooner or later the plants are going to receive some unwelcome attention from aphids. Aphids can be among the most destructive insect pests on cultivated plants in temperate regions. The damage they do to plants has made them enemies of farmers and gardeners the world over. From a zoological standpoint however, they are a highly successful group of organisms, due partly to their ability to reproduce asexually.
About 4,400 species are known, all included in the family Aphididae.
Aphids are small, soft-bodied insects with long slender mouthparts that they use to pierce stems, leaves, and other tender plant parts and suck out fluids. They have long legs and antennae and may be green, yellow, brown, red, or black, depending on the species and the plants they feed on. A few species appear woolly or waxy, due to the secretion of a waxy white or grey substance over their body surface. Many aphid species are difficult to distinguish from one another.
Most species have a pair of tube-like structures called cornicles projecting backward out of the hind end of their body. The presence of cornicles distinguishes aphids from all other insects.
Almost every plant has one or more aphid species that occasionally feed on it.
Smallholders should take special note of the fact that some aphids transport viruses and disease as they move from one plant to another.
Winged aphids carry a troublesome virus known as the Barley Yellow Dwarf Virus or BYDV and farmers need to know when these aphids are active in an area. BYDV is a worldwide virus disease of our most important grasses, including wheat and maize.
The Agricultural Research Council has established four suction traps to monitor aphid flight patterns, including one in Brits. Winged aphids migrate in upper-air currents, especially those of 12.2 m and higher.
Check your plants regularly for aphids ~ at least twice a week when plants are growing rapidly, in order to catch infestations early. Many species of aphids cause the greatest damage in late spring when temperatures are warm but not hot. For aphids that cause leaves to curl, once aphid numbers are high and they have begun to distort leaves, it’s often difficult to control these pests, because the curled leaves shelter aphids from insecticides and natural enemies.
Many aphid species prefer the underside of leaves, so turn leaves over when checking for aphids. On trees, clip off leaves from several areas of the tree.
You might be able to contain the infestation by spraying the aphids off the plants with a hose. If you don’t mind getting your hands dirty, small infestations can be wiped out by hand.
The best approach to good vegetable production is to prevent pest and disease attack rather than trying to cure it. For this you need to ensure a healthy soil and stable environment for plants to grow in. The main way in which this is done is to promote diversity.
Work with nature and copy the natural ways in which plants grow. Insects and “weeds” are a part of nature.
We can encourage those insects and plants that help us in the garden. Ladybirds, praying mantis, lacewings, wasps, frogs, lizards and birds all eat the insect pests that harm our gardens. If you leave these natural predators in your garden, they will help you.
It is also possible to mix vegetables with other plants, particularly strong smelling plants that deter pests and attract predators. Camphor, mints, scented pelargoniums, feverfew, African wormwood, pyrethrum, southernwood, lavender, rosemary, sage and many other herbs have spicy/bitter scents rather than sweet ones. They can also be used as aphid-repelling mulch, by spreading the leaves around newly planted seedlings.
You can use plants as trap plants: nasturtiums for example, attract aphids away from other plants because they are more attractive to the pests.
When actively growing amongst desirable crops, these herbs can confuse pest insects by masking attractive scents. Marigolds and garlic chives are also insect repellents.
There are home-made sprays that you can try. If you must use insecticide sprays try to use natural remedies, so that you don’t kill off beneficial insects at the same time. Chemical sprays also break down slowly, so their damage continues for a long time.
Remember that non-toxic insect sprays are used to deter or deflect the pest, or to disturb its breeding cycle. They don’t kill the insects.
Use the following plants in your battle against aphids: aloe leaves, nettle leaves and stems, blackjack seeds, whole marigold plants, whole khakibos plant or tomato leaves. Half fill a bucket with the plant matter, add just-boiled water, stir and leave to stand overnight. Strain out the leaves and stems and add them to your compost. Add 2 tablespoons of dish-washing liquid and mix. The spray will keep for up to a month. Spray onto affected plants every few days, as the herbal insecticide will break down quickly. Be sure to spray the underside of the vegetables as well. Spray the plants and the ground surrounding the plant, as aphids might jump off or sit on the ground until it is safe to attack the plant again.
Another option is the onion and garlic spray: Roughly cut a full pod (including the skins) of garlic and 4 onions. Place in a container. Some suggest adding a tablespoon of crushed, dried or fresh chilli or chilli seeds, or one teaspoon of chilli powder. Pour 3 litres of boiling water over the material, close the container and allow it to stand for one day. Strain and keep the fluid. Add 2 tablespoons cooking oil and 2 teaspoons liquid soap, and mix well. Mix one cup of this mixture with 5 cups of water. Spray weekly, making a fresh batch every week.
Another remedy specifically for aphids is citrus tea. Chop the peels of three oranges or of two lemons and cover with hot water. Leave overnight, take out the peels, microwave the liquid for 5 seconds and store in the fridge. When required, add a teaspoon to 1L of water, 1tsp of dishwashing soap and 1tsp of white spirit vinegar.