Aphids

Aphids are a very common garden and greenhouse pest and can be found in a variety of guises. Most aphids are what are more commonly known as greenfly or blackfly but there are also a variety of other pests including the woolly aphid, root aphids and the cabbage aphid.

These tiny pests have several stages and the adults can fly so once they are established they can spread around a greenhouse or garden with great speed. Aphids can cause a range of problems. Their main form of attack is to suck the sap from fresh young shoots. In a greenhouse this can have a devastating effect on early crops as the warmer climes inside the glasshouse encourage these bugs to breed very speedily. The range of plants affected is immense and the initial results are stunted growth, and weaker plants. However the problems don’t stop there. Aphids can also spread disease. Just as mosquitoes can pass malaria to humans in areas where this disease is prevalent, aphids can spread plant viruses. These can be debilitating for crops such as tomatoes, potatoes, cucumbers, peas, marrows and squashes and many more besides and can mean the falure of that crop for the year. And if that isn’t bad enough there’s even more. Another problem related to the presence of aphids is sooty mould. Sometimes this is the most obvious sign of aphid presence and the first thing you notice, but if you look carefully you will find a mass of aphids somewhere near. They secrete sweet sticky honeydew, which covers the leaf surfaces, and sooty moulds grow on this residue, creating unsightly blackened leaves.

Although the mould is not considered to be harmful, if there’s enough of it, it can reduce the amount of light that reaches the leaves and so reduce the plant’s abilities to make its own food. Ants can sometimes be seen herding groups of aphids and are thought to be farming the bugs to harvest the stcky sweet residue that they excrete.

Aphids are almost always active except in an overwintering egg stage. But if it’s mild enough adult aphids can keep on feeding. In optimum conditions the adult female can actually give birth to live young, missing out the egg stage and increasing the population very rapidly. It is perhaps the aphid’s ability to breed and multiply so prolifically that makes it such a persistent problem.

Pest control
There are two main approaches to aphid control. If you prefer to keep your garden and greenhouse free from chemicals you must use integrated pest control which employs a range of methods to deal with the problems. Organic gardeners justifiably put great faith in the ability of nature to deal with population explosions of aphids. At just the time when aphids are breeding so prolifically, young larvae of hoverflies and ladybirds are hatching looking for food. Aphids provide an excellent, nutritious meal. Tiny bug eating birds, such as tits, may flutter in the roses picking off tasty aphid morsels to boost their die, while a range of other predators do their bit too. If your garden lacks colour and a diversity of plants you may have to wait too long for nature’s assistance. Organic gardeners find that the populations of predatory insects and animals increase year on year as their garden starts to mimic and benefit from the cycles of nature. But gardens where chemicals have been consisitently used, sometimes struggle to rebalance when the pesticide use is ceased and the gardener turns to nature to control pest invasion. To ensure better pest control naturally, plant brightly coloured annuals and grow a mixture of plants to encourage a wide variety of natural predators. Feed the birds and create wildlife havens to provide food, water and shelter such as hedges and ponds.

For greenhouse control you can even import aphid busting bugs such as the aphid-eating midge Aphidoletes or the aphid parasite Aphidius. These are biological controls that are used to deal with aphids. The former is best employed for large aphid colonies and the latter is better where there are fewer aphids over a range of plants. Some gardeners collect ladybirds from the garden and place them into the greenhouse in spring, where they benefit from the early crop of aphids on greenhouse plants and can start to breed in the warmer temperatures. Outside, gardeners can encourage a natural population of lacewings and ladybirds or add to it by purchasing packs larvae to speed the natural process.

There are many chemicals available at the garden centre that can be used to control aphids. Check the label and ask for assistance. Be very careful of using any chemicals on open floweres and in daylight when bees and other beneficial insects are flying. Insectides will affect good and bad insects and can have a detrimental effect on garden friends and essnetila pollinators. Always read the label carefully and never apply any product to a plant not included in the instructions.