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Saturday, 2 May 2009
Attack of the Greenfly!
Greenfly are amazing creatures. They survive the winter as eggs and during the warmer months they give birth to young greenfly that are already pregnant with a pregnant offspring. Not only that, but they can ride the winds for hundreds of miles to find their way to your window box. The mind boggles. So how do you kill them?
My favorite method is to gently squash them between finger and thumb, taking care not to damage delicate stems. It’s cheap, organic and effective for container plans. An alternative is blast them off with a hose. It won’t kill them all but there will be fatalities. Both these methods require persistence for success.
Insecticides are the next resort. Soft soap, approved by organic growers, contact insectides (containing bifenthrin) kill greenfly and other insects they come in contact with, and systemic insecticides (imidacloprid and thiacloprid) ingested by plant and poison insects that try to eat them. My advice would be to use insecticides sparingly to deal with the first big wave attack. You don’t really want to kill the ladybirds, lacewings, ground beetles and spiders that will eat enough greenfly to prevent them become a further problem once the population is under control.
The sugary droppings from greenfly and other aphids can often be a bigger problem than the direct damage they cause to plants. This becomes covered with a black mould that blocks out light to the leaves. Don’t worry if you see this, the plants are not diseased; they just need to be washed.
Ants farm aphids for their sugar droppings and will viciously defend them against predators. A ring of Vaseline around the base of the plant stem will close down the ants’ access to their herd.