Greenfly & Other Pests

It’s a good year for greenfly, blackfly and aphids.  The real answer is to grow strong, healthy plants, and encourage as many natural predators as possible. We’ll look at why spraying works against you in the long run.

The trouble starts when you have a delicate and extravagant plant growing in your herbaceous border, bred without regard to natural strength. Or with vegetables, susceptible plants are fast growing ones with thin, speedily growing stems that are under strain of carrying a heavy crop. In my garden, my main fly problem is blackfly on broad beans.  The risk is worse on spring sown beans than on the Aquadulce variety, which we sow in October and finished harvesting this year in early June. Spring sown beans are more susceptible because they grow more quickly in the warmth of June, when the likelihood of attack is greatest.

An almost daily inspection is useful in early summer. As soon as you see them, you should pinch off the top 2” of your plants, or more if the individual plant is badly infested. It is better to pinch the tops out before you get blackfly, when there are already plenty of flowers on the stem. In mid June, I have so far found two infected plants. One of them had several ants on them, and many dead blackfly. Note here that you shouldn’t plant your beans too close together, or they’ll set less beans from their flowers.

Many people remember the TV programme that showed ants holding aphids while sucking the sap out of them, without killing the aphid. However, there are only a few species of ant, uncommon in the garden, that do this. Most kill the aphid. This happened last year, when a bad attack of blackfly soon turned into an awe-inspiring sight of black skeletons which impressed my children.

Whitefly on cabbage can  also helped by encouragement of predators, a strong plant and choice of variety.  Keeping the plant watered, but not over watered, helps in dry periods. A thick coating of compost on the soil slows water evaporating out of the soil. It is said that marigolds can help by attracting hoverfly, whose larvae eat aphids, mealy bugs and thrips. I have not noticed any difference, but the marigolds look good!

Try not to use artificial fertiliser. This leads to unbalanced, speedy growth, whereas compost gives a balanced uptake of  nutrients that make a thicker stem. This is too tough for most aphids to penetrate.

Natural predators. The less fungicides and insecticides you use, the more specialist aphid eating species there will be in your garden, such as ladybirds, midges, parasitic wasps, hoverfly larvae, crab spiders and lacewings, not to mention certain fungi that kill them as well. So, try not to spray.

Last winter I used a few slug pellets in my greenhouse to try and stop an annoying slug eating my pak choi in the greenhouse. Immediately the pak choi was covered in greenfly.  A few weeks later, after throwing the slug pellets away, the greenfly started to disappear again. It just shows that once you treat one problem with chemicals, you create another.

Some people spray naturally occurring pyrethrins, extracted from African chrysanthemum, to combat greenfly. To make the compound store well, chemical companies have altered them, and they now result in a variety of symptoms, especially in pets, including drooling, lethargy, muscle tremors, vomiting, seizures and death, not to mention the effects on humans.

If you have time, wiping affected areas with a soft, soapy brush will eventually knock them all off for good.

To sum up, if you have an aphid problem, think about how you are looking after your plant first and foremost. And look after your wildlife.

Big fleas have little fleas on their backs to bite them. And little fleas have other fleas And so on, ad infinitum.

And if you want more wit, come to our garden  opening at Yews Farm in Martock for charity on Monday 13th & Tuesday 14th July, 2-6 pm.