Dealing with Pests in the Garden

By Steve Malsher MCIHort

For a professional or keen amateur gardener, keeping your area looking at its best is what we all strive for. At this time of year, roses in fine bloom and regimented rows of vegetables, soon to be ready for the table, is quintessential of a British summer.

There is, however, lurking in the undergrowth, an army of pests ready to deprive you of aesthetic quality and the vegetables you have nurtured. There have been some more noticeable offenders this year and I would like to offer some solutions to consider before you reach into the chemical aisle at the garden centre.

Dealing with Pests in the Garden
Dealing with Pests in the Garden

Black Fly and Green Fly

These little pests attack a multitude of plant species. They feed by inserting their stylet (feeding tube) into the soft tissue of a plant, meaning they can spread bacterial and viral infections. Primary damage consists of leaf curl and blistering, bud and flower distortion and reduced vigour of the plant. As a secondary, they excrete “Honeydew”, which turns into sooty mould on leaves, reducing the plant’s ability to photosynthesis. Ants actually feed on the honeydew and are often seen farming aphids; sedating them so they do not leave the plant. A female aphid, which at this time of year they all are, can give birth to five live aphids a day without the need of a male.

Fortunately, we have lots of allies in the garden. All of the tit species feed on them, so nest boxes are a must. Ladybirds and lacewing larvae also feed voraciously on them, so encouraging those into the garden by setting up specialist nesting boxes will help enormously.

For self-help without using chemicals, don a pair of gloves and simply wipe them off. Nip out the soft tops of broad beans and spray with a jet of water from a hose, which breaks their stylets so they are unable to feed. Spray with a weak soapy solution.

Glasshouse whitefly is a sap-sucking true bug that can reduce the vigour of plants and excretes a sticky, sugary substance called honeydew on the leaves, stems and fruits of its host plants. They are generally found on the underside of leaves and fly into the air when disturbed.

It attacks many vegetables and ornamental plants grown in greenhouses – as well as houseplants. These include: cucumbermelontomatopeppersChrysanthemumGerberaPelargoniumFuchsia, poinsettia and Verbena. Outdoor plants can also be attacked, but not to such a damaging degree. Note that whiteflies seen on brassicasViburnum tinus, honeysuckle, evergreen azalea and rhododendron are other species of whitefly specific to those plants.

Dealing with Pests in the Garden

Glasshouse whitefly thrives in warm conditions, which is why it is not usually a problem on outdoor plants. This insect is active all year round on houseplants and in greenhouses.

There are three easy ways of controlling this pest and although the first is quite comedic, it is effective. Take your vacuum cleaner to the greenhouse, disturb the plants so they fly up and suck them all in. Secondly, you can hang up yellow sticky traps, flies are attracted to yellow. The only problem with this is you may trap some beneficial insects. Lastly, employ some help from a tiny wasp called Encarsia Formosa. You can buy these little fellows online in the form of a piece of card with infected whitefly larvae. Simply hang the card in the greenhouse and when they hatch, they go to work.

Adult vine weevils cause notch like leaf damage, which can be unsightly, but rarely affects plant growth. The adults are 9mm (about 5/16in) long, dull black beetles with a pear-shaped body when viewed from above. Adult weevils may be seen on the foliage at night; during the day they hide in dark places. They are slow-moving insects that cannot fly but they are excellent crawlers and climbers. The adults are all female and can lay as many as 200 eggs each, so controlling these can go a long way to controlling the more devastating grubs.

Dealing with Pests in the Garden
Dealing with Pests in the Garden

Again, there are a number of options before reaching for the chemicals. On mild spring or summer evenings, inspect plants and walls by torchlight and pick off the adult weevils. Shake shrubs over an upturned umbrella, newspaper, or similar, to dislodge and collect more.

  • In greenhouses, look under pots or on the underside of staging benches where the beetles hide during the day.
  • Trap adults with sticky barriers placed around pots or on greenhouse staging, even around the stems of trees and shrubs
  • Encourage natural enemies. Vine weevils and their grubs are eaten by a variety of predators such as birds, frogs, toads, shrews, hedgehogs and predatory ground and rove beetles.

One can now buy nematode traps for the adults containing Steinernema carpocapsae. The traps should be placed on the ground below plants damaged by the weevils during the summer. The adults enter the trap during the day and are infected by the nematodes.

Good luck and happy hunting in your garden. Of course, if you do suspect any kind of pest or disease damage, N I C H O L S O N  S have a wide range of solutions and expertise available to you. Just give us a call on 01869 340342 (option 1) or email

Dealing with Pests in the Garden