Garden Pests and Diseases – Barriers and Traps
Garden Pests and Diseases – Barriers and Traps
The age-old technique of netting plants against pests or using other forms of barriers to protect them can be most effective. Traps can be used in the garden to reduce pests in a small area and to monitor new arrivals so that the timing of an appropriate spray or introduction of a biological agent can be made accurately. The use of traps to catch pests or devices to scare them off can also help to reduce damage to plants.
A wire mesh or electric fence is the only effective method of keeping rabbits out of a garden.
Tree guards and shelters
Newly planted trees can be protected from grazing animals, and the weather, by the use of tree shelters — tall, thin cloches that are placed over individual plants.
Spiral tree guards wrapped around the trunk of young trees will protect them from rabbits and deer which may otherwise strip their bark in winter.
This proprietary product consists of a cord composed of thousands of threads of rayon which are teased out into a “spider’s web”. It is placed over fruit trees and bushes to protect buds from bird damage.
Grouping soft fruit plants together within a fruit cage can be an efficient method of protecting the ripening fruit from birds. Proprietary fruit cages are available in various sizes, and the sides of the cage should be covered with netting which has a mesh size 12-18mm (½ – 3/4in). Cover the top of the cage with 18mm (3/4in) netting. The top netting should be removed when fruiting has finished and not replaced until after blossom has set. This allows access for pest-clearing birds and pollinating insects and also avoids the danger of snow bringing down the roof.
Individual fruit trees and bushes can be protected from birds by draping netting over them. This is much simpler where the plants are trained against a wall.
Strawberries can be covered with a low netting, supported on posts about 40cm (16in) high. A glass jar or plant pot placed upside down on top of each post will prevent it pushing through the netting. For individual rows, the netting can be draped over wire cloche hoops.
Vegetables can be protected in the same way, varying the height of the netting as appropriate.
Very fine mesh materials are available that can be used to protect plants against smaller pests such as flea beetle, carrot root fly and cabbage caterpillars. These covers are very lightweight and some can be placed directly over a growing crop without the need for any framework for support. These covers have an advantage over traditional cloches in that they allow air and rain to penetrate, so you do not have to remove them every time you want to water the crops or let in air to avoid overheating.
When using a crop cover, it is important to put it in place before the pest is present —usually as soon as a crop is sown. They can, if necessary, be left in place for the life of the crop. Be sure to check regularly for weeds and diseases, both of which can thrive in the sheltered environment.
Wherever possible, remove covers as soon as the plants can look after themselves. Choose a still, overcast day to reduce the shock and replace covers at night for a while until plants are hardened off.
A fine, lightweight, spun polyester material which is placed directly over a crop. The fleece should be cut to the size of the plot to be covered, allowing at least an extra 30cm (1 ft) all round, depending on the height the plants will reach before the cover is removed. The material is held down by covering the edges withor using proprietary pegs made for the purpose. It should be pulled fairly tight, the excess material being held at the edges; this must be released as the plants grow. Horticultural fleece also gives some protection against frost.
A fine mesh plastic material that can be used in the same way as fleece or to cover tunnel cloche hoops. It is longer lasting than fleece but does not give as much protection against the weather. Other materials of a similar nature are available.
Root fly barriers
Cabbage root fly
Cabbages and other members of the brassica family can be protected from the cabbage root fly by the use of small squares of carpet underlay.
Cut 13cm (Sin) squares of rubbery carpet underlay. Make a slit to the centre. Lay the squares around newly planted brassicas, making sure that they lie flat on the soil. The underlay, which will stretch as the plant grows, will prevent the cabbage root fly from laying its eggs in the soil around the roots.
Carrot root fly
A 75cm (30in) high barrier erected around a plot of carrots can give considerable protection against the carrot root fly. The barrier can be made of polythene, clear plastic or fine mesh netting (the best in windy areas) supported by four sturdy corner posts. It should be erected as soon as the carrots are sown.
Cloches to cover individual small plants can be made from plastic drinks bottles. These can give protection against many pests, including slugs.
Use the biggest size of bottle available to give the plants room to grow. Cut the bottom off, using a sharp serrated knife or scissors. Remove the screw tops for ventilation.
Pheromone baited traps
Some proprietary traps use synthetic pheromones (sex hormones) to attract specific moth pests into a trap from which they cannot escape. They can be used against the codling moth and the plum moth. On their own they may reduce pest damage to an acceptable level; alternatively, by indicating the presence of a pest, they can help to time a spray effectively.
Sticky yellow traps
Yellow plastic cards covered with a non-drying glue are available for use in houses and. They will trap a variety of pests including whitefly. This may be sufficient to control the pest; alternatively, they can be used to indicate the presence of a pest so that the appropriate biological control agent can then be introduced in time.
A band of grease can help to protect fruit trees and ornamentals from winter moths and ants—pests that climb up the trunk of the tree. A proprietary fruit tree grease should be used. This can be applied directly to older trees in a 10cm (4in) band around the trunk, 1-2m (3-¼ – 6-1/2ft) above ground. In the case of young trees, where the bark can be damaged by the grease, a proprietary paper-based grease band should be used.
If the plant has a stake, either apply the band above the point where the stake is attached or grease band the stake too.
A non-drying glue is available that can be used to make a sticky barrier on pots and legs of greenhouse staging which will act against vine weevil, ants and woodlice. Where applicable, wrap a strip of wide PVC tape around first then smear it liberally with the non-drying glue. This can then be removed easily at the end of the season.
Slug traps (see Slugs and Snails – Garden Pest Control)
Scaring and repelling devices
Various devices for scaring and repelling larger pests such as cats, rabbits and moles are available. Most are not that effective but may be worth a try if you have a persistent problem.