Plants are food for many types of animal – from microscopic eelworms to large mammals – but very few of these could be called pests. Unless an animal causes damage great enough to destroy the feature for which the plant is grown, it cannot be termed a pest. Examples of a pest species include: carrot root fly maggots that bore in the roots of carrots, making them useless; codling moth grubs that feed inside apples causing them to fall prematurely; greenflies, which by their presence, render lettuce inedible.
The simplest way to solve a particular pest problem is not to grow the pest’s food plant, but, if it is decided to grow the plants, and there are pests in the vicinity, control measures may be necessary.
Slugs and snails
Slugs and snails are closely related molluscs; snails have shells, slugs do not. These attack many kinds of plants, especially young plants and the soft, succulent growth of herbaceous perennials and vegetables. Slugs provide a useful function by eating dead plant tissue and they are more prevalent on soils with high organic matter where manure and compost have been applied. They are more active in wet years.
Slugs and snails can be simply collected and disposed of. Collection is made easier by laying out traps of old cabbage leaves or fruit skins. Stale beer is attractive too and a shallow dish at soil level allows them to enter and drown. Some people simply walk on every slug or snail they see. Apart from this general control, it is particularly important to protect young plants and strawberries.
A barrier of soot or egg shells gives mixed results. Otherwise, chemical slug-killers can be used. These include Draza, Hygeia Slug Pellets, Tumbleslug, Slugit, ICI Miniblue Slug Pellets, Slug Mini-pellets and Fertosan. Some of these are liquids or powders with the advantage that birds or pets cannot eat them.
Mini-pellets are smaller and more difficult for birds and pets to find than large pellets. These should be covered by a slate supported on a few stones.
Earwigs are not really pests, only occasionally eating parts of the petals of flowers such as dahlias, delphiniums and pansies. They are often responsible for ‘mystery’ damage to flowers, but this is generally so slight as not to need control. Besides, they are beneficial predators of certain kinds of greenflies and red spider mites.
The removal of debris reduces their hiding places. Upturned pots with wood-wool or dry leaves make good traps and the earwigs can then be removed. Tapping flower heads is usually enough to dislodge them.
Dogs and Cats
Considerable damage is caused to lawns, by female dogs, and to small shrubs, by male dogs, urinating on them. Keep gates closed and fence off the garden. Solutions of strong-smelling disinfectant, Scent-off or Pepper Dust have a temporary effect. Dogs often wear tracks on lawns and can be diverted by placing obstacles such as dead, leafless boughs, in their path.
Cats are attracted to freshly disturbed soft soil, in the same way that they are attracted to cat litter. Firm freshly cultivated soil and water it heavily to settle it down and make it unattractive to cats. Small twigs, especially with spiny leaves, deter cats without hurting them – they recognise the spines and go elsewhere. Be sure to remove the spiny leaves before they wither, because they can make weeding a painful business!
Caterpillars are the larvae of butterflies and moths. Typically, caterpillars feed on the shoots and leaves of plants for a few weeks before pupating in the soil, or in a dry place, and emerge as adults some weeks later, or the following spring. They vary considerably in size. Some are only a fraction of an inch long; others can reach 7.5 centimetres.
Caterpillar damage is easily recognised – irregular holes of various sizes, often bounded by leaf veins. The holes will have traces of caterpillar droppings, by contrast with slug damage which has slime trails.
Some kinds of caterpillar burrow into plant tissues, such as heads of cabbage and cauliflower. Practically every plant – trees, flowers, fruit or vegetables – has its own caterpillar pest, but they usually do not cause damage serious enough to warrant control measures.
Cabbage caterpillars are the major exception – they almost always cause considerable damage. Caterpillars can be picked or knocked off the plants, and killed. Batches of yellow or white eggs, often visible on the undersides of leaves, can be destroyed. If small holes appear on houseplants, a careful search may uncover a single, small caterpillar which can then be removed.
Chemical control is not usually necessary, except on the cabbage family. Suitable insecticides include Derris, Malathion, Hygeia Caterpillar Spray, Sybol, Picket, Crop Saver, Fentro and Fenitrothion.
Many different bird species can cause damage to plants. Fruit and vegetables are the main targets, being good food sources. Pigeons are major pests of all cabbage family plants, peas, raspberries, gooseberries and blackcurrants. Crows attack peas in rural areas. Bullfinches and sparrows strip out the buds of fruit trees and bushes.
Blackbirds, thrushes and redwings eat strawberries, cherries, apples, pears and any sort of red berries such as cotoneaster, mountain ash and pyracantha. Starlings eat cherries and, along with crows, commonly peck at lawns to get leather jacket grubs but this is at least as beneficial as it is damaging.
Netting is the most effective solution to bird damage. Crops are only vulnerable for a part of the year and can be netted at those times. Damage to cabbage family plants usually ceases when they are about 20 centimetres tall because the birds cannot see over the plants, but if they are hungry enough, damage will continue.
Scaring devices such as strips of foil or plastic work quite well, but the birds can get used to them eventually.
Ants are not strictly a garden pest because they do not damage plants. However, their presence in large numbers can be a real nuisance. Ants are social insects, living in nests in dry soil under stones and paving.
They actually farm colonies of greenflies for the honeydew they excrete and they often move greenflies to new plants. Burrowing by ants while building nests sometimes undermines small shrubs, leaving them high and dry and prone to wilting in a warm summer.
There is no effective method of physical control. Pouring hot water into the nests does not work. If the nest can be found, soak it with Hexyl or dust with BHC powder. If the nest is hard to find, leave some sugar in a little heap where the ants have been seen and a couple of days later there will be a trail of ants back to the nest.
Apply ant-killers at the entrance to the nest. These include Anti-ant Powder, Murphy’s Antkiller, ICI Antkiller, Nippon Ant Destroyer and Panant. They can need to be renewed several times until the ants are no longer seen.