Pests and Diseases Affecting Vegetables

There is no known method of preventing attacks on the garden by insects and diseases which can be put into action early in the year and the job be complete for the whole season. Alas, during every part of the year, some particular pest is beginning to attack either flowers, fruit or vegetables.

There are of course hundreds of different entries that should be made when dealing with the subject completely, but for the purposes of a basic general guide, only the few habitual attackers have been listed.

There is no doubt that, although not a sure preventative, healthy plants grown in well fed soil are able to put up a far better fight than weaker ones, and this should always be remembered during the whole year of preparation and planting the garden.

Although it is possible to list the troubles along with details of the kind of treatment most effective for their cure it must be fully understood from the outset that all chemicals for this purpose have their own particular instructions printed on the containers in which they are supplied and these should be read carefully before use.

Many of the branded names of insecticides have a basis of either nicotine, derris or pyrethrum and these have all been thoroughly tried and tested by the manufacturers and are guaranteed to be effective when applied correctly.

Naturally all insects are not injurious to the garden and indiscriminate action should not be taken until the troublesome ones are identified. Such insects as ladybirds, centipedes and generally speaking most beetles along with dragon-flies and lacewings do far more good than harm as many of them eat large quantities of greenfly and other insects during the season.


It will not be necessary to describe this pest as they are of course very well known, and are most unpleasant when they appear in large numbers in the greenhouse or open garden.

There are several ant killers marketed either in liquid or powder form and these should be sprayed or dusted onto the affected areas after a watch has been made to discover the ants’ run.

Aphids (Greenfly and Blackfly)

This group of insects can be found in several colours and attack the young shoots and leaves by sucking the juices from them. They are particularly destructive on roses, chrysanthemums and most soft fruit bushes.

At the first signs of attack spray well with a solution of liquid Derris or liquid Malathion and repeat this treatment every 10—14 days until the pest has been eradicated. Throughout the year it will be necessary to keep an eye on all plants and repeat the spraying when required.

Big Bud

This causes bud swelling and is mainly found on black currants. It is in effect the results of an attack by the black currant Gall Mite and infected buds must be removed and the whole bush sprayed with a solution of lime-sulphur before the flowering period begins.

Any really badly infected bushes should be removed and at once burned.

Black Spot

This disease frequently attacks the leaves of roses and can be identified by the round black patches which appear on the surface of the leaves.

Remove all fallen leaves which have become infected and burn them at once. Spray the roses with Bordeaux Mixture or a good rose fungicide every 10-14 days until the treatment is effective.

Cabbage Caterpillar

This is the larva of the well known Cabbage White Butterfly and can be most destructive on all green vegetable leaves.

At the first sign spray with a solution of liquid Derris or a branded insecticide.

Capsid Bug

This pest attacks the leaves and fruits of apples, currants etc. and the effects appear as brown marks on the leaves and rough scars on the fruit.

It can be treated with a good wide-area spraying of liquid DDT including the surrounding ground on which the bugs have fallen.

Fruit trees should however be winter sprayed to help combat this pest.

Carrot Fly

These are yellowish-white maggots which are found in the roots of carrots and parsnips.

Very little can be done after the maggots have entered the crop but at the egg laying stage an application of Gamma Dust or powdered Napthalene will help to discourage the fly.

Club Root

A fungus disease which causes cabbage, cauliflower and similar crops to grow with swollen roots and poor top growth. Usually found in conditions where the soil is lime deficient. This can of course be dealt with and if the disease is expected the young plants can be dipped into Calomel Dust paste before transplanting to the vegetable garden.

Cuckoo Spit

Usually seen on many plants as a white froth attached to the stem near to the buds. Each piece of froth contains the larva of the froghopper.

This can be eliminated by a spraying of Nicotine solution applied with force.

Damping Off

This fungus disease usually attacks seedlings of many plants particularly those being raised in the greenhouse. Its effect can be seen when the seedlings begin to fall over and die. The usual causes are an excess of moisture, poor ventilation and overcrowding. These can be remedied easily and the greenhouse soil used for planting and potting sterilised with Formaldehyde when the house is empty.

A liquid fungicide watered onto the seedlings from time to time will also discourage this condition.


In most parts of the garden the earthworm is the gardener’s friend as it is continually aerating the soil and at the same time pulling down decaying leaves etc. which will help to provide useful food.

However, the earthworm can be a nuisance if continually throwing up worm casts on an ornamental lawn and they may be then dealt with by an application of wormkiller. Their aerating work must in this case be taken over by regular use of the garden fork.


These well known insects may be found on plants in the greenhouse or the outside borders. They are particularly troublesome on dahlias and should be treated with a spraying or dusting of liquid or powdered DDT.

Gooseberry Sawfly

The caterpillars of the gooseberry sawfly are green with black spots and can be seen eating the leaves of gooseberry bushes in early May.

As soon as they are noticed they must be immediately sprayed with liquid DDT before they are able to do too much damage.

Greenhouse White Fly

Small moth-like insects which attack tomatoes and other greenhouse plants. They suck the sap from the leaves causing them to discolour and appear spotted.

Treatment with one of the smoke fumigating cones will be effective, provided that the manufacturer’s instructions are carefully followed. These are not usually recommended when the greenhouse has direct access to the home. An alternative would be to spray the plants with liquid DDT at fortnightly intervals.


These are the brown or greyish-black grubs of the Daddy-long-legs or Crane Fly and do their damage by eating away the roots of plants under the surface. They are particularly injurious on lawns during- November and December and whenever located they must be treated with an application of DDT dust. On lawns the dust may be distributed more evenly if it is mixed first with a quantity of sand.

Mealy Bug Small white waxy insects found together with a mass of woolly substance and often seen on greenhouse vines and other plants under glass.

Treat with a spraying of liquid Malathion. The stems of affected vines should however be scraped before spraying and the treatment completed before the fruit has begun to swell.


A fungus disease found on the leaves of many plants and it is usually recognisable by white powdery patches which have appeared on the surface of the leaves.

Roses affected by this condition should be well sprayed with a brand of rose fungicide repeated at weekly intervals. Most other plants can be dealt with in a similar way using a mildew fungicide and when the plants are under glass they must be given adequate ventilation.


These insects are cylindrical in shape and on most segments of their body they have two pairs of legs. They usually curl up when they are disturbed. This must be understood as they should not be confused with Centipedes, beneficial in the garden, which have only one pair of legs to each segment and are flatter in appearance Millepedes can be discouraged by regular hoeing and generally cultivating the soil, but if the pest continues an application of Gamma Dust can be hoed into the surface of the soil.

Potato Blight

This disease can cause serious losses to a potato crop during June and July if the weather is warm and damp. It is easily recognised as brown blotches spread across the leaves beginning at the edges and finally affecting the whole plant.

A thorough spraying with either Bordeaux Mixture or a liquid copper fungicide should be made but never during the sunniest part of the day. This treatment should be given in June as soon as the symptoms appear and repeated if necessary in July.

Raspberry Beetle

The grubs of the raspberry beetle are often found in the ripe fruit of raspberries and blackberries. This is often the first sign of trouble and to prevent this happening the fruit bushes should be sprayed with liquid Derris 10 days after the flowers are in full bloom and repeating the treatment again after the following 10 days.

Red Spider

These small red mites attack the underside of the leaves of a wide range of fruit trees and plants both outside and in the greenhouse. The leaves become mottled and turn yellow.

Particular plants to watch for this pest are tomatoes and carnations and trees such as apples and plums. Thorough spraying with liquid Derris, repeated when necessary, should cure the attack.

Silver Leaf

This disease is the result of a fungus infection which attacks the branches of trees, particularly plums, causing the leaves to turn a metallic silver colour.

All infected wood should be removed and burned during the early summer and all cuts made must be clean and painted over with lead paint to stop further entry of the disease spores.


These well known pests are continually at work in the garden eating their way through many young plants. Whenever located they should be destroyed with applications of a proprietry brand of slug killer used according to the instructions.

Tomato Leaf Mould

Greenhouse tomatoes are frequently infected with this fungus disease and severe losses can be suffered if it is not recognised and treated as soon as possible.

It begins as yellow spots on the leaves accompanied by a grey mould on the underside. The leaves finally shrivel and die.

If this happens the overhead watering must immediately be reduced and plenty of ventilation given to the greenhouse.

All badly damaged leaves should be removed and burned and after the season is over the complete house must be cleaned thoroughly and fumigated.


Wireworms are the larvae of the Click Beetle and spend their time eating away the roots of most garden plants and vegetables. They are shiny yellowish-brown grubs and are often seen in newly dug soil.

They are most destructive and should be treated with Gamma Dust or other insecticide suitable for the purpose. This may be lightly hoed into the surface of the soil.


These are usually found hiding during the day under flower pots and boxes and anywhere that is damp and offering shelter. They frequently attack greenhouse plants and any rubbish that is harbouring them should be cleared away. If they are found in large numbers a treatment of suitable insecticide such as DDT may be given.

At the end of each application of insecticides or other garden sprays, the syringe must be thoroughly cleaned and stored in a dry place.

Always keep packets or containers of chemicals in the dry and always out of the reach of children.

26. August 2013 by admin
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