Unfortunately from time to time our fruit, flowers and vegetables can be attacked either by pests or by virus or fungus disease. The nature and intensity of these attacks varies from season to season. In the average garden the damage caused is of no great consequence, but it is a wise gardener who is prepared to combat either of these problems. Of course, in these days when more and more people are growing their own food crops it would be foolish for the gardener to allow pests or disease to reduce the yield.
It is the intention of this article to deal with the more common pests and diseases because these are the ones most likely to be encountered. For convenience the attack is defined by the part of the plant which is affected, and first of all we deal with the foliage of plants. The signs of an attack are described briefly to aid identification, and the relevant control or preventive measure is given in each case.
Irregular areas or holes eaten out of leaves
This can be a sign of attack by one or two different types of insect. Caterpillars can cause a great deal of damage and the period of attack is normally from about March onwards.
Control: Spray with BHC, derris or malathion.
Earwigs can also cause irregular holes in foliage and these are generally seen during the period between May and late September.
Control: Spray or dust the foliage with BHC.
Scalloped edges on leaves
The scalloped effect is an indication that the plant has been attacked by either leaf cutting bees, vine weevils or the pea and bean weevil. The period of attack is from about March to June as far as the pea and bean weevil is concerned and from about June onwards for the leaf cutting bee and the vine weevil. Control: Spray with BHC dust.
White flies on leaves
Masses of tiny white flies on crops such as cabbages and also indoor plants such as tomatoes are a sign of whitefly attack. The period of attack is from about early May to late September.
Control: Spray with BHC, pyrethrum or malathion. There are also special fumigating preparations available for use in greenhouses, but the instructions must be followed very carefully.
Insects on leaves and young shoots
Lots of tiny flies of black, green, pink or even red colour are indications of aphid attack. The spring and early summer are the critical periods outdoors, but under glass these creatures can attack during any part of the gardening year. Control: Use malathion, BHC or derris.
Woolly or mealy white covering on foliage
This is a sure sign of attack by the mealy bug. These insects can attack at most times of the year.
Control: Use a systemic insecticide such as dimethoate or formothion.
Leaves practically reduced to a skeleton of veins
This is an attack by the gooseberry sawfly, and the period of attack is likely to be from about April to late August.
Control: Spray with dcrris or malathion.
Chocolate coloured spots on leaves
There is a disease which aflects broad beans known as chocolate spot. The trouble usually affects plants grown during the winter.
Control: Apply potash in the form of sulphate of potash to encourage sturdier and healthier growth at the outset.
Dark spots on rose leaves are an indication of black spot, a virus disease which is less common in town gardens than in the country.
Control: Spray with a fungicide if plants are badly affected. The best control is just to burn affected leaves and prunings.
Brownish mould spots or areas underneath leaves
This is the leaf mould disease which chiefly affects tomatoes in the greenhouse. It can occur early on in the year in May, but is more prevalent in the middle of the summer. The cause is poor ventilation and general damp conditions.
Control: Allow more ventilation, leave plenty of spacing between plants, and grow the modern, more resistant varieties. Plants can also be sprayed with a copper preparation such as zineb.
Leaves with white tunnels in them
This is a sure sign of the chrysanthemum leaf miner. It affects plants from early July to late autumn, and it can affect several other plants as well as chrysanthemums. Control: The badly affected leaves should be removed and burnt, and spraying with 131IC or diazinon should effect a good control.
Frothy areas on foliage
This is a sign of the cuckoo spit caused by the frog hopper. It can affect a wide range of plants and is usually found during the height of the summer.
Control: Light attacks are fairly harmless, but a spray with either 131 IC or malathion will be effective if the trouble is serious.
Leaves wilting badly or drooping
This can just be a sign of dryness, and it can also be a sign of some check to growth due to root damage. A distinct wilting of foliage in tomatoes, however, is a sure sign of a disease called verticillium wilt. The plants can be affected at any time of the growing period.
Control: The best control is the severest—pull up and burn the affected plants, and at the end of the season thoroughly sterilize the soil. Some plains not badly affected may be encouraged to grow on by top dressing with moist peat around the base of the stems. This action encourages roots to form higher up the stems in that area and it may save the plants.
Streaks and black and brownish marks on foliage
This could well be a virus disease and can occur at any time of the year on plants both indoors and outdoors. Quite often too the markings continue into the stems. Control: There is unfortunately only one treatment, and that is to dig up and burn the affected plants and to sterilize the soil where the plants have been growing.
Leaves badly curled
This can affect many plants and is usually an indication of attacks by aphids. The usual period is from about late spring to late summer.
Control: Spray frequently with a preparation such as 131 IC or dimethoate.
Kim foliage dying
It is important here to make mention of the Dutch elm disease. It is identified by the foliage which turns yellow and then brown, and then hangs from the branches which are themselves slowly killed. The time it makes itself known is from about May to late September, and it is vital that the affected trees are destroyed. It is in fact important to notify the local authority at once if a tree on your property is suspected of having this trouble.
Stems rotting at ground level
This chiefly affects seedlings in their very early stages but can also affect more mature plants. It is a disease which is called ‘damping off’, and eventually the affected plant collapses and dies.
Control: One of the best ways to avoid the trouble is always to use sterilized seed mixtures and to make sure that receptacles such as pots and trays are scrupulously clean. It pays to dip these in dilute Jeycs fluid, formalin, or any other suitable sterilizing preparation for horticultural use. Also seedlings in boxes can be watered with a dilute solution of Cheshunt compound.
Buds failing to open
This can affect fruit and flower buds and is caused by a weevil. The period of trouble extends from about April to late May. Usually apples are badly affected, and in this case the apple blossom weevil is responsible.
Control: The best preventive measure is to spray with BHC or fenitrothion just before the buds begin to open.
Buds grossly enlarged
This is usually seen on blackcurrant bushes and is caused by the blackcurrant gall mite. It is usually seen in February and March.
Control: The buds should be picked out and burnt as quickly as possible, and the plants sprayed with lime sulphur as soon as the first flowers open. A repeat spray should be given about three weeks later.
Flower petals badly eaten
Many flowering plants are affected but especially dahlias and chrysanthemums. The culprit is the earwig. The damage is usually seen from about May to late September. Control: Spray frequently with BHC. The pest can alsb be trapped in rows of corrugated cardboard or flowerpots stuffed with straw or hay and the pots placed either near ground level or on top of cane sticks by the plants. The contents should be examined each day and destroyed.
Caterpillars found in the centre of fruit
The trouble usually affects apples and pears, and is caused by the caterpillar of the codling moth. The period of attack is from about June to late August. Control: Prevention here is better than cure. Spray about mid June with malathion and repeat the operation three weeks later.
Young fruit eaten into the centre by caterpillars
This is a type of damage which occurs obviously much earlier in the fruit formation stage and chiefly affects apples. The attacks occur from about May to late June. Control: Apply a spray of BHC or dimethoate as soon as the petals have fallen.
Raised areas or bumps on fruit
This usually affects apples and is caused by the apple capsid. It affects the fruit from about April to August.
Control: Use a DNOC petroleum or tar oil petroleum in the dormant time, which kills the eggs. Just before flowers are produced a spray of BHC or fenitrothion should be applied.
Brown or black scabs on fruit
This is closely allied to the visual type of damage of the previous apple problem. It is caused by a disease known as scab and can affect the fruits during the whole of the growing period.
Control: The treatment is to give frequent spraying as soon as the flower buds are formed, using captan of lime sulphur, but take care that lime sulphur is not used on those varieties of fruit that are known as ‘sulphur shy’.
A brown rot on fruit
This can affect most fruit trees and bushes and is caused by a fungus which produces a ringed spore over the surface of the fruit. It affects the fruit during the summer and can also affect fruit in store. That is why it is always wise to check through stored fruit regularly during the storage period and remove and destroy those which are affected, even though slightly. Control: A spray of thiophanate-methyl can be given later on in the season.
White grubs found in soft fruit
This affects loganberries and raspberries, and the culprit is the grub of the raspberry beetle, which is found from June to late August.
Control: Spray with derris or malathion when the early fruits begin to turn colour.
Fruits rotting and covered with grey mould
This affects all soft fruits and is caused by the grey mould fungus. The trouble is not often seen until the fruit is well on the way to becoming ripe. Control: The treatment is to spray as soon as the first flowers begin to open, repeating the spray at 14 day intervals. A suitable spray is bemoyl or thiophanate-methyl. Badly affected fruit should be removed and destroyed.
A circular black or brownish area at the base of tomato fruits This unfortunately can be rather common and is known as blossom end rot. It is seen when the fruit is beginning to swell.
Control: Prevent fluctuations in the water supply to’the plants and also avoid plants drying out before they receive a watering.
Brown area on tomato fruits
This usually affects the outdoor tomatoes and is caused by a fungus disease. It is more prevalent in bad wet summers and usually affects the fruit when it begins to ripen.
Control: Remove and destroy badly affected fruits and spray at 14 day intervals with Bordeaux mixture or maneb.
White grubs in pea pods
This is an irritating discovery and ruins whole crops of peas. It is caused by the maggot of the pea moth caterpillar and is seen usually in the height of summer. Control: The plants should be sprayed when the flowers begin to open, using a preparation such as fenitrothion. It may be necessary to apply a second spray about two or three weeks after the first one.
Quite often when bulbs such as daffodils are lifted the bulb is soft and rotten and a little maggot is found inside. This is the grub of the narcissus fly and it attacks between April and late June.
Control: The affected bulbs must be destroyed and the soil should be dusted with BHC dust as a precautionary measure before any bulbs are planted in future.
Holes and tunnels in tubers
This is a sign of attacks by slugs, and plants such as potatoes are particularly affected.
Control: The slugs can attack at any time of the year, and as they are usually prevalent in wet badly drained soils one control is to improve drainage by deeper digging. Proprietary slug baits are very effective but these should be used with care if domestic animals are present and are best covered with slate or a seed tray to prevent accidental damage.
Brownish discoloration of potatoes
Blight disease is the trouble and can affect potatoes especially in a wet season. The potatoes which are badly affected should be destroyed, and any doubtful potatoes should not be stored away for winter use.
Control: Earth up the potatoes to prevent infection entering around the root area.
The control for blight is to spray at fortnightly intervals from early July until late September with Bordeaux mixture or zineb.
Brownish-red area on the top or crown of parsnips This is caused by parsnip canker and it can affect the plants during the entire growing period.
Control: The parsnips should be kept covered with soil and a more resistant modern variety should be grown.
Maggots in carrot roots
These are the grubs of the carrot fly and are usually seen in the main summer period. Control: Water plants with diaimon in late August. Another way of avoiding the trouble is to sow in late May.
Cabbage plants collapsing
This is a result of attack on the root system by the cabbage root fly maggot. The time to look out for trouble is from late April until the end of September. Control: The ground should be treated with bromophis or a solution of diazimon can be watered in. Affected plants must be lifted and burnt. Collapsing cabbages can be caused by the attacks of the leather jacket maggot which is a fat grey brown colour. It is usually active between April and late June. Control: Protect the plants by working BHC into the soil.
Distorted enlarged roots
This usually affects the brassicas (members of the cabbage family) and is discovered when plants begin to collapse. This is caused by the disease club root. Control: Affected plants must be lifted and destroyed. The affected ground must be given a good limine; in the autumn and winter using hvdrated lime. It is interesting to note that if the fertility of the ground is built up with plenty of organic matter the disease can be reduced over the seasons. It is important also to practise a strict rotation of vegetable crops, and members of the brassica family must not be grown in affected ground for two or three seasons at least.
It is as well to remember that ah hough plants can show signs of distress by discoloration of foliage this may not always mean that pests and diseases are affecting the plants. It could well be that plants, especially young ones, are chilled through cold winds or poor hardening off. It could also be that the soil is in a poor way as far as drainage is concerned, or even that the plants are not receiving sufficient feeding. Healthy plants will always be produced if the ground is well manured and the plants given an occasional tonic or feed during their growth. Liquid feeds are especially good because these are assimilated so quickly by the plants that a rapid recovery often follows.
Finally, never put diseased plants on the compost heap: wherever possible leave them in a neat heap until they can dry out and be burnt later on.