PESTS OF THE VEGETABLE GARDEN
APIIIDS (Greenfly, Blackfly, etc.)
These are the most abundant pests in the garden, and most plants, including vegetables, are liable to attack by one or more species of aphids. A close watch should be kept for them and, even if only a few are seen, they should be destroyed immediately as they can multiply very quickly, especially when the weather is warm. Aphids feed by sucking the sap from a plant and, by congregating on the tender young growth, can quickly cripple it and cause general stunting. Many species also transmit virus diseases which can reduce or wipe out a crop. The following are the most important species which attack vegetables: The Black Bean Aphid, greenish-black in colour, is found on beans,and . The Carrot Aphid is very difficult to see since its colour is almost exactly the same as the leaves of the carrot. The Cabbage Aphid has a mealy, greyish-white appearance and is found in tightly packed colonies on the leaves of , Brussels sprouts and . It must be controlled in the early stages of infestation because, once it has invaded the inner leaves of cabbage hearts and sprouts, it is difficult to reach with insecticides and it makes the plants practically inedible. The Lettuce Aphid is green and transmits a virus which severely stunts lettuces.
Spray or dust with malathion, lindane or nicotine, repeating the application as necessary.
Caterpillars of the Large White Cabbage-Butterfly, which have green, black and yellow markings, and the velvety green caterpillars of the Small White Cabbage Butterfly are common pests of cabbages,and related plants. They eat holes in the leaves, starting on the outer ones, and leaving nothing but the skeleton of main veins. The caterpillars of the less common Cabbage Moth, yellowish-green on the underside and dark, brownish-green on the back, are less common but more difficult to control, because they tunnel into the interior of cabbages and destroy the hearts. They also attack , lettuces and .
If possible crush the yellow eggs which are laid singly or in clusters on the underside of the leaves. The best control is obtained when the caterpillars are young. As soon as damage is seen, spray or dust with D.D.T. Apply derris if the crops are within two weeks of harvesting.
The pale green maggot of the Celery Fly feeds inside the tissues of the leaves of celery and parsnip, forming large blisters which turn brown, and eventually cause the death of the leaves.
As soon as the first signs of attack are seen, spray with lindane or malathion, and give a further two to three applications at weekly intervals. Early treatment will prevent more serious trouble later.
Cutworms attack many types of vegetable, especiallyand brassicas.
Eelworms are so small that they are not normally visible to the naked eye, but they can, nevertheless, cause serious damage to certain plants and are difficult to eradicate. As chemical control is difficult and very expensive at present, the most practical control is to starve out the eelworms by not planting their food plants on infestedfor a number of years.
Potato Root Eelworms attack, feeding on the roots and causing them to rot. The growth of such potatoes is poor, the lower leaves wither and drop off, and on infested land the yield of tubers dwindles progressively each year.
To prevent infestation buy only certified ‘seed’. Do not plant potatoes on heavily infested land for five to eight years. On medium or heavy soils, grow maincrop potatoes once in four years, and on light soils once in six to seven years. Grow-early potatoes every three years or twice in succession every five years.
Stem and Bulb Eelworms sometimes attack onions, causing them to become swollen and puffy at the base with distorted, twisted leaves (‘onion bloat’). The plants later start to rot. This pest also feeds on, , , beans, , and strawberries.
Do not grow any of the food plants on infested soil for three years, and thereafter practise a three-yearly rotation.
There are a number of species of Flea Beetle which attack garden plants, particularly cabbages,, and swedes. They are black, or black and yellow, insects, one-tenth in. long, which leap off the plants on to the soil w hen disturbed. The beetles eat small holes in the leaves, which eventually look as though they have been peppered by small shot. The worst damage occurs on , which are often killed off by these pests.
Spray or dust the seedlings at weekly intervals with D.D.T. or lindane until the rough leaves are well developed, when the plants should be able to withstand later attacks.
Pea Moth caterpillars are pale yellow with black heads, and can cause serious damage in some localities. They are found inside the pods, feeding on the peas, and produce what are known as ‘maggoty peas’. Peas which are in flower between mid-June and mid-August are most susceptible to damage.
In areas where this pest is prevalent, sow-early varieties of peas to escape the worst of the damage, or sow in late June or July. Peas which come into flower between June and August should be sprayed with D.D.T. Seven to ten days after flowering has begun and again ten days later.
Thrips are minute insects, seldom noticeable, which are particularly abundant in warm, dry weather. The Pea Thrips, the only important species which attacks vegetables, is black and only one-fifteenth in. long. It attacks peas and, injuring the flow ers so badly that the pods may fail to develop or, if they do develop, they are often small and distorted or have a distinctive, silvery, mottled appearance. The leaves are also speckled silvery-white where the insects have sucked the sap from the cells.
As soon as the first signs of damage are seen, spray or dust with D.D.T., nicotine or malathion, and repeat applications at ten-day intervals as necessary. Regular syringing with water in dry weather also helps to reduce damage.
The larvae of certain flies are common and destructive pests of vegetables in many areas. The maggots are small, whitish, peg-shaped creatures without legs or visible heads, which feed on the roots of vegetables.
The maggots of the Cabbage Hoot Fly eat away the lateral roots of cabbages and related plants, and then tunnel in the main root. Attacked plants are retarded in growth and may wilt and die. This pest also tunnels in the roots of turnips, swedes and radishes.
To prevent damage to root crops and to the seedlings of the cabbage family, dust the seed drills with aldrin before covering. When transplanting, dip the roots of brassicas in a liquid solution of aldrin or dieldrin, or apply either of these chemicals as a root drench within four days of planting.
Carrot Fly maggots tunnel in the roots of carrots,and celery, so that the roots are deformed and the plants stunted. The foliage of carrots may become reddish in colour. Attacked seedlings are often killed in dry weather.
Dust the seed drills with aldrin before covering, or apply a 4-in. band of lindane dust along the rows of seedlings when they are 2 to 4 in. high. Carrots sown in late May or early June or in exposed, windy positions, are less likely to be attacked. Garden twine, soaked in creosote and strung on pegs between the rows, will help ward off egg-laying flies. The maggots of the Onion Fly burrow into the bulbs of onions and shallots. The leaves turn yellow and collapse and the bulbs may be reduced to a soft, rotting mass. Dig up such plants immediately and also the soil round them because the maggots will often move on to feed on healthy plants.
Onion and shallot sets which have been dipped in liquid aldrin or dusted with aldrin powder before being planted will not be attacked. Protect growth from seed by dusting the drills with aldrin before covering, or by applying a 4-in. band of dust along the rows of seedlings when they appear.
Slugs attack lettuce, spinach, cabbage and celery.
TURNIP GALL WEEVIL
Round swellings on the roots of turnips, swedes, cabbages and related plants may be caused either by the disease Club-root, in which case the swellings will be solid, or by the larvae of the Turnip Gall Weevil, in which case the cutopen gall will reveal a cavity, often containing a small, white, curved grub. These pests cause stunting of young plants and make them less able to withstand dry weather.
Apply a 2-in. band of lindane dust along the rows of seedlings when they have two rough leaves. Wherever possible, discard galled plants when transplanting but, if they must be used, cut off the galls first and feed the plants well. Burn galled cabbage stumps.
Wireworms attack potatoes, carrots and turnips.