Chapter 13. Diseases And Pests

It cannot be too strongly impressed that every effort should be made to detect the presence of pests at the earliest possible moment and to set about destroying them immediately.

The largest group of pests is formed by insects, most of which develop in four stages, egg, larva or grub, pupa or chrysalis and adult. The grub stage is generally the most damaging for it is then that the insect needs the most food, and the adult stage is usually the most infective when the females seek new quarters for egg-laying. Many insects produce more than one generation a year and some, like aphides, produce living young as well as eggs.

Among pests the gardener includes all those animals which attack plants; insects, mites, slugs, snails, birds, etc. But many are beneficial and these should be carefully preserved. Ladybirds, lacewings, hover flies, centipedes and some of the ground beetles live on other insects. Shrew mice and hedgehogs are also good friends and birds do much more good than harm, particularly if seedlings, certain flowers and berries are protected by netting or cotton. Plants that are well grown and well managed are much less liable to be attacked by diseases or pests than those which are unhappy in their surroundings. General tidiness does much to remove potential sources of infection. Weeds should be kept down, hedges trimmed and cleared of rubbish at their base, and boxes, pots, stakes, etc., kept clean and stacked tidily instead of being left lying about the garden.

Pests are more or less controllable if tackled as soon as they make their appearance, but if allowed to run unchecked, will soon multiply exceedingly and do untold harm.

The soil in a newly constructed rock garden is almost certain to be pest-ridden, and should be fumigated or sterilized, then allowed to rest before any planting is done.

In the Alpine House, too, very much better results will be obtained with some of the choicer alpines, if their compost is thoroughly sterilized before they are potted-up.

We will show in the following pages the best ways of combating a few of the pests that most frequently attack our rock gardens, and complete the chapter by articles on soil fumigation and sterilization, also on insecticides and fungicides.

Ants. The best time to get rid of ants is in the early spring, when all the young brood is hatched and food is greatly in demand. Sprinkle sugar round their haunts, and they will reveal their nest by carrying the sugar into it. Empty honey jars or old treacle tins make good traps for the little pests, and hundreds may be easily destroyed by plunging the traps, when infested into boiling water. Old pieces of sponge, dipped in syrup, are, equally efficacious. There are one or two proprietary articles now on the market for their control but, where one dare risk the use of a poison, sodium arsenate mixed with some dissolved sugar, at the rate of ten grammes to six ounces of sugar in one pint of water is effective. If this be absorbed in cotton wool in a tin with the lid pierced to allow the ants to enter, it may be plunged near the nest and out of reach of children for it can be deadly.

Aphis. The greenfly is perhaps one of the greatest nuisances both outside and in for practically everyone who has a garden must have seen them on his Roses or other tender shoots. There are on the market numerous emulsions, some of which are poisonous, consequently read the directions carefully before spraying the plants affected. Inside, there are a number of fumigants which may be used periodically to keep down the pest, particularly during the growing season.

Earwigs. Earwigs are easy to trap, owing to their propensity to hide in anything during the day. Thus a handful of straw, shavings, or hay, pushed into a flower-pot and placed on a stick, will be found full of earwigs in the morning. Crumpled paper, hollow stalks, pieces of corrugated cardboard, and all such things, make effective traps.

Leather Jackets (Tipula). These are the grubs of Daddy-longlegs. They do great damage to the roots of many plants, feeding just below the soil and working their way right into the centre of large roots, and, in damp weather, and at night, attacking the stems of the plants. The Daddylonglegs, or Crane-fly, as it is sometimes called, needs no description.

These flies should not be confused with the Daddy-longlegs spider, which is quite harmless. The Leather Jacket is so called because of its hard leathery skin. The larva is cylindrical in shape, and of an earthy-brown colour. The head is black and the tail-end is blunt with several short finger-like projections. The eggs are laid from June to September on the ground or just below the surface. They hatch in a fortnight, and the grubs feed for ten months or more and remain just below the surface of the earth through the winter and spring. Early in summer they become pupae, which have several spines pointing backwards and a couple of horns in front. The flies soon emerge from the pupae cases, which are left projecting half out of the soil.

Prevention and Treatment. Break up new land thoroughly in the summer, as the grubs will soon die if exposed to hot sun and dry soil, and where possible keep weeds well in check by constant hoeing. Use one pint of D.D.T. Emulsion to fifty gallons of water. Water frequently until the pest is removed.

Millepedes. Millepedes attack the leaves of seedlings and the roots of a large number of plants and frequently eat into bulbs. They often extend the damage caused by wounds of other insects and generally set up decay. They must be distinguished from Centipedes which are beneficial. (Centipedes are flat in appearance, have one pair of legs to each body segment and are very active; millepedes have two pairs of legs to each segment, are more rounded and usually curl up when disturbed.)

Treatment Regular hoeing and good cultivation is generally sufficient. In bad attacks the soil should be dressed with naphthalene or seedlings may be dusted with D.D.T. Large numbers may be trapped in pieces of potato or carrot buried in the soil.

Mosquitoes. Mosquitoes, particularly the blood-sucking females, are a pest of the gardener and not of the plants he grows. In some gardens where there are ponds, streams or exposed water and liquid-manure tanks they can be a great nuisance. The larvae, sometimes called "wrigglers", live and feed in the water, continually rising to the surface to breathe through their tails.

Treatment. Fish in ponds will readily eat all the eggs and larvae they can reach, and they should be helped by preventing plants from spreading over the surface of the water and providing hiding-places for the pest. D.D.T. may be sprayed on to the water only where there is no danger of its coming into contact with fish.

Red Spider. Red spider does not usually cause much trouble outside, in our damper regions particularly, but under glass it is a pest which must be treated seriously. It will be seen generally beneath the leaves in minute specks covered with an almost invisible web which protects it from most insecticides. I have found the best to be, however, cyanide fumigant "Cyanogas," which is a very dangerous poison and should be handled with extreme care. Make sure the houses are locked, where there are children or animals, or people who are unaware of what the air inside the house contains, otherwise it would be fatal.

Slugs. Slugs bury themselves in the ground or under leaves and other rubbish and come out at night-time to feed on young foliage. They are always more numerous and destructive after long, wet, mild winters and will continue to feed all the year through under favourable conditions.

For prevention and treatment, see Snails. When found, they may be gathered and dropped into salt water.

Snails. Do not allow rubbish to accumulate in odd places; keep the garden tidy. Encourage frogs and toads and insectivorous birds, such as the thrush, which devour snails and slugs. Dust young growths over with a mixture of soot and lime to prevent the pests from devouring them. At night or early in the morning sprinkle lime thickly on the soil and repeat the process two or three days in succession, this will kill numerous snails; others may be trapped in orange skins, lettuce leaves, or boiled potatoes placed under slates. These traps must be looked at periodically so that the pests can be collected and destroyed. Much may be done by diligent searching in the early morning or evening. A ring of cinders round choice plants will do a great deal to discourage the attentions of slugs and snails. There are several anti-slug and snail powders on the market; most are very effective. One of the best is "Meta" Slug Destroyer, read the directions carefully.

Thrips. Thrips, one of the minute pests which trouble the indoor worker are best controlled with the aid of cyanide fumigant, which as I have said before is deadly poisonous to humans as well as the insect. You can also spray or dust with pyrethrum powder.

White Fly. The nuisance to most growers inside and during the dryer seasons outside in the south of England. There are emulsions on the market for spraying, a little stronger than those required for the green Aphis, whilst inside I have always found "Cyanogas" the most deadly poison and most effective. Warning, read the prescriptions carefully.

Woodlice (Onisidce). These insects are very destructive, especially to seedlings. Indeed, where woodlice abound many persons are often under the impression that the seed has never come up at all. Woodlice congregate in rubbish, at the bottom of pots in a hotbed, and round the sides of wood edgings, fences, and stones. They should be searched for every morning and destroyed by having boiling water poured over them. They may be trapped by means of small flower-pots filled with dry manure or old hay. Powdered borax sprinkled in infested places will also do much to keep down this pest. Inside where one is raising seedlings there are on the market poisoned baits which are more effective, but again these should be handled with extreme care.

In the rock garden these do not assume the importance they do in fruit culture, yet even so, a fungus well established in a patch or pot of plants will wipe them out. This is especially true in the Alpine House, where there is more humidity and less draught than outside, and in frames containing cuttings, where plant life is at its lowest ebb, the young plants not having the virility to fight the pest and overcome it.

Causes. There are one or two outstanding causes of fungus, the first and the most common being poor culture, that is to say, plants grown weak through quick changes of temperature; over-watering and consequent cessation of root action; poor drainage in soil, pots or pans, as well as in the frames, may also be amongst the chief causes; dirty glass that does not allow enough light to penetrate it in the dull weather; poor ventilation that keeps the plants hanging with moisture, especially after watering. Another frequent cause of fungus is carelessness in the division of roots in late autumn. Open wounds are left and fungus is allowed to penetrate. This applies to cuttings, more especially as they are very often in a closed frame, an ideal place for attack.

Prevention. First of all correct any errors in culture. Here lies the great difficulty with alpines, for their foliage, often woolly and lying close to the ground, helps rather than hinders the growth. Plants affected should be watered from below by dipping so that the water does not come in contact with the foliage. A layer of chips on the surface of the soil will also help to keep more air round the neck of the plant and will provide quicker drainage. Keep the plants in as light and airy a position as possible, especially those known to be weakly.

Remedies. For saxifrages and plants of similar nature and habits a good fungicide is permanganate of potash. In preparing this add sufficient crystals to a pail of water to colour it lightly, and no more; if too strong, the cure may be worse than the disease. The plants should be syringed with this solution on a mild, dull day, repeating the dose in two or three days' time.

For cuttings and shrubby plants quite a cheap and efficacious remedy will be found in an occasional dusting with flowers of sulphur.

Soil Fumigation And Sterilization

Fumigation. Newly-broken land is nearly always infested with wire-worms, leather-jackets, and other pests, and a dressing with some soil fumigant is invariably necessary. There are quite a number of fumigants on the market today, which are comparatively safe to plant life. Anyone who has not approached this subject before will be well advised to approach a horticulture specialist explaining his needs.

Soils that have been under cultivation for some time also frequently become pest-ridden. The presence of these pests is indicated by the weak and sickly state of plants whose roots are perhaps attacked. It is in the autumn that most of these pests will be present in the soil; at this time not only those that dwell in the earth all the year round will be found, but those that descend from plants to pass the winter in the soil can also be here destroyed at this period, if properly treated. For this reason soil fumigants should be used in the autumn or early winter.

Where plants must remain in situ in the soil to be treated, naphthalene will be found the safest fumigant to use, as it can be employed with impunity fairly near the stems of plants. Other chemicals must be kept well away from the roots.

Most of the chemicals used are very poisonous and give off gases when exposed to the air and moisture. The fumigant should be applied to the surface of the soil either as a powder or a liquid, as the case may be, and must be dug in at once so that the fumes may be retained in the soil, as they are the chief agencies in destroying the pests. Fumigants left lying about for one day even, soon lose their strength and efficiency.

SOIL FUMIGANTS

NOTE. 30J square yards =1 square rod.

Sterilization. This process consists in burning or heating the soil to such a degree that all pests and seeds of weeds are destroyed and plant-growth is stimulated. Sterilization cannot, save the process of burning to be described later, be applied to any great extent to ground in the open, and is generally confined to soil used in pots.

Plants in sterilized soil will at first be slow in growth, as numbers of the bacteria which promote this are destroyed with the pests. Those remaining, however, are free from the influence of pests and quickly multiply, so that after a time the growth of the plants becomes surprisingly vigorous and rapid.

There are several methods of effecting this sterilization; that by which the largest area can most easily be treated is by:

Burning. In this method, all available combustible garden refuse, such as straw, hard and fibrous vegetable matter, and leaves, is collected and spread evenly over the soil to be treated. This refuse is set fire to and encouraged to smoulder, rather than to burn fast, so that the process of burning is spread over the longest possible period. This method is best pursued in the late autumn or early winter, at which time the pests will be nearest the surface of the soil. Apart from the sterilization effected by the heat, the ashes will greatly benefit the soil.

Where the area of soil to be treated is not so extensive, other methods can be used.

(1) Baking. Here the soil is placed in a shovel, or is spread thinly on a metal sheet over an open fire, and is heated until the soil cannot be grasped and held in the hand. The moisture will evaporate in steam, but the soil must be removed from the fire before actual smoke appears. After baking, the soil should be well mixed and must have nothing planted in it until two months have elapsed.

(2) Steaming. This is undoubtedly the best and most effective method of sterilizing soil. It consists of passing quantities of steam into the soil until the temperature rises to 212 F. and retaining this temperature in every part of the soil. There are several well-known methods in operation as used in greenhouses both by private and commercial growers. They are the "Small Grid," the "Harrow," the "Tray" and the "Spike" methods.

For the amateur who requires a small but effective outfit, portable steam sterilizing plants can be obtained to take from a bushel of soil upwards, while for those who prefer to make their own plant, a wooden box can be constructed with several parallel pipes running at intervals across the bottom; these pipes are riddled with holes. The box is filled with soil and covered over the top, and steam at the pressure of seventy pounds to the square inch is forced along the pipes and up through the soil until it is heated to a temperature of 210 F. or as near that as possible. This temperature should be maintained for 20-30 minutes.

(3) Scalding. When this method is adopted, the pots filled with compost ready for planting have boiling water poured over them until the soil is thoroughly heated all through. They are then well drained and allowed to cool.

A better method, perhaps, is to stand a pail full of the soil in a bath of boiling water and to leave it there until the soil is thoroughly heated through and through; a fire must be kept burning under the bath or the water will cool.

On a larger scale in the open fumigation is more practicable and preferable to sterilization.

Fumigation Of Alpine House

The best time for this important operation in the Alpine House is the evening in calm, fine weather, or in the morning on a dull, windless day. To prepare a house for fumigation, shut all ventilators, and cover with damp matting all broken or cracked lights and all roof ventilators which are likely to leak at all.

Where convenient, plants which are in full flower should be removed before the actual process.

Most gardeners will find the fumigating or vaporizing materials sold ready for use, with the necessary apparatus for burning, highly satisfactory; the makers give detailed instructions which should be closely followed.

Where the house is badly infested with any insect pest, it should be dealt with two or three times on successive evenings; this is almost always necessary when extirpating red spider. The next morning, or when the fumes have thoroughly cleared, open the doors and ventilators and go round the house with the syringe and warm soft water, and free all plants from dead insects.

Insecticides And Fungicides

When and How to Use Them

Insecticides And Fungicides

When and How to Use Them

Are You Ready To Move Onto The Next Lesson? Click Here...