Flower Pests and Diseases

A number of pests and diseases attack nearly all plants, so I will deal with these first. Then I will deal briefly with the troubles that attack individual flowering plants in the garden.



This is the larva of the click beetle. It is browny yellow in colour, very wiry and may be distinguished from millipedes and centipedes by the fact that it has only 3 pairs of legs situated in the first 3 segments of its body. Millipedes and centipedes have legs all down their bodies. Wireworms will stay in the ground for 5 or 6 years; so if you have trouble in your flower garden it is worth while spending money to get rid of it.

Control The simplest way of doing this is to make holes with a walking stick or crowbar, 600 mm (2 ft) apart all over the area of ground concerned, and drop into the bottom of these holes a piece of paradichlorobenzene the size of a French bean. Tread down the holes immediately afterwards.


Some people consider these very serious pests but others say they do little harm. If earwigs are found in large numbers in any garden they should be destroyed. They are often a serious pest from the month of August onwards. Control With 5 per cent Derris or Pyrethrum – or both – dust all round the outsides of gardens and along the edges of paths where the earwigs collect.

Inverting flower-pots stuffed with straw, hay or wood wood on bamboos stood among plants is the old-fashioned method of trapping them. In the morning the straw is removed and the earwigs collected there are shaken out into a bucket of paraffin.

Slugs and Snails

There are, unfortunately, many different kinds, some of which are more numerous than others. The slugs may be classified as follows:

1. The Large Black Slug, which is less commonly injurious to plants, but sometimes causes damage.

2. The Garden Slug, a small dark species with a yellow foot and a very tough skin, common both in gardens and fields.

3. The White-soled Slug, also a small species, generally grey in colour with a flattened appearance and with a strikingly white foot.

4. The Field Slug, variable in colour but usually mottled grey with a reddish or yellow tinge – probably the most uniformly and generally injurious slug throughout the country.

5. The Keeled Slug – dark brown or grey with body keeled along the back. Very troublesome species, largely subterranean in habit, feeding on the underground parts of plants and often specially injurious to potatoes.

The two principal snails are:

1. The Large Garden Snail, the most common and widely distributed species of snail, easily distinguishable by large brown-grey shell with paler markings.

2. The Banded Snail, more injurious to farm crops than to garden crops as a whole. The shell may be white, grey, pale yellow, pink or brown with one to five spiral darker bands.

Generally speaking, slugs and snails eat anything fresh and green and succulent. Some seem to prefer roots and tubers and so attack below ground – others go for the parts of the plant above ground level. The majority of the dirty work is done at night time, and during the day the pests hide in any damp dark spot. Slugs will burrow deep down during the winter in order to escape the frost. Snails, on the other hand, collect in large numbers in a dry sheltered place.

Slugs usually prefer soils rich in moisture – the heavy soils, clays, etc. They love a wet winter and go on feeding and doing damage all the time. Given a chance they will get into a frame or a greenhouse, for there they can play havoc all the winter. Unfortunately, they revel in organic matter, and when heavy dressings are given on land which is not sufficiently well limed, trouble occurs because the partially rotted vegetable refuse may provide food for them. All vegetable refuse should therefore be properly composted before being used as a mulch on the soil.

The gardener feels that slugs and snails have far too few natural enemies, but this is not so. Birds eat them greedily, especially rooks, starlings and blackbirds. Ducks love them, and some people allow their Khaki Campbells or Indian Runners to roam the vegetable garden in the winter when there are few crops about to harm. Toads and moles eat slugs, whilst snails are devoured by thrushes.

Control Measures for Slugs and Snails

Everyone knows about the arduous method of hand collection: placing used orange skin and grapefruit skins upside down on the soil – picking up the slugs that have collected under them – and putting them in a tin of paraffin. But there are much better schemes than that. 1 – Copper Sulphate and Lime Method Use powdered copper sulphate and hydrated lime, mixed together in equal parts. Dig this mixture in when bastard trenching. It is quite safe to use 35 g/m2 (1 oz per sq yd), and even slightly heavier dressings than this have been used. A second similar dressing may be worked in 15 days before sowing seeds or setting out plants. The danger is the copper sulphate, which when overdone may poison the soil.

2 The Methiocarb Method The most recent develop ment in slug control has been the introduction of slug pellets containing methiocarb. The advantage of these is that under damp conditions they are more effective than slug pellets on other chemicals and it is, of course, under warm moist conditions that slugs are most active.

Methiocarb is available in a mini-size form of pellet under the trade name ‘Draza’. The small size of the pellet allows wide coverage economically and provides a large number of baiting points per unit area. Additionally, the small size of the pellet is far less likely to attract the attention of domestic animals which increases their safety factor. As a further point, from the safety angle, they are dyed blue, a colour which birds do not associate with food.

‘Draza’ pellets should be sprinkled about 125 mm (5 in) apart in areas where slugs are causing trouble or known to be active.

3 The Barrier Method Some of the copper sulphate and hydrated lime mixture may be used from time to time along the edge of flower gardens to prevent the passage of slugs on to one’s own particular portion of ground.

By this means it is possible to prevent the slugs travelling from one allotment or garden to another.

If the beds of flowers are covered with sedge peat an inch deep, the slugs cannot move about on the soil and so they never attack the plants. At the 3.2 hectare (8-acre) gardens at Arkley Manor, near Barnet, slugs never cause trouble because all the beds are properly mulched.


Tiny little black creatures which are slender and elongated. Being only about 1 mm (½ to ½ in) in length, they are very inconspicuous. They damage the petals of flowers particularly, and cause them to be marked with white streaks. They may distort the blooms and mottle the leaves. Sometimes they suck the sap from the tips of seedlings. The simplest way of telling if a plant is being attacked by thrips is to hold a clean handkerchief close to the plant and

tap it, and see if any little black specks drop on to the material. These, if thrips, will be found to wriggle, and if examined with a magnifying glass will be seen to be as already described.

Control Spray with nicotine, dissolving 35 g in 50 litres (1 oz in 10 gallons) of water. Soak the plants thoroughly with this on a warm day for preference. Spray three times at weekly intervals, so as to make certain of catching insects that may have hatched out late from eggs.

Eel Worms

Minute little worms invariable invisible to the naked eye. They are eel-shaped, with a body slightly tapering towards the head. Eggs are usually laid somewhere in the plant tissues. In the case of phlox, sweet Williams and chrysanthemums the eel worm swims up the film of moisture around the stems and enters the leaves by their breathing pores.

The eel worm also attacks bulbs. It enters through the tip and lives in the bulb, breeding for long periods. The bulbs thus attacked produce short foliage, and flowers on short stem, if they flower at all. In bad attacks the bulbs become soft.

Control To kill the eel worm in the bulbs it is necessary to give a special warm water bath treatment, a rather difficult thing for amateurs to do.

With chrysanthemums it is possible to give the stools and roots a warm water bath at exactly 43 °C (110° F) for 20 minutes just before they are put out into the frames or boxes to grow cuttings. Some gardeners prefer to immerse the cuttings themselves in warm water at this same temperature and then to strike them in the No-Soil compost.

In the case of phlox, cuttings should be taken from washed roots only, for the eel worms live in the stems and leaves and not in the roots. The roots should be washed in running water.


These are sometimes called monkey-bugs, pill-bugs, cheesey-bugs, slaters, etc. They are often abundant in town gardens. They like shady situations and decayed organic matter. They usually hide away in the daytime in crevices in brickwork, on the edgings of paths and under heaps of leaves, etc.

Control Dust along the edges of paths, the sides of walls and anywhere it is thought woodlice may hide, with a Derris and Pyrethrum dust.

Fresh powder dusted on after dark when the creatures are moving about will kill hundreds.


Millipedes must be distinguished from centipedes for the former are harmful and the latter beneficial. Millipedes, when babies, are white; when a little older are often grey and when fully grown may be yellowish brown. They are slow to move whereas centipedes move quickly. They have 2 pairs of legs to each segment of their body whereas centipedes only have one pair of legs to each segment, and their bodies are rounded. Millipedes will feed on seedlings, underground stems and roots; they will burrow into bulbs, corms and tubers, and they are a great nuisance because their nibblings may cause an entry for the invasion of fungus diseases.

Control Fork whizzed naphthalene into the ground at 35 g/m2 (3 oz per sq yd) when preparing the soil, if millipedes have been bad in the past. If you incorporate this into the top 50 to 75 mm (2 to 3 in) of soil it will usually act as a repellant for some months.


There are a large number of green flies, blue flies, black flies – plant lice as they are often called – which attack all kinds of flowering plants.

Control The best way of controlling these pests is to use a good Derris wash or it is possible to make up your own nicotine wash by dissolving 6 g of nicotine liquid.

50 g (2 oz) of a liquid detergent to 10 litres (2½ gallons) of water. You can of course use half the quantity.

Leather Jackets

These are the larvae of the daddy-longlegs and in the north they are called bots. They feed on all parts of plants growing underground – roots, tubers, corms and so on. They sometimes do harm to herbaceous borders. They may feed throughout the winter; they are usually 40 mm (1½ in) long and of greyish brown or blackish colour. They are legless and have a tough leathery skin.

Control A Gamma Dust when applied all over the soil and forked in will kill the leather jackets. I do not like using a Gamma Dust, but as yet have found no other good method of control. I would never use it in the vegetable garden however.

Club Root

This disease is sometimes known as finger and toe and will attack the roots of any member of the Cruciferae family. It often gives great trouble with wallflowers, stocks and annuals like Virginia stock. Roots of affected plants swell and when broken open will be found to contain rotten, evil-smelling material. The plants will be dwarfed and look sickly.

The Virus Problem

It is very difficult to describe virus diseases. They attack flowering plants in different ways. There is what is called Break in tulips, where the colour of the flowers is broken up. There is Yellow Stripe in narcissus. There is Stripe in irises. There is the dreaded Spotted Wilt which will attack chrysanthemums, asters, zinnias and so on. In this case you get a kind of spotted depression on the leaves, and the plants, if badly attacked, wilt and look miserable.

A virus is said to be a crystallized protein which is injected as it were into the plant by one of the sucking insects like the Green Fly (Aphides), Capsid Bugs (Tarnished plant bugs) and maybe Thrips. The disease is thus transmitted from one plant to another and the infection will spread extraordinarily quickly. The infection may cause dwarfing, distortion. It sometimes causes blotching of the flowers and foliage and sometimes yellowing of the tips of the foliage.

Control No definite cure is known. The only thing to do is:

(1) Compost the infected plants properly.

(2) Always start with virus-free material from reliable nurserymen.

(3) Keep down sucking pests by spraying regularly with a good nicotine wash.

Growing healthy plants in plenty of humus always helps matters. The great thing is to keep the plants happy and resistant to disease by seeing that plenty of well-rotted vegetable refuse is incorporated into the ground year by year.

Cuckoo Spit

Most people know this spittle-like deposit on plants. A green bug is found inside, sucking the sap, and causing the shoots to wilt.

Control Spray with a pyrethrum wash.


1. ANGLE SHADES MOTH CATERPILLAR This moth when resting on a tree or on foliage folds its wings into its body and simply looks like a crumpled decaying leaf.

The young caterpillars are olive-green in colour, or sometimes brownish, and feed on the leaves of flower buds and on open blossoms. They attack plants both out of doors and under glass.

Control Spray directly the caterpillars are seen with a pyrethrum wash like Pysect, giving a thorough soaking.

2. SWIFT MOTH CATERPILLAR The white active larvae of the moths live in the soil and may feed on the herbaceous plants, strawberries, vegetable crops, bulbs, corms, tubers and rhizomes.

Control Hoe the ground regularly and fork in whizzed naphthalene at 35 g/m2 (3 oz per sq yd) during soil pre-paration.

3. TORTRIX MOTH CATERPILLARS These attack herbaceous plants, especially phlox, solidago, heleniums and rud-beckias. These caterpillars draw together two or three leaves of a plant, fastening them with silk-like threads. They may be olive or greyish green.

Control Spray with liquid derris, and, if possible, hand-pick and burn all affected shoots and leaves.

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