Beware of Garden Pests for Flower Crops

Common Garden Pests of Flower Crops

Here I have dealt with the more common pests which can attack our flowers.  For convenience, these are listed under “Sucking Insects”, such as aphides which feed on the sap in shoots or foliage; “Caterpillars”, which feed on the leaves or shoots; “Soil Pests”, such a wireworms, which damage the roots mainly, and “Other Pests”, such as earwigs and woodlice:


Sucking Insects

These, often feed on the tips of growing shoots, i.e. the most tender parts of the plant and, if allowed to multiply, can severely check or damage the plants or even kill them. Where insecticides have to be utilised, use them as soon as possible, and employ a syringe or sprayer which will apply the solution at good pressure, directly on to the insects concerned.

garden pests and diseases Some of the materials that are used to kill sucking insects are:


This is poisonous to humans and must be used with care. It is however a widely-used insecticide. It is most efficient if applied in warm weather at a temperature of over 60 degrees F. It gives a very good control of aphides. Dusts and liquid preparations are available. With the latter, it is best to use a wetter or some soft soap as a spreader, to obtain maximum efficiency.


This is obtained from a species of chrysanthemum, and is grown in Kenya in large quantities for this purpose. It is non-poisonous to humans and can be used in combination with derris, thus providing a useful control material against caterpillars as well as many species of aphides. Pyrethrum powder costs about 6/- per lb. and, where a wettable preparation is used, 1lb in 5 gallons of water is an effective solution. Pyrethrum dust is also available. Proprietary pyrethrum preparations should be used at makers directions.

Some of the most common sucking pests are:


These are probably the most commonly met with of all the flower pests, and there are many different species. An aphid is illustrated in Fig. 13. They all cause similar damage however, and all can be dealt with, if needs be, by one of the above preparations. Roses and chrysanthemums are especially liable to attack, also dahlias, but one must be prepared to find some species of aphides on a very wide range of flower plants, especially in warm weather when they breed very rapidly if allowed to go unchecked. Remember that it is the tips of the growing shoots that are most likely to be attacked first, and an examination should be made regularly with this factor in mind.

Capsid Bug

There are several species, the green capsid being one of the most common. It attacks flower crops such as dahlias and salvias. The young stages of the pest, the nymphs”, cause spots on the foliage, which enlarge and have brown edges. Another type of capsid, can cause damage to chrysanthemums, in that it feeds on the flower buds which become distorted and often one-sided. It also attacks many annuals and perennials. The keeping down of weeds in the vicinity is important as an indirect control against these pests, for weeds serve as host plants in many cases. Pyrethrum sprays or dusts will give a good control.


This pest which attacks a wide range of flowers is often known as cuckoo spit, due to the froth-like liquid with which it surrounds itself. Some plants frequently attacked are roses, geums and lavender which is particularly susceptible. Damage is caused by the nymphs, an immature stage of the insect which is most troublesome in May and June. It causes the leaves to wilt and can distort the shoots. It is essential to spray at a good pressure, to penetrate the “froth” with an insecticide, and pyrethrum may be used.

Greenhouse White fly

There is a useful biological control measure that should be used against this pest, namely introduction of the small chalcid wasp, Encarsia Formosa. This lays its egg in the immature stage of the whitefly and the parasitic larvae feed within. The parasite can often be obtained from a tomato growing enthusiast as it is used to good effect against whitefly attacking this crop also.

Many gardeners are trying a few plants of African Marigolds in pots, as a deterrent against whitefly, and a plant or two of Nicandra, the shoo-fly plant, can also be grown in pots in a greenhouse as a trial deterrent against some pests that attack greenhouse plants.

Leaf Miner

The larvae of this pest, tunnel into the foliage and cause channels in the leaves. In heavy attacks the whole leaf may be damaged and plants badly checked. If the first signs of damage can be spotted at an early stage, pick off the leaves concerned. The larvae can be crushed between the thumb and finger, on a small scale. The weed, sow thistle, is also affected, so this plant should not be allowed to develop nearby, or it will serve as a source of infection.

Chrysanthemums are sometimes attacked by one of these pests, as are cinerarias. Other species can attack aquilegas, roses, sweet peas and azaleas. A useful deterrent on the foliage of plants liable to be affected out-of-doors, is old, well-weathered soot, which can be sprinkled on lightly, when the leaves are damp.


These “thunder flies” cause a mottling on the foliage where they suck the sap during feeding. Plants attacked include chrysanthemums, roses and many pot plants under glass, e.g. cyclamen, fuchsias and begonias. In this latter case, frequent syringing with cold water is a good control, but this must be applied at good pressure. Out of doors and under glass, spraying with pyrethrum is effective. Warm, close weather often brings on attacks very rapidly and damage should be anticipated under these conditions.



There are many different types of caterpillars which can attack flower crops; one type is illustrated in Fig. 15. In each case, if their presence can be spotted soon enough, they can be picked off by hand and disposed of. If this is not done, or if you have been away for a time, then spraying or dusting may have to be resorted to. The aim here is to paralyse the caterpillars, or to render the leaves on which they feed unattractive.

Where only a small number of plants are attacked a suitable dust can be applied from a small muslin bag, shaken on to the foliage when this is damp, as in early morning.

One of the best materials that can be used as a control against caterpillars is derris. This can be obtained as a dust, or in liquid form. In either case, it is non-poisonous to humans and animals. It is, however, toxic to fish, and should not be used near ponds or streams, where there is a danger of it reaching the water. There are many other materials that can be used but some are poisonous. Derris can be relied upon for controlling caterpillar attacks on flower crops.

Some of the more common pests in this group are:

Angle-shades Moth

The larvae (caterpillars) attack a wide range of flower crops, including gladioli, chrysanthemums, dahlias and many herbaceous plants. They are about 2ins. long, brownish-green in colour, with a pale stripe along each side of the body. They eat leaves, buds and flowers. Watch for the first signs of attack, when early infestations can be removed by hand-picking, otherwise use derris sprays applied as soon as possible.

Cabbage White Butterfly

In addition to feeding on brassica plants, the larvae may attack nasturtiums and stocks. They eat small holes in the foliage to begin with and, later, can reduce the leaves to just the mid-ribs. Handpicking is effective or the plants can be sprayed with salt and water (2ozs. of common salt to each gallon of water). Derris or pyrethrum can also be used, but spray at the first signs of attack before the caterpillars increase in size, or in numbers, as they are much more readily killed in the early stages.

Tortrix Moths

One species of these moths attacks young leaves and new shoots of heleniums and phlox and some other herbaceous plants. It spins the shoots together and causes considerable distortion. At the first signs of attack, pinch the larvae between thumb and finger or pick them off. It is not easy to kill them by spraying once they are within the protection of the leaves they join together.

Other species of caterpillar may be found, but in all cases, the same methods of control, as suggested above, may be employed.


Soil Pests


These damage the roots of many subjects and cause wilting or even the death of plants attacked. They are particularly troublesome on new land, i.e. that which was recently grass turf. In such cases, aldrin dust at 1 oz. to each square yard, before seeds are sown, or plants are put out, is often used. This dust should be hoed into the top few inches of soil during the initial preparations.

Where wireworms are troublesome on established plants, try trapping them by pushing pieces of carrot or potato, into the soil around the flower plants, and taking these “baits” up each day, to see if they contain wireworms. If they do, drop the whole in a tin of boiling water.


These feed on the roots of many flowering plants, and may attack seedlings or mature plants. Bulbs are also liable to damage. There are differing types of millipedes but all curl up when disturbed and resemble a watch spring in appearance.

The control measures are to trap on a small scale, with pieces of potato or carrot set just beneath the soil surface (remove the “traps” when millipedes collect in them), or to apply aldrin dust to the soil between attacked plants, and hoe it in.

Napthalene can also be used against these pests (also against wireworms). When applied to empty ground the rate of application is 3ozs. to each square yard. Napthalene is still a useful material to use where damage from soil pests has to be dealt with.


These large white larvae often found in soil that was recently grassland, may attack the roots of many flower plants. Normal cultivation exposes many to birds and indeed, as the ground is brought into cultivation, this pest, finding the new conditions not to its liking, is considerably reduced in numbers. Trapping with pieces of potato buried about 1/4in. deep will help, if the traps are examined early in the day before the larvae go deeper into the soil.


It is said that if toads are placed in a greenhouse where woodlice are a plague, they will clear this pest, but I have no first hand knowledge of this method of control. Woodlice are usually associated with wet conditions, as under stones, beneath rubbish or in shaded positions in a greenhouse. They cause some damage to roots of certain plants, particularly to ferns in a greenhouse, if these are not well tended. Some herbaceous plants can be attacked also at the roots. Trapping can be resorted to if necessary, by means of flower pots loosely filled with damp moss or with scooped-out potatoes. No decaying pieces of wood should be left lying in the garden, or any other rubbish be allowed to accumulate which could attract these pests and give them shelter.


These are most troublesome in damp, warm, weather, or where the conditions generally are damp, or plants are shaded. Slugs of one type live mostly below ground and are difficult to control for this reason. Those which live above ground, i.e. the ordinary type, are most active on warm, dull nights and, if trouble is anticipated and young seedlings are most likely to be attacked, proprietary “baits” can be set in position, either near the seedlings or in flower pots lying on their sides nearby. The aim here should be to keep the baits dry. I would, however, prefer to use a mixture of lime and soot, equal parts of each. This is best placed in a ring around the plants likely to be attacked or, if this is not possible, on the soil amongst the plants.

Subjects known to be susceptible, including delphiniums, can have a ring of fine ash placed around them, and even over them, in winter, but this needs replacing or rather renewing when the first applications become wet. The principle of these deterrent materials, is to give the slugs conditions over which they cannot travel freely. With this in mind, dry wood ash, is a useful material to use, but needs to be renewed after rain.


Other Pests


These, especially troublesome on dahlias and chrysanthemums, damage the flowers by eating the petals, thus giving mis-shaken blooms. They feed at night, which means that they sometimes go un-noticed, and one cannot immediately account for the damage.

A well-tried method of control is to trap earwigs by inverting flower pots on canes stood in the ground between the plants, and filling the pots with hay, soft straw or even crumbled newspaper. The earwigs gather in this protection by day, and both they and the trapping material can then be collected and immersed in boiling water.

Chafer Beetles

The adult May bugs or cockchafers are a familiar sight in May and June, when they may be present in large numbers. They attack the foliage and buds of roses and, during the evening, can be shaken from the plants being attacked, or handpicked. If spraying is done, derris is an efficient control measure.

Eel Worm

Mention has been made of the trial work being done at present with the growing of African Marigolds as either a control, or a deterrent, against this pest.

The most frequent cause of trouble may be with chrysanthemums. If plants are affected, the lower leaves turn black and blooms may be distorted. Commercial growers dip the stools from which cuttings are to be taken, in warm water at 115 degrees F. for 5 minutes, thus ensuring a clean start with the newly-propagated material.

If new plants are purchased, make sure that they come from a clean source. Infected plants should not be used for cuttings, unless the warm water treatment is given.

Phlox can also be affected by a species of eel worm. The taking of root cuttings can be used as a method of propagation which ensures clean stock. Plants are lifted in winter, and Sin, long pieces of root inserted in a cold frame, either flat, and covered with 1/2 in. of a half soil, half compost mixture, or inserted upright, tips level with the surface, 5 ins. apart.


17. September 2010 by admin
Categories: Garden Management, Pest Control | Tags: | Comments Off on Beware of Garden Pests for Flower Crops


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