Flower problems FAQs

My chrysanthemums are infested with reddish-brown insects which look like greenfly. What are they?

These are indeed aphids. Although we talk about greenflies and blackflies, in reality these insects range in colour from pale yellowish-green through pink and dark brown to purplish-black. They are all sap feeders, weakening and distorting the plants. In addition they transmit virus diseases and deposit sticky honeydew which becomes covered with sooty moulds, further disfiguring the foliage. Some control is provided by predators such as ladybirds, lacewings, and hover flies but it is usually necessary to spray the plants with a greenfly killer or general insecticide. Sprays based on pirimicarb are specially valuable because they kill the aphids but have no ill effect on the predators.

Many of the plants in my garden are disfigured with white, spittle-like foam in the leaf and flower axils. Is this due to a pest or is it a disease?

The masses of foam, sometimes called ‘cuckoo spit’, are produced by the sap sucking larvae of the common frog-hopper. Attacked plants are weakened and their growth may be distorted. Light attacks can be dealt with by picking off the larvae. Heavier attacks are best controlled by using a forcible spray of general insecticide.

The young leaves on my annual asters and hydrangeas are showing numerous small brownish spots and some of the older leaves are becoming ragged. What is the cause of this trouble?

These symptoms are typical of capsid attack. These bugs are difficult to spot since they drop off the plants when disturbed. The damage spots are caused by them piercing the plant tissue to feed on the sap. Heavy attacks cause distorted growth and may even result in ‘blind’ shoots. Many types of plants are subject to attack. Control by repeated spraying with a general insecticide, and also spray the ground under the plants.

Caterpillars cause quite a lot of damage in my garden but I don’t like to kill them as I love to see the butterflies. What do you advise?

Caterpillars on garden plants are mostly the larvae of moths. Indeed the only butterflies which commonly cause damage are the large and small cabbage whites. These species are still all too common in spite of the control measures taken by most gardeners. Killing a few caterpillars in your garden will not seriously reduce the moth population since they also breed on a wide range of wild plants. Caterpillars can be controlled by hand picking or by spraying with a general insecticide. Permethrin-based products give particularly long-lasting control.

Some of the young shoots of my delphiniums have been bitten through, and similar damage has appeared on my tulips. Can this be slug damage?

Slugs or snails are indeed the likely cause of the trouble. These pests also eat large ragged holes in plant leaves. Both pests, however, generally feed at night and hide during the daytime. Slugs and snails are fairly readily controlled by the use of slug pellets. Alternatively, they can be caught in special traps if you do not want to use a pesticide.

Could you identify the tiny, dark-coloured, slender insects which have begun to infest the shoots, leaves, and flowers of some of my plants?

These are almost certainly thrips (thunder-flies) which feed by scratching the surface tissue and sucking up the sap. Damaged leaves show a fine, pale yellow mottling, while flowers develop white flecks on the petals. Thrips also exude small liquid drops which get covered with a brown mould. Not only do they weaken and disfigure the plants but they also transmit some virus diseases. Thrips are readily controlled by general insecticides.

Deep notches have developed in the leaf margins of several of my shrubs but there is no sign of any pest. How and when does this damage occur?

This type of notching is characteristic of vine weevil damage and can occur on a wide variety of shrubs. Other weevils eat holes in leaves and also gnaw the young stems. These small, wingless beetles live in the soil and feed only at night. Control them by repeat sprays of a general insecticide applied to both the bushes and the surrounding soil.

What is the cause of the thin yellow, twisted lines which have developed on the leaves of many of my plants?

These ‘mines’ are produced by the caterpillars and maggots of leaf-mining moths and flies. Some species of leaf miners, however, produce rounded blister-like blotch mines. Established plants are weakened and disfigured by these pests, while young plants may be killed. Carnation fly, which produces blotch mines on carnations, pinks, and sweet Williams (all species of Dianthus), is particularly damaging since the maggot may migrate into the stem, killing the shoot. Here the best approach is to remove and burn the affected leaves. In other cases spray with an insecticide at the first signs of attack.

My wallflowers seem to be very stunted this year and are tending to wilt in warm weather. What can have caused this?

From your description of the trouble it seems likely that your wallflowers (Cheiranthus) have been attacked by cabbage-root fly (Delia brassicae). You can easily confirm this by digging up one of the wilted plants and examining the roots for the presence of the fly maggots. Incidentally, this pest can also attack aubrieta and stocks (Matthiola). Prevent future attacks by dressing the seed rows and the transplants with a soil-insecticide powder. Apply also a heavy soil-drench of insecticide based on pirimiphos-methyl or trichlorphon.

Brown powdery spots have developed on the undersides of the leaves of my antirrhinums and the plants are not doing at all well. What is the cause of this trouble?

Your antirrhinums have become infected with antirrhinum rust (Puccinia antirrhini), which can be very destructive. If the infection is still fairly light you should start a programme of sprays at intervals of 10-14 days using benomyl or thiram. If, however, most of the leaves are infected it is better to cut the shoots back hard and then protect the new growth by repeat sprays. Rust-resistant varieties of antirrhinums are now available from nurseries and should be used for future plantings.

As my Brompton stock plants were showing poor growth I dug one up and found that the roots were swollen and distorted. Could this be a form of clubroot?

Yes. It is not generally appreciated that clubroot (Plasmodiophora brassicae) not only attacks brassicas (the cabbage family) but can also infect stocks (Matthiola} and wallflowers (Cheiranthus). For long-term control the beds should be limed before sowing or planting out and a clubroot-control powder applied to the seed drills and planting holes. 947

The flowers of my chrysanthemums are beginning to rot. Some show browning only of the inner florets, while others are completely brown. Can you tell me what has caused this damage?

Since the damage starts in the centre of the blooms, this rot is caused by an attack of the fungus disease called ray blight (MycosphaereUa Hgulicola). The disease is favoured by hot, humid conditions, so the risk of attack is reduced if plenty of ventilation is given. It is also worthwhile applying a protective spray of benomyl, mancozeb, or triforine before the blooms open.

The outer florets of my chrysanthemums are beginning to rot. What is the cause, and is there a suitable treatment?

Chrysanthemum flowers are prone to a number of diseases. Since, however, the damage is showing up first on the outer florets the probable cause is petal blight (Itersonilia perpexans). The first sign of this disease is the appearance of small water-soaked spots on the outer florets. It then spreads inwards to spoil the bloom. This disease is favoured by wet weather and can be prevented by repeat sprays of fungicides containing benomyl, mancozeb, or thiram.

Some of the shoots of my peonies are rotting at the base and are becoming covered with a grey mould. Nearby leaves have brown patches. What can I do to cure this trouble?

Your peonies (Paeonia) have been attacked by wilt (Bottytis paeoniae) and you need to take immediate action to save them. Cut out the infected shoots well below ground level and apply a copper dust to the crowns. Follow this treatment by applying repeat sprays of benomyl or thiram to the foliage.

My dahlia flowers are being notched and chewed up by some pest. What action can I take?

Dahlia and chrysanthemum flowers are commonly attacked by earwigs, which can also damage the foliage. This not only spoils their appearance but increases the risk of grey mould invading the blooms. Regular spraying at fortnightly intervals with a general insecticide is one way of controlling these pests. An alternative approach is to trap the earwigs in inverted flower pots filled with straw or dried grass and placed on top of the plant support. Petroleum jelly smeared around the stems will also prevent the pests getting to the flowers, provided that it is renewed regularly. 951

The foliage and stems of my chrysanthemums are beginning to get covered with a white powdery deposit. How do I deal with it?

This trouble is caused by a powdery mildew (Oidium chrysanthemi). The initial infection is usually on the underside of the lowerleaves, and the upward spread of the disease can be checked by repeat sprays of a mildew fungicide such as benomyl, bupirimate, carbendazim, or thiophanatemethyl. These should be applied every 10-14 days.

This year there were quite a few gaps in my established bed of daffodils, and some bulbs developed only a circle of grassy leaves. What produced this effect and how can I prevent it in future?

Assuming your bulbs are well fed and in a spot that suits them, the likeliest cause is an attack by narcissus flies (Merodon equestris). These flies lay their eggs on the neck of the bulb, and the emerging maggots bore into the base of the bulb, destroying the central parts. When the foliage has died down you should dig up the bulbs and reject any which are rotten or show tiny entrance holes in the base. From the end of April protect freshly planted bulbs by repeat applications of an insecticidal dust.

What is the cause of the angular brown and black areas which are showing on the lower leaves of some of my chrysanthemums?

This damage indicates that the plants are infested with chrysanthemum leaf and bud eelworm (Aphelenchoides ritzemabosi). Infested plants must not be selected for propagation as this will only spread the disease. They can, however, be saved from further damage by ringing the stem above the topmost damaged leaf with petroleum jelly every week or two. This pest can also attack asters, delphiniums, phlox and pyrethrums, for all of which the treatment is the same.

The young flower buds on my sweet peas are turning yellow and dropping off instead of developing into flowers. Is there any way of preventing this?

This type of bud drop on sweet pea (Lathyrus odoratus), which can also occur on camellias and wisterias, is caused by unsuitable cultural conditions, not by a pest or disease. The commonest cause is shortage of water during bud formation. Shortage of potash and phosphate fertilisers, coupled with an excess of nitrogen, may also be contributory factors. Liquid feeding with a well-balanced fertiliser and regular watering should relieve the problem; surface mulching also helps.

Checking over my planting of Solomon’s seal, I found that many of the leaves were completely shredded but I could see no trace of any pest. What coud have caused this damage?

The pest which has attacked your Solomon’s seal (Polygonatum x hybridum) is the Solomon’s-seal sawfly (Phymatocera aterrima). This fly lays its eggs in early summer and the caterpillars which hatch out then start feeding on the undersides of the leaves in June. When fully fed they drop off onto the soil to pupate. You can protect your plants next year by applying an insecticide based on longlasting permethrin in early June.

Some of my pansies are dying from a stem rot. Could this be due to the fact that the soil is heavy clay?

Pansies (Viola x wittrockiana) are liable to suffer from stem rot in heavy soil which is poorly drained. You should therefore improve your soil by digging in plenty of sharp sand, grit, or bulky organic matter such as compost, peat, or composted bark. Several fungi are associated with this rot, so I would advise you to sprinkle calomel (mercurous chloride) dust in the planting holes.

Some of my tulips emerged looking very distorted and stunted. Nearby bulbs are now developing yellowish streaky spots on their foliage. What action should I take?

Your tulips have been infected with the disease called tulip fire (Botrytis tulipae). In moist conditions this can spread very rapidly throughout the planting. First dig up and destroy any badly affected bulbs. Then spray the remainder with one of the fungicides based on benomyl or thiram.

Brown ring-like powdery growths have begun to appear on the undersides of the leaves on my geranium plants. Could this be a form of rust and, if so, what can I do about it?

The brown powdery rings on the leaves of your geraniums (Pelargonium x hortorum) indicate that the plants have become infected with pelargonium rust (Puccinia pelargonii-zonalis). Heavily infected leaves should be removed and burnt and the plants then sprayed with a fungicide containing mancozeb, thiram, or triforine. Repeat sprays at 10-14 day intervals will be needed to protect the new growth effectively against this disease.

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