Plant health

Many plants grown in containers are tough and long-sutfering, others are delicate and easily upset, but all will show signs of distress sooner or later if they aTe not looked after as the\ need to be. Most of these signs appear as a result of a 'physiological disorder'. !n other words an upset in the plant's system because it hasn't hat) enough water, or has had too much, or the light is too harsh, or something similar.

So you must alter your care of an ailing plant to correct its deficiencies. For instance, a plant « hose leaves are yellowing can be revived by giving it more warmth, different water or extra nitrogen. There are small differences in the kind of yellowing, according to the cause, which you will gradually learn to notice as you acquire more experience ot plant care and become more observant of plant reactions.

The wrong kind of care leads to a weakened plant, which ma\ lx attacked by and infested with insect pests and fungus diseases, possibly so badly that it is killed. If you notice cither pests or diseases on a plant, more often than not it means that you have not been growing the plant correctly. The most common faults are not enough liyht or warmth, too dry an atmosphere or too much water. On the other hand, mam plants will not lx- infested with pests or diseases at all during their lives. The list given below details all possibilities, so that you know how to cope in any situation.

The lea\es of indoor plants arc the parts which generally reflect ill health, and have the widest range of symptoms. \n extensive list of these signals of distress and their causes is given on pp. iH 9.

Pests and diseases

It' you rind from the list of symptoms that your plant's troubles are mainlv due to insect pests or fungus disease, rather than your ill-treatment of it, then the detailed descriptions which follow will help you to identify what is attacking your plant and how best to deal with it.

Fungus diseases are rarely troublesome. Mildew and grey mould, Bofry/is cintrra, are the two most likelv to infect plants, but sometimes rust is seen, and fungal gall m

Treating Azalea Fungus Disease

Fai left Aphids feed on the young growth of plants They are the most troublesome pests, unsightly in themselves and in the damage they do Inspect plants frequently and immediate action if you detec! this pest, as thay breed rapidly Left Boot mealy tlug are difficult to detect until the plant has already suffered some damage A sttong plant will be less damaged by then attacks invades azaleas occasionally.

Although there are man\ pesticides available for treating plant pests and diseases often the same chemical with different trade names there is reallv no need to keep more than the two or three mentioned on the following pages. Even these should only be used in an emergency. If you keep your eyes open and cultivate the ability to observe the small changes that take place in your plants as they grow, you will be able to spot an infestation as soon as it starts. Cutting off the affected parts is then all that will be necessary at such an early stage, and you will save time, money and possibly a plant, *ince death would follow a buiid-up of bad infection.

Always, always, read the directions for use and dilu tion on the container of a pest killer. If you don't, you ma\ damage the plant, or not eradicate the trouble. \ I ways keep the containers out of the reach of pets and children.



Comparatively large, up to j.i cm (1 in) long, these arc generally the young or larval stage of moths or butterflies. < iften green, sometimes brown, sometimes spotted or striped in these and other colours, they eat irregular holes in leaves, soft stems and flower petals, during the spring and summer. They are not often seen on indoor plants, though plants in hanging baskets and on window sills may provide a feast for them, and it pays to keep a particular eye on such plants. There is no need to use chemicals on caterpillars |ust remove them by hand.

Grernfy ( Aphids)

These insect pests are a very successful species. Thev reproduce extremely rapidly, and are now becoming resistant to the various chemical insecticides with which

Fai left Aphids feed on the young growth of plants They are the most troublesome pests, unsightly in themselves and in the damage they do Inspect plants frequently and immediate action if you detec! this pest, as thay breed rapidly Left Boot mealy tlug are difficult to detect until the plant has already suffered some damage A sttong plant will be less damaged by then attacks control ha^ been attempted. Aisp called plant lice, they are tinv green creatures up to 2 mm (J in) long, sometimes with wings. They feed by sucking the sap from a leaf through needle-like mouthparts which are stabbed into the lea! tissue. Thev move very little, and can be seen clustered at the ttps of new shoots, and on the underside of leaves. Plant growth becomes distorted and stunted. Leaves curl and sometimes turn yellow. Mew shoots stop growing until the greenflv have gone. Infested plants become weakened. The insects secrete honey dew, a stickv liquid which falls onto leaves, and on which sooty mould can grow.

Thumb and finder squashing "will get rid of most of them, and sometimes complete removal of a shoot tip is the best solution. Spraying with water under pressure will wash off the rest, or vou can spray with derris, res me thrin or ma lath ion.


The adult leaf miner is a minute fly but it is the tiny maggot which does the damage. F.ggs are laid on the leaves of plants, ami the maggot which hatches eats its way into the leaf tissue. ¡ust below the skin, and sravs there, moving about as it feeds. Yerv pale brown or light-green wavy lines and blisters appear on the upper surface of the leaf, and can cover it. Chrysanthemums and cinerarias suffer badly, but almost anv plant may be attacked. Remove affected leaves and sprav the rest with malathion.


The mealy bug is an almost stationary dark-grey insect w hich covers itself with a small blob of white fluff and feeds as greenfly do, mainly at stem joints or on bark, or tucked into crevices such as the necks of hippeastrum bulbs. MeaK bugs are often not noticed until there is a big infestation which has done a good deal of damage. Scraping them off with the hack of a knife is a good way of dealing with them, and the point can be inserted into awkward parts of the plant where the bugs mav be lurking. The young have no protective fluff, but are flattish blobs of pale brown, red or yellow on the stems, easy to miss. A hand lens or magnifier will help you to see them clearly. Spray the plant afterwards with malathion, or usi- methylated spirits on individual bugs if the plant is sensitive to malathion. Treat root mealy-bug on cacti as you would root aphis, using resmethrin for the insecticide.

Red spider mite

C )ne of the most frequent and troublesome pests on indoor plants, as the hor dry atmosphere of central hearing suits them perfectly, A hand tens is needed to see them on the underside of the leaf. They are pale yellow or pale red, tiny round pests which suck the sap, and moult their skins as they grow, leaving a white ghost-like replica of themselves behind. They also produce webbing, which can be seen festooning sterns. Thev take only a month to become adult and lav eggs and increase rapidly during the summer. Prevent them appearing by always keeping the atmosphere humid and ensuring that the plants never run short of water. Plants which arc infested should be thoroughly sprayed with malathion solution, repeating twice more at about ten-day intervals.

Root i!plus

Root aphis lives in the soil and, like greenfly above ground, it sucks the sap from the plant, but through the roots not the leaves. Root aphis is whitish-grey in colour and will be found on the roots and in the compost. Treat i lie plant by washing away from the roots all the com post and root aphis you can see. 7'hen repot in un contaminated compost. Water with a solution of malathion, and repeat the process about ten days later. For plants sensitive to malathion, use bioresmethnn instead.

Scale insects

I,ike mealy bug, scale insects arc immobile, feeding in the same place throughout their lives, protected by a hard horny case, brown, grey or black in colour. The adults lay eggs under rhe scales and the resultant young move out to their own feeding grounds and grow their own protective shells, which gradually enlarge and darken in colour from pale green as time goes on. Their feeding results in the production of large quantities of stickv honevdew, on which sooty mould grows. This and the feeding may weaken a plant considerably. The scales will be found on rhe stems and bark as well as on the leaves, close to rhe main veins on the underside. Scrape off gently with the back of a knife onto a sheet of paper beneath, and then spray thoroughly with mala thion, repeating twice more at ten-day intervals.

Slags and snails

Most likely to be a problem with window sill and hanging-basket plants, but if you see large holes in leaves and lumps missing from stems on any plant, for no apparent reason, suspect slugs and snails, They hide during the day and feed at night, so are seldom seen, I ,ook for (hem tn the base of pots, just inside the drainage hole, rucked into the undergrowth of a group of plants, or am kind of crack or crevice near to the damaged plant. Remove and destroy.


Minute, white-winged, fly-like creatures, found on rhe underside of leaves. The damage is done by the larvae which arc also minute, and look like round, transparent, green scales adhering to the leaf. They suck out their food and produce honevdew in large quantities. Leaves turn greyish and become very mess\ and curled in bad attacks, and the plants cease to grow and may die. Re move badly infested parrs and spray the remainder several times at intervals of three to four days with bio resmethrm. which destroys the larvae—the adults eventually die naturally.



A white powder in patches on the surface of leaves and stems, sometimes also on flowers, is the main symptom of mildew, to which begonias and chrysanthemums are especially prone. Ir is seen mainly in summer, when plants are dry at the roots, rather enclosed and very warm. Remove affected parts as far as possible, and Spray plants with dinocap or benomyl, or dust with flowers of sulphur.

Grey mould, Botrytis cincrea

Cirey mould starts with brown patches on leaves or stems from which grey fur grows and rotting quickly spreads. It is most likch to break out in ox>l, damp conditions and following an injury to a plant caused In insect attack, mechanical damage and soon. Tut off the infected part and spray with benomvl.

Sooty mould

Sooty mould is .1 fungus disease which lives and feeds on the honevdew that is produced by the insect pests that suck s.ip. Sooty mould does not live on plants and does no harm to them. But the mould and rhe honevdew block the stomata, collect dust and prevent transpira tion, so the\ should be wiped off with a moist cloth.

Rkit and a^alta gall

Rust takes rhe form of raised reddish-brown powdery Spots underneath leaves. \/alc.i gall results in thickened and blistered leaves, g rev-white in colour, anil sometimes also discoloured flowers, Hand removal of diseased leaves and flowers is usually sufficient to keep either disease under control.

Houseplants Spotted LeavesIvy Plants With Diseased Leaves
Left to righi Pests-Mealy bugs scate itisects aiicfwtntefly Diseases-Botrytis (grey mould) the lungal spots shown on the ivy ate unattractive, but not often seen arid not seriously damaging Remove affected leaves it necessary and spisy weekly with Benomyl thiee times

Symptoms of trouble on leaves

Lower leaves turning slowly yellow and eventually falling.

Lower leaves turning yellow and falling quickly.

Leaves turning yellow, bur not dropping.

Gradual appearance of yellow mottling, rings or streaks, stunting of plant and slow growth.

Minute yellow speckling, possibly with webbing on leaf or leaf stems.

Leaves pale green, gradually turning yellow; plant straggly and with poor new growth.

Naturally variegated leaves change to plain green.

Coloured leaves fading, or becoming all-green.

Pale green or white speckling in patches, increasing very slowly.

Brown edges and tips to leaves.

Brown spots on leaves.

Raised brown or pale-yellow spots on leaf under-surfaca.

Too much water in the compost. Remove from the container for a day to dry, and do not water for several days.

Sudden cold, or drop from normal temperature.

Lime in the compost, or the use of limey or hard water; use rainwater or soft water, or boiled tap-water.

Virus disease, spread by greenfly or other sucking insect pests.

Red spider mite; see page 26.

Lack of nitrogen: give extra liquid fertilizer with higher nitrogen content, or pot into fresh compost, or give more light,

Not enough light, if all leaves do it. If those on one branch only become plain, then reversion is occurring: cut off such shoots,

Quantity and quality of light insufficient. Also keep compost slightly on dry side, to give best and most intense colours.

Leaf-hopper, worst with plants on a window sill or in a hanging basket in hot weather.

Atmosphere dry-, or draughts, or lime in the compost or water; occasionally, a lack of potash in the compost.

Cold, especially if a succulent; dry fertilizer on leaves; feeding too heavily; sun shining through drops on the leaves; gas; poorly structured compost.

Scale insects, see page 27,

Symptoms of trouble on leaves cont'd

Large pale-brown patches on leaves, which may become papery.

Beige coloured, wavy lines and blisters on leaf.

White markings on leaves, especially furry ones, sometimes looking like marbling.

White powdery patches on leaves (also stems and flowers).

Fluffy white spots on leaves and at stem joints.

Patches of grev fur on leaves, with brown and yellow marking.

Greyish appearance to green leaves, lack of new growth, leaves withering and falling.

Thickened leaves with a grey-covering, on azaleas.

Leaves hanging down, limp and whole plant wilting.

Leaves curling and distorted, also yellowing sometimes.

Black sooty patches on leaves.

Stickv patches on leaves.

Large holes in leaves.

Fleshy leaves which turn brown at soil level.

Leaves falling without discolouring.

Sun scald, especially with African violets.

Leaf-miner, see page 26.

Cold water on the leaves, or watering with water that is cold instead of at room temperature-often affects African violets and gloxinias.

Powdery mildew, see page 27.

Mealy-bug, see page z6.

Grey mould, see page 21.

Red spider mite, see page 26 (has different effects on different plants).

Azalea gall fungus disease, see page 27.

Too dry a compost, or too much water if wet. Remove from pot for a day. Do not water for several days.

Greenfly, sometimes also scale insect, see page 27.

Sooty mould, due indirectlv to scale insect, whiteflv or greenfly, see pages 2^-7.

Scale insect, whiteflv or greenfly, see pages zj 7.

Slugs, especially if lower leaves are affected, or caterpillars, see page 27.

Too much water and or too low a temperature. Cease watering for a few days.

Draughts or sudden drop in temperature. Change position.

Symptoms of trouble on other parts

Flowers falling prematurely, or flowerbuds dropping without opening.

\o flowers at all on a plant norm all v grown for its flowers.

Hyacinth florets brown or flower spike wholly discoloured or stunted.

Flowers not setting fruit.

Fruit badly shaped. Fruit shrivelling or falling.

Raised brown, grey or black spots, round, ova! or mussel shaped, on bark of trunk and branches; plant growing slowly or not at all.

Fluffy white spots on stems and inside neck of bulbs, especially hippeastrum.

Brown rotting of stems at soil level, also crowns of complete plants, grey fur may follow on brown areas.

Complete plant looks 'tired', rather greyish, not growing, has a rather dry appearance.

of plants

Draughts; dry atmosphere; infestation by red spider mite (see page 26); cold, insufficient or excessive water; moving the plant; turning it away from the sun. Be particularly careful with watering, humidity and temperature at start of flowering.

Insufficient nourishment and light; too much nitrogen, especially if plant very lush and leafy; not enough warmth; give high-potash feed and increase humidity.

Not enough water when the bulbs were in the dark developing their roots.

A dry atmosphere; insufficient food.especially potash; compost too dry.

A dry atmosphere at pollination.

Shortage of water at roots, high temperature and dry* atmosphere.

Scale insccts, sec page 27.

Mealy-bug, see page 26.

Cold combined with overwatering, often happens in winter; grey mould then infects. See page 27.

Possibly root aphis or root mealybug, see page 26. Turn plant out of pot and examine root-ball to confirm. Or, too much water, roots then brown, stunted and easily broken off. Healthy roots are white and strong. Remove from pot for a day, and do not water for several days.

Food Producing Houseplants

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