Diseases And Pests Of House Plants

Diseases And Pests Of House Plants

What fungal or virus diseases attack house-plants come mainly as a result of bad treatment. They are not easy to diagnose or to cure and in general it is advisable to throw the plant out and begin again. Even if you were able to save the plant it is doubtful if it would ever be the same again and there would always be great danger that it might pass on some of its weaknesses to neighbouring plants.

Pests, as opposed to diseases, are quite few in number and comparatively easy to clear. The easiest both to recognise and to deal with is the ubiquitous aphid, usually greenfly but occasionally blackfly.

Greenfly are not always easy to see unless you examine your plants very thoroughly and very frequently. The first evidence is likely to be a curious twisting or warping of certain tender shoots and possibly a change in colour. Immediate action is called for directly the pests are found, for they can multiply at an astonishing rate and could do great damage to all your indoor plants if not attacked at once.

If the attack is a light one, that is to say if only one plant is affected it may be possible to deal with it in position. A light spray with an AEROSOL fly killer will kill the greenfly also. But keep a careful watch on all the house-plants in the vicinity to make sure that other greenfly do not appear in the next few days.

A word of warning about pesticides. All garden pesticides are what they say: garden pesticides. They must never be used in the house. They are poisons and although safe to be used out of doors you will nevertheless be advised on the label to avoid getting any of the liquid or the spray on the skin and always to wash carefully after using them. So, never ever use a garden insecticide in the house in the form of a spray. The only way any can be safely used is when a systemic insecticide is watered in weak solution on to the soil of certain plants. Systemics are absorbed by the roots and carried in the sap to all parts of the plant. Aphids are suckers, so when they suck at the sap they become poisoned and they die. This, then, is the only way in which garden insecticides can safely be used indoors and even this is not recommended, nor, in fact, is it really necessary if you are looking after your plants correctly. The big plant nurseries take every precaution to ensure that our plants come to us clean and in good condition, and it is up to us to keep them that way.

The red spider mite

There are only three other pests which are at all common with the normal run of house-plants. You may come across one of your plants where the shoots are curling and twisting and changing colour, yet no greenfly or blackfly are present. The leaves affected will probably feel rough, dry and even brittle to the touch. This almost certainly indicates an attack by the unpleasant red spider mite, unpleasant because it is both difficult to detect and to clear. Even the name causes difficulties, for this mite is not a spider nor is it red. It makes fine, hairy, web-like secretions, mainly on the back of leaves and it can be identified for certain by looking for these. The mites themselves are almost invisible to the naked eye.

Red spider mite appears only when the atmosphere is too dry, that is to say when there is a dangerous lack of humidity. If your humidity levels are acceptable then your plants should never be attacked by this pest. So if you do find it the first thing to do is to increase the general level of humidity in the room that has been affected. The pest itself can be cleared by spraying thoroughly with an insecticide such as malathion, but only outside the house. If the attack is not severe it is worth while trying to clear it by spraying simply with clean water, making sure that every inch of the plant is drenched. It is possible to do this indoors if floor and furnishings are safely draped with newspaper.

Mealy bugs and others

It is possible also that when tending your plants you may see a curious white fluffy substance in one or two of the joints. It looks innocuous, almost as though a tiny feather or even a minute piece of cottonwool has been caught by the plant. But it will be mealy bug, a comparatively rare pest but one which is a nuisance for the only way to clear it on large plants is to pick it off by hand. If the white woolly blobs are examined closely you will find they contain one or more reddish mites and it is these that do the damage.

If the infestation is on a small plant it will be possible to take it outdoors

and, turning the pot upside down, dip the entire foliage of the plant into a bucket of a special solution of white oils by the name of voLcK. This should clear the attack. But as it is usually the larger, older and hence more static plants that are involved, other methods are usually necessary. I use a voLcK solution (made up quite simply according to directions) and a fine watercolour paint brush or sometimes a matchstick. The brush or the matchstick is dipped into the white ails and then the white fluff is carefully picked off the plant, every little piece of it. It can be a lengthy business if the plant is heavily infested but this should only be the case if it has been neglected or if it is in a room which is seldom used.

The last of these insect pests that we are at all likely to find is called scale, and it is a small insect in appearance something like a very small woodlouse except that it does not appear to move but remains stuck to a leaf surface, usually on the underside of the leaf, where it sucks at the sap. It is grey-green in colour and difficult to see unless you find one specimen and then specifically look for others.

This pest once again must be removed by hand and scraped with considerable effort from its limpet-like hold on the leaf surface. Alternatively it will be killed by the application of a systemic insecticide to the soil surface, but this will require several days to take effect while the plant can normally be cleared by hand in a matter of half an hour or so. It is probably the rarest of these very few common insect pests.

So we have seen that pests and diseases are nothing to frighten us. They are fewer, less important and infinitely less lethal than the pests and diseases we find in our gardens and we find to our shame that the greatest dangers facing house-plants are those brought by man.

It is a sad and curious fact that it is so frequently those who mean best, try hardest and wish most fervently for success with their house-plants who do them the greatest ill in the shortest possible time.

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