Chapter 9 - Some Pests And Diseases

For the average home gardener insect pests and plant diseases are not particularly pressing problems. In nine out of every ten cases plant failure can be traced not to an invading horde of hungry insects or a mysterious mold or blight but rather to those greatest enemies of house plants, neglect and improper living conditions. We can't, however, completely disregard the problem of pests and disease because that one plant out of ten that fails because of pests or disease may be your favorite Begonia plant, and we want to avoid that if we possibly can.

If you exercise proper care and take the right precautions you should be able to prevent destructive insects from ever getting into the house. There are two times when you should be extra cautious: when you bring home a new plant which you have bought or been given, and when you bring your plants back into the house after a summer in the garden. No matter where a new plant comes from, whether you buy it from a florist or a friend who grows plants himself has given it to you, you can't go wrong if you check it over carefully for insect pests and, for good measure, give it a thorough washing down. A few minutes spent on inspection of a new plant may well save considerable trouble later on. Plants sunk into the ground outside for the summer have benefited from the natural surroundings, but they have also been exposed to the dangers of the outside world. These, too, should be given a careful inspection and a preventive bath before going back on the shelves in your living room.

Another preventive measure the good home gardener takes is to give his plants a regular weekly spraying. To be really effective, this operation should take place where it can be done vigorously, without making a mess. The ideal spot is the bathtub or shower stall. The plant's leaves (again, with the exception of African Violets and other hairy-leaved contenders) should be sprayed with room-temperature water so that both sides of its leaves are drenched. This serves two purposes. It gives the foliage the moisture it needs to maintain health, and it washes off any insects that have started to attack it.

Diseases

In the chapter on plant propagation we mentioned that seedling are often attacked by a disease known as "damping off." As we said there, the use of a sterilized starting mixture has cut down the chances of this fungus affecting the seedlings grown in it. If, however, any of your seedlings are so affected, the only workable way to handle it is to throw away those attacked to keep the disease from spreading to the healthy plants.

Leaf mold is another scourge of house plants, especially of rubber plants and screw pines. The leaves, which have become diseased should be removed and burned so as to keep the fungus from infecting the rest of the plant. If this remedy doesn't work, then the only thing to do is to throw out the whole plant. If you let the condition continue for too long, other neighboring plants will catch the disease. This is probably the point for us to set down a general rule to be followed in all cases of serious blight or insect pest infestation. If one or several of your plants are badly affected, either by a fungus mold or by a heavy invasion of insects, the wisest thing to do is to throw the plant or plants away immediately. It is generally not worth the time, trouble and effort it takes to cure them, and every minute the diseased plants are in the house all your other plants are threatened. There are times, of course, when this rule is very difficult to follow, especially with a plant you have had for some time and grown fond of, but no matter how much it hurts you to do it, destroying a badly infested or infected plant is the wisest precaution you can take for the health of your garden. If you have a comparatively mild case of rot or infestation in one of your favorite plants and you really want to save it, you should at least move it from its usual location and keep it isolated during its period of recuperation.

Insect Pests

There are five primary groups of insects which attack house plants in varying degree of intensity. Aphids, otherwise known by the unhappy name of plant lice, are small, soft-bodied sucking insects which are usually found on the underside of the leaves. They vary in color from green to brown or black and are sometimes difficult to detect if their color is close to that of the leaves they are living off. You should first try to get rid of them with a good hard spray with clear water. If this doesn't work, try one of the commercially available insecticides such as our own New Era African Violet and House Plant Spray. Several sprayings will probably be necessary to clear up the trouble completely as the spray must actually come in contact with the insect to be effective. Be sure to spray the plant with clear water after the last treatment.

Mealybugs are small white insects up to a quarter of an inch in length which are usually found on the underside of the leaves or on the stems. Spraying with plain water generally is not enough to dislodge them and so a combination of remedies should be used. First spray with water, then use a commercial insecticide. Follow up this treatment by going after the die-hard remaining few by hand. With a wisp of cotton wound around the end of a toothpick and dipped in alcohol you can pry off those that remain. Be sure that the plant is clean before returning it to its shelf since like all insects mealybugs reproduce with amazing speed and if you have missed a few you may have to repeat the whole process within the next few weeks.

Scale insects come in all varieties of shapes, round, oval or oyster-shaped, and are dark brown or black. They are readily identified, however, by the fact that adults of the species cannot move and they affix themselves tenaciously to the plant and refuse to budge. They most often attack ferns, palms, ivy, rubber plants and citrus fruits. Insecticides are not totally effective and so the only way to rid your plants completely of these pests is to pick them off individually by hand. Here again the toothpick wrapped in cotton and dipped in alcohol is useful and effective.

Red spiders are those minute red bugs so small that they are difficult to detect without magnification. Often the first indication you have of their presence is a fine web at the joint of the stem and a leafstalk. These insects thrive in hot dry air and an infestation of spider mites indicates that the air is too dry and more humidification is needed. They can be washed off with a strong spray of clear water, but as an extra precaution it is wise to treat also with a nicotine-based insecticide.

White flies are tiny moth-like creatures which attack Geraniums, Lantana and other plants. They are hard to control as they will fly off whenever the plant is sprayed, and will return later. The best approach is to spray several times a week with an insecticide until the pest disappears.

The list compiled here may seem long, but remember what we said at the beginning of the chapter; with proper care you never need face the situation of an insect-infested home garden. Below is a list of symptoms and things to watch for concerning the health of your plants. As you will see, good general care and attention will remedy most of the ills listed.
 
Symptom

Leaves dropping

browning of leaf tips

yellowing foliage

spindly growth

rot on leaves

wilting

spotted foliage

Probable Cause

The most frequent cause of defoliation is gas poisoning. The gas leak affecting the plant may be so small you won't detect it, but it can still be enough to kill your plants. Occasionally plants will lose their leaves as the result of the shock of being moved from one environment to another — from bright sun to heavy shade, for instance.

Over or under-watering, sun scorch, or insect attacks are to be suspected, in the order given.

Over-watering or soil exhaustion. Check the ball of earth to determine whether repotting is necessary. Also check for gas, lack of humidity and drafts. Occasionally yellowing leaves are a sign of red spider, scale insects or mealy bugs.

Lack of sun and hot dry air are the most common causes of this failure to flourish.

Fungus growth is the cause here. Treat as noted earlier in this chapter.

Under-watering or soil exhaustion.

Too much sun with those plants that like shade, or over-watering can cause spots on the leaves.

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