Control: eradication is not easy; several sprayings at five-day intervals with a suitable insecticide are essential.
Diseases
Black leg: a disease mainly of cuttings, especially of pelargoniums; the bases become black and soft.
Control: this is encouraged by cold, wet, airless compost, so ensure compost is well aerated when taking cuttings. If cuttings are infected, they are best removed and destroyed; for rare or unusual varieties, remove cuttings, cut off the blackened area, and reinsert the base in fresh compost.
Botrytis: also known as gray mold, it attacks soft parts of plants, such as flowers, shoots, and young leaves, covering them with a gray, furry mold.
Control: cut off and destroy infected parts. Spray infected plants with a suitable fungicide. Remove dead flowers to discourage spreading. Avoid damp, still air and excessive water.
Damping off: attacks seedlings soon after they germinate, causing them to turn black and collapse.
Control: sow seeds thinly in well-drained compost and place in a warm and well-aerated location. Avoid excessively watering the compost.
Powdery mildew: fungal disease that produces a white, powdery coating. It usually appears in spring and summer, infecting leaves, flowers, and stems.
Control: remove badly infected leaves, stems, and flowers; increase ventilation and keep the atmosphere dry.
Rusts: complex diseases that are more problematic in sunrooms and conservatories than indoors. They produce raised rings of brown or black spots. Plants become unsightly and lose their vigor.
Control: remove and burn infected plants and increase ventilation. Do not propagate from infected plants.
Sooty mold: black, fungal disease that grows on leaves, stems, and flowers covered with honeydew. At first it appears in small clusters, but later covers the entire surface.
Control: spray with a suitable insecticide against sap-sucking insects. Use a damp cloth to remove the black growth from leaves. Flowers are best cut off.
Viruses: microscopic particles that invade plants (and animals), causing disorders in the tissue but seldom killing the host immediately.
Control: regularly spray with a suitable insecticide against sap-sucking insects (which probably introduced the problem to your plants) and burn badly infected plants.
Nonchemical Control of Pests and Diseases
Apart from growing plants healthily, with adequate moisture, food, and circulation of air, there are other ways to keep them healthy and to ward off pests and diseases.
1 Mist plants with clean water where there is a risk (or presence) of red spider mites.
2 Regularly remove dead leaves and flowers.
3 Use insecticidal soaps, which are ideal against a wide range of insects and mites.
4 Investigate biological controls, which means using other insects and mites to control pests. These are especially suitable where insects have developed resistance to chemical controls. Biological controls exist for aphids, caterpillars, mealy bugs, soft scale insects, red spider mites, thrips, vine weevil larvae, and whiteflies. Ask your garden center for advice.
Cultural Problems
Also known as physiological disorders, these are not caused by pests or diseases but by environmental problems.
Wilting: there are several causes, including too much water, too little water, and the result of soil pests that eat and destroy roots. Usually, plants wilt because they are short of water; if the compost is dry, water the plant several times. Alternatively, stand the plant, in its pot, in a bowl of water. Later, remove and allow excess water to drain. If a plant wilts and the compost is exceptionally wet, remove the pot and dry the root-ball.
Leaves fall off: occasionally, leaves fall off as a result of factors such as dry or wet soil, pests and disease, and cultural influences, including a sudden drop in temperature. Reposition the plant and keep it in an even, warm temperature away from drafts. Leaves that become yellow and gradually drop off are the result of excessive watering or inadequate feeding.
Flower buds fall off: this may happen if the plant is in a draft or a dry atmosphere or has received a sudden chill. Buds often drop off if a plant is severely knocked.
Damaged leaf surfaces: lack of water may make the edges of leaves become crisp and brown, but straw-colored patches on leaves, especially soft and hairy ones, are the result of water splashing on the surface, which is then burnt by strong sunlight.
Applying Chemicals
There are several ways in which insecticides and fungicides can be applied to plants.
1 Spraying is the most common method. One way to treat a plant in a small house or apartment is to put it in a large plastic bag, which can be temporarily sealed after spraying is complete.
2 Dusting is popular, and a puffer-type applicator is readily available.
3 Insecticidal sticks can be pushed into the compost. The plant’s roots absorb the chemical and the whole plant becomes toxic to insects.
Safety Tips
1 Follow the manufacturer’s instructions and never use stronger or weaker solutions.
2 Unless recommended, never mix two different chemicals.
3 Check that the chemical is suitable for the plants being sprayed—some plants are susceptible to specific chemicals.
4 Store chemicals away from children and household pets.
5 Avoid spraying if animals are in the room; fish and birds are especially harmed by chemical sprays.
6 Never allow children or animals to lick or chew plants that have been sprayed.
7 Only apply chemicals suitable for use indoors. This will be indicated on the label, but if in doubt, ask your nursery or garden center for advice.
Increasing Houseplants
There are several easy ways to increase your houseplants and, for a few of them, very little equipment is needed. Some methods produce many new plants, while in others just one new plant is created, such as when air layering a Ficus elastica (Rubber Plant).
Sowing Seeds
Many houseplants can be increased from seeds. If you want several plants of the same type, this is a relatively inexpensive method. Bear in mind, though, that equipment such as seed trays, pots, and compost are needed, as well as a greenhouse, sunroom, or conservatory where gentle warmth can be provided.