Growing in a home and in general greenhouse gardening is a lot more fun now than it was 50 years ago. Since then there have been many drastic changes in greenhouse management.
It is a lot easier now to keep the greenhouse free from insect plant pests, thanks to the development of new insecticides both chemical and natural along with IMP – Integrated Pest Management.
Back in the’50′s aerosol bombs provided a very efficient way of distributing insecticides in very fine droplets. Aerosol bombs were prepared by dissolving the insecticide in a liquid that had a low boiling point, such as methyl chloride or freon 12, and sealing the liquid under pressure in metal cylinders. When the cylinder valve is opened, the mixture was ejected as a fine spray; the propellant vaporizes almost immediately leaving the less-volatile insecticide suspended in air as tiny particles which then fall on the leaves and the insects.
Aerosol bombs were far more convenient and economical than are the ordinary spray or dust forms of insecticides. Commercial growers found that better results were obtained if leaks in the greenhouse are eliminated and the application was made when little or no draft or wind was blowing.
Whenever there is a choice. I would prefer to use the emulsifiable solution rather than the wettable powder. The former leaves far less visible residue on the plants and is a more efficient insecticide than the wettable powder. However, to some greenhouse plants emulsifiable solutions are toxic.
Some spray materials are more efficient if a wetting agent is added. For the home grower liquid household detergents can be used. Only a very tiny amount of detergent need be added to the water before the insecticide or fungicide is mixed in.
An systemic insecticide applied to the soil will control many insects and mites which infest African-violets, cyclamen, delphinium and foliage plants. Enough water should be added to assure good distribution of the insecticide in the soil. Gadgets used to proportion and apply liquid fertilizers can also be used to apply systemic insecticides. Remember that chemicals must be handled with great care; also, soils to which these materials are applied cannot be used for vegetable production.
Now we know that proper use of water in the greenhouse will reduce the amount of disease. For example, excessive or careless watering of such plants as African-violets, primulas and begonias will promote leaf and stem decay. Overdoses of water, especially on heavier soils, will also increase the possibility of root and stem rots caused by the pythium, phytophthora and sclerotinia fungi.
Leaf infections by fungi can be largely prevented by carefully applying water to the soil and not to the leaves. Most fungus and bacterial spores must stand in free water for several hours before they can germinate and cause infection.
One important exception to this rule is the powdery mildew fungus, a serious problem to roses, African-violets, begonias, verbenas, calendulas, phlox and snapdragons. This fungus does not infect leaves when free, liquid water is present. As a matter of fact, mildew infections are more prevalent on plants growing near doors or broken or leaky windows where there is a draft and evaporation is rapid.
Botrytis fungus becomes troublesome in dark humid weather. On begonias it causes stem rot: on cyclamen it affects the leaves; on geraniums, lilies, bougainvilleas and snapdragons it affects both leaves and flowers.
An old-fashioned but still fairly effective way to keep botrytis infection to a minimum is to practice sanitation. Infected flowers and leaves should he removed as soon as noticed, and burned or carted out of the greenhouse. They should never be thrown beneath the bench or into any container in the greenhouse. Reducing the humidity by control of heat and ventilation, increasing air circulation and avoiding the splashing of water all help to reduce botrytis infection. Where the botrytis problem is serious, occasional spraying with zineb or captan will also help. Soil-borne diseases are more difficult to control.Tags: flowering, greenhouse, pest