Most plant diseases which may be caused by fungi, bacteria or viruses are far more easily avoided than cured. Fungus and bacterial diseases breed in unhealthful conditions of atmosphere. Proper control of greenhouse ventilation, temperatures, watering and sanitation are the important factors in preventing infestation, but, since these details are also vital to healthy plant growth, you’ll want to give them careful attention in any event.
Never let the air in the greenhouse become rank and musty. At the first sign of it open the roof ventilators a crack, even in winter when it means wasting heat. In the spring and fall, raise the temperature slightly (up to 5) and open the vents to dispel excess humidity. Water only in the morning, and on a rising temperature. Do not water a plant unless it needs it, and keep water from splashing on the foliage.
Clean housekeeping habits in the home greenhouse are also most important in the prevention of diseases. They can get a good start in decayed foliage, if it is allowed to be thrown on the walks or underneath the benches. Dirty pots, flats and rubbish have no place in the greenhouse either, for they, too, provide ideal places to harbor potential disease and insect enemies.
Dead or infected foliage should be picked off the plants, and any plants that are badly infected ought to be discarded entirely. If a diseased plant has special value, and you don’t want to throw it away, segregate it from the others so they will not become infected. Take cuttings from clean stock only, and do not permit diseased plants to be brought into the house. Wash benches with a bleach solution before refilling-mixed 1 to 10.
Virus diseases are something which we continue to learn more about. Plants affected by them appear stunted or wilted and can never be cured. The only thing to do is throw them out.
With these precautions, diseases should not be a serious problem in the small greenhouse. The preventive measures may sound like a lot of bother, but they take very little time and are really no trouble at all. Wettable sulfur dust, not the coarse flowers of sulfur, will keep mildew in check, if used every now and then. A Bordeaux mixture is valuable in the control of leaf spot and rust.
Stem rot, root rot, wilt and nematodes are caused by infected soils. They won’t be a bother to you, however, if you plant disease-free stock purchased from reliable sources and use clean soil to start with. Soil sterilization is a helpful precaution, and, while you may not be able to sterilize with steam under pressure, using a clean professional sterilized soil is a good starting point, before filling the benches or pots.
It’s only natural, when considering insects and diseases-the many kinds there are, the rapidity with which they multiply, the way they attack and the damage they can do – that you wonder how it is possible to grow anything. But, in practice, with good growing conditions and five to ten minutes spent periodically with simple control measures such as described above, they are really no bother at all.