Plant diseases can be grouped into 3 main microscopic categories: bacterial, viral and fungal. Here is some information to keep in mind about these common plant diseases and the preventative steps that can be taken to defend against them.
The most common plant diseases one encounters in the garden are those brought on by fungi and fungus-like organisms. The fungi reproduce via the production of spores that may be spread long distances by air or water, or they may be soil borne. Proper watering techniques and drainage are an important preventative defence since many of the fungi that cause plant diseases thrive in moist conditions. Fungal diseases can be controlled through the use of fungicides in agriculture, however new races of fungi often evolve that are resistant to many conventional fungicides. Alternatively, fungicides like OxiDate use a chemical reaction that oxidizes enzymes and proteins that make up simple cell organisms, on contact. As the oxidation happens very quickly and leaves no residual chemical, the disease has no opportunity to mutate and form resistance. Some of the most common plant diseases brought on by fungi and fungus-like organisms include, Downy and Powdery Mildew, Gray Mold (Botrytis), Fusarium wilt and Blight.
Bacterial diseases can occur within houseplants and greenhouse-grown varieties, but are more common in outdoor plants. This is partly due to the fact that many types of bacteria that infect plants are often transmitted by insects that create a wound in the plant, allowing the bacteria to get inside. Several types of parasites like whiteflies, scale and aphids can act as carriers of the bacteria, which is transmitted to the plant when the insects feed on it. Bacteria can also be transmitted by pruning equipment shared between infected and non-infected plants.
A two-pronged approach to bacterial prevention would include include controlling the parasites with a natural insecticide like AzaGuard. Plant wounds can be treated for bacteria using a foliar spray like OxiDate (for food crops) or ZeroTol (for ornamentals). These organic chemistries can be tank-mixed for ease of application.
Viruses, like bacterial infections, require an opening in the plant through which the virus can get past the cell’s rigid cell wall. Humans can transmit plant viruses via grafting and parasites can also act as carriers of the virus. Unlike bacteria, viruses actually infiltrate the plant’s cells, and then replicate themselves to create more infected cells. Since the virus lives inside the plant’s cells, there is no way of removing a virus without destroying the plant cells in the process, making chemical treatments futile.
Normally plant viruses only cause a loss of crop yield. Therefore it is not economically viable to try to control them, the exception being when they infect perennial species such as fruit trees.