There are three main causes of plant disease: bacteria, fungi and viruses. Garden pests pose a different problem, because they are a natural part of the garden and eradication can upset the garden's natural balance. When choosing forms of intervention, select methods that will destroy or deter damaging insects and pests, while restoring this natural balance to the garden. Prevention is the first step.
Bacteria are single-cell organisms that enter through wounds or natural openings in plants. Conditions that are favorable to the spread of bacterial diseases are high humidity, poor air circulation and crowding. Plant stress makes them more susceptible to bacterial diseases. Conditions that cause plant stress include too much moisture, too dry, irregular watering, a pot that doesn't fit the plant properly, low light intensity, poor soil drainage, an improper amount of nutrients or fluctuating temperatures. Symptoms of bacterial diseases include blights, tip burns, leaf spots, rots, wilts or complete breakdown of plant tissue.
Fungal diseases are some of the most widespread plant diseases, due to the fact that they spread by spores that are carried on the wind. If a spore germinates and grows, it produces infections that are damaging to the plant. Fungal diseases can be prevented through good sanitation and cultural practices. Fungal diseases include damping off, leaf spots, scab, rust, powdery mildew, black spot and peach leaf curl.
Viral diseases produce symptoms, such as growth abnormalities, color variegations in foliage or color distortions in blooms. They effect growth and productivity and can be very detrimental to plants. Prevention for viral diseases is to remove affected plants from the garden before the disease can spread to nearby plants or through control of the insect populations that carry the diseases: leafhoppers, aphids, thrips, etc. One of the most well-known viral plant diseases is tobacco mosaic virus.
Pest management may not always be necessary at the first sight of damaging insects. Often, if you wait, nature will correct the imbalance on its own, but if major plant damage begins to occur, other measures may need to be taken. Such measures include washing plants, repelling pests and physically destroying pests.
Natural Methods of Pest Control
Many natural methods of pest control are effective. Heating the soil by placing plastic over garden beds once the soil has been cultivated is effective in eliminating many soil-inhabiting pests, such as grubs, weevils, sod webworms and carpenter worms. Mechanical controls such as hand-picking, traps, barriers, floating row covers or a strong spray of water are effective against many pests, especially in the early stages of infestation. Keeping the garden free of plant debris where pests and diseases breed is also effective. Other natural measures of pest management include soaps and horticultural oils, companion planting to encourage beneficial insects or to repel damaging pests and planting early to avoid heat-loving pests. Beneficial insects that destroy garden pests include parasitic wasps, lady bugs and Cryptolaemus beetles, lacewings, predator mites and parasitic nematodes.