Plants are vulnerable to many diseases. These diseases are mostly caused by fungi and viruses. There are also a few bacterial infections that attack plants and produce similar symptoms to those of fungi. Their is a long list of ways plant diseases can sneak into a garden and attack the plants. They can already be present in the seeds you sow. They could be in the soil around the roots of a plant, or carried in the soil on the soles of your shoes. They may also come in on new plants or plant material from the nursery or garden store where you purchased them. They can even arrive in the garden on a wind. Here is a list of some very common plant disease, what they infect, symptoms and how to prevent and control them.
MILDEW: This affects peas, onions, lettuce, spinach and cabbage. The powdery and downy mildew produce a white or gray mold, it is often found in round patches. Downey mildew appears on the undersides of leaves in cool, damp conditions. Powdery mildew forms on the top in dry conditions. To prevent this disease do not overcrowd plants or over water them. Look for mildew resistant varieties. Remove any plant debris promptly. To chemically control them you will use green and yellow sulfur for powdery mildew and for down mildew you will use the chemical mancozeb.
BLIGHT: This disease affects potatoes and tomatoes. Blight favors warm,wet weather. It progresses rapidly on potatoes. The first signs are dark blotches on the leaves, followed by rapid wilting and yellowing of the foliage and stems. Then the plant will usually collapse in a few days. Blight is less dramatic on tomatoes, but is still serious. The leaves start collapsing and the fruit develop brown rotting patches. A different organism is responsible for early blight, which causes brown spots on the leaves it is much less serious. Warnings are often given when the right combination of humidity and temperature are present. To prevent further damage when you spot the disease on potato foliage remove and burn the top growth. If you harvest the crop right away the tubers may be unaffected. Destroy infected crop remains by burning them. Planting tomatoes in greenhouse are less likely to be attacked by this disease. There are a few different types of chemicals you can use on this disease they are mancozeb, copper sulfate and copper oxychloride.
BOTRYTIS (GRAY MOLD): This disease affects many different crops, especially lettuce and tomatoes. It produces a fluffy gray mold growth, under this growth the plant tissue rots. This fungus starts on dead tissue but spreads quickly to live parts. It is found quite often in greenhouses. It prefers cool, damp places. To help prevent this disease keep greenhouses well ventilated. Make sure your plants are not overcrowded, water early in the day and do not splash water. When you spot any of this disease clear all the dead and dying plant debris away.Cut out and destroy any affected parts.
WILT: This disease affects tomato and cabbage family. Fusarium wilt is the most common type. Young plants become pale and stunted, lower leaves yellow and wilt. The symptoms move upward and plants may die. Verticillium wilt causes similar symptoms but without one-sided effects. Wilt diseases are worse in the hot weather. To prevent this disease grow only disease resistant plants. Clear away any infected plant debris and rotate crops. Their are no chemicals to use on this disease.