Nothing can take the fun out of gardening faster than disease-ridden plants. The most prudent and useful advice is to start with plants that have good disease resistance. Other things that can be done to help control problems include the following:
Common diseases to be on the look out for include the following:
Anthracnose - Caused by a fungus, Colletotrichum orbiculare, it can attack and affect many garden plants, especially cucumbers, cantaloupe and tomatoes. Look for yellow spots and water-soaked areas on leaves and fruits. It is most prominent in the hot temperatures and humidity of August.
Bacterial Wilt - Mainly affecting squash and cucumbers, this is caused by a bacterium, Erwinia tracheiphila, which clogs the vascular system of the plants. Watch for wilting leaves and branches, and if you know the plant has adequate moisture, suspect Bacterial Wilt. This is spread by the cucumber beetle. They can overwinter and emerge in the spring, carrying the bacterium in the digestive tract. The beetles eat the leaves, exposing the plant to their excrement that infects the plants.
Powdery Mildew - Caused by a fungus, it can affect many plants, especially your vine crops. Very fast moving, it can infest your plants in as little as 3 days. Hot, dry days and cool, humid nighs can contribute to the spread. As the name implies, it looks like someone has sprinkled powder on the plants. Crowded plants with poor air circulation are the most susceptible. There are many different types of powdery mildew, each being host specific (each affects only a certain type of plant) but each will multiply under the same conditions. Spores are produced continually and released into the air.
Verticillium Wilt - Caused by a soil-borne fungus, it can affect a numer of different vegetables in the garden, including tomatoes, peppers, potatoes and eggplants. If your garden space is affected, use a long rotation period (4-6 years) avoiding the above plants in the area. Also avoid strawberries and raspberries, which are highly susceptible.