Dry climates limit the number of diseases that are common in vegetable gardens but there are a few serious problems that should be monitored.
A number of common virus diseases occur on vegetable crops. These include, but are not limited to, zucchini yellows, cucumber mosaic, potato leafroll virus, tomato spotted wilt, and tomato mosaic. The only solutions to a virus infection is removal of the affected plants and control of the vectors (other organisms, usually insects, that spread the disease). Control of a serious recurring virus problem may require getting help from a Master Gardener, county extension educator, nurseryman, or other qualified person.
Many of the fruit rots and some leaf spot diseases are caused by bacteria. There are no chemical controls for bacteria. The best methods for controlling these diseases are cultural. Keep fruit off the ground and make sure irrigation practices allow plant surfaces to dry between watering. Also, from the garden any refuse from diseased plants.
The most common diseases of plants involve fungal pathogens. Some fungal diseases live in the soil and attack the plant through the roots; other fungal pathogens directly attack leaves, stems, flowers, and fruits. Soil diseases are usually controlled through crop rotation, meaning moving each vegetable to a different place in the garden each year. Fungal leaf and fruit diseases can be reduced my allowing foliage to dry between irrigations and keeping plant parts off the ground. Occasionally, fungal diseases may require fungicidal applications.
To learn more about controlling diseases in vegetable gardens, use the following resources:
University of Idaho: Management of Vegetable Diseases in Home Gardens
Cornell University: Minimizing Diseases in Vegetable Gardens
University of Illinois: Controlling Diseases in the Home Vegetable Garden