Plant Diseases in Desert Gardens: Bacterial, Viral and Fungal Pathogens

There are millions, perhaps billions of bacteria and fungi that come into contact with plants every day.


Many of these are called saprotrobes, most of which are harmless to living plants. In fact, most saprotrobes are scavengers, living on dead organic matter. They are responsible, in a large part, in converting organic material into nitrogen, carbon and other nutrients necessary for plants to survive.

There are other organisms that live in the soil (and in water and air), which are not so beneficial to plants. These organisms are pathogens, and can cause serious diseases in plants. Pathogens can be bacteria, fungi or even viruses.

There are a lot of ways plants can become infected. Contaminated or infected seed, infected cuttings, transplantings and grafts are some ways.

Many plant diseases are spread by the wind, which blows pathogens from one plant to another. Others are carried to plants by water (through irrigation, rain, or other movement of water through the soil).

But the most common way plant diseases are spread are through vectors, which could include insects, people (and equipment, such as contaminated pruning shears), animals, fungi, nematodes, mites and parasitic plants.


Plants are generally quick to show disease infection. A plant might show yellowing leaves, spots on leaves, stunting or other abnormal signs.

But, remember that in plants, symptoms are non-specific. That means that you can’t tell what’s wrong with a plant just by looking at it.

Many different diseases (and other plant disorders) have the same affect on plants. Plus, symptoms have the tendency to change over time.

The best way to diagnose a plant’s problem is to observe it over time, and take notes of the development of the symptoms.

Diagnosing Plant Problems

This is actually a seven-part process and involves

  • Identifying the plant species.
  • Observing the symptoms.
  • Collecting accurate information.
  • Collecting a sample of the diseased plant.
  • Identifying the cause.
  • Confirming the cause.
  • Getting recommendations for treatment.

Who makes the Treatment Recommendations?

A good source for diagnosis and treatment recommendation is your local county agent. You can find them in the phone book or check on Cooperative Extension Services to find the location of your local county agent. He or she may be able to assist you in identifying a plant disease.

There is also a link at that site for Cooperative Extension Universities in your state. Most of these universities have a diagnostic lab which will provide a diagnosis for a small fee.

Another great thing about the Cooperative Extension Service is that they provide numerous publications on growing plants and vegetables for your specific region and USDA cold hardiness zone.

A third choice is to contact your county Master Gardeners Association. The American Horticultural Society maintains a list of all Master Gardener Associations in the country.