Viruses are submicroscopic pathogens that increase in number once they are inside the host plant. Viruses can be spread by insects, nematodes, seeds and infected propagating material and by mechanical methods. Individual virus cells can be observed only with the aid of an electron microscope. Symptoms can often be confused with those of plant mutations, nutrient deficiencies, toxicities or other pathogens. Virus diseases are controlled with the use of resistant varieties, rotations, and weed and insect controls.
Disease prevention is more effective than controlling them. Once a plant becomes infected, there is little to do other than pruning out the diseased part or removing the entire plant in the case of root rots or virus infection.
A disease prevention program should use a combination of cultural and chemical treatments. This requires some understanding of the disease-causing organisms and the chemicals to be applied.
Identify the plant(s) involved.
Inquire into site history of plant disease or other problems.
Look for patterns of symptoms on plant parts or whole plants.
Assess spatial distribution of disease symptoms in the landscape.
Examine disease symptoms and disease signs using a hand lens when necessary.
Compare disease symptoms and signs to the images in reference books and those posted on the Internet.
Perform simple examinations for potential bacterial and nematode diseases with the aid of basic tools listed above.
Consult with a local Extension agent, then a professional diagnostician, if necessary,
or send a sample to a public or private diagnostic lab, depending on the nature of the diseases
to be examined.