Extension agents and growers may occasionally receive diagnostic reports from the University of Kentucky Plant Disease Diagnostic Laboratory that indicate, “no disease was found.” This may result from an insufficient sample and/or that the plant problem does not result from an infectious disease.
One possible cause for “no disease” diagnoses is insufficient sample size. This occurs when the sample size is too small or does not represent the affected area. Often leaves, small twigs, or dead plant material (Figure 1) provide little information to determine potential causes. When leaf symptoms or dying branches are present, the area affected by the pathogen may be lower in the plant.
When diagnosticians assess inconclusive above-ground symptoms, they may recommend an agent or grower re-examine the entire plant to provide additional information.
Another reason for “no disease” diagnoses is that symptoms are caused by an abiotic factor as opposed to a plant pathogen. Many environmental or cultural conditions can cause symptoms that are similar to those of infectious diseases. In 2015, non-diseased samples comprised 49 percent of all submissions to the Diagnostic Laboratory. Diagnosticians evaluate whether symptoms are suggestive of one or more environmental/cultural factors and suggest possible causes.
For more information on a “no disease” diagnosis, review the publication Diagnosis of “No Disease” (PPFS-GEN-11).
- Diagnosis of “No Disease” (PPFS-GEN-11)
- Submitting Plant Specimens for Disease Diagnosis (PPFS-GEN-09)
- Plant Pathology Publications (Website)
By Kimberly Leonberger, Plant Pathology Extension Associate, and Nicole Gauthier, Plant Pathology Extension Specialist