The distribution of the problem is very important. If the problem occurs on a number of plant species, it is most likely the result of environmental or chemical damage. If the problem is occurring on a single plant, and others of the same species are not affected, it is unlikely that the problem is associated with the foliage. Look for problems on the trunk, stem, or roots. Record specific symptoms on individual plant parts.
Symptoms are the expressions of disease on the host plant.
These expressions may include abnormal plant growth, color, taste, odor, etc. Determine whether symptoms are primary or secondary. Look for signs of the pathogen or insect. A sign is the presence of a pathogen structure or product on or in a diseased plant. They include fungal fruiting bodies, bacterial ooze, insects, and other structures.