Plants symptoms may be caused by biotic (living organism) or abiotic (nonliving) agents. Many abiotic factors can cause symptoms in a landscape or garden. These factors include nutrient imbalances, drought or excess soil moisture, limited light, reduced oxygen availability, air pollution, soil pH extremes, pesticide toxicity, compaction, cultural practices, mechanical damage, and low or high temperatures.
Stunting: Hindering of normal growth or overall development of a plant.
Insects, mites, fungi, bacteria, nematodes, viruses, parasitic higher plants, protozoa, and grazing or browsing animals are all examples of biotic agents that damage plants.
Symptoms of an unhealthy plant are expressed as visible changes in its appearance. When whole plant symptoms such as wilting are observed, 100 percent of the plant has visible symptoms. Plant part symptoms can affect any portion of the plant, including flowers, fruits, leaves, stems, or roots.
Catfacing: A deformity of fruit induced by initial scars caused by insect punctures or plant disease lesions, followed by continued fruit growth.
Along with the type of symptoms being expressed by the plant, it can be important to observe the colors that are associated with those symptoms. When making a diagnosis, description of color can be a useful tool, such as the yellowing of leaves associated with chlorosis. Being able to correctly define or describe the abnormal appearance of an affected plant strengthens the ability of a gardener or landscape manager to correctly identify the cause.
Slot: Short, rectangular or linear openings in a leaf, where plant tissue has been consumed by chewing insects.
In addition to the symptoms observed on the plant, there also may be signs of the problem. Signs are visible, direct evidence of the causal agent on the affected plant part. Signs may include tracks, bite marks, chemical residue, honeydew, egg, masses, frass (insect fecal excrement), fungal mycelium and spores, or bacterial ooze.
Spore: A fungal reproductive unit consisting of one or more cells.
Signs can be very useful when making a diagnosis but must be interpreted with care. for example, fungal growth on the surface of a plant part may be a sign of a saprophyte (a nonparasitic fungus growing on nutrients and organic matter on the plant surface) and thus might not be related to the actual cause of disease.
Hole: Removal of plant tissue caused by biotic agents such as insect feeding, or openings caused by abiotic agents such as hail.
When working on diagnosing a plant problem, remember to examine the surrounding area to observe the presence of any patterns. Biotic problems typically have an uneven margin between the affected tissue and healthy tissue, are randomly distributed, affect one plant species or related plants species, and progress to related plants nearby. An example of abiotic problem pattern is the movement of a black spot from one rose to another. Abiotic problems typically have distinct margins between healthy and affected plants tissue, have a uniform pattern of the distribution, affect multiple species, and do not spread to related plants. An example of an abiotic problem pattern is the uniform browning of turf resulting from a plugged or leaking sprinkler head.