What do you see that looks abnormal in plants?

What do you see that looks abnormal in plants?

Plant abnormalities are categorized in terms of “signs” and “symptoms.” Signs are the actual causal agent; some part of the pathogen is visible. A fungal pathogen that causes interior rot in a tree is revealed when it produces bracket-like fruiting structures that grow out of the side of the tree. Powdery mildews reveal themselves when they produce white, powdery mycelia that cover leaf surfaces. Both the bracket-like fruiting structures and the powdery mycelia are “signs” since they are the actual causal agents for the diseases.
Symptoms result from interactions between the plant and pests, pathogens, or environmental elements (e.g. high soil pH). In other words, a “sign” is the actual pathogen while a “symptom” is what the pathogen does to the plant. Symptoms include such abnormalities as: off-colored foliage; deformed or stunted foliage; leaf spots, blotches, blisters, or scabby spots; stem dieback; stem cankers; root rot or root loss; canopy thinning; and overall plant decline.

Remember that the same symptom may be produced by multiple causes. Twisted, deformed leaves can be caused by sucking insects such as aphids, or exposure to plant growth regulator herbicides. Tiny leaf spots can be caused by a leaf-spotting fungus or bacterium, or lace bugs and mites. Yellowed leaves (leaf chlorosis) may be caused by nutrient deficiencies in the soil, or by a soil pH that makes the nutrients unavailable to the plant.

It is important to clearly consider and list what signs and symptoms are present that make you believe there is a problem in the first place. For example, are there signs of insect or mite feeding? If so, is injury from pests with chewing or sucking mouthparts? Similarly, are there signs of fungal diseases, such as the orange fungal growth of rust disease? Are leaves missing off-color, abnormally small or scorched? Is there abnormally peeling bark? Are there girdling roots — or are roots rotted in the pot or in the soil? Are there abnormal growths such as galls or discolored cankered areas on stems?
The list can be extended and extended. It is important to walk around the plant — looking at it up close and from far away — and to catalog every noticed item as you work on your diagnosis of what may possibly be multiple problems.
Finally, when considering symptoms, keep in mind that there are often a series of symptoms, known as the “symptom complex,” which together helps fingerprint a particular problem. When questioning if lace bugs are a problem, check not only for flecking and yellowing of leaf tissue, but also for tarlike excrement deposits. When checking for Verticillium wilt on maple, check not only for leaf scorching and stem dieback but also for discolored streaking of the vascular tissue.
Source: The Ohio University