When did symptoms first appear in plants?

When did symptoms first appear in plants?

This is a very important question: when did the symptoms of the problem in question first become evident? Sometimes the answer is unreliable; we have all heard “it up and died overnight.” We can check this out, though, by looking at annual growth and symptoms, such as long-term branch decay and peeling bark. Sometimes people do provide crucial information that helps solve the problem, such as noting that foliar collapse occurred soon after a spring frost.

Plant symptoms sometimes progress through a series of different “looks.” It is helpful to consider symptom progression in the context of having a beginning, middle, and end. The oak shothole leafmining fly (Agromyza viridula) uses its sharp ovipositor to puncture young expanding oak leaves to cause liquids they feed upon to flow. They often produce holes in a row, and if new leaves are punctured prior to unfolding, the holes will appear as mirror images on different parts of the leaf. In the beginning, the holes are extremely small; however, they become larger as the leaves expand. In the end, they may measure over 1/2 inch in diameter. Of course, by this time, the fly is long gone.

Plant stress may also produce a progression of symptoms. However, there are two types of plant stress: acute and chronic. Acute stress is caused by an immediate event, such as flooding, drought, or defoliation by an insect pest. Symptoms are usually immediately evident and easy to diagnose since the cause is close at hand.

Chronic stress is caused by more subtle conditions such as the site problems listed in Question #8 or horticultural problems that will be covered in the next question. The effects of chronic stress are usually cumulative, meaning that the damage adds up over time to eventually produce dramatic results. A mature oak tree that has had its root system damaged or reduced by construction may take years to show the full effects, with symptoms such as a thinning crown gradually progressing towards the death of the entire tree. The tree does not “up and die overnight” — it began the slow spiral towards death when it was first exposed to chronic stress.

Source: The Ohio State University