As diagnosticians, we often receive foliage with spots, blotches, or scorching. More often than not the question is "Why is this plant dying?"Although leaf spots and blights can injure plants, loss of even half the leaf area is not enough to kill a tree or shrub. If the plant is declining or dying, something more is involved. In most cases, the leaves do not provide enough information to tell why the plant is dying. Annual stem growth may help in diagnosis.
Get a sample of a terminal branch including about 15 inches of stem and all attached leaves. It is important that this branch be on the outside of the plant. You can determine the annual growth if you follow the tips of the branch to a series of very close rings encircling the stem. That is one year's growth. Continue down the stem to the next set of rings for the previous year's growth, etc. Most tree species put out 8 to 10 inches per year in our area. Look in Michael Dirr's book, Manual of Woody Landscape Plants, for the growth to expect for many woody species. If the sampled tree is growing only an inch a year, it is obviously stressed. Determine how long the tree has been growing poorly. If you can get the client to think about changes that happened when growth slowed, you may get your best clues to the cause of decline. This information, along with leaf symptoms, weather information, soil type, drainage, etc, can lead you to the cause(s) of the decline.