Answer: There are quite a few variables in your question, which makes it difficult to provide an answer. Does decline in green foliage mean that the tree isn't producing much foliage, or that the leaves are yellowing, as opposed to green? Yellow leaves could be a lack of iron (if green veins show) or a lack of nitrogen (if the older leaves are yellowing completely). Have you actually seen insects on the tree? Note that pests will seek out stressed plants, so if there are insects, they may be after the fact, not the real problem. Since this is an important tree to you, I suggest that you contact a certified arborist to make a diagnosis. Another possibility is to take or send a sample of the affected leaves to your County Cooperative Extension office. They are at 640 Temple St., 6th floor, Detroit, MI 48201, 313-833-3412. They have a hort. agent on staff. Good luck!
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