Q. I have a 6-8 yr. old ash that has this white powdery looking substance on the newer growth. Can you tell me what it is and how to eliminate it.  Picture from reader of white growth on ash A.  I have seen this kind of “growth” on several vegetables and herbs as well including peppers and basil over the years. I have sent pictures of these two a good friend of mine, a well-known horticulturist in Arizona asking him what he thought they were. I could tell he was giving me his best guess as well but I don’t think he was very sure himself.  Here is a post on something similar I made back in 2012 http://xtremehorticulture.blogspot.com/2012/07/what-are-those-white-fuzzies-on-my.html Although not exactly the same thing it appears to be more insect related than disease or physiological in nature. I wish I could give you a better response than just to keep your eye on it and let me know if things get worse. If things do get worse, then I would direct you towards a soil applied systemic insecticide for the tree if it is needed. That is the best I can do for you at this point. Perhaps some are other readers might hazard a guess?