|I have several mature (approx 20' tall) Taxus yews. Both old and new needles are wilted or distorted. My local nursery diagnosed scale and mealy bugs. I applied the insecticides and horticultural oil as directed last summer, and fertilized the trees.|
|The word "distorted" sends me in a bit of a different direction. Generally, scale and mealy-bugs will not cause "distortion". So I have to wonder if you haven't gotten an infestation of a weevil, probably the Black Vine Weevil. With these guys the new shoots stop growing and turn yellow in midsummer. The tips droop looking a bit like a "shepherd's crook". In the fall and winter those shoots are brown and dry. If you look at a dead shoot it should contain small holes. Also, the bark has a white resin on it.
Black Vine Weevil (Otiorhynchus sulcatus), is a difficult pest to control. The weevils overwinter in debris at the base of the tree so be sure to use good "houskeeping techniques" and rake out and neaten up under your trees. Destroy all needles and branches you rake up, and any prunings.
There is a biological control that might help in your situation. The beneficial nematode "Steinernema carpocapsae" attacks soil-dwelling pests and may help reduce adult weevil populations. The product is mixed with water and used as a soil drench. It must be used when soil temperatures are above 55F. The product has a short shelf life, so get further information before purchasing. You can purchase it from Peaceful Valley Farm Supply, PO Box 2209, Grass Valley, CA, 95945, ph# 916-272-4769.
In late winter, prune out the affected branches and destroy them. Do NOT put them in your compost. Cut the branches back in such a way as to make your tree look balanced.
On a good note, weevils usually don't usually kill the entire tree, though they will cause damage to one- and two-year old wood. To be sure that this is the problem, you might want to bring an affected twig to your University Cooperative Extension agent for a definitive "diagnosis"! Without seeing the problem, it's difficult to give you a sure fire cure. Your Extension number is 516-454-0900.