I have three Japanese Yew (Taxus cuspidata ‘Nana’), which I bought from a nursery and planted nearly 15 years ago. They don’t have any obvious signs of disease (e.g. no bumps, webs, crawly things). However, they look unwell; the leaves are discoloured and no longer glossy. I live in Toronto mid-town. The yews are in part shade. The soil is loamy. I dig in compost every year, and mulch with cedar. The area is generally well, drained, but we did have a lot of rain last summer.
Thank you for contacting the Toronto Master Gardeners.
Yews are often referred to as “tough as nails” so I can appreciate your concern since obviously your Yews have been happily growing in your garden for 15 years. I appreciate that you have thoroughly examined your trees for signs of disease and pests, in the absence of these we must look at environmental causes; Taxus cuspidata is particularly resistant to pollution, and it sounds as if they are properly situated and that you have given them all the appropriate care with mulching etc. But the bronzing of leaves does point to environmental stresses. You mentioned that last summer was rainy, did the soil at the site every get “soppy wet” so that trees were in standing water? I would check the site now to see if the water is draining properly. If it is the case that the ground now is very soggy, I would consider removing the mulch for now and trying to dry up the site. Watch very carefully for signs of fungus that will include white fungal thread like growth at the base of the tree and between the layers of bark of the trunk and honey coloured mushrooms growing at the roots. One other thought is that we had some extreme wind this winter and if your trees are not in a sheltered position they may be suffering from a bit of wind burn. The photo you provided does not show extreme damage, so with a bit of TLC I am sure they will recover. You should remove any browned branches using clean, sharp secateurs, and shake off any excess brown needles. Hopefully they will bounce back and return to full health.
Best of luck with them.