Q.Euonymus is turning yellow and brown
Last year we treated our euonymus for scale and everything looked fine in the fall. Now, we notice that there are no bugs or mold, but the leaves are still turning yellow, then brown, and dying. What could be the problem? Should we retreat?
Thanks,
Joanne

In early stages it can be nearly impossible to see the Scale insects.
I would prune away any dead or damaged plant material and dispose of.
Treat the plant with Neem Oil. Neem Oil is organic and will work as both an insecticide and fungicide.
Here are some links with more information.
https://www.gardeningknowhow.com/plant-problems/pests/insects/control-plant-scale.htm