Without seeing the condition of the foliage, it's hard to say if the discolored leaves are already dead (it sounds as if they are desiccating due to the damage pictured, though), but the trunk damage in the photos is severe and suggests the problem has been progressing for some time now (likely months if not years). It's not a treatable condition.

Bark detaches when the wood underneath it is dead and drying out, which pulls it away from bark as it shrinks. The only living layer of tissue in a healthy trunk, the sapwood, lies just under the bark and doesn't go too deeply into the trunk's interior. (Like fingernails, bark is produced by live cells, but the bark itself is not alive, just as fingernail keratin is not living.) The heartwood at the center of the trunk is naturally dead wood. Anything that damages that live sapwood can cause significant canopy dieback or kill a tree or shrub outright by interrupting the flow of nutrients and carbohydrates between the canopy and the roots.

Wood-boring insects and fungi that decay wood generally take advantage of plants that are already injured or stressed; relatively few of them attack healthy, live wood on a vigorous tree. The holes pictured don't look quite like borer holes, but if they are, they would be borer exit holes (made as the insect leaves the tree), so unless there is another generation present unseen within the wood, the initial population is already gone. It's possible any borers that created those holes or winding marks on the dead wood where bark is missing were tunneling into wood that was already dead at the time, in which case they are not the original cause of the problem.

Some wood-boring beetles do carry infectious fungal spores on their bodies and inoculate the wood as they chew tunnels, and these beetles eat the fungal growth that results (they don't consume the wood itself), and in that case, even if the beetles could be eliminated, the fungus cannot. However, insect borers can't be treated with insecticide once they enter the wood, as few (if any) pesticide ingredients will reach them where they are feeding. Some tunnel into heartwood and are consuming wood that isn't alive anyway, while others tunnel in the sapwood can cause more short-term plant stress or dieback.

Environmental stressors that can predispose trees to being targets of beetle borers include drought and excessive root moisture from flooding or other inundation. Some species of holly tolerate temporary soil sogginess fairly well, but we've been in a drought for the better part of two years now, and it might be what's taking a toll on this tree in particular, unless it's been watered periodically during dry spells. We can't tell from the photos was initiated the holly's decline in this case. If any of the visible English Ivy was forcibly removed from the tree's trunk, that could be a factor if it damaged bark or tools cut into the bark as ivy was being cut down. Root or bark exposure to certain herbicides or root damage from any digging in the area are other possibilities.

You can have the tree examined by a certified arborist for a more thorough evaluation of how extensive the damage is, but nothing can reverse the current degree of dieback, and use of a pesticide to try to control any insect or fungus present is not likely to be successful, practical, or cost-effective to try.

Miri

Thanks for the information.  We’ll make a decision  about what to do soon.

 

Chris

You're welcome.