Limb I cut out yesterday. This would’ve progressed to dead brown leaves and needed to be removed in a week or so.

Apologies for the wordy post! It won’t let me go back and edit or shorten it.

I’m concerned about root rot, because we’ve had an unusual amount of rain and flooding the last two years. I have clay soil, so it does drain quite slowly. I thought if the roots were too wet for a long time that they could develop fungus or something and slowly kill off the plant?? I read it late last night and may have misunderstood;) I will look into doing that. Thanks.

The 'rot' actually occurs from the roots drowning in overly wet or poorly draining soil. Too much water = lack of oxygen and roots smother and die. And it usually happens rather rapidly, not very slowly at all. And since typically the entire root system is affected, it is most common to see the entire plant fail, rather than branch by branch.

There are other soil borne pathogens that move with excess water - oomycetes or water molds. But I am not aware of any that specifically affect euonymus....although I am by no means an authority :-)

Interesting. Thanks! I live far from the extension office, but sent them a picture...we’ll see what they say and if they’d like me to bring in a sample.

Is it possible your neighbor did something intentional to try to kill them? Like brush killer, roundup, etc.?

I don’t think he’d try to kill it, but you never know I guess. I got a reply from the master gardener! They said it’s probably powdery mildew. I don’t see powder on any of the leaves though. I’ve had other plants with powdery mildew before, and usually you can see it on the leaves. Whereas these leaves look perfectly green/shiny/healthy, until one day they just start wilting and eventually die.

I'm not sure that the master gardener you got knows what they are talking about :-) Powdery mildew on euonymus looks nothing like what is happening with your plant. It will typically affect all new growth, not just random stems. And will produce a visible white mat that can be easily rubbed or washed off. I have also never seen it cause stem die off on any woody plant. It is almost entirely cosmetic although a heavy infestation can cause leaf drop.

https://hgic.clemson.edu/factsheet/euonymus-diseases-insect-pests/

Thanks, gracie01! I’ve looked at those lists, and they don’t seen to match what’s going on...