My post is speculation - I don't know that a virus is the causal agent, though evidence makes it seem a likely suspect. My observation suggests a problem with the rootstock but doesn't rule out involvement of the rest of the tree. So it may be that a commensal virus of the rootstock becomes distributed throughout the tree in a latent form. If scions are taken from this tree and grafted elsewhere, it is possible that the viruses will later become active and the signs of the disease will be expressed. So the problem with your multi-grafted tree is that there may be a higher chance of infection since any of the scions could have brought latent virus to the tree,

We don't have it here, but the next-door county does. 8-( I have friends in Chicago who fifty years ago lost the elms that lined their street. Then decades later they happened to live on the original block for the Asian longhorn beetle infestation: they lost every tree on the block except a lone conifer. I never expected anything like that here.

Well, the roof rats may, indeed, be the cause of the demise of your tree. I see a large amount of bark chewed off, which means the tree may have been girdled, thus cutting off the supply of nutrients traveling up to the tree's canopy. I agree with Mike, here (citrange). It could also be due to Phytophthora infection which can cause foot-rot as Mike mentions, as well as traveling up the tree (the odd discoloration on the branches and bark). Whatever caused the bark damage at the base of the tree (roof rats, a weed whacker, sprinklers hitting the trunk of the tree and the bark simply rotted and fell off) are most likely the cause of the death of this tree. The other concern I would have is how close the tree is to your house and roofline. You are providing those roof rats a clear path to your roof, and thus your attic. Which is where they love to live. We have a serious issue with the Norway rat (also known as roof rats or citrus rats). I would make sure you remove all trees or vegetation from the sides of your house the provide a "ladder" to your roof. Plus, the roots aren't good for your house's foundation and plumbing, either. Set traps or bait stations around your house to reduce the rat population (they carry disease as well as damaging your fruits, and what you're seeing with your lemons is clearly rat damage. They eat the sweeter skins of your sour citrus, and will hollow out the insides of your sweet citrus - classic rat damage). They are unhealthy pests, and you need to get rid of them. Bait stations can be set with non-kill through bait, so you do not kill birds of prey, just know that there is not antidote for that type of poison, so don't let dogs or small children get into the bait stations. Patty S.

I have 2 huge Cherry trees that also look like they got a frost or something. They appear to be recovering but they have lots of blackened leaves and even many apparently healthy leaves have fallen. They have put out new leaves in the past 2 weeks or so but I wonder what happened ot it. This is our first year in this house so I had no way to know if this was normal for these trees. Sorry your tree didn't make it! Cathie