I have an apple tree that I believe was exposed to either a butternut or...
I have an apple tree that I believe was exposed to either a butternut or black walnut tree. I've read that these two trees are toxic, and the apple tree is showing signs of stress; the leaves are drying up and falling off. Is there anything I can do to nurse the tree back to full health or do I just have to let it run its course?
Per the site http://www.bordines.com/Care_Sheets/PDF/BlackWalnut.pdf apples are resistant to juglone so your apple is being stressed by something else. You haven't said what the apple is, how old it is, soil conditions, planting questions, mulch or water. Has there been any physical damage to the tree and what have the winter conditions been like.
The tree is a Sweet 16 which was planted 21 years ago. I haven't put any maintenance into it (monitoring soil conditions, mulching, etc.) because there has never ben a need. I has always been healthy until now. There is no physical damage, but this past winter was harsh. I initially thought it was juglone because the tree came out of hibernation this spring wonderfully - the white flowers bloomed and all seemed well. Then some nearby black walnut or butternut trees came out hibernation and developed lush foliage. Shortly thereafter the apple tree started showing stress. The flowers and leaves wilted and fell off without any other plausible cause.
Your systems sound very much like winter damage. Frost tears the fine roots stopping the tree from getting moisture so it uses what it had stored from last season and when that is gone the leaves wither and die. Plants suffering from juglone grow poorly, are deformed and lack vigor, it takes a period of time for them to die, this was too sudden.
Is there anything that can be done?
If there are no leaves it cannot live. Treat it as a opportunity to select a new one.