Insurance Company Says: Get the Ivy off That Tree!
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A. First, for those of you who are wondering: Yes; insurance companies can cancel your policy if you don't take care of clear and present dangers. (We once had an ice dam flood in our kitchen [it was Christmas night and we came home to a lovely indoor waterfall; but I wanted new gloves foo Christmas instead!]. Our homeowner's policy covered the wall repair and other damage, but they told us they would cancel our policy if we didn't get a new roof, as our old shingles were...eh, too old.)
An ivy-covered tree is another matter. The American Ivy Society (www.ivy.org ) still insists that climbing ivy will not kill a healthy tree. But they focus on interference with photosynthesis--the ivy preventing sunlight from hitting the leaves. I respectfully disagree with that theory and add that a much bigger danger is the ivy covering so much of the bark that the poor tree can't dry out. And once the bark starts to rot from continued dampness in large areas, the tree is obviously threatened. So I agree with the insurance company here. At the very least the ivy does not help the tree have a normal happy life.
But the ivy is also NOT sucking the life out of the tree. There are many kinds of ivy (and climbing non-ivies like Virginia creeper), but none of them are parasites like the famous (and poisonous) mistletoe--which interestingly, is also thought by many experts to only kill previously weakened trees. Clinging ivies are epiphytes, plants that latch on to other plants (and the walls of old University buildings) but draw no nutrition from their hosts. Any food they receive comes from where the roots are firmly planted in soil.
So here I also agree with the arborist; if you sever the connections to the roots, the ivies that are up in the tree will slowly die. And I mean sloooowly; English ivy, Irish ivy and the like are almost succulent in their ability to store water. And their waxy coating makes it easy for them to retain that water for quite a while, even after their roots are severed.
Side note: That waxy coating is why your ill-advised poisonous herbicides had no effect; the sprays just rolled off that slick surface. The Devil's Juice Roundup and other spray-on poisons are "broad-leaf herbicides"; they work by sticking to the 'broad leaves' of plants that have--well, broad leaves. But on ivy, it's like trying to get them to stick to Teflon. Negative Bonus: You certainly further stressed the tree by spraying those plant-killing poisons around it.
And "poison ivy spray" is even more of a joke. Maybe the herbicide can kill the actual plant, as poison ivy (not a real ivy) does not have waxy leaves. But its toxic allergenic oil does survive the death of the leaves for a long time--so people who kill poison ivy with poison ivy spray still get poison ivy when they pull out the dead poison ivy.
Just don't use chemical herbicides, OK?
Now, how will we assure the insurance company? Go around the base of the tree, prune or cut any ivy coming up from the ground, wait a few days and then carefully pull or cut the lowest growth off the bottom two feet of the trunk. Don't worry about higher up; you have cut off the ivy's blood supply and it will die. Show the adjuster that no living ivy is touching the tree and assume them that you will be vigilant about new ivy coming out of the ground. Get the arborist to vouch that any remaining ivy up in the canopy will turn brown and wither away over the summer.
Now; presumably their issue was that the ivy was eventually going to kill the tree and when that happened, the tree fall down and go boom or your home or your neighbors'. So make sure the arborist 1) removes any limbs overhanging either home and the property line (if a dead limb falls in your neighbor's yard it's your tree; your fault); 2) removes any dead or severely damaged limbs; and 3) rips out any ivy that's easy to pull while he's up there.
The ivy will continue to try and grow back up out of the ground. Be ready with one of the new non-toxic herbicides whose active ingredient is iron and spray it on the new growth right away--before the leaves can fully wax up.