We are told that all trees put out varying degrees of toxins to help reduce competition in the neighborhood. Some tree varieties are capable of killing grape vines. In North America, the most lethal variety of tree in close proximity to grapevines is the American Black Walnut and, in the eastern and central United States, it grows in abundance. If you plant a grapevine near the drip line (edge of foliage canopy) of a Black Walnut tree, the vine root system will take a couple of years to penetrate deep enough to be near the tree roots. Then the vine's leaves will turn yellow and it will die. A young tree at the edge of the vineyard may not demonstrate its lethal ability for a few years, but one day you will look up above the last vine in the row and the canopy will be over your head. This means the root system is under your feet and beginning to penetrate the vineyard area.
If you decide to remove a vine-toxic tree from a vineyard site, leaving the root system intact will defeat your purpose. The roots will go on killing vines in the immediate area for an indeterminate period (as of three years ago, no botanical research was available in the U.S. on how long the roots would remain active). DO NOT REMOVE THE STUMP at this point in the process. You are going to use it to kill the root system. If the stump is an obstacle, work around it for a season.
Immediately after cutting down the tree, drill small holes in all of the exposed root "knees" and in the base of the stump itself. With an eye dropper, fill the holes with "2-4-D Amine concentrate" (in the U.S. this herbicide is labeled for this purpose). Inject as much material as the wood will absorb until you see the concentrate in the hole. That's all there is to it.
The following spring, make a wound in one or more of the root knees with an axe. You should find dead wood. After berry set, if you don't see any sap, in the wound, remove the stump. If you do see sap, repeat the herbicide injections and send us an email (we have yet to see the necessity for a second injection).
If you know of other trees that should be added to this list, growing anywhere on the globe, please send us names and a description of their behavior toward grapevines. We will post them here.
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