Green Horizons

Grapevines - Are they good or bad?

By SCOTT BRUNDAGE | Consulting Forester
By GENE GARRETT | Outreach Specialist

Grapevines can be a major problem in forest management on high quality sites and, to a lesser extent, on poorer quality sites. Since grapevines need sunlight, as do trees, to maximize their growth and development, they rapidly climb through the trees' crown until they reach the top. At this point they lay down a blanket of leaves that serve to intercept sunlight that should go towards the production of food for tree growth. Once established, grapevines can be found growing throughout the trees' crown creating undesirable shade. This shade results in a dramatic reduction in the growth of the tree. Moreover, the sheer weight of the vines can cause physical damage resulting in reducing a once potentially valuable tree to a cull that is in need of removal. Breakage in the tops of larger trees and bending and distortion of stems in smaller "pole size" trees are especially prevalent under conditions that combine the weight of the vines with high winds, snow, and ice.

Most professional foresters would argue that, due to the damage caused by grapevines, they should be eliminated in managed stands. Wildlife biologists, on the other hand, see them as a food source for wildlife and might argue that a certain percentage of them should be retained. So, what is right for a landowner? The answer lies in "the eyes of the beholder"! If a landowner wishes to emphasize "aesthetics", then it may be desirable to leave some vines to increase the diversity of food available. However, it is important that the landowner understand the problems created by the vines and the "tradeoffs" that will occur. Not only will the grapevines cause physical damage to their host trees, those trees will also lose their vigor which means, there will be a sharp reduction in the production of their food crop (acorns, berries, etc). While the diversity of food available on an acre may increase, the quantity may actually decrease.

Regardless of the position one takes on the value of grapevines, there is always an occasion where a grapevine is in need of removal. Simply cutting the vine is ineffective and will only result in multiple sprouts developing—where you once had a single vine you now have many to contend with. The success in killing grapevines is found in the timing and the application of an herbicide known to be effective. Grapevines can be killed at any time during the year except between about March and mid-May, a period when sap is actively flowing. The flow of sap makes it very difficult for the herbicide to enter the plant and be translocated to the root system. The vine should be severed just above the ground. In many instances, a single vine may have more than one rooted area and it is important that it be cut just above each location where it enters and exits the soil. The herbicide of choice should be applied directly to each cut surface immediately after cutting. While there are undoubtedly many herbicides that can be effectively used on grapevines, one that is often used and is known to be effective and economical is Pathway (active ingredients Picloram 5.4% and 2,4-D 20.9 %) used in an undiluted concentration. Pathway is identical to Tordon RTU."