Monday, March 23, 2009

Weekly Word on Weeds

English Ivy Control – Best Done in the Spring

Although English ivy is a popular ornamental ground cover, it can also be an invasive and aggressive weed of woody parks and landscapes. Woody evergreen plants like English ivy can be quite tolerant of common herbicides such as glyphosate. In fact, I recall hearing recommendations in the 1970’s for over the top applications of glyphosate to remove poison ivy in English ivy beds (not something we currently recommend by the way). In response to many requests for information on how to control this weed, Dr. Walt Skroch, Professor Emeritus at NCSU directed his young and inexperienced graduate student (that was me in 1983) to find out how to kill this pest.

We found that English ivy was controlled by glyphosate applied in the spring, when plants had 2 to 4 new leaves. Later applications were much less effective. Late summer and Fall applications were essentially ineffective. I’ve not seen anything better since those experiments.

So, here is my recommendation for control of English ivy:

Glyphosate -- use any of the 41% or greater active ingredient formulations
Ø Mix 2 to 3 percent by volume with water
Ø Apply in the spring when plants have 2 to 4 new leaves, thorough coverage is essential but NOT to the point of run off
Ø Re-treat when re-growth appears (about 6 weeks later)
Ø Repeat next spring if needed.

Will this recipe work for other evergreen vines like common periwinkle (Vinca minor)? Had you asked me this question two years ago, my answer would be “most likely”. But recent research at NCSU has show otherwise. Vinca was best controlled with glyphosate applied in the fall but poorly controlled by spring applications. So, sometimes our “best guesses” turn out to be wrong and there is no substitute for actually doing the research to find the most effective treatments.

Joseph C. Neal
Professor and Extension Specialist -- Weed Science

For more information contact your local Cooperative Extension Center and ask for the Commercial Horticulture Agent.