I want to thin out some of my walnut trees this winter. Two questions: 1. If I apply Roundup to the cut stumps, will that help prevent recurrance of sprouts in the Spring? 2. Since some of the trees are close together, will the application of Roundup to a stump affect the adjacent trees , possibly getting into their root system and kill them?

Hi Chuck:

Whether in natural stands or plantations, I'm an advocate of using Triclopyr herbicide products (e.g., Garlon 3A, Tahoe 3A, Garlon 4, Tahoe 4E, etc.). Why? Triclopyr products do not have residual soil activity, nor are these products generally encumbered by flashback (i.e., herbicide translocated to adjacent like-species trees via root grafting).

Yes, triclopyr herbicide products tend to be a little more expensive compared to other suitable woody cut stump/girdle herbicide options; however, I'm a firm believer in the old adage, "You get what you pay for."

Getting back to your original question...

1. Yes, select Glyphosate products are labeled for cut stump treatments and yes they will prevent future stump sprouting if applied according to label directions.

2. Yes, Glyphosate product labels specifically state these products "may" cause flashback. Therefore, it is important to know what flashback is and to know how to manage flashback potential when dealing with woody species as flashback potential does not mean "these" herbicides should be avoided.