Homegrown: Leaf burn, violets
We have a great old cottonwood in our yard. Several years ago, an arborist told us that the leaf burn on the tree was probably caused by the weed killer we had applied to our sizable lawn.
We stopped the treatments and now I pull weeds in our gravel driveway, but they’re getting away from me. My neighbor says it shouldn’t hurt the tree if I just spot-treat the weeds in the gravel with Roundup. Is she right? — Cyndi
You mention that you applied the weed killer to the lawn, which makes me think you weren’t using Roundup (glyphosate), because that would have killed your grass.
Some of the broadleaf herbicides we use on lawns conceivably could have been the problem. Many of them have both foliage activity (they’re absorbed by the leaves) and soil activity (they’re absorbed by the roots).
If you have quit using those types of products, you’ve probably solved the initial problem, assuming the leaf scorch has disappeared. If not, we need to talk about other potential causes.
Even if you were using glyphosate in other areas, I don’t think it would have caused the leaf burn. There are other herbicides that might do it, but glyphosate has little soil and root activity.
As long as you kept it off any green tissue — green leaves and stems — and any open wounds, it shouldn’t have affected your tree.
As you’ve probably surmised by now, using glyphosate around the tree in the gravel area shouldn’t be a problem.
One thing I will mention is that I don’t think glyphosate does all that great of a job of controlling broadleaf weeds. It’s dynamite on grasses, but so-so on the other guys.
For them, I like to mix one of the broadleaf herbicides with the glyphosate to do a great job killing pretty much all the weeds you may have there.
Whenever you’re doing this, follow the label directions. I’ll put a gallon of water in my little pump sprayer and put the directed amount of each of the weed killers in the same gallon of water.
Now, I can hear you thinking, “why would I want to use one of those guys if they hurt my tree before?”
A fair question. The answer is that it’s more an issue of the amount of chemical that the tree might take up through the roots. A little bit shouldn’t affect your tree, so just use a bit of caution and common sense and you should be OK.
When you spray, you’re just trying to wet the foliage of the weeds that are there and then stop. Don’t soak the soil with the weed killer solution.
Also, just spot spray the weeds. Plastering the entire area will lead to over-application and could result in damage to the tree.
Lastly, don’t spray over and over and over. One, two or perhaps three spot treatments should serve to control the weeds without getting too much of the chemical into the soil where your tree could take it up.
There are some broadleaf weed killers that have less soil activity than others.
The most well-known of them is 2.4-D. Using it will give you a bit more margin than using the others. However, it doesn’t work quite as well as those other guys so you may need to put down more applications with it.
Thanks for the weekly column. I have a lot of violets in my yard and would like to give some to a friend. When is the best time to dig them? — Mary
Dig them up right away.
We try to transplant most things early in the spring before they break dormancy.
Though they may be starting to wake up, they should be tough enough to handle it. Just ask anyone who has had violets get away from them in their yard and has tried to kill them.
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