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I was all throughout the summer but mainly July/August, could be the case but the barberry were all fully leafed out and their leaves all shriveled up and died after spraying
150mL/5oz of Triclopyr + 300mL/10oz of glyphosate, mixed into 4.5 Gallons of water
I don't know. I could speculate about a half-dozen different reasons why, and not one might be of value. Translocation of the herbicides would be a big factor but why plants in the sun died and those in the shade did not, hmmm. Could be the shade. It could be timing. It could be age of the plants. Older one's probably have a bigger root/rhizome area and maybe those are the one's in the shade. I have no first-hand experience with japaneese barberry but have read about control methods. Cut stem application of herbicides seems to be preferred. If spraying, leaf applications are preferred in the spring while vascular activity is strong. I guess it all comes back to the differences in how the preferred herbicide gets moved thru the plant and the amount of plant, both above and below the ground, it needs to move thru. I do think your herbicide mix is a little weak for this kind of application. Me, I would double the concentrate, maybe even go to a pint. Ten ounces of gly is only 4 oz of active ingredient in 576 oz of water making it a less than 1% finished spray application. That might be ok for annuals but, I think, not here.
extension.psu.edu
