I saw these for sale at Costco yesterday and I grimaced! I wanted to post a buyer beware notice and if I had seen anyone with it in their cart I would have overcome my shyness and warned them.
I apologize that I dont have any advice to offer you, I have never used Roundup but I wish you luck.
Jill

I always have a problem with those spray bottles too, Connie. I just canÂt keep my hand going! It sounds like youÂre going to have to spray them repeatedly. I guess the fact that mine were so completely covered with mildew when I sprayed them is what helped kill them so easily. So I guess mildew is good for SOMETHING! (Wanna borrow some mildew?) If you want to apply the roundup a different way so you donÂt have to keep pumping the sprayer, mix the roundup in a bucket, then put on long kitchen style rubber gloves, put a pair of cheap cotton jersey gloves on top, dip your hands in the solution and pull your hands over the foliage several times. Doing it this way will also help get the weed killer on the bottoms of the leaves. As always, be sure youÂre not getting it on anything good. And be sure if you need to scratch your nose you do it before you dip your hands in the stuff! Roundup might not kill oenothera, but it would probably kill your nose! ;-) Are you using Roundup brand? IÂve gotten cheaper brands a couple time that I didnÂt think did much of anything. And IÂve been trying to kill off some thistles in my front lawn for a couple years now! I just keep spraying them over and over, and each time I kill off a little circle of grass around themÂbut the thistles just keep going and going and going.............

If it helps, I killed mine 2 years ago, and I STILL have a few little pieces coming up this spring on the OTHER SIDE of the sidewalk. I just pulled a couple more out yesterday. At least they seem to be pretty weak, and I donÂt think itÂll be too hard to get rid of them.

Good luck,
Skybird