I combine one gallon of vinegar, one pound of salt, and a nice squirt of dish soap. I mix them all together and spray the mixture though a regular pump sprayer. My hubby just went through four gallons of the stuff yesterday on our driveway and most of the weeds were dead in an hour. You just have to make sure not to get it on things you like. Of course, it's best if you can spray the weeds when they are little, but I have been sucessful in killing some bigger stuff.
I was under the impression that 2,4-d did didly against knapweed. Not so?
My understanding is that for chemical warfare, only tordon and clopyralid will work against knapweed. But they have such huge downsides, most folks have stopped using it and some places have even banned it.
Mowing at the right time (when it has its big growth spurt) kills off about 90% of it. Irrigation helps because knapweed exudes niacin to kill off any plants that might try to compete with it. Irrigation will wash away the niacin and help other plants outcompete.
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