Another tidbit from my notes on weeds :
Canada Thistle: (Cirsium arvense) Most of you are probably familiar with this noxious, perennial weed. One way to control it is by cutting it down to the ground several times a season. This will eventually starve the thistles tough plant roots and kill it. In large, heavily infested areas planting a smother crop of alfalfa or buckwheat after mowing the thistles has proven to be very effective. Alfalfa is so aggressive in its search for moisture and nutrients it can eradicate thistle. The alfalfa can then be tilled under in late summer to enrich the soil.
One method that can be used in small areas is to inject white vinegar into the center of the thistle. We use a veterinarian type syringe to do this so the solution is in contact only with the target plant. This has worked so well that after several applications the thistle shrivels up, dies, root and all. Vinegar does act as a soil sterilant so you must be careful what it contacts. If you can find 30% acidity vinegar, this is the best to use versus the store brands with about 5% acidity.
