I have almost zero weeds, but when I went out of town to visit my mother I did a few experiments on her weedy lawn. I happened to use Gordons new product called T-Zone. I sprayed individual weeds and watered them with about one gallon of water from a sprinkling can after different intervals of several minutes, (simulating a rain shower). I also compared the results of adding a detergent as surfactant, without "raining" on the weeds after treatment. I found that: Simulated rain after one minute nullified the herbicidal effect. Simulated rain at 15 minutes resulted in partial loss of herbicidal effect. Simulated rain at 45 minutes did not reduce the effectiveness of the herbicide. Adding a surfactant increased the herbicidal effect, (not rinsed). Weeds tested were clover, dandelions, wild geranium, oxalis and wild violets. The T-Zone product did not have much effect on wild violet, except there was a burning of the leaves when the surfactant was added. http://www.pbigordon.com/pdfs/T-Zone-SL.pdf T-Zone contains triclopyr, sulfentrazone, 2,4-D and dicamba.