The compounds of the formula and their salts 1where the radicals R1 to R4, A1, A2, L0, X and n are as defined in claim 1 are suitable as herbicides and plant growth regulators and can be prepared by processes as claimed in claim 6. The acid is converted to a salt and the salt extracted into a polar solvent, yielding acid of high purity. It is installed using screws, nails, staples, glue, Velcro, or any other type of fastener. The wedge is secured to a cap that threadedly engages the body.