The most I know (apparently not enough) about red sorrel (aka sheep sorrel) is that you should try to kill it in early spring, and that a different spray is reuired in summer. It rains so much here in spring you do not have 2 days with out moisture so normally effective "crossbow" cannot be used without being diluted or washed off., The only hot summer/fall spray I found is obscenly expensive and has not worked . This soil is acidic and this weed's playground. Anyone conquer this weed?