digging up the Arum is a good way to spread the plant. It survives the glyphosate because the plant is either stressed as Tim said, or the peripheral offset tubers are not in leaf and therefor remain unaffected. Seeds in the soil may also germinate subsequent to treatment. In my experience follow up applications in subsequent years are needed. Small doses of glyphosate are not always enough to kill a plant but they weaken it -reducing uptake from subsequent applications. Large doses on the foliage burn the leaves and the plant survives as if it had received an inadequate dose. Therefore I find it more effective to repeat application of a weak dose two or three times in a two to three day period. On 23 April 2014 17:39, Jane McGary <firstname.lastname@example.org> wrote:If there's that much arum in a wetland, it does need to come out. It will have to be dug -- the tubers can survive herbicide application.