Postemergence herbicides are applied to standing weeds. To be effective, tank mixing with surfactant and thorough coverage of all weed parts are required. Contact herbicides . Top-kill will control annual weeds but perennials will regrow from underground organs like rhizomes, tubers or roots. Repeat applications, however, will deplete reserve materials in the underground storage organs and ultimately cause plant death.
Contact herbicides provide the best control when applied to small weeds.
In addition to contact activity, materials such as Evik , Hyvar X , Hyvar L , Karmex, Krovar 1, and Krovar II also have residual activity against germinating weeds. MSMA is effective against grasses except bermudagrass. To broaden the spectrum of weeds controlled, tank mixes of MSMA with Hyvar X or Karmex are recommended. Observations indicate, that these tank-mixes are effective against most weeds. Horse purslane, however, escapes control where tank-mixes of MSMA with Hyvar X are used.