Abstract

Slow-release tablets made of dicalcium phosphate containing a herbicide and a surfactant were evaluated for weed growth. The addition of 1-2% surfactant to herbicides having a very low water solubility, such as Gallery (isoxaben), Surflan (oryzalin), Ronstar (oxadiazon), and Goal (oxyfluorfen), and for comparison, to Dual (metolachlor), markedly enhanced the release of herbicide and enlarged the area of weed inhibition. The surfactants that produced the best results were Triton X-100 and X-77. Tablets placed on the surface of containers filled with Metro Mix 350 or a pine bark-peat moss-sand medium, under intermittent mist in the greenhouse, or under sprinklers outdoors, produced up to 15 cm (6 in) diameter circular areas of weed control, around a single tablet. Initial release of herbicide from tablets was rapid upon exposure to moisture and the area of activity became close to maximum within a few days after placing the tablet on the soil surface. Tablets placed on surface produced larger areas of activity than when buried. The tablets retained their shape after 3 months of outdoor exposure.