Busey, P. 2001. Irrigation management of dollarweed in St. Augustinegrass lawns. Agron. Abstr. (electronic).

Abstract

Dollarweed, Hydrocotyle umbellata, (Bayer code HYDUM, also called pennywort) is the most serious weed of St. Augustinegrass lawns in Florida; St. Augustinegrass, Stenotaphrum secundatum, is the most widely used lawn species in Florida. It is commonly said without documentation that reducing irrigation also reduces dollarweed infestation in turfgrass. The objective was to evaluate the relationship of irrigation management and dollarweed infestation. A field area was planted with sprigs of dollarweed and plugs of St. Augustinegrass, and the two species were grown to cover intermingled. Independent irrigation zones were programmed to provide plots representing irrigation levels: high (daily to replace evapotranspiration), moderate (weekly to saturate the root zone when wilted), and low (only rarely under extreme wilt). There were eight replications. The 24 irrigation main plots were 9.4 m X 9.4 m. Canopy coverages of dollarweed and St. Augustinegrass were estimated visually as a percent of apparent canopy. The null hypothesis is that variations in irrigation have no effect on dollarweed coverage. Other management variables, fertilization, mowing, and their interactions with irrigation, are also being evaluated as split block treatments. Preliminary results after 5 months were highly significant (P < 0.0001) differences in dollarweed coverage among irrigation treatments: high (59%), moderate (32%), and low (14%).