Evaluation of Non-Traditional Herbicides for Crabgrass Management In St. Augustinegrass.

Southern crabgrass (Digitaria ciliaris) is a common weed found in Florida. New regulations and loss of registered herbicides have greatly limited postemergence options for crabgrass control in St. Augustinegrass (Stenotaphrum secundatum).  Alternative herbicides (defined as non-synthetic chemicals that have herbicidal properties) were evaluated for weed control efficacy.  These included acetic acid (vinegar), borax, sodium bicarbonate (baking soda), and Garden Weasel AG Crabgrass Killer (an improved sodium bicarbonate formulation).  Greenhouse and field trials were conducted to test product effectiveness in controlling crabgrass and turf injury. In the greenhouse, one rate of vinegar (2x 280.6 L ha^-1) and two rates of AG Crabgrass Killer (976.6 and 1464.9 kg ha^-1) provided ≥ 70% control for 1-2 leaf crabgrass 7 days after application (DAA).  By 21 DAA, only asulam (a synthetic herbicide included for comparison) provided ≥ 70% control at any weed stage.  No alternative herbicide provided ≥ 70% control at any weed stage longer than 7 DAA.  Initial turf injury was very high for most rates of vinegar, sodium bicarbonate, and AG Crabgrass Killer, causing ≥ 20% damage 7 DAA.  By 21 DAA, turf injury levels were ≤ 20% for all treatments except the higher rates of sodium bicarbonate and AG Crabgrass Killer.  Although acceptable levels of control were not consistently seen from any alternative herbicide tested, they may be useful for crabgrass suppression in St. Augustinegrass.