Evaluation of Bioherbicidal Control of Tropical Signalgrass, Crabgrass, Smutgrass, and Torpedograss

Abstract

Tropical signalgrass (TSG) causes serious problems for sod production and turf maintenance in Florida. Other grasses such as large crabgrass (CG), smutgrass (SG), thin paspalum (TP), and torpedograss (TG) can be problematic as well. Several emulsion formulations composed of mycelium or mycelium-free culture filtrate (or both) of the fungal pathogen Drechslera gigantea (DG) and Sunspray 6E oil were tested with or without ammonium sulfate or pelargonic acid (n-nonanoic acid; a natural product registered as a biorational herbicide) in greenhouse and field trials. A 30% Sunspray 6E oil formulation containing DG mycelium (10 g), DG culture filtrate (70 ml), and 4.5 g of ammonium sulfate caused 88 to 100% injury on TSG, CG, SG, and TG in greenhouse trials. The injury resulted from disease as well as phytotoxicity of the culture filtrate, oil, and ammonium sulfate. An emulsion formulation composed of 30% Sunspray 6E oil and 70% DG culture filtrate amended with 2% (v/v) pelargonic acid killed SG 2 wk after application. DG formulations containing ammonium sulfate or pelargonic acid produced lower levels of injury when treated grasses were exposed to a 24-h dew period compared with those treated and not exposed to dew. Formulations containing DG mycelium, DG culture filtrate, and ammonium sulfate or pelargonic acid are effective and promising for control of weedy grasses. Further evaluations of these formulations under field conditions are justified.