Thermal Weed Control for Turfgrass Management: Past Ideas Refined for Present Application.

Early thermal weed-control measures were known to be rudimentary and hazardous.  Thermal weed control has progressed in sophistication, application, and efficiency and has resulted in many commercial systems available for common row-cropping applications.  Flame weeding for established turfgrass is not effective because of the inability to treat weeds without injuring the turfgrass system.  Aesthetically this type of treatment would be unacceptable. Therefore, past thermal weed control measures can be refined to utilize direct soil heating by flame from propane burners for the production of a stale seedbed. Initial soil-sterilization and flame heating studies conducted in 2009 and 2010 demonstrated a high potential for reducing weed populations before turfgrass establishment. Many factors can alter the efficacy of this type of thermal treatment including seed heat tolerance, seed depth, thermal conductivity, and soil moisture content.  For acceptable weed control utilizing this method, adequate soil temperatures need to be achieved.  Planting depth in a Marvyn loamy sand (Fine-loamy, kaolintic, thermic Typic Kanhapudult) and seed heat tolerance research was conducted to evaluate germination and emergence of weed seeds. Large crabgrass (Digitaria sanguinalis), Virginia buttonweed (Diodia virginiana), and cocks-comb kyllinga (Kyllinga squamulata) emerged from 8, 6, and 2 cm maximum planting depths, respectively.  Temperature and duration effects on weed germination experiments resulted in 0% germination of large crabgrass, Virginia buttonweed, and cocks-comb kyllinga at 120, 250, and 120°C, respectively, for 5 second heat exposure.  Heat transfer studies utilizing a PL8750 Poultry House Flame Sanitizer (Flame Engineering, Inc; LaCrosse, KS) in Marvyn loamy sand at 0.1 volumetric water content (θ) resulted in only surface temperatures adequate to prevent weed germination.  Further experimentation resulted in a thermal conductivity of 0.96 W m^-1 K^-1. Compilation of results shows potential for effective present application of thermal weed control in turfgrass management.