Efficacy and environmental safety of flame weeding in the humid tropical region

Weed management in agriculture and landscaping is a great need, especially in the humid tropics where there is a vast species diversity and conducive environment for weed growth. High cost and residual effects of popular pre-emergent herbicides urge for low cost and eco-friendly alternatives. Even though manual weeding is eco-friendly, its small operational scale and low disturbance to the underground parts does not meet the efficacy of control. At this backdrop, thermal stress caused weed suppression by flame weeding was carried-out with the objective of detecting its efficacy as well as possible negative effects on the micro flora in the top soil. A five-burner flame weeder was used for the experiment conducted at the experimental farm of the University of Peradeniya, Sri Lanka (under humid tropical conditions) during the dry season in 2021, in a replicated trial. Moisture content of the top soil was maintained at near 40±8.5 % (w/w) of the field capacity. Rates of plant mortality and reemergence of three prominent weed species, and also the rate of suppression of the microbial population due to burning were determined before and after the application of flame. The theoretical and actual field capacity of flame weeding was 0.162 ha/hr and 0.119 ha/hr, respectively while weeding efficiency was 73.5 %. Effect of flame weeding on delaying re-immergence of broad leaves was faster than the sedges and grasses, limiting the rate of re-immergence of the weed population to initial population density by 24 days. Effect of flame weeding on micro-flora in soil is insignificant, both at the top level and at 5 cm depth. Eventhough CO2 emission rate (26.9 kg/ha) was higher than mechanical weeders, less frequent repeated weeding need makes it similar to them on seasonal or yearly basis. Based on its field capacity, weeding efficiency and environment friendly nature, flame weeding could be recommended to dry regions and seasons of the humid tropics.