Evaluation of a laser diode array as an efficient approach to laser weeding

Abstract In-crop site-specific weed recognition systems have enabled precise and selective use of alternative nonchemical weed control technologies to provide much-needed support for weed management programs in large-scale cropping systems. Laser weeding has long been proposed, but only recently has it been commercialized as a highly precise, nonchemical weed control option for cropping systems. The weed control efficacy of several laser types (e.g., CO 2 , diode, fiber, and Nd:YAG) has been identified; however, no studies have investigated the use of readily available, high-power, low-cost consumer-grade laser diode arrays. The weed control efficacy of a 97-W, 445-nm laser diode array was investigated with the aims of evaluating 1) the irradiation energy requirement (as determined by treatment duration) of spot laser treatments required to control key grass (rigid ryegrass) and broadleaf (wild radish) weeds and 2) the influence of growth stage on energy requirement for annual ryegrass and wild radish control. Seedlings of rigid ryegrass and wild radish at growth stage 1 (GS1) were controlled by low laser energy densities of 0.2 to 0.5 J mm −2 . As plant size increased, the energy densities required to control the seedlings increased substantially. For example, 2.0 J mm −2 was required to control GS4 rigid ryegrass, representing a 10-fold increase over that required for GS1 seedlings. Similarly aged but substantially larger wild radish seedlings remained mostly uncontrolled by 2.0 J mm −2 treatments. Wild radish was consistently more tolerant of laser treatments than annual ryegrass, but this difference was likely due to the more rapid growth rate that resulted in larger plants at the time of treatment, especially during warmer growing conditions. These results clearly define the potential for laser weeding using laser diode arrays and also identify the need for additional testing across a wider range of weed species with higher-powered, affordable diode arrays.