Optimizing Laser and Liquid Nitrogen Treatments for Weed Control in Turfgrass Systems

Abstract

The increasing prevalence of herbicide-resistant weeds and growing environmental concerns surrounding synthetic pesticides are driving innovation in non-chemical weed control technologies. This research evaluated two emerging approaches based on the premise of machine-vision-based, individual-plant treatments to problematic turfgrass weeds: cryogenic liquid exposure and patterned laser energy. In the cryogenic study, a custom-built applicator was used to deliver precise doses of liquid nitrogen (LN) to individual plants of goosegrass (Eleusine indica) and annual bluegrass (Poa annua). Four field trials were conducted across two sites in Blacksburg, VA, testing seven LN doses (0–5.1 mL). LN reduced green cover rapidly (3 days after treatment) in both species, with 90% control achieved at ≥2.2 mL. Annual bluegrass responded consistently across trials, while goosegrass exhibited site-dependent recovery. In the laser study, a 10 W diode laser was used to treat four turf and weed species across varying pattern-averaged energy densities (PAED), pattern line spacings, and pass numbers to simulate systems where patterns of equidistant lines would be targeted to unwanted weeds in turf. A factorial design revealed that 4-mm line spacing improved control compared 1- or 2-mm line spacing, likely due to increased line-specific energy density. Bermudagrass (Cynodon dactylon) fully recovered from all treatments within 24 days, while creeping bentgrass (Agrostis stolonifera) had recovered less than 50%, emphasizing the need for accurate weed targeting systems. These results demonstrate the feasibility of LN and laser-based precision weed control in turfgrass systems and highlight the importance of dose optimization and spatial pattern design to balance efficacy with turfgrass safety. Future work should focus on integrating these tools with autonomous delivery platforms for scalable, selective weed management.