Cutting weeds with a CO2 laser

Stems of Chenopodium album. and Sinapis arvensis. and leaves of Lolium pere nne. were cut with a CO2 laser or with a pair of scissors. Treatments were carried out on greenhouse-grown pot plants at three different growth stages and at two heights. Plant dry matter was measured 2 to 5 weeks after treat ment. The relationship between dry weight and laser energy was analysed usi ng a non-linear dose-response regression model. The regression parameters d iffered significantly between the weed species. At all growth stages and he ights S. arvensis was more difficult to cut with a CO2 laser than C. album. When stems were cut below the meristems, 0.9 and 2.3 J mm(-1) of CO2 laser energy dose was sufficient to reduce by 90% the biomass of C. album and S. arvensis respectively. Regrowth appeared when dicotyledonous plant stems w ere cut above meristems, indicating that it is important to cut close to th e soil surface to obtain a significant effect. When cutting L. perenne plan ts with 2-true leaves at a height of 2 cm from the soil surface with a lase r, the biomass decreased significantly compared with plants cut by scissors , indicating a delay in regrowth. This delay was not observed for the dicot yledonous plants nor for the other growth stages of L. perenne.