Impact of dose and adjuvant on herbicidal efficacy of birch-based pyrolysis liquid

Reduction of pesticide use to benefit the environment is a topical issue in the EU. There is a call for development and more widespread use of sustainable alternative weed control measures. Pyrolysis liquid (PL), a by-product of charcoal and biochar production, contains numerous compounds, including organic acids, alcohols, phenols and furans. PL has shown promising results when used against several broad-leaved weeds but its effect on grassy weeds is largely untested. To provide an alternative to synthetic herbicides, PL should be effective and applicable at field scale. In this research, we initially evaluated the potential of birch (Betula sp.) based PL to control mono- and dicotyledonous plants under greenhouse conditions and determined if efficacy is improved by addition of an adjuvant. Second, the efficacy of PL for controlling Elymus repens (L.) Gould was compared with glyphosate and two other synthetic herbicides in a no-tillage system under field conditions. As expected, dicotyledonous plants were more sensitive to acid-based herbicides than monocotyledonous plants. In contrast to our expectations, the herbicidal efficacy of PL was lower than an acetic acid-based herbicide and addition of an adjuvant did not improve efficacy. In conclusion, when used at commercially and practically realistic doses, the efficacy of PL control on monocotyledonous weeds such as E. repens is weak. More product development is needed to improve PL quality and efficacy and to establish practical and cost-effective application levels for weed control on the field scale.