Microwave Control of Reynoutria japonica Houtt., Including Ecotoxicological Aspects and the Resveratrol Content in Rhizomes.

Japanese knotweed (Reynoutria japonica Houtt.) is Poland's invasive weed, for which there is no efficient control method. The rhizomes of this species are rich in resveratrol. In this work, we evaluated (1) the effectiveness of electromagnetic microwaves (MV) in destroying Japanese knotweed using an original device, HOGWEED (MV of 2450 MHz), (2) the ecotoxic effect of the MV on the soil environment, and (3) the resveratrol content in knotweed rhizomes after MV treatment. The field studies were carried out in 2022 in southern Poland. Cut plants were MV-treated for times of 5.0-25.0 min. The MV efficiency was checked 10 and 56 days after treatment (DAT). After MV treatment, fresh soil samples were taken to analyze their ecotoxicity. As a result, at 56 DAT, knotweed was controlled if MV was used for at least 20.0 min. The MV did not affect the soil ecotoxicity. The MV-treated soils were classified as non-toxic or low-toxic. To analyze the resveratrol content, healthy knotweed rhizomes were dug out, treated with MV in the laboratory at 2.5-10.0 min, and analyzed for resveratrol content in HPLC-MS/MS. As a result, the resveratrol in the rhizomes significantly decreased in a time-dependent manner following MV exposure.

Biochemistry of microwave controlled Heracleum sosnowskyi (Manden.) roots with an ecotoxicological aspect.

Sosnowski hogweed is an invasive weed in eastern-middle Europe that is dangerous to human health and the environment. The efficacy of its control using chemical and mechanical methods is limited. Electromagnetic radiation (microwaves) could be an environmentally friendly alternative for controlling this species. This study aims to: (1) Determine the effect of varying microwave treatment (MWT) durations on the control of S. hogweed using a device emitting microwaves at 2.45 GHz, 32.8 kW/m2; (2) Evaluate the impact of MWT on soil by an ecotoxicological bioassays; (3) Analyze biochemical changes occurring in the roots during the process. A field study was performed to assess the efficacy of S. hogweed control using MWT in times from 2.5 to 15 min. The MWT-treated soil was collected immediately after treatment (AT) and tested using bioassays (Phytotoxkit, Ostracodtoxkit, and Microtox). Fourteen days AT, the MWT hogweed roots were dug out, air-dried, and analyzed for the content and composition of essential oil, sugars, and fatty acids. According to the ecotoxicological biotests, the MWT soils were classified as non-toxic or low-toxic. The regeneration of hogweed was observed only in non-treated plants (control). Hogweed MWT for 2.5-15 min did not regenerate up to 14 days AT. The average weight of roots in hogweed MWT for 15.0 min was ca. two times smaller than the control plants. Those roots contained significantly higher amounts of sugars and saturated fatty acids than the control. We did not find a correlation between S. hogweed root essential oil content and composition and MWT time. The main compounds of essential oil were p­cymene and myristicin. No highly photosensitizing compounds were identified in the tested root oil. We conclude that MWT of S. hogweed could be an environmentally safe and prospective control method, but more studies are needed.