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Method Article
This protocol provides a method for microwave control of Japanese knotweed in the field and disposal of dug-up rhizomes in laboratory conditions. The advantages and disadvantages of both methods are discussed. Future research directions are also suggested to optimize the use of microwaves for controlling Japanese knotweed.
The study aims to assess the effectiveness of microwave treatment (MWT) at a frequency of 2.45 GHz and a power of 800 W to control Japanese knotweed (Reynoutria japonica Houtt.) using a self-propelled device that was built in the in-house facility. The MWT was applied in the field population of knotweed in July 2022. First, plants were mechanically moved from the area of 1 m2, and next, the cut shoots around 4 cm high were microwave-treated for 25 min, 20 min, and 15 min. The control treatments were: 1) only cut plants and 2) rhizomes dug out to 30 cm deep. The effectiveness of the microwave treatments was observed for the next 11 months by counting the number of newly grown shoots. The results showed that a 25 min MWT was 100% effective in Japanese knotweed loss of vitality, while a 15 min MWT microwave treatment stimulated plant growth by around 50%, compared to controls. Rhizomes were dug out in a separate in vitro experiment for laboratory testing. The rhizomes were categorized by thickness and subjected to a 60 s MWT using a commercial microwave, after which their temperature and vitality were assessed. The temperature of rhizomes following MWT depended on their thickness. Those rhizomes that warmed to temperatures above 42 °C were effectively destroyed. Summing up, the time plants are exposed to microwaves plays a major role in the effectiveness of this method. The longer the exposure to MWT, the better control. The thinner the rhizomes, the more effective the in vitro MWT rhizomes disposal.
Japanese knotweed (Reynoutria japonica Houtt.) is one of the seven invasive plant species that threaten the natural environment in Poland1. This plant, outside its original range, exhibits a wide spectrum of habitats from anthropogenic habitats, including railway embankments, roadsides, parks, cemeteries, home gardens, various types of urban and post-industrial wastelands to natural ones, e.g., forest edges, riverbanks, thickets. It can also sometimes be found in agricultural areas. It copes well with various types of soils with various pH, from acidic to slightly alkaline2,3. It exhibits high tolerance to high temperature, salinity, periodic flooding, and drought2. It is also very resistant to soil contamination, including sulfur compounds4. Knotweed seriously threatens nature and contributes to the decline in plant species richness. They effectively compete with native species, preventing their regeneration through rapid growth and limiting light access5. They affect other plants alleopathically and cause changes in the physical and chemical properties of the soil. In addition, they negatively affect the human economy by limiting visibility along roads, destroying flood protection, reducing the attractiveness of investment and tourist areas, and causing economic losses associated with their control6,7.
Many attempts have been made to control Japanese knotweed, mainly using synthetic herbicides such as glyphosate or 2,4-D8. However, due to unfavorable environmental effects, this method is not recommended for most sites occupied by knotweed. On the other hand, mechanical methods involve regular mowing of plants, which are ineffective due to the deep system of rhizomes from which new shoots emerge9. An interesting solution is to use dense nets that limit the growth of knotweed, but this method also has limitations due to possible damage to the net or shoots growing outside its area. Therefore, lateral methods of controlling this species are sought. One such method may be using microwaves10.
Microwaves are electromagnetic waves with frequencies from 0.3 GHz to 300 GHz and wavelengths from 1 m to 0.001 m. Microwave radiation is invisible to the human eye. The electromagnetic spectrum of a microwave oven falls within the range of infrared radiation and radio frequencies11. Of the wide range of microwave frequencies, only a few are intended for medical or industrial applications. Federal Communications Commission regulations specify the use of specific microwave frequencies. Microwaves are transmitted through electrically neutral materials such as paper, glass, ceramics, and most plastics and are reflected by metals. In the absorbing material, they cause heat to be generated12. The electromagnetic field at microwave frequencies mainly provides energy to living organisms within its range. The thermal effect consists of increasing the body temperature due to the body's absorption of some energy. The appropriate frequency, field intensity, and the organism's ability to thermoregulate are required to increase the temperature of the tissue. It also depends on the time of exposure and the type of tissue. When a critical tissue heat level is exceeded, protein denaturation occurs13.
Microwave radiation has been used in natural sciences for many years. It is used, for example, for heating air in greenhouses14, disinfecting soil15,16,17, and drying fruits and vegetables18,19,20. Microwaves can also destroy insect pests of crop plants21,22,23 or weeds at a seedling stage24. Recent studies also indicate the high effectiveness of the microwave method in combating invasive Sosnowsky's hogweed10,25.
The device HOGWEED was built in the Faculty of Forestry of the University of Agriculture in Krakow26. It has its drive and moves on a caterpillar chassis, which can be used in areas with difficult access. Such a drive system does not damage the ground because the rubber tracks exert low unit pressures on the terrain. A radio remote control remotely controls the vehicle. The device was constructed to study the effect of microwaves on invasive weeds in natural ecosystems.
The study aims to determine the effectiveness of microwave radiation with a wave of 2.45 GHz, a power of 800 W, and an assumed operating time (from 15-25 min) for controlling the growth of Japanese knotweed plants (Reynoutria japonica Houtt.) in the field using the HOGWEED device. The study also aims to determine the disposal of rhizomes in laboratory conditions using a commercial microwave device. Disposal is important in the safe management of invasive plant waste so that it does not threaten environmental safety.
We conducted the field experiment using a field population of invasive Japanese knotweed (Reynoutria japonica Houtt.) localized in Kraków (50.04 N, 19.63 E) under the written agreement with and supervision of the Kraków Municipal Greenery Board, which manages this area.
1. Field control of Japanese knotweed using a specialized device emitting microwaves
2. In vitro disposal of Japanese knotweed rhizomes using microwaves
Field control of Japanese knotweed using a specialized device emitting microwaves
The average number of shoots per 1 m2 of the microwave-treated area was 27. Figure 1 shows the average number of shoots per 1 m2 that grew after microwave treatment for 11 months after microwave exposure. No new knotweed shoots appeared in areas treated with microwaves for 25 min. Compared to the control area, a decrease in the number of above-ground shoots was noted...
The effectiveness of Japanese knotweed (Reynoutria japonica Houtt.) control using the constructed device and knotweed rhizomes disposal using a commercial microwave oven were demonstrated. Both devices emitted microwaves at a frequency of 2.45 GHz and a power of 800 W.
It was observed that the longer the exposure of knotweed plants to microwave radiation, the lower and later their regeneration. In Japanese knotweed, 25 min microwave treatment effectively destroyed 100% of plants in th...
All authors declare no conflicts of interest.
This research was funded by the Ministry of Science and Higher Education of the Republic of Poland.
Name | Company | Catalog Number | Comments |
AXIS BTA2100d | AXIS Sp. z o.o. | balance | |
CompAir C50 | LECTURA GmbH Verlag | mobile compressor | |
FLIR E60 | FLIR Systems, Inc. | thermal imaging camera | |
FLIR Tools | FLIR Systems, Inc. | software to analyse the temperature from the thermogram | |
HDL_ANT version 3b4 program | PC Software by W1GHZ | software | |
Heraus UT 6120 | Heraeus | laboratory drier |
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