Hannover, Germany
May 15, 2013
Chickweed, dandelion and shepherd’s purse are much dreaded enemies of cultivated plants in both agriculture and gardening. Young maize, rape or beet plants compete with such weeds for light, water and nutrients. Herbicides are today’s medium of choice for weed control. But the use of these toxic substances is both controversial and expensive. A team of scientists from Leibniz Universität Hannover and Laser Zentrum Hannover (LZH) is now investigating an alternative: weed control using laser. When herbicides are used, overdoses and the distribution of the substances by the wind can lead to harmful residues in the soil and the water. In organic farming, weeding is done by hand or by using flame throwers, which has only a limited effect on the weeds and is not practicable in conventional farming.
Could robots or drones weeding beds and fields using laser be the answer? At the moment this is only a pipe dream, but in a few years such scenarios could be far from impossible. The laser beam is directed into the growth centre of the plant, thus killing it. In a project funded by the German Research Council (DFG), the scientists started by adjusting the energy of the laser precisely and effectively to the type and height of the plant. “We have to place the beam directly where it is needed,” says project leader Prof. Thomas Rath from the Institute of Biological Production Systems.
The intensity of the radiation also has to be precisely adjusted. “We discovered that laser with an energy level that is too low tends to encourage growth, in other words does the opposite of what we want,” explains Dipl.-Ing. Christian Marx, scientific assistant at the Department of Biosystems and Horticultural Engineering. In cooperation with the Laser Centre, the scientists in the current project are concentrating on CO² lasers, which emit beams in the mid-infrared range.
The second major challenge is recognising the plant. What is an undesirable plant and what is desirable, and where precisely must the laser be aimed? Here the scientists have developed a clever system. Cameras film the plants, and software measures the contours of each individual plant so that the laser beam can be optimally positioned. “We have algorithms for many different weeds,” says Professor Rath. It becomes difficult when weeds and cultivated plants are very close together and overlap. “The key to success is recognising them so that we destroy only the weeds,” explains Marx.
At the moment the equipment runs on rails in a greenhouse. Under this an area of about one square metre can be “treated”. The application of laser technology is conceivable in many different areas, and industry has shown great interest. “The system could soon be used wherever it is relatively easy to set up tracks over a bed – for example in greenhouses or nurseries,” Professor Rath predicts.
It is more difficult in large fields: setting up lasers on trailers is out of the question, as it would be impossible to aim precisely due to the vibrations. “We are currently investigating the use of drones – little robots that would swarm over the field,” says Professor Rath. Laser is also of interest for weed control in water protection areas or near stations, where the use of herbicides is not permitted.
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