Pesticides may not be needed for clearing weeds after the demonstration of a laser system that could be used by field roaming robots to kill individual plants.
An infrared CO2 laser with a wavelength of 10.6µm is fired at weeds that are identified by a stereo camera system, which also optimises the laser beam position. Researchers have determined how much energy is needed to destroy plants’ sensitive growth centres, known as meristems, making the method very efficient. The researchers expect that large fields could be swept by autonomous field robots that would identify weeds and laser them. Researchers know seedlings can be killed with 35 Joules.
Using image analysis techniques such as threshold level filtering and edge detection, the position of a plant’s leaves can help locate the meristem position. By using a galvanometer scanner with a flexible mirror system, the laser beam can be focused with high precision on the near-surface meristems. Under laboratory conditions, an accuracy of <±1mm could be achieved, and under greenhouse conditions, a laser on a rail carriage achieved accuracies of ±3.4mm. The use of a galvanometer scanner with a flexible mirror system also enables the laser to be moved quickly from plant to plant.
Funded by the German Research Foundation, the work is being carried out by Laser Zentrum Hannover and Leibniz Universität Hannover’s Biosystems and Horticultural Engineering faculty.