Laser-optics-based method to suppress Mikania micrantha growth

Mikania micrantha is an exotic and aggressive species that can reproduce asexually and sexually through its germinative stem and its featherlike seeds. Present weeding methods cannot effectively or economically control the spread of Mikania micrantha. In this article, we propose a method to suppress the growth and spread of Mikania micrantha by applying a high-energy laser beam to penetrate its stem. The threshold penetrating optical intensity is 3.1 W/mm(2). To optimize the damage to the inner tissue of the stem, which includes the vascular bundle and medulla for transporting organic nutrients, water, and inorganic salt, the absorption spectrum of the tissue and laser beam size are analyzed. According to the absorption spectrum of the tissue and growth mechanism of Mikania micrantha, a 455 nm blue laser is used as an irradiated light source. A single beam with two different beam sizes or two laser beams with the same beam size is used to optimize the stem damage. By the time the cumulative energy reaches 15 Joules for a single laser beam with dimensions of 0.81 mm × 0.74 mm, the inner tissue will be damaged 97.5%. We perform laser irradiation on the fresh Mikania micrantha grown hydroponically, with the result that all samples withered in 30 days. Therefore, using the method before the flowering season of Mikania micrantha can effectively inhibit its reproduction.