Rotating a field of mature miscanthus × giganteus to glyphosate-resistant crops

Miscanthus × giganteus Greef and Deuter ex Hodkinson and Renvoize is a perennial C4 grass being studied as a potential bioenergy feedstock in the United States. It is a triploid, sterile hybrid with high biomass potential. Adoption of a perennial crop is likely to be met with skepticism unless methods of controlling the crop are established. Proposed methods of controlling M. × giganteus typically require at least one full growing season, thus excluding the possibility for revenue from the field for a year. An experiment was conducted from 2007 to 2010 to examine the feasibility of controlling M. × giganteus by planting glyphosate-resistant soybean [Glycine max (L.) Merr.] followed by glyphosate-resistant corn (Zea mays L.) directly into a mature (4-yr old) field of M. × giganteus with typical agronomic practices without significant crop yield loss. Results showed that soybean yields were not significantly reduced with two sequential glyphosate (N-(phosphonomethyl)glycine) in-crop applications compared with a weed-free control, but were generally reduced with one glyphosate application (6.2 and 14.0%, respectively). Corn yields also were not significantly reduced with two sequential glyphosate applications, but were generally reduced with one glyphosate application (0.3 and 7.0%, respectively). Miscanthus × giganteus shoot numbers were reduced by as much as 85.8 and 94.3% over the course of the experiment in plots receiving one and two glyphosate applications per season, respectively. Complete control, however, was not achieved indicating treatments will likely need to be employed for more than two growing seasons to completely control M. × giganteus.