Ryegrass as a Divider
On golf courses that have creeping bent grass greens surrounded by couch grass, encroachment of the couch grass into the green can be a serious problem. Strategies for minimising encroachment have included hand-picking, chemicals, use of barriers, and using different turf grass species as a barrier. Handpicking along with the instalment of barriers generally requires intensive management, reflective in the labour required. Chemical removal can be costly and variable.
The use of a turf grass species offers the opportunity at a low cost method over time to minimise encroachment. Turf grasses that have been used include zoysia grass and perennial ryegrass.
The use of zoysia grass overtime has produced variable results. Couch grass stolons and rhizomes tend to spread through the zoysia grass and into the creeping bentgrass or creeping bent grass/Poa annua green. A strip of perennial ryegrass (Lolium perenne L.) planted in the collar or as a strip between the green and couch grass has worked well. The width of the strip may vary but is normally a metre in thickness.
The reason for the success of perennial ryegrass is not clear but it may be due in part to the production of an allelopathic substance that inhibits the stolons of couch grass. Where perennial ryegrass has been used as a successful barrier it is established on a sandy soil (similar to the green if it’s constructed with high sand content). It appears the perennial ryegrass strip established on a high clay content soil does not work.
Obviously the perennial ryegrass is susceptible to high temperatures and thus must be overseeded frequently. At high overseeding rates, brown patch and pythium blight need to be monitored.