Effects of perennial ryegrass competition on bermudagrass and hybrid bermudagrass cover, biomass, and total nonstructural carbohydrate accumulation

To extend golf play in early summer or hasten athletic field preparation in late summer, turf managers often desire to allow perennial ryegrass (Lolium perenne L.) to persist and compete with overseeded bermudagrass (Cynodon dactylon L. Pers.) or hybrid bermudagrass (Cynodon dactylon x C. transvaalensis Burtt Davy) during optimal growing conditions. Understanding how competition-free growing degree-days (CFGDD) influence bermudagrass total nonstructural carbohydrates (TNC), biomass, and visual green cover may aid in turf-use scheduling. Twenty-four weekly treatments of foramsulfuron eliminated perennial ryegrass competition in replicate plots and allowed assessment of competition-free bermudagrass coverage, biomass, and TNC as related to cumulative heat and light units. Results from this study indicate that bermudagrass coverage is a function of cumulative CFGDD and competition-free daily light integral (CFDLI) but is dependent on locations or years where cultivars or seasonal legacy are variable. At three locations, 'Patriot' and 'Midiron' hybrid bermudagrass and 'Riviera' bermudagrass required 603, 709, and 959 CFGDD and 2,447, 3,271, and 4,556 mol m(-2) CFDLI to reach 97% coverage, respectively. Trends of TNC per unit area, however, continued to increase after full coverage was achieved and up to the point at which no more heat or light units were accumulated in fall. Absence of a clear asymptote in the trends suggests that heat or light units that were seasonally accumulated in Blacksburg, VA, were insufficient to achieve maximum bermudagrass carbohydrate reserves before winter dormancy.

Automated summary

The study shows that the coverage of bermudagrass is closely related to the cumulative competition-free growing degree-days and daily light integral, but may vary depending on locations or years. Different bermudagrass cultivars require varying amounts of heat and light units to achieve 97% coverage.