Cool-season grass development response to accumulated temperature under a range of temperature regimes

Persistence and productivity of pastures containing mixtures of warm and cool-season forages may be compromised by interspecific competition when growing periods overlap. An ability to predict the onset and termination of growth of component species would facilitate timing of management interventions to minimize harmful competition in mixed pastures. Experiments were undertaken in controlled environment to assess the use of accumulated temperature values to indicate development stages in three cool-season grass species, and to evaluate the consistency of this relation under a range of temperature regimes that included variable exposure to below-freezing, temperatures. When grown under light and dark temperature regimes of 22.5 and 7.5, 17.5 and 12.5, 15.0 and 0.0, or 10.0 and 5.0 degrees C, respectively, leaf appearance in Italian ryegrass (Lolium multiflorum Lam.), tall fescue (Festuca arundinacea Schreb), and tall wheatgrass [Elytrigia elongata (Host) Nevski] showed a close linear relationship with accumulated temperature, within each temperature regime. The interval between appearance of successive leaves on seedling mainstem (phyllochron) was increased by increased average daily temperature. In seedlings grown under a 15.0 and 0.0 degrees C temperature regime, phyllochron was increased linearly by up to four 15-h exposures to -5.0 or -7.5 degrees C dark-cycle temperatures in successive 24-h periods. The effects of variation in mean daily temperature and of plant exposure to below-freezing temperature on phyllochron should be considered if accumulated temperature is used to predict development stage of cool-season grasses in the field.