2018 ASHS Annual Conference

During winter, bermudagrass (Cynodon spp.) enters a dormancy period resulting in a brown, unattractive appearance and inability to recover from traffic. In some cases, turf managers overseed bermudagrass with perennial ryegrass (Lolium perenne L.) in order to maintain an actively growing surface during winter and early spring months. An acceptable spring transition back to a bermudagrass surface can be difficult as perennial ryegrass can effectively compete for light and nutrients during this period. Transition aid herbicides have become a commonly-used tool for turfgrass managers seeking to expedite the spring transition. The objective of this study was to quantify the effect of transition aid herbicide timing on photosynthetic rate and botanical composition of an overseeded bermudagrass turf in Oklahoma.

To achieve this objective, a field study was conducted on an overseeded hybrid bermudagrass (C. dactylon x C transvaalensis ‘Patriot’) field during the winter of 2016-17 at the Oklahoma Agriculture Experiment Station Turfgrass Research Center in Stillwater, OK. The field was mowed three times per week at 25 mm. The experiment was arranged as a randomized complete block with three replications, two products, and eight application dates (between Mar 27 and Jun 5) plus a non-treated control. The products evaluated were foramsulfuron (Revolver) at a rate of 0.13 mL m^-2 or ammonium sulfate at a rate of 24 kg ha^-1 N. Visual ratings of percent ryegrass, percent bermudagrass, and percent brown straw were recorded throughout the spring transition period. Gross photosynthesis was measured on three dates using a Li-Cor 6400XT and a custom chamber.

Fertilizer treatments did not show consistent effects (positive or negative) in terms of gross photosynthesis, perennial ryegrass decline, or bermudagrass recovery. Reductions in gross photosynthesis were greater but more delayed after early season applications of foramsulfuron. Perennial ryegrass decline was similarly delayed following early season applications as compared to late season applications. Results suggest applications of transition aid herbicides when soil temperatures (5cm depth) are above 16 C result in a markedly faster response than when applied earlier in the season.