Conversion of Fairway‐Height Perennial Ryegrass Turf to Kentucky Bluegrass without Nonselective Herbicides

Abstract

Many golf course superintendents wish to convert perennial ryegrass (Lolium perenne L.) fairways to other cool‐season species such as Kentucky bluegrass (Poa pratensis L.) because of the former's high fungicide requirement. However, interseeding into a mature turfgrass stand often results in poor seedling survival because of competition from the existing stand. The objective of this research was to evaluate methods for enhancing Kentucky bluegrass (KB) establishment when interseeded into a mature perennial ryegrass fairway turf. Core aeration, scalping, plant growth regulators (PGRs), postseeding low mowing (PSLM), high seeding rates, and multiple seedings were used singly and in factorial combinations. Postseeding low mowing (0.6 cm twice weekly for 4 wk) and high seeding rates [196 kg pure live seed (PLS) ha−1] were most effective in enhancing KB establishment. Plots receiving PSLM averaged 31.9% KB 21 months after seeding (MAS) compared with 18.1% in non‐PSLM plots. Seeding KB at 196 kg PLS ha−1, both fall and spring, resulted in an average of 29.8% KB 21 MAS while seeding at 98 kg PLS ha−1, in the fall only, resulted in only 19.7% KB. A single preseeding core aeration or scalping treatment did not increase KB establishment, nor did preseeding applications of the PGR trinexapac‐ethyl [4‐(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxo‐cyclohexane‐carboxylic acid ethyl ester]. Mefluidide {–[2,4‐dimethyl‐5‐[[(trifluoromethyl)‐sulfonyl]amino]phenyl] acetamide} increased KB establishment at 6 MAS, but the effect was gone by 21 MAS. Where nonselective herbicides are not used, fastest conversion to KB will occur with a combination of PSLM and high seeding rates.