Nitrogen Selection and Growth Regulator Applications for Improving Shaded Turf Performance

Abstract

Managing turf for shaded golf course tee boxes is difficult due to few species to choose from and a lack of defined management practices. Supina bluegrass (Poa supina Schrad.) is a novel cool‐season turfgrass with good shade tolerance at mowing heights above 2 cm. This study compared the suitability of supina bluegrass, Kentucky bluegrass (Poa pratensis L.), and creeping bentgrass (Agrostis stolonifera L.) for golf course tees under 80% shade. Treatments included three application timings of trinexapac‐ethyl [4‐(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxo‐cyclohexane‐carboxylic acid ethyl ester] (TE) and two N types, liquid and granular. Supina bluegrass provided the best overall turf quality among the three species tested. Liquid urea (foliar uptake) improved turf quality of creeping bentgrass while Kentucky bluegrass responded better to granular urea (root uptake). Supina bluegrass response to fertilizer type was seasonally dependent. Both monthly and bimonthly applications of TE (0.05 kg ha−1) significantly improved turf quality, density, and chlorophyll levels of all species, though visual effects of bimonthly applications dissipated before subsequent applications. Creeping bentgrass divot recovery was faster than for either Kentucky bluegrass or supina bluegrass. Divot recovery was not influenced by TE or N source. Supina bluegrass had significantly greater growth rates during late autumn through spring than either Kentucky or creeping bentgrass. The best turf quality was achieved using supina bluegrass, treated monthly with TE, and fertilized with granular N in the spring and liquid N in the summer and autumn.