Trinexapac‐Ethyl and Iron Effects on Supina and Kentucky Bluegrasses Under Low Irradiance

Turf use in covered stadiums and other environments with reduced irradiance is limited due to lack of suitable turf species and management practices. This study compared the tolerance of supina bluegrass ( Poa supina Schrad.) and Kentucky bluegrass ( P. pratensis L.) with reduced irradiance of approximately 1 to 5 mol m −2 d −1 Treatments included trinexapac‐ethyl {[4‐(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxo‐cyclohexane‐carboxylic acid ethyl ester]} (TE), foliar iron, and simulated athletic traffic inside a covered stadium simulator facility. Analysis of variance showed supina bluegrass was more responsive to TE than Kentucky bluegrass. Trinexapac‐ethyl reduced supina bluegrass clipping yields approximately 60%; Kentucky bluegrass yields were reduced by 20% or less. In non‐trafficked turf, TE increased supina bluegrass tillers by 50% and leaves by 33% but did not change tillering and leaf number of Kentucky bluegrass. Without traffic, TE‐treated supina bluegrass provided an acceptable turf at 10 to 15% solar irradiance for at least 4 to 6 mo, while Kentucky bluegrass and untreated supina bluegrass became unacceptable within 2 to 4 mo. Under traffic, TE‐treated supina bluegrass provided acceptable turf for up to 5 wk, while Kentucky bluegrass did not provide acceptable turf for more than 2 to 4 wk. Trinexapac‐ethyl enhanced supina bluegrass color and increased chlorophyll levels of both species. Foliar applications of iron had negligible effects on all of the parameters evaluated. Supina bluegrass is a useful turf for reduced irradiance situations but requires more than 5 mol m −2 d −1 to sustain traffic for periods longer than 5 wk.