Implications of repeated trinexapac-ethyl applications on Kentucky bluegrass

Reducing turfgrass clipping production is often the goal of managers who re cognize the need to save time, money, or landfill space. The objective of t his study was to investigate the long-term implications of repeated trinexa pac-ethyl [4-(cyclopropl-alpha -hydroxy-methylene)-3, 5-dioxocyclohexanecar boxylic acid ethyl ester] applications at two fertility levels (150 and 300 kg N ha(-1) yr(-1)) on Kentucky bluegrass (Poa pratensis L.). Trinexapac-e thyl (TE) was applied at 0.17, 0.23, or 0.29 kg a.i. ha(-1) every 4 wk or a t 0.23, 0.29, or 0.34 kg a.i. ha(-1) every 6 wk for three growing seasons. Clippings were reduced by 22 to 41% when TE was applied every 4 wk (five ap plications per season) from May through August, and turfgrass quality as im proved. A 6-wk application schedule (four applications per season) did not reduce clipping production as consistently as the 4-wk application schedule due to a postsuppression rebound effect. Nitrogen fertility above 150 kg N ha(-1) yr(-1) was not necessary to maintain excellent turfgrass quality. T urf treated with TE consistently displayed better visual quality than untre ated turf regardless of the TE application rate. Repeated applications of T E resulted in less dollar spot disease (Sclerotinia homeocarpa F.T. Bennett ). Applications of TE not only reduced Kentucky bluegrass clipping producti on but were also effective in managing turfgrass growth. The postsuppressio n rebound effect can be utilized to manipulate turfgrass growth, allowing t he turf to grow rapidly when it is beneficial to do so. No deleterious impl ications were observed following repeated TE applications.