Influence of Trinexapac‐Ethyl on Diamond Zoysiagrass in a Shade Environment

Abstract

‘Diamond’ zoysiagrass [Zoysia matrella (L.) Merr.] has excellent shade tolerance when compared with other zoysiagrass cultivars. However, because of excessive shoot growth and carbohydrate depletion, turf stand declines with time when shade levels exceed 80%. Two separate studies were conducted to determine if the plant growth regulator trinexapac‐ethyl (TE), which suppresses shoot growth, could improve turf performance of Diamond zoysiagrass under shade conditions. Well‐established turf was subjected to a constant 86 and 88% shade in the greenhouse and polyhouse, respectively. Trinexapacethyl treatments included monthly applications at 0.048 kg a.i. ha−1 (MTE), bimonthly applications at 0.096 kg a.i. ha−1 (BTE), trimonthly applications at 0.192 kg a.i. ha−1 (TTE), and the untreated control. Treatments in 1997 were made from January through August for the greenhouse study and from April to September for the polyhouse study. Diamond receiving MTE and BTE maintained acceptable turf quality throughout the study, while turf quality of the control deteriorated to unacceptable levels <3 mo after shading. Diamond treated with TTE maintained better turf quality than that of the control, but was inferior to MTE and BTE treatments. Compared with control plots, turf receiving MTE and BTE had (i) 76 to 73% less shoot vertical growth and 77 to 75% less clippings, (ii) 40 to 38% higher total nonstructural carbohydrate content, (iii) 60 to 50% higher root mass and 51 to 46% higher root viability, and (iv) 48 to 42% higher photosynthesis. Results suggested that monthly or bimonthly repeated application of TE at 0.048 or 0.096 kg a.i. ha−1 greatly enhanced the shade tolerance of Diamond zoysiagrass.