Influence of trinexapac-ethyl on diamond zoysiagrass in a shade environment

'Diamond' zoysiagrass [Zoysia matrella (L.) Merr.] has excellent shade tole rance when compared with other zoysiagrass cultivars. However, because of e xcessive shoot growth and carbohydrate depletion, turf stand declines with time when shade levels exceed 80%. Two separate studies were conducted to d etermine if the plant growth regulator trinexapac-ethyl (TE), which suppres ses shoot growth, could improve turf performance of Diamond zoysiagrass und er shade conditions. Well-established turf was subjected to a constant 86 a nd 88% shade in the greenhouse and polyhouse, respectively. Trincxapac-ethy l treatments included monthly applications at 0.048 kg a.i. ha(-1) (MTE). b imonthly applications at 0.006 kg a.i. ha(-1) (BTE), trimonthly application s at 0.192 kg a.i, ha(-1) (TTE), and the untreated control. Treatments in 1 997 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. Di amond treated with TTE maintained better turf quality than that of the cont rol, but Has inferior to MTE and BTE treatments. Compared with control plot s, 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 car bohydrate content, (iii) 60 to 50% higher root mass and 51 to 46% higher ro ot viability, and (iv) 38 to 42% higher photosynthesis. Results suggested t hat 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.