The gibberellic acid inhibitor trinexapac-ethyl (TE) is widely used in the turfgrass industry, as a management technique for improving the quality of creeping bentgrass (Agrostis stolonifera) putting greens. Annual bluegrass (Poa annua L.) is an invasive weedy grass that is undesirable on golf greens due to its reduced stress tolerance. Past research on plant growth regulators has shown to increase annual bluegrass populations in creeping bentgrass stands (Gaussoin and Branham 1989). We investigated the effect of TE and gibberellic acid (GA₃) on photosynthesis rates, concentration of total non-structural carbohydrates (TNC) and chlorophyll content on creeping bentgrass and annual bluegrass. Research has shown that TE increases photosynthesis rates and total non-structural carbohydrates (TNC) (McCann and Huang 2007). Treatments were trinexapac-ethyl at 3.8ml/100m² in a 3ml solution, 3ml of water (control) and 3ml of a 10ppm GA₃ solution. All treatments were made twice at a 10 day interval. Photosynthesis rates were recorded using the LICOR LI-6400 before the first application date and then 7 days after each of the application dates. The results indicate when TE is applied to turfgrass there is an increase in photosynthesis of both creeping bentgrass and annual bluegrass compared to applying GA₃.

Gaussoin, R.E. and B.E. Branham. 1989, Influence of cultural factors on species dominance in a mixed stand of annual bluegrass/creeping bentgrass. Crop Science. 29:480-484.

McCann, S and B. Huang. 2007. The effects of trinexapac-ethyl foliar application on creeping bentgrass responses to combined drought and heat stress. Crop Science. 47:2121-2128.