Subsurface drip irrigation (SDI) can sustainability improves water use efficiency by decreasing surface evaporation and control of deep percolation. However, emitter clogging due to root and soil penetration is a threat to the long-term sustainability of the system. The goal of this study was to examine the effect of Treflan injection on the prevention of emitter clogging by roots of two grass species. The experiment was conducted at the field research of Isfahan University of Technology in 2012 and 2013. The experiment included three levels of Treflan (0 (C 0 ), 100 (C 1 ) and 300 (C 2 ) milligrams net Treflan per emitter per year) and two grass species (Festuca (F) and Brmudagras (B)). The experimental treatments were arranged in a factorial experiment according to completely randomized block design with three replications. Each plot was 2.2 square meters containing 20 emitters. The Treflan injection started two months after planting and it was repeated every 45 days. The time of irrigation was determined based on MAD (management allowed depletion) equal to 50% and 70% in 2012 and 2013, respectively. The data on grass canopy color was read and grass length was measured every two week before cutting the grass. The samples were taken from depths of 0-5 cm and 5-13 cm to measure root volume, root fresh weight, and root dry weight three times during the growing season. The hydraulic parameters, including CU, DU, EU, CV and Range were evaluated at the end of the first year (9 emitters from each treatment) and at the end of the experiment (50 emitters for each treatment). All emitter were cut open and checked for clogging. At the depth of 0-5 cm, the percentages of the root volume were 4.1 and 2.6, the density of root wet weight were 3.4 and 3.4, and the density of root dry weight were 3.3 and 2.9 times more than their corresponds at the depth of 5-13 cm for Festuca and Brmudagras, respectively. For Festuca , at the depth of 0-13 cm, the densities of root volume were 1.35, 1.54, 1.56 %, the densities of root wet weight were 18.2, 21.5, 19.7 kg m -3 , and the root dry weight densities were 3.5, 3.9, 3.6 kg m -3 , for C 0 , C 1 , and C 2 levels, respectively. For Brmudagras , at the depth of 0-13cm, the root volume density were 0.5, 0.6, 0.7 %, the densities of root wet weight were 6.7, 8.2, 8.5 kg m -3 , and the root dry weight densities were 1.7, 2.7, 1.2 kg m -3 for C 0 , C 1 , and C 2 levels, respectively. The injection of Treflan into SDI system decreased roots around the emitter outlet and consequently no emitter clogging was observed. The Treflan injection had no negative effect on percentage of root volume, density of root wet weight, and density of root dry weight at the depth of 0-13 cm. The results showed that after two growing seasons (14 months) there was no emitter clogging in high Treflan injection level. The amount of DU was 77% for BC 0 , 78% for BC 1 , 84% for BC 2 , 85% for FC 0 , 82% for FC 1 , and 85% for FC 2 treatments, The maximum values of EU and CU was observed for FC 2 and the minimum value was observed for BC 0 treatments. On the whole, the results showed that, there was a positive effect of Treflan injection to prevent the clogging of emitter in SDI system. It is concluded that the 300 mg Treflan per year per emitter with 45 days injection interval can prevent emitter from grass root clogging. Also, by placing emitter at the depth of 10 cm, Treflan injection has no negative effect on the development of grass root system. Keywords : Festuca, Brmudagras, Irrigation systems, Herbicide, Drripper