Introduction
Paclobutrazol is a growth regulator used to control growth and reduce the frequency of mowing in all types of turfgrass plants. This material also affects the height and quality of different types of turfgrass. Therefore, the purpose of this research is to compare the growth behavior of two types of turfgrass subjected to paclobutrazol treatment and also to evaluate the possibility of using paclobutrazol to reduce the growth of turfgrass in areas with the same climate of Tabriz.
 
Materials and Methods
To determine the effect of paclobutrazol on height, and visual properties of turfgrass such as density, clippings fresh weight, leaf chlorophyll index, length and width of leaf blade, two grass plants Poa pratensis and Festuca arundinacea were treated with paclobutrazol in different concentrations. Grass plants were tested with concentrations of zero (control), 15, 30 and 45 mg/L^-1 paclotrazol as foliar spray in 4 replicates of each treatment. This research was carried out in as a split plot experiment in the form of a randomized complete block design, so that the type of grass as the main factor in 2 levels and paclobutrazol as a secondary factor were considered in all the evaluated traits in both plant species.
Results and Discussion
The results of this research showed that paclobutrazol significantly affects the height of P. pratensis and F. aranudinaceae turfgrass plants. This effect was in the form of a significant reduction in the height of plants and controlling their growth. By increasing the concentration of paclobutrazol from zero to 45 mg/L, the height of the plants decreased. In both mentioned types of turfgrass, the most effective concentration was 45 mg/L. By increasing the concentration of paclobutrazol, the density of P. pratensis and F. aranudinaceae turfgrass plants has increased. The increase in density after paclobutrazol treatment was more evident in F. aranudinaceae. In general, the fescue turfgrass plant has stronger foliage, deep and strong roots, and lower density. The only exception was the increase in the chlorophyll index of fescue leaves (10 days after treatment) and P. pratensis (20 days after treatment) and in both of them under the concentration of 30 mg/L of paclobutrazol. Following paclobutrazol treatment and increasing its concentration, the length and width of the leaf blade as well as the clippings fresh weight of turfgrass plants were decreased. The reduction in the length and width of the leaf blade was similar in both plants, and the most effective concentration of paclobutrazol was 30 mg/L. However, the optimal effect of paclobutrazol was observed up to 30 days after the treatment. In the fourth measurement (40 days after the treatment), the effect of paclobutrazol decreased and there was no significant difference in the length and width of the leaves of the treated plants and the control plants.
 Conclusion
In general, with the treatment of different concentrations of paclobutrazol, the number of aerial branches produced in F. aranudinaceae was more than that of P. pratensis. Since paclobutrazol is a growth inhibitor and by preventing the synthesis of gibberellin hormone, it prevents plants from elongation, this substance can be used to control the growth of turfgrass plants. This growth control reduces the number of mowing times, reduces fertilizer consumption, increases the efficiency of water use, and ultimately saves the cost of maintaining turfgrass plants. Since paclobutrazol accumulates in the roots and eventually causes the formation of new branches, it can be concluded that the effect of paclobutrazol on the density of F. aranudinaceae is greater than that of P. pratensis.
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