The Effect of Spray Pattern and Volume on Haloxyfop-r-methyl Efficacy against Wild Barley (Hordeum spontaneum)

Herbicides should be sprayed on weeds after diluting in water. Since the spray volume can affect the efficacy of herbicides; therefore, selecting an appropriate spray volume has always been considered a simple, inexpensive and available method to optimize the efficacy of herbicides. Changing the sprayer speed and the nozzle size are two possible methods to adjust the spray volume. If a very low or high spray volume is required to achieve optimal herbicide efficacy, the applicability of the first method will be problematic. For this reason, the method of changing the nozzle size always seems to be more feasible.. When a graminicide is sprayed with a single flat fan nozzle, which is currently the most common type of nozzle available to most Iranian farmers, the spray droplets which move perpendicular to the ground are mostly oblique to the leaf surface of the grass, having erect leaves. Hence, it is likely that a large number of the spray droplets bounced from the leaf surface to the soil. A twin flat fan nozzle can create two non-vertical sprays, reducing the possibility of impacting obliquely the spray droplets to the leaf surface. Therefore, the bouncing of spray droplets from the leaf surface is significantly reduced. To date, the efficacy of twin symmetrical and asymmetrical flat fan nozzles has not been compared. On the other hand, the effect of spray volume on haloxyfop-r-methyl efficacy against wild barley has not been evaluated. Therefore, this experiment was intended to fill the gaps mentioned in science.

To compare the efficiency of single, twin symmetrical and twin asymmetrical flat fan nozzles under different spray volumes, a dose-response experiment was performed in the Research Greenhouse of Bu-Ali Sina University. In this experiment, seven doses of haloxyfop-r-methyl (0, 10.8, 21.6, 43.2, 64.8, 84.4 and 108 g a.i. ha-1) were used using three types of nozzles (single flat fan, twin flat fan 2020 and twin flat fan 3070) in six sizes of them (110015, 11002, 110025, 11003, 11004 and 11005, which create the spray volumes of 150, 200, 250, 300, 400 and 500 L ha-1, respectively) were sprayed on wild barley at a three-leaf stage. Simultaneously with spraying 108 g a.i. ha-1, another experiment was performed as a factorial in a completely randomized design. In this experiment, the amount of spray settling from three types of nozzles in six sizes of on moisture-sensitive papers was evaluated in three situations. Paper No. 1 was mounted horizontally on the ground and papers No. 2 and 3 were mounted vertically facing the back and back of the nozzle, respectively. 

In paper No. 1, in all types of nozzles, more surface of the paper was wetted by increasing the nozzle size (spray volume). In all types of nozzles at 11003, 11004 and 11005, the highest wetting rate was provided (100%). The lowest wetting rate was obtained with twin flat fan 3070 at 110015 (7.3%). In paper No. 2, in all types of nozzles, more surface of the paper was wetted by increasing the nozzle size. The highest wetting rate (100%) was observed with single flat fan and twin flat fan 2020 nozzles at 11003, 11004 and 11005. The lowest wetting rate (24-19%) was observed with single flat fan nozzle at 110015 and 11002. In paper No. 3, in two twin flat fan nozzles, more surface of the paper was wetted by increasing the nozzle size. A single flat-fan nozzle could not wet the paper at all. In general, the performance of the nozzles used in this experiment is twin flat fan 2020 > single flat fan = twin flat fan 3070. In all types of nozzles, with increasing the size of nozzles (spray volume), the rate of haloxyfop-r-methyl is required to reduce 50 and 90% of the dry weight of wild barley (ED50 and ED90) increased significantly, indicating a decrease in the efficacy of haloxyfop-r-methyl against wild barley. As the best treatment, the lowest values of ED50 and ED90, which were equal to 9.34 and 38.21 g a.i. ha-1, respectively, were obtained with twin flat fan 2020 at 110015. Increased efficacy of haloxyfop-r-methyl when spray volume was reduced can be explained as follows small size nozzles create a greater small droplet. Smaller droplets may give better spray retention over the leaf surface, resulting in increased efficacy of haloxyfop-r-methyl. In low spray volume, the higher concentration of herbicide in the spray solution may create a greater concentration gradient between the spray solution and leaf, increasing the diffusion of herbicide into the leaf.

Although the spray coverage increased with increasing spray volume for haloxyfop-r-methyl, it has an adverse effect on its efficacy. Therefore, smaller and more concentration droplets resulted in greater control of wild barley with haloxyfop-r-methyl than did larger and more dilution droplets.