بررسی تغییرات pH آب در مخزن سمپاش بر کارایی علف کش های گلایفوسیت و نیکوسولفورون در کنترل علف های هرز سوروف و گاوپنبه

Abstract

Introduction: Many factors affect the absorption, transport and performance of herbicides, include; physical factors (such as the orientation, shape, size, cuticle thickness, and its amount downy of the plant leaves), physiological factors (such as the growth stage and its succulence), environmental factors (like rainfall after spraying, relative humidity, wind, and temperature), as well as water quality in spray tank (32). The quality of natural water resources is very important, because the water passes through soil and rocks and dissolve natural salts and transfer them to groundwater reserves (12). pH is a chemical scale for measuring the concentration of hydrogen ions (H+) in the water (21). When pH of solution is less than herbicides pKa (ionic dissociation constant), increasing pH can increase the solubility of herbicides, especially when the absorption limitation of herbicide is because of its solubility (14). To investigate the effect of water pH in herbicide spray tank, testing the effectiveness of weed control is appropriate method. The different species of weeds may have different amounts of ions in the tissue that showed different responses to herbicide solution (14). Accordingly, these basic experiment conducted to study the pH variation of water in spray tank on glyphosate (Roundup®) and nicosulfuron (Cruse®) performance on barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] and velvetleaf (Abutilon theophrasti Medicus.) control in the greenhouse condition. Materials and Methods: Two separate experiments were performed as factorial arrangement of treatments 2×7 based on completely randomized design with six replications at Research Greenhouse of the Ferdowsi University of Mashhad in 2010. Factors included were: pH at 7 levels (4, 5, 6, 7, 8, 9, and 10) obtained by using buffer prepared solutions (+3 control pots for each pH level), and two weeds (barnyardgrass and velvetleaf). Glyphosate and nicosulfuron herbicides were applied post emergent 158 and 22 g ai ha-1 (based on ED50 outcome preliminary test (11)), recpectively, at the 3-4 leaf stage of the weeds in a spray volume of 250 L ha-1. Four weeks after treatment, survival, plant height, leaf area, shoot fresh and dry weight of weeds (% control) were calculated. The data of experiment were subjected to ANOVA using MSTATC software. Means of the treatments were separated using Duncan’s Multiple Range Test at α = 0.05. Based on the distribution of data, regression analysis was used as two, third, and four-degree polynomial. Result and Discussion: The results showed significant effect (P≤0.01) of water pH variation in spray tank of herbicides on survival, plant height, leaf area, shoot fresh and dry weight of weeds (% control). Nicosulfurone herbicide in water pH equal 7 and 8 showed the highest effect on barnyardgrass weed, so that, the highest activity of nicosulfuron herbicide on velvetleaf was found in water pH= 8. Whereas, glyphosate herbicide in water pH equal 6-7 and 6 showed the highest effect on barnyardgrass and velvetleaf, recpectively. The total, more alkaline pH of water in spray tank was suitable for nicosulfuron compared to glyphosate performance (9, 28). Comparison between two weeds was showed that nicosulfuron effect on barnyardgrass control was more than of velvetleaf. So that in the best performance of the herbicide (water pH= 8), values of survival, plant height, leaf area, fresh weight and dry weight (% control) were estimated equal 25.8%, 16.7%, 21.6%, 4.6%, and 2.6% for barnyardgrass, respectively. The corresponding values for velvetleaf were 50.0%, 61.1%, 53.6%, 32.9%, and 24.5%, respectively. In general, the solubility of sulfonylurea herbicides in water decreases with decreasing pH. Therefore, an acidic solvent prevent from their optimal distribution and their efficiency are reduced (18, 22). In this regard, Matocha and Senseman (15) reviewed the half-life of Trifloxysulfuron herbicide in water pH 5, 7 and 9 and found that this herbicide hydrolyzed faster in acidic pH than neutral/ alkaline pH. Green and Cahill (9) also were showed when alkaline agents added to spray tank, increased the pH of nicosulfuron solution and finger grass (Digitaria sanguinalis) was well controlled by this herbicide. The researchers, increasing the nicosulforon performance on weed knew because of its higher solubility at high pH. In research conducted by Buhler and Burnside (4) concluded that an increase in the water pH of glyphosate spray tank (400 g ai ha-1) by from 2.4 to 7 and 9, reduced herbicide performance on oat (Avena sativa) 14 days after spray at the greenhouse experiment (P≤0.05). So that, shoot fresh weight of oat was lost by 69 percent at pH= 2.4 (compared to the control without spraying). The corresponding values for pH 7 and 9, were estimated 62% and 55%, respectively. Field test results also coincided with greenhouse experiment (4). Conclusion: Results of current study emphasized the role of water pH in spray tank of glyphosate and nicosulfuron on barnyardgrass and velvetleaf control.