Evaluation of the Inhibitory Effects of Different Salts on 2,4-D Efficacy in Control of Kochia (Kochiascoparia L.) and Redroot pigweed (Amaranthusretroflexus L.)

Quality of water used in spray tanks can affect herbicide efficacy, especially acidic herbicides such as 2,4-D. Water is the primary carrier for herbicide applications and it usually makes up over 99% of the spray solution. Considering that, it should be no surprise that the chemistry of water added to the spray tank greatly impacts herbicide effectiveness. Some ions such as calcium and magnesium cations that dissolve into the water, creating various levels of hardness in the water supply. 2,4-D is weak acid herbicide that can be influenced by hard water cations or foliar fertilizers. It has shown reduced activity when applied in water containing calcium and magnesium cations. Hence considering the quality of the water tank sprayer especially hardness helps optimize the efficacy of herbicides. Thus this research was conducted to determine the effect of different salts to 2,4-D on kochia and redroot pigweed as indicator weed species.
Material and Greenhouse experiments were conducted during 2014 at Ferdowsi University of Mashhad to determine the effect of sodium bicarbonate, calcium carbonate, magnesium chloride and calcium chloride in 500 ppm and deionized water as the control on the efficacy of 2,4-D in three doses including 135, 270 and 540 g. a.i. ha-1 (SL 72%) with and without ammonium sulfate (AMS) ( 2% w/v). Kochia and Redroot pigweed were planted after breaking dormancy in plastic pots. Herbicide was applied using a backpack sprayer calibrated to deliver 290 L ha−1 at 200 kPa with flat-fan nozzles (Tee Jet 8002 flat-fan spray nozzles). Spray solutions were thoroughly agitated each time a new solution was prepared and immediately prior to application to bring herbicide into solution. Living plants were recorded 3 weeks after herbicide treatment irrespective of the timing of application. In addition to survival, the above-ground dry weight of Kochia and redroot pigweed in each pot was determined 3 weeks after the optimum timing of herbicide application. The experimental design was a randomized complete block with 3 replications. Data were subjected to ANOVA for a factorial treatment arrangement using Minitab ver.17. Means of significant main effects and interactions were separated using Fisher’s Protected LSD test at p≤0.05.
Results of ANOVA showed that all factors included 2,4-D doses, type of salt and AMS application had significant effects on survival and dry matter of Kochia and redroot pigweed three weeks after treatment. In this experiment, 2,4-D toxicity to Kochia and redroot pigweed was antagonized by salts available in the spray carrier. Reducing in 2,4-D efficacy for Kochia control in the presence of salts such as calcium, magnesium and sodium by Nalewaja and Matysiak (1993b) was reported. In Kochia, sodium bicarbonate was more antagonistic than the others. But there is no difference between inhibitory effects of all salts in redroot pigweed. Mueller et al. (2006) reported that calcium and magnesium concentrations greater than 250 ppm antagonized glyphosate activity on the weeds such as broadleaf signalgrass, pitted morningglory, Palmer amaranth and yellow nutsedge. Nalewaja and Matysiak (1991) showed that the glyphosate toxicity to wheat was antagonized by sodium, calcium, and magnesium. In addition, results indicate that antagonism of salts on 2,4-D efficacy can be overcome by AMS in both two species, Kochia and redroot pigweed. Shahverdiet al. (2009) showed that the activity of the weak acid herbicides such as glyphosate, chlopyralid, 2,4-D increased with the addition of ammonium sulfate to the spray solution. Also, Roskampet al. (2013) showed that the activity of the 2,4-D and dicamba increased with the addition of ammonium sulfate to the spray solution for control of redroot pigweed, grass horse and lambsquarter. Results of interaction effects between 2,4-D dose and type of salt show that by increasing herbicide dose antagonism effects of cations were decreased. According to our results application of ammonium sulfate in on hard water increased the efficacy of 2,4-D four times in Kochia and more than four times in redroot pigweed.
The efficacy of 2,4-D on Kochia and redroot pigweed was affected by salt type in the spray carrier. Type of salts was different between two species, in Kochia, sodium bicarbonate had more negative effects and in redroot pigweed each four salts had similar effects. Numerous studies have shown that cations can influence herbicide efficacy depending weed species. Also our results showed that control of Kochia and redroot pigweed increased when AMS was added to 2,4-D in spray solutions. AMS has been considered important to herbicide enhancement or to overcoming herbicide antagonism by salts in spray carrier, AMS also enhance 2,4-D phytotoxicity in the absence of antagonistic salts that this confirm previous reports. It was concluded that weed species responded differently to the inhibitory effects of different cations in spray solution and AMS application, thus making a simple recommendation for all conditions is difficult.