Influence of Carrier Water pH, Hardness, Foliar Fertilizer, and Ammonium Sulfate on Mesotrione Efficacy

Abstract

Most pesticide formulations such as dry flowables, emulsifiable concentrates and wettable powders are designed to be diluted with water as the carrier. A water pH higher than 7 which creates alkaline conditions can cause some pesticides to undergo degradation or chemical breakdown, a process known as hydrolysis. In general, insecticides are much more susceptible to hydrolysis than are fungicides, herbicides, defoliants or growth regulators. Organophosphate and carbamate insecticides are more susceptible than chlorinated hydrocarbon insecticides. Some pyrethroids exhibit susceptibility to hydrolysis.Tables reporting the pH of water sources across the U.S. list only a few states that have water with a pH below 7 which is in the acid range. The rest all have sources with varying degrees of alkalinity. Both surface and ground water supplies usually contain sufficient natural alkalinity to produce pH levels between 7 and 9.Some pesticides hydrolyze very rapidly. The hydrolysis rate can be rapid in the pH range of 8 to 9. For every pH point increase, the rate of hydrolysis will increase by approximately 10 times. The severity of losses due to alkaline hydrolysis is governed by the degree of water alkalinity, the susceptibility of the pesticide, the amount of time the pesticide is in contact with the water and the temperature of the mixture.The solution to the problem is lowering the pH of the water to the optimum range of 4 to 7 before mixing with the pesticide. This is accomplished by adding the recommended amount of buffering or acidifying agent. It should be noted that the buffering does not affect the residual activity of the pesticide. The buffering effect starts at the time of mixing, continues during storage in the tank, and does not stop until the water has evaporated from the spray droplet. Some materials, such as fixed copper fungicides including basic copper sulfate, copper oxide, and Bordeaux mixtures, should not be buffered as the acid solution may make the metals soluble and produce a phytotoxic effect when sprayed on plants. Products used to acidify tank solutions may be straight acidifying agents or in combination with surfactants or nutrient materials like trace elements or fertilizer products.A pH meter is the most accurate method of determining the pH of water. The use of test papers, such as litmus paper can be non-reliable and can be as much as two pH points in error. There air liquid color indicators (example: Bromothymol Blue) available which can indicate pH to within a half point. Water sources, both surface and ground, can and do change in pH with the passage of time. The change in pH is usually towards a more alkaline condition.

Glufosinate Efficacy as Influenced by Carrier Water pH, Hardness, Foliar Fertilizer, and Ammonium Sulfate

“…Carrier water hardness antagonism on weak-acid herbicides are well documented by previous researchers (Buhler and Burnside 1983;Devkota et al 2016a;Nalewaja and Matysiak 1993;Roskamp et al 2013a;Woznica et al 2003;Zollinger et al 2010). Glyphosate is the most widely studied herbicide in terms of water hardness and most of the studies show a reduction in efficacy when applied with hard water (Abouziena et al 2009;Buhler and Burnside 1983;Shilling and Haller 1989;Wills and McWhorter 1985).…”

“…affected by the variation in carrier water hardness, pH, turbidity, and temperature (Buhler and Burnside 1983;Devkota et al 2016aDevkota et al , 2016bGreen and Hale 2005;Nalewaja and Matysiak 1991;Roskamp et al 2013b). Carrier water pH is reported as a critical factor that can influence herbicide efficacy (Green and Cahill 2003;Devkota et al 2016a;Roskamp et al 2013b;Sarmah and Sabadie 2002). Green and Hale (2005) reported increased uptake of weak-acid herbicide into the leaf with carrier water pH below the pK a .…”

“…Nash], pitted morningglory (Ipomoea lacuonosa L.), and Palmer amaranth control was reduced with Ca 2þ or Mg 2þ cations at a concentration greater than 250 mg L À1 (Mueller et al 2006). Devkota et al (2016a) reported that mesotrione efficacy was reduced on giant ragweed, horseweed, and Palmer amaranth at carrier water hardness consisting of Ca 2þ and Mg 2þ greater than 200 mg L À1 .…”

Effect of Adjuvants and pH Adjuster on the Efficacy of Sulcotrione Herbicide

“…Water hardness is determined by the number of ions contained in it. The high value of this parameter contributes to the reduction in herbicide effectiveness [30]. The highest level of herbicide effectiveness at a reduced dose was observed in the combination where the spray liquid pH was modified using citric acid with the addition of adjuvant MSO.…”

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“…Beck et al (2017) were of the view that growers can pair nitrogen and post-mesotrione applications toghter or place in closed proximity for better weed control as integration of N and mesotrione causes more bleaching and necrosis. The ammonium sulphate (AMS) addition also enhanced the mesotrione efficacy (Devkota et al 2016). Adjuvant MSO plus fertilizer origin adjuvants (AMN, UAN) are typically applied with HPPD-inhibitor herbicides (tembotrione or mesotrione), which substantially improve the weed control (Young et al 2007).…”