Enhancing Weed Control by Reducing Hard Water Antagonism of 2,4-D in Spray Tank Mixtures

Geoffrey P Schortgen, Purdue University

Abstract

The ability of weak acid herbicides to control weeds, such as dandelions, is reduced when mixed with hard water. Hard water is commonly used to spray herbicides causing herbicide antagonism. Reversing hard water antagonism is possible by using a water conditioning agent. Adding a water conditioning agent results in increased weed control by allowing applications to be more effective in hard water without increasing the amount of herbicide applied. Further, optimum weed control results in reduced labor (re-application) and herbicide inputs, thus reducing costs. While a great deal of research on the hard water antagonism of glyphosate is available, less is known about the antagonism of other herbicides. Despite the fact that we know 2,4-D dimethylamine is susceptible to hard water antagonism, there is much we don’t know. Greenhouse and field experiments were conducted to determine how increasing levels of water hardness influences dandelion control with various 2,4-D formulations. Also, multiple water conditioning agents were examined to test their ability to reverse hard water antagonism of 2,4-D. In greenhouse experiments, dandelion control from 2,4-D was reduced when water was ≥422 mg CaCO3 L-1. Hard water antagonism was overcome by the addition of 20 g L-1 ammonium sulfate (AMS) into the tank-mixture prior to application. Results also showed thatt spray solution storage time did not influence dandelion control, regardless of water hardness level or adjuvant inclusion. As such, water hardness and subsequently the decision on whether to use an adjuvant should be a primary concern for applicators using 2,4-D dimethylamine and not spray solution storage time. Other experiments determined that tank mixing 2,4-D dimethylamine with ammonium nitrate or urea ammonium nitrate (UAN) at either fertilizer or adjuvant rates reduced hard water antagonism, but AMS will only mitigate hard water antagonism at an adjuvant rate (2% w/w). Greenhouse results also illustrated that water-soluble (amine and choline) formulations of 2,4-D were antagonized by hard water, but water-insoluble (esters) formulations were not antagonized. In field experiments, it was revealed that for all treatments applied in spring or fall, those with AMS in the tank-mix performed better than those without the adjuvant. Further, dandelion control was reduced at water hardness levels ≥ 450 mg CaCO 3 L-1 which supported the greenhouse experiments. Fall applications reduced dandelion ground coverage 42% more than spring applications when evaluated 52 weeks after application. In summary, it is advised to include a water conditioning agent, such as ammonium sulfate, when applying water-soluble (amine or choline) formulations of 2,4-D in hard water (> 400 mg CaCO 3).

Degree

M.S.

Advisors

Patton, Purdue University.

Subject Area

Horticulture

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