Spray-Tank-Mix Compatibility of Manganese, Boron, and Fungicide: Solution pH and Precipitation1

Abstract

Abstract Foliar application of manganese and boron mixed with pesticides in water solution is a common practice for peanut (Arachis hypogaea L.) production. This study was conducted to determine the compatibility of mixing manganese, boron, and leafspot fungicides using water from three sources. Spray mixtures of the chelated manganese salt of ethylene diamine tetra-acetate and the inorganic salts of manganese as manganese sulfate(TECMANGAMTM), manganese sulfate monohydrate, manganese chloride, and manganese nitrate were developed using deep-well water, shallow well water, or distilled water. Boron was added to these mixtures using boric acid or disodium octaborate tetrahydrate. In addition, all combinations were mixed with the leafspot fungicides chlorothalonil or cupric hydroxide plus sulfur. Mixtures were equivalent to recommended rates of manganese, boron, and fungicide applied to the foliage in 140 L ha-1 of spray volume. Measurements were made of solution pH and manganese remaining in solution after filtration. Development of precipitates was noted. In the deep-well water solution (pH = 8.0), addition of manganese sulfate, manganese sulfate monohydrate and manganese chloride caused precipitates to form. Manganese nitrate and chelated manganese solutions did not form precipitates. Addition of disodium octaborate tetrahydrate increased the tank-mix pH for all waters source, and caused increased precipitation of the manganese inorganic salts, but not the chelated manganese. Use of boric acid in the water lowered solution pH, and all manganese sources remained in solution. Spray-tank-mix pH was critical in keeping all manganese inorganic salts in solution. For all pH levels studied (pH 4.6 to 8.4) the chelated manganese remained in solution without formation of a precipitate. Chemical analyses of the filtrate showed that only 75 to 80% of the inorganic salts of manganese remained in solution with disodium octaborate tetrahydrate, while 100% of the chelated manganese salt remained in solution. Inorganic salts of manganese and disodium octaborate tetrahydrate should not be mixed with chlorothalonil, and none of the manganese materials should be mixed with cupric hydroxide plus sulfur as a spray-tank-mixture for foliar application.