Many known agrochemicals have shown to be more effective in combination than when applied individually.
Herbicides, and in particular glyphosate, are usually sprayed in combination with adjuvants which aid or modify the action of the agrochemical and/or the physical characteristics of the composition applied on the fields.
Adjuvants can be divided in different classes: activator adjuvants, such as surfactants and crop oils; utility adjuvants, such as water conditioning agents (water conditioners), antifoam agents, buffering agents and compatibility agents; and spray modifiers, such as stickers, spreader-stickers, foaming agents and drift control agents.
Among the utility adjuvants, the water conditioners help to reduce the antagonism and inactivation of some herbicides due to certain cations found in water used as the carrier. In fact hard waters contain varying levels of calcium, magnesium and iron cations, which tie up weak acid herbicides, such as 2,4-D, dicamba and glyphosate, reducing their availability.
Certain water conditioners have been shown to maintain the effectiveness of weak acid herbicides interfering with their association with the magnesium, calcium and iron ions or by binding said metal ions.
Moreover, there are some evidences that some water conditioners also contribute to more rapid uptake of the herbicide into the plant and across cell membranes through ion trapping or protonation of the herbicide molecule
Several water conditioners are known in the art, perhaps the best examples being ammonium containing compounds such as ammonium sulfate (AMS), urea ammonium nitrate (UAN) and diammonium phosphate (DAP). However salts of alkali metal, such as potassiumsulfate, di-potassium phosphate, potassium nitrate, potassium citrate and the like, can be also used.
Unfortunately all water conditioners are not equal in their effectiveness, and ammonium containing compounds, and in particular AMS, remain the reference for performance.
Ammonium sulfate is effective and quite inexpensive. However, the use of ammonium sulfate sometime is problematic because the solubility of dry formulations of ammonium sulfate in water varies with variable water parameters. Water temperature, hardness and mineral content all effect the mixing of dry ammonium sulfate into the spray mixture. This unpredictable solubility is problematic for mixers and applicators of crop protection products. In fact insoluble matter can easily plug sprayer hoses, strainer, filters and nozzle tips, causing an uneven application of the spray solution. This could cause inconsistent and unacceptable control of weeds, plant disease or insects in addition to directly exposing individuals applying the spray solution to the targeted area or crop. These problems can be exacerbated when ammonium sulfate is formulated with certain types of surfactants.
Moreover the use of ammonium containing water conditioners does not appear to be ideal with all weak acid herbicides. In particular it has been found that the use of ammonium containing compounds in combination with weak acid herbicides of the auxin class, such as alts of dicamba, can produce an undesirable volatilization of the herbicide from the area of application and thus posing a risk for off-target movement and crop injury. Volatilization of auxin herbicides is known in the art, for example in Behren, R. and Lueschen, W. E., Weed Science 27, 5, 486-493 (1979); however it appears that this phenomenon is amplified when certain herbicides such as dicamba are applied in combination with ammonium containing compounds.
For these reasons, it would be advantageous to develop water conditioners, which do not contain ammonium ions and at the same time show an efficacy comparable to ammonium sulfate.
As already stated, potassium salts, such as di-potassium phosphate, potassium nitrate, potassium sulfate and tri-potassium citrate can be used as water conditioners in substitution of ammonium compounds. Unfortunately they exhibit a fairly lower efficacy than ammonium sulfate.
We have now discovered that specific mixtures of these three potassium salts show an effectiveness as water conditioner comparable ammonium sulfate and effectively protect certain pesticides from deactivation.
Aqueous concentrates of these potassium salts are stable even at low temperature and can be used in adjuvant formulations to be tank mixed with a wide range of pesticides, but in particular glyphosate and/or dicamba formulations, without showing the problems found with ammonium sulfate compositions.