Water accounts for more than 90% in the agrochemical spraying solution. As the foundation of the spraying process, water is overlooked in many cases.
Several key elements about the water quality which will affect the spraying performance:
Some negatively-charged pesticide molecules can attach to the positively charged cations,if present in water,like Al+++, Fe+++, Fe++, Mg++, Ca++, Na+. The cations listed are in the order of most potential to bind to pesticides.
This binding leads to the reduction of the solubility, which resulting in the pesticide molecules unable to penetrate the leaf tissue or target pest, or enter at a much lower rate. Thus the performance of pesticides is largely reduced. In other cases, the hard water can cause some chemicals to precipitate and affect the properties of surfactants in the formulation or adding in tank mix, thus may block nozzles and pre-filters and cause additional wear of spray rigs.
Measurements of hardness are given in terms of the calcium carbonate equivalent, which is an expression of the concentration of hardness ions in water in terms of their equivalent value of calcium carbonate. The greater the concentration, the harder the water.
Many herbicides carry a negative charge, such as glyphosate, glufosinate ammonium, 2,4-D, and other weak-acid products.
So next time if the Glyphosate did not perform well, in addition to the reasons of resistance, short dosage, etc, you should consider about the hard water.
Solution
The most commonly used water conditioner is ammonium sulfate (AMS). AMS in solution disassociates, and the sulfate binds with cations in the spray solution, preventing the development of glyphosate-cation complexes that tend to have lower absorption into plant leaves. In addition, the ammonium ion can associate with the glyphosate molecule, which helps facilitate glyphosate absorption into the leaf.
Also some sequestering or chelating agents can be used to remove the antagonistic ions by holding cations and prevent attachment to herbicides.
The pH value of the water may affect the stability and efficacy of pesticides.
Pesticides normally are formulated as weak acids, or neutral to weak alkaline products. Generally, pesticides perform best in slightly acidic water, pH 4-6.5. Pesticides such as sulfonylurea herbicides perform better in water that is slightly alkaline.
A higher or lower than optimal pH range can cause some pesticides degradation or breakdown. This process of hydrolysis is usually permanent and irreversible, which will reduce the life of pesticides in solution, affect the physical properties of some formulations and reduce the efficacy. Besides, deposits in pipes and blockage of equipment(high pH case), and corrosion of metal pipes and fittings(low pH case) can happen.
Solution
Use buffer to get an idea pH. Acid such as sulphuric or phosphoric acid lowers pH while alkaline such as potassium hydroxide increases pH.
Sometimes the water from ditch, river or ponds are visibly muddy. This kind of water may contain suspended particles of clay, silt and fine organic matter. The effectiveness of herbicides such as glyphosate and paraquat are reduced once they are binding to the suspended sediments, rendering them unable for plant uptake. And muddy water which is not sufficiently filtered can cause equipment problems.
Solution
Filter the water before filling into the spray tank. Heavy particles can sink into the bottom in a settling tank, while very light particles can be settled out by using some certain surfactants.
Testing of spraying water quality is far from the above contents, other items like temperature, salinity, etc can also affect the spraying performance.
Always read the label before using the pesticide!
