Water quality
The quality of the water used can adversely effect a pesticide’s performance. Ideally water should be clear, colorless, odorless and neutral in pH. When available, rain water is best. If water contains excessive solids, obvious problems such as nozzle blockages will occur. Less obvious will be the binding of the chemical to the suspended materials and subsequent loss in effectiveness. The effectiveness of some chemicals can be drastically reduced by suspended clay particles. As well, solids accelerate nozzle wear. If a coin at the bottom of a bucket of water cannot be seen, that water it is too dirty to use for spraying.
Water that is either acid or alkaline in pH may break down or hydrolyze specific chemicals. If the water is known to be alkaline, spraying should start immediately after mixing. Water high in calcium or magnesium salts (hard water) may also cause problems with mixing as they reduce the stability of suspensions and emulsions.
A quick guide to the suitability of water for mixing agricultural chemicals can be obtained by using the following procedure:
Make up 500 ml of correctly diluted spray in a clear glass, sealed container according to the manufacturer’s instructions
Mix thoroughly
Allow to stand for 30 minutes. If, after this time, creaming, sedimentation or separation into layers occurs, the water may be unsuitable for mixing with sprays. If suspected of being unsuitable, a sample of this water should be chemically analyzed for slat and hardness levels.
It is important to test each chemical you use because different brands of the same chemical may react differently because of different additives in each formulation.
If poor quality water has to be used, spray immediately after mixing, ensure adequate agitation is occurring in the tank and reduce the total water volume if at all possible.
Water volume
Reduced water volumes have proved to be the single most important means of improving spraying efficiency. Most pesticides are applied in water volumes between 50 to 200 l/ha. Knockdown herbicides such as glyphosate have been effectively applied in water volumes as low as 30 l/ha on small weeds with wide angle (110 degree) nozzles under suitable environmental conditions. If weeds are large, populations are dense or environmental conditions less than suitable (high temperatures, low humidity), then 50 l/ha is a minimum water volume and 100 l/ha preferable especially for contact pesticides.