Water quality is an often overlooked aspect of spraying herbicides, yet it is very important in determining how effective your spray is going to be on your target weeds. There are a number of factors that can affect the quality of your spray water including; pH, water hardness, turbidity and sometimes even electrical conductivity.
The one most are familiar with is pH, which is also probably one of the biggest factors when looking at your water quality. The pH scale isn’t difficult to learn, it ranges from 0 to 14 with 0 being the most acidic, 14 being the most alkaline and 7 being neutral. Therefore, any number below 7 is considered acidic and any number above 7 being considered alkaline. A lot of our pesticides used today across Canada prefer a more acidic water vs. a more alkaline water. When water pH rises above 7, and especially gets closer to 8 there are a number of pesticides that are susceptible to alkaline hydrolysis within the tank which essentially means the product breaks down and becomes inactive. This will cause less than ideal results with the product you are applying. The 2 products you may be most aware of that are susceptible to this alkaline hydrolysis are Reglone (diquat) and Glyphosate products. Glyphosate for example prefers a pH of around 4-5. If your water is tested at a pH above 7 there is the options of water conditioners that will lower your pH or the option to add Ammonium Sulphate. When talking about other products besides glyphosate, typically a range of 4-6pH is ideal.
Another important factor when it comes to spray water is the hardness. This is measured by the amount of calcium, magnesium and iron that are present in the water. The more of these present in the water, the easier it is for active ingredients to becomes tied up and therefore inactive. 2,4-D is known to be susceptible to this as the salt basis of the chemical can become tied up by calcium and magnesium molecules. You can have your water tested for these levels as well so you are aware of what you are dealing with when it comes to your water.
The turbidity of water is known as simply the amount of foreign material there is present in your water. The more dirt or little specs of trees or plants there is in the water you are using the more possibility there is to deactivate a molecule. For example glyphosate used in water that has a high turbidity will cause a significantly lower efficacy due to the foreign material. The glyphosate gets into the plant via a salt ion, but what these foreign objects do is knock off the glyphosate molecule from the salt ion, therefore there is no chance of the proper amount of glyphosate to enter the plant.
This is a newer problem that has been brought to the attention of a lot of growers more recently and by getting your water tested taking a pro active approach to treat your water or use a different source is going to benefit your farm.