Del Voight- Penn State Extension
I read with interest an article from an Pesticide Education Specialist Reeves Petrof from Montana regarding Pesticides and water. Pesticides and Water . Here is a breif over view of key points Reeves Petrof details in his factsheet.
Pesticides are chemicals and when introduced into water may react depending on the hardness of the water. Cations(+) and anions(-)are similar ot magnets. Hard water typically has a positive charge so if a pesticide is an anion or negative charge they will bind together and will not seperate once applied to the pest in question. This reduces the effectiveness of the product. A simple water test of your primary spray water supply now will determine how you manage the water this season.
Soft is below 50ppm
Medium Hard is 50-100ppm
Hard is from 100-200ppm
Hardness is the make up of the minderals in the water and may contain either Ca++, Mg+++or Fe+++
salt-formulated herbicides such as Roundup (glyphosate), Poast (sethoxydim), Pursuit ( ) imazethapyr), and Liberty )
(glufosinate) are subject to being bound in the water and for this reason many labels instruct to lower the pH of the water to ensure optimum performance.
These minerals may bind with salts of certain herbicides and with some surfactants to form an insoluble salt. These insoluble salts then “fall out” out of solution decreasing herbicide or surfactant efficiency. In the case of isopropylamine salt formulations of glyphosate, the positively charged cations of calcium (Ca2+) and magnesium (Mg2+) salts compete with the isopropylamine in the formulation for association with the glyphosate anion
(negatively charged). This results in the herbicide having a greater difficulty absorbing into the plant leaf.
In addition, research has shown that extremely hard water, 600 ppm (35 grains/US gallon), can almost completely antagonize 2,4-D amine applied at a low rate of about 4 to 8 ounces per acre. Hard Water also affects fungicides and insecticides so it is important to read the labels of all products to determine ideal pH ranges.
So how do you reduce the hardness of the water?
Note: Acidifiers should not be used in conjunction with some organo-silicone adjuvants as increased
acidity may enhance chemical breakdown of the adjuvant. In addition, sulfonyl urea herbicides can
degrade in acidic environments below 7. READ THE LABEL!
The most widely used materials to help with hard water is AMS.
1. Ammonium Sulfate (NH4SO4). Ammonium sulfate
(AMS) has been used successfully to increase herbicide efficacy on a broad spectrum of weed
species. This is particularly true for the weak-acid herbicides like Roundup (glyphosate), 2-4--D,, Pursuit
(imazethapyr),, Poast (sethoxydim) and Basagran (bentazon).. The AMS adjusts the pH so that more of
the active herbicide is transported across the leaf surface and into the plant.. An added benefit is that t
sulfate ions (SO4) bind up with hard water minerals. In addition, ammonium-herbicide combinations are
more easily absorbed by some weed species. A general rule-of-thumb for adding AMS is the addition
of 2% AMS by weight or 17 lb of dry AMS per 100 gallons of water for most applications. AMS should be added to the spray carrier solution prior to the herbicide and always, consult the pesticide label for mixing instructions. There may be limitations on the use of fertilizer-based surfactants.
2. Organic Acids. A very effective treatment is utilzing citric acid.. The addition of an organic acid such as food grade citric acid will effectively remove hard water ions from solution. Organic acids are effective because the conjugate
base (negative portion) of the acid binds to and removes positively charged cations from solution. A weak acid, such as citric acid, will provide a stronger conjugate base, and therefore, will be more effective
than a strong acid such as nitric or hydrochloric acid. The addition of the organic acid will also lower the
spray solution pH because of the addition of hydrogen (H+) ions. Organic acid is added to the water carrier prior to the addition of the herbicide. A use rate of 2.2 lbs of citric acid per 100 gallons of water should be adequate for water with 250 ppm of Ca2+.
3. Some sources of Urea Ammonium Nitrate(UAN) may also reduce the hardness but not as effective as AMS and this is why AMS is preferred over UAN.
Use the following general guidelines once you have determined the pH is of your spray water. Remember, READ THE PESTICIDE LABEL.
• pH 3.5-6.0 Satisfactory for most spraying
and short-term (12 to 24 hours) storage of
most pesticide mixtures in the spray tank.
Read the label. Not suitable for sulfonyl urea
• pH 6.1-7.0 Adequate for immediate spraying
of most pesticides. Do not leave the spray
mixture in the tank for over 1 to 2 hours to
prevent loss of effectiveness.
• pH 7.0 and higher. Add buffer or acidifier.
You can offset the effects of water pH by adding certain adjuvants (additives) that can either change the pH or your spray mixture or maintain (buffer) the levels of dissolved solids and organic particulate matter….dirt! These soil particles decrease Roundup (glyphosate) and paraquat activity and can cause equipment wear. This type of antagonism cannot be corrected by adding AMS or an organic acid. Always choose a water source that is free of dirt, grit, and organic matter.
Adjuvants and Surfactants.
Water softening additives designed for pesticide applications are available to offset hard water problems. While nonionic surfactants will generally enhance herbicide activity on most weed species, they will not
overcome the antagonism between salt-based herbicides and hard water. Therefore, under hard
water conditions, AMS or organic acids should be used in conjunction with nonionic surfactants to
maximize herbicide absorption. Read the label of surfactants that you buy. Some AMS surfactants
already have a nonionic surfactant added pH if it already at the desirable level. Here is a Factsheet that UAP has out regarding its LI700 product that is a penetrant as well as a hard water solution .LI 700 UAP this product is designed to aid in penetration as well as reduce pH.