I read with interest an article from an Pesticide Education Specialist Reeves Petrof from Montana State University regarding pesticides and water. Here is a brief overview of key points Reeves Petrof details in his fact sheet. I have also added items for the Penn State Vegetable guide as well as the Penn State Water Resources Team.
Pesticides are chemicals and when introduced into water may react depending on the hardness of the water. Cations (+) and anions (-) are similar to 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 separate 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. Most farms water sample for either dairy, swine and poultry so a water test should be relatively simple to locate and or gain.
Here is a simple table to the hardness of water. Hardness is the makeup of the minerals in the water and may contain either Ca++, Mg+++ or Fe+++
|Soft||below 50 ppm|
|Medium Hard||50-100 ppm|
I have had several herbicide and insecticide failures that I could not diagnose for certain but I had suspected issues with the water. All of the cases that I was involved in happened to be in spray tanks that were filled and then sat overnight before being emptied and I had theorized a reaction with the water rendered the pesticide useless. One take home message is to avoid allowing certain pesticides to remain in the tank for any long term time frame. One example I was involved with included Dimethoate which can react in literally minutes after mixing pending the water pH. 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 surfactefficiency. 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.
Here is a small list of some common products in addition to the glyphosate formulations which is more widely recognized.
|Common name||Trade name||Half-life at different pH values|
|Propiconazole||Tilt||Most effective in pH 5 to 9; use within 12 to 16 hours|
|Captan||Orthocide||pH 5 = 32 hours, pH 7 = 8 hours, pH 8 = 10 minutes|
|Carbaryl||Sevin||pH 7 = 24 days, pH 8 = 2.5 days, pH 9 = 1 day|
|Dimethoate||Cygon||pH 4 = 20 hours, pH 6 = 12 hours, pH 9 = 48 minutes|
|Permethrin||Pounce||Optimum stability pH 4|
|Paraquat ||Gramoxone Extra||not stable in pH above 7|
|Plant growth regulator|
|Gibberellic Acid||Promalin||A buffered wetting, final spray should not exceed pH 8|
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 (Accent, Harmony etc) can degrade in acidic environments below 7.
Read the label!
The most widely used materials to help with hard water is AMS. With the Xtend technologies, it is critical to read the label as additional water modifications can can change the dicamba and change the acid to a more volatile form.
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 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 pounds 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. The industry has strived to make this process simpler for the applicator by liquifying AMS and there are numerous products that are liquid AMS (Turbo and numerous others) and each product needs to be added at the appropriate rate according to the label to effectively bind the hard water. They can range from a per acre to a per 100 gallon dilution. There are some new products in this arena that either are AMS and or UAN derrivitives. Halo is relatively new the area and has been used to replace AMS, Turbo, Request, Choice, and other similar products.
2. Organic Acids.
A very effective treatment is utilizing 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 pounds of citric acid per 100 gallons of water should be adequate for water with 250 ppm of Ca2+.
From my travels, many poultry growers have citric acid on hand for use in the poultry watering system.
3. Urea Ammonium Nitrate (UAN)
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. Some UAN utilizes a Sulfuric Acid source to add Sulfur to the fertilizer mixture and may enhance the acidification from 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 sulfonylurea (Accent, Harmony) herbicides.
- 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 an older, however useful, fact sheet that UAP has produced with Loveland regarding its LI 700 UAP product that is a penetrant as well as a hard water solution. This product is designed to aid in penetration as well as reduce pH. I am not promoting their product, rather the fact that they have a large list of pesticides and their pH requirements. There are numerous other products similar to this product so check with your supplier for these products and use.
- The key is to read the label
- Gain a water test
- Fill the tank half to 2/3rd full and add the water treatment before adding any of the products that are affected by the pH or hardness.
- Add other products in the right order to ensure mixing.
By following some simple rules the maximum effectiveness of herbicides, insecticides, fungicides and plant growth regulators may be achieved and avoid failures in the field.