Poor Water Quality May Negatively Impact Pesticide Performance

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Water qualities that may impact pesticide application are the water pH, carbonates, water hardness and turbidity. Whether one uses a private well, surface water or a municipal water source, these parameters will vary greatly and should be evaluated before making pesticide applications. Poor water quality can greatly reduce the half-life of pesticides as well as make some product efficacy extremely poor.

Water pH – Ideally, one should apply pesticides in a water solution that has a pH range of 5.5-6.5. Regrettably, much of the water pH within NC ranges from near neutral to slightly basic. Having thus said, a few shallow wells, especially within the coastal areas of NC, may contain water that are very acidic with water pH of 3 or lower. These water pH values may rapidly reduce the half-life of pesticides, make

Graph of North Carolina showing highly variable surface and groundwater pH values

Image by Emily Mueller, Tom Bowman, and Wayne Buhler, NC State

Chart showing the negative impact to pesticide applications as water pH values increase

By Emily Mueller, Tom Bowman, and Wayne Buhler, NC State

Bicarbonate – Bicarbonate, often referred to as alkalinity, is the measure of carbonate (CO3 ) and bicarbonate (HCO3) levels in water. Pesticide water sources with high carbonates may result in a slower absorption rate of the pesticides or result in degradation of a pesticide’s active ingredients to reduce pesticide performance. Furthermore water with high carbonate levels may cause excessive salt accumulation within hoses and nozzles resulting in poor distribution of the pesticides. Pesticides commonly adversely effected by water with high carbonates are usually those that are salt-formulated pesticides such as glyphosate, glufosinate, and 2, 4-D. If the water source is consider as hard water (high sodium and calcium) then even moderate alkalinity increases the probability of poor mixing and rapid degradation of pesticides.

Water Hardness – Water hardness is primarily the measure of calcium and magnesium and is usually expressed as CaC03 ppm. However, other positive ions such as sodium, potassium, iron, or aluminum can interact by binding with some pesticides to form precipitates. These ions bind with active ingredients of pesticides reducing performance by reducing the half-life of pesticides or creating poor mixing/dissolving of product in source water.

Chart showing classification of water hardness based on parts per million of carbonates

Image by Emily Mueller, Tom Bowman, and Wayne Buhler, NC State

Turbidity – Water may contain suspended solids, organic matter, or clay. These particles readily adsorb or bind to some the pesticide’s active ingredients making the product less effective

Typically, larger producers utilize very large tanks to move water from farm to farm. If the pesticide is mixed with this water at the application site and immediately applied, then no negative impacts to pesticide application would be anticipated. However, if pesticides are mixed and stored in a tank with poor water quality, pesticides efficacy may be greatly reduced.

Regrettably, there is no list of pesticides that may be impacted by water quality. Even noting active ingredient of pesticides is not sufficient since the pesticide formulation, additives, or the presence of multiple active ingredients will alter potential reactions. The label of each product must be read to determine what, if any, actions should be taken.

Within North Carolina, the NCDA & CS Agronomic Division Solution Lab offers testing of source water for a small fee. Testing results include water hardness, bicarbonate level (reported as alkalinity within results), water pH, iron content, salt concentration, electrical conductivity, nutrient content and more. Simply fill out Form AD-7 and follow the directions on the form for handling and submission. To collects samples, the water source should be run for at least 10 minutes. Approximately 20 ounces should be collected in a clean plastic bottle. The sample should be refrigerated until sent to the lab.

Corrective actions for poor water will vary. Below are some general guidelines. For more specific discussion of potential corrective measures based on water sample results, contact your local N.C. Cooperative Extension office.

Corrective Measure Based on NCDA & CS Solution Analysis Lab Results

  • Add buffering solution to correct for improper solution pH
  • Add acid or buffering solution to correct for high alkalinity
  • Add ammonium sulfate (AMS)or 30% nitrogen to correct for hard water*
  • Mix pesticides in the field and apply within two hours
  • Filter turbid water or water with high organic compounds.
  • Find an alternative water source if mitigation is not feasible

*Generally, add 8.5 to 17.5 lbs. dry AMS per 100 gallons water or 1.25-2.5% by volume of liquid fertilizer such as 28%N, 32% N or 10-24-0.

Written By

Mike Carroll, N.C. Cooperative ExtensionMike CarrollCounty Extension Director, Field Crops & CRD Call Mike Email Mike N.C. Cooperative Extension, Craven County Center
Updated on Feb 14, 2024
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