Whenever you drive around the Midwest in the middle of summer, you will likely see acres and acres of weed-free crop fields scattered all over. Perhaps, you will be thinking how wonderful herbicides are and that when they are applied … voilá … the result is perfectly clean fields.
But sometimes you come across some crop fields that are weedy and wonder what might have gone wrong. Were herbicides not applied? Was the herbicide application made unsuccessful? And if so, why was it unsuccessful?
Successful herbicide application depends on a number of factors:
- Proper product selection for the weed problem,
- Adherence to the product label instructions,
- Accurate calibration of application equipment, and
- Correct timing of the herbicide application.
Recommendations from industry personnel, university extension specialists, and through farmers’ own trial and error attempts, help applicators fine-tune their techniques to arrive at methods they use to control weeds.
When an herbicide fails to control targeted weeds, suspected reasons include:
- Something wrong with the herbicide,
- Something within the spray tank, such as an incompatibility issue,
- Resistance of the weed species to the herbicide, or
- Environmental factors, such as climate.
One factor that is often neglected and is more often the reason for poor herbicide performance is water quality. Most people think that as long as the water is relatively clean it can function well. That is not always the case.
Herbicides are normally delivered using water which is the foundation of the herbicide application process. Understanding the physical and chemical characteristics of water can help determine whether it is suitable for herbicide application.
Physical and chemical characteristics of water that affect herbicide function
- Debris – plant material such as leaves, sticks, and seeds that are floating or suspended in water. Plant debris is usually found in water from lakes, ponds, rivers, and ditches.
- Suspended solids – materials such as silt, clay, and organic matter that can be suspended in water but will settle at the bottom if water is left undisturbed. ‘Turbidity’ is a term used to describe water in which suspended solids can be seen floating on the water.
- Dissolved minerals – all natural sources of water have dissolved minerals such as calcium, magnesium, and iron. The dissolved minerals remain suspended, do not settle, and are what give water it’s “good” taste. Distilled water has had dissolved minerals removed and tastes flat.
- A high concentration of dissolved minerals, measured in parts per million (ppm) in a gallon of water, may cause the water to be classified has hard water.
- The World Health Organization (WHO) has four classes of water hardness based on the concentration of dissolved minerals:
- Soft 0 – 114 ppm
- Moderately hard 114 – 342 ppm
- Hard 342 – 800 ppm
- Extremely hard >800 ppm
- Salinity – the presence of high concentrations of sodium chloride and calcium chloride results in saline water. The occurrence of saline water is common in arid regions where crops are irrigated and in areas where soils have high concentrations of salt.
- pH – a value that describes the acidity (concentration of hydrogen ions) or alkalinity of a solution. The scale runs from 0 to 14 where a pH value less than 7 is considered acidic, whereas a pH value of 7 is considered neutral, and a pH value greater than 7 is alkaline.
Why is water quality important for herbicide application?
First, water is ‘nature’s solvent’ capable of dissolving or suspending minerals and organic matter.
Second, most herbicides are formulated with water as the primary diluent, and it makes up greater than 90% of spray solutions.
Third, most postemergence herbicides are a type of chemical known as a weak acid. Examples are 2,4-D amine, atrazine, dicamba, glyphosate, imazamox, paraquat, and sethoxydim. Weak acid herbicides have the ability to accept or donate a hydrogen ion depending on the pH of the solution and can be affected by water turbidity and hardness.
Addressing water quality factors affecting weak acid herbicides
Water turbidity
- A measure of the total suspended solids (TSS) as opposed to the total dissolved solids (TDS).
- Positively charged herbicide molecules are attracted to negatively charged particles found in water, making them unavailable for plant uptake.
- Using appropriate filters to remove debris from the water or not using water from ponds or ditches that is visibly murky or muddy can prevent herbicides from being tied up and ineffective.
- Using a water conditioner like Surfactant PH™ with Nitrogen, will help reduce the negative effects of TDS on herbicide performance.
Water hardness
- Negatively charged herbicide molecules bind with positively charged calcium, magnesium, and iron molecules in hard water creating molecules which precipitate out of solution, enter the target pest at a much slower rate, or cannot enter the target pest.
- Adding ammonium sulfate into the spray mixture can counter the effects of water hardness. Ammonium sulfate also enhances herbicide action.
- Using a water conditioner like Surfactant PH™ with Nitrogen, helps combat all the hard water cations that negatively affect weak acid herbicides.
Water pH
- Weak acid herbicides perform best in slightly acidic water with a pH 4 – 6.5.
- When the pH of the herbicide spray solution is outside this desired range, the performance of the herbicide will be compromised. Sometimes the herbicide falls out of solution.
- The pH of the spray solution can also influence how long the herbicide molecule stays intact. If the pH is higher or lower than optimal, the herbicide may be hydrolyzed and degraded.
- A water conditioner like Surfactant PH™ with Nitrogen, that also functions as a buffering agent, can be used to either lower or raise the pH of the spray solution and maintain the pH at a predetermined level.
Now that you understand how water quality can impact the efficacy of weed control with weak acid herbicides, here are some benefits of using Brewer International’s Surfactant PH™ with Nitrogen.
Surfactant PH™ with Nitrogen
- A nonionic buffering and conditioning agent which contains nitrogen to enhance the uptake of herbicides. Nitrogen is an ammonium sulfate replacement.
- Use rate: 1 – 2 quarts per 100 gallons of water.
- Benefits include:
- Lowering the pH of the spray solution.
- Buffering water.
- Chelating iron and sequestering hard minerals like calcium and magnesium salts.
- A great wetting agent that promotes the uptake of herbicide.
Adjuvants are used to overcome problems associated with weed control due to water quality issues and weak acid herbicide chemistry. As a leader in the adjuvant market, Brewer International has several outstanding adjuvant products. Please visit https://brewerint.com/ for more information.
References
- Hartzler, B. Role of Spray Adjuvants with Postemergence Herbicides. https://crops.extension.iastate.edu/encyclopedia/role-spray-adjuvants-postemergence-herbicides. Accessed, August 30, 2021.
- Voight, D.G., Jr. pH and Water Modifications to Improve Pesticide Performance. https://extension.psu.edu/ph-and-water-modifications-to-improve-pesticide-performance#. Accessed, August 30, 2021.
- Whitford, F., Penner, D., et al. 2009. The Impact of Water Quality on Pesticide Performance. https://www.extension.purdue.edu/extmedia/PPP/PPP-86.pdf. Accessed, August 30, 2021.
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