Read time: 5 minutes

Don’t start mixing until the water quality is right

Water quality is often overlooked as a possible contributor to herbicide failure and can lead to confusion over the herbicide resistance status of weeds on a property. The careful management of spray events is highlighted in the The Big 6 for managing herbicide resistance.

Spray application specialist, Craig Day of Spray Safe and Save at Cowra, NSW says water should be considered as one of the chemicals in any mix, given that water quality varies markedly depending on its source.

Spray application specialist, Craig Day of Spray Safe and Save at Cowra, NSW says water should be considered as one of the chemicals in any mix, given that water quality varies markedly depending on its source.

“It would be great if all herbicide sprays were applied using rainwater but that is often not practical,” he says. “The pH, hardness, electrical conductivity and dissolved solids in water all interact with the herbicides and adjuvant products in a mix. It is essential that these parameters are all addressed before any crop protection products are added to the water.”

Mr Day says a water test is a cheap way to ensure that the herbicide applied will be as effective as possible in a weed control program. “Generally, water is considered hard when the calcium carbonate levels exceed 300–400 ppm,” he says. “If glyphosate is added to hard water, the calcium and glyphosate ions react, effectively reducing the uptake of the glyphosate into the plant. By adding ammonium sulfate to the water, the positively charged calcium ions bind with the negatively charged sulfate ions. When glyphosate is added to properly agitated and dissolved ammonium sulfate solution the glyphosate does not bind to calcium ions.”

It is critical that no undissolved ammonium sulfate, via a handling system or within the spray tank, comes into contact with 2,4-D amine formulations. The resulting precipitate is irreversible.

“Hard water will affect formulations of 2,4-DB, glyphosate, 2,4-D amine, Lontrel Advance and Tigrex. If hard water is used with these formulations, there is a greater potential for a reduction in the effectiveness of the chemical,” he says.

Water with a pH over 8 supports alkaline hydrolysis, which can affect the efficacy of many herbicide and insecticide products, and is often associated with hard water. Like the example of 2,4-D in hard water, chemicals tend to separate out over time in a high pH environment and the mix become less effective over time.

“The trend toward larger spray tanks means that product is in the tank longer and will be adversely affected when there is a high pH,” says Mr Day. “At a pH of 8, which is common for tap water in many areas, many products will only remain fully potent for a matter of 1.5 or 2 hours at the most. The use of an acidifying surfactant helps lower the pH to an optimal 4.5 or 6.”

“Aside from herbicides, organophosphates and carbamates are particularly susceptible to alkaline hydrolysis so pH needs careful consideration when spraying aphids with a carbamate formulation.”

When obtaining a water quality test, Mr Day suggests that growers ask specifically for the presence of bicarbonates in water to be included in the report. “A bicarbonate level of 75 ppm and above will lead to reductions in the efficacy of 2,4-D amine and Group A formulations,” he says. “Ammonium sulfate can be used to reduce the effect of bicarbonates on Group A herbicides, but will produce little improvement on 2,4-D amine formulations.”

Both total dissolved salts and saline water cause stability issues that can result in separation and blocking of filters, especially if there is insufficient agitation during the mixing process. Also, high salt levels in water will resist manipulations of pH.

Mr Day recommends growers get their water source tested regularly. “If you take two samples and retain the second jar of water you can use it to calibrate your eye using a pool and spa testing kit and the test results. This can become an ongoing monitoring tool,” he says.

Another problem Mr Day commonly sees is the incorrect use of batching tanks, where products are concentrated in small tanks without sufficient water. He suggests that growers avoid having the entire tank load amount of acidifying adjuvant in direct contact with other chemistry and that 2,4-D amine is never allowed to sit on undissolved ammonium sulfate.

“Similarly, high concentrations of glyphosate and 2,4-D amine in a batching tank can cause the glyphosate to lose its effectiveness,” he says. “It is very important that water is conditioned first, and that sufficient water and ample agitation is used when preparing a spray load. Time is always against growers but there is no point hurrying just to apply a load that won’t work because the chemistry is wrong in the tank.”

As new products come to market, Mr Day suggests growers ask their advisors where the product fits in the mixing order and to highlight any interactions with water quality parameters. “Ask your advisor to provide the correct mixing order when writing the advice sheet,” he says. “You will then have this advice to follow and can record the mixing order on file. This information, and a water quality test, will help unravel any issues with a spray’s efficacy and, in combination with a herbicide resistance test, assist with developing a robust herbicide program.”

The GRDC GrowNote Herbicide Use technical manual provides detailed information about the water quality and adjuvant requirements for each herbicide MOA group.

More resources:

From the NSW DPI ‘Weed control in winter cropping 2016’ publication. http://www.dpi.nsw.gov.au/agriculture/broadacre-crops/guides/publications/weed-control-winter-crops

Related Articles

View all
Article
News

Never cut the herbicide application rate

Scientific studies have demonstrated that resistance can rapidly evolve in weeds subjected to low doses of herbicide. Some weeds can develop resistance within a few generations. Full rates when mixing herbicides too! When mixing herbicides it is important that each product is still applied at the full label rate to ensure high mortality. Applying different chemicals in one mix can provide an additive advantage. It is important to understand the mode of action of each herbicide on the plant when preparing a herbicide mix. This is just as important for pre-emergent grass weed mixes as it is for post-emergent mixes aimed at broadleaf weed control. ALWAYS READ THE LABEL. Surrounding weed seeds with a combination of pre-emergent herbicides with different modes of action can give a high level of control and help extend the useful life of all the chemicals used. The high level of control must be supported with additional control measures for all survivors. All products with different modes of action must be applied at full label rates for this to be an effective strategy.   Mixing two chemicals with the same mode of action can achieve some additional efficacy, however, the mix should deliver the combined full rate to ensure a lethal dose. The amount of stubble present and crop safety are all important considerations when mixing chemicals. For example, when using a tank mix of Avadex® and trifluralin to control ryegrass in wheat, the rates used will vary depending on the sowing system and level of stubble retention. Be sure to get good advice. Many herbicides on the market are a combination of two or more modes of action within the one product. These products must be applied at the full label rate to be effective. Having dual action does not negate the need to change herbicide products and rotate modes of action. Repeated use of any single strategy will reduce the effectiveness of that strategy over time.  
Article
News

Spray well – correct nozzles, adjuvants and water rates

Spray application is a technical field and growers need to make sure their equipment and application techniques are spot-on. The GRDC Spray Application GrowNote provides detailed information and about 80 videos to demonstrate key skills. Prevent spray-drift The focus of spraying herbicide needs to be on doing the job right so the weeds receive the correct dose and die, and this includes reducing the air borne fraction to a bare minimum. Bill Gordon’s 10 Tips for Reducing Spray Drift Choose all products in the tank mix carefully. Understand the product mode of action and coverage requirements. Select (and check) the coarsest spray quality that will provide effective control. Expect that surface temperature inversions will form as sunset approaches and will likely persist overnight and even beyond sunrise on many occasions. DO NOT SPRAY. Use weather forecasts to inform your spray decisions. Only start spraying when the sun is about 20 degrees above the horizon and when the wind speed has been above 4–5 km/hr for more than 20–30 minutes, and clearly blowing away from any adjacent sensitive crops or areas. Set the boom height to achieve a double overlap of the spray patterns. Avoid higher spraying speeds. Leave buffers unsprayed if necessary and come back. Continue to monitor conditions, particularly wind speed, at the site during the spray operation High water rates don’t have to slow you down Some growers are concerned that increasing the water rate when applying herbicide will slow down their spray operation and cost them money. However, the biggest financial loss during spraying usually comes from a failed spray job. To keep your spray operation as time efficient as possible when using more effective and reliable application volumes, you can: Use nurse tanks around the farm to reduce the time spent travelling back to a central re-fill point. Use a larger pump, e.g. 2.5 inch, to make re-filling quicker. Pre-mix the batch while the sprayer is operating. Many mixes can be held in the mixing tank for up to 6 hours. However, wettable granules and suspension concentrates will need agitation to keep them in solution. For pre-emergent herbicides in high stubble situations, carrier volume has a large effect on the level of control achieved. Across four trial sites Dr Borger’s research demonstrated that ryegrass control with trifluralin or Sakura® increased from 53% control when the carrier volume was 30 L/ha to 78% control when the carrier volume was increased to 150 L water/ha in high Water quality and mixing order Water quality is often overlooked as a possible contributor to herbicide failure and can lead to confusion over the herbicide resistance status of weeds on a property. Water should be considered as one of the chemicals in any mix, given that water quality varies markedly depending on its source. Getting the mixing order right is essential for effective spray results. Don’t start mixing until the water quality is right Podcast – Mixing herbicides Adjuvants Sometimes adding an adjuvant is beneficial and sometimes it is detrimental; and there is an art to knowing how to best deploy these additives. When weeds are susceptible to the applied herbicides, the effectiveness of adjuvants generally goes un-noticed. Correctly applied adjuvants can reduce the impact of low level herbicide resistance by helping to maximise the amount of herbicide taken up by the plant.
Article
News

Clean borders – avoid evolving resistance on the fence line

About one-quarter of glyphosate-resistant populations within broadacre cropping situations across Australia come from fencelines and other non-cropping areas of the farm. Along paddock borders, where there is no crop competition, weeds can flourish and, if not controlled, set lots of seed. The traditional approach has been to treat these weeds with glyphosate to keep borders clean but after 20-odd years this option is now failing and paddock borders are becoming a significant source of glyphosate-resistant weed seed. Weed researcher Eric Koetz said the limited options for managing weeds along irrigation infrastructure and other non-crop areas is a problem and is putting additional pressure on knock-down herbicides in irrigated systems. In some situations, cultivation can be used to kill the weeds and provide a firebreak, but on light soils this may pose an erosion risk and mowing or slashing may be safer options. Another possible tactic is to continue using herbicides but to ensure that a clean-up operation is carried out before any survivors can set seed. Some growers are choosing to increase the heat on weeds along the borders by planting the crop right to the fence and then baling the outside lap and spraying with a knockdown herbicide to kill any weeds and provide a firebreak. Another good option in some situations is to maintain a healthy border of vegetation using non-invasive grasses. In Queensland, buffel grass is a good example of a grass that can outcompete other weeds while not invading crop lands. If only herbicides are used on fencelines, resistance is inevitable. Surviving weeds on fencelines have no competition and access to plenty of soil moisture, so they set a lot of seed and resistance can easily flow into neighbouring paddocks. Other resources It’s time for a glyphosate intervention Farm hygiene cottons on – Cleave Rogan, St George What’s new in management of herbicide resistant weeds on fencelines? Keeping the farm clean – Graham Clapham, Norwin Don’t jeopardise glyphosate for clean fencelines Keeping fencelines clean Resistance risk to knock-down herbicides on irrigated cotton farms

Subscribe to the WeedSmart Newsletter