Agronomist Notes

We are coming into pre-burn season and it has me thinking about glyphosate efficacy and the problems surrounding product application. To start, what we do know is that glyphosate works very well at lower water volumes (5gal/ac). We know that waiting a day or two to spray glyphosate after a frost reduces the risk of poor performance. We’ve also seen improved glyphosate performance in the wheel tracks when we add ten-gallon nozzles behind the wheels to offset the impact of dust. What we don’t often talk about is glyphosate efficacy and the impact of hard or soft water on its performance. This week’s agronomy section covers glyphosate efficacy and the impact of hard or soft water.

Agronomy

Hard Water Can Hinder Chemical Efficacy

It may leave your dishes spotted and your showerheads clogged, but hard water can have more costly effects when it comes to your field herbicide applications. Chemicals like Roundup aren't "tied up" as much with soft water, thereby improving efficacy.

What hard water does

According to Michigan State University Extension Integrated Pest Management (IPM) specialist Gary Thornton, hard water containing high concentrations of salt, calcium and magnesium can lead to "hard water antagonism," a condition in which chemical absorption becomes blocked by compounds created when the water is mixed with a chemical. It's especially poignant with glyphosate, Thornton and MSU entomologist emeritus Jim Johnson writes.

"The glyphosate, which is negatively charged, will combine with soluble salts, calcium and magnesium to form glyphosate-magnesium and glyphosate-calcium compounds," write Thornton and Johnson. "These compounds are not as easily absorbed by the plant and the result is poor uptake and poor weed control."

Glyphosate is not the only herbicide inversely affected by hard water. According to Montana State University IPM specialist Reeves Petroff, chemical ingredients sethoxydim (Poast Ultra, Pursuit Ultra), imazethapyr (Odyssey, Pursuit) and glufosinate (Liberty) can also create compounds that can block efficacy.

Soft water, surfactants help

Tank mixing with soft water is just one way to offset the damage hard-water minerals can cause. If soft water is not available, surfactants and chemical additives like ammonium sulfate (AMS) and urea-ammonium nitrate (28% liquid nitrogen) can be added to the mix to lessen the formation of compounds that can cut chemical efficacy.

But, softened water is not always ideal, according to Kansas State University Extension weed specialist Dallas Peterson. Much the same as with magnesium and calcium in hard water, the sodium that's typically used in water softeners can also bond with glyphosate to form compounds that can block spray efficacy.

"I'm not sure soft water takes care of the problem," Peterson says. "It will add sodium, and if the concentrations are high enough, it can cause the same problem, only creating different compounds." He adds inserting ammonium sulphate (AMS) into the tank mix may be the most effective protection against such compounds.

When adding AMS to a glyphosate mix, Thornton and Johnson advise adding 17 pounds of the compound per 100 gallons of spray water before the glyphosate is added. The benefit is two-fold.

"First, the sulfate ions tie up the calcium and magnesium ions by forming conjugate salts," they write. "Secondly, some of the glyphosate ends up as a glyphosate-ammonium compound which some species of weeds preferentially absorb into their leaf tissue over glyphosate alone."

Thornton and Johnson add that, while it can have similar effects, ammonium nitrate may not be as effective in all cases.

Adding organic acids can have a similar effect in eliminating hard water antagonism. "The addition of an organic acid such as food-grade citric acid will effectively remove hard water ions from solution," Petroff writes. "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."

Petroff adds it's important to follow label instructions with both chemical surfactants and organic acids.

Other controls

One benefit of going this route versus using a water softener is cost. In addition, with a few specific weeds, glyphosate works better with AMS added in.

Some weeds have a lot of calcium in the leaves...the AMS helps prevent the glyphosate from binding to minerals on or in the weeds. Using AMS would still be cheaper than putting in a larger softener.

Even though AMS is a less expensive additive, cost savings can also come from lowering either total spray volume or, when mixed with soft water, the amount of chemical applied.

"Reduced gallons of spray solution per acre will also have the effect of increasing the efficacy of the glyphosate," write Thornton and Johnson. "Fewer gallons of water equals fewer calcium and magnesium ions to tie up the glyphosate."

As a general rule, monitoring spray water's pH is the best way to gauge the penetration of chemicals applied and need for spray additives or softer water. Some pesticides, however, do have pH restrictions while some herbicides can break down in water with a pH higher than 7.

In general the ideal pH for water used for spraying pesticides is slightly acidic (pH 4-6). However, there are always exceptions. Make sure to read the label of the pesticide you intend to use.

Source: Michigan State University Extension

Market News

The weekly November canola futures is still stuck in a sideways trading pattern as the market awaits fresh news for further direction. The non-commercial traders have been adding to their net short position indicating a bearish outlook. Keeping the decline in the canola market smaller than the US soy market and leading to the choppy firm close was the lack of significant selling, traders said.

Also weighing on the market was the lack of fresh export demand, ideas canola is overvalued and bearish technical signals. Farmer selling was light as the current poor farm prices have caused them to avoid any marketing at these levels, cash dealers said. The main selling today was speculative.

Source: Winnipeg Commodity Exchange

The downtrend in wheat beginning in February is firmly established although the recent threat of frost damage to the US winter wheat crop has corrected most of the markets recent losses. However, the underlying fundamentals remain bearish.

As a side note from a scientific point of view, we are coming into another year with low sunspot activity. Those of you who have read my reports in the past know that high wheat prices occur 100% of the time during periods of low sunspot activity. To confirm this, 2006 was a year of low sunspot and wheat prices set record levels. Coincidence?

Market News Section

This will be the last Beyond Agronomy News that includes a Market News section. The mission of Beyond Agronomy is to provide our clients with timely, relevant and accurate information. I feel I can fulfill my mission with respect to agronomy but not with market news. I will continue to search for the right person to deliver market news to my clients. Until then you will start to receive a larger more in depth Agronomist Notes and Agronomy section. It has been my pleasure keeping you informed with market information and I look forward to finding that right individual and return to providing you with agronomic and market information.

Yours truly,

Steve Larocque