Water Quality and Herbicide Performance Question

— Written By

E-Mail Correspondence to Mitch Smith and Alan York on a Water Quality/Herbicide Efficacy Question.

We did some work several years ago with 30 or 40 water samples across the state (certainly a very small percentage of all sources) primarily with glyphosate. We saw very little difference in control, and really the only time we did was when we used a fertilizer solution like manganese, zinc, etc. The only adjuvant I would add to glyphosate if I am applying glyphosate only is ammonium sulfate (AMS) in the tank BEFORE I added the glyphosate. Give it a little time and the AMS (or equivalent nitrogen product, folks would rather have a liquid) and just about any water hardness issue goes away. Problems arise when we purposely (for good reasons in many cases) add a fertilizer to glyphosate (other than AMS) or other pesticides. And then I don’t think adjuvant selection is going to influence the interaction all that much (the herbicide interaction issue is physiological in nature, generally…stress on the weed that limits absorption or translocation, for example.) In the Midwest where they really do have major water hardness and high pH solutions they routinely add AMS and I think that probably eliminates any major issues. We simply have much fewer cases of high pH and water hardness, and when they happen I think the AMS (or probably more expensive liquid nitrogen products) would eliminate the issue. In the vast majority of cases even AMS is not needed. For example, my folks in Chowan county never have a problem with glyphosate when they spray on time and they do not add AMS. The research stations like Rocky Mount and Lewiston never have a problem when they spray on time (outside of resistance) and I suspect other stations would not either and they never add AMS. Our water for research trials generally comes from Raleigh or one of these stations and we never have a problem when we spray on time (I guess you need to ask farmers if they ever have problems when they spray on time, and that will help answer the question of a water quality issue.) Well water could be different, but if they are worried, add AMS they should be fine (BEFORE the glyphosate goes in.) I agree that most other herbicides we apply would be affected less so than glyphosate (which is affected little in our state,) perhaps other than sethoxydim and maybe clethodim, and based on the literature maybe 2,4-D. But then the literature clearly shows that AMS minimizes the adverse effect.

So, very wordy response above. But, I don’t think this is a major issue, in fact probably a very miniscule issue, given our geography and relatively low level of water hardness. AMS, however, is pretty good insurance. I have often said, but I am no guru, that a reputable crop oil concentrate or nonionic surfactant (based on label recommendations) and some AMS with glyphosate in some cases (put in BEFORE the glyphosate goes in the tank) covers us in North Carolina in terms of optimizing herbicide performance. Things like timing, weed size, plant stress, spray volume, coverage, rate, other pesticides, etc. are far more important than water quality.

And, I am going to do the last thing you want me to do, send a scientific article with NC water sample information (okay skip to last paragraph…note that we always use words like “may” or “could” in writing.)

You guys (Alan, Wes, Mitch) can forward this email or the article to agents if you want. I will send this to the peanut people through PEANUT NOTES which will capture many of the agents in the sandy areas of the coastal plain.

—–Original Message—–

From: Alan York

Sent: Saturday, January 05, 2013 9:27 a.m.

To: Mitch Smith

Cc: David Jordan

Subject: RE: Surfactants, adjuvants, and organic acids?

David Jordan is the closest thing we have to a water quality guru, so I have copied him in. Maybe he can set us straight. As far as the impact of water hardness (cations) on herbicide performance, it can make a difference with glyphosate. Beyond that, we don’t normally consider it as a problem, but maybe that is our ignorance.

Is it possible you heard a lot about potential water quality concerns because the folks speaking to you just happened to have a product that is supposed to alleviate those problems? Did they show you data from what you consider to be a reliable source?

—–Original Message—–

From: Mitch Smith [mailto:rmsmith4@ncsu.edu]

Sent: Friday, January 04, 2013 11:53 a.m.

To: Alan York

Subject: Surfactants, adjuvants, and organic acids?

Dear Alan,

Today, I along with about 13 other Ag agents, have just completed a training where we have been addressed by various companies concerning their 2013 product lines.

One common theme among all of these has been their products that could be classified as surfactants, adjuvants, and or organic acids. Also, many commented on the overlooked area of water hardness and its affect on herbicide performance.

So, my question is this:

1) What should Extension say about the effect of these products on product performance?

2) Is the impact of water hardness widespread enough for us to caution growers to investigate?

Please advise.



Sent from my iPad

Article first appeared as North Carolina Peanut Note (PNNC-2013-004)