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[nafex] page3 pH
Photos removed, Not clear.
BY LOWERING SPRAYER WATER pH,Duane Kiess gets better weed control from
his burndown with lower rates of herbicides.
Chemist for Helena Chemical Company. When the pH of carrier water is
above 7. Many pesticides go through hydrolysis, a chemical reaction that
splits apart a pesticide's molecular makeup and hurts activity.
Hydrolysis occurs faster with a higher pH. And gets worse the longer
the pesticide stays at that pH. At a pH of 9. alrazinc has a half-life
(the point where half the active ingredient has decomposed) of less than
an hour. Yet when placed in water with a pH of 5, the half-life is 9.6
That's an important point to remember even if you don't allow
pesticides to sit in the tank overnight. Weed leaves have extremely high
pH levels that can accelerate breakdown as the pesticide sits on the
leaf. Penner says. Velvetleaf, for example, has a 9.7 pH. The problem is
especially important with insecticides, which need to remain active on
the leaf until the insects feed.
Chemists believe many herbicides also move into the plant better at
lower pH. "Roundup and many post soybean herbicides (such as Blazer and
Basagran) have a negative charge." Penner says. "When you lower the pH.
You put that herbicide into a more nonpolar state." That helps the
herbicide move through the waxy coating on many weeds. The coating is
Before you start adding products to buffer and adjust pH. You need
to know your water's condition, says Jim Garvin, technical services
agronomist with Cole Growers Service in Madison, Wis. "Where that water
came from, and it's pH, could explain a lot of the variation in control
farmers see with essentially the same herbicides." Garvin says. Many labs
and water softener companies will test for hardness and pH. Garvin
suggests tracking pH through the season.
"Some farmers see the pH rise as water is drawn down in the
aquifer," Garvin says. "If you start with 7.5. That water could be 7.9
later in the spring."
Electric pH meters, when properly calibrated, can be a quick
accurate test. A reliable meter will likely cost $200 or more. Test
strips and dyes, like those used for swimming pools, are cheaper, but
take more time to compare their color with a corresponding pH chart.
There are a host of acidifiers and buffering agents that will fix
problem water. Some are simply an acid, such as food-grade citric acid or
Joe Beam uses citric acid to adjust his well water, which has a pH
of 8.4. The Xenia, Ohio, farmer mixes a cup of citric acid into 100 gal.
of water to lower pH to around 5. The food-grade citric acid comes
in 50-lb. bags and costs pennies per acre. Beam says. Adjusting pH, plus
use of surfactants, helped him cut total herbicide use in half.
Kiess adds 2 pints of Quest per 100 gal. of water to his burndown
mix of 12 oz. Roundup, 16 oz. 2,4-D and I pint surfactant. Quest is a
liquid form of ammonium sulfate plus water conditioners.
"I apply the burndown with just 5 gal. of water per acre," Kiess
says. The low volume rate helps him cover more acres with his Spra-coupe.
"At that low rate, we had trouble keeping dry ammonium sulfate in
It's important to check labels before adjusting pH or hardness of
carrier water. For its sulfonylurea herbicides (Classic, Pinnacle, Glean)
DuPont Agricultural Products Company recommends low rates of 28% N or up
to 4 lb. of spray-grade ammonium sulfate per acre to increase activity on
certain weeds. The company does not recommend wholesale lowering of
In a 1993 demonstration plot, FARM JOURNAL Field Agronomist Ken
Ferrie tested several herbicides at varying pH levels. Taking the pH too
low on some can damage beans. "Taking Classic and Pinnacle down to 4.3 pH
increased the activity on weeds, but also tended to crinkle and shorten
the beans," says Ferrie, who owns Crop-Tech Consulting Inc. "It wasn't a
replicated plot, but you could certainly see a difference across the pH
Mike Hughes, DuPont product manager for soybean herbicides, says
environmental conditions may have played a role in Ferrie's Findings.
"That's why we have a lot of warnings on the labels about what to use
with the products and how weather can affect performance."
Editor's Note: For a free listing of acidifiers and buffering agents,
send for "A Compendium of Herbicide Adjuvants, " by George Kapusta.
Address: Department of Plant & Soil Science, Southern Illinois
University, Carbondale, III. 62901.
FARM JOURNAL MARCH 1994
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