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What's up in Iowa agronomics
There was a whole lot of agronomy
discussed during this month’s Iowa State University (ISU) Integrated Crop
Management conference. Here are a few things Extension specialists discussed.
Mix ‘em up
Using several herbicide modes of
action in a weed control program is a good component of a diversified program.
One hurdle to this, though, is the perception it will cost more money.
On the industry front, Monsanto
(Roundup’s manufacturer) is working with companies like Valent and FMC to offer
financial incentives for use of FMC and Valent preemergence herbicides with postemergence
Roundup applications in the Roundup Ready program.
“The biggest impediment to
diversification is the thought that it is costing farmers money to buy another
herbicide,” says Mike Owen, ISU Extension weeds specialist. Incentivizing
farmers to use preemergence products with Roundup in Roundup Ready systems helps
make it more palatable costwise, adds Owen.
For applicators, splitting
between preemergence and postemergence applications also helps reduce time
crunches by widening the application window, he adds.
Dealing with resistance to SCN resistance
You’ve probably read about or even encountered soybean cyst
nematodes (SCN) that resist SCN-resistant varieties. SCN resistance is highly
concentrated in the PI 88788 resistance source. Soybean farmers who have
encountered SCN resistance to varieties with the PI88788 source might consider other resistant
varieties with different resistance
sources, such as Peking or Hartwing.
Still, planting alternative
resistant source varieties is no guarantee they’ll outyield PI88788 resistance
source varieties. Some ISU tests show varieties with alternative resistance sources
as the highest yielders in SCN-infested soils. Conversely, varieties with the
PI88788 resistance source have been top yielders in other trials.
What to do? “Look
SCN-resistant varieties that consistently yield well in various SCN-infested (field)
trials,” says Greg Tylka, ISU Extension nematologist.
Some top yielders may be PI 88788-based, others may not.
Just because a variety has PI88788 resistance, though, doesn’t mean it won’t be
a high-yielding variety, says Tylka.
Wonder if glyphosate is spurring
manganese deficiency in your soybeans? This issue that has been
raised in scientific
journals and reports by some agricultural scientists.
In 2001, Purdue University researchers found Roundup Ready
soybean varieties were more sensitive to manganese deficiencies than conventional
varieties. However, subsequent trials found manganese deficiencies were related
to the parentage of the soybean variety, and not the Roundup Ready trait, says Bob
Hartzler, Iowa State University Extension weeds specialist
Concerns regarding glyphosate inducing manganese
deficiencies are theoretically possible, he adds.
“There are published papers supporting these claims,” he
says. “However, the majority of research does not support these concerns. If
these things were occurring (with more frequency), we would have more people
picking up on it in the field.”
Thinking about applying a fungicide on soybeans? How about a
two-in-one shot with insecticide and fungicide?
First, make sure you need them, says Rebekah Ritson, an ISU
entomology graduate student who reported on ISU fungicide and insect trials
across three Iowa sites from 2008 to 2010. Treatment time also makes a
ISU researchers examined various treatment types and types.
One was conducted under Integrated Pest Management criteria of infestation
levels reaching 250 aphids per plant on 80% or more of plants. Insecticide
treatments were viable across a wide range between R1 (beginning bloom) and
R5.5 (beginning to full seed). A preventative application applied at R3
(beginning pod) also was economically viable.
That wasn’t the case, though, with earlier insecticide
“R1 (bloom) applications of pesticides provided poor
protection from aphids and/or foliar disease,” says Ritson.
In some site-years, favorable reconomic returns resulted
with fungicide and insecticide combinations. A favorable return for fungicides
alone, though, hinges on treatment stage, likelihood of disease, and soybean
“A fungicide alone at R1 has a very low probability of a
return on investment,” Ritson says. “At R3, the probability of a return is
variable, depending on the price of soybeans.”
At $6 per bushel prices, the probability of a favorable economic
return is 41%. That jumps to 89% for $10 per bushel soybeans, and 94% for $12 per bushel soybeans.