Addressing NW Iowa crop concens
By ANGELA KNIEFL
SIOUX CENTER – Rootworms, erosion and its reduction, and weed resistance were the topics for more than 150 people who traveled by trailer to four stations at a Dordt College/Iowa State University Extension field day.
Erin Hodgson, an ISU entomologist, said western and northern corn rootworm are the most prevalent species in the region. No matter what management strategy farmers use, Hodgson said, they should monitor fields for larval corn root damage.
The larvae of the rootworm are the most important stage because they only eat corn roots, decreasing corn yield.
Approximately 10 roots pruned back to 1 and 1/2 inches are all it takes to be considered injured, she said. Eating the root system creates less stability and increases the chances of blow over.
Western rootworms, in particular, Hodgson said, have developed a resistance Bt corn, showing that some continuous cornfields have larvae that can survive successfully in high numbers. The western rootworm is extremely adaptable and will outsmart farmers who keep repeating the same strategies.
To remain profitable, she said, the No. 1 tool would be managed crop rotation. Continuous corn just creates the perfect environment for rootworms to thrive and multiply, Hodgson said.
Yet, the use of crop rotation eliminates a great deal of the problem since corn rootworms do not feed on other crops. This in combination with insecticides can nearly eliminate the problem of rootworm, she said.
Trying to control rootworm in its adult stage is much more difficult, Hodgson said. It requires diligent scouting and determining the sex of the pests. Spraying must be done at least two to three times, at the time when there is an abundance of females ready to lay their eggs.
The males emerge 5 to7 days before the females. The females then begin to deposit eggs 10-14 days later and proceed to do for the next 30 days, in all, laying as many as 350-400 eggs each.
In Sioux County, Greg Marek, district conservationist with the Natural Resources and Conservation Service, based in Sioux City office, outlined some of the ways to protect against soil loss and erosion. Listing no-till as one of the best, he also talked about terracing, filter strips, grass waterways and cover crops as good options.
No-till, Marek said, not only saves the soil, it keeps weeds down. However, he also offered reasons why no-till isn’t more popular in Sioux County. The first, he said, was the high rate of using livestock manure locally and the fact that it has to be incorporated in a short amount of time; no-till is not conducive to that. Also, there can be a slightly lower yield for corn crops but mentioned there is no loss in beans. A third reason is that some farmers just prefer doing things the traditional way.
However, Marek said, one reason more farmers might want to consider no-till is the increased CRP incentives for some of these conservation techniques.
Agronomist Joel DeJong got everyone’s attention by standing next to a 9-foot-deep hole beside a corn field.
DeJong pointed out that the corn’s root system reached all the way to the bottom of the hole. In other parts of the country, he said, root systems go as deep as 5 foot and emphasized that this is the best crop growing soil in the country.
DeJong explained what each layer of soil was made of and why they were the colors they were. The black top layer, he said, is mostly organic matter – as was the layer at the bottom of the hole. That soil, he said, was brought to the area by the glaciers, while the 9-feet of soil resting on top of it had been blown there over the years.
He also detailed how roots grow and what they need to grow well.
“Soil does not grow where there is no oxygen and they need temperatures of around 50 degrees or warmer to grow,” said DeJong.
Corn plant roots grow mainly during the pollination stage, and soybean roots were still growing until as recently as 2 to 3 weeks ago.
At the final station, Evan Wielenga, of the Hull Cooperative, talked about weed resistance.
Among the most problematic this year has been water hemp in soybeans. fields. Wielenga said water hemp was extremely prolific because of its resistance to Round Up.
Looking to the future, he said that there are three companies developing genetically engineered beans, which would be resistant to other herbicides besides Round Up. The three companies listed were Bayer, that would be resistant to three corn herbicides; Dow, that would be 2-4D tolerant; and Monsanto, which will be Banvil tolerant.
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