Iowa State University Extension crop specialists say they've fielded dozens and dozens of questions about corn-on-corn management the last six weeks or so.

"On the corn-on-corn topic, we are planning to continue current work and start some new trials looking at various aspects of this topic in research trials next year. We will cover the topic in many meetings this winter," says Kyle Jensen, Iowa State University Extension crop production specialist in southwest Iowa.

Thinking about corn on corn?

"I have been bombarded with questions and comments from seed company agronomists, dealers and farmers dealing with changing rotations from the traditional corn-bean to a corn-corn system," says Roger Elmore, Iowa State University Extension agronomist at Ames.

Generally the comments are that growers are considering this change due to the somewhat flat bean yields they have endured, and the seemingly never-ending stream of pest problems associated with soybeans. And, of course, the ethanol boom is causing high interest in growing more corn. Corn demand and subsequent pricing has entered into some interesting dynamics due in no small part to the ethanol boom.

While things can turn on a dime (only a few seasons ago agronomists were fielding hundreds of questions from growers considering beans on beans), the near-term outlook has many producers considering going to corn-on-corn acres.

Here are some points to ponder from ISU Extension when making your cropping decisions for the next season or beyond.

A few of the key corn-on-corn issues

In light of the past few seasons, and the predictions of several climatologists, you may want to consider choosing hybrids with good drought tolerance. Several researchers have shown that late-summer drought conditions increase yield losses more in corn on corn compared to corn on beans. Work with your local dealer to choose the right hybrids for corn on corn, based on stress emergence, high residue/cool wet soil tolerance, stalk and root strength, leaf and stalk disease resistance, seedling disease resistance to name a few.

Most major seed companies have a pretty good scoring system that can utilize to help you select corn hybrids to plant.

In general, corn on corn will require more nitrogen. The last several seasons, with the N prices at or near record highs, this has been a larger factor for farmers to consider in comparing cost/benefit analysis of our rotation options than in the past. While overall the cost impact is small in comparison to overall production costs, you have to factor it in.

A quick estimate is that at 120 pounds of N for corn on beans, compared to around 180 pounds for corn on corn, the increased costs are roughly $14 to $15 per acre.

Can you afford to plant corn-on-corn?

"I agree with what many farmers are thinking, if we manage our agronomics and marketing well, the increased N costs aren't much of a factor," says Clarke McGrath, an ISU Extension crop specialist at Harlan, Iowa.

Another interesting point: Research from Minnesota done by Randall and Vetsch showed that corn on corn fertilized with manure as an N source yielded better than corn on corn with commercial fertilizer. While not a huge bump, it was significant, so if you have manure to apply, you should think about putting it on your corn-on-corn acres, advises McGrath.

Also it is imperative to have your P, K and pH levels at optimum for corn on corn as well, notes McGrath. Work with your fertilizer dealer to help you choose the better fertility fields for corn on corn. Or soil test and bring up the low testing fields by applying fertilizer or manure before heading into corn on corn.

Rootworm control is very critical

Rootworm control is a must with corn on corn. You have several choices here; granular insecticides, liquids, insecticide seed treatments and the new biotech rootworm resistance events. "I think we can all agree that for the nonrefuge acres, a resistance event is the top choice," says Virgil Schmitt, an ISU Extension crop specialist at Muscatine, Iowa.

A few things to remember are the rootworm resistance does not cover the secondary pests that many insecticides do, so be sure a seed treatment is included on the seed you buy. It usually is, but be sure to ask, or else have another plan to control secondary insects on corn. Also, be aware of any marketing challenges associated with the rootworm resistant corn.

"You have three events to choose from for 2007, all look very effective," notes Schmitt. "I wish I had a better answer for you on refuge acres than applying granular insecticides to the soil or using the insecticide seed treatments. But we don't. There are some differences in performance of insecticides. Ask your dealer or ISU area crop specialist for advice."

Increased disease pressure with corn on corn

Farmers typically face higher disease pressure in corn on corn. Gray Leaf Spot, Pythium, Diplodia, Anthracnose as well as several other diseases tend to cause more problems in corn on corn, so choose hybrids with disease ratings that will give you good protection against at least these diseases, says Schmitt.

Some research indicates that tillage may help reduce the levels of these pathogens by reducing the amount of "trash" on the soil surface, which is a host for many of our crop diseases. But how does tillage fit in with your current soil management program, and your soil conservation plan?

Much research has been done on comparing the yield of corn on corn to corn on beans. "The consensus is that we suffer a 10% to 15% yield loss when we plant corn back into corn compared to a corn/bean rotation, with higher losses in "stress" years. But this may depend on the yield level of your field," says John Holmes, ISU area crop specialist at Clarion, Iowa.

Some work in Minnesota--a four-year study looking at field yield levels and the yield advantage to rotating corn/beans compared to corn/corn—shows the following.

Average Field Yield Advantage for Corn/Bean
Yield Level Rotation Over Corn on Corn
110 bu/acre 32 bu/a
120         17
140         24
155         25
165         12
180         5
200         5

So, if you are thinking about planting corn on corn, this work may persuade you to plant corn on corn on the better yielding fields, and rotate crops on fields with traditionally lower yields.

How to handle increased crop residue

Planter performance will need to be more closely monitored in corn on corn. The increased levels of trash and "root balls" will make managing planting depth, seed spacing, and seed-to-soil contact challenging. Uneven distribution of heavy corn residues often leads to variable soil temperature and moisture levels, which can lead to uneven emergence.

In looking at seed company and university research, uneven plant spacing and emergence has been shown to combine for yield losses as great as 7 to 15 bushels per acre according to some work. Proper planter care and field by field adjustment can minimize these issues. A great paper pertaining to this issue can be found at www.agry.purdue.edu/ext/pubs/AGRY-91-01_v5.pdf.  

"I have worked with a wide array of seed firmers, many coulter systems, spade closers, toothed closers, single vs. double closers, crowfoot closers, smaller inside diameter gauge wheels, many trash whippers, and a bunch of other stuff I have forgotten about," says McGrath. "Most of the time, the grower who had them made them work pretty well under good conditions. A common theme was that not much worked when the soil was wet."

It is easy this time of year to say something like "plant only when soil conditions are dry enough to prevent sidewall compaction and/or soil buildup/movement by coulters and gauge wheels." In reality, there is no easy answer. Some growers plant corn on cornfields after corn on beans, so soils have a chance to warm up. Some growers plant non-HEL soils to corn on corn and use a tillage program. Some find other ways to deal with these issues. Talk to local growers who are successfully raising corn on corn and see if they have some useful tips to share.

Weed control is more challenging

Weed control is usually more challenging in corn on corn. "My recommendation is almost always some type of residual herbicide applied slightly ahead or after planting, followed by scouting and a post-emerge application based on what is in the field and what is expected to possibly emerge in the near future," says McGrath.

"Several Midwest researchers have shown that two-pass corn programs consistently give better weed control and higher yields than one-pass programs. I am not a big fan of one-pass programs, especially in corn on corn, so to get another opinion, ask your local dealer as well," he advises.

Soil management, nitrogen issues

If possible, choose soils with good structure and be careful to avoid compaction when planting corn on corn. While there are varying opinions on tillage programs and no-till, whatever system you run with, it appears to be important to clear trash from the row area. "ISU is doing some large tillage studies for corn-on-corn systems at the research farms across the state; we hope to have good data to share in the near future," says Holmes.

There is much interest among farmers in applying low rates of fall surface applied N to help speed the breakdown of cornstalk residues. "Right now, we have no conclusive data on this practice," says McGrath. "But we are working with several retailers across the state to implement trials looking at different ways of doing it."

He adds, "While I wouldn't recommend doing it field wide yet, it would be great if farmers want to run some side-by-side comparisons this fall. The majority of the farmers running them this fall are looking at comparing three or four sprayer wide strips of around 20 pounds of liquid N compared to untreated strips, randomly run across the field. Yield monitor data will give us some idea of the benefits of this practice. We are trying to run the same sets of strips over multiple years to see if there is a cumulative yield effect for doing this."

On the flip side - other considerations

Farmers know that corn on corn takes a different type of management than corn on beans, and many agronomists and growers would say a lot higher degree of management. "But, when we look at our rotation options, recently soybeans have not been the piece of cake they used to be, either," says McGrath. Some issues with soybeans are:

* Aphids. Most entomologists concur that we will be fighting this pest in the Midwest on a consistent basis. Yield losses from not treating, or costs of scouting and treating, can take income off the bottom line and in some operations narrow the income gap when compared to corn on corn. True, resistant beans are in the pipeline, but will not be available for farmers to plant for at least a couple years from now.
* Bean Leaf Beetles. This pest has been problematic the last several seasons, and may continue to impact yields in the Midwest.
* Diseases. Charcoal rot, brown stem rot, sudden death, bean pod mottle virus have been problematic for many growers in Iowa the past few years. Depending on weather conditions, these pathogens can flare up and cost you yield.

"Luckily Asian soybean rust has not been a factor in the Midwest yet and we hope it stays that way," says Schmitt. "The rapid movement of rust over the last few weeks (79 counties in seven states with new finds since Oct. 9) gives an indication of the speed with which it could become an issue in the Midwest, though."

Good luck sorting out all the agronomic information about corn on corn. "You need to analyze the government program and crop insurance issues, input costs, output per acre, and match your abilities and fields to the crop rotation that will make you the most money," says McGrath. "If I missed a corn-on-corn issue you have questions about, let me know and we can work on it."