Corn planting progress ground to a halt again in late May with 85% of Iowa's corn planted—15% of the acres unplanted. Rain continued to hamper planting progress the following week too. As of June 2 there was still 12% of the state's corn acres that remained unplanted, according to the weekly USDA survey. And water was ponding in fields across the state. Some of the corn in these flooded fields will need to be replanted.

SORT OUT YOUR OTIONS: Farmers must make accurate late-planting and replanting decisions by carefully evaluating the situation in terms of projected yields and profitability. It's been a soggy spring in Iowa and now we're into the first week of June and there's still some corn acres to be planted—and many fields and parts of fields that will need to be replanted.

There are crop insurance concerns and economic concerns regarding crop insurance and delayed planting and prevented planting. The bottom line: talk to your insurance agent and analyze various options using spreadsheets at the Ag Decision Maker website. Planting other crops—such as soybeans--may be an option. However, either nitrogen or herbicides already applied to some fields may eliminate the possibility of planting of other crops. Thus, many farmers still want to plant corn—even though it's already the first week of June.

Roger Elmore, Iowa State University Extension corn agronomist, provides the following observations regarding yield potential, hybrid maturity and other information to help you make the right decision for your situation.

When should I change to earlier maturing corn hybrids?

Agronomic questions need answered in order to generate options, says Elmore. From the corn perspective, two issues come to mind that revolve around a central question: When should I change hybrids? Extension agronomists often counsel farmers not to change locally adapted hybrids for earlier-season hybrids until late May. With later planting, the potential to get caught by frost before the grain reaches maturity in the fall increases with full-season hybrids. "It is for that reason that we need to consider planting earlier-season hybrids," he notes.~~~PAGE_BREAK_HERE~~~

With the rain already received and more in the forecast, farmers likely won't be in the field for several more days. Should they consider planting shorter-season hybrids then?

Modeling methods can help answer corn hybrid maturity question

In a separate article (See Part 2, following this article) Elmore addresses the hybrid-change question using actual 2010 and 2011 data generated from four ISU Research & Demonstration Farms (Northwest, Northeast, Central and Southeast Iowa). In this article, he discusses the question using simulations from the corn model Hybrid-Maize. He used the computer model to predict maturity dates, yield and frost potential at maturity for the same four ISU Research and Development Farms and the same planting dates which he will talk about in the next article.

"The crop model helps us better understand the interaction between management, genetics and weather," he says. "Its strength lies in that it allows us to simulate the same management – such as planting date, plant population, etc. - and hybrid maturities across several years." See the results in Table 1 at the end of this article--weather is the only variable that changes across the years. The weather data base used varies at each location but at all locations included here goes back to the mid-to-late 1980's (see Table 2). The model estimates maturity dates, frost potential, and yields given the weather conditions experienced in previous years through 2012. It assumes that there are no other limiting factors like diseases, insects, low N availability, etc.

Table 1 shows the common model input factors across all locations and years. Table 2 displays information on the hybrids and locations where they were modeled. Maturity, frost risk and yield predictions follow in Table 3 for the four locations based on actual weather form the mid- to late 1980's through the 2012 cropping season.

Fuller season hybrids take longer to mature and are more prone to risk of early fall frost

Results and discussion: Results of the computer model simulations are shown in Table 3. Among hybrids, fuller-season hybrids as expected take longer to mature, are more prone to late-season frost, but when planted at the earliest planting date, yield as well as the two mid-season hybrids. Within hybrids, as planting delays occur at each location, R6 date – physiological maturity – is delayed and the risk of a frost before maturity increases.~~~PAGE_BREAK_HERE~~~

If planting at the middle planting date, June 11, the two earliest-season hybrids yield the best at the two northern locations; of course frost risk is higher with the 93 day hybrid than the 83 day hybrid at those locations when planted on June 11. For the Central location planted on June 11, the three earliest hybrids outperform the latest hybrid (112d) with the least frost risk (33 percent, with the earliest hybrid (93d)). At the Southeast location, all four hybrids had similar simulated yields when planted on June 11; of course higher frost risks are associated with the later-maturing hybrids. With the last planting date, June 25, the earliest hybrid had the highest simulated yield at all locations. However, at the northern locations, frost risk was at or near 100% even with the earliest-season hybrid (83d).

Summary of what we learned and what you need to know to make a sound decision

Conclusion: Decisions to plant corn late or replant are never easy. A checklist for replanting is included on the ISU agronomy corn production website. As mentioned above, Part 2 (the article that follows this one) looks at the same question using actual field data. In that article, we also compare and contrast the two approaches. The crop-model simulation discussed in this article summarizes average simulated hybrid responses with a weather data base going back to the mid to late 1980's. Certainly the data are most useful in estimating maturity dates and frost potentials on those dates.

Part 2: Late Planting and Replanting Corn—June 2013

Producers must make accurate late-planting and replanting decisions by carefully evaluating the situation in terms of projected yields and profitability.~~~PAGE_BREAK_HERE~~~

* For planted fields, one must ascertain populations of emerged plants. Replant tools (replant checklist) are available for this decision. Corn will withstand two-days of submersion (Corn survival in flooded or saturated soils), so digging plants to check their viability is important too.

* For unplanted fields and replanting corn, yield projections for late planting will help estimate returns. Hybrid maturity choice also becomes important when planting in June. Full-season hybrids take longer to mature and are thus more likely impacted by fall frost events. The companion article (Part 1) addressed frost risk inherent with different hybrid maturities using a crop model and provides yield estimates based on long-term weather records. Some may be able to plant soybeans rather than corn and others may choose the 'prevented planting' option of their crop insurance policy (see Johnson and Edwards ICM article). In any case, discuss your options with insurance agents before proceeding on any course of action.

Re-planting the current crop is often an option, but there are several considerations

Re-plant decisions require extensive management skill. In considering replanting, producers must evaluate replant costs, risks and returns against the current crop's predicted yield. Evaluation of weather patterns and weather predictions for the area, time available, available hybrids, additional fertilizer/herbicide/seed costs, and market trends all must be factored into the decision.

Understanding how hybrids respond to different planting dates is crucial to ensuring optimum yields and maximum profitability in re-plant situations. This report summarizes 2010 and 2011 field research studies aimed to provide producers with more accurate recommendations in corn re-plant situations. We evaluated how commonly-used relative maturity or RM corn hybrids responded to a range of re-plant/late-planting dates. We included four corn hybrids ranging in their RM at four Iowa locations.

Methods: Multi-year (2010, 2011) and multi-location (four ISU Farms) research was conducted, compiled and analyzed for a total of eight site-years of data. Each site-year incorporated at least four replications and five planting dates ranging from April 30 to June 25 in approximately 14-day increments. Hybrids planted at the two northern locations ranged in RM from 83 to 105 days; those at the Central and SE locations ranged from 93 to 112 day RM. These were hybrids with the same RM – with the same Growing Degree Units – used in the companion article with the crop model.

Results and Discussion: Data from the four locations are shown in Tables 1 to 4. Dates of first 28 degree F at locations near the experimental sites varied with location and year (Table 5).~~~PAGE_BREAK_HERE~~~

* Grain moisture content: As expected, grain moisture content at harvest in general was greater with longer season hybrids and increased with delayed planting at all four locations. Hybrids responded differently at the different planting dates at the Northwest, Northeast and Central locations. These differences – technically known as interactions – were due to the wider spread in grain moisture among hybrids with later planting. This did not happen at the Southeast location because of a smaller range in moisture content among hybrids especially at the later planting dates. Thus the over-date averages for hybrids explain responses at Southeast best; likewise, at Southeast the over-hybrid averages best represent moisture contents at the different planting dates.

* Grain yield: Grain yields were greater with earlier planting dates at all four locations. Fuller- season hybrids yielded as well or more than earlier-season hybrids at all locations. However, at the Northwest and Northeast locations, hybrids responded differently at the different planting dates. These differences – interactions – appear to be related to a wider yield spread among hybrids at the earlier planting dates than with later planting dates. At both the Central and Southeast locations, hybrids responded the similarly at all planting dates. Thus, at those locations, hybrid responses are best interpreted when averaged over planting dates, and planting date means are best understood when averaged over hybrids.

Actual 2010 and 2011 data compared to modeled data: Table 5 presents a comparison of potential yield losses derived from the work reported in this article and that reported in the companion article using modeled data. Similar trends occur between the two different approaches. The differences between them are likely due in part to the two year data included in the 'Actual' columns and the multiple year data included in the 'modeled' columns.

To summarize Table 5 we could say that:

Acknowledgements: Roger Elmore and his graduate students Anthony Myers and Warren Pierson thank the following ISU farm personnel who established and maintained these research trials: Mike Fiscus, Ken Pecinovsky, Ryan Rusk, and Kevin Van Dee. In addition thanks go to Stephanie Marlay and Lori Abendroth who helped coordinate this research project.