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6/3/2013 - 6/9/2013

2013 Weed Science Field Day Cancelled

By Mike Owen, Department of Agronomy

The Iowa State University Weed Science Field Day scheduled for June 27 has been cancelled.

As you are likely aware, the anticipated drought for 2013 has evaporated.  Unfortunately, the rain that restored the water table has put planting in Iowa behind. There is still considerable acreage of corn and soybean that has yet to be planted across the state and Central Iowa likely represents the worst case. Records for the amount of rain in a spring and in May have been broken this year and the accumulation of growing degree days lags far behind the normal situation. 

With regard to the Iowa State University Weed Science program, most of the corn trials have been established at the Curtiss Farm in Ames but there are still many that have yet to be planted. Similarly, we have not been able to plant any soybean trials yet this year at the Curtiss Farm. Given the rain we received overnight, it is unlikely that even with the best of drying conditions, we will be back in the field by June 12. 

It is suggested that most plots may be at an appropriate stage of development for viewing by the second week of July. Some of the earlier corn trials might be a bit beyond prime time, so two trips may be necessary to view all experiments at the best time. 

We will make field books available after June 27; they can be picked up at the Curtiss Farm Pesticide Mixing Facility on South State Street in Ames. Experiments will be labeled and a map with directions to the field locations will be included in the field book. If you make arrangements in advance, someone will be available to take you to the field. 

I apologize for this decision but I feel that it would be a waste of everyone’s time to attend an event on June 27. If you have questions, please do not hesitate to contact me at (515) 294-5936 or

SCN Females Already Seen on Soybean Roots

By Greg Tylka, Department of Pathology and Microbiology

The soybean cyst nematode (SCN) is one of the most damaging pests of soybean in Iowa and the Midwest. SCN can cause foliar symptoms of soybean sudden death syndrome (SDS) to occur earlier in the season and to become more severe, leading to increased yield losses from the disease.

SCN females on roots marks end of first generation

The appearance of SCN females on the roots of soybean plants usually occurs five or six weeks after planting in Iowa and represents completion of the first of multiple generations of the nematode in a growing season. 

On Sunday, June 2, Tom Hillyer of Hillyer AgriServices in West Liberty, Iowa, observed emerging SCN females (see figure) on roots of susceptible soybeans that were planted on May 8. These soybeans were only in the V2 stage of development when the SCN females were observed. 

Increased early SCN activity troublesome

It is unusual for SCN females to be evident on soybean roots so early in the growing season. Increased early activity of SCN is problematic because yield loss from SCN is directly related to their population densities in the soil, and SCN numbers may increase more if the generation time is shortened because more generations can occur in a growing season. 

It has been reported that the wet spring weather may have resulted in an increase in the root rot phase of SDS for soybeans that were planted already this year (see June 4 ICM News article). The early appearance of SCN females on soybean roots, indicating increased early season SCN activity, also may increase the risk of severe symptoms of the foliar phase of SDS later this growing season.

Manage SCN for direct and possible indirect benefits

Managing SCN will reduce yield loss by lessening direct damage from the nematode and indirectly by possibly lessening the effect of SCN on SDS foliar symptoms. Management options for SCN include use of resistant soybean varieties and nematode-protectant seed treatments and growing nonhost crops such as corn in a rotation with soybeans.


Figure 1. Emerging soybean cyst nematode females (blue arrows) on susceptible soybean roots planted 26 days earlier.
(Photo by Tom Hillyer)


Greg Tylka is a professor with extension and research responsibilities in management of plant-parasitic nematodes in the Department of Plant Pathology and Microbiology at Iowa State University. He can be reached at or 515-294-3021.

Is it Palmer Amaranth?

By Bob Hartzler and Mike Owen, Department of Agronomy

Numerous weedy species in the pigweed family (Amaranthaceae) are found across Iowa, including waterhemp, redroot pigweed, smooth pigweed, Powell amaranth and others. At this time, Palmer amaranth has not been confirmed in the state, but because of its presence in surrounding states we suspect it may be here, or will appear in the near future (see April 24 ICM article).

Identifying infestations of Palmer amaranth when they first get started is the key to preventing its spread in Iowa. It is difficult to differentiate vegetative plants of waterhemp and Palmer amaranth. Both have glabrous (hairless) stems and both species have variable leaf shapes. 

Purdue University recently published an article and video providing information on differentiating Palmer amaranth and waterhemp. They state that Palmer amaranth frequently has a single hair in the notch found at the leaf tip, and that this trait is a reliable way to differentiate the two species. We have examined waterhemp plants and photos of waterhemp, and find that this hair is commonly present on waterhemp in Iowa. Thus, we do not recommend this as a trait for differentiating the two species.

Palmer amaranth frequently (but not always) produces leaves with a petiole much longer than the leaf blade. This probably is one of the most consistent vegetative traits for separating the two species but it also is variable. Plants with inflorescences present are best to identify and confirm the Amaranthus species.

We are willing to aid in identifying any plants suspected of being Palmer amaranth. In most cases, digital images will be insufficient to differentiate vegetative Palmer amaranth and waterhemp. Contact us via e-mail or phone to determine how to proceed in confirming the identification of any suspected Palmer amaranth.


Bob Hartzler and Micheal Owen are professors of agronomy and weed science extension specialists with responsibilities in weed management and herbicide use. Hartzler can be reached at or 515-294-1164. Owen can be reached at or 515-294-5936.

Sudden Death Syndrome and Heavy Spring Rains: Another Bad Year?

By Daren Mueller and Leonor Leandro, Department of Plant Pathology and Microbiology

Soybean sudden death syndrome (SDS) is one of the most damaging diseases of soybeans in Iowa and much of the Midwest. There are two phases of this disease – a root rot phase and a foliar symptom phase. SDS will be most problematic when weather conditions are conducive for disease development during both phases. The early cool, wet weather we have seen so far in 2013 helps increase the root rot phase of the disease. This can lead to development of severe SDS later in the growing season, as was seen in 2010 in Iowa.

In a recently published journal article, several plant pathologists at Iowa State University looked at rainfall, soil moisture and soil temperature in years with SDS (e.g., 2010) vs. years with little SDS (e.g., 2011). In this study, rainfall in April and May was similar in “SDS years” to “non-SDS years.” However, rainfall in June and July differed between disease years and non-disease years (Table 1). This highlights the importance of rainfall a bit later in the season to trigger the second phase of the disease. Also, soil temperature was less correlated to SDS severity compared to rainfall. The entire article is available in the Plant Health Progress Journal on the Plant Management Network.

Table 1. Average total precipitation in four years with high SDS prevalence (1993, 1998, 2008, and 2010) and five years with low SDS prevalence (2001, 2004, 2005, 2007, and 2011). Values are means of two locations: Ames (central Iowa) and Mount Pleasant (southeastern Iowa).

One bit of good news for the 2013 season is that severe SDS usually is associated with early planting of soybeans. As many farmers are experiencing, the wet spring weather has delayed planting throughout the state. Fields with delayed planting should have less SDS develop in them. However, we have found research plots planted as late as June 15 still get SDS, so you are not completely out of the woods. SDS severity in these late planted fields is very low, and much lower than fields planted in May.


Daren Mueller is an assistant professor in the Department of Plant Pathology and Microbiology. He can be reached at 515-460-8000 or e-mail Leonor Leandro is an Associate professor in the Department of Plant Pathology and Microbiology.

Agricultural Health Study Participants Encouraged to Respond

By Betsy Buffington, Department of Entomology

Be a part of important research about the health of farmers and their spouses by completing the Agricultural Health Study (AHS) survey.  The health follow up will be mailed starting in June 2013 to all AHS participants. Over 40,000 people completed the last interview, and the study investigators would like even more to participate this time around. 

The more people who complete it, the better the AHS can do at understanding the risks and benefits to all farming families. To have complete records on everyone, study investigators are trying to follow up on all participants, including those who have passed away.  Study investigators want to hear from everyone, even if you are no longer farming. Keep an eye on your mailbox! When you receive your survey, please return it as soon as possible. If you have any questions, please contact the Health Follow up Survey Center by calling 1-855-443-2692 or visit the survey website

The AHS is a large, long-term study of farm families and commercial pesticide applicators. The study includes 89,658 enrollees from Iowa and North Carolina. Enrollment began in 1993. Data is now being analyzed to assess links between agricultural practices including pesticide use and cancer risk. Many other health effects are also being studied including respiratory and reproductive health and diseases of the nervous system. To learn more about the AHS and its findings, please visit

Betsy Buffington is a program specialist on the Pest Management and the Environment team. She can be reached at or 515-294-7293.

Flooding Impact and Crop Insurance Frequently Asked Questions

The frequent rains that have soaked Iowa this year have left many corn and soybean fields unplanted or with flooded areas. Many producers are wondering what options they have under their multiple peril crop insurance (MPCI) policies.

Fortunately, over 90 percent of the insured corn and soybean acres in Iowa are covered by MPCI, which includes replant, delay and prevented planting coverage.

Q: What should a producer do if their planted crops are affected by the flooding?

A. Notify their crop insurance agent within 72 hours of the loss. If they qualify, the replant option provides a payment reflecting 8 bushels of corn or 3 bushels of soybeans per acre times the projected price of $5.65 per bushel corn and $12.87 per bushel soybeans, respectively. So replant will provide about $45 per acre for corn and over $38 per acre for soybeans in 2013.

Q: What if a producer didn’t have their crops planted yet, what are the late planting dates in Iowa?

A. May 31 – Final planting date for Corn
June 15  – Final planting date for Soybeans

In Iowa, the crop insurance “late planting period” for corn begins on June 1. Corn can still be planted after this date, but the insurance guarantee on those acres is reduced by 1 percent per day until they are planted.  Corn acres planted after June 25 will receive insurance coverage equal to 60 percent of their original guarantee. Producers should keep accurate records of planting dates on all remaining acres. The late planting period for soybeans in Iowa is from June 16 through July 10.

Beginning June 1, corn producers with unplanted acres have three choices: plant corn as soon as possible with a reduced guarantee, shift to soybeans with full insurance coverage, or apply for prevented planting. Prevented planting acres are insured at 60 percent of their original guarantee. Those acres may have a cover crop established on them or may be left idle (black dirt).

Q: Isn’t there a 20-20 rule for coverage?

A. Yes, to qualify for an indemnity payment under the replanted, delayed or prevented planting provisions, a minimum area of 20 acres or 20 percent of the insured unit, whichever is smaller, must be affected.

A unit could be a field or a farm – if you elected an optional whole farm or basic unit. An enterprise unit could also have been elected. This choice reflects the insured's corn acres combined in a particular county to determine loss or their soybean acres. 

Q: I chose enterprise units to save on premium. Can I now change to basic or optional units because flooding has damaged my planted crop acreage?

A: Because unit structure impacts the premium cost, and in the case of enterprise units, also the premium subsidy, the policyholder’s decision to elect enterprise units is made no later than the sales closing date to reflect the binding contractual agreement between the two parties on or before March 15, 2013. Changing the enterprise unit structure would be a contractual violation between the approved insurance providers and the policyholder, and leave the government vulnerable to a breach of contract. Therefore, any change to the contract at this time shifts risk to approved insurance providers from previously negotiated financial commitments within the terms and conditions of the Standard Reinsurance Agreement.

Q: If I am physically unable to get to a field for planting am I covered by prevented planting?

A: Prevented planting payments can be made if an insured cause of loss resulted in there being NO way into a field that otherwise could be planted. These types of cases are expected to be very limited. If there is ANY way into the field, even if it means the producer has to drive out of the way to reach the acreage, then the producer would be expected to do so if the field was dry enough to plant. Prevented planting payments would not be made if there was any access to the acreage. Producers, however, are not expected to go to extreme measures like airlifting equipment into a field.

Q: If I am prevented from planting by the final planting date, what are my choices under the terms of my policy provided I meet all other policy provisions and I do not qualify for double cropping?

A: You may

  • Plant the insured crop during the late planting period, if applicable, and insurance coverage will be provided. The late planting period is generally 25 days after the final planting date but varies by crop and area. For most crops, the production guarantee is reduced 1 percent per day for each day planting is delayed after the final planting date.
  • Plant the insured crop after the late planting period (or after the final planting date if a late planting period is not applicable), and insurance coverage will be provided. The insurance guarantee will be the same as the insurance guarantee provided for prevented planting coverage.
  • Leave the acreage idle (black dirt) and receive a full prevented planting payment.
  • Plant a cover crop and receive a full prevented planting payment provided the cover crop is not hayed or grazed before Nov. 1, or otherwise harvested at any time. If the cover crop is hayed or grazed before Nov. 1, the prevented planting payment on the first crop is reduced to 35 percent of the first crop prevented planting guarantee.
  • Plant another crop (second crop) after the late planting period, or after the final planting date if no late planting period is applicable, and receive a prevented planting payment equal to 35 percent of the prevented planting guarantee.

Q: If my first insured crop was planted and failed, what are my choices under the terms of my policy provided I meet all other policy provisions and I do not qualify for double cropping?

A: Several choices under what is called “first crop-second crop coverage.”

  1. If it is not practical to replant the first insured crop:
    • The acreage may be left idle (black dirt), or planted to a second crop and not insured, and receive a full indemnity for the first insured crop;
    • Plant and insure a second crop and receive a 65 percent reduction in indemnity for the first insured crop – the policyholder pays 35 percent of the premium for the first insured crop;
      • If there is not a loss on the second crop, the policyholder will receive the remaining 65 percent of indemnity on the first insured crop and pay the full premium on the first insured crop; or
      • If the second crop receives an indemnity, the first crop indemnity remains at 35 percent and the second crop indemnity is fully paid (no reduction). The policyholder may choose to not accept the second crop indemnity and receive a full indemnity on the first insured crop.
  2. If it is practical to replant the first insured crop and it is not replanted, no coverage for the first insured crop will be provided.
  3. If it is practical to replant the first insured crop and the first insured crop is replanted, a replanting payment will be made and coverage for the first insured crop will remain at the production guarantee.

ISU Extension Resources
More details can be found in the ISU Extension publication “Delayed and Prevented Planting Provisions,” file A1-57 on the Iowa State University Extension and Outreach Ag Decision Maker website, at

An electronic decision spreadsheet is also available to help analyze alternative actions.  Producers should communicate with their crop insurance agent before making decisions about replanting or abandoning acres.

Additional flood recovery resources are available from ISU Extension and Outreach at Dealing with Flooding - 2013.

CCA Credit Opportunity – June 27

By Jim Fawcett, Extension Field Agronomist

Certified crop advisers (CCAs) can earn five hours of credit (3.0 hours in soil and water management, 1.0 in crop management, 0.5 in pest management and 0.5 in nutrient management) by attending a special CCA morning session, followed by the afternoon spring field day tour at the Southeast Iowa Research and Demonstration Farm near Crawfordsville on June 27.

The morning session will begin at 9 a.m. with a presentation by Mark Carlton, extension field agronomist with Iowa State University, on “Cover Crops – What Are Your Goals?” Also in the morning will be a presentation on “What You Should Know About Corn Suitability Rating 2” by Lee Burras, Iowa State agronomy professor, and will conclude with a presentation by John Sawyer, agronomy professor at Iowa State University with extension and research responsibilities in soil fertility, on “How Can We Meet the Nitrogen Goals of the Nutrient Reduction Strategy?”

Topics covered on the afternoon tour will include: Crop Season Review by Myron Rees, farm superintendent; Crop Weather Outlook and How New Weather Stations Will Benefit Iowa Farmers by Virgil Schmitt, ISU extension field agronomist; Managing Nitrogen in Corn After a Rye Cover Crop by John Sawyer, ISU extension agronomist – soil fertility; and Managing Glyphosate Tolerant Waterhemp in Soybeans by Jim Fawcett, ISU extension field agronomist. Tours will begin at 1 p.m.

Registration for CCAs will begin at 8:30 a.m. The registration fee is $50, which includes lunch. Pre-registration is required. Please pre-register by calling the Johnson County Extension Office at (319) 337-2145 or send an e-mail note to Jim Fawcett at by June 25.  The registration fee (cash or check) can be paid at the door. To reach the research farm go 1 3/4 miles south of Crawfordsville on Highway 218, then 2 miles east on G-62, then 3/4 mile north.


Jim Fawcett is a field agronomist with Iowa State University Extension and Outreach serving eastern Iowa.

Late Planting and Replanting Corn - June 2013 (Part 2)

Part 2: 2010 and 2011 Field Research Data

By Roger Elmore, Anthony Myers, and Warren Pierson, Graduate Research Assistants Department of Agronomy

Fifteen percent of Iowa’s 2013 corn crop remains unplanted as we write the last week of May. After early concerns about drought continuing to plague us, wet conditions have taken the spotlight. To add insult to injury, more rainfall forecast may refill field ‘ponds’ and re-submerge corn in flood plains of our rivers and streams.

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

  • 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. 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 (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.

Multi-year (2010, 2011) and multi-location (four Iowa State University Research and Demonstration 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 inTables 1-4.  Dates of first 28 degree F at locations near the experimental sites varied with location and year (Table 5). (Scroll through the entire PDF file to see all five tables.)

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 NW, NE 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 SE 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 SE best; likewise, at SE 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 NW and NE 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 SE locations, hybrids responded 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:

  • Yield losses associated with delayed planting are greater at NW and NE than at the other two more southern locations.
  • If planting occurs on or before June 11:
    • Northern locations: yields could range from about 80 to 85 percent of  May 28 yields.
    • Central and SE locations: yields could range from about 85 to 95 percent of May 28 yields.
    • Using the ‘actual’ data only, yield on or before June 11 was about 70 to 80 percent at the Northern locations, and 88 to 96 percent at the southern locations compared to those of April 30 yields.
  • If planting occurs near the end of June (based on Table 5):
    •  Northern locations: yields could range from about 50 to 60 percent of  May 28 yields.
    • Central and SE locations: yields could range from about 55 to 85 percent of May 28 yields.
    • Using the ‘actual’ data only, yield  before the end of June was about 50 percent at the Northern locations, and 70 to 85 percent at the southern locations compared to those of April 30 yields.
  • Data from the actual 2010 and 2011 replant studies consistently show less percentage yield losses with delayed planting than those of the crop simulation model. However, 2010 and 2011 may not have been average years and may have provided distinct advantages for later planted crops. The crop simulation model uses weather data from the mid to late 1980’s to 2012 and the output reports ‘average’ year performance in this situation. 

The tables in this report and the companion article should serve as a guide for producers when making late-plant and replant decisions. Producers must consider weather predictions for the area, time available, available hybrids, additional fertilizer/herbicide/seed costs, and market trends plus the data observed here. Only after all other economic variables have been considered should producers utilize the values within this report to estimate likely yields in similar situations.

For more detailed information
Some of the information in this report for the NW, NE, and SE locations was previously reported in the following Research and Demonstration Farm annual reports.  More details on plot layout and experimental procedures are included there if you are interested. Central Iowa data has not been reported previously.

We thank the following Iowa State University farm personnel who established and maintained these research trials: Mike Fiscus, Ken Pecinovsky, Ryan Rusk, and Kevin Van Dee. In addition we thank Stephanie Marlay, who helped coordinate this research project, and  Lori Abendroth, who designed the study and developed the experimental protocol.


Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at or (515) 294-6655.

Late Planting and Replanting Corn - June 2013

Part 1: Crop Model Output

By Roger Elmore, Department of Agronomy

Corn planting progress ground to a halt again in late May with 85 percent of Iowa’s corn planted (USDA-NASS). Fifteen percent of our corn acres remain unplanted for the first time, and as water sits in ponds across the state, some of the planted corn may need replanted (see article about flooded corn).  Last week Steve Johnson and William Edwards provided ideas on crop insurance concerns relative to delayed and prevented planting, and replanting (ICM News). Their bottom line: talk to your insurance agent and analyze various options using spreadsheets at the Ag Decision Maker website. Planting other crops may be an option. However, either nitrogen or herbicides already applied to some fields may eliminate the possibility of planting of other crop.

When should I change to earlier maturing hybrids? 
Agronomic questions need answered in order to generate options. 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 hybrids for earlier-season hybrids until late May (see ICM article). Frost potential increases before maturity of full-season hybrids with later planting. It is for that reason that we need to consider planting earlier-season hybrids.

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

Modeling Methods
In a separate article (Part 2) we will address the hybrid-change question using actual 2010 and 2011 data generated from four ISU Research & Demonstration Farms (NW, NE, Central and SE). Here I discuss the question using simulations from the corn model Hybrid-Maize. I used the model to predict maturity dates, yield and frost potential at maturity for the same four Iowa State University Research and Development Farms and the same planting dates we’ll talk about in the next article.

The crop model helps us better understand the interaction between management, genetics and weather. Its strength lies in that it allows us to simulate the same management – e.g. planting date, plant population, etc. - and hybrid maturities across several years (Table 1); 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 (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.  

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. 

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 SE 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 percent even with the earliest-season hybrid (83d).

Summary of Modeling Approach

  • Full-season hybrids planted in June will encounter high probabilities of frost damage before maturity.
  • Earlier hybrids perform as well or better than full-season hybrids when planted late at all locations.
  • Late-planting of full-season hybrids carries more risk and lower yield potentials than earlier-season hybrids especially at the northern locations.

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 in this series will look at the same question using actual field data. In that article, we will 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. 


Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at or (515) 294-6655.

Soil Profile Nitrate – Spring 2013 Sampling Summary

By John Sawyer, Department of Agronomy

I wrote an ICM News article this spring (Soil Profile Nitrate in Corn Fields Following the 2012 Drought) summarizing the fall soil profile residual nitrate-N from 2012 drought affect corn fields. The same field areas were sampled again this spring before planting. As mentioned in an earlier ICM News article (Wet Conditions and Change in Soil Profile Nitrate), the amount of nitrate-N in the soil profile has changed with the wet conditions this spring.

Following was the procedure used to collect samples and summarize the results. After harvest last fall, Iowa State University Extension Field Agronomists, ISU FARM specialists, and staff in our research group collected profile soil samples from 38 field sites, and resampled 35 of those sites again this spring. Most of the fields were on-farm, with some samples collected from a research study conducted at several ISU Research Farms. Samples were collected by one-foot increments to either a two foot or three foot depth. Samples were analyzed for nitrate-N concentration by depth, with concentration converted to pounds nitrate-N/acre amount (lab analysis ppm x 4 = lb nitrate-N/acre). The amount in the profile sample was then summed across the depths sampled.

Soil Profile Nitrate Summary
The amount of profile nitrate-N has decreased from the fall amounts due to the spring rainfall (Table 1). Unfortunately the wet weather and decrease in profile nitrate is what we were worried about. Based on common sites sampled last fall and again this spring, and with the same sample depths, the reduction in profile nitrate-N was 54 lb/acre for the 0-2 foot depth and 27 lb/acre for the 0-3 foot depth. Since these amounts are from a different total number of sites, one cannot compare the change between the two depths. Also, individual sites had quite different amounts of profile nitrate-N, and changes from fall to spring sampling (examples in the 5/6/2013 ICM News article). Fig. 1 shows that about forty percent of the field sites sampled this spring had more than normal background profile nitrate-N levels. Therefore, sampling fields is important to best know the potential value of carryover nitrate.

As mentioned earlier, nitrate has moved down in the soil profile. For all sites sampled, the change from fall to spring preplant sampling in the 0-1 foot depth was -41 lb nitrate-N/acre, for the 1-2 foot depth was -13 lb nitrate-N/acre, and for the 2-3 foot depth was +21 lb nitrate-N/acre. This shows the movement with water percolation, but also the accumulation in the third foot and that not all nitrate-N has moved below the three-foot depth or out of the rooting zone. As discussed in the previous ICM articles, do not subtract the full profile amount from the 2013 corn N fertilization rate, rather, first subtract a 50-60 pound N amount to account for the typical profile nitrate-N level. Based on the spring sampling, there is still carryover nitrate-N that can be accounted for in 2013 corn crop N applications; just not as much as was there last fall. If above normal rainfall continues, then the amount of carryover nitrate will continue to decrease.

Website to View Individual Soil Profile Nitrate Information
In an effort to assess residual soil nitrate-N following 2012 corn crops, a soil nitrate monitoring network map was developed in conjunction with the University of Wisconsin. The amount of residual nitrate-N at each site and sample timing, along with field information, can be found at the University of Wisconsin website Appreciation goes to Carrie Laboski and the nutrient management team in Wisconsin for developing the website.

Predicting the Three Foot Nitrate-N Amount
The data from the Iowa spring preplant profile sampling shows a reasonable relationship between the two foot and three foot depth nitrate-N amount (Fig. 1). Although it is preferred to collect samples to a three foot depth, if that sample depth is not possible due to soil conditions, then results from the two-foot depth can be used to estimate the three foot amount. The equation shown in the Fig. 1 gives that conversion (y is the predicted three foot amount in lb nitrate-N/acre and x is the two foot amount in lb nitrate-N/acre).

Fig. 1. Relationship between the two foot and three foot profile nitrate-N amount, spring 2013 preplant samples.


The relationship between a one foot sample and the three foot profile amount was also determined. That relationship was weak, and highlights the need that when sampling for residual or carryover profile nitrate-N, a deeper sampling than one foot is needed. The spring sampling results also highlight a potential problem where presidedress nitrate tests (LSNT) this spring could miss nitrate deeper in the profile, since that test is only collected to a one foot depth.

John Sawyer is a professor in the Department of Agronomy with research and extension responsibilities in soil fertility and nutrient management. He can be contacted at

Stalk Borers Moving in Southern Iowa

By Erin Hodgson and Adam Sisson, Department of Entomology

Iowa has been slowly accumulating degree day temperatures in 2013; the state is about four weeks behind 2012. About 10 percent of common stalk borer larvae can begin moving to corn after accumulating 1,300-1,400 degree days (base 41 degrees F). This week, some parts of southern Iowa reached this important benchmark (Fig. 1). Scouting for migrating larvae in corn should begin this week to make timely treatment decisions. 

Figure 1. Growing degree days accumulated (base 41 degrees F) for stalk borer in Iowa (January 1 – June 2, 2013). Begin scouting around 1,300-1,400 degree days. Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy

Stalk borer larvae in central and northern Iowa should accumulate enough degree days to begin migration next week. But to more accurately predict larval movement in May, use this website to generate up-to-date information. Click on the “View Degree Day Map” button in the left corner of the page, and then set the parameters for degree days to create a new map. Make sure to set the start date to January 1 of the current year and the end date to today; set base temperature to 41 degrees F and ceiling temperature to 86 degrees F.

Description. Stalk borer larvae have three pairs of true legs and four pairs of fleshy prolegs. The body is creamy white and dark purple with brown stripes. Often there is a creamy white stripe running down the back. A distinctive feature is an orange head with two dark lateral stripes (Photo 1). The adults are dark grey and brown colored moths, with jagged white lines and two to three clusters of white spots.

Photo 1. Common stalk borer larva. Photo credit Marlin E. Rice.

Biology. Stalk borers have one generation in Iowa. Stalk borer eggs are laid on grasses and weeds in the fall and overwinter in this cold-hardy stage. Egg hatch typically occurs around April 19 – June 5, and about 50 percent egg hatch happens at 494 growing degree days. Young larvae will feed on grasses and weeds until they outgrow the plant. The number of larval molts is variable depending on food quality, and ranges from seven to nine instars. Migration to larger hosts begins around 1,300-1,400 degree days. Fully developed larvae drop to the soil to pupate. Approximately 50 percent of pupation happens at 2,746 growing degree days, with 50 percent adult emergence at 3,537 growing degree days. Peak adult flight occurs during the first two weeks of September.

Corn adjacent to grassy and weedy areas become a suitable host during migration. The most susceptible stages of infestation are at V1-V5, or about 2-24 inches in plant height. Larvae can damage corn by defoliating leaves and burrowing into stalks. Stalk borers do not typically cause economic damage when feeding on the leaves, but can clip newly emerging plants and cause death (Photo 2). More often, larvae kill corn plants by entering the stalk and destroying the growing point (i.e., flagging or dead heart). A dead heart plant will have outer leaves that appear healthy, but the newest whorl leaves die and can cause barren plants.

Photo 2. Stalk borer can shred corn leaves and destroy the growing point.

Control. Stalk borer infestations are more likely in corn surrounded by giant ragweed. Female moths prefer to lay eggs in weedy areas in August and September, so minimizing weeds in and around corn during that time will discourage egg laying. Using herbicides to kill spring weeds can force stalk borer larvae to infest young corn plants. Long term management requires controlling grassy edges around corn so that mated females will not lay eggs in that area during the fall.

To prevent stand loss, scout and determine the percent of infested plants. The use of an economic threshold (Table 1), first developed by Iowa State entomologist Larry Pedigo, will help determine justifiable insecticide treatments based on market value and plant stage. Young plants have a lower threshold because they are more easily killed by stalk borer larvae.

Table 1. Economic thresholds (expressed as percent of infested plants with larvae in the whorl) for stalk borer in corn, based on market value, expected yield and leaf stage

Fields with persistent stalk borer infestations should be monitored every year. Applying insecticides to infested corn is not effective because the larvae are protected once tunneled into the stalk. Instead, target foliar applications to larvae as they migrate from grasses to corn. Look for larvae inside the whorls to determine the number of plants infested. The larvae are not highly mobile, and typically only move into the first four to six rows of corn. Look for new leaves with irregular feeding holes or for small larvae resting inside the corn whorls. Larvae will excrete a considerable amount of frass pellets in the whorl or at the entry hole in the stalk. Young corn is particularly vulnerable to severe damage, but plants are unlikely to be killed once reaching V7 (seven true leaves).

If an insecticide is warranted, some products can be tank-mixed with a fast burndown herbicide, or applied seven days after a slow burndown herbicide. Border treatment should be considered if infestations are localized. Insecticides must be well-timed so that products are reaching exposed larvae before they burrow into the stalk. Make sure to read the label and follow directions, especially if tank-mixing with a herbicide, for optimal stalk borer control.

For more information on stalk borer biology and management, read a Journal of Integrated Pest Management article by Rice and Davis (2010), called “Stalk borer ecology and IPM in corn.”


Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at or phone 515-294-2847. Adam Sisson is an Integrated Pest Management extension specialist. Sisson can be contacted by email at or by calling 515-294-5899.

Corn Nitrogen Rate Calculator Update

By John Sawyer, Department of Agronomy

What is the Corn Nitrogen Rate Calculator?

The Corn Nitrogen Rate Calculator is an online tool that allows determination of nitrogen (N) application rates for corn production and is helpful in determining the effect of fertilizer and corn price on needed rates. The method for calculating suggested N rates is based on a regional (Corn Belt) approach to N rate guidelines. Details on the approach are provided in the regional publication Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn. This approach and the Corn Nitrogen Rate Calculator are now being used by seven states across the Corn Belt: Iowa, Illinois, Indiana, Michigan, Minnesota, Ohio and Wisconsin.

Nitrogen (N) Response Trials Added

The Iowa N response database in the calculator was recently updated, with response trials added from 2012 research. There are now 230 trials for corn following soybean and 125 trials for corn following corn. Being able to easily update the database with recent data is one of the many advantages to this dynamic database approach for corn N rate guidelines. Having new response trial data allows rapid updating with changing hybrid genetics, rotations and climatic conditions.

With the updated database, calculated N rates have decreased slightly from previous years, the result of a lower N fertilization rate requirement in the dry 2012 season. The table below gives the N rate at the maximum return to N (MRTN) and the profitable N rate range from the updated calculator for several N: corn grain price ratios (price of N fertilizer in dollars per pound N divided by the price of corn in dollars per bushel). You can work with any price of N and corn you wish when running the calculator. Output information includes the N rate at the MRTN, the profitable N rate range, the net return to N application, the percent of maximum yield and the selected N fertilizer product rate and cost.

Nitrogen rates determined from the calculator are directly the total fertilization amounts for each rotation, with no need to further adjust rate for previous crop. That is, for the soybean-corn rotation, there is no need to subtract a “soybean credit” as the rotation effect is already accounted for by the N rate trials that the database is derived from.

Resources for N Rate Decisions

The Corn Nitrogen Rate Calculator Web tool is located at:

The regional publication Regional Nitrogen Rate Guidelines for Corn (PM 2015) can be ordered through any ISU county extension office, from the ISU Extension Online Store at , or by calling (515) 294-5247. An electronic copy of the publication is available at

The ISU Agronomy Extension Soil Fertility website is located at:


John Sawyer is professor with research and extension responsibilities in soil fertility and nutrient management.

This article was published originally on 6/10/2013 The information contained within the article may or may not be up to date depending on when you are accessing the information.

Links to this material are strongly encouraged. This article may be republished without further permission if it is published as written and includes credit to the author, Integrated Crop Management News and Iowa State University Extension. Prior permission from the author is required if this article is republished in any other manner.