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6/16/2008 - 6/22/2008

Is It Time to Switch Soybean Maturity Group Varieties?

By Palle Pedersen, Department of Agronomy


Many farmers were able to get back into the field this week and start finishing up planting. However, there are still many areas where fields remain flooded and it will take awhile before we can get back in and replant. Some fields need to be replanted and some don’t. It is important to accurately estimate a surviving stand and then evaluate the economics of replanting.


Consider the yield potential of late-planted soybeans, along with costs associated with late planting. Final stands of at least 73,000 uniformly distributed plants per acre will consistently yield more than 90 percent of optimum plant population. If you are replanting an area that has been flooded, it is highly recommend to use a fungicide seed treatment and Bradyrhizobium inoculants. The level of seedling diseases probably will be high with our current conditions and the level of Bradyrhizobium in the soil could have been reduced, particularly in fields that were flooded for an extended period of time.


After the flood in 1993, an extensive research project was conducted by Keith Whigham (former ISU Extension agronomist) throughout Iowa from 1995 to 1997 to assess management decisions when planting occurs in late June and early July. Based on that data, the yield potential from planting in mid-June was approximately 60 percent of the optimum yield in northern and central Iowa and 80 percent of the optimum yield in southern Iowa. When planting was delayed until early July, soybean yield potential dropped even further and producers would have approximately 33 percent of the maximum yield in northern Iowa and 50 percent in central and southern Iowa available. 


Another thing that was investigated in that study was when we should be switching to earlier maturity group varieties. Based on that study, it was concluded that producers should plant their original soybean variety unless planting is delayed beyond late June in northern and central Iowa and beyond early July in southern Iowa.


We are frequently concerned about late maturity of full-season varieties planted in mid-June or later. Planting a full-season variety in Iowa in late June or early July will, on average, delay physiological maturity of the soybean crop to mid October. Soybean yield potential and seed quality may be negatively affected if frost damages the soybean crop before the plants reaches physiological maturity (R7).


Therefore, we are recommending that growers in central and northern Iowa switch to a shorter maturity group and shorten the maturity group by 0.5 to 1.0. Southern Iowa growers can wait another 10 days before needing to switch to a shorter maturity group. No data supports planting soybeans as a grain crop after mid July in Iowa.


More information about soybean management can be found at 


Palle Pedersen is an assistant professor of agronomy with research and extension responsibilities in soybean production.

Yellow Corn, Wet Soils and N Loss

By John Sawyer, Department of Agronomy


Yellow Corn

As many are well aware, the wet conditions this spring have resulted in tremendous corn coloration and growth variation across fields. In my travels to the ISU research farms west of Ames this week for research work, it is clear that corn is recovering and beginning rapid growth, but that growth is very uneven and varies on a quite small scale.


Where soils were “wetter” for a longer period, the corn is still yellow and stunted. At this time, this variation is mostly due to water, rooting and compaction issues, and much less to nitrogen (N) supply. When corn is small, the total plant N requirement is low and easily met by soil and applied N. As soils dry and rooting depth increases, plants will improve growth and access to N.


Crop rotation is also having an impact on early growth of corn this year. At our crop rotation by N rate study site at the ISU research farm west of Ames (on a Clarion loam), the corn following corn (CC) is not growing nearly as well as corn after soybean (SC). The CC is not as “tall” and is not as “green” as the SC, even at the highest N rate (240 lb N/acre). This means the growth response difference is not due to simply N supply. The N in this study is spring preplant incorporated urea. Looking at the corn plants in the SC rotation, there is good response to the applied N and the plants are getting their “deep green” coloration. 


Response to Anhydrous Ammonia Timing – Some Observations

It is very confusing to look at corn plants and decide if the yellow coloration is due to water stress, roots not reaching applied N, or N loss. To help answer these questions, I visually evaluated corn plants in an anhydrous ammonia rate study being conducted at the ISU research farm between Ames and Boone. In this study, anhydrous ammonia is applied in late fall (October 31, 2007), spring preplant (April 30, 2008), and sidedressed (June 18, 2008) at different depths of injection and application rates. Corn was planted May 15. The study is “low” on the landscape, with soils going from a small area of Clarion loam to mostly Webster clay loam and Harps loam.


Corn plants showing nitrogen deficiency
The white stake is in the border between two four row plots. The plot on the right had no N applied and the plot on the left had 80 lb N/acre applied last fall. (J.E. Sawyer, June 19, 2008)


Like many fields this year, part of the study area is wetter than the rest, with a small part where the corn is dead due to standing water. As of Thursday, June 19, the corn is around the V4 growth stage, so is still small. Plants on the “higher” ground are growing better and responding better to applied N, plants on the “lower” ground are smaller and not showing much growth response to applied N, and plants near the “dead” area are quite small but alive and showing no response to applied N.


Looking at the plant coloration and growth, I can generally see a better response to the spring applied ammonia compared to the fall applied ammonia, especially at lower N rates. It is too early to tell what amount of N may have been lost this spring, but it is clear either N loss is greater from the fall application, or nitrate from that timing is deeper in the soil and roots have not gotten to the N, or wet soil is restricting deeper root growth, or a combination of all.


It is clear that the corn is not growing as well on the more poorly drained (lower landscape, wetter) areas compared to the “higher” and better drained areas, and the corn response to fall and spring applied N is better on the areas where corn is growing better.


What does this all mean? I suspect N losses have occurred with the fall application, less with the spring application, and time will tell how much. It’s just too early now to make a determination of how much N loss from the visual corn growth and coloration. Also, wet conditions have restricted corn root growth and access to the applied N. I will attempt to watch these plots over the next week or so and see how the corn continues to grow and respond.


Rescue N Applications

The best approach is to get sidedressed N into the soil. Injection several inches into the soil places N in the root zone, and helps avoid placement on or near the surface where dry soils can limit root uptake. Injection is not always an option and sometimes it is just necessary to surface apply N materials. In those instances, rain will be needed to move the N into the soil. This (rain) is not exactly what we want right now, but the N needs to get into the soil for plant uptake.


Past research has also shown that sidedress N will not perform as well in dry conditions. At this time we want corn to grow root systems. Trying to “green up” corn with foliar application of fertilizer materials or application of low nutrient rates will not help promote root growth or help plants recover from poor aeration in the root zone. Corn will soon reach a rapid growth phase, and adequate N must be present in the active root zone to meet plant demands. Corn requires a large amount of N for high yields, and the way this large N demand is met is through root uptake.


Additional References

The wet conditions this spring have been widespread throughout the Midwest. Folks in many states are struggling to deal with N losses and determining rescue N applications for the corn crop. Following are links to several university articles for assessing N losses. These may provide you with some different perspectives and additional help as you make decisions about rescue applications. Do remember that geographic and soil differences will influence N losses, suggested N applications and potential for corn to respond to additional N.


Purdue University


University of Minnesota


University of Missouri


University of Wisconsin


University of Illinois



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

Flooding and Mosquitoes

By Laura Jesse, ISU Plant and Insect Diagnostic Clinic

Flooding per se, does not lead to mosquitoes. It is the water that stands AFTER the flooding that creates opportunities for mosquitoes to breed. Heavy, frequent rainfall may lower mosquito population numbers because there is no standing, stagnant water in which the larvae can feed on grow (mosquito larvae do not live in running water).

It takes 7 to 10 days of standing water for the mosquitoes to develop, which is why we recommend to homeowners that they "flush" the bird bath at least once per week. We expect that with these drier conditions, the mosquito problem may increase in many areas across Iowa over the next few weeks.

Protecting yourself with a repellants containing DEET is the best option if you have to be outside during peak mosquito activity hours. Usually dusk, although mosquitoes can be active all day. Female Aedes vexans, a floodwater mosquito, usually rest during the day and seek out blood meals at dusk. This species can become prevalent after flooding, but is a species that has minimal involvement in the transmission of West Nile Virus.

Ken Holsccher, ISU Extension entomologist, wrote a more details article about mosquito management in the June 18, 2004 issue of the ISU Extension Horticulture and Home Pest News

Laura Jesse is an entomologist with the Iowa State University Extension Plant and Insect Diagnostic Clinic.

The article was originally published in the June 16, 2008 issue of the ISU Horticulture and Home Pest News

Weed Science Field Book Available

Despite the cancellation of the Iowa State University Weed Science field day originally scheduled for June 26, there is still an opportunity to review the weed management demonstrations and research at the ISU Curtiss Farm on South State Street in Ames. 

Since planting and herbicide applications are still underway, particularly for soybeans, it is suggested that a good opportunity to see the weed science research exists after the first week in July. 

The field book , which details the research, is available online and can be downloaded. If a hard copy is desired, it can be purchased for $20 and picked up at the Weed Science Mixing Facility on South State Street. Please call (515) 292-7084 to arrange for hard copies of the field book. If you have other questions, please contact Mike Owen at (515) 294-5936. 

Iowa Soybean Sentinel Plots

By Daren Mueller, Department of Plant Pathology

Currently, soybean rust has been reported on kudzu in Alabama, Florida, Louisiana and Texas. Rust was also reported in three states (5 municipalities) in Mexico on yam bean and soybean. These have been destroyed or are no longer active, except for the recent find in Chiapas in extreme southern Mexico. Although soybean rust has been found this season in Texas, Louisiana and Mexico, predictive models suggest that soybean rust activity is behind last year’s pace because of drier conditions in Texas and parts of the southeast.


 sbr in US


Figure 1. Current distribution of soybean rust in 2008 (last updated June 15, 2008)

Soybean rust scouting in sentinel plots across the U.S. creates information for the real-time USDA ipmPIPE Web site ( The sentinel plots system is sponsored by the North Central Soybean Research Program, the United Soybean Board, and the United States Department of Agriculture. These plots of soybean or kudzu stretch from Florida to Texas and up through the Midwest. In 2008, sentinel plots have been established in Mexico for the first time.

This spring, 20 sentinel plots (see map) have been established across Iowa. We will be monitoring fields in these counties with the help of several Iowa Soybean Rust Triage members and ten Iowa State University Research farm staff. To date, several leaf samples have come in and the only disease found is Septoria brown spot.

soybean rust sentinel plots 

Figure 2. Counties with sentinel plots for soybean rust scouting in 2008

Assessing Private Well Safety After Flooding

By Tom Glanville, Department of Agricultural and Biosystems Engineering

As the floodwater recede, we are getting lots of questions from rural residents wanting to know if their wells are safe to use. Here are three of the most common questions.


There was no flood water on my property, but the nearby fields and road were flooded. How do I know if my well should be tested. 

Any well that has been submerged beneath flood waters or high groundwater tables (for well heads located below ground in well pits) definitely needs to be tested, but even if the well has not been submerged, the current saturated soil profile increases the risks of pollutant transport and so now would be a good idea for all rural well owners to consider having their well water tested for coliform bacteria and nitrate.


Both the Iowa City and Ankeny branches of the University Hygienic Lab (UHL) are operational and are offering free water test kits to residents of counties that are included in the Governor Culver's disaster declaration. These kits are available through local county health departments. The best point of contact would be your county sanitarian.


Hog confinements couldn’t spread manure because the cropland was so wet. Now a confinement operation near my farm has been, do I need to have my well checked?

The risks of private well contamination always go up during wet weather, regardless of whether a well is located near to a livestock operation or not. This is due mainly to the fact that many of the private wells used in rural Iowa are old, shallow and leaky.


Even during “normal” years about 30 percent of private water well samples submitted voluntarily to the University Hygenic Laboratory (UHL) by well owners are found to contain unsafe levels of coliform bacteria and/or nitrate. 


Are there any other places besides the University Hygenic Lab that can test my well water?

Several commercial labs throughout the state also offer water quality testing. To make sure, however, that a commercial lab is properly qualified and equipped to perform accurate drinking water testing, clients should inquire whether the lab is state-certified to test water for Iowa public water supplies. Personnel and equipment at state-certified commercial labs are periodically tested and reviewed by the Iowa Department of Natural Resources and UHL to insure that their work is accurate and done according to approved procedures.


Tom Glanville is a professor of agricultural and biosystems engineering with research and extension responsibilities.

Wet and Wetter

During the week of June 8, Iowa witnessed record high flood crests on several interior rivers that made national news. But for agricultural interests, the sheer volume of rainfall remains the story even more than the flooding rivers. Total statewide rainfall for Iowa in the 6 weeks from May 1 to June 15 averages 13.3 inches, which is double the normal precipitation load. The wettest areas are central Iowa (9+ inches above normal) and northeastern Iowa (8.5+ above normal).

Aerial view of Boone County June 14, 2008

This is a view near Boone, Iowa on June 14, 2008 illustrating the ponding of farm fields that is common in many parts of Iowa. (photo by John Kennicker)

Most crop fields that are out of the floodwaters are progressing acceptably, but prevented weed management is putting some at peril for yield loss. Because field work time is at a premium now, and everything cannot happen at once, growers should carefully judge the order of tasks. Generally, the major field activities during the next couple of weeks include planting and replanting, weed spraying, forage harvest and possibly side-dressing additional N fertilizer.

Accumulateed degree days through June 15

And finally, remember to document damaged fields with your insurance carrier where appropriate before destroying a stand, and to explore options for prevented plantings and keep good records of planting dates.  This link: 2008 Crop Insurance Decisions and Dates   is from the Ag Decision Maker Newsletter.

Crop Insurance May Help Flooded and Wet Corn and Soybean Acres

By William Edwards, Department of Economics


Wet weather has delayed planting of corn and soybeans across the state, and flooding has severely damaged many acres that have been planted. Fortunately, nearly 90 percent of the corn and soybean acres in Iowa are covered by multiple peril crop insurance (MPCI), which can provide some relief.


MPCI provisions may apply in two distinct situations: replanting and prevented planting.  Part of the cost of replanting a damaged crop can be covered by insurance if two thresholds are met.  First, a minimum of 20 acres out of the area insured as a unit must be affected.  If the unit has less than 100 acres in the affected crop, the minimum drops to 20 percent. Second, the projected yield as estimated by an insurance adjustor must be less than 90 percent of the guarantee. 


For example, a farm with a proven yield of 160 bushels of corn per acre with a 75 percent coverage MPCI policy would have a 120-bushel guarantee, so the projected yield would have to be less than 108 bushels for the acres to be eligible. The requirement is the same for revenue insurance policies as for yield insurance policies. The maximum replanting payments in 2008 are $43.20 per acre for corn and $40.08 per acre for soybeans. Producers with revenue insurance policies that have an increasing guarantee feature could receive slightly higher payments if prices at harvest are higher than they were in February.


Some producers may have land that they have not been able to plant at all, due to extended wet conditions. They may be eligible for “prevented planting,” and could receive an indemnity payment equal to 60 percent of their original guarantee. However, with current high grain prices, even a partial crop may produce higher net revenue than the insurance payment. Prevented planting acres must have a cover crop sown on them, and must be reported to the appropriate insurance agent by June 28 (corn) or July 13 (soybeans).  An acreage report on all insured acres must still be submitted to the agent by June 30.


In addition, acres that produce below average yields in the fall could still qualify for an indemnity payment under the normal yield or revenue insurance guarantees.  Coverage levels are gradually reduced for corn acres planted after May 31 and soybean acres planted after June 15, so it is important for producers to record the number of acres planted on each date.


William Edwards is a professor of economics with extension responsibilities in farm business management.

This article was published originally on 6/23/2008 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.