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12/8/2008 - 12/14/2008

Soybean cyst nematode confirmed in Ida County in 2008

By Greg Tylka, Department of Plant Pathology

The soybean cyst nematode has been known to exist in Iowa since 1978.  The first Iowa finding was in Winnebago County.  In the 1980s and 1990s, SCN was found for the first time in many different Iowa counties.  By 2000, SCN had not yet been found in only nine Iowa counties. By the end of 2007, it had not yet been found or officially confirmed in only three Iowa counties – Allamakee, Ida, and Lyon County.  Earlier in 2008, SCN was confirmed to be present in Lyon County.

Recent results reveal that SCN also is present in Ida County. Soybeans were grown in the greenhouse for one month in soil from an Ida County field and numerous SCN females were observed on the roots of the plants.

So there now is only one Iowa county, Allamakee County, in which there is no official record of SCN.


Iowa SCN distribution map

Counties in which SCN has been found in Iowa – December 2008. (SCN-infested counties in red)


Although SCN has been found in all but one Iowa county, not every field in the state is infested with the nematode. A comprehensive, random survey of Iowa currently is being conducted by ISU personnel in collaboration with the USDA National Agricultural Statistics Service (NASS) personnel and supported by soybean checkoff funding from the Iowa Soybean Association.  In 2007, soil samples were collected from 205 randomly selected fields, and the nematode was found in 71 percent of the fields. A summary of the 2007 survey findings is available. The survey continued in 2008 and will be conducted again in 2009.  Results of the 2008 survey will be made available in the near future.

If anyone knows of SCN in Allamakee County fields, they are encouraged to send soil samples from the fields to the Iowa State University Plant and Insect Diagnostic Clinic, 327 Bessey Hall, Ames, Iowa 50011, so that soybeans can be grown in the soil to verify that SCN is present.


Iowa map of first SCN infestation by county 
Years of discovery of SCN infestation in Iowa counties – June 2008.



November 2008 US SCN infestation

Counties in which SCN has been found in the United States and Canada – December 2008 (SCN-infested counties in red).



Greg Tylka is a professor of plant pathology with extension and research responsibilities in management of plant-parasitic nematodes.

Is All Well that Ends Well? Iowa Corn – 2008

Roger Elmore and Lori Abendroth, Department of Agronomy
(This article is a summary of the complete report and all figures, which is available from this link Iowa Corn - 2008 full report.)

Shakespeare penned “All’s well that ends well” over 400 years ago.  Scholars say the play itself cannot easily be classified either as a tragedy or a comedy. Can the same be said of the 2008 growing season? 

The Dec. 1, 2008 USDA-NASS report says with 6 percent of Iowa’s corn is yet to be harvested the 2008 crop finished well, with the third best yield expected in Iowa’s history – 172 bushels per acre based on USDA’s November estimate. And yet 2008 started out with low expectations. We’ll be talking about this season for years.

The Growing Season
Planting started slow because of rain and cool weather. The rate of planting progress in 2008 was similar to 1975-1979 until rains and flooding necessitated replanting over a million acres. Replanted or ‘to be replanted’ area reached a maximum of 11 percent on  June 23 - please realize that Figure 1 displays these percentages as not planted even though some were already replanted before that date.  Iowa’s corn was not completely planted until the end of June 2008.
We also know that in general, early planting dates are better than later ones when it comes to yields. We generally recommend to plant corn in Iowa by May 10.  Yet this year, only half of the acres were planted in the western third of the state by then. It took until May 15 for the rest of the state to reach 50 percent planted.  And then, over a million acres were replanted after flooding or drowning out (Figure 1).  

Iowa corn planting progress

Figure 1. Iowa Corn Planting Progress.


Although projected corn acreage was high in late March, 13.3 million acres, only 12.5 million acres of corn were harvested in Iowa; this is a reduction of 6 percent from the initial estimate. These reductions were most likely the result of producers switching some acres to other crops, or flooding or ponding, and the inability to replant corn.  The difference in estimated and actual corn acreage in 2008 is second only to 1993 when there was an acreage reduction of 8.3 percent. After the crop was in the ground, the growing season – and corn growth – crept along,  not unlike a Shakespearean play – sorry Shakespeare lovers! 

Silking is the most critical growth stage for corn with late silking dates typically causing greater yield reductions. Again, 2008 went against this trend.  Silking dates in 2008 are clearly different when compared to the last few years (Figure 2). Fifty-percent silking occurred 15 days later in 2008 than in the two previous years. In fact, 2008 was the slowest year on record.  Incidentally, we should question the rule-of-thumb that a late-silking date correlates to lower yields as it is dependent on weather conditions after silking. Note that corn in 2004 was also “behind” in silking yet resulted in the highest Iowa corn yields ever.

Iowa corn silking dates

Figure 2. Iowa Corn Silking Dates 2004 - 2008.


Delayed planting and silking dates obviously resulted in a delayed harvest. Although harvest timing hasn’t changed much on average over the last 30 years (data not shown), 2008 is much slower than recent years and is two weeks behind last year. 

Yields and Estimated Yields
In spite of the seemingly poor year and all of the doomsday talk, USDA-NASS estimated Iowa yields third best in history. Average corn yield in Iowa continues to increase 2.25 bushels per acre per year. The 2008 estimate, 172 bushels, is four bushels above the trend line. Gross production will be high, 2.15 billion bushels, because of the acres grown and high yields.

The northwest Iowa cropping district posted exceptional yields this year due to near normal heat unit accumulation, ordinary planting dates and less saturated soils in the spring.  Yields in southwest Iowa were reduced from drought and storm damage. High reported yields surprised most of us. Yield-reducing factors, such as insect pressure and fungal diseases, had minimal impact this year.

Why did 2008 turn out well?
During the 2008 growing season we used a crop model, Hybrid-Maize, to help us understand weather interactions with the crop. Using the model, we developed a synopsis for the Ames 2008 growing season with weather data from 1986 through October 5, 2008.

Weather conditions this year, provided an excellent opportunity to maximize corn yield. In fact, according to the model, 2008 had the second highest potential yield. Only weather and the input parameters affect yield potential in the model; it does not consider yield reductions due to diseases, insects, weeds, soil compaction, hail, lodging, etc.

The model calculates potential yield weekly during the growing season. As harvest approached, the range in predicted yield narrowed between the best possible and the worst possible outcomes. For example, on June 29 if the worst possible weather year occurred from that point forward, potential yield was 45 percent of that of the best possible weather year, about 140 bushels per acre.  Because late season weather was conducive to higher yields, the projected yields continued to move upward from what was predicted earlier in the season. After silking on 3 August, yield potential in the worst possible year was up to 64 percent – about 188 bushels per acre. At maturity it was 87 percent of potential or about 277 bushels per acre. As the season played out, yield potential for 2008 was 94 percent of maximum, 299 bushels per acre.

How did this happen? The answer lies in the late-season weather. Table 1 provides data on solar radiation, temperatures, rainfall, and silking and maturity dates for 2008 in addition to three other possible years.  Although 2008 silk dates were late, sunlight (solar radiation) after silking, and rainfall were similar to those of the best year.  Temperatures after silking were cooler than in the worst years. This, coupled with slow heat unit accumulation, resulted in slow crop development (Figure 2) and subsequently longer grain-fill period.  Without a late frost though, this all would have been for naught (note crop maturity dates in Table 1).  The crop season finished well, better than we could have ever hoped.

corn growing season conditions

The late harvest and cool fall did contribute though to high grain moisture, an increase in grain molds, and in some cases low test weights. Much attention should be applied towards handling grain this winter. 

2008: Tragedy or Comedy?
The curtain is nearly down. The last act is coming to a close. Was all well in 2008 since it ended well? The first acts made us think it was a tragedy. We can certainly say that the 2008 drama certainly wasn’t a comedy. Those who know about dramas would say 2008 was a tragicomedy; it provided a happy ending to a potentially tragic story.  During a critical point in a tragicomedy, the viewer is uncertain whether to laugh…or cry.  That was 2008! 

And in the end, the tragicomedy, Iowa Corn-2008, turned out well. Yields were better than we could have expected. We will remember this one!



Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. Lori Abendroth is an agronomy specialist with research and extension responsibilities in corn production.

Effects of N-Hibit™ Seed Treatment on Soybean Yields – 2008 Iowa Research

By Greg Tylka and Chris Marett, Department of Plant Pathology

Harpin protein is a natural plant compound that can stimulate plant defense responses. And N-Hibit™  is a seed-treatment containing harpin protein that is sold in the United States for management of the soybean cyst nematode (SCN).  Iowa State University Extension evaluated the effects of N-Hibit™  seed treatment on soybean yield and SCN population densities in nine field experiments located throughout Iowa in 2007 and in nine different field experiments in 2008. The work was supported by the soybean checkoff through funds from the Iowa Soybean Association.

In 2008, the experiments were conducted in Laurens, Mason City and Winthrop in northern Iowa; Gowrie, Nevada, and Urbana in central Iowa; and Council Bluffs, Hills, and Malvern in southern Iowa.


Figure 1. 2008 Experiment Locations

N-Hibit Iowa test plot map


In both years, an SCN-susceptible and an SCN-resistant variety were grown at each experiment, and the seeds of each of the two varieties were either left untreated or were treated with N-Hibit™  at a rate recommended by Plant Health Care Inc., the distributors of the product. All of the plots were four 17-foot-long rows spaced 30 inches apart. There were four replicate plots per variety-seed treatment combination, and 16 plots total per experiment. The center two rows of each four-row plot were harvested with a plot combine, total seed weight per plot and seed moisture were determined, and total plot seed weights were converted to bushels per acre.

Soil samples were collected from the plots to determine the SCN population densities. Ten soil cores were collected from the center two rows of each plot immediately after planting and again at the time of harvest. SCN cysts were extracted from a 100-cc subsample (a little less than a half cup) of each soil sample, and SCN eggs were extracted from the cysts and counted. 

The yield results from all experiments and the end-of-season SCN egg population densities from three of the nine locations are presented in the table below.


Table 1. 2008 Results - N-Hibit™  seed treatment experiments in nine Iowa locations.

Effects of N-Hibit table


In 2008, N-Hibit™  did not significantly affect the yield of the SCN-resistant or the SCN-susceptible soybean variety at any of the nine experimental locations. But overall, yields of the SCN-resistant varieties were significantly greater than the SCN-susceptible varieties in the experiments at Council Bluffs, Malvern, Mason City, and Urbana.

At this time (early December 2008), the final (end-of-season) SCN population densities are available only for three of the experiments (Gowrie, Hills, and Winthrop) conducted in 2008.  In those experiments, there was no significant difference in final SCN egg population densities in plots of SCN-susceptible or SCN-resistant soybean varieties left untreated or treated with N-Hibit.  However, at all three locations, there were significantly greater final SCN population densities on the SCN-susceptible soybean varieties than the resistant varieties.

In the experiments conducted in 2007, N-Hibit™  had no effect on yield of the SCN-resistant soybeans at any of the experiments and no effect on yield of the susceptible soybean varieties at seven of the nine locations. Yields of N-Hibit-treated susceptible soybean varieties were 2.1 and 3.0 bushels per acre greater than yields of untreated soybeans at the Melrose and Urbana experiments, respectively, in 2007.

When the end-of-season SCN egg population density data are obtained for all nine of the experiments conducted in 2008, a revised report of this work will be published in Integrated Crop Management News that will include all nematode data from 2008 and also a combined analysis of yield and SCN egg population density data from all 18 experiments conducted throughout Iowa in 2007 and 2008.


Greg Tylka is a professor of plant pathology with extension and research responsibilities in management of plant-parasitic nematodes. Chris Marett is an assistant scientist with responsibilities for research on the biology and management of the soybean cyst nematode.

This article was published originally on 12/15/2008 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.