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3/10/2008 - 3/16/2008

Welcome to the Integrated Crop Management News Web site

By Wendy Wintersteen, dean, College of Agriculture and Life Sciences, and Gerald A. Miller, associate dean, College of Agriculture and Life Sciences, and Director, Agriculture and Natural Resources Extension

We are pleased to offer this online source for crop production news and information that provides greater access to Iowa State University Extension resources and enhances the timeliness of information you need to make decisions in your fields.

New features of the site include:

  • Weekly or daily e-mail notification of new articles
  • Quick access to crop production sites at Iowa State University
  • Easy-to-print single articles and weekly compilations
  • Rapid response when a crisis occurs

We encourage you to bookmark our site, This ISU Extension site will grow and change over the next few months, so please visit often.

We welcome your comments. Please send them by e-mail to

 Thank you.

Pesticide Drift Reduction Starts Now

Bob Hartzler, Department of Agronomy

The number of drift complaints in 2007 regarding ground applications of agricultural pesticides received by the Iowa Department of Agriculture and Land Stewardship increased by 36 percent compared to 2006, and was nearly double that of 2004. 

The first step in preventing problems with drift is to develop an effective drift management strategy prior to the spray season.  Important considerations include:

  • equipping sprayers with appropriate spray nozzles,
  • effective use of drift retardants,
  • sprayer setup - boom height, operating pressure and driving speed, 
  • identification of drift sensitive locations (organic production, vineyards or other high value crops, concerned neighbors), and 
  • proper education of personnel operating the sprayers. 

While advances in spray technology have improved our ability to keep pesticides on target, successful management of drift ultimately relies on good judgment by the sprayer operator.

By Bob Hartzler is a professor weed science with extension, teaching, and research responsibilities.

Should I Be Concerned About Corn Rootworms Now?

By Jon Tollefson, Department of Entomology

It is March already, the tillage equipment is being readied, and we are thinking eagerly about planting the 2008 crop of corn. Yet it seems a long time until we have to worry about corn rootworm larval feeding on the corn roots. However, there is something that you should be thinking about now, before you plant the corn.

If you have a threat of corn rootworm infestation(s) in one or more of your fields, you may have bought and are intending to plant a genetically-modified, corn rootworm-resistant variety. If you are planting a Bt corn rootworm variety (YieldGard, Herculex, or Agrisure) remember that the contract you probably signed with the purchase of the genetically-engineered variety commits you to planting a 20 percent, non-Bt refuge.

The refuge planting is intended to slow or prevent the development of resistance of the corn rootworm to the Bt produced by the resistant corn. For the corn rootworm, the refuge is to be planted within the same field or immediately adjacent to the Bt field.

The non-Bt corn planting will produce rootworms that have not been exposed to the Bt. Planting the refuge within, or close to the Bt field, is intended to increase the likelihood that the beetles from the refuge will disperse into the planting of Bt corn, increasing the likelihood that they will mate with those that survived the genetically-engineered, rootworm corn. The intermating will result in progeny that are heterozygous for resistance and they will continue to be susceptible to the Bt produced by the resistant corn.

With this understanding, you will agree to plant a 20 percent refuge for every field of Bt corn rootworm corn that you plant. So what are the decisions that must be made now? By now you should have purchased the seed for the refuge planting and you should be making the decision on where the refuge will be planted. The refuge must by grown the same way the Bt rootworm corn is; that is if the rootworm corn is corn on corn, then the refuge must also be continuous corn. If the rootworm corn is rotated corn, the refuge should also be corn grown in rotation.

It is likely that you will want to and it is permissible to protect the refuge corn from rootworm larval attack. If you will use granular or liquid insecticides applied over the seed row, you may choose to plant the refuge as a block and treat the block.

If there are no insecticide applicators, seed may be purchased that has insecticide on it. The seed treated with insecticide may be planted as a block or as rows within the Bt corn, producing a strip refuge throughout the field.

Most importantly, remember that when genetically-engineered, insect resistant corn is planted, you must also plant a refuge to delay the development of resistance!

Jon Tollefson is a professor of entomology with responsibilities in field crop pest management.

Soybean Rust Overwintering in the South

Daren Mueller, Department of Plant Pathology

Despite soybean rust infecting fields in Iowa last fall, the pathogen needs to retrace its steps to get back to Iowa in 2008. The first critical step is for the pathogen to survive somewhere over the winter in places like Florida, Texas or Mexico.

An extensive study on the survival of soybean rust was completed in Florida by  W. Jurick, J. Marios, D. Wright and P. Harmon. Their data was presented at the National Soybean Rust Symposium. Some of the main conclusions were:

  1. Pathogen populations in a kudzu patch are reduced each year and build from low levels of initial inoculum
  2. Local survival of the pathogen is dependent on temperature and moisture conditions (they had some kudzu patches die from drought)
  3. Protected live vines or dried leaf litter in niche microenvironments may harbor pathogen until favorable conditions for disease occur
  4. Pathogen may survive further north than was previously predicted

As spring nears (at least in the South), there have been a couple of noteworthy developments. First, soybean rust continues to survive in kudzu patches in Louisiana and Texas, which are further west than survival in previous years. Second, the ipmPIPE web site has made their service available for Mexican plant pathologists to track soybean rust in Mexico. This winter they reported soybean rust on jicama (yam bean) and soybean in a couple of different locations.

Texas Kudzu, 1-8-08, Photo by Tom Isakeit

Temperatures in the south are beginning to warm, but there is still a chance for more killing frosts. Researchers in the southern states will continue to track the survival of soybean rust on kudzu in the U.S. and jicama and soybean in Mexico. For now, the soybean rust pathogen has survived in expected places (Mexico, Florida, southern Georgia and Alabama) and some unexpected places (central Texas and Louisiana).

Soybean rust overwinter map
March 5, 2008 Rust Observation Map,

Having this information is critical for the accuracy of the predictive models for the movement of soybean rust during the season. For growers, if soybean rust continues to survive in Mexico, Texas and Louisiana, this means the pathogen has passed the first critical step in getting back to Iowa. The next step will be to build up the inoculum this spring when the soybean plants and kudzu vines begin to grow in the southern states.

Daren Mueller is an extension specialist in the Department of Plant Pathology.

Check Fields for Soybean Cyst Nematode

By Greg Tylka, Department of Plant Pathology

Damage due to the soybean cyst nematode (SCN) can reduce soybean yields in Iowa by 50 percent or more, particularly under very dry conditions. And some believe the chances of severe drought conditions occurring in Iowa are greater for 2008 than for any year since 1990.

Most of this yield loss can be prevented by growing SCN-resistant soybean varieties in fields infested with the nematode. The resistant soybean varieties prevent SCN population densities from increasing as well as produce profitable soybean yields, thereby preserving the productivity of fields for future soybean production.

SCN often does not cause obvious symptoms to soybeans for many years after it becomes established in the field. Many infestations may go undiagnosed or the effects of the nematode on yield are unnoticed, especially in fields with high yield potential and in growing seasons with adequate or excess rainfall.

Results of a 2007 survey of Iowa, funded by the soybean checkoff, revealed the presence of SCN in 71 percent of 205 randomly selected fields in the state. This percentage was very similar to what was found in an identical random survey conducted in 1995-96. The survey results indicate that many fields in Iowa in 2008 are infested with SCN.

It is not too late this spring to check fields for SCN. Samples can be collected once the snow and ice have melted and the soil drains.

Guidelines for collecting a useful soil sample to check for SCN in the spring are as follows:

  • Ideally, the soil samples should be collected using a soil probe.
  • Soil cores should be collected to a total depth of 6 to 8 inches.
  • Collect soil cores from 15 to 20 places in a zig-zag pattern in a sampling area.
  • If the field was last cropped to soybean, there is a greater chance of discovering SCN if soil cores are collected from under the old crop row.
  • If corn was grown in the field last season, it doesn’t matter if soil cores are collected from under the crop row or between the rows.
  • Another good location to check for SCN is areas of the field with high ph (>7.2)
  • Collect a separate set of soil cores for each 20 acres or so.
  • Combine and mix soil cores, and fill a sample bag with one cup or more of soil.
  • Label the outside of each sample bag with a permanent marker.

Numerous private soil testing laboratories in Iowa offer SCN analysis of soil samples.

Additionally, the Iowa State University Plant and Insect Diagnostic Clinic tests soil samples for SCN.

Mail to:

Plant & Insect Diagnostic Clinic
327 Bessey Hall, Department of Plant Pathology,
Iowa State University,
Ames, IA 50011-1020.

The current fee for SCN analysis is $15 per sample for samples from Iowa. Samples sent to the Plant and Insect Diagnostic Clinic should be accompanied by a completed Plant Nematode Sample Submission Form, available at

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

How Soon Should I Start Field Operations?

By Mahdi Al Kaisi, Department of Agronomy, and Mark Hanna, Department of Agricultural and BioSystems Engineering

It is not too early to start thinking about spring and field operations, even though the cold and snowy weather appears not to fade away. It is a good time now to direct our thinking by focusing on next spring and the promise of enjoying being outside and shake up the winter hold on us. Having said that, the decision to conduct any field operation whether tillage, applying anhydrous, etc, needs to be pursued carefully giving the potential for very wet conditions with amount of snow we have this winter. 

Wet early spring can be very challenging, when the soil profile is fully charged and the soil very susceptible to great damage and significant compaction  if the fields are entered early when the soil is at field capacity or saturated condition. When soil conditions are near field capacity, soil aggregates are "lubricated" by water and readily reposition themselves through the air spaces, especially when heavy equipment is used.

In addition, equipment operators need to remember that soil compaction can occur during the application of manure or anhydrous as well when soil moisture exceeds field capacity (maximum amount of moisture retained by the soil). Under wet conditions, the use of heavy equipment can significantly change soil structure and cause soil compaction. Operating in wet conditions and especially doing extra tillage will increase fuel use per acre as well.

Soil compaction near the surface, within the top 3 to 6 inches of the soil, is generally associated with the amount of surface pressure. Compaction below that is primarily associated with axle weight. For example, if soil a foot below the surface is at field capacity and the tractor's axle load is 7 to 8 tons or greater, compaction can occur at this depth, despite lower surface pressures. This is true especially, when tillage or any other field operations are done in wet conditions or early wet spring. 

It’s tempting to jump start the process and hit the field, but soil below the surface couple of inches in most cases is still holding significant amounts of moisture from winter snow. Living plant roots are not present to remove infiltrated water and soil moisture is at or near field capacity, making it too wet for suitable working soil conditions. 

The potential damages to soil, such as creating clods unsuitable for later planting, exceed the perceived benefits of early spring operations. During wet conditions soil compaction can be very costly in terms of good stand development, soil compaction induced nutrient deficiency such as potassium, root development and ultimately yield reduction.

By Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science and Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery.

March 2008 La Nina Update

Elwynn Taylor, Department of Agronomy

An area of warm sea surface temperature has formed off the Peru coast. Watch this to possibly “kill” La Nina.  By March 3 the water north of Australia was cooling and west of Peru was warming.Two signs of a La Nina about to fade (and with it the risk of serious Midwest drought diminishes somewhat). 

Also the slight cooling north and east of Hawaii is a step toward a good season for the High Plains. The Trade Winds on March 3  remained stronger than usual near the “date line,” but have diminished to below normal off the coast of S. America (110W). This is may be a step toward a shift to El Nino.

Weather conditions in the U.S. continue to be approximately typical of La Nina and the Southern Oscillation Index (90-day) at 1.58 appears to have passed its peak intensity.  It is too early to say that the risk of widespread drought is reduced because of a diminished La Nina event.

Elwynn Taylor is a professor with responsibilities  for developing and implementing of extension education and information programs in agricultural climatology.

Try Side-by-Side Trials to Check Fungicide Impact on Corn Yield

By Roger Elmore, Department of Agronomy

The decision of whether we should apply a fungicide to corn in mid-season will depend on two sets of factors. First are the main economic drivers: the value of the corn produced, and the costs of the fungicide and its application. The second factor that balances these is the degree to which yield is actually affected. 

If yields are not affected or if the yield gains are real but when translated into dollars per acre are less than the costs of the fungicide and its application, then the application was not profitable. However, if the yield changes are real and the price of corn is high enough to push the return over the cost of the fungicide and application, then it may be profitable.

But how can we know if the yield changes are real or not? The only way to really know is to put out some check strips in your own field and do some side-by-side testing with replication.It is not fair or accurate to compare year to year because too many other variables play into yields from one year to the next. Instead, split the field into equally sized portions and randomly apply different treatments to each. The harvest area of each treatment needs to be identical.

For example, this could be accomplished by treating a 16-row section with fungicide, leaving the next 16-row section untreated and then harvesting the middle four rows for comparison. If the fungicide is applied by air, wider strips are necessary to accommodate the spray pattern and alleviate possible drift concerns.

The best way to compare is by replicating the process within a field or across multiple fields. For example to replicate across fields, if 10 farmers in the area are interested in using preventive fungicide to increase yield, they should all conduct the tests in about the same way. This will provide the most accurate results.

Whatever you do, you have to do it in a fair and nonbiased way.

Roger Elmore is aprofessor of agronomy with research and extension responsibilities in corn production.

Weather Situation and Outlook for 2008

By Elwynn Taylor, Department of Agronomy

Corn yield has been less variable during the past 12 years than the previous 20. However, the yield of the past 5 years in Iowa exceeded trend. The national yield has a run of 5 above-trend years; this is an historical record. A run of 4 above trend years occurred in 1984-87 (with a major drought at each end). 

On average, a new record corn yield is achieved every 4 or 5 years.  Improved genetics and management get the credit for the consistent improvement, and weather is the reason that yields are somewhat erratic over a period of years. Weather is the major uncontrollable risk factor in agriculture. The weather is not controllable, but the risk is manageable.

Widespread drought in the Corn Belt is occasional, the most recent being in 1988. Even the 1988 drought did not decimate the crops of the western Corn Belt, but it reduced yields by 30 percent over much of the central and eastern portion. Serious drought tends to follow a 19-year cycle and the next 4 years fall into the higher risk portion of that cycle. The majority of seasonal weather indicators imply increased crop production risk for the 2008 crop season. Attention to soil condition has benefited crops the past few years and will remain important.

Indicators for 2008: 

Southeast Drought:  Residual moisture deficiency persists in the southeastern U.S. Some level of drought in South Carolina precedes initiation of widespread Corn Belt drought (greater than 90 percent of all major Corn Belt droughts are preceded by drought in South Carolina). The risk of serious drought in Ohio is greater than 60 percent if June drought occurs in South Carolina, and there is a 36 percent chance of Corn Belt-wide drought within 15 months.

60-Year Cycle:  The “dry” conditions of the desert Southwest may, with some justification, cause concern for Corn Belt weather. Drought originating in the Southwest is not known to sweep the Midwest; however, a series of dry years in the Southwest may precede below normal moisture years developing in the eastern half of the U.S.  Tree ring studies from Arizona to Virginia show that wet and dry intervals of approximately 30 years are not uncommon and do not appear to be random. 

During the past 100 years the wet/dry relationship is discernable in weather records. The similar pattern seems to lag somewhat, moving from west to east. The “dry” trend in Arizona may be an indication of a 30-year trend toward more arid conditions there. The trend appears to have initiated about 1980. It is possible that much of the Midwest reached the “peak” of moisture in the mid-90s and may experience diminishing annual moisture over the next two decades.

ENSO:  There are weather factors that influence Midwest weather more than does the so called ENSO (El Nino/Southern Oscillation).  However, the SOI (Southern Oscillation Index) is one of the “best” indicators in that it provides some “lead time.” 

A negative SOI (El Nino) tends to persist 6 to 14 months and the Midwest has, historically, not experienced widespread drought during these conditions. The SOI does have an influence on crop production risks in the Corn Belt. The movement from “El Nino” to neutral did influence the 2007 growing season. The 90-day SOI average reached La Nina on Dec. 25, 2007.  Some researchers state that the event may begin to dissipate before June 2008. This indicates above average risk for 2008 crops, but is a lesser risk than a strong La Nina that persists into mid-summer.   

Appendix I: 19-Year Drought Cycle

By Louis M. Thompson 1989 (revised 9/24/2006)
Adapted by E. Taylor (9/27/2006)


*Lunar declination reaches the minimum (18.5 degrees) during the wet phase and the maximum (28.5 degrees) in the dry phase.  Some evidence relates weather trends to lunar gravitational influence.
Very High Yield  
High Yield   
1937¤ +
Low Yield   1995
Very Low Yield (drought) 
Very Low Yield (combined) 1974!) Very wet spring, summer drought, early freeze
Very Low Yield (flood) 
Low yield years in   “wet” phase:  10
Low yield years in   “Dry” phase:   20
Good yield years in “wet” phase:  16
Good yield years in “dry” phase:   14
The chance of a “good” year is about the same in either phase.
The chance of a “poor” crop doubles during the “dry” phase.
The average is 4 good and 4 bad crop years in each 18-19 year cycle.

 Elwynn Taylor is a professor with responsibilities  for developing and implementing of extension education and information programs in agricultural climatology.

This article was published originally on 3/17/2008 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.