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4/27/2009 - 5/3/2009

Pay Attention to Soil Crusting After Heavy Rain Events

By Mahdi Al-Kaisi, Department of Agronomy and Mark Hanna, Department of Agriculture and Biosystems Engineering

Recent rain brings another challenge that farmers may need to deal with, especially in conventionally tilled fields that were planted recently to corn or soybean.  In addition to the immediate effect on soil erosion and potential damages to newly seeded waterways, there are after effects of the rain when weather conditions improve and the soil surface starts to dry. The potential problem is soil crust.

soil crusting

This could occur especially in intensively tilled fields where residue cover is not adequate, as well as with fine texture soils, and soils with low organic matter content. These conditions could increase the potential for soil crust formation. Residue cover plays a significant role in reducing soil crust by absorbing the impact of rain drops that destroy soil surface structure.  The destruction of soil structure impacts plant germination and seedling emergence for both corn and soybean. 

Soil crusting can also result in poor growing conditions and reduced water infiltration. Soybean seedling emergence can be a problem if a dense surface crust forms. In this situation, hypocotyl is broken when pushing up against a solid crust. Monitor high-risk fields for soil crusting, especially where plant emergence has not yet occurred, in order to avoid damage to seedlings.

Rotary Hoe
The quick-relief solution to such a problem is the use of a rotary hoe. This tool is commonly used in treating soil crusting to improve seedling emergence. However, the timing is critical in order to achieve the intended results and prevent seedling damage.  The rotary hoe is a potentially good tool to use to break up soil crust, but make sure you've got a crust that is actually sealing the soil surface before using it. 

To minimize the damages to the seedlings and to increase success, rotary hoe at a time when the soil surface is at the right moisture conditions. This will require frequent field scouting to ensure that soil surface moisture is just above field capacity. Field capacity is the point when a handful of soil will crumple easily in your hand under minimum pressure, leaving a trace of moisture on your palm.  This moisture condition will ensure less damage to emerging seedlings and less soil compaction during the hoeing process. 

Rotary hoe at high field speeds (8 to 10 miles per hour) unless safety is a concern.  However, if soybeans are the crop emerging, make sure both cotyledons aren't broken off by the hoe. Corn will likely be the crop emerging from rains this past weekend.  Expect a minor stand loss (approximately 1 to 2 percent) from hoeing, but this should be insignificant if corn is truly having difficulty breaking through a crust.  Getting off the tractor and checking for stand loss is a good idea when starting a field.  If loss seems excessive (greater than 3 to 5 percent), you may want to slow your travel speed to be less aggressive with the tool.  

It is very important to check early-planted fields periodically, especially those conventionally tilled with fine soil texture and low organic matter.  Timing is important to manage soil crust at the proper moisture conditions.


Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at or (515) 294-8304.
Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. Hanna can be reached at or (515) 294-0468.

Avoid Alfalfa Winter Injury – Next Time

By Stephen Barnhart, Department of Agronomy

There have been reports of localized areas of winterkill and winter injury to forage and winter cereal grain crops this past winter in Iowa.  

The reports indicate damage on sites across the state, but the most extensive areas are in northeast Iowa.  There are reports of damage to alfalfa, orchardgrass, perennial ryegrass, winter wheat and winter triticale.

Most of the affected stand damage is either in low spots where ice and standing water were the main problems; or on hilltops with snow cover loss and exposure to cold and crown damage, or associated localized ice sheeting. The injury is often worse in old alfalfa stands,where established hay stands were harvested or grazed in late fall, or new forage or cereal grains were planted late in the fall season.

By now most producers have inspected and either reseeded or over seeded forage stands.

While the risk of winter injury is with us every year, producers can consider some risk reducing management practices in the future.

• Select alfalfa varieties with Fall Dormancy index scores of 3 and 4, and Winter Survival Index scores of 2 to 3.5 (or lower).

• Orchardgrass is a grass species with moderate winterhardiness, so expect occasional winter injury. Select orchardgrass varieties that are well adapted to your location, and avoid varieties from unknown origins or adaptation.

• Perennial ryegrass is a high quality and useful forage grass, but it has less consistent winter survival in Iowa than orchardgrass. While there are some perennial ryegrass varieties with improved winter survival, avoid including it as a high proportion of a forage mixture or consider it in regular oversowing practice. And don’t count on an initial ryegrass seeding to be a long-term component in your stands.

• Plant late-summer forage seedings and ‘winter-cereals’ (rye, winter wheat and winter triticale) fields during the planting periods recommended for your area.

• Avoid harvesting or grazing alfalfa stands during the fall and early winter.


Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management. Barnhart can be contacted at (515) 294-7835 or by email

April 27 Crop and Weather Report

By Doug Cooper, Extension Communications and External Relations

On April 27, Doug Cooper, Extension communications specialist, interviewed Iowa State University Extension climatologist Elwynn Taylor, integrated pest management specialist Rich Pope and corn agronomist Roger Elmore for the weekly crops and weather update.

Pope relays a planting update from Extension field agronomists that say statewide about 65 percent of corn is planted. The official USDA’s NASS report as of April 26 says 47 percent. Elmore discusses what it means for producers to be well ahead of last year’s planting pace and how recent storms and heavy rains are a concern for many. Taylor’s weather report includes information that La Niña is still in place, but may be showing signs of decline.

Soybean after Soybean

By Palle Pedersen, Department of Agronomy

A few people have called me this week regarding planting soybean after soybean. All cases were from southeast Iowa where many river bottoms were flooded for an extended period of time last year and growers were forced to plant soybean even though their plan was to plant corn. To get back into their field rotations this year soybean would need to be planted after soybean. Is that a problem?

No, it is not. Planting soybean continuously year after year is something that should be avoided, but having the second year for the reason stated is OK for a short term decision. I have conducted rotation work with corn and soybean since 2003 here in Iowa. I am doing the work here in Ames and then also at the ISU Northwest Research Farm near Calumet. On average, if I compare second year soybean versus soybean rotated annually with corn, I do not see a yield difference between the two rotations.

A few things need to be considered when planting soybean after soybean.

• First, review your soil tests and phosphorus (P) and potassium (K) fertilizer applications to make certain you have rates adequate for the change in rotation. This is especially important for K as soybean grain harvest typically removes more K than corn grain harvest. If you are uncertain as to the need for either nutrient application, soil sample your fields to determine soil P and K test levels and to check soil pH.

• Second, were there any particular problems with diseases in that field last year? If so, be sure to make the necessary adjustment this year when selecting varieties. And, if there were problems with seedling diseases then use a fungicide seed treatment.

I have not measured in my research any differential response to tillage in second year soybean. Therefore, if you use no-tillage on your farm then you can plant soybeans without tillage this year as well.


Palle Pedersen is an assistant professor of agronomy with research and extension responsibilities in soybean production. Pedersen can be reached at or by calling (515) 294-9905.

Early planting IS important in Iowa

By Palle Pedersen, Department of Agronomy

This winter there has been a lot of information in the media and on the web regarding soybean planting date. In part, the reason is that a paper was published in the Agronomy Journal by two researchers from University of Kentucky stating that there is no consistent advantage for planting soybean early in the United States, but it is first after late May and early June that yields start to drop off. That is NOT correct for Iowa and is not correct for many of the states adjacent to Iowa as well.     

I have done a lot of research in cooperation with the Iowa Soybean Association on planting dates – 4  planting date studies in 2003, 14 studies in 2004, 14 studies in 2005, 15 studies in 2006, 18 studies in 2007, and 19 studies in 2008. I have a good idea on the best soybean planting date for Iowa. Thus, I can say with great confidence that early soybean planting IS important to maximize yield in Iowa but early planting requires more management.

With regard to the paper recently published in the Agronomy Journal, nine previously published papers from the Midwest were in this paper and used to assess the response to planting date in the Midwest. Eight of the studies were from 1990 or earlier and one paper, from 2002, specifically reported on bean leaf beetles (BLB) and soybean planting date. My point is that the recent published paper was written based on old data; probably using binrun beans; not using excellent and efficient post emergent weed management systems as we do today; not using fungicide/insecticide seed treatments as we do today; and probably also using excessive high seeding rates as was a norm previously but not today since it will give us more pathogens (eq. white mold).  Furthermore, the experiments upon which the conclusion is based were from conditions of much lower yield potential than in Iowa. One thing that we have identified in Iowa is that management decisions often are not that critical when our yield potential is low (30-40 bu/acre). So, the next time you read something on the web or in the media that does not agree with my recommendations in Iowa, please do not hesitate to contact me. I am here to help and my phone is open 24/7.

What do we know about soybean planting dates in Iowa
As mentioned above, we have done, and continue to do, a tremendous amount of research funded by the checkoff and the Iowa Soybean Association regarding soybean planting dates. Based on this research, Iowa recommendations were changed a few years ago. The new recommendations are based on two variables and probably the biggest change is that the new recommendation does not take soil temperature into consideration. Soybean planting date is now based on calendar date and seedbed conditions.

We want to start planting on April 25 for the southern 2/3 of Iowa and on May 1 for the northern 1/3 of Iowa if we have good seedbed conditions. Another thing to also watch is the weather forecast for the next couple of days after planting so you do not plant just before a heavy rain. If you plant earlier than the recommended time period, you increase your risk of having to replant simply because of the chance of getting a late freeze.

Early planting vs. management
It takes more management to achieve higher yields when planting early. Planting early just to plant early and then ignoring everything else is not recommended.  Things like variety selection are more critical at early planting since plants are more vulnerable to soilborne pathogens such as sudden death syndrome (SDS). There seems to be more SDS in early planted soybeans but that should not dictate a later planting date. Growers can continue to plant early in Iowa and the yield benefit will outweigh the impact of SDS if resistant varieties are used. Planting a variety without any resistance to both SDS and soybean cyst nematode (SCN) early is like playing roulette! 

Another important factor when planting early that should be monitored and that requires weekly scouting is the over-wintering generation of BLB. Frequent scouting is critical to be sure that no yield is lost from them. The bottom line is that farmers should not hold back from planting early, because they can easily manage BLB if they reach threshold and it will only cost a fraction to manage them if needed – compared to the yield loss that occurs due to delayed planting. Today, many farmers are now using a seed treatment to manage the over-wintering generation of BLB if it is a yearly problem on their farm.

No matter where you are in Iowa, early soybean planting will always give you greatest potential to achieve the highest yield. However, there are cases where early planting will yield the same as planting in mid-May. This is mostly associated with establishment problems such as soil crusting if you do too much tillage and planting is done just before a heavy rain. Early planting or the optimum time to plant soybean is the last week of April for the southern 2/3 of Iowa and the first week of May for the northern 1/3 of Iowa.

A target day for producers is to get soybeans planted by May 15. After that day, you start loosing a significant amount of yield potential every day no matter where you are in the state. The yield you loose depends on your yield potential. A higher yielding field is loosing more yield potential per day than a lower yielding field. At a higher yield potential you are loosing a significant amount of yield already after May 8. More information on soybean planting dates can be found at


Palle Pedersen is an assistant professor of agronomy with research and extension responsibilities in soybean production. Pedersen can be reached at or by calling (515) 294-9905.

Quick facts About Corn Nematodes

 By Greg Tylka, Department of Plant Pathology

Recent changes in corn production practices in the Midwest may be responsible for an increase in crop damage caused by plant-parasitic nematodes. And new products for corn nematode management will be available to growers in the near future. These recent developments have led to increased interest in corn nematodes among growers and those who advise them. 

Following are quick facts about plant-parasitic nematodes that feed on corn:
• Nematodes are microscopic worms that live in the soil, but not all soil-dwelling nematodes feed on plants.

• “Corn nematodes” are a group of numerous different species of organisms (see table), just like “corn weeds” or “corn insects.”

• Soils of all textures, not just sandy soils, can have infestations of corn nematodes.

• Some corn nematode species can reduce corn yields by 10 to 20 percent or more.

• The number of corn nematodes thought to cause yield loss vary by species (see table) and range from one worm per half-cup soil (for needle and sting nematodes) to up to 1,000 (for spiral and lesion nematodes).

• Two corn nematode species, the sting nematode and the needle nematode, only occur in soils with greater than 70 percent sand.

• Many species of nematodes that feed on corn also can feed and maintain their numbers on soybeans.

• Many corn nematodes are thought to be native to the Midwest, feeding on prairie grasses before corn was cultivated as a crop.

• Some corn nematodes, called endoparasites, are found only in the roots, not in the soil, during the growing season. (See image below.)

• The population densities (numbers) of corn nematodes may not be at damaging levels when the season begins, but numbers increase throughout the growing season. This is why results obtained from soil samples collected in the spring, before planting, often are not useful.

• Most every field in Iowa has some corn nematodes, but not necessarily at damaging levels.

• Many instances of damage by corn nematodes are small reductions in yield – on the order of 2 to 10 bushels per acre – and such yield loss may be difficult to detect.

• There is a corn cyst nematode that is somewhat akin to the soybean cyst nematode (SCN), which thoroughly infests Iowa and the Midwest. But currently, the corn cyst nematode isn’t really a concern or eminent threat to corn production in the Midwest.

Names of nematode species that feed on corn and population densities thought to cause damage to corn (damage thresholds).


corn nematode

Endoparasitic nematodes (stained red) inside root tissue.



Greg Tylka is a professor of plant pathology with extension and research responsibilities in management of plant-parasitic nematodes.Tylka can be contacted at or by calling (515) 294-3021.

When to Inoculate Soybean Seed in Iowa

by Palle Pedersen, Department of Agronomy

Soybean is a legume with a seed content of approximately 38 percent protein. Because of its seed protein concentration, soybean has a large nitrogen demand and continues to increase as yield increases. Total nitrogen accumulation for soybean is supplied by two sources: the nitrogen fixation and from the residual soil nitrogen pool.

Nitrogen (N) fixation is the symbiotic process of converting atmospheric nitrogen into a usable form for the plant and is critical for producing high soybean yields. For nitrogen-fixation to occur, the nitrogen-fixing bacteria known as Bradyrhizobia japonicum need to be readily available in the soil or must be applied to the seed.

When the soybean seed germinates, the rhizobia bacteria invade the root hairs of the seedling and begin to multiply. Nodules, which are structures that house the bacteria, form on the roots. Under field conditions, nodule formation can be seen shortly after emergence but active nitrogen fixation does not begin until about the V2 to V3 growth stage. After this, the number of nodules formed and the amount of nitrogen fixed increase with time until about R5.5 (midway between R5 and R6), when the fixation decreases sharply.

Nitrogen fertilization of soybean is not recommended because it typically does not increase grain yields in Iowa production systems. The total number of nodules that form decreases proportionately with increasing amounts of applied N. In addition, N fertilization will inactivate nodules or cause them to become inefficient, proportionately to the amount of N applied. Although the soybean plant can use both symbiotically fixed N from bacteria and inorganic soil N (both mineralized and fertilizer N), soil N is used in preference to fixed N if available in the soil.

Soybean does not respond with increased yield to the addition of N, even though plants remove a significant amount of it from the soil. In Iowa soils, which have appreciable organic matter and mineralized N, up to 50 percent or more of the total N accumulated by soybean can come from the soil system rather than N2 fixation. Increasing N supply by adding fertilizer, animal manure, sludge, or a green manure crop simply substitutes N from these sources for N that would otherwise be fixed by the bacteria in nodules on the roots, and hence an economically wasted input.

Today, most fields in the Midwest have experienced soybean in the rotation, likely increasing the population density of Bradyrhizobia bacteria in the soil. Improved inoculant technology coupled with higher commodity costs, ease of application, and low cost inoculant products have many growers reconsidering the use of inoculants.

I have since 2003 conducted numerous inoculation trials every year to assess new inoculants on the market. Overall, I have not seen a consistent response to use of soybean inoculant in fields in Iowa with a history of soybean. Current recommendations for states of the upper Midwest are to use an inoculant if fields have no history of soybean production in the past three to five years, soil pH is below 6.0, sandy soil, low organic matter, or have been flooded for more than a week.

Consider fields that were flooded last year
This year, we need to consider the fields that were flooded last spring. Some of these fields were flooded over an extended period of time, and plants were injured or died. These fields may need to be inoculated because the anaerobic conditions may have reduced the level of Bradyrhizobia bacteria in the soil.



Palle Pedersen is an assistant professor of agronomy with research and extension responsibilities in soybean production. Pedersen can be contacted at or by calling (515) 294-9905.

Black Cutworm Treatment Options

By Jon Tollefson, Department of Entomology
As technology traits in corn seed increase seed prices and the price received per bushel increases, it is wise to consider black cutworm management in corn.  Many areas of Iowa were cool and wet last spring, 2008. That weather often delayed planting and created flooded areas that had to be replanted. These conditions may have caused black cutworms to be more common than usual.

Producers this spring must consider the economics – higher seed corn prices and high grain prices, and the environmental factors – recent rains that may delay some planting and the presence of winter annual weeds,  when deciding how to manage black cutworm.

Some producers are asking, “Should I add insecticide to my herbicide to attempt to prevent an infestation, or should I spend time scouting the corn fields and treat only those that have the insect? I am applying the herbicide so there is no additional application cost and saving one bushel of corn is likely to pay for the insecticide.”

A sound premise of pest management is to purchase and apply controls only when necessary. Preventive treatments are generally not warranted unless there is reason, usually from past experience that the pest is likely to be present and there are no curative controls available.

black cutworm larvea on soil

A black cutworm larvae on soil.


With the black cutworm, however, the infestations are sporadic and uncertain. Also there are sampling techniques for the larva, treatment thresholds, and therapeutic control options for this pest. With the therapeutic management options it would make more sense to watch for cutworm infestations and apply insecticides when they are present.

An example, you are planting 1,000 acres of corn and, based on past experience, it is probable that you will have 10 percent infested with cutworms. If you purchase insecticide at $4 per acre and treat all of the fields, the cost would be $4000. If you scouted the fields and treated the 10 percent infested, assuming there is a treatment cost for the insecticide and its application of $12 per acre, the cost to you would be only $1200. But the catch is you must scout all those fields carefully to find the cutworms before economic losses occur.

Scouting for black cutworm
To reduce scouting time and costs, first scout the fields that are most likely to have cutworms. These fields are generally:
• Low lying fields that are poorly drained
• Located near natural vegetation areas, such as streams
• Weedy fields, especially winter annual weeds present
• Reduced tillage
• Planted late
• Soybeans the previous year’s crop
• A history of cutworm infestations

Can you picture this field in your mind? A low-lying field; could be in the flood plain of a stream or river. It is poorly drained so it takes time in the spring to dry and consequently is planted later. With the soybeans there the previous year there was no fall tillage. Now there is a good crop of winter annuals present that are getting ready to flower. If you have cutworm infestations, it is frequently in those types of fields.

Where should you start your scouting to detect cutworms? Wouldn’t these be the fields? Don’t forget to check the rest of the fields if you find infestations in the “sentinel” fields.

The economic threshold for black cutworms is:
• When larvae average less than ¾ inch in length, an insecticide should be considered if 2 or 3 percent of the plants are wilted or cut;

• If cutworms are longer, treatment should be applied if 5 percent of the plants are cut.

If the field has a poor plant population, (20,000 or less) these thresholds should be lowered. 



Jon Tollefson is a professor of entomology with extension and research responsibilities. Tollefson can be reached at (515) 294-8044 or by emailing tolly@iastate.ed .

This article was published originally on 5/4/2009 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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