Skip Navigation

6/9/2008 - 6/15/2008

In this issue:

Flooding Increases the Risk of Certain Diseases in Corn

By Alison Robertson, Department of Plant Pathology


Infection by a number of pathogens is favored by flooded conditions. Excess soil moisture and anaerobic soil conditions also favor the development of certain diseases.


Root Rots

Over the past week, I have received a number of reports of crown, mesocotyl and root rot of corn. Although root rots of corn occur to some extent every year, under wet conditions, they can cause economic losses.


Oxygen deficiency as a result of flooded conditions predisposes plants to infection by root rot pathogens (Pythium graminicola, Fusarium spp. and Exserohilum pedicellatum) that thrive in these conditions. Root rots develop further into mesocotyl and crown rots under wet conditions and thereby make a bad situation worse, especially if this occurs prior to V6. Seed treatment trials completed in 2007 by my graduate student showed a positive correlation between the incidence of mesocotyl rot at V4 and crown rot at V6. 


Remember, prior to growth stage V6, a healthy kernel, seminal root system and mesocotyl are vital for seedling survival. This is because a developing corn seedling relies on the kernel endosperm and seminal roots for nourishment until the nodal root system has fully developed, usually around the six-leaf stage.


Thus, the mesocotyl acts as the “pipeline” for translocation of nutrients from the kernel and seminal roots to the seedling stalk and leaf tissues. Therefore, as the flood waters recede and you start to assess plant stands, it is important to dig up seedlings every now and then to check below ground, as well as crown health.


Pythium and Bacterial Stalk Rot

Pythium stalk rot and bacterial stalk rot are favored by warm, wet conditions. Unlike most other stalk rots that occur after tasseling, these stalk rots can occur at any time during the season.  Symptoms caused by both pathogens are similar: the rind and pith of the first internode above the soil becomes soft, brown and water soaked (as seen in the photo below).  Affected stalks often twist and fall over. A foul odor is associated with bacterial stalk rot.


Pythium stalk rot

Pythium stalk rot in a corn plant


Crazy Top

Infection by the crazy top pathogen (Sclerophthora macrospora) occurs during periods of flooding when infective spores are produced. This fungus survives as oospores in the soil. Under saturated conditions, oospores germinate to produce sporangia within which are borne zoospores. Swimming zoospores infect the growing point of young corn plants. The most characteristic symptom of crazy top is a leafy proliferation instead of a tassel.  Other symptoms include short or long internodes, narrow, strap like leaves, excessive tillering and compete lack of ear formation.


Corn with Crazy Top

Corn plant exhibiting symptoms of crazy top


Foliar Diseases
The frequent rains we have had have also been favorable for sporulation and dispersal of the anthracnose fungus Colletotrichum graminicola. There have been a few reports of symptoms of anthracnose leaf blight starting on the lowest leaves of corn seedlings, particularly in corn-following-corn fields.


Anthracnose leaf blight in corn

Corn plant showing symptoms of anthracnose leaf blight


At this stage of the growing season it is difficult to predict if other common foliar diseases (gray leaf spot, common rust, northern corn leaf blight) will be a problem on corn this year. Foliar disease severity depends on numerous factors, the most important being weather and hybrid susceptibility. If the weather continues to be wet, there is increased risk of disease especially since planting corn was delayed this spring, and the cool condition thus far has slowed crop development.


Alison Robertson is an assistant professor in plant pathology with research and extension responsibilities in crop diseases.

Request for Phytophthora of Soybean Plant Samples

by Alison Robertson and Silvina Stewart, Department of Plant Pathology

We have had ideal conditions for the development of Phytophthora damping off. Plants infected by Phytophthora have a brown discoloration extending from the root up the stem.


Our lab is continuing to assess the diversity of Phytophthora in Iowa and requests your help in this project. The lab would like to obtain plant samples from suspected Phytophthora-infected plants, as you find them.

Please place whole plants with Phytophthora symptoms in an open plastic bag. Include at least part of the root system and information on the location from where the plants were collected (preferably GPS co-ordinates; or township and county). Mail the samples to:

Robertson Lab/Phytophthora Project
Department of Plant Pathology
351 Bessey Hall
Ames, IA 50011-1020

Alison Robertson is and assistant professor of plant pathology with research and extension responsibilities in field crop diseases. Silvina Stewart is a graduate research assistant working in Alison Robertson’s lab.

Additional Eastern Iowa Emergency Crop Meeting Scheduled

By Virgil Schmitt, Iowa State University Extension

Farmers faced with difficult agronomic and economic decisions this year have another opportunity to get some advice from ISU Extension crop, livestock and economic experts.

The  Emergency Crop Production Program will be held June 20, 1:30-3:30 p.m. at the Durant Community Center, 605 5th Avenue, Durant. The topics include:

  • economic Issues including crop insurance government payment issues
  • livestock Issues
  • crop Issues

The program is free and open to the public. Pre-registration is not required.

Virgil Schmitt is an Iowa State University Extension field agronomist serving Jackson, Clinton, Cedar, Scott, Muscatine, Louisa, Henry and Des Moines counties.

The Nation’s Wet Spot

Elwynn Taylor, Department of Agronomy

It only takes a glance at the year’s (water year begins in October) precipitation map to identify the region of ABNORMAL wetness. The record setting floods of 2008 are no surprise in light of the records. If it seems that high water years in the Midwest are increasingly common since about 1970; they are.

National Percipitation Map

The 2008 floods have arrived earlier than did the floods of 1993 and in many cases the record high flood levels of 1993 have been surpassed.  Also the 2008 event is more wide spread in the Midwest. The 1993 floods became serious in July and continued into August, past the date when corn will vigorously develop new and extensive root systems resulting in greatly reduced corn yields in every county of Iowa (only three reached 100 bushels per acre levels).

Flooding is more extensive in 2008 than it was by June 10 in 1993.  The very wet conditions of 2008 in the Ohio River Valley and southern Missouri were mainly in March and April.  The moisture in the north was mainly in May and June 2008. The extreme moisture of 1993 was mainly in July and August.

The Climate has Changed
The Midwest receives about 10 percent more annual precipitation since 1980 than was received before 1970.  This increase has effectively doubled the annual stream flow in much of the region.  Accordingly rivers are more often over their banks.  In the 40 years up to 1970 there were two “high” water years.  In the subsequent 40 years there were 12. 

Accordingly an event that might have been expected once every 200 years in the past would be expected every 33 years or so under current climate conditions.  Rivers and streams across the western Corn Belt have responded to the changing climate.

Storm System Features
The Bermuda High is a consistent and persistent feature of summer. It is the primary force moving moisture into the Midwest and should it fail to develop, wide spread drought is the result.  In 2008 an “early arriving” Bermuda High together with a Colorado Low (that has been late migrating to a more typical summer location in Canada) resulted in a much stronger than usual flow of moist air into the Midwest (RI, or Reman Index). The Jet stream associated with the Low system, also not a typical spring resident of the High Plains, provided the necessary impetus for extensive storms to develop.

There has been a gradual migration of the Low toward a more typical summer location in Canada. The extreme cold and snow in the state of Washington and the extreme storms of the Midwest will likely diminish when the Low pressure system diminishes or moves.

Similar conditions existed in 1947, a year with many record high flood reports followed by severe drought in the Corn Belt. 1983 was also similar with a very wet spring and a harsh dry summer. The chance of changing to drought conditions appears to be about 25 percent and to the warm and dry side of usual (sufficient to reduce Cornbelt yields to below trend) is about 62 percent.

Likely Yield Impacts
The sum of factors (including the long range forecasts from the National Weather Service)  indicate that 2008 may be an extreme year. The U.S. corn yield is most likely to be 148 bushels per acre, and the chance of wide-spread drought remains higher than average at slightly less than one chance in three.  However, extremes are likely during the coming years and a somewhat below trend harvest in 2008 is, at this time, expected.

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

Corn Size Restriction for POST Herbicides

By Mike Owen and Bob Hartzler, Department of Agronomy

Weeds have continued to grow thus making the application of POST herbicides imperative despite the slow development of the corn crop. However, it is also important to follow the size restrictions that exist on the herbicide label, particularly given that corn is under stress due to the poor growing conditions. 

Recognize that taller corn is generally more sensitive to potential herbicide injury, particularly when nozzles are applying the herbicide directly into the whorl of the plant. If possible, herbicides should be applied directed POST whenever corn exceeds 12 inches tall in order to improve coverage of weeds and reduce exposure of the corn. Furthermore, be particularly cautious about tank mixing herbicides. Follow the most restrictive label and be sure that the adjuvants are appropriate for all herbicides in the mixture. 

In addition to size restrictions, consider the impact of late applications on the potential for carryover injury to rotational crops. For example, products containing atrazine state only to rotate to corn or sorghum if applied after June 10.

Table 1.   Application restrictions for selected corn postemergence herbicides1. 

POST Herbicide Tables

1 Where both height and leaf stage are provided, use most restrictive classification.

2Not all POST herbicides registered for corn are included; refer the label for specific application restrictions.


Mike Owen is a professor of agronomy with research and extension responsibilities in weed management and herbicide use. Bob Hartzler is a professor of weed science with extension, teaching and research responsibilities.

Livestock and Farm Buildings After a Flood

By Jay Harmon, Department of Agricultural and BioSystems Engineering
Once the water recedes after a flood there are many things that need to be dealt with before putting a building back in service. These involve dealing with safety issues, service issues and other efforts that will prolong the life of the building. 
When a building has been submerged or partly submerged the electrical system and water system have likely been compromised. Of course the electrical system is the most immediate safety concern because of the implication of electrocution.

Care should be taken to be sure all systems are not energized. All electrical panels and wiring will need to be opened and thoroughly dried. Wiring and connections will need to be checked for corrosion and loose fittings. Any elements showing corrosion should be replaced if not easily cleaned. Open all conduits to drain water. Outlets and switches that can not be cleaned or checked for corrosion should be replaced. Motors will likely need to be disassembled and should be checked by a qualified electrician. 
Water systems, including pumps and treatment systems should be checked and thoroughly purged with sanitary water, especially before using for human consumption. Check pressure tanks and any electrical components. Examine other components such as propane regulators, tanks and lines. Tanks may have floated, compromising the system integrity.
Service issues include thoroughly checking every component including fans, heaters, controllers and lighting. Deep pit swine buildings will likely need to have the pit pumped before the building can be put into service. Wet feed should be removed from all bins and and feed lines. Wet feed can be very corrosive. Feed bins may have to be repositioned if they have been moved by rising water. Service roads also will need to be repaired to make them capable of handling farm service traffic. 
To reduce the chances that the building life is not unduly shortened by continuing flood issues, do such things as removing interior wall coverings to dry walls thoroughly. This will prevent further wood and fastener deterioration. Rigid board insulation may be reused but fiberglass and cellulose insulation that has become wet loses it's insulation properties. A thorough inspection of building integrity, including foundation anchors, should be conducted. Clean all moldy and mildewy sufraces to prevent potential health effects on animals and workers.
Before undertaking any repair work, check with your insurer for the necessary documentation for proof of loss. Company requirements may vary.
Jay Harmon is a professor of with responsibilities for extension, teaching, and research in area of agricultiral and biosystem engineering.

Hayfield Lodging – Management Concerns and Guidelines

Stephen K. Barnhart, Department of Agronomy and Mark Hanna, Department of Agricultural and Biosystems Engineering  


Rain, wind, hail, and unavoidable harvest delays have led to lodged and flat hayfields across the state. This is not usually a concern in more normal seasons, but if it occurs, producers have to manage for and around it.  

A ‘bright side’ of delayed harvest is that the forage plants have longer to accumulate carbohydrate ‘stores’ and maintain plant vigor. 

Just because hay lodges, does not mean that it will ‘smother itself.’ New alfalfa and grass shoots that will become the second growth will emerge through the older, lodged first growth. However, harvesting this combined first and partial second growth will interrupt the development of the second growth and likely slow its eventual regrowth. So, there may be a slightly longer interval between your first and second cuts this year.

A delayed first harvest often shortens the number of harvests for the season – instead of a normal four cuts you may only get three this year. In addition, the sequence of the remaining harvests should be spaced to allow for a 4 to 5 week ‘fall rest’ during September and early October to maintain the vigor of the stand going into winter.

The mature plants will be of low nutritive quality, so should be sampled and tested for forage quality and for efficient ration balancing when feeding.

Leaf and stem diseases are favored in a high-humidity, lodged canopy.

Some producers who had a chance to cut hay between storms may not have been able to bale or chop it. Windrows left in place for a long period can lead to smothering of regrowth forage. If you have windrows that have been in place for days, try to turn or harvest them as soon as possible.

In some cases, the nutritive value has deteriorated to the point that the hay may not be worth the money and effort to bale or chop it for forage. Producers sometimes sacrifice this yield option and chop or shred the weathered hay back onto the field. If you resort to this, ensure that the chopped forage is uniformly spread.

The physical process of cutting lodged hay presents challenges. Whether you are using a sickle mower or a disc mower, some machine adjustments may be necessary for effective cutting.

  • Tip the cutter bar down.
  • Take some weight off the knife or disc platform to protect the knives using the lift assist springs.
  • Keep the cut height reasonably low to get down under mat of crop.
  • Use disc cutter knives with a twist to get a little more lift, and consider use of ‘crop lifters’ designed for the disc mower
  •  If the mower has a pick-up reel, bring the reel forward and increase the reel speed if adjustments are available. 
  • Consult your operator manual for proper adjustments.

Cutting in one direction against the lodge is an effective harvest management practice, but greatly slows harvest productivity. It may be more practical in the long run to cut as usual, leaving longer, partially-cut stems on half the passes in the field and get a better overall quality on the field as a whole. Timeliness may be more economically valuable than the appearance of the field.

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management. Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery. 

Measuring the Nitrogen Status

By John Sawyer, Department of Agronomy


Tools are available that can aid decisions about applying supplemental nitrogen (N) when there have been losses of applied fertilizer or manure N. These can provide more site-specific information than estimating losses and can also provide N rate application guidance.


Late Spring Soil Nitrate Test

Details about this test can be found in ISU publication PM 1714, Nitrogen Fertilizer Recommendations for Corn in Iowa.


Soil samples are collected when corn is 6 to 12 inches tall, often in late May to early June. This year the corn growth is behind, and with the wet soils some fields will be sampled later than normal. Late sampling may complicate test interpretation. Soil conditions should allow the collection of good samples from the entire one-foot depth and with no excess water “leaking” from the sample bag. With the current wet conditions, this will be difficult. A large number of cores are needed, especially in fields with band-injected N.


Test interpretations are adjusted when spring rainfall is well above normal. In fields where less than full rates of N were applied preplant, lower the critical concentration from 25 ppm to 20–22 ppm when rainfall from April 1 to time of sampling is more than 20 percent above normal. With full rates of N applied preplant (fall or early spring) or with manured soils, the suggested critical concentration is 15 ppm if May rainfall exceeds 5 inches. In these fields, if tests are between 16 and 20 ppm, consider a small N application. In situations where manure or full rates of N were applied, a suggestion is to limit additional N application to 60–90 lb N per acre, even if the test result is 10 ppm or less.


Corn Plant N Status
A method to determine the N status of corn plants is explained in ISU Extension publication PM 2026, Sensing Nitrogen Stress in Corn. The corn plant expresses N stress through reduced leaf greenness, which can be seen as you look at corn plants and measured with sensors such as a chlorophyll meter, active canopy sensors or remote images. Measurements need to be compared with adequately fertilized (non-N limiting) reference areas in order to reduce bias due to different growing conditions, soils, hybrids or factors affecting corn plant color other than N deficiency (like plant yellowing in response to wet soils or sulfur deficiency).


Nitrogen affected corn

N-deficient corn and well-fertilized, non-N limiting strips (photo by John Lundvall).


If you are concerned about N losses, then apply two or three supplemental N strips (a rate that is non-N limiting) across fields or in targeted field areas and watch the corn. These will be the reference areas that are compared with the rest of the field. When corn gets some size to it, around the V8 to V10 growth stages, and you see differences in the color between the strips and the rest of the field, then additional N should be applied to the field or field areas showing deficiency. These applications should be made as quickly as possible in order for the corn to have best chance to respond to the supplemental N.


A method to quantify N deficiency stress and amount of N to apply is to monitor the crop with a chlorophyll meter, other sensing instrument, or aerial image. Relative chlorophyll meter values (readings from the field area of interest divided by readings from the reference area) give an indication of the severity of deficiency; that is, the lower the relative value the greater the N deficiency and the larger the N application rate needed.


Chlorophyll readings can aid in confirming suspected N-loss situations and need for supplemental N. This is especially helpful when corn has recovered from wet conditions, resumed good growth, and is putting pressure on the available N supply in the soil. The later into the growing season these readings are taken, the more they can indicate deficiencies and the better they relate to total crop N fertilization need. Small plants usually do not reflect potential N shortages because the amount of N taken up is small. Therefore, corn plant sensing is more reliable with larger plants.


Measurements from approximately V10 to VT stages should provide similar results. The table below gives suggested N rates to apply at various relative chlorophyll meter values. Readings are taken from the uppermost leaf with the collar visible until the VT stage (tassel emergence), and then from the ear leaf. Average 15–30 representative readings per field location or reference strip location.


Nitrogen Sensing Table


An advantage of plant N stress sensing or visual observation, and comparison with reference areas, is the ability to monitor the crop multiple times as the season progresses to see if the N supply is adequate, remains adequate, or N stress develops. Wet soils will cause corn to have poor coloration and rooting, and can also limit yield potential. Therefore, it is important to allow plants to recover fully from wet conditions before assessing the N status. Another advantage to plant N stress sensing is that plants integrate N supply across a period of time.


Since mineralization of N from soil organic matter is an important source of N for crop growth, waiting to determine the N status allows the plant to respond to N accumulated in the soil from mineralization. Warm, moist soils with high organic matter levels can have considerable mineralization (even when flooded), and this source of N can help offset N losses. Plant sensing and comparison to reference areas is a way to determine this contribution, as well as nitrate located deeper in the soil profile.


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

Managing Manure Storage Structures During Wet Weather

By Robert Burns, Department of Ag and Biosystem Engineering 

During excessively high rainfall periods Iowa producers with open manure storages should closely monitor manure levels to prevent these structures from over-topping.


If manure levels in storage ponds or tanks approach full capacity producers should make plans to remove manure from these structures. The over-topping of bermed earthen storage ponds and lagoons could result in breaching of earthen berms and loss of the structures. Producers should transfer manure from full storage structures to alternative storage if available during saturated soil conditions since land application of manure to saturated soils could result in run-off into surface waters.


If no alternative storage is available producers should contact the Iowa Department of Natural Resources to discuss emergency wet-weather land application before allowing a storage tank or pond to overflow. The Iowa Department of Natural Resources (IDNR) suggests that producers should contact their local field office if manure levels reach one foot below the top of a concrete or steel structure, or within two feet of the top of an earthen bermed structure.


Contact Information for IDNR Field Offices is shown below.


Field Office # 1 - Manchester (563) 927-2640

Field Office # 2 - Mason City (641) 424-4073

Field Office # 3 - Spencer (712) 262-4177

Field Office # 4 - Atlantic (712) 243-1934

Field Office # 5 - Des Moines (515) 725-0268

Field Office # 6 - Washington (319) 653-2135


Robert Burns is an associate professor with extension and research responsibilities for animal manure management.

Good Seed Supply Available from Most Companies in Iowa

By Palle Pedersen and Roger Elmore, Department of Agronomy


Excessive rainfall in Iowa over the last 2 months has challenged most farmers, agronomists, extension workers, and researchers. With another front of storms moving into Iowa today (June 11) we do not know when we will be able to get back into the fields. Our best estimate is that it will first be next week at the earliest.


Yield potential for both soybean and corn has dropped significantly in Iowa since we are more than a month after the optimum planting date for both crops. However, we still have a chance to get a crop but the yield may not be what we have experienced over the last few years. As of June 8, USDA predicted that only 86 percent of Iowa’s soybeans were planted and an estimated 6 percent of that was in need of replanting. Ninety-eight percent of the corn was planted while 7 percent  was in need of replanting. These numbers will likely increase in the next report because of recent flooding.


When planting late we need to consider planting shorter season varieties and hybrids to insure they mature prior to the first killing freeze in the fall. Remember we had a killing freeze on September 15 throughout a large part of north central Iowa last year. For soybean it is recommended to plant the “original” full season variety until June 20 in northern and central Iowa and early July in southern Iowa. If planting occurs after these dates shorten the maturity group by 0.5 to 1.0. For corn, planting earlier-season hybrids was recommended in late May.


Many have asked if there are seeds available for replanting. We sent an email earlier this week to several major seed companies in Iowa. We asked them about their inventory for replanting. Responses from the different companies varied but over all we are in a good situation. The reason is that planting progress in more northern states has been easier than in Iowa this year and left over seed is being moved south into Iowa.


All companies have soybean and corn seed available. Here is a summary of the responses we received:



  • Supply of soybean seed this year was down because of quality issues. Yet there is plenty of seed available in maturity group 2.
  • Most companies’ seeds are conditioned. If more conditioned seed is necessary, the demand will easily be met.
  • Soybean seed in maturity group 1 and 3 are less available than in maturity group 2.
  • Seed quality varies across the companies from 80 to 95 percent germination.



  • Corn seed is available. Many companies are positioning themselves by moving 90 and 100 day corn into Iowa.
  • The open window for planting corn, however, is getting close to closing. Yield potentials for corn planted today might be 70 percent of normal. In two weeks, it may be down to 50 percent.
  • Farmers will continue to plant corn until June 25 because of high prices, if nitrogen and/or herbicide have been applied, or just to be sure to qualify for the federal crop.


The best advice is to be calm, manage the planted fields and hope that we get some dry weather in the near future. More information on soybean and corn management decisions can found at and at


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

ISU Weed Science Field Day Cancelled

By Mike Owen, Department of Agronomy


The ISU Weed Science Field Day scheduled for June 26 has been cancelled due to an inability to get into the field. We apologize for this inconvenience but unprecedented weather has resulted in continuous flooding and saturated soils making it impossible to establish demonstrations and research protocols. 


However, it is anticipated that all demonstrations and research protocols will be established as soon as conditions improve.  If you are interested in viewing the field research and demonstrations, contact  me at to arrange for a tour. Field books will be available online or they can be purchased on site ($20). All visits will be accommodated and appropriate guided tours provided as requested. If you have any questions, please do not hesitate to contact me.


Mike Owen is a professor of agronomy with research and extension responsibilities in weed management and herbicide use.

Forage and Cover Crop Considerations for Delayed Planting and Flooded Sites

By Stephen K. Barnhart, Department of Agronomy

Extended periods of rainfall, flooding, hail or all of the above have producers scrambling for replant or prevented planting options. Each choice has practical and economic implications, so should be approached with some thought. William Edwards, ISU economist, provides a good overview of crop insurance implications for many of these choices. See his article Economic Impact of Delayed and Prevented Planting Provisions.

Some options come down to forage crop alternatives and simply ‘cover crop.’  When considering crops for an annual forage, practical issues include: 

  • Can I use the forage?
  • If I will not be using the forage, can it be sold or rented?
  • Will the forage crop be harvested as silage, dry hay, or will it be grazed?  

While many species may fit the criteria for these uses, the following are among the most practical, predictable, and economical.

Dry Hay Options

Silage Options

Grazing Options

  Foxtail Millet

 Foxtail Millet

Foxtail Millet

  Japanese Millet

  Japanese Millet

Japanese Millet





  Sorghum X Sudan Hybrid 

Sorghum X Sudan Hybrid


Hybrid Pearl  Millet

Hybrid Pearl  Millet




Seed supplies of some of these forage crops are in short supply in normal production years. As you consider these as options for your needs, check on seed availability. 

Table 1. Forage Planting Date, Harvest Date, Yield and Quality of Annual Forages

Table 1 Forage Dates
*RFV = Relative Feed Value, 100 equals approximately the digestibility and feed energy value of full bloom alfalfa.

Below are general production and feeding details for each type of forage. 

Sudangrass - multiple-cut, summer annual; used for fresh cut forage, pasture (rotation grazing is recommended), or silage; difficult to dry thoroughly for hay; varieties vary in height and leafiness. Plant through early-July.

The first growth is useable in about 50 days. At this late planting date you may get a 2nd harvest or grazing. A hydrocyanic acid poisoning (Prussic acid) risk is minimal, but avoid pasturing severely drought stressed or very short (<12 inches) growth/tiller regrowth, and use caution if grazing soon after frost.

Hybrid Sorghum X Sudangrass - multiple-cut, summer annual; used for fresh cut forage, pasture (rotation grazing is recommended) or silage; varieties vary greatly in height, leafiness, grain yield depending on the parent lines making up the hybrid. Plant through early-July. The first growth useable in about 50 days, Regrowth is from tillers. At this late planting date you may get a 2nd harvest or grazing. There is a hydrocyanic acid poisoning (Prussic acid) risk if plants or tillers are grazed or green fed at short height (<24 inches) or during severe drought and use caution if grazing soon after frost.

Sudangrass, and sorghum X sudangrass hybrids are better adapted than most species to drought, high temperature and low soil pH than corn, but will yield less in seasons with cool August and September temperatures. Sudangrass and sorghum X sudangrass hybrids should be harvested at 2 to 3 feet of height (two to three cuttings for season). Harvesting at later maturity may increase yield but will result in very low forage quality. 

Short Grain Sorghum/Forage Soybean Mixture - planted through early summer. Harvestable within about 60 days. Requires good fertilization for production. Harvest at late vegetative or very-early head stage of the sorghum.

Foxtail Millet - also called German, Siberian or hay millet. Summer annual grass; used as harvested or grazed forage; Plant through mid-July. Useable  in about 50 days. One summer growth (vegetative 1-2 ft, with seedhead 2-3 ft); best of the 'millets' for an emergency hay crop; can become a weedy grass if allowed to produce mature seed.

Japanese Millet - a summer annual grass; relatively coarse (stemmy) forage; used as fresh cut forage, hay, silage or pasture. Plant through mid-July. Useable in about 50 days. Very little regrowth if first growth is allowed to reach maturity - if cut at vegetative growth stage, regrowth yields are more likely. Closely related to the grassy weed barnyard grass, so avoid allowing seed formation.

Hybrid Pearl Millet - a multiple-cut, warm-season annual; used for fresh cut forage, pasture (rotation grazing is recommended), or silage; resembles sorghum  X sudangrass hybrids in plant structure; plant through early July. Useable in about 50 days. Somewhat slower regrowth than sorghum X sudangrass hybrids;  poor production in cool summer seasons; no risk of hydrocyanic acid (Prussic acid) poisoning.

These annual millets have been of particular interest in recent years. Remember that these are warm-season crops and perform best in warm, sunny growing seasons. They have not performed up to expectation during cool, cloudy summers.  

Oats - planted June or July as a cover crop, can be grazed about any time. Will likely head at a short height. Can be cut and stored as dry hay or silage form late-vegetative through early milk stage. At dough stage, the stems decrease feeding value greatly. Other cereal grains may also fit this use, such as barley, spring wheat, or spring triticale, but their seed will likely more expensive and in shorter supply than for oats.

While it is the farthest thing from our minds now, these annual forages can come under scrutiny later in the growing season for high nitrate risk if the season turns dry.

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management.

Emergency Iowa Crop Production Program Offered

By George Cummins, Iowa State University Extension


The 2008 crop production season has had many challenges. The cool, wet spring delayed or prevented planting and recent flooding has damaged or destroyed crops. Farmers are faced with difficult agronomic and economic decisions. To help farmers understand the options available, Iowa State University (ISU) Extension is holding an Emergency Crop Production Program. It will be held, Friday, June 13, 1:30  to 3:30 p.m. at the ISU Northeast Research Farm, 3321 290th St., Nashua, Iowa.
This program will feature individuals with a wide range of expertise. The topics and experts include:

Economic Issues including crop insurance government payment issues

  • Robert Tigner, ISU Extension Farm Management Specialist
  • Max Brandau, Iowa Farm Bureau Insurance Representative
  • John Bahnsen, Floyd County FSA Director

Livestock Issues

  • Russ Euken, ISU Extension Livestock Specialist

Crop Issues

  • Brian Lang, ISU Extension Field Agronomist
  • George Cummins, ISU Extension Field Agronomist
  • Ken Pecinovsky, Northeast Research Farm Superintendent

The program is free and open to the public. Pre-registration is not required. To reach the Northeast Research Farm, go west of Nashua on B60 to Windfall Avenue, go one mile south, turn east on 290th Street and the Research Farm is on the north side of the road.


Questions about the program should be directed to your ISU County Extension Office or George Cummins (641) 228-1453.


Flooded Iowa Farmstead

Flooded Iowa Farmstead

Estimating Nitrogen Losses

by John Sawyer, Department of Agronomy


One method to judge nitrogen (N) loss is to calculate an estimate. Predicting the exact amount is quite difficult as many factors affect losses. However, estimates can provide guidance for supplemental N applications.


Excess rainfall this spring occurred in two “periods.” The first arrived early. Loss during that time should have been moderate compared to the same situation that has occurred this late spring. In the early spring, soils were colder, so conversion to nitrate and denitrification was slower. However, wet soils in late spring are warmer and have been saturated for a prolonged period. This significantly increases the chance for loss.


Research Measurement of Nitrate Loss

Research conducted in Illinois* indicated approximately 4 to 5 percent loss of nitrate-N by denitrification per day that soils were saturated. An all-nitrate fertilizer was applied when corn was in the V1 to V3 growth stage (late May to early June). Soils were brought to field capacity and then an excess 4 inches of water (above ambient rainfall) was applied by irrigation evenly over a 3-day period (which maintained saturated soils for 3 to 4 days on the heavier textured soils) or an excess of 6 inches of water was applied over an 8-day period (which saturated soils for an additional 3 to 4 days).


The excess water application resulted in loss of 60 to 70 lb N/acre on silt loam and clay loam soils, due to denitrification loss. On a very coarse-textured, sandy soil, virtually all nitrate-N was moved out of the root zone by leaching. On the heavier textured soils, an addition of 50 lb N/acre after the excess water was sufficient to increase corn yields to approximately the same level where no excess water was applied. This was not the case on the sandy soil because considerably more N was due to leaching.


Nitrate loss via tile drainage does increase with wet conditions. At the Gilmore City, Iowa ag-drainage research site where tile-flow nitrate has been monitored since 1990, nitrate loss is greatest in years with higher precipitation and hence greater tile flow. At N fertilization rates of 150 to 160 lb N/acre, the annual nitrate-N loss per acre was 52 lb in the 1990-1993 time period, 9 lb in the 1994-1999 time period, and 39 lb in the 2000-2004 time period (average nitrate-N losses for the combined corn-soybean sequence).


The range in yearly nitrate-N loss for the years studied was 1.0 lb nitrate-N/acre in 1997 to 75 lb nitrate-N/acre in 1990. The climatic conditions in years prior to tile flow can significantly affect nitrate loss and corn responsiveness to applied N in subsequent years. For example, dry years preceding years with considerable tile flow will increase concentration and loss. The 1990 year followed several dry years, and that year had the highest nitrate-N loss of the years studied. In 1993, the wettest year of those studied and with a somewhat similar spring to this year, the annual nitrate-N loss was 53 lb nitrate-N/acre.


Typically a high portion of tile flow and associated nitrate-N loss occurs in the springtime. The impact of excess precipitation on potential for nitrate remaining in the soil for crop use in wet springs like this year is that more nitrate-N is lost via tile flow, and overall the annual loss would be in the range of perhaps twice the “normal” loss amount, increasing from around 15-25 lb N/acre to 40-50 lb N/acre.


Estimating Nitrate Loss

According to research at the University of Nebraska, the estimated denitrification loss of nitrate when the soil temperature is 55 to 60 degrees F is 10 percent when soil is saturated for 5 days and 25 percent when saturated for 10 days (2 to 2.5 percent loss per day). Loss increases with warmer soils. Research conducted in Illinois with late May to early June (soil temperatures greater than 65 degrees F) excess application of water on silt loam and clay loam soils indicated approximately 4 to 5 percent loss of nitrate present per day that soils were saturated.


To estimate N loss, the first step is to estimate the amount of ammonium converted to nitrate-N. By the end of May this year (cooler than normal), one might assume late fall anhydrous ammonia and manure ammonium to be 60 percent or more converted to nitrate and with early April preplant N application, approximately 50 percent or more converted to nitrate. Less conversion to nitrate would occur with use of a nitrification inhibitor.


Recent ammonium applications (within the last two weeks) would still be predominantly in the ammonium form, especially for anhydrous ammonia. Recent application of nitrate-containing fertilizers would result in more nitrate present during the same time period. Urea-ammonium nitrate solutions (28 or 32 percent UAN) contain one-quarter nitrate-N, and nitrify more rapidly. The second step is to estimate the percentage of nitrate-N loss as described in the research above. The amount of N loss is calculated from these two estimates.



The following might be an example of a situation with an early spring application of UAN solution and the wet conditions encountered this late spring. If 85 percent of a 120 lb N application is converted to nitrate, and soils were then saturated for ten days when warm, the N loss estimate would be (120 lb N per acre x 85% nitrate/100) x (4% per day/100) x (10 days) = 40 lb N per acre. Add in increased tile flow on tile-drained fields, and the loss estimate could be 60 lb N per acre. Variation of lower or higher losses could easily occur depending on warmer or cooler conditions, different forms of applied N, more or less time from N application to wet conditions and more or less time soils are saturated. The same will occur for different landscape positions and soils. With very coarse-textured/sandy soils, significant rainfall events (4 to 6 inches or more) in addition to already moist soils could easily result in all nitrate leaching out of the crop rooting zone.


*Reported in the 1993 Iowa State University Integrated Crop Management Conference proceedings, pp. 75–89, and in Torbert et al., 1993, “Short-term excess water impact on corn yield and nitrogen recovery,” Journal of Production Agriculture 6:337–344


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

Disease Management in a Flooding Season

By XB Yang, Department of Plant Pathology


This planting season has been so wet in Iowa with flood happening every week. This naturally leads to questions what will happen to crop diseases. So far this season has some similarity to what happen in 1993, my first year at Iowa State University and those experiences have stayed with me. That year planting was so delayed that planting related questions were a major topic to ISU agronomy extension even in early summer field days. Looking at what happened in 1993 may provide some clues to disease management this season if the weather pattern continues to produce the similarity. 


In corn, two diseases were prevalent in 1993, crazy top and corn rusts which include both common corn rust and southern corn rust. Corn plants which stood in water for a long time had relatively high incidence of crazy top, a disease caused by downy mildew fungus. Southern corn rust showed up as early as late June and was widely spread. However the disease may not be a problem this year because in 1993 the disease spread to Iowa from south. This spring has been dry in Florida and Texas; both are the source regions of the fungus. The disease is unlikely to arrive so early. If the disease was prevalent, we may see return from the use of fungicide control.


Soybean diseases were production problems in 1993. Brown stem rot, a disease occurs in cool and wet weather, was prevalent in the season causing lodging in severely infested soybean fields. 


SDS was prevalent in many north central states and was found in Iowa for the first time. This year the disease may be problem even we had a late planting because prolong cool weather during the planting season is favorable to the fungus.Because the management measures for these two diseases are made before or during planting, there is nothing we can do about now, except for scouting to gather management information for future  crop years.


In the fall of 1993, premature defoliation from foliar diseases was prevalent and many soybean fields turned yellow before September. Two reasons caused the premature defoliation that fall. First, fields were flooded for so long and soybean did not have good root systems. Second, the excessive rainfall led to the outbreaks of brown spot, a rain-borne fungal disease, and other foliar diseases, which defoliated soybean leaves.


So keep an eye on foliar diseases, especially brown spot this season. Preventative measures can control this disease. The first is to use mid-season tillage which can improve root growth.  Secondly, we could control foliar diseases with the fungicides if the disease risk is high this summer. Numerous studies consistently show that fungicide sprays pay off when significant number of diseases are present.


Soybean white mold has been a concern to many producers in eastern Iowa and the disease was prevalent in every even-year in the last ten years. In this season, this disease poses less threat because of delayed planting, making it unlikely the canopy will close early, a necessity for a white mold outbreak. White mold was not a problem in 1993.


It is difficult to predict what the climate will be for the rest of growing season.  So watch national weather forecasts and scout for diseases to help you make good management decisions.  Also, it may be worth to dig out 1993 ICM articles.


XB Yang  is a professor of plant pathology with research and extension responsibilties in crop diseases.

Rainfall has Affected Hay and Hay-Crop Silage Harvest

by Stephen K. Barnhart, Department of Agronomy


Hay is an agricultural product that varies greatly in nutritional quality. The ‘hay market’ frequently uses descriptive terms like ‘dairy quality,, ‘beef-cow quality’ or more quantitative terms like ‘premium,’ ‘good’, and ‘fair’; which have some forage testing guidelines to place hay lots in these categories.


For hay, alfalfa- or grass-dominant, to be good enough to be marketed as ‘dairy quality’ or ‘premium,’ it has to be harvested at a growth stage where the plant is composed of a high leaf proportion and less fibrous stems. Forage harvested and stored as hay-crop silage can be placed into the same general nutritional categories.


Producers in the Midwest have seen rain and flooding prevent them from cutting their first hay or silage harvest of the season at an early maturity stage, so very little ‘dairy’ quality’ or ‘premium’ hay or silage has been stored.


The June 2, Iowa Crop and Weather newsletter from the USDA-National Agricultural Statistical Service provides the first indication of ‘first cut’ hay and forage harvest in Iowa. The report says that in a ‘normal’ year, Iowa producers would have harvested about 32 percent of intended first cutting hay by June1.


Statewide this year, only 8 percent of the first cutting of forage has been cut and stored. The northeast and east central crop reporting areas of the state are only slightly ahead of the state average at 15 percent.


Any first cut hay or silage harvested after June 1 will be more mature and will not have the nutritional characteristics to be classified as ‘dairy quality’ or ‘premium.’ Since forage crops can be harvested three, four or even five times per year, there is still a good opportunity for Iowa producers to harvest higher quality hay later in the growing season to make up some or all of the deficit. 


A feed supply problem still exists, however, on many dairy farms in the state that depend on a ‘normal’ first cutting. We are at the end of the 2007-2008 ‘winter marketing season’ so there are limited supplies of ‘old crop hay’ still available, but at ‘top price’ for those who need high quality hay for their livestock.


States to the west, South Dakota, Nebraska and Kansas, have had a better opportunity for producing ‘dairy quality’ hay this season, so producers can find some ‘new crop’ hay coming into Iowa hay auctions, and can locate hay on www-based ‘hay net’ and ‘hay list’ sites. The prices for ‘dairy quality’ or ‘premium’ hay are similar to winter prices, until a firmer picture of regional hay availability comes. A few Web-based hay marketing sites are listed  in the column to the right.

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management.

Nitrogen Loss – How Does it Happen?

by John Sawyer, Department of Agronomy


Much of Iowa is experiencing excessively wet conditions this spring. With the continued large rainfalls and flooding conditions, nitrogen (N) loss is an issue. While the wet period early this spring had an influence on N in the soil, excessively wet conditions now are especially critical for N losses due to warm soils and considerable conversion of applied fertilizer and manure N to nitrate.


This month will be an important period to assess crop conditions, productivity potential and needed N applications. Remember, if the corn crop is severely damaged by excess water, application of N will not overcome that damage and lost yield potential. In some cases, application of additional N will not be warranted. This is the first of a series of three articles discussing N losses this spring.


Nitrogen Processing in Soil

If applied N or mineralized organic matter N (conversion from organic to ammonium) would stay in the ammonium (NH4+) form, then losses would not occur because ammonium attaches to soil and does not leach (move through the soil with water) or denitrify (microbial conversion to N gases when soils become saturated). Unfortunately, that isn’t the way it works. Ammonium is converted to nitrate (NO3-) via nitrification.


Nitrate is the form that can be moved out of the soil profile by leaching or lost by denitrification. The conversion of ammonium to nitrate and the conversion of nitrate to N gases are both microbial processes. Hence, potential N loss is dependent upon factors that influence each – for nitrification, soil temperature is very important (faster with warm soils, slower with cold soils), for denitrification, soil temperature, soil moisture (only occurs when soils are saturated – anaerobic conditions) and readily available organic matter for an energy source. If fertilizer N is applied in the nitrate form, then that N is immediately subject to these loss pathways. Mineralization does occur when soils are saturated, so ammonium can accumulate in flooded soil and add to crop available N.


Potential for N losses

Greater losses occur when soils enter the spring season with recharged subsoil moisture, when more N is in the nitrate form and when soils are warm. Deciding if losses are substantial enough to warrant supplemental N application, the following factors should be considered:

  1. amount of nitrate present, which is affected by time of N application, form of N applied, rate applied, and use of a nitrification inhibitor;
  2. when and the length of time soils are saturated;
  3. subsoil recharge, leaching rate, and drainage – water amount moved through the soil; and
  4. loss of crop yield potential from water damage.

Leaching and denitrification are not uniform across the landscape. Thus, the potential for N loss is variable and difficult to predict. For example, with high intensity rains, runoff occurs and not all of the water soaks into the soil. Instead, water in excess of infiltration moves to the lower landscape where it may form ponds or spill over stream banks into floodplains.


An important consideration is the conversion to nitrate. In Iowa, a substantial amount of anhydrous ammonia and ammonium containing manure is fall applied. The computer simulation model “Fate of Anhydrous Ammonia in Iowa Soils,” developed at ISU by R. J. Killorn and S. E. Taylor, indicates that in a cooler-than-normal scenario, and with ammonia applied November 1, 30 percent or more of the ammonium would be converted to nitrate by May 1 (with use of the nitrification inhibitor N-Serve, estimated ammonium remaining on May 1 would be about 75 percent for a November 1 application).


With cool spring temperatures and an April 1 application, by May 1 approximately 70 percent or less would still be ammonium and by June 1, 45 percent or less. For a May 1 application and cool temperatures, by June 1, 50 percent or less would remain as ammonium.


The winter and early spring were cold this year, which would result in slower than normal nitrate formation. However, the wet soils are continuing well into June and soils have warmed, and unless ammonium fertilizer or manure was applied recently, a high proportion of applied N would be nitrate by this time.


If an N form was applied in the spring that has more rapid nitrification than anhydrous ammonia (urea, ammonium sulfate, ammonium in manure) or contains part of the N in the nitrate form (ammonium nitrate or urea-ammonium nitrate solution – UAN 28 or 32 percent), then conversion to nitrate would be faster.


Conversely, if an ammonium-containing fertilizer (anhydrous ammonia, urea or ammonium sulfate) or manure was applied shortly before a wet period, then loss would be negligible because little nitrification to nitrate would have occurred because nitrification does not occur in saturated soils and will not resume until soils dry and become aerobic.


Conversion to nitrate does not equal loss; it just means the N is susceptible to loss. Rapid and large losses occur only with excess leaching (predominant concern with sandy/coarse-textured soils) or with saturated soils (predominant concern with heavier textured, poorly drained soils).



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

Summer Flooding of Hay Fields and Pastures

By Stephen K. Barnhart, Department of Agronomy

Most forage crops perform best when soils have adequate, but not excessive, soil moisture. Standing water, flowing water and waterlogged soils following heavy summer rainstorms or extended periods of higher than normal rainfall patterns can all cause management concerns for forage crops.

Management Suggestions

  • As soon as possible, check hay fields and pastures for flood debris that might damage harvest equipment or harm livestock.
  • Try to avoid moving into hay fields or pastures too soon because they are still quite susceptible to wheel traffic and compaction damage, which also will limit the future productivity of the field. 
  • Flooded forage may be silt-covered, which will add to plant disease potential, detract from the palatability of the harvested hay, add to the ‘ash’ content on a forage test, and possibly affect normal silage fermentation.
  • Plants growing in saturated soils can be damaged physiologically. Delay harvest for a week to 10 days to allow the plants to regain what vigor and recovery that they can. This management approach will produce a more mature forage crop of lower nutritive value. In addition, take extra care to schedule a 5- to 6-week "fall rest" period for these stands.

Alfalfa, clovers, and most forage grasses cannot live for very long under water. Most forage plants can tolerate a short term of flowing water (for a few days to a week).

Standing or ponded water that "heats" in the sun and "cooks" the submerged forage plants is more of a concern and can kill or severely damage most plants within hours. After the surface water recedes, an extended period of saturated soils continues to be reason for concern.

Forage plants (other than perhaps reed canarygrass) will live for a week or two in saturated soils, but the lack of oxygen in the root zone will adversely affect their growth.

These plants do not take up soil nutrients normally, an increasing part of the root system deteriorates, and legumes cease "fixing" nitrogen. They appear stunted and yellowish-green in color. If the soils drain quickly, plants begin to recover.

If flooded areas are recovering slowly and you are concerned about the viability of the stand in those areas, dig random plants in several areas and evaluate the condition of the root systems.

Legume plants with a firm taproot, creamy white in color with no evidence of root rot, and that have green and visually healthy crowns and crown buds have the greatest likelihood for survival. These plants need a week or more of sunshine and drying soils.

Legume or grass plants with watery, mushy, textured roots, yellowish or tannish in color, and those with no evidence of active crown buds will be the least likely to survive, even with good growing conditions during the next few weeks.

Pasture plants are affected much the same as alfalfa when under standing or flowing water and growing in water-logged soils. Grasses are, however, slightly more tolerant of these conditions than are legumes.

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management.

Economic Impact of Delayed and Prevented Planting

By William Edwards, Department of Economics

Most crop producers know that to achieve optimum yields it is important to plant early. However, in years like this when cold weather or frequent rains prevented tillage and planting from being completed, some adjustments may be made to the amount of coverage provided by Multiple Peril Crop Insurance (MPCI) as well as other types of crop insurance. These adjustments are subject to revision each year by the Risk Management Agency and crop insurance vendors.

There are a few tools available to help Midwest crop producers make the tough decisions on delayed and prevented planting.

The first is my  Delayed and Prevented Planting publication. On the ISU Extension Ag Decision Maker site there is an interactive online Excel spreadsheet that allows you to calculate the impact on your operation.

In addtion, the University of Illinois farm business management experts have pulled together some additional tools to aid Midwest crop producers.

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

SCN Confirmed for First Time in Lyon County

By Greg Tylka, Department of Plant Pathology

Research and extension personnel in Iowa have tracked soybean cyst nematode (SCN) infestations by county since initial discovery of the nematode in Winnebago County in 1978.

Years Iowa Counties were Infested with SCN

This map indicates the years that counties were Infested with soybean cyst nematode.

SCN was discovered for the first time in many different Iowa counties in the 1980s and 1990s. But by 2000, there were only nine Iowa counties in which SCN had not yet been found.  The nematode was discovered in a few new Iowa counties from 2000 to 2006, but, it had still not yet been found, or at least officially confirmed, in three Iowa counties – Allamakee, Ida, and Lyon Counties – by the end of 2007.

ISU Extension field agronomist Joel DeJong conducted a survey for SCN in several counties in the northwest corner of Iowa in 2007, including Lyon County. The survey was supported by the ISU Corn and Soybean Initiative and soybean checkoff funds from the Iowa Soybean Association. 

SCN had informally been known to be present in Lyon County for a few years, and cyst nematode eggs were recovered by private laboratories from soil samples taken from Lyon County in the past. But SCN had never been officially confirmed by greenhouse testing. 

Eggs believed to be from SCN were recovered from soil samples collected as part of the survey from two fields in Lyon County in 2007. To confirm that the sampled fields were infested with SCN and not some other cyst nematode, follow-up soil samples were collected from the Lyon County fields early in 2008, and susceptible soybeans were grown in the soil samples in a greenhouse for a month. Many SCN females were observed on the soybean roots, confirming the presence of SCN in the county.

Iowa Counties Infested with SCN

Iowa counties (in red) infested with soybean cyst nematode as of June 2008.

There now are only two Iowa counties in which there is no official record of SCN – Allamakee and Ida County. If anyone knows of SCN in fields in either Allamakee or Ida County, they are encouraged to send soil samples from the fields to the Plant and Insect Diagnostic Clinic, 327 Bessey Hall, Iowa State University, Ames, Iowa 50011, so that soybeans can be grown in the soil to verify the presence of SCN.

Although SCN has been found in almost every Iowa county, every field in the state is not infested with the nematode. A comprehensive 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. This survey will continue through 2008 and 2009.  A summary of the 2007 survey findings is available.

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

Stalk Borers Set to Invade Border Rows

By Marlin Rice and RIch Pope, Department of Entomology

Stalk borers are notorious for killing or stunting corn rows next to fences, grassed waterways and conservation terraces. To stop this damage, fields must be scouted and an insecticide applied on a timely basis before the larvae have an opportunity to tunnel into the growing point of the young plants.

Stalk Borers in Grass
There is one generation of stalk borers each year, and the eggs were laid late last summer and early fall. By early June, stalk borer larvae will have hatched in Iowa and most of the larvae will be inside brome grass, other grasses or giant ragweed.

However, a few stalk borers may already be in corn because they moved there first instead of to grass. Stalk borers in brome grass eventually kill the grass seed head, causing "dead heads." The larvae eventually grow too large for the grass stems and then they crawl out in search of larger diameter plants, including corn.

Degree Days and Migration
Mid June is the predicted time for southern Iowa when stalk borers will move out of grass and into corn. Approximately 10 percent of the larvae will move out of the grass by 1,400 degree days (base 41 °F) and 50 percent of the larvae will have moved by 1,700 degree days. When 1,300-1,400 degree days have occurred in your area (Table 1), scout to determine whether the larvae are moving into corn. These dates predict when 10 and 50 percent of the larvae will move into corn.

Stalk borer damage
Stalk borer damage to border rows

Scouting Border Rows
If stand loss has occurred in your corn fields in past years, then there is a good damage may occur again. In these situations, an insecticide can be sprayed to the border rows. However, if you are uncertain whether stalk borers are a potential threat, then scout the corn adjacent to grass terraces, waterways, ditches and fencerows at 1,300 degree days.

Stalk borers don't crawl very far from grass, so only the first four rows of corn next to grass would need to be sprayed. Look for small larvae resting inside the whorls or for new leaves with feeding holes. Larvae that are still feeding in the whorl, but that have not yet tunneled into the plant, can be killed with an over-the-top insecticide. The smaller the corn, the more likely it is to be killed by stalk borers. Once corn reaches the 7-leaf stage (V7 stage), stalk borers are unlikely to kill the plants.

Fields with Weeds
An exception to the border row problem is when weedy grasses, and especially giant ragweed, are growing throughout a corn field. If these weeds are killed with herbicides, the stalk borers move out of the weeds and into the corn. Stalk borers can destroy a corn stand under these circumstances.

To prevent this destruction, an insecticide should be tank mixed with the herbicide (if it is a fast burndown herbicide) or the field should be sprayed with the insecticide approximately 7 days after the herbicide (if it is a slow burndown herbicide). Be sure to read the insecticide label before mixing pesticides.

Bt Corn
In some of our experiments, we have found that Bt corn (YieldGard® Corn Borer hybrids) suppresses or slows down stalk borer injury. Hybrids with this technology do not have the same toxic effect on stalk borers as on European corn borers, so don't expect complete control of this pest in Bt corn. You may want to scout your Bt corn acres as well if you have historically had a problem with stalk borers. We have not evaluated Herculex® I or Herculex® XTRA hybrids, so we are unfamiliar with the performance of this technology against stalk borers.

Table 1. 2008 projected dates for migration of stalk borer (base 41 °F).

Iowa Crop Reporting Districts

Accumulated DD41

(as of June 8)

Projected 10% migration

(1400 DD)

Projected 50% migration

(1700 DD)



June 23

July 2



June 24

July 2



June 23

July 1



June 17

June 26



June 18

June 28



June 16

June 25



June 13

June 22



June 13

June 22



June 11

June 20

Marlin E. Rice is a professor of entomology with extension and research responsibilities. Rich Pope is an extension program specialist working in the Corn and Soybean Initiative.

June is Bustin' Out All Over!

And then it rained, and rained some more. Heavy and severe thunderstorms were generated by a lingering front that parked over Iowa for the bulk of the week. Consequently, little field work was accomplished in most fields in Iowa.

In addition to the heavy rains, the clash of air masses is evidenced by the degree day accumulations for the week. Southeast Iowa gained 40 base-50 degree days over average, while Northwest Iowa was about on average. The 40 degree days represents approximately 2 days of normal weather for crop growth, so it is like getting a 9 day work week in for growing plants.

Degree day accumulations on June 8

Seasonal accumulations are now just slightly behind normal (since May 1). Because of the significant field delays now, keep an eye on the Integrated Crop Management News site for articles on specific concerns. These include late planting and replant considerations, potential losses of nitrogen from waterlogged fields, weed problems exacerbated by the delays, and prevented planting options.

Crop Advisers Can Earn Credit at Southeast Iowa Field Day

By Jim Fawcett,  Iowa State University Extension

Certified crop advisers (CCAs) can earn 5 hours of credit (2 hours in soil and water management, 2 in crop production, and 1 in pest management) by attending a special CCA morning session, followed by a controlled drainage tour and afternoon field day tour at the Iowa State University Southeast Iowa Research and Demonstration Farm near Crawfordsville on June 26.

The morning session will begin at 9 a.m., featuring a presentation by Kendall Lamkey, ISU Agronomy Departgment chair and corn breeder, on Corn Yields – How High Can They Go? Next I will talk about Corn Herbicide Management and Mismanagement. The mornng session wraps up with Matt Helmers and Greg Brenneman, ISU Extension ag engineers, leading a tour on the controlled drainage research occurring on the farm.

The afternoon tours start at 1 p.m. and topics include:

  • Crop Season Review and Current Crop Concerns, Kevin Van Dee, Farm Superintendent, and  Mark Carlton, ISU Extension field agronomist;
  • Food vs. Fuel vs. Feed by Kendall Lamkey;
  • Does Tiling Pay? by Matt Helmers; and
  • New Corn Herbicides by Jim Fawcett 

Registration for CCAs will begin at 8:30 a.m. The registration fee is $50, which includes lunch. Please pre-register by calling the Johnson County Extension Office at (319) 337-2145 or send an e-mail to Jim Fawcett ( by June 24 to avoid a $20 late fee. Registrations made after June 24 will be $70. The registration fee can be paid at the door. To reach the research farm go 1 and 3/4 miles south of Crawfordsville on Highway 218, then 2 miles east on G-62, then 3/4 mile north.

Jim Fawcett is an Iowa State University Extension field agronomist serving Benton, Linn, Jones, Iowa, Johnson, Keokuk, and Washington counties.

This article was published originally on 6/16/2008 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.