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9/22/2008 - 9/28/2008

Time to Scout for Stalk and Ear Rots

By Alison Robertson, Department of Plant Pathology
When corn reaches black layer, the crop should be scouted for stalk and ear rots. Anthracnose stalk rot is apparent in many fields across the state and Diplodia ear rot  has been reported. 

The incidence of corn ear rot should be determined before harvest since ear rot diseases can reduce yield and quality of the corn harvest. Furthermore, some of the fungi that infect corn ears may produce mycotoxins, which are harmful, and can be fatal, to livestock.

At least 100 plants, scattered throughout the field, should be assessed. Look for visible symptoms of ear rot by stripping back the husks. For a description and photographs of ear rots you might encounter in the field see corn ear rots. If more than 10 percent of the ears have significant mold that is greater than 25 percent of the ear, the corn should be harvested in a timely manner and dried to below 15 percent moisture as quickly as possible to prevent further mold growth and, in some cases, mycotoxin accumulation.

For stalk rot, at least 100 plants, scattered throughout the field, should be assessed.  Test stalk firmness at the lower internodes with thumb and forefinger. If more than 15 percent of the stalks are rotted, schedule for the earliest possible harvest because significant lodging is possible. Scout different hybrids and fields with different tillage, rotation, or fertilization histories separately.

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

Valuing Immature Grain Crops as Forage

By William Edwards, Department of Economics and Steve Barnhart, Department of  Agronomy

Late planted corn, soybeans and oats crops can be harvested as forages instead of for grain. Options include corn or oat silage, earlage, and oat or soybean hay. Estimating a value for these crops is made difficult by the fact there are few reported prices or significant markets in which they are bought and sold. However, there are two other general approaches to valuing grain crops harvested as forage. Both are based on comparisons to alternative actions by either the forage buyer or seller.


For the Forage Buyer
The alternative for the buyer is to compare the price of substituting other common feedstuffs into rations instead of the grain crop forage. What would be the cost of the other feedstuffs that the corn, oats or soybean forage would replace? The first step is to determine which feedstuffs and how much of each one could be replaced. Advice from a livestock nutrition consultant or Extension livestock specialist may be useful. The second step is to multiply the quantity of each one by its current market price, and sum them.  This represents the most the buyer would rationally pay.

Care must be taken to adjust each feedstuff to a comparable dry matter level.  Transportation costs may need to be subtracted from the feed value, depending on whether the forage is purchased delivered to the buyer, at the location where it is harvested, or standing in the field. Where a market price is available, such as for oat hay, the most local price should be used. For soybeans harvested for hay, price comparisons for legume hay of similar feeding values can be used as a guide.


For the Forage Seller
For the seller, the alternative is to harvest the crop as grain and sell it, possibly accepting quality or moisture discounts. For this approach a realistic estimate of the potential grain yield is important. The cost of harvesting, drying and transporting the grain crop is subtracted from the current market value of the grain. If the forage crop is sold in a harvested state, the costs for harvesting it as forage must be added to its value.  Any other additional costs, such as added fertilizer costs for the following year, must also be included. The potential income from selling the crop as grain, adjusted for differences in harvesting costs, represents the minimum price the seller would accept.

The final price for the forage should fall somewhere between the buyer’s maximum price and the seller’s minimum price. This range may be wide or narrow, depending on current market conditions. If the seller’s minimum price is higher than the buyer’s maximum price, then the buyer could achieve lower feed costs using other feedstuffs instead of the forage in question, and/or the seller could achieve higher net revenue by harvesting and selling the crop as grain. In other words, harvesting the crop as forage would not be economically justified.

An electronic decision aid for pricing corn silage and other forages, “Corn Silage Pricer”, decision aid A1-65, is available on the Ag Decision Maker Web site. It follows the general approach described above and can be adapted for crops such as oats and soybeans, as well.



William Edwards is a professor of economics with extension responsibilities in farm business management. Steve Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management.

Cool and Calm, Now Hopefully We Collect!

By Rich Pope, Department of Plant Pathology

It is September 24 and thankfully no frost to speak of yet.   The 2008 season will be one to look back on as a reference for variable weather effects on crops.

I last posted degree day data in mid-August.  As mentioned in that article, daily degree day accumulations are less critical once corn and soybean progress to reproductive stages, when general water and temperature stresses and solar radiation drive development.

Iowa Degree day map for September 24

In the last month, we have continued the season-long pattern of lagging in degree day accumulations behind long-term averages. But last month's lag has actually been good, especially with corn, in that the plants have stayed healthier longer. Many parts of the state needed lower stress conditions to make up for the tumult of the early growing season, and it appears that for the most part we got what the doctor ordered.

Average date of first killing frost (28°F or below) in Iowa ranges from the first week of October in northwest Iowa to around October 20--25th in southeast Iowa.  Every day we make it until and past those times will be increasingly good news!


Rich Pope is an Extension specialist working in the Corn and Soybean Initiative

Combine Harvesting Tips for 2008 Harvest

By Mark Hanna, Department of Agriculture and Biosystems Engineering

Proper combine settings will maximize grain quality while minimizing machine field losses. Taking time to achieve proper combine settings and harvest safety will benefit producers in the long run. Following are a few general tips, and some that relate directly to soybeans and corn.

  • To minimize seed coat damage, start with the lowest recommended rotor or cylinder speed and use only enough speed to adequately thresh grain while keeping loss to acceptable levels.
  • Cleaning fan airflow is normally set at a high level, and then reduced just below the point where grain is blown out the rear of the cleaning shoe. 
  • Adjust one setting at a time, and then evaluate the change.
  • If different planting dates have caused maturity differences in the same field, consider harvesting by maturity and dry-down rather than by field.  Areas with lodging should be moved earlier in the harvest schedule.
  • Four soybeans or two kernels of corn per square foot equals one bushel per acre grain loss. Machine-related losses should be about one bushel per acre or less if the crop is standing well. 

Safety related tips
Although most operators are familiar with traumatic injuries associated with the limits of human reaction time around falling grain heads or spinning corn stalk rolls, many more chronic injuries are associated with falls from combines.

Check fire extinguishers and clean debris from the combine periodically to avoid both fire danger and slips on residue, mud, or (later in the season) ice/snow. 


Delayed plantings and slower than normal canopy closure in soybeans will present unique harvesting challenges this fall.  Research suggests that 90 percent of machine losses are at the head, with the majority of those occurring at the cutterbar.

Lower pod set from slow canopy closure in 30-inch rows makes condition and operation of the flexible cutterbar and header height control potentially more important than usual.  Combine operators should periodically stop the combine and measure losses, particularly early in the season as conditions change and time may be more available.  Each one inch of uncut stubble can result in a one bushel per acre yield loss. 

If soybeans are small, cleaning fan speed may need to be reduced to avoid blowing soybeans out of the combine. Similarly, if sieve openings have been reduced slightly for small soybeans, airflow should be reduced a bit to compensate as greater air velocity is created at a given flow when the sieve opening is narrowed. 


Deck plates over snapping rolls should be adjusted for predominant ear size to avoid shelling of kernels on the butt of the ears. Spacing between plates is about 1.25 inches in normal crop. Maintain ear savers on the corn head.  Each 0.75 pound dropped ear in 0.01 acre (436 square feet) equals a one bushel per acre yield loss. 

If stalks are lodged, keep gathering snouts low.  Keep the ear above the leading edge of gathering chains and snapping rolls.  Drive a bit slower or consider using a corn reel.  Consider harvesting against the grain of lodged stalks. Check machine field losses to evaluate effectiveness of various strategies.  

 large residue on sieves

Sieve openings may need to be adjusted for smaller seeds.





Mark Hanna is an extension agricultural engineer in agricultural and biosystems engineering with responsibilities in field machinery.

Making Fertilization Decisions As Fertilizer Prices Escalate and Production Costs Are High - Part 2

By John Sawyer and Antonio Mallarino, Department of Agronomy

This article continues the discussion begun in Making Fertilization Decisions As Fertilizer Prices Escalate and Production Costs Are High - Part 1 where soil testing and phosphorus and potassium applications were discussed.

Limestone Applications
Liming soils and maintaining soil pH is a long-term investment and payback should not be expected in just the year of application. Decisions to apply or not apply should therefore look at expectations for multiple crops as well as potential yield increase from liming (or yield loss if not applied).

For row crop production, PM 1688, A General Guide for Crop Nutrient and Limestone Recommendations in Iowa, states that pH 6.0 is sufficient for grass pasture and grass haylands, 6.5 for corn and soybean, and 6.9 for alfalfa. Because of high pH in the subsoil, pH 6.0 is sufficient for corn and soybean in the Clarion-Nicollett-Webster, Galva-Primghar-Sac, Moody, Ida-Monona, Marshall, and Lutton-Onawa-Salix soil associations. For corn and soybean, liming rates are suggested to raise pH to 6.5. If lime is going to be applied, the rate needed to achieve the suggested pH should be used. Corn often is less sensitive to soil acidity than soybean and much less than alfalfa. However, N fertilization is a major cause of soil acidification. Therefore, monitoring soil pH is important with continuous corn.

Nitrogen Fertilization
Nitrogen applications should be tailored for the crop rotation (Figure 1). First-year corn following well established alfalfa often needs no N fertilization, and when required only 30-40 lb N/acre. Unfortunately, corn in other rotations almost always needs N application, and yield increase to fertilization on the long-term is quite good (Figures 1 and 2). Hence, there are not many opportunities to eliminate application when N prices are high or in short supply.

Fertilizer decisions Figure 3

Figure 1. Corn grain yield response to fertilizer N application rate across time with various corn rotation sequences, Northeast Research Farm at Nashua, IA.


Fertilizer decisions Figure 4

Figure 2. Direct comparison of corn grain yield response to N fertilizer rate for corn following soybean (SC) and continuous corn (CC) across seven sites in Iowa, John Sawyer and Daniel Barker.


Nitrogen can be supplied from manure, but that is also a valuable commodity when fertilizer prices are high and the amount of manure produced in Iowa cannot meet the needs of all corn production. Second-year corn following alfalfa has reduced N fertilization requirement, and similar yield response and rate as with corn following soybean (Figure 1). Compared to continuous corn, corn in rotation with soybean has lower N requirement, on the order of 50 lb N/acre less (Figures 1 and 2). If N fertilizer is in short supply or purchases have to be limited, it is better to apply some N to all fields than to skip fields (other than corn after alfalfa) as the largest yield gains come from the first increments of applied N (Figure 4).

Application rates can be adjusted downward somewhat when N fertilizer costs are high relative to corn prices. However, closely observe both N and corn prices before deciding on reducing N applications. Despite the high N prices, corn prices are also high and therefore the ratio between the two has not changed dramatically.

The Corn Nitrogen Rate Calculator was updated this summer with Iowa data from N rate trials conducted in 2007. Based on that dataset, the suggested N rates and rate ranges for four N: corn price ratios are listed in Table 1 and shown in Figure 3. The advantage of the calculator is that specific N and corn prices can be compared. The output from the calculator gives suggested N rate ranges that provide similar profitable return. With high N costs, high production costs, and perhaps the need to allocate limited funds for N fertilizer purchase, one can consider using rates in the lower part of the range. Those rates should provide similar yields, but risk of N supply shortage to the crop is greater if N losses occur or if there is greater corn N need.

The rates suggested from the Corn Nitrogen Rate Calculator are the same whether N is applied in late fall, spring, or sidedress, therefore do not decrease the rate for sidedress application timing. Fall application carries more risk of loss, however, that risk cannot be predicted and it is not appropriate to guess and just increase the rate in an attempt to cover potential losses. When N is expensive, applications above Maximum Return to N (MRTN) result in large economic losses. This can be seen in graphs produced from the Corn Nitrogen Rate Calculator (Figure 3).

Fertilizer decisions Figure 5

Figure 3. Effect of N:corn grain price ratio on return to N application with corn following soybean, based on the current Corn Nitrogen Rate Calculator dataset.



Fertilizer Decisions Table 1

Table 1. Nitrogen rates suggested for corn following soybean and continuous corn based on the current Corn Nitrogen Rate Calculator dataset


If possible, grow more corn after soybean than after corn. Yields will typically be higher with the rotation and N application need lower (Figures 1 and 2). If fall fertilization is considered, apply only anhydrous ammonia and wait until soils are cold and remain so, less than 50 degrees F and cooling (the colder the better), which usually means waiting to apply until early- to mid-November. Good application timing helps reduce N loss and allows the best yield return from applied N. Typically best efficiency is obtained with spring or split spring/sidedress application. Having plant-available N in the root zone is important for good early corn growth, and especially for corn following corn.


The above mentioned publications, as well as other nutrient management information, are available on the ISU Agronomy Extension Soil Fertility Web site. Another resource focusing on N rate management is publication PM-2015, Concepts and Rationale for Regional Nitrogen Rate Guidelines for Corn .



John Sawyer and Antonio Mallarino are professors of agronomy, both with research and extension responsibilities in soil fertility and nutrient management.

Making Fertilization Decisions As Fertilizer Prices Escalate and Production Costs Are High - Part 1

By John Sawyer and Antonio Mallarino, Department of Agronomy

Fertilizers are at unbelievably high prices, with reports of tight supplies and potash allocation to dealers. Total crop production costs are causing credit supply issues, which complicates decisions to allocate available funds for production expenses. These issues are causing producers to consider changing production practices, including cutting back on inputs like fertilizer. What can be done?

There is a lot of uncertainty, with no clear or definitively correct answer for all situations. Remember crop prices are also very high, which certainly helps pay for more expensive fertilizer. High crop prices can even  result in greater net return to fertilization where there is a yield response to added fertilizer than when crop prices are low. So there is no simple answer, and sometimes no change to production practices is the correct approach.

Consult with Advisers and Dealers
Producers should work closely with their crop adviser and dealer to figure out the best options and production plans for this fall and next spring. This is always important, but more so right now as the fertilizer purchase/supply dynamics are changing dramatically and quickly.

Soil Test
Soil test to know what P, K, and lime applications are really needed. Avoid applications to fields or field areas that do not need the nutrients or lime. Compared to the cost of nutrient and lime inputs, soil testing is inexpensive and provides a good return on investment. See the ISU Extension publication PM-287, Take a Good Sample to Help Make Good Decisions, for soil sampling suggestions.

Evaluate soil test results to determine P, K, and lime requirements. See ISU Extension publication PM 1688, A General Guide for Crop Nutrient and Limestone Recommendations in Iowa for soil sampling suggestions. As stated in that publication, the percentage of P and K applications expected on average to produce a yield response within each soil test category is 80 percent for Very Low, 65 percent for Low, 25 percent for Optimum, 5 percent for High, and  less than1 percent for Very High. This means that as soil test levels increase, the probability of a yield increase to fertilization and the amount of expected yield increase decrease, and net return also decreases and usually becomes negative at High and Very High test levels (Figure 1).

figure 1 fertilizer decisions

Figure 1. Net return to P application at different soil test levels and crop/fertilizer prices, Antonio P. Mallarino.


Phosphorus and Potassium Applications
For making fertilization decisions, P and K should be applied where the chance of yield increase is large, and the expected yield increase is sufficient to at least pay for the applied nutrient (Figure 1). Remember, manure can supply P and K (as well as N and other nutrients) but its market value has also increased with high fertilizer prices and is not available to many for various reasons.

Due to crop removal, withholding fertilizer or manure applications will result in a gradual soil-test decline (Figure 2). Therefore, if soil tests are in the High and Very High categories, some of the P and K “banked” in the soil can be used for next year’s crop production and no application is needed. Only apply P and K to soils testing Low and Very Low, with optional application when tests are Optimum.

figure 2 fertilizer decisions

Figure 2. Change in soil test over time with different beginning soil test level and rates of applied P, Antonio P. Mallarino.


Application to maintain soil-test values in the Optimum category is considered a good practice to sustain profitable crop production over time. However, applications can be withheld until the next year especially when product supply is really short, funds are needed for other more critical inputs, or land tenure is uncertain.

This is because the expectation for economical response to P and K  in the year of application is small in the Optimum category and it becomes more uncertain as the price ratio becomes unfavorable (Figure 1). Crop yields in many fields are high again this year, so crop removal will be influencing soil test levels. In fields severely impacted by the wet conditions, lowered yields will result in removal of less nutrients and some fertilizer applied for this year would be available for next year’s crop.

Therefore, withholding applications may work in some fields or field areas, with the number of skipped years depending on the beginning soil test level, but will not work in other fields or field areas. Soil testing is the only way to know.

An option instead of not applying any P or K when the soil test is in the Optimum category would be to apply partial crop removal. This would slow the soil test decline and should provide adequate fertilization for the small and occasional first-year yield response.

For the corn-soybean rotation, many producers apply P and K needs for both crops once, before corn. This is as effective as applying those nutrients ahead of each crop as long as the fertilizer need for both crops is correct. However, if fertilizer price/availability will be better next fall, money could be saved now by applying the nutrient need of one crop and fertilizing again next year. Also, the cost of application, in relation to total fertilizer cost, is less now than in previous years so making single-year applications should be more viable.

The above mentioned publications, as well as other nutrient management information, are available on the ISU Agronomy Extension Soil Fertility Web site.

(Sawyer and Mallarino continue this topic in Making Fertilization Decisions As Fertilizer Prices Escalate and Production Costs Are High - Part 2 . They discuss liming soils and factors to consider when making nitrogen fertilization decisions.)



John Sawyer and Antonio Mallarino are professors of agronomy, both with research and extension responsibilities in soil fertility and nutrient management.

Fall Management of Alfalfa

Steve Barnhart, Department of Agronomy
Rain in May and early June this year put most alfalfa producers behind two to three weeks for their first, and correspondingly their second and third cuttings. Now in mid-September, producers are taking advantage of a favorable week of drying weather to make what is their last summer cutting. 

This is crowding into the normal four to six week fall rest period for the alfalfa stands. Producers should consider if these mid-September harvests will put the stands at risk. 

Our locally adapted alfalfa varieties, and most other perennials, are genetically programmed to respond to external factors. Their response to shortening days and cooling average daily temperatures of fall begins the gradual “cold hardening” process. Cold hardening will continue six to ten weeks.

The genetics of the variety determines how cold tolerant the plant crown and taproot can be during the winter months. Most winterhardened alfalfa plants can withstand soil temperatures in the crown area to about 0 to 4 degrees F without crown tissue damage. At lower soil and crown temperatures, varieties and individual plants will vary in the degree of cold damage they may experience. 
Fall Management strategies and considerations.
Producers may be considering these questions about alfalfa fields this fall.

Will this field be saved for hay next year?  If the answer is no, harvest anytime. There will be only slight reduction in N credits to next crop if last top growth is removed. If the field will be hay next year, take last summer cut by late August or very early September, and leave fall re-growth stand in the field - no late cut or grazing.  If field was not fertilized in the summer, topdress any needed K in late August or early September.

The alfalfa is knee high in mid-September, should it be cut then?  Again, if the field will not be hay next year, cut anytime. If the field will be hay next year, ask yourself if you need the hay. If not, leave the last growth in the field and don’t graze in fall or winter. If there is a need for the hay, it is best to wait until at or after the killing freeze to cut; killing freeze that stops seasonal alfalfa growth is not the first frost of fall, but 23-24 degree F or colder period for several hours. Leave a 4 – 5 inch stubble.

Hay doesn’t dry in October - at least not very rapidly, what is the risk of cutting in mid-September? The best scenario is that the alfalfa plants have accumulated “root reserves”, and, if left uncut, can do very well in the coming winter.

The next best scenario, if you cut in mid-September, is the plant will begin to regrow and begin to use the stored reserves. During fall regrowth, root reserves will decrease for a week to ten days while new growth is starting, and will gradually rebuild root reserves until a killing freeze stops seasonal growth. If the ‘fall rest’ or fall regrowth period is long enough (four to five weeks), the plants will likely recovery sufficient root reserves for good plant vigor and winter survival.

The worst scenario would be that during fall regrowth following a mid-September cut, root reserves will decrease for a week to ten days while new growth is starting, and will gradually rebuild root reserves until a killing freeze stops seasonal growth. If the fall rest or fall regrowth period is not long enough - less than about four weeks - the alfalfa plants will be left with a relatively low level of available root reserves and will have minimal levels of reserves to both get through the winter and to regrow from in the spring. From a low level of stored carbohydrates, even a minor premature spring recovery and freeze-back will put the plants in a very poor physiological state.  

Factors which improve alfalfa winter survival

  1. Management of insects (potato leafhoppers) during the growing season   
  2. Good levels of available potassium in the soil
  3. A variety with winter/cold tolerance
  4. A variety with a good disease resistance traits
  5. Three summer cut harvest systems with good regrowth between cuttings
  6. Five to six weeks of uninterrupted growth during September and October
  7. All of the last growth of the season left in the field (no cutting or grazing)
  8. Soils with average soil moisture or slightly drier during fall and winter
  9. Four inches or more of winter-long snow cover
  10. Young stands (first or second production year); we see more consistent winter injury in older stands  (third production year and older) 


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

This article was published originally on 9/29/2008 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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