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10/26/2009 - 11/1/2009

A Tough Harvest - Frequently Asked Questions

By Charles R. Hurburgh, Department of Agricultural and Biosystems Engineering

The difficult harvest has not gotten any easier. With most of the corn and still a significant percentage of soybeans still in the field, several management questions have come up very often.

Q.   With all this rainy weather, should we shut off fans and wait for the weather to improve?

A.  If you are drying with heated air, no. Keep the drying moving; in fact the rainy weather may be the only chance to catch up or keep up with the fast pace of wet grain once the weather improves. If you are drying with natural air, or are just cooling/holding wet grain, then it depends.  If the grain is reasonably dry (corn below 17 percent, soybeans below 15 percent), with uniform moisture and cool temperature (below 50F), then you can shut off the fans but remember to turn them back on. Otherwise no. You do not want to stop a drying or cooling front in the bin, and wetter grain heats so you need to keep control of temperatures. Grain picks up moisture from the air at about one-fourth the rate at which it dries so rewetting over short periods is not usually an issue.

Q.   Corn moistures are in the upper 20s or 30s and my dryer cannot keep up at all. What are options – time is getting late.

A.  There will likely not be much field drying any more. Recent rains have rewet some corn if the upright ears trapped water; sprouting in these cases may occur also. At this point, any choices are designed to buy time so that corn can be harvested, held and drying completed later. I will talk about elevator drying and shrink in another question. 

Natural air/low temperature will still work, although slowly. In most air drying bins (depth less than 20 feet), about 1 hp/1000 bushel will handle up to 20 percent moisture, 2hp/1000 up to 22-23 percent. Beyond that, fan horsepower becomes too large and spoilage risk too high. Natural air will not finish drying this fall.

Heated air drying can be speeded up by removing hot corn and cooling in storage. Consider drying very wet corn in stages – down to 24-25 percent; cool, hold with air, redry to below 20, then use air the rest of the way. This will buy some time but will take more management, effort and cost.  Producers and elevators with a combination of drying systems will find more options to move and hold grain to capture short term capacity.

Q.  Corn test weights are low; why and what impact will that have?

A.  Corn lost test weight because of the rapid maturity advance in late August of what was a crop lagging in maturity. Kernel fill was not complete. Dry corn test weights are in the 52 -54 lb/bu range, with less than normal increase during drying. This is about 3 lb/bu less than average. Test weight loss during kernel fill means loss of weight per acre, in this case approximately 5 percent. 

Low test weight corn spoils more rapidly and breaks more in handling, as we saw in 2008.  There will be storage problems in spring and summer of 2010, especially with the shortage of drying capacity and more grain held at higher moistures. Ethanol yields should not be significantly affected; light corn tends to be softer and lower protein, both of which favor ethanol yield. Feed users should test for mycotoxins from field molds, and expect lower protein corn with more small particles after grinding.

Q.  What about wet soybeans and high temperature drying?  Some soybeans are above 18 percent  in the field yet.

A.  As with corn, there will probably not be much more field drydown. Soybeans react in storage like corn with 2 percent higher moisture – 15 percent soybeans respond about like 17 percent corn. Natural air is the best; the November air will dry beans to about 13.5 percent moisture which is dry enough to hold over the winter. The goal in heated air drying should be either to get the beans to 14 percemt, still able to be held overwinter with aeration, or to the acceptance moisture of the market.

Many markets this year are cutting off acceptance at 15 percent moisture. Elevators are generally not designed to dry two products. The dryer, aeration and grain flow of wet material is usually arranged for corn only. In normal years, the few wet soybeans that are harvested are blended with the larger amount of dry beans. This year there are few dry beans. Crush processors cannot handle wet soybeans either; they are too soft to split correctly in the cracking rolls, which then makes the hulls (fiber) hard to remove.

Q.  Shrink and other charges for moisture seem to be going up. Why? 
Soybeans are the most subject to these increases because the commercial elevators do not have the capability to dry soybeans efficiently. There have been dryer fires as a result of soybeans in corn dryers. Farm drying systems, especially bin dryers are more suited to soybean drying.

Normally moisture is handled with a combination of shrink deductions of weight and fees for drying. Shrink is intended to calculate, as closely as possible, the ending weight after both drying and storage-handling operations. Equivalent bushels after shrink to the market standard moisture are used for settlements, warehouse receipts and their regulatory verification, and other production related needs such as proven yields, loan collateral, and insurance adjustments.

Shrink adjustments are made with a percentage deduction per percent of moisture. Drying (water) loss is mathematically fixed depending on the ending moisture (15 percent normally for corn and 13 percent for soybeans), and independent of starting moisture or grain condition. Drying to 15 percent removes 1.18 percentage point of moisture; drying to 13 percent removes 1.15 percent. The difference between these figures and the actual factor used by the grain buyer is an allowance for handling and storage loss. In Iowa, shrink must be disclosed as the sum of the water and handling percentages – e.g. the common 1.40 percent per point is 1.18 for water and 0.22 for handling allowance. The total handling allowance goes up with the amount of moisture removed.   Two points removed gives 0.44 percent in this case; 5 points removed gives 1.1 percent, and so on.

Scientific tests have shown that, overall, grain elevators actually experience about 1 percent loss during storage and handling, and that farm systems loose about 0.5 percent, beyond the moisture removal.  The normal shrinks taken by elevators (1.35 percent or 1.40 percent) allow about enough handling loss at typical harvest moistures, with progressive increases for the less typical and more difficult-to manage higher moistures.

Problems arise when shrink factors are used as discounts or incentives beyond inventory weight balance. To keep accuracy in inventory and in other non-market uses of production data (such as proven yields, crop insurance settlements, and loan collateral), shrink should be used for weight only. There is no restriction in Iowa on either the shrink scale used or on the drying/handling fees that can be imposed to provide incentives. Recently soybean shrinks as high as 3.0 percent per point (1.2 for water and 1.8 for handling loss, per point) have been seen.  These are discouragements to high moisture beans, but will result in significant “long” inventories, from beans present but not listed on settlements.

Financially, the producer and elevator may end up in the same place with a high shrink or a lower shrink plus higher fees for drying, but producers needing accurate quantities for production records should discuss with buyers how to get weight records reflective of the actual dry bushels delivered. At 20 percent moisture dried to 13 percent, the 3.0 percent scale deducts 21 percent of the weight; 8.4 percent for water and 12.6 percent for handling losses.

Drying charges normally range from 4-6 cents per bushel per point of moisture, and must cover both the variable cost of dryer operations (fuels, labor, etc.) and the fixed cost return to the dryer investment. Farm dryers may dry at lower costs for variable costs only, but when the fixed cost of the dryer is included, total costs are often similar.


Charles Hurburgh is a professor of Agricultural and Biosystems . He can be contacted at (515) 294- 8629 or by email at

How Delayed Harvest Might Affect Ear Rots and Mycotoxin Contamination

By Alison Robertson and Gary Munkvold, Department of Plant Pathology

The corn harvest is later than it has been any time in recent memory, and the prolonged moist conditions are conducive for molds to develop on grain in the field. Over the past few days we have received numerous reports of ear rots developing in the field and questions concerning mycotoxin production when conditions are cool but wet. 

Cladosporium ear rot
Apart from Fusarium, Gibberella and Diplodia ear rots, we are starting to see and hear of more reports of Cladosporium ear rot. Cladosporium ear rot symptoms we have seen are dark, greenish-black, blotched or streaked kernels that are scattered over the ear (Figure 1). In some cases, the pericarp has split to reveal clumps or tufts of dark mold growth. In addition we have seen the ear rot develop as dark green, fuzzy growth that grows on and between the kernels (Figure 2 and 3).  This fuzzy growth looks very similar to the fuzzy growth associated with Trichoderma ear rot, though Trichoderma is usually a more intense green (Figure 4). Microscopic examination is necessary to definitively distinguish between the two fungi. Cladosporium ear rot is often associated with insect, hail or frost damage. 

There are no reports of economic losses due to either Cladosporium or Trichoderma ear rot. Furthermore, no associated mycotoxin issues have been reported. If the percentage of damaged kernels is 5 percent or less, the grain is still acceptable as No. 2 corn. However, since corn ears can be infected with more than one ear rot simultaneously, mycotoxin contamination of grain should not be ruled out. All grain coming from fields suspected of being moldy should be tested for mycotoxins.

How will cold, wet weather affect ear mold development and mycotoxin contamination?
Unfortunately there is a lot of high moisture corn still in the field and current weather conditions are contributing little to dry down. Kernel moistures above 18 percent favor the growth of all ear mold fungi. Temperature affects the rate of growth of ear mold fungi. Cool temperatures slow the growth of most fungi, but they are still active, and the potential for mycotoxin production still exists. Past experiences indicate that extended wet falls, and therefore delayed harvests often result in elevated levels of DON (vomitoxin).

Management decisions
Fields should be scouted to determine if ear rots are prevalent. Problem fields (greater than 10 percent of the ears have mold on 10-20 percent of the grain) should be harvested as soon as possible, and dried to 15 percent moisture or less to prevent further mold growth. For more details on drying and storage of grain see 2009 Corn Quality Issues – Field molds.  When harvesting, ensure the combine is properly adjusted to avoid additional damage to the kernels.  Cleaning the grain with a rotary cleaner can reduce mycotoxin levels by removing fines which tend to have higher mycotoxin levels than whole kernels. Grain from fields with obvious mold problems should be tested for mycotoxin contamination. See Risk of Mycotoxins Associated with Hail Damaged Corn for guidelines on testing for mycotoxins. 

cladosporium dark kernels

Figure 1.  Dark kernels scattered around the ear are symptoms of Cladosporium ear rot. (Robertson)


cladosporium ear rot

Figure 2.  Cladosporium ear rot may also develop as dark (brown to green) fuzzy mold growing on and between kernels. (Robertson)


cladosporium on grain

Figure 3. Cladosporium ear rot on grain (Munkvold)



trichoderma ear rot

Figure 4.  Trichoderma ear rot (Munkvold)


Alison Robertson is an assistant professor of plant pathology with research and extension responsibilities in field crop diseases. Robertson may be reached at (515) 294-6708 or by email at Gary Munkvold is an associate professor of plant pathology and seed science endowed chair in the Iowa State University Seed Science Center with research and teaching responsibilities in seed pathology. He can be reached at (515) 294-7560 or by email at

Soil Management of Harvest Ruts

By Mark Hanna, Department of Agricultural and Biosystems Engineering, and Madhi Al-Kaisi, Department of Agronomy

Combines working in wet conditions to harvest crops have formed ruts in fields.  About three-fourths of combine mass and virtually all of loaded grain tank weight are carried on the combine front axle.  With good yields, grain tank extensions, and a 12-row head, front axle load can be 18 to 20 tons. 

The consequences of such wet conditions are significant soil compaction caused by this heavy equipment and yield reductions that will be realized next season. Compacted soil created beneath the rut may interfere with subsequent crop rooting and development. Ruts deeper than about two inches can also interfere with maintaining seed depth during planter operation next spring, unless they are leveled. 

Using tillage to loosen the soil and relieve compaction requires soil to be dry enough so that soil shattering is effective.  Because soil moisture has refilled the top 12 to 24 inches of the soil profile, deep tillage with a chisel plow or subsoiler this fall or next spring will use fuel and time – but is unlikely to loosen soil effectively between tillage shanks. However, the full soil moisture profile in upper layers will freeze and thaw over the winter and help loosen soil, depending on air temperatures and snow cover. Entering the field this fall in wet moisture conditions for deep tilling or any type of tillage will be counter productive by creating much deeper soil compaction. 

Ruts deeper than planting depth will need to be leveled before planter operation.  A good strategy may be to wait until a week or two before planting next spring and use a light tillage pass, such as with a field cultivator, light disk, harrow, or soil finisher.  If only a portion of the field is rutted, consider tilling only that area to avoid recompacting subsoil in other parts of the field. Waiting until warmer weather next spring allows for some potential drying of the top two or three inches of soil and avoids further compaction of wet, plastic soil on the surface – which will happen with a tillage pass this fall. If compaction effects are observed during the 2010 growing season and soil is dry after harvest, tillage next fall may be considered deep enough to break through the compacted layer.

• Rutting creates compacted soil and an irregular soil surface.
• Avoid deep tillage this fall to correct the problem as wet soil does not shatter/loosen.
• Shallow tillage next spring will level ruts for planter operation.



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

Crop and Weather Report Week of Oct. 26

The October 26 crop and weather report guests are Charles Hurburgh, Iowa State University professor of ag and biosystems engineering and professor in charge of the Grain Quality Initiative, ISU Extension climatologist Elwynn Taylor, integrated pest management specialist Rich Pope, and corn agronomist Roger Elmore.

High moisture corn and soybean continues to be a problem as the 2009 harvest is delayed by rain and muddy fields. Taylor says well drained soils need a week to handle a reasonable amount of traffic, but even then producers should minimize activities that compress the soil. Pope talks about grain dryers working overtime and concerns about wrapping up the season. Elmore says corn harvest is at least two weeks behind, probably further than that when new reports come out this week. All this rain will help the soil recharge moisture, but it is making it impossible to complete get crop out and create additional problems with soil compaction. Hurburgh talks about ways to handle beans and corn in the wet situation we have. He says producers need to have patience; they won’t be able to take crops out at usual speed, and must move more slowly with harvest.

This article was published originally on 11/2/2009 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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