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7/30/2012 - 8/5/2012

Corn Crop Development and Conditions at the End of July 2012

By Roger Elmore, Department of Agronomy

To no one’s surprise, Iowa corn conditions declined throughout the month of July. Dry hot weather hammered the crop to the point where some crops were written off as unproductive several weeks ago and others are seemingly hanging by a thread. Some producers are salvaging what remains as silage.

Nevertheless, some Iowa producers are quite satisfied with their crop’s potential. They are among the fortunate few perhaps with a bit better soils and  more rain at critical periods. Undoubtedly, this  group may also have an edge on management practices: excellent hybrid selection, less soil compaction, timely planting dates, better seed placement, uniform seedling emergence, optimum plant populations, top-notch weed control, wise insect and disease management, etc.  This will be the year where the management differences among fields and producers - and their skills - will come to light.


Rapid 2012 corn development stages, July 29, 2012

USDA-NASS reports corn development stages weekly during the growing season. As of July 27th, 8 percent of Iowa’s corn was denting – R6 (Figure 1). Crop development in 2012 is well ahead of both that of last year and the five-year average. Eight percent dented is the most advanced development stage we’ve had since 1987 when 10 percent of the crop was at that stage by the end of July. We’ve learned the hard way that fast progression through development stages is not conducive to higher yields.

Figure 1.


Crop condition declines– July 2012

In the same weekly report as the development stages, USDA-NASS also publishes crop conditions. Corn condition began to decline in early July from 62 percent ‘Good to Excellent’ on the 1st to only 20 percent in that category on July 29th (Figure 2).  Of course, on the other end, the percent of the crop in ‘Poor or Very Poor’ condition escalated to 46 percent. The remaining 34 percent was rated as ‘Fair.’ 

Figure 2.


For comparison, at the end of July in 1988 - one of the worst years for corn that some of us remember -  only 15 percent of the crop was rated ‘Good to Excellent,’ 36 percent ‘Fair’ and 49 percent was rated ‘Poor or Very Poor.’ These are records we don’t like to emulate.  

Remember, though, crop condition reports like these are subjective. “The Crop progress and condition surveys are non-probability surveys that include a sample of more than 5,000 reporters [nationwide] whose occupations provide them opportunities to make visual observations and frequently bring them in contact with farmers in their counties. Based on standard definitions, these reporters … provide subjective evaluations of crop conditions. “ USDA-NASS


Crop condition reports and yield

Figure 3 presents another way to look at crop condition report data. The chart includes crop condition reports for the last week of July from 1986 to 2012. I highlighted several years in the chart as reference points. Obviously, 2012 is not in good company! Yields in 1988 were 29 percent below the 30-year trend line, and those of 1993 were 39 percent below trend line. You must know, though, that high 'good to excellent' ratings the last week of July usually - but not always - foretell good news about yields.

Figure 3.

To explain that further, 1994, 1986, 1987, 1992 and 2004 all had yields considerably higher (9 to 15 percent) than trend line yields. But 1990 yield was only 0.5 percent above the trend line although the crop condition the last week of July was one of the five best since 1986. 

On the other hand, 2009, the year of our best yield ever, had 5 percent of the crop rated poor or very poor in late July and yielded only 5 percent above trend line yields.  Of the five other years clustered with 2009 between 40 and 50 percent 'good to excellent' yields ranged between 2 percent above trend line yield to 9 percent below. It appears that if less than half of the crop is rated in the 'good to excellent' category the last week in July, historic yields were at or below the trend line. 2012 clearly - and not surprisingly - falls into that category. Obviously, as we proceed through August, the crop condition reports should reflect forecast yields with more precision than they do the last week in July.

Declining corn crop conditions, rapid progression through later development stages, and the short-term and long-term forecast for more hot and dry conditions are not encouraging for corn yields. 


Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at or (515) 294-6655.

Early Corn Harvest and Residue Management this Fall

By Mahdi Al-Kaisi, Department of Agronomy

This growing season has had many challenges that could affect potential yield, including drought, insect problems, plant diseases and others. Many farmers in some areas entertain the idea of cutting corn for silage or have already done so. Certainly, we can expect an early grain harvest across the state. These decisions will present challenges regarding residue and tillage management this fall, as they did to a lesser extent last fall.

Corn residue can reduce soil erosion under high rain intensity, increase soil moisture storage and improve soil and environmental quality, particularly in dry conditions. Other short-term impacts of corn residue removal include:

  • Increases the need for N, P and K and other nutrient applications to replace those removed in crop residue
  • Reduces water infiltration and increases surface runoff with sediment and nutrient losses
  • Reduces soil organic matter and microbial biomass carbon

Appropriate crop residue management minimizes any future negative effect of soil erosion, sediment and nutrient losses. Researchers have documented that significant removal of residue has negative impacts on several soil quality indicators, including soil structure, water infiltration, soil moisture holding capacity and soil bulk density.  During dry conditions, removing residue while cutting for silage or baling can affect those parameters, especially at the soil surface where, under rain events, surface sealing can occur to create a crust layer (Figure 1).

Figure 1. (Top) No-till with complete residue removal vs. (bottom)  no-till with no residue removal.

Soil surface sealing increases surface runoff and ultimately reduces subsoil moisture recharge or storage during rain events. Here are a few ideas for managing crop residue this fall:

  1. Harvesting, shredding or cutting corn for silage needs to be done with care, especially on high slope areas where potential soil erosion can be significant when fields are exposed to high intensity rain. Removing residue or baling should be kept to a minimum (remove less than 30 percent) and no residue shredding should be done. Shredding residue after grain harvest will reduce its effectiveness in protecting the soil surface.
  2. Generally, standing residue will be highly effective in trapping soil moisture and reducing water movement or surface flow over the field and increases soil water infiltration and subsoil moisture recharge for the following season. Keeping crop residue intact on the soil surface with roots anchored in the soil can help protect soil and reduce soil erosion.
  3. Consider cover crops this fall. But soil moisture conditions are critical for establishing cover crops. The use of cover crops will be a good option on fields where corn was cut for silage or chopped, especially on high slope areas. Cover crops will help reduce soil erosion and increase soil water storage. Also, cover crops can help extract excess nitrogen in the soil profile after cutting corn for silage or grain harvest. This may be especially important in low-yield areas this season.
  4. Avoid any unnecessary tillage this fall. Conventional tillage to incorporate residue, such as deep ripping, chisel plow, moldboard plow, etc., can have negative effects, especially after persistent drought conditions where soil structure is weakened. 
  5. The expected early harvest will leave soils exposed to weather conditions for a long period of time this year; therefore, leaving crop residue intact will provide protection from potential late season rain events. One management decision farmers should consider is the use of cover crops because there will be a good window of time to establish them this year.

(See Legume Living Mulches in Corn and Soybean or Small Grain Cover Crops for Corn and Soybean)

In summary, residue plays a very important role in sustaining soil quality, which must be kept in mind when deciding how much corn residue to harvest and how much to leave on the field. Corn residue left on the field after harvest is a critical source of soil organic matter. It provides protection for the soil against water and wind erosion, and it contributes to the improvement of soil storage and water quality.

(See How Much Crop Residue to Remove.) Tillage should be the last resort and minimum to prevent soil structure destruction and prevent soil surface sealing under heavy rain, which can lead to soil loss.


Mahdi Al-Kaisi is a professor in agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at or 515-294-8304.

Aspergillus Ear Rot and Aflatoxin Production

By Alison Robertson, Department of Plant Pathology and Microbiology

Not surprisingly, the hot dry conditions we have been experiencing across the Corn Belt have many farmers and the grain industry concerned about aflatoxin, a potent mycotoxin that is produced by the fungal pathogen, Aspergillus flavus, which causes Aspergillus ear rot.

This article will briefly summarize the biology of Aspergillus ear rot, aflatoxin production and management recommendations for the next few weeks of this growing season.


How do I recognize Aspergillus ear rot?

Aspergillus ear rot is an olive-green powdery mold  (Figure 1), not to be confused with Penecillium ear rot, a powdery denim-blue mold. Higher aflatoxin levels are associated with discolored, shriveled kernels that are often found near the tip of the ear.

Figure 1. Characteristic signs of Aspergillus ear rot


What conditions favor infection of corn by A. flavus?

Infection of corn by A. flavus and consequent disease development is favored by hot (>86F) dry conditions at pollination and during grain fill. Yellow brown silks are most susceptible to infection. Spores landing on the silks germinate, rapidly grow down the silk and colonize the surface of the developing kernels. Around physiological maturity, when moisture content (MC) drops to around 32 percent, the fungus starts to colonize the internal tissues of the kernels, and it continues to grow until MC is around 15 percent.


What conditions favor aflatoxin production?

Aflatoxin is a secondary metabolite that is produced by A. flavus under certain conditions. Drought and high temperatures (80 to 105F) during grain fill are the most common factors associated with pre-harvest aflatoxin production. Warm nights (>70F) may can also increase risk of aflatoxin contamination.

Toxin production depends on kernel moisture and temperature. As kernel moisture decreases, aflatoxin production increases. Toxin production is highest at 20 to 18 percent kernel moisture and stops at around 15 percent moisture. Aflatoxin production occurs between 52 and 104F with the optimum temperature range being 77 to 95F.


Can I determine if my corn is at risk for aflatoxin?

Because aflatoxins are associated with Aspergillus ear rot, farmers can scout for the ear rot. From dent through to harvest, several (five to 10) locations in a field should be assessed. Target areas of the field with plants that appear most stressed. At each location, peel back the husks of 10 ears and inspect them for olive-green powdery mold (Figure 1) that is characteristic of the ear rot. If greater than 10 percent of the ears show signs of Aspergillus ear rot, schedule the field for an early harvest. 


Harvesting fields with Aspergillus ear rot

Notify your insurance adjuster immediately if you have fields with Aspergillus ear rot. Infested fields need to be inspected before harvest or strips left in the field for a claim to be made.

Harvest grain at approximately 20 to 25 percent moisture. Adjust combine settings to ensure minimal damage to the grain. Damaged grain is at risk to infection by A. flavus in storage. 

Cool and dry grain to 16 percent moisture or less immediately. One study showed that if corn grain at 21 percent MC was put in bin at 86F and cooled with air immediately, little fungal growth was detected and no aflatoxin was produced. If cooling was delayed 20 to 40 h, the fungus grew and aflatoxin was detected.



Thanks to Tom Isakeit at Texas A & M for reviewing an earlier draft of this article and sharing his experiences with aflatoxin.


Alison Robertson is an associate professor in the Department of Plant Pathology and Microbiology with extension and research responsibilities; contact her at or phone 515-294-6708.

This article was published originally on 8/6/2012 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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