Monthly Archives: August 2012

Aflatoxin Concerns in #Corn

Aspergillus ear rot. Photo courtesy UNL Plant Path Dept. and the following publication: http://www.ianrpubs.unl.edu/epublic/live/ec1901/build/ec1901.pdf

This article originally appeared in http://cropwatch.unl.edu written by Dr. Tamra Jackson-Ziems, UNL Extension Plant Pathologist.

Drought and high temperatures promote development of the disease Aspergillus ear rot (pictured right). The fungi that cause this disease (most commonly, Aspergillus flavus) can produce aflatoxin. Aflatoxin is one of many chemicals in a group known as mycotoxins that are produced by fungi (molds). Mycotoxins, such as aflatoxin, can be toxic to animal and human consumers and, at certain concentrations, can lead to dockage or rejection of grain at elevators.The unusually high temperatures and drought this summer are having severe impacts on Nebraska corn. In addition to reductions in test weight and overall yield, secondary problems are developing in some corn fields as a result of these conditions.

Corn harvested for grain to this point has been predominantly from fields that sustained substantial drought damage leading to early maturation and plant death. Notable aflatoxin contamination appears to be in a small percentage of southeast Nebraska fields, based on samples submitted to several laboratories in the area.

Mycotoxins are common and can be safely consumed at low concentrations. The concentration of aflatoxin that is considered safe for consumption depends on the age and species of the consumer. An abbreviated summary listing the Action Levels identified by the FDA for aflatoxin is listed in Table below.

Testing for Aflatoxin:  Farmers and crop consultants can scout high risk fields for Aspergillus ear rot as an indicator for aflatoxin, but only lab testing of grain samples can accurately identify the concentrations of aflatoxin in the grain. Accurate lab test results for aflatoxin will depend greatly on the quality of the sample that is collected and the laboratory methods used to test it. The test results are only applicable to the sample that is submitted, so it is very important to collect an adequate sample for the best results. Refer to the publication, Sampling and Analyzing Feed for Fungal (Mold) Toxins (Mycotoxins) for recommendations on how to collect and submit a high quality sample for mycotoxin analysis.

Contact and submit samples to a laboratory that is certified by the federal Grain Inspection Service and Grain Inspection, Packers, and Stockyards Administration (GIPSA) for mycotoxin analysis for the most accurate results. A GIPSA website lists laboratories certified to conduct testing in Nebraska. They include

  • Lincoln Inspection Service, Inc.;
  • Fremont Grain Inspection Department, Inc.;
  • Omaha Grain Inspection Service, Inc; and the
  • Sioux City Inspection and Weighing service Company.

Some grain elevators and individuals may be using a black light (ultraviolet light) to detect for fluorescence as a method for rapid screening of grain samples. This practice is NOT recommended when making decisions about aflatoxin contamination in loads of grain. The component that produces fluorescence under black light is called kojic acid. Although kojic acid is produced by the same fungus that produces aflatoxin, its presence is not necessarily an indicator of aflatoxin and might lead to false positive results and unnecessary rejection of grain.

High Risk Factors for Aflatoxin Contamination in Corn

  • Drought-damaged fields, including rainfed (dryland) fields and non-irrigated pivot corners
  • Fields or areas with higher incidence of corn ear-feeding insects, such as the corn ear worm
  • Grain damaged before or during harvest or after harvest while in storage

Ear rot diseases and aflatoxin are not evenly distributed across fields or in the grain, so scouting and/or sampling should include a substantial portion, at least several acres. The presence of the fungus in kernels does not always correlate well with the presence of aflatoxin, nor does the absence of visible fungal growth necessarily indicate the absence of aflatoxin.Scouting For Aspergillus Ear Rot

  • Open husks to view a large number of ears.
  • Look for the presence of dusty yellow-green to olive-green spores, especially on the surface of damaged kernels or ear tips (Figure above).
  • Pay special attention to higher risk areas.

Harvest and Storage:  If fields have documented Aspergillus ear rot and/or risk of aflatoxin contamination, it is recommended that you harvest and keep grain separate from other grain at less risk, such as irrigated fields. Storage of affected grain is not recommended because ear rot diseases and mycotoxins can continue to accumulate during storage. If storage is necessary, cooling and drying grain to less than 15% moisture within 48 hours of harvest will help to slow fungal growth and aflatoxin production. Grain intended to be stored for longer periods of time should be dried to less than 13% moisture.

Presently, it is too early in the harvest to know the extent of aflatoxin contamination in this year’s corn crop, but at this time only a small percentage appears to be affected.

Resources:  For more information, refer to the list of publications below or view this week’s episode of Market Journal.

Table 1: FDA action levels for aflatoxin contamination in corn intended for livestock.

Commodity Action Level (ppb)
Finishing (feedlot) beef cattle  300
Finishing swine of 100 pounds or greater  200
Breeding beef cattle, breeding swine, or mature poultry  100
Immature animals and dairy cattle  20
For animal species or uses not otherwise specified, or when the intended use is not known  20
Human food  20

Source: FDA Action Levels for Aflatoxin

More on Last #Irrigation

It’s been a long irrigation season thus far, but we are so thankful for irrigation in this part of the Country during this drought of 2012!  Questions continue to roll in regarding last irrigation for corn and soybeans.  Corn at 1/2 starch only needs 2.25″ to finish up so it’s important to know what your soil moisture status is.  For most irrigated producers, at 1/2 starch, you should be finished irrigating.  

For soybeans at R5 or beginning seed fill, you still need about 6.5″ to finish out the crop.  At R6 when the seeds are filling, that drops to 3.5″.  At R7 when you begin to see leaves yellowing, that is beginning maturity and you are finished irrigating.  They key is we don’t want to fill the profile going into the fall as we’d like to replenish the profile with fall and spring rains and winter snow.  However, with soybeans, it’s also critical not to stop irrigating too soon during seed fill.

Gary Zoubek, Extension Educator in York County sheds more light in the following video produced by UNL’s Market Journal.

Latest 2012 #Corn Yield Predictions

The 2012 corn growing season has been unusually hot and dry. To evaluate the impact on potential production at 12 sites across the Corn Belt, we used the Hybrid-Maize model to estimate end-of-season yield potential based on actual weather up to August 13 and historical long-term weather data thereafter. (Data  from each of the past 30 years was used.) This approach gives a “real-time,” in-season estimate of expected yield potential (the median value shown inTable 1), and the most probable range (25th to 75th percentiles) depending on weather conditions from August 13 until the corn crop reaches maturity.

By comparing this range of possible simulated end-of-season yield potential against the long-term average (long-term Yp, fourth column from right in Table 1), it is possible to estimate the likelihood for below-average (25th percentile), average (median), or above-average (75th percentile) yields. Comparing estimated 2012 yield potential versus the long-term average gives the size of the expected yield difference. While the 25th percentile projection is most likely if weather conditions are harsher than normal from August 13 until crop maturity, the 75th percentile scenario is more likely if weather is more favorable than is typical at a given site. There is roughly a 50% probability that final yield potential will fall between the 25th and 75th percentile levels, a 75% chance that yield will be at or below the 75th percentile, and a 25% probability that it will be at or below the 25th percentile value.

Simulations were run for dryland corn in Iowa, Illinois, and South Dakota, and for both irrigated and dryland corn in Nebraska. Simulations were based on the typical planting date, hybrid relative maturity, plant population, and soil properties at each location. Underpinning data used in these simulations are provided in Table 1. Details about the Hybrid-Maize model and our simulation forecast methods can be found in a previous CropWatch article.

As the season progresses, the range of yield outcomes shrinks and the 25th and 75th percentile values converge toward the median value. Indeed, August 13 projections give a much narrower range than our projections two weeks earlier based on July 30 simulations. The good news is that projected yield potential since July 30 has stabilized or even increased slightly at 7 of 12 sites as weather has improved, especially during the most recent week. The bad news is that projections of final yield potential are below the long-term average at all but two sites.

Dryland Corn

Even in hot, dry years like 2012, parts of the Corn Belt escape untouched and catch adequate rainfall. This appears to be the case in the northern tier of the Corn Belt (e.g. Brookings, South Dakota) and near the Great Lakes (e.g. Dekalb, Illinois) where projected dryland yield potential is within 2% of the long-term average. In contrast, there is moderate yield loss of 26-33% for dryland corn in south central Nebraska (Clay Center), central and northeast Iowa (Gilbert and Nashua), and west central Illinois (Monmouth). Severe yield loss of 40-65% is projected for dryland corn in eastern and northeastern Nebraska (Mead, Concord), northwest Iowa (Sutherland), and south central Illinois (Bondville).

Irrigated Corn

In contrast to large loss of yield potential in these dryland systems, drought years like 2012 highlight the value of irrigated agriculture and the stability it provides to our food system. Although hotter than average temperatures have shortened the grain filling period at all irrigated sites, which reduces yield potential somewhat, projected decreases are modest at about 5% in south central Nebraska (Clay Center, Holdrege), and 10% in east and northeast Nebraska (O’Neill, Concord, Mead). High grain prices are likely to offset the impact such losses will have on profits from irrigated corn.

Model Reliability

Given the severity of reductions in yield potential at some locations, and the apparent lack of negative impact at others, the question arises as to how reliable these projections are? In areas with relatively little heat or water stress, past experience indicates that predictions of yield potential using Hybrid-Maize are robust. In contrast, we would expect predictions of yield loss to be underestimated by Hybrid-Maize in areas where there was high temperature stress during the critical two to three day period of pollination, or where there were large water deficits that severely reduced development of the leaf canopy before tasseling. Both phenomena are not well accounted for in the current version of the model although we plan to release an improved version of Hybrid-Maize later this year that addresses these deficiencies.

Summary

The bottom line is that 2012 will be a difficult year in terms of U.S. corn production. Although irrigated yields will be somewhat lower than long-term averages, dryland corn yield potential in much of the Corn Belt will be moderately (25-33% below normal) to severely reduced (40-65% below normal). Where both prolonged drought and high temperature stress at pollination occurred, yields could be reduced by 65% or more. The final outcome will be determined by weather conditions until maturity. Fortunately, predicted weather patterns indicate a trend toward more normal temperatures and rainfall in many places.

While 2012 will certainly be a significant drought year, episodic droughts of this magnitude have occurred at regular intervals in the U.S. Corn Belt over the past 100 years of recorded weather data. Nebraska is fortunate that about 70% of total corn production comes from irrigated systems, and that improved agronomic management practices such as conservation tillage and more stress-tolerant hybrids can significantly reduce dryland corn yield losses under moderate drought. But there is little that can be done to mitigate the impact of severe, prolonged drought especially when coupled with high temperature stress at critical growth periods.

Patricio Grassini, Research Associate Professor, Department of Agronomy and Horticulture
Jenny Rees, UNL Extension Educator
Haishun Yang, Associate Professor, Department of Agronomy and Horticulture
Kenneth G Cassman, Professor, Department of Agronomy and Horticulture

Table 1.  2012 In-season yield potential forecasts as of August 13  using UNL Hybrid-Maize Model

Location, State

Water Regime

PP(ac-1)

RM¶ (days)

Planting Date

Long-term
Yp (bu/ac)

 2012 Forecasted Yp (bu/ac)

 75th*

 Median


Holdrege, NE

Irrigated

 32.4k

113

 April 27

 248   

 239

 232

Clay Center, NE

Irrigated
Rainfed

32.4k
24.0k

113

April 23
April 23

 250
146   

241
115

237
104

Mead, NE

Irrigated
Rainfed

32.4k
28.0k

113

 April 30

 240
160   

221
60

216
56

Concord, NE

Irrigated
Rainfed

32.4k
29.0k

104

May 3

235
154   

210
92

208
86

O’Neill, NE

Irrigated

 32.4k

106

 May 3

225   

 212

203


Brookings, SD

Rainfed

 30.0k

98

 May 4

120   

 127

118


Sutherland, IA

Rainfed

 31.4k

99

 May 1

168   

 110

99

Gilbert, IA

Rainfed

 32.4k

 110

 April 26

200   

 157

144

Nashua, IA

Rainfed

 32.4k

99

 May 1

198   

 152

147


Monmouth, IL

Rainfed

 32.4k

112

 April 27

212   

 161

143

DeKalb, IL

Rainfed

 32.4k

111

 May 1

201   

 227

204

Bondville, IL

Rainfed

 32.4k

114

 April 20

197   

 110

105


  Simulations based on dominant soil series, average planting date, and plant population (PP) and relative maturity (RM) of most widespread hybrid at each location (Grassini et al., 2009).
 Average (20+ years) simulated yield potential (Yp).
* 75th percentile yields, which represent favorable and unfavorable weather scenarios for the rest of the season.

Cover Crops & Fall/Spring Forage Options

With corn being harvested for silage, corn maturing early, and livestock producers looking for forage options, I’ve received questions about seeding cover crops or forage options.  Mike Burgert from the Clay County Natural Resources Conservation Service also wanted me to share the concern of the loss of reside and the increased likelihood of soil erosion.  He said if harvesting crops for forage takes place on a USDA program participant’s “highly erodible” acres, this would likely not be an approved conservation system and could cause ineligibility for USDA programs on all of their land in programs. He also said they have cost share for drought related practices (cover crops for forage on cropland, stock water well/pipe/cross fencing/water facility, etc.).  

Dr. Bruce Anderson shared the following information:  Before planting anything, review your herbicide history. Prior use of contact herbicides like glyphosate won’t cause any problems, but some herbicides have a long soil residual effect that could prevent successful establishment of some crops.  Double crop choice is likely to be different for rainfed and irrigated conditions. One ton (dry weight) of forage production is likely to use 4-5 inches of water. For rainfed conditions, a crop that will winter kill is preferred in order to accumulate soil water from snow melt and spring rainfall for the next crop. For irrigated conditions, forage production will be more with a crop that survives winter and is spring harvested—although irrigation for the forage and following crop will likely need to be increased compared with no double cropping.

Fall Forage options:  Determine when the forage crop is to be harvested and how it will be used. For fall-harvested hay or silage, oats or other spring cereals will outyield all other options. Plant about 100 lb. of seed per acre. Various legumes like hairy vetch, field peas, or winter peas can be added to increase protein concentration a percentage point or two, but they are unlikely to increase dry matter yield; the forage from the cereal alone will meet most cattle protein needs. Also be wary of spending more for the seed than the extra protein might be worth. For grazing this fall and winter, turnips and oats (separately or in a mixture) usually will provide the most feed.
     Early planting and emergence (irrigation or soil moisture must be available immediately) is essential for successful fall forage. Plantings after Labor Day rarely produce sufficient growth for mechanical harvest in the fall and the amount of fall grazing becomes negligible for plantings made after mid-September. Even earlier planting dates may be needed for sites north of the Platte River. Later plantings should consist of winter cereals. Also, the chances for successful establishment are low unless soil is sufficiently moist to at least an eight-inch depth at time of planting.

Spring Forage Options:  For spring forage, the winter cereals rye, triticale, and wheat tend to be the best choices. Rye is your best choice for early spring pasture and produces much growth before being terminated for timely planting of a row crop. Some rye varieties also provide enough fall growth for some light grazing if planted early enough. Rye also may be the most reliable crop when planted under stressful conditions. Rye has some drawbacks. It turns stemmy and matures much earlier than triticale or wheat, with a loss in feed value and palatability, although this should not be an issue if harvest ends in time for spring planting of a row crop. Also, it should not be used in fields that will be used to grow grain wheat due to potential contamination that could lead to discounts/dockage when wheat grain is sold.
     Triticale holds on to its feed value best into late spring. This makes it well suited for hay and silage, or for stretching grazing well into June if grazing begins two or three weeks later than it could begin with rye. Triticale often is more susceptible to winter injury than rye and wheat.
     Winter wheat will provide very little grazing for fall. During spring, forage quality and acceptance is very high but forage yield is less than rye and triticale. It can be grazed and then allowed to produce grain if grazing ends when plants begin to joint and elongate.
     Mixtures often can be desirable and can be designed for individual needs. For example, an early planting of 30 lb. of oats plus 75 lb. of winter rye per acre may provide both fall grazing from the oats and spring grazing from the rye. 

#UNL South Central #Ag Lab Field Day

We have a great field day coming up on August 22 at South Central Ag Lab near Clay Center.  Check out the flyer below for more details and hope to see you there!

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