On-Farm Grain Storage Fumigation Workshop

Doug Johnson, Extension Entomologist

The University of Kentucky Grain Science Working group will be offering a Grain Storage Fumigation Workshop on Tuesday May 13, 2014 from 1:00 PM to 4:30 PM CDT, at the UK-REC in Princeton, KY. This workshop follows the Annual Wheat Field Day that will be held at the center from 8:00 AM to noon the same day. These two programs are complementary, developed by the same working group, but are separate events. Additionally, the Fumigation Workshop will cover all grain crops. Each event will have its own registration and have requested separate pesticide continuing education units (CEU’s).

To store or not to store this year’s Soft Red Wheat Crop

By Cory Walters, Sam McNeill and Doug Johnson, University of Kentucky

Each year producers decide whether to store or sell their Soft Red Wheat (SRW) crop. Producers typically choose the latter and sell their crop off of the combine. This year the Chicago wheat (SRW) futures contract is offering a large storage incentive. The relationship between July 2011 Chicago wheat futures and March 2012 Chicago wheat futures is a plus $1.04/bu (March = $8.63, July = $7.59). Putting grain in storage AND selling a March 2012 futures contract will gain you an additional $1.04/bu. However, there are other costs and risk associated with doing this. Storage decisions should be made based upon the carry offered in the futures market, storage constraints (coming from other crops), harvest constraints, storage costs, opportunity costs of money, and other costs.

Aflatoxins in Corn

Paul Vincelli, Extension Plant Pathologist, University of Kentucky
Sam McNeill, Extension Agricultural Engineer, University of Kentucky

Aflatoxins are showing up in occasional lots of harvested corn from this season’s crop. Aflatoxins metabolites of the fungus Aspergillus flavus, are potent toxins and carcinogens in animals, and may also be human carcinogens. Aflatoxins are probably the most well-known mycotoxins, because they have long been regulated by the US Food and Drug Administration.

During grain fill, many Kentucky corn fields experienced high temperatures (highs above 90°F, with warm nights) and drought conditions, which favor Aspergillus infection and aflatoxin contamination of the kernels. Kernel injury caused by insects, mechanical damage during harvest or handling, or other causes can lead to an increase in aflatoxin levels (Figure 1), though infection and contamination can occur even in undamaged kernels if conditions are highly favorable for the fungus.

Figure 1. Yellow-brown sporulation of Aspergillus flavus in an insect-injured corn kernel. 


Grain Storage
Mycotoxins such as aflatoxin can accumulate in corn in storage.Table 1 below provides recommended conditions that will suppress mold growth in storage. Corn with evidence of mold or mechanical damage or excess trash should be held at 0.5 to 1% lower moisture content than recommended here. Monitor stored corn regularly for mustiness and grain heating.





Permissible levels Aflatoxins are regulated at the parts-per-billion level, an extremely low level. To put this in perspective, one part-per-billion is equivalent to one second in 32 years, or one kernel in a 10,000 bushel bin.

For many uses, grain must have less than 20 parts-per-billion (ppb) of aflatoxin. However, there are some permissible uses for corn with higher levels. For example, mature cattle can be fed corn with up to 300 ppb aflatoxin. Details on the permissible levels of aflatoxins in livestock feeds and human foods are available in the UK Extension publication, Aflatoxins in Corn, ID-59, http://www.ca.uky.edu/agc/pubs/id/id59/id59.pdf.

Blacklight testing
Examining the kernels for yellow-green fluorescence under a blacklight is commonly used as a quick preliminary test. The entire sample should be cracked or coarse-ground for blacklight testing. However, yellow-green fluorescence under a blacklight does not indicate the presence of aflatoxins. Fluorescence simply indicates that aflatoxins may be present in the kernel. A blacklight test can often give a "false positive"; that is, a positive result from a clean load of corn. A similar glow under blacklight may be produced by tips of corn kernels, corn beeswings (glumes), soybean hulls, certain weed seeds, and strains of A. flavus that do not produce aflatoxins. Plus, it is also possible to get a negative blacklight result from a contaminated sample. Thus, blacklight testing is not considered to be a reliable method for detecting aflatoxin.

Sampling Corn for Testing
Aflatoxin testing is notoriously variable. Sampling for any contaminant in grains at the parts-per-billion level is highly variable. See Table 2 below for an illustration of this variability.


 Table 2. Aflatoxin test results (parts-per-billion, ppb) in ten properly collected samples obtained each of three peanut lots (arranged in ascending order for ease of interpretation). 

One can’t prevent this sort of variability when testing for aflatoxin, but one can make it worse by not sampling correctly. The recommended sampling procedure for corn is as follows: Take at least ten probefuls and collect at least 10 lb of corn. The corn must be below 16% moisture unless the test is being performed immediately. Test results from high-moisture corn may not be accurate if the test is delayed, as the fungus can continue to grow and produce aflatoxins. The 10-lb sample must be ground and mixed well before drawing a small subsample for testing. The AOAC International (formerly the Association of Official Analytical Chemists) requires that the entire 10-lb sample be coarsely ground to pass through a No. 14 sieve and mixed, and that a 2- to 4-lb subsample be ground to pass through a No. 20 sieve (about the consistency of fine instant coffee), before aflatoxin testing.

Test kits are available from several manufacturers. Some of these test only for the presence or absence of aflatoxins. Other, more sophisticated kits estimate the concentration of aflatoxin. If using one of these, grain should be ground and mixed as described above, and operators should be well-trained in the use of the particular test kit being employed.

Analytical laboratories provide the best estimates of aflatoxin concentration. Drawbacks of laboratory testing include expense and time delays while waiting for results.

Management for 2011
Stored corn should be managed as described above, so as not to allow aflatoxin accumulation in storage. As far as planning for the 2011 crop, any fields with aflatoxin this year have only a very, very modest increase in aflatoxin risk next year. Of course, most of those will be rotated as normal, and aflatoxin is only a concern in corn. Even for those that are sown to corn in 2011, aflatoxin contamination is driven much more by environmental conditions than by cropping history and agronomic practices. Of course, since aflatoxin contamination is commonly associated with drought and grain damage, it is advisable to use good agronomic practices such as: sowing adapted hybrids, avoiding excessive plant populations, reducing soil compaction (if present), and managing kernel-feeding insects.


Additional Resources Details on many aspects of aflatoxins are available in the UK Extension publication, Aflatoxins in Corn, ID-59, http://www.ca.uky.edu/agc/pubs/id/id59/id59.pdf 

Grain storage recommendations are available in the UK Extension publication, A Comprehensive Guide to Corn Management in Kentucky, ID-139, http://www.ca.uky.edu/agc/pubs/id/id139/id139.pdf

A multi-state Extension publication entitled Moldy Grains, Mycotoxins, and Feeding Problems is available at http://www.oardc.ohiostate.edu/ohiofieldcropdisease/Mycotoxins/mycopagedefault.

Grain Storage and Drying Calculators

A lot of the grain harvested this fall was wet. Immediate sale of this grain resulted in dockage at the elevator. On-farm storage and artificial drying of the grain also has costs. Now that farmers have most of their grain out of the field, they can pay closer attention to how much on-farm storage is costing compared with the expected dockages at the elevators.

An excellent website on Grain Storage was has several calculators to help producers estimate the costs of drying grain, grain shrinkage, grain bin capacity, and related topics. Dr. Sam McNeill, Extension Agricultural Engineer, was the author of most of these calculators.

A related website for Proper Grain Storage and Handling includes additional relevant topics.

Corn Yields may be Hurt by Fungi

Sam McNeill, Extension Agricultural Engineer and Paul Vincelli, Extension Plant Pathologist with the University of Kentucky College of Agriculture Cooperative Extension Service

USDA’s mid-September crop report predicted record level corn yields for Kentucky of 155 bushels per acre. Coupled with increased acreage, the state’s production could top 175 million bushels, which is also a record. However, a potential ‘fly in the ointment’ with this year’s crop is the delayed harvest coupled with damp weather which has led to stalk, ear and kernel rots. As noted in previous news stories, potential problems with field fungi (Diplodia, Gibberella, Fusarium, etc.) have lead to concerns about subsequent storage. While not all fungi produce mycotoxins, mold-damaged kernels are more susceptible to those that do. So it is best to err on the side of caution and check corn lots with field mold for mycotoxins before feeding to livestock.
When harvesting mold-damaged corn, adjust combines to minimize mechanical damage so that sound kernels are protected and to maximize cleaning, so that lightweight kernels are removed. Harvest, handle and store damaged corn separately when feasible and market early to reduce demands on storage management.

Grain moistures above 18-20% favor the growth of field fungi and the longer corn remains in the field the greater the chance of mycotoxin production. Thus, damaged corn should not be allowed to dry in the field to avoid drying costs. Corn with light damage should be dried to 15% within 24 hours after harvest and cooled to 40 degrees as soon as weather permits, in order to control mold growth during storage. This will create a storage environment within the grain mass that is below 65% humidity, which is dry enough to control mold growth and development (see values in the equilibrium moisture table). Corn with heavy to moderate damage should be dried to 13 to 14%, respectively, cooled as quickly as possible and moved before March.

The table below presents the equilibrium moisture contents for shelled yellow corn at different temperature and relative humidity conditions. Example: Corn that is 40 degrees and 13.7% moisture will create a relative humidity of 55% within the grain mass, which is safe for storage.

Temp.	Relative Humidity
oF	%
	45	55	65	75	85
	Corn Moisture, %
40	12.2	13.7	15.3	17.2	19.6
50	11.6	13.1	14.7	16.5	18.9
60	11.1	12.5	14.1	15.9	18.3
70	10.6	12.0	13.6	15.4	17.7

If mycotoxin problems are suspected, check with crop insurance providers to see if adjustments may be needed and how to account for the areas that are impacted. Insurance adjustments generally need to be made on standing corn at or before harvest.

The following publications provide more information on vomitoxin, aflatoxin and grain testing labs:
http://www.ca.uky.edu/agc/pubs/id/id121/id121.pdf
http://www.ca.uky.edu/agc/pubs/id/id59/
http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-MISC-1.pdf

Storing Diplodia Ear Rot-Affected Corn

Paul Vincelli, Plant Pathology

Diplodia ear rot (DER) is being reported rather widely this year. Questions have arisen about storage of DER-affected corn. The fungus that causes DER won’t develop further if moisture content is below the normal target of 15.5%. However, rotted kernels are damaged kernels, and since the grain integrity is compromised, other fungi more tolerant of low moisture will have an easier time growing. Our agricultural engineers recommend drying damaged corn an extra 0.5 to 1.0 point of moisture for better storability and cooling it as quickly as possible. Producers should make sure to keep that grain well aerated and dry, and market it sooner rather than later.

Fortunately, there are no known mycotoxins produced by the strains of the DER fungus found in North America. In addition to several recent Kentucky Pest News articles on this subject, more information on this disease is available in a UK Extension publication available at http://www.ca.uky.edu/agc/pubs/ppa/ppa43/ppa43.pdf.