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9/6/2010 - 9/12/2010

The 2009 Crop Won’t Quit – and Here Comes 2010

By Charles R. Hurburgh, Jr., Department of Agricultural and Biosystems Engineering and Alsion Robertson, Department of Plant Pathology

Most of us would probably rather forget the 2009 crop, at least as far as storage and quality goes. Unfortunately, as we thought it might, this crop just kept on giving – headaches. The wet, incompletely developed and low test weight conditions led to about 50 percent shortening of the normal shelf life, at any moisture and temperature condition. Storage norms were covered in an ICM News article last fall, 2009 Corn Quality Issues – Storage Management.

My expectation was that in July or August, the shelf life would run out, and in-storage molding would increase, even in dry corn. This happened. The common consequence was “blue-eye” mold appearing almost overnight in many cases, in late July and early August. Once the shelf life is gone, and the grain is warm and in equilibrium with about 65 percent relative humidity or greater, blue eye can become a problem.  At 80 F, this is about 13.5 percent moisture—even dry corn can spoil in these conditions.

Blue eye is predominantly caused by the fungi, Penicillium oxalicum and Aspergillus glaucus, neither of which is aggressive enough to generate heating nor do they produce mycotoxins.  There are however other species of Penecillium that can cause blue-eye and may produce mycotoxins. All moldy grain should be tested for mycotoxins.

The situation was complicated by the warm, high humidity period in July and August.  Few days had humidity below 65 percent which meant that aeration only controlled heating. Fungi active at ambient conditions grew steadily.
 
Blue eye is not extremely destructive of feed value; the germs are most affected, which is where the oil but not the starch is located. However, it will grade as damage, and it is very hard to grade accurately because kernels often need to be cut to determine interior infection. Its effect on ethanol processing is not known, although most molds reduce the effectiveness of fermentation enzymes. At this time, the grain market has so much damaged corn in channels that few buyers are able to absorb more until the new crop arrives.

Recommendations for flood damaged corn fields
There was some flooding of corn fields in August 2010. These fields are now drying out.  If water was over the ear, the cobs are mushy and rotten. Blue-green ear rot is common on warm wet cobs, which will move to the grain, and raises the potential for toxins in this corn. My recommendation is to work with crop insurance to avoid taking this corn to market. Flood waters are notoriously impure in addition to the mold issues. If harvested, clean well to remove cob parts and store separately until toxin testing can be done. Feed only under the direction of a veterinarian, depending on the test data.

Pre-harvest storage preparations
We are all hoping for a good 2010 crop. Prepare by completely cleaning storage bins, under floors, around air ducts and in all corners of grain handling systems. Likewise clean out dryers very thoroughly. Dispose of all the fines and residual grain; insects liked 2009 corn as well as mold.

The 2010 crop should be much drier and therefore be less at risk for mold development. We are average to above average in heat units, but much above average in rainfall this year. The downside of all the rain is that crops contended with warm high humidity days and nights, which probably expended energy and reduced grain fill in corn. There was also loss of nitrogen, which created light green colors in August. This will show up in test weight; we are expecting average test weights (54-55 lb/bu) but not very high test weights this year. The last week of warm weather increased maturation, which also may limit kernel fill. The best opportunities to absorb some of the carryover of problem grain may be early in the marketing year.

Soybean outlook
Soybeans look to have good quality, except for the irregular seed size created by SDS. There will be some increased foreign material issues stemming from less than timely applications of herbicide in wet fields.

The key storage management items
- Harvest will start in warm weather.  Warm grain from the field or dryer will take an extra cooling cycle. Do not let hot grain sit without air and cooling. Piles, flat storages and other situations with less airflow will be vulnerable.

- Crop years should never be mixed prior to storage. Especially this year, the old crop will provide a fungal load for the less stable new crop and problems occur.

- Consign grain to storage structures carefully; there will not be any leeway for more condition problems. Use test weight as a gauge of storability and market accordingly.

-Combines will break more corn and create more fines at low moistures (below 17 percent). An extra cleaning on farm,and removal of bin centers immediately after filling will help this problem.  2010 corn will not break as much in subsequent handling as the low test weight 2009 corn did.

The 2009 crop was the most difficult in memory to handle, all the way through the season. The 2010 crop promises to be better but perhaps will not be of outstanding quality. This means paying attention to grain in storage, planning ahead and moving questionable grain quickly so as not to add to the carryover problems. We will update as the harvest progresses.
 

 

 

Charles Hurburgh is an agricultural and biosystems engineering professor who manages the Grain Quality Research Laboratory and the extension-based Iowa Grain Quality Initiative. He can be contacted at (515) 294-8629 or by email at tatry@iastate.edu. 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 alisonr@iastate.edu.

Good Harvest in Corn Should Help Manage Soybean SDS

by XB Yang and SS Navi, Department of Plant Pathology

This year is one of the worst soybean sudden death syndrome (SDS) epidemics since the disease was found in Iowa in 1994. Preliminary research data suggest that corn has much to do with SDS pathogen and there are things we can do about the disease as we begin harvest. Management of SDS should start when we harvest corn fields.

We have been puzzled by the fact that SDS is more prevalent in the Corn Belt when the disease was first reported in Arkansas. This summer many people in Iowa reported that SDS occurred in soybean fields where little or no SDS had been seen previously. These fields have been in a corn and soybean rotation for years. And there have been many reports of severe outbreaks of SDS in fields which had been in continuous corn for years. We speculated that rotation with corn may have something to do with it; specifically, corn may harbor the SDS pathogen in the absence of soybeans.

With funding from the Iowa Soybean Association, we conducted studies for two years, both in greenhouse and field plots to examine the survival of SDS fungus in corn. We wanted to see if corn residue harbored SDS pathogen in the absence of soybeans. We compared the survival of SDS fungus in two crop residues (corn or soybean) which included different parts of a plant (root, stalk, kernels). We consistently found the highest SDS fungus population in the treatment with corn kernels at a density of average harvest loss.

We repeated the experiments in both greenhouse and fields, and the results are consistent over the two years. Figure 1 shows the frequency of the SDS fungus isolated from field plots that had a variety of crop residues plus the SDS fungus; Figure 2 shows the frequency of the fungus isolated from similar treatments in the greenhouse.

 

Soil samples also were collected from one field each of the following counties - Boone, Blackhawk and Delaware. These fields had SDS in previous growing seasons and were in corn-soybean rotation.  Cropping history and yield data were collected from these farms to better understand survival of SDS fungus in soil and on residues.  Results from these farms are on par with the results shown in Figures 1 and 2.

Our findings are consistent with the following observations:
1) severe SDS occurs in corn/soybean rotation fields although little or no previous SDS was observed;
2) severe outbreaks of SDS occurred after a few years of continued corn production; and
3) severe SDS was found in seed-corn fields which often have a lot of unharvested kernels due to quality control. 

Although we are yet to experiment which tillage measures better reduce SDS pathogen in corn/soybean rotation, our results suggest that a nice and clean harvest of corn should help reduce the risk of SDS, while a high amount of harvest loss increases SDS risk. 

 

 

XB Yang is a professor of plant pathology with responsibility in research and extension. SS Navi is an assistant scientist. Yang can be contacted by email at xbyang@iastate.edu or by phone at (515) 294-8826.

Video Offers Guidance for Coping with Soybean Sudden Death Syndrome

by Alison Robertson and Leonor Leandro, Department of Plant Pathology

As soybean sudden death syndrome (SDS) continues to ravage Iowa fields in one of the worst outbreaks in many years, Iowa soybean growers are increasingly worried about the damage the disease will cause, while others are unsure whether their plants have been infected.
 
To help answer questions and offer guidance in managing the disease, Iowa State University has produced a video that explains why SDS is so severe this season; tells how to assess and manage SDS; offers practical advice growers can follow now to prepare for next year; and highlights new and ongoing ISU research on the problem.
 
In the video, we explain how a perfect storm of early planting and wet weather at key points during the growing season created the ideal circumstances for SDS to thrive.
 
Highlights from the video
This year we’ve had particularly severe SDS due to a combination of early planting into cool, wet soils and the continuation of a wet season with a wet July during reproductive stages that is also thought to favor the disease.  We also see the disease moving north and west year to year, probably as a result of an increase in the pathogen density in the soils that’s building up over the seasons.

A fungus infects soybean plant roots soon after planting, producing a toxin that later moves up the plant damaging soybean leaves and eventually causing them to die and drop. Survival of the fungus on corn debris may be another reason why SDS is so widespread this year.
 
Recent soybean checkoff-funded research at ISU has shown the fungus can survive on corn kernels and corn stalks. The corn debris is likely allowing the fungus to carry over from year to year. 

Growers are unaware plants have the disease until yellow patches start to appear on soybean leaves. The yellow patches will extend, turn brown and eventually (the leaf will) die, falling off and leaving a bare stem. 

Other SDS symptoms include severe root rot, and sometimes the blue color of the fungus may be visible growing on the outside of the root. If uncertain, one way to definitively diagnose SDS is to cut into the soybean plant taproot and observe its color. The inside of the root is discolored brown. It’s not a creamy white color like you would see with a healthy soybean plant.
 
Plants that have the disease are likely to experience some yield loss, though the extent will depend on how early SDS appeared during the reproductive stages of plant growth.
 
While SDS can’t be treated, it can be managed with appropriate variety selection and improved field drainage. In addition, Iowa State has developed germplasm with resistance to SDS that has been released for seed companies to develop commercial varieties.
 

 

 

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 alisonr@iastate.edu. Leonor Leandro is an assistant professor of plant pathology with research and teaching responsibilities. Leandro may be reached at (515) 294-8855 or by email at lleandro@iastate.edu.

Answers to Questions About Soybean Sudden Death Syndrome in Iowa 2010

By Alison Robertson and Leonor Leandro, Department of Plant Pathology

Sudden death syndrome (SDS) is now among the top four yield robbing diseases in soybeans. From 1999 to 2004, average losses in the U.S. were estimated at $190 million a year, and the disease is spreading and intensifying. SDS has been widespread and severe in Iowa this growing season, generating many questions of researchers. The most frequently asked questions are included in the following series of questions and answers.

sudden death syndrome

Field foliar symptoms of soybean sudden death syndrome. Photo by Daren Mueller.

What has caused soybean sudden death syndrome (SDS) to be so severe in Iowa this year?
• SDS is caused by a fungus present in many Iowa soils that infects soybean roots and produces a toxin that moves up the plant and kills the leaves.
• The occurrence of SDS is greatly affected by soil and weather conditions; the disease will not develop if the weather conditions are not favorable.
• The weather in 2010 was ideal for development of the SDS disease.

Is SDS severe in other states this year, too?
• Yes.  Extension plant pathologists are reporting widespread and severe cases of SDS in Illinois, Indiana, South Dakota, Minnesota, and Wisconsin.

Has Iowa State University’s recommendation to plant soybeans in late April-early May resulted in the severe outbreak of SDS in Iowa?
• No. The severe SDS occurring in Iowa this year is not the result of any single factor.
• There has been a gradual buildup of SDS in Iowa over the past ten years, and the unique weather conditions in Iowa in 2010 were ideal for severe SDS disease development.
• Results of soybean checkoff-funded research at ISU conducted in years when environmental conditions are not favorable for development of SDS indicate that early planting maximizes the ability of the soybean crop to produce yield.

What weather and soil conditions favor SDS?
• Temperatures below 60 F at planting favor infection of soybean roots by the SDS fungus. However, greenhouse research has shown that infection can occur at temperatures up to 82 F.
• Moderate temperature (about 80 F) during the growing season leads to SDS symptoms developing on the leaves.
• Wet weather and soil compaction favor SDS disease development.

What are the symptoms of SDS?
• Soybean roots will appear rotted and plants will be easily pulled from the soil.
• The fungus that causes the disease may appear as blue fungal growth (spore masses) on the main or tap root of the soybean plant.
• When split lengthwise with a knife, the internal tissue of the main or tap root will be gray to reddish brown, not healthy white.
• The areas between the leaf veins will turn bright yellow, then eventually brown. The dead, brown tissue between veins may fall out, leaving large ragged holes in leaves.
• The leaf blades will fall off of the petioles (petioles are the thin “stems” that connect the leaf blades to the main stem), but the petioles remain attached to the stem.

How much soybean yield loss is expected from SDS in Iowa this year?
• This year’s yield losses to SDS are expected to exceed 20 percent in some fields.

Is Iowa State University conducting research on SDS?
• ISU has a strong team of plant pathologists, agronomists and soybean breeders working on various aspects of SDS and the fungus that causes the disease.
• The ISU scientists collaborate with scientists at other universities to find solutions for SDS management.
• Most of the SDS research at ISU is funded by soybean checkoff dollars from state, regional and national organizations, namely the Iowa Soybean Association, the North Central Soybean Research Program and the United Soybean Board.

What can growers do differently to prevent SDS from happening again next year?
• An integrated, multifaceted approach is needed to manage SDS.
• The foundation of an SDS management program is use of resistant soybean varieties. Consult with seed company personnel and agribusiness agronomists for information on varieties that are resistant to SDS.
• Grow soybean varieties with the greatest resistance to SDS in the fields with the greatest history of SDS problems.
• Take measures to avoid or reduce soil compaction.
• Fields with a history of SDS should be planted later, rather than earlier in the spring. But do not delay planting to the point of compromising yield potential.
• Consider improving soil drainage, if possible, in fields with recurring SDS problems.

Is there a spray or seed treatment that growers can use to prevent or control this disease?
• Unfortunately, no. Currently there are no seed treatments or foliar sprays that can be applied to protect plants from SDS.

Can SDS be confused with other diseases on soybeans?
• Yes. Soybean sudden death syndrome leaf symptoms look very similar to symptoms of a disease called brown stem rot (BSR).
• To distinguish SDS from BSR, split a soybean stem lengthwise with a knife. The center of the stem (called the pith) will be brown with brown stem rot but it will remain white with SDS.

Can SDS affect corn too?
• No. Sudden death syndrome does not occur on corn.
• However, recent soybean checkoff-funded research at Iowa State University revealed that the SDS fungus survives on corn kernels and other corn debris.

Will the SDS disease reduce grain quality and cause grain storage problems after harvest?
• No. Plants that are severely affected by SDS will produce smaller seeds. But the fungus does not infect the soybean seed, so it does not cause any grain storage problems.

 

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 alisonr@iastate.edu. Leonor Leandro is an assistant professor of plant pathology with research and teaching responsibilities. Leandro may be reached at (515) 294-8855 or by email at lleandro@iastate.edu.



This article was published originally on 9/13/2010 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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