Goss\u27s Bacterial Wilt and Blight ... Symptoms ... 2011 Survey results ... New alternate hosts identified ... Goss\u27s Wilt Management Strategies ... More Resources ... Literature Cited
Aspergillus Ear Rot and Aflatoxin Contaminated Grain ... Table 1. FDA Action Levels for Aflatoxin in Feed and Food ... Testing for Aflatoxin ... High risk factors for aflatoxin contamination in corn ... Scouting for Aspergillus Ear Rot ... Harvest and Storage ... More Resources
Stalk Rot Diseases ... Scouting for Stalk Rot Diseases ... Management ... More Resource

Jackson-Ziems, Tamra A.

Kruger, Greg R.

Langemeier, Craig B.

English

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnPapers in Plant Pathology Plant Pathology Department2013Corn Disease UpdateTamra A. Jackson-ZiemsUniversity of Nebraska-Lincoln, tjackson3@unl.eduCraig B. LangemeierUniversity of Nebraska-Lincoln, c_langemeier@hotmail.comGreg R. KrugerUniversity of Nebraska-Lincoln, greg.kruger@unl.eduFollow this and additional works at: http://digitalcommons.unl.edu/plantpathpapersPart of the Other Plant Sciences Commons, Plant Biology Commons, and the Plant PathologyCommonsThis Article is brought to you for free and open access by the Plant Pathology Department at DigitalCommons@University of Nebraska - Lincoln. Ithas been accepted for inclusion in Papers in Plant Pathology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.Jackson-Ziems, Tamra A.; Langemeier, Craig B.; and Kruger, Greg R., "Corn Disease Update" (2013). Papers in Plant Pathology. 534.http://digitalcommons.unl.edu/plantpathpapers/534Corn Disease Update  Tamra A. Jackson-Ziems, Extension Plant Pathologist Craig B. Langemeier, Graduate Research Assistant Greg R. Kruger, Extension Cropping Systems Specialist   Goss’s Bacterial Wilt and Blight   Goss’s Bacterial Wilt and Leaf Blight, or more commonly referred to as Goss’s wilt, was prevalent early in the 2012 growing season, but disease progression slowed, presumably due to the extreme heat and drought through most of the state.  Goss’s wilt was prevalent in the 1970s and 1980s, but only developed sporadically from the late 1980s until 2006.  Around 2006, the disease reemerged in western Nebraska, northeast Colorado, and southeast Wyoming.  From there, the disease appeared to quickly progress eastward and in 2008 it was first reported in Indiana (Ruhl et al., 2008).  The disease has also been documented as far south as the northern panhandle of Texas, and as far north as North Dakota (Korus et al., 2011) in the U.S. and two provinces of Canada, Ontario and Manitoba.     Symptoms   As the name implies, there are two phases of the disease.  The wilt phase usually occurs following early season wounding (e.g. sandblasting, hail, high winds, or heavy rainfall).  The wilt phase is usually most severe when plants are injured when nodes are stacked beneath the soil line during the early vegetative stages V3-V5 (Suparyono and Pataky 1989).  Stand reductions around V4 have been reported to be as high as 30% when the systemic wilt phase was severe.  The wilt phase is caused by a buildup of bacteria in the vascular bundles, which reduces the plant’s ability to transfer water, thus causing the plant to wilt and die.  The wilt phase can also occur when plants are larger, but disease occurrence is usually not as severe (Suparyono and Pataky 1989).  The wilt phase was confirmed in June 2012 in York County, which was especially early further east than normal during recent years in Nebraska.    The second and more common phase of the disease is leaf blight.  Leaf blighting caused by this disease is also most commonly seen in association with the wounding events as previously described.  Leaf blighting often is accompanied by water soaked lesions with discontinuous water soaked spots, often called freckles, along the lesion margin.  The lesions run parallel to the veins, but are not confined between veins.  Shiny bacterial exudate or “ooze” may also be observed on mature lesions giving it a glossy or wet appearance.     2011 Survey results   In 2011, a survey was initiated to begin to understand which agronomic factors and environmental conditions had the most impact on disease development.  More than 500 surveys were returned from eight states and were accompanied by 486 leaf samples.  The two statistical analyses used identified several factors that could have a significant impact on the development and severity of Goss’s wilt in the Corn Belt.     The top five factors associated with the development of Goss’s wilt are: 1. planting population density 2. Goss’s wilt rating for the hybrid (assigned by the seed company) 3. crop rotation sequence 4. planting date 5. percentage of residue cover  This study confirmed that the best way to avoid Goss’s wilt in a field is to plant a resistant hybrid.  It also showed that crop rotation and percent residue cover affected the ability of the pathogen to infect in subsequent years.  Since the pathogen is residue-borne, planting continuous corn, or leaving large amount of infected corn residue on the soil surface increased the likelihood that the sample tested positive for Goss’s wilt.  The other two factors associated with Goss’s wilt development were planting population and planting date.  Future research efforts will need to be made on these two topics before any recommendations can be made to better understand their impact on disease development and to better manage for Goss’s wilt.     130  2013 Proceedings : Crop Production ClinicsNew alternate hosts identified   In greenhouse trials, 3 previously unconfirmed hosts of Goss’s wilt were confirmed during the spring of 2012.  Green foxtail was the only foxtail species previously identified as a host to the Goss’s wilt bacteria (Schuster, 1975).  Research conducted in the greenhouse showed that yellow foxtail, bristly foxtail, and giant foxtail are also hosts, in addition to green foxtail, and could be providing a reservoir of bacterial inoculum.  Symptoms on these foxtail species were similar to those observed for the leaf blight phase of the disease on susceptible corn hybrids.    Other known hosts include eastern gama grass, barnyard grass, sudangrass, grain sorghum, teosinte, and volunteer corn.   Goss’s Wilt Management Strategies  • Plant resistant hybrids • Rotate with nonhost crops, such as wheat or soybean  • When practical, reduce the amount of residue, if planting into infected corn residue  • Control alternate hosts, such as volunteer corn, foxtail species, and other known alternate hosts  More Resources  Additional information on these and other diseases and their management can be found at the website Plant Disease Central at http://pdc.unl.edu/ or in the following UNL Extension publications:  Goss’s Bacterial Wilt and Leaf Blight of Corn http://www.ianrpubs.unl.edu/sendIt/g1675.pdf  Literature Cited  1. Korus, K. A., Timmerman, A. D., French-Monar, R. D., and Jackson, T. A. 2011. First report of Goss’s bacterial wilt and leaf blight (Clavibacter michiganense subsp. nebraskensis) of corn in Texas. Plant Disease 95:73.  2. Ruhl, G., Wise, K., Creswell, A., Leonberger, A. and Speers, C.  2009.  First report of Goss’s wilt and leaf blight on corn caused by Clavibacter michiganense subsp. nebraskensis in Indiana.  Plant Disease 93:841.  3. Schuster, M.L. 1975. Leaf freckles and wilt of corn incited by Corynebacterium nebraskense Schuster, Hoff, Mandel, Lazar 1972. Agricultural Experiment Station. IANR University Nebraska Lincoln Research Bulletin 270. 40pp.   4. Suparyono and Pataky, J. K. 1989. Influence of host resistance and growth stage at the time of inoculation on Stewart’s wilt and Goss’s wilt development and sweet corn yield.  Plant Disease 73:339-345.   Aspergillus Ear Rot and  Aflatoxin Contaminated Grain   The drought conditions of 2012 had severe impacts on Nebraska corn.  In addition to reductions in test weight and overall yield, secondary problems developed in some corn fields as a result of these conditions.  Drought and high temperatures promote development of the disease Aspergillus ear rot.  The fungi that cause this disease (most commonly caused by Aspergillus flavus) can produce aflatoxin.  Aflatoxin is one of many in a group of chemicals, 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.   Mycotoxins are common and can be safely consumed at low concentrations.  The concentration of aflatoxin that is considered safe for consumption depends upon the age and species of the animal consumer.  An abbreviated summary listing the Action Levels identified by the FDA for aflatoxin is listed in Table 1.         2013 Proceedings : Crop Production Clinics  131Table 1.  FDA Action Levels for Aflatoxin in Feed and Food  Consumer Action Level in parts per billion (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 Humans 20  Action Levels were established by the U. S. Food and Drug Association (FDA) for Aflatoxin are available at: http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/ChemicalContaminantsandPesticides/ucm077969.htm#afla  Testing for Aflatoxin  Corn harvested from fields where there was Aspergillus ear rot should be tested for aflatoxin prior to use, sale, or storage.  Corn is at higher risk for Aspergillus ear rot if it was grown under drought-stressed conditions or if injury occurred to the kernels.  The concentration of aflatoxin in a sample can be determined by laboratory testing. The U.S. Grain Inspection, Packers and Stockyards Administration (GIPSA) certifies some laboratories for aflatoxin testing.  A list of laboratories certified for aflatoxin testing in the Nebraska region is below. Accurate lab test results for aflatoxin depend greatly on the quality of the sample that is collected and methods used by laboratories conducting tests.  The test results are only applicable to the sample that is submitted, so it is very important to collect an adequate and representative sample for the best results.  Refer to the publication, Sampling and Analyzing Feed for Fungal (Mold) Toxins (Mycotoxins) (link below) for recommendations on how to collect and submit a high quality sample for the most accurate mycotoxin analysis.  In addition, you should contact and submit samples to a laboratory that is certified by the Federal Grain Inspection Service (FGIS) and Grain Inspection, Packers & Stockyards Administration (GIPSA) for mycotoxin analysis.  A list of GIPSA-certified laboratories in and near Nebraska is below:  • Fremont Grain Inspection.  603 East Dodge St., Fremont, 402-721-1270; email fgid@neb.rr.com •  Hastings Grain Inspection, 306 E. Park St., Hastings, 402-462-4254; email Hastings at hgihast@hastingsgrain.com; email Grand Island office at hginsp@hastingsgrain.com •  Kansas Grain Inspection Service, 517 13th Ave., Sidney, Nebr., 308-254-3975 •  Lincoln Inspection Service, 505 Garfield St., Lincoln, 402-435-4386; email lismf@neb.rr.com •  Omaha Grain Inspection Service, 2525 South 13th St., 402-341-6739; omahagrain@gmail.com •  Sioux CIty Inspection and Weighing Service, 840 Clark St., Sioux City, Iowa, 712-255-8073; email tomd@scigrain.com  The complete list of laboratories certified by GIPSA for aflatoxin testing can be found at: http://www.gipsa.usda.gov/fgis/svc_provid/providers.html Black (ultraviolet) lights have been used by some grain elevators and individuals in an effort to detect 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 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 132  2013 Proceedings : Crop Production Clinics Scouting for Aspergillus Ear Rot  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.  And, the presence of visible 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.   • 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 • Pay special attention to corn in 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.   Based on aflatoxin test results from the Lincoln Inspection Service, only about half of the samples submitted had detectable concentrations of aflatoxin.  And, only a low percentage of samples had aflatoxin concentrations of more than 20 ppb.   For more information, refer to the list of publications below or to the article in these Proceedings entitled, “Grain Storage Management to Minimize Mold and Mycotoxins.”  More Resources  Plant  Disease Profiles #3:  Ear Rot Diseases and Grain Molds http://www.ianrpubs.unl.edu/sendIt/ec1901.pdf  Sampling and Analyzing Feed for Fungal (Mold) Toxins (Mycotoxins)  http://www.ianrpubs.unl.edu/sendIt/g1515.pdf  Understanding Fungal (Mold) Toxins (Mycotoxins)  http://www.ianrpubs.unl.edu/sendIt/g1513.pdf  Use of Feed Contaminated with Fungal (Mold) Toxins (Mycotoxins)  http://www.ianrpubs.unl.edu/sendIt/g1514.pdf    Stalk Rot Diseases   The crop stress created by the harsh growing conditions in 2012 led to the development of stalk rot diseases and lodging that slowed harvest progress in some areas.   Weakened stalks became evident in some of the corn still waiting to be harvested across the state late this past fall.  The high winds in October 2012 led to lodging in corn where some stalks were weakened by stalk rot diseases and other problems.  Crop stress during the 2012 growing season contributed to the development of some stalk rot diseases.     Scouting for Stalk Rot Diseases  Affected plants often have stalks that are hollow and easily crushed by hand or bent using the “push or pinch” test.  Stalk rots can occur at any point in the stalk from the crown at/below the soil line all the way to the tassel.  Rotting that occurs at an upper node and kills only the upper plant parts is referred to as “top rot” and does not necessarily cause lodging of the whole plant.  However, degradation of the stalk below the ear can lead to plant lodging and losses during harvest.  Scouting for Stalk Rot Diseases   Walking through a field, randomly select a minimum of 100 plants representing a large portion of the field.  To test for stalk rot you may choose to PUSH the plant tops away from you approximately 30° from vertical.  If plants fail to snap back to vertical, then the stalk has been compromised by stalk rot.  An alternative method is to use the PINCH test to evaluate plants for stalk rots.  Pinch or squeeze the plants at one of the lowest internodes above the brace 2013 Proceedings : Crop Production Clinics  133roots.  If the stalks crush easily by hand, then their integrity is reduced by stalk rot and they are prone to lodging. If more than 10% of plants exhibit stalk rot symptoms, then harvesting that field should be a priority over other fields that are at less risk in order to reduce the chance of plant lodging and the potential for yield loss.   There are several fungi that are common in our production fields that can cause stalk rot diseases.  Some of the most common stalk rot diseases this year are listed below:  • Charcoal rot is one of the few diseases that are more common during drought conditions, and so, is more likely to affect non-irrigated crops.  The disease is characterized by the presence of many minute black round structures inside the stalk that can give it a gray to black appearance (hence the name).  In addition, the fungus that causes charcoal rot, Macrophomina phaseolina, has a wide host range and can cause the same disease in several crops, including soybean, sorghum, and alfalfa.   • Fusarium stalk rot is especially common during damp conditions, but may occur anywhere, including in irrigated fields this year.  The pathogen, Fusarium verticillioides, can sometimes be visible as white fungal growth on the outside of stalks at the nodes.  Eventually, the disease may cause discoloration of the inside of stalks to pink or salmon.  • Anthracnose stalk rot can also cause a leaf disease and is a common cause of top rots in corn.  In more advanced stages the disease can cause the development of black lesions visible on the outside of the stalk and is caused by the fungus Colletotrichum graminicola.    Management  Usually, there is nothing to be done to stop stalk rot development once it is identified in the field.  In most cases, stalks will continue to degrade over time further weakening them.  But, you can work to minimize your losses by identifying which fields have the worst stalk rot diseases and adjust the harvest order of those fields.  Consider harvesting those fields that are heavily impacted by stalk rots first to minimize losses after lodging.    More Resources  For more information on stalk rot diseases of corn, see the UNL Extension publications:  Corn Disease Profiles II:  Stalk Rot Diseases http://www.ianrpubs.unl.edu/sendIt/ec1868.pdf  Common Stalk Rot Diseases of Corn http://www.ianrpubs.unl.edu/sendIt/ec1898.pdf  Crop Watch  http://cropwatch.unl.edu/   If you are in doubt about the identity of a disease or cause of another plant problem, you may submit a sample to the UNL Plant and Pest Diagnostic Clinic (P&PDC) for diagnosis.  For more information about these and other plant diseases or for submission forms for the P&PDC and submission instructions, visit the Plant Disease Central website at: http://pdc.unl.edu/       134  2013 Proceedings : Crop Production Clinics

Corn Disease Update

Goss\u27s Bacterial Wilt and Blight ... Symptoms ... Management ... 2011 Survey ... Literature Cited
Gray Leaf Spot
Seedling Diseases and Stalk/Crown Root Diseases
More Resource

Jackson, Tamra A.

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnPapers in Plant Pathology Plant Pathology Department2012Corn Disease UpdateTamra A. JacksonUniversity of Nebraska-Lincoln, tjackson3@unl.eduCraig B. LangemeierUniversity of Nebraska-Lincoln, c_langemeier@hotmail.comGreg R. KrugerUniversity of Nebraska-Lincoln, greg.kruger@unl.eduFollow this and additional works at: http://digitalcommons.unl.edu/plantpathpapersPart of the Other Plant Sciences Commons, Plant Biology Commons, and the Plant PathologyCommonsThis Article is brought to you for free and open access by the Plant Pathology Department at DigitalCommons@University of Nebraska - Lincoln. Ithas been accepted for inclusion in Papers in Plant Pathology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.Jackson, Tamra A.; Langemeier, Craig B.; and Kruger, Greg R., "Corn Disease Update" (2012). Papers in Plant Pathology. 545.http://digitalcommons.unl.edu/plantpathpapers/545 Corn Disease Update Tamra A. Jackson, Extension Plant Pathologist Craig B. Langemeier, Graduate Research Assistant Greg R. Kruger, Extension Cropping Systems SpecialistGoss’s Bacterial Wilt and Blight  Goss’s Bacterial Wilt and Leaf Blight, or more commonly referred to as Goss’s wilt, was commonly seen across the Corn Belt in the 2011 growing season.  Goss’s wilt was prevalent in the 1970s and 1980s, but only developed sporadically from the late 1980s until 2006.  In 2006, the disease reemerged in Western Nebraska, Northeastern Colorado, and Southeastern Wyoming.  From here, the disease quickly progressed eastward and in 2008 it was first reported in Indiana (Ruhl et al., 2008).  The disease has also been documented as far south as Texas, and as far north as North Dakota (Korus et al., 2011).  In 2011 the disease was seen widespread by the UNL Plant and Pest Diagnostic Clinic as part of a regional survey funded by the NCRIPM program.  Samples with Goss’s wilt were received from several states from throughout the Corn Belt, including WY, CO, NE, KS, SD, ND, MN, WI, and IN.   Symptoms   As the name implies, there are two phases to the disease.  First, there is the wilt phase.  This phase usually occurs in conjunction with early season wounding (e.g. sandblasting, hail, high winds, or heavy rainfall).  The wilt phase is usually most severe when plants are hit in the early growth stages when nodes are stacked beneath the soil line V3-V5 (Suparyono and Pataky 1989).  Stand reductions around V4 have been reported to be as high as 30% when the systemic wilt phase was severe.  The wilt is caused by a buildup of bacteria in the vascular bundles, which causes the plant to be unable to transfer water, thus causing the plant to wilt and die.  The wilt phase can also occur when plants are larger, but disease occurrence is usually not as severe (Suparyono and Pataky 1989).     The second and more common phase is a leaf blight.  Goss’s wilt leaf blighting is also most commonly seen in association with the wounding events as previously described.  Leaf blighting often is accompanied by water soaked lesions with discontinuous water soaked spots, often called freckles, along the lesion margin.  The lesions run parallel to the veins, but are not confined between veins.  The leaf blight phase was common during the 2011 growing season with 99% of Goss’s wilt samples received in the survey being leaf blight samples     Management  There are four management techniques currently recommended.    The first and best management technique is use of disease resistant hybrids.            The second recommendation is to control alternative hosts (e.g. green foxtail, shattercane, sorghum, barnyard grass, and volunteer corn) (Schuster et al., 1975).    The third recommendation is to use tillage to bury residue and reduce inoculum concentrations.                                           The final recommendation is to rotate to a non-host crop like soybean or alfalfa.  Our lab has also conducted efficacy trials using several products, but results have been inconsistent to this point.  A summary of some of those results can be found in the article Effects of Crop Injury on Disease Development in the 2012 Crop Production Clinic Proceedings.  2011 Survey   During the 2011 survey, 506 samples were received with 359 samples testing positive for Goss’s wilt.   Several states submitted samples that tested positive, as stated above.  Most samples submitted came from areas where the disease had not been observed before.  When samples were received, they were tested for Goss’s wilt using an ImmunoStrip Test kit sold by Agdia.  A 1’’x ½’’ segment of expanding lesion was cut from each sample and ground up to extract the pathogen.  Usually after about 5 minutes a result would be expressed in the form of two pink lines for a positive sample, and one pink line for a negative sample.  Samples that did not show good lesion development, but tested positive were checked for bacterial streaming as a precaution against false positives.  The purpose of the survey was to help identify which cultural practices were affecting the development of Goss’s wilt across the Corn Belt, and an advanced statistical analysis will begin in the coming months.  The results of which will help to prioritize which cultural practices have the biggest impact on disease development, and can thus be targeted for more effective management  recommendations and future research.  Literature Cited  1. Korus, K. A., Timmerman, A. D., French-Monar, R. D., and Jackson, T. A. 2011. First report of Goss’s 2012 Proceedings- Crop Production Clinics    128 bacterial wilt and leaf blight (Clavibacter michiganense subsp. nebraskensis) of corn in Texas. Plant Disease 95:73.  2. Ruhl, G., Wise, K., Creswell, A., Leonberger, A. and Speers, C.  2009.  First report of Goss’s wilt and leaf blight on corn caused by Clavibacter michiganense subsp. nebraskensis in Indiana.  Plant Disease 93:841.  3. Schuster, M.L. 1975. Leaf freckles and wilt of corn incited by Corynebacterium nebraskense Schuster, Hoff, Mandel, Lazar 1972. Agricultural Experiment Station. IANR University Nebraska Lincoln Research Bulletin 270. 40pp.   4. Suparyono and Pataky, J. K. 1989. Influence of host resistance and growth stage at the time of inoculation on Stewart’s wilt and Goss’s wilt development and sweet corn yield.  Plant Disease 73:339-345.  Gray Leaf Spot  Gray leaf spot was atypical during 2011 in Nebraska.  In general, development of the disease was delayed in southern counties during the midseason when night temperatures remained warm and inhibited dew development.  In these areas, disease developed more rapidly later during grain fill.  In contrast, counties in the northern areas of the state experienced cooler night temperatures that hastened dew development and led to earlier and more severe gray leaf spot development.   Each year foliar fungicide trials are conducted on corn at the UNL South Central Agricultural Laboratory (SCAL) where gray leaf spot is the predominant foliar disease.  Yield results were not yet available from these trials at press time for these proceedings.  Trial results can be viewed at the Plant Disease Central website at http://pdc.unl.edu/ under “Management Trials.”  In addition, a new publication summarizing results of foliar fungicide trials conducted across the north central states is available in hard copy or on the website.    Seedling Diseases and Stalk/Crown Rot Diseases  Stressful conditions for much of 2011 in parts of Nebraska created a high risk environment for the development of both seedling diseases and stalk rot diseases.     Excessive rain and flooded conditions early in the season led to nitrogen leaching and deficiencies in corn in many areas of the state and created a favorable environment for seedling disease.  Although all commercial field corn seed is treated with one or more seed treatment fungicides to protect against seedling disease, during extended periods of wet and/or cool conditions seedling germination and growth  can be inhibited and overcome by one or more common seedling pathogens.  During the spring and early summer of 2011, Pythium root rot was the most common cause of seedling damping off and seed decay, with some additional Fusarium root rot.  However, some infected plants out grew the early season infections only to be overtaken by them late in the season.   Many cases of stalk and crown rot diseases were reported late season in 2011.  In addition to the common stalk and crown rot diseases that are typical for Nebraska, Pythium stalk rot was also a problem and likely due to latent infections that initially occurred early in the season.  The fungus-like organism Pythium requires wet conditions for its swimming zoospores to locate roots and infect them.  Pythium stalk rot may have a similar water-soaked appearance to that of bacterial stalk rot, but lacks the putrid odor that can accompany bacterial stalk rot.  In some cases, the stalks infected by Pythium were also very wet inside, in contrast to the rotted stalk caused by other more common pathogens, such as Fusarium and Anthracnose.   Often the first indication of rotted stalks may be the rapid and premature desiccation of some plants in the field that appear to be senescing more rapidly.  These plants often have stalks that are hollow and easily crushed by hand or bent using the “push or pinch” test.  Stalk rots can occur at any point in the stalk from the crown at/below the soil line all the way to the tassel.  Rotting that occurs at an upper node and kills  only the upper plant parts is referred to as “top rot” and does not necessarily cause lodging of the whole plant.  Premature desiccation of plants can also be caused by below-ground infections, such as crown and root rot diseases that were also common in 2011. Evidence of those infections can be seen by splitting stalks all the way through the root ball where discoloration and decay can be more evident.  Crown and root infections can prematurely kill plants by shutting down water movement up the plant and lead to accelerated desiccation.   There is nothing to be done by the time these symptoms are observed during the season to stop stalk and crown rots.  But, they can impact harvestability if plants lodge prior to harvest.  Consider harvesting those fields that are heavily impacted by stalk rots early or first to avoid losses after lodging.  The costs required to dry grain harvested early from a field with severe stalk rot may be less than that of the additional costs that will be required to harvest a field of downed corn.   There are several fungi and bacteria that are common in our production fields that can cause stalk rot diseases.  Some of the most common in samples submitted to the UNL Plant & Pest Diagnostic Clinic in 2011 are listed below:   Pythium stalk rot is a less common stalk rot disease that occurred in 2011 due in part because of the excessive rainfall.  Infected plants may collapse and appear water-soaked inside, but lack the foul odor that accompanies bacterial stalk rot.   2012 Proceedings- Crop Production Clinics    129   Anthracnose stalk rot can also cause a leaf disease and is a common cause of top rots in corn.  In more advanced stages the disease can cause the development of black lesions visible on the outside of the stalk.   Fusarium stalk rot is especially common during damp conditions and may lead to white fungal growth visible at the nodes.  Eventually, the disease may cause discoloration of the inside of stalks to pink or salmon.   Bacterial stalk rot tends to occur mid-season.  The most diagnostic feature of this disease is the very foul odor it causes.  Plants that develop the disease late in the season are sturdy enough that they do not typically collapse like those infected earlier in the season.  More Resources  Additional information on these and other diseases can be found at the website Plant Disease Central at http://pdc.unl.edu/ or in the following UNL Extension publications:  Gray Leaf Spot of Corn http://www.ianrpubs.unl.edu/sendIt/g1902.pdf  Goss’s Bacterial Wilt and Leaf Blight of Corn http://www.ianrpubs.unl.edu/sendIt/g1675.pdf  Common Stalk Rot Diseases of Corn in Nebraska http://www.ianrpubs.unl.edu/sendIt/ec1898.pdf  Rust Diseases of Corn in Nebraska http://www.ianrpubs.unl.edu/sendIt/g1680.pdf     2012 Proceedings- Crop Production Clinics    130

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University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Papers in Plant Pathology Plant Pathology Department
2013
Corn Disease Update
Tamra A. Jackson-Ziems
University of Nebraska-Lincoln, tjackson3@unl.edu
Craig B. Langemeier
University of Nebraska-Lincoln, c_langemeier@hotmail.com
Greg R. Kruger
University of Nebraska-Lincoln, greg.kruger@unl.edu
Follow this and additional works at: http://digitalcommons.unl.edu/plantpathpapers
Part of the Other Plant Sciences Commons, Plant Biology Commons, and the Plant Pathology
Commons
This Article is brought to you for free and open access by the Plant Pathology Department at DigitalCommons@University of Nebraska - Lincoln. It
has been accepted for inclusion in Papers in Plant Pathology by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln.
Jackson-Ziems, Tamra A.; Langemeier, Craig B.; and Kruger, Greg R., "Corn Disease Update" (2013). Papers in Plant Pathology. 534.
http://digitalcommons.unl.edu/plantpathpapers/534
Corn Disease Update 
 
Tamra A. Jackson-Ziems, Extension Plant Pathologist 
Craig B. Langemeier, Graduate Research Assistant 
Greg R. Kruger, Extension Cropping Systems Specialist 
 
 
Goss’s Bacterial Wilt and Blight 
 
 Goss’s Bacterial Wilt and Leaf Blight, or 
more commonly referred to as Goss’s wilt, was 
prevalent early in the 2012 growing season, but 
disease progression slowed, presumably due to 
the extreme heat and drought through most of the 
state.  Goss’s wilt was prevalent in the 1970s and 
1980s, but only developed sporadically from the 
late 1980s until 2006.  Around 2006, the disease 
reemerged in western Nebraska, northeast 
Colorado, and southeast Wyoming.  From there, 
the disease appeared to quickly progress 
eastward and in 2008 it was first reported in 
Indiana (Ruhl et al., 2008).  The disease has also 
been documented as far south as the northern 
panhandle of Texas, and as far north as North 
Dakota (Korus et al., 2011) in the U.S. and two 
provinces of Canada, Ontario and Manitoba.   
  
Symptoms 
 
 As the name implies, there are two phases of 
the disease.  The wilt phase usually occurs 
following early season wounding (e.g. 
sandblasting, hail, high winds, or heavy rainfall).  
The wilt phase is usually most severe when 
plants are injured when nodes are stacked 
beneath the soil line during the early vegetative 
stages V3-V5 (Suparyono and Pataky 1989).  
Stand reductions around V4 have been reported 
to be as high as 30% when the systemic wilt 
phase was severe.  The wilt phase is caused by a 
buildup of bacteria in the vascular bundles, 
which reduces the plant’s ability to transfer 
water, thus causing the plant to wilt and die.  The 
wilt phase can also occur when plants are larger, 
but disease occurrence is usually not as severe 
(Suparyono and Pataky 1989).  The wilt phase 
was confirmed in June 2012 in York County, 
which was especially early further east than 
normal during recent years in Nebraska.   
 The second and more common phase of the 
disease is leaf blight.  Leaf blighting caused by 
this disease is also most commonly seen in 
association with the wounding events as 
previously described.  Leaf blighting often is 
accompanied by water soaked lesions with 
discontinuous water soaked spots, often called 
freckles, along the lesion margin.  The lesions 
run parallel to the veins, but are not confined 
between veins.  Shiny bacterial exudate or 
“ooze” may also be observed on mature lesions 
giving it a glossy or wet appearance.   
  
2011 Survey results 
 
 In 2011, a survey was initiated to begin to 
understand which agronomic factors and 
environmental conditions had the most impact on 
disease development.  More than 500 surveys 
were returned from eight states and were 
accompanied by 486 leaf samples.  The two 
statistical analyses used identified several factors 
that could have a significant impact on the 
development and severity of Goss’s wilt in the 
Corn Belt.   
  The top five factors associated with the 
development of Goss’s wilt are: 
1. planting population density 
2. Goss’s wilt rating for the hybrid 
(assigned by the seed company) 
3. crop rotation sequence 
4. planting date 
5. percentage of residue cover 
 This study confirmed that the best way to 
avoid Goss’s wilt in a field is to plant a resistant 
hybrid.  It also showed that crop rotation and 
percent residue cover affected the ability of the 
pathogen to infect in subsequent years.  Since the 
pathogen is residue-borne, planting continuous 
corn, or leaving large amount of infected corn 
residue on the soil surface increased the 
likelihood that the sample tested positive for 
Goss’s wilt.  The other two factors associated 
with Goss’s wilt development were planting 
population and planting date.  Future research 
efforts will need to be made on these two topics 
before any recommendations can be made to 
better understand their impact on disease 
development and to better manage for Goss’s 
wilt.  
 
  
130  2013 Proceedings : Crop Production Clinics
New alternate hosts identified 
 
 In greenhouse trials, 3 previously 
unconfirmed hosts of Goss’s wilt were 
confirmed during the spring of 2012.  Green 
foxtail was the only foxtail species previously 
identified as a host to the Goss’s wilt bacteria 
(Schuster, 1975).  Research conducted in the 
greenhouse showed that yellow foxtail, bristly 
foxtail, and giant foxtail are also hosts, in 
addition to green foxtail, and could be providing 
a reservoir of bacterial inoculum.  Symptoms on 
these foxtail species were similar to those 
observed for the leaf blight phase of the disease 
on susceptible corn hybrids.   
 Other known hosts include eastern gama 
grass, barnyard grass, sudangrass, grain 
sorghum, teosinte, and volunteer corn. 
 
 
Goss’s Wilt Management Strategies 
 
• Plant resistant hybrids 
• Rotate with nonhost crops, such as 
wheat or soybean 
 
• When practical, reduce the amount of 
residue, if planting into infected corn 
residue 
 
• Control alternate hosts, such as 
volunteer corn, foxtail species, and 
other known alternate hosts 
 
More Resources 
 
Additional information on these and other 
diseases and their management can be found at 
the website Plant Disease Central at 
http://pdc.unl.edu/ or in the following UNL 
Extension publications: 
 
Goss’s Bacterial Wilt and Leaf Blight of Corn 
http://www.ianrpubs.unl.edu/sendIt/g1675.pdf 
 
Literature Cited 
 
1. Korus, K. A., Timmerman, A. D., French-
Monar, R. D., and Jackson, T. A. 2011. First 
report of Goss’s bacterial wilt and leaf blight 
(Clavibacter michiganense subsp. 
nebraskensis) of corn in Texas. Plant 
Disease 95:73. 
 
2. Ruhl, G., Wise, K., Creswell, A., 
Leonberger, A. and Speers, C.  2009.  First 
report of Goss’s wilt and leaf blight on corn 
caused by Clavibacter michiganense subsp. 
nebraskensis in Indiana.  Plant Disease 
93:841. 
 
3. Schuster, M.L. 1975. Leaf freckles and wilt 
of corn incited by Corynebacterium 
nebraskense Schuster, Hoff, Mandel, Lazar 
1972. Agricultural Experiment Station. 
IANR University Nebraska Lincoln 
Research Bulletin 270. 40pp.  
 
4. Suparyono and Pataky, J. K. 1989. Influence 
of host resistance and growth stage at the 
time of inoculation on Stewart’s wilt and 
Goss’s wilt development and sweet corn 
yield.  Plant Disease 73:339-345. 
 
 
Aspergillus Ear Rot and  
Aflatoxin Contaminated Grain 
 
 The drought conditions of 2012 had severe 
impacts on Nebraska corn.  In addition to 
reductions in test weight and overall yield, 
secondary problems developed in some corn 
fields as a result of these conditions.  Drought 
and high temperatures promote development of 
the disease Aspergillus ear rot.  The fungi that 
cause this disease (most commonly caused by 
Aspergillus flavus) can produce aflatoxin.  
Aflatoxin is one of many in a group of 
chemicals, 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.   
Mycotoxins are common and can be safely 
consumed at low concentrations.  The 
concentration of aflatoxin that is considered safe 
for consumption depends upon the age and 
species of the animal consumer.  An abbreviated 
summary listing the Action Levels identified by 
the FDA for aflatoxin is listed in Table 1.      
 
  
2013 Proceedings : Crop Production Clinics  131
Table 1.  FDA Action Levels for Aflatoxin in 
Feed and Food 
 
Consumer Action Level in 
parts per 
billion (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 
Humans 20 
 
Action Levels were established by the U. S. 
Food and Drug Association (FDA) for Aflatoxin 
are available at: 
http://www.fda.gov/Food/GuidanceComplianceR
egulatoryInformation/GuidanceDocuments/Che
micalContaminantsandPesticides/ucm077969.ht
m#afla 
 
Testing for Aflatoxin 
 
Corn harvested from fields where there was 
Aspergillus ear rot should be tested for aflatoxin 
prior to use, sale, or storage.  Corn is at higher 
risk for Aspergillus ear rot if it was grown under 
drought-stressed conditions or if injury occurred 
to the kernels.  The concentration of aflatoxin in 
a sample can be determined by laboratory 
testing. The U.S. Grain Inspection, Packers and 
Stockyards Administration (GIPSA) certifies 
some laboratories for aflatoxin testing.  A list of 
laboratories certified for aflatoxin testing in the 
Nebraska region is below. 
Accurate lab test results for aflatoxin depend 
greatly on the quality of the sample that is 
collected and methods used by laboratories 
conducting tests.  The test results are only 
applicable to the sample that is submitted, so it is 
very important to collect an adequate and 
representative sample for the best results.  Refer 
to the publication, Sampling and Analyzing 
Feed for Fungal (Mold) Toxins (Mycotoxins) 
(link below) for recommendations on how to 
collect and submit a high quality sample for the 
most accurate mycotoxin analysis.  In addition, 
you should contact and submit samples to a 
laboratory that is certified by the Federal Grain 
Inspection Service (FGIS) and Grain Inspection, 
Packers & Stockyards Administration (GIPSA) 
for mycotoxin analysis.  A list of GIPSA-
certified laboratories in and near Nebraska is 
below: 
 
• Fremont Grain Inspection.  603 East 
Dodge St., Fremont, 402-721-1270; email 
fgid@neb.rr.com 
•  Hastings Grain Inspection, 306 E. Park 
St., Hastings, 402-462-4254; email 
Hastings at hgihast@hastingsgrain.com; 
email Grand Island office at 
hginsp@hastingsgrain.com 
•  Kansas Grain Inspection Service, 517 
13th Ave., Sidney, Nebr., 308-254-3975 
•  Lincoln Inspection Service, 505 Garfield 
St., Lincoln, 402-435-4386; email 
lismf@neb.rr.com 
•  Omaha Grain Inspection Service, 2525 
South 13th St., 402-341-6739; 
omahagrain@gmail.com 
•  Sioux CIty Inspection and Weighing 
Service, 840 Clark St., Sioux City, Iowa, 
712-255-8073; email tomd@scigrain.com 
 
The complete list of laboratories certified by 
GIPSA for aflatoxin testing can be found at: 
http://www.gipsa.usda.gov/fgis/svc_provid/provi
ders.html 
Black (ultraviolet) lights have been used by 
some grain elevators and individuals in an effort 
to detect 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 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 
132  2013 Proceedings : Crop Production Clinics
 
Scouting for Aspergillus Ear Rot 
 
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.  And, 
the presence of visible 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.   
• 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 
• Pay special attention to corn in 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.   
Based on aflatoxin test results from the 
Lincoln Inspection Service, only about half of 
the samples submitted had detectable 
concentrations of aflatoxin.  And, only a low 
percentage of samples had aflatoxin 
concentrations of more than 20 ppb.   
For more information, refer to the list of 
publications below or to the article in these 
Proceedings entitled, “Grain Storage 
Management to Minimize Mold and 
Mycotoxins.” 
 
More Resources 
 
Plant  Disease Profiles #3:  Ear Rot Diseases 
and Grain Molds 
http://www.ianrpubs.unl.edu/sendIt/ec1901.pdf 
 
Sampling and Analyzing Feed for Fungal 
(Mold) Toxins (Mycotoxins)  
http://www.ianrpubs.unl.edu/sendIt/g1515.pdf 
 
Understanding Fungal (Mold) Toxins 
(Mycotoxins)  
http://www.ianrpubs.unl.edu/sendIt/g1513.pdf 
 
Use of Feed Contaminated with Fungal 
(Mold) Toxins (Mycotoxins)  
http://www.ianrpubs.unl.edu/sendIt/g1514.pdf 
 
 
 
Stalk Rot Diseases 
  
The crop stress created by the harsh growing 
conditions in 2012 led to the development of 
stalk rot diseases and lodging that slowed harvest 
progress in some areas.   
Weakened stalks became evident in some of 
the corn still waiting to be harvested across the 
state late this past fall.  The high winds in 
October 2012 led to lodging in corn where some 
stalks were weakened by stalk rot diseases and 
other problems.  Crop stress during the 2012 
growing season contributed to the development 
of some stalk rot diseases.   
  
Scouting for Stalk Rot Diseases 
 
Affected plants often have stalks that are hollow 
and easily crushed by hand or bent using the 
“push or pinch” test.  Stalk rots can occur at any 
point in the stalk from the crown at/below the 
soil line all the way to the tassel.  Rotting that 
occurs at an upper node and kills only the upper 
plant parts is referred to as “top rot” and does not 
necessarily cause lodging of the whole plant.  
However, degradation of the stalk below the ear 
can lead to plant lodging and losses during 
harvest. 
 
Scouting for Stalk Rot Diseases  
 
Walking through a field, randomly select a 
minimum of 100 plants representing a large 
portion of the field.  To test for stalk rot you may 
choose to PUSH the plant tops away from you 
approximately 30° from vertical.  If plants fail to 
snap back to vertical, then the stalk has been 
compromised by stalk rot.  An alternative 
method is to use the PINCH test to evaluate 
plants for stalk rots.  Pinch or squeeze the plants 
at one of the lowest internodes above the brace 
2013 Proceedings : Crop Production Clinics  133
roots.  If the stalks crush easily by hand, then 
their integrity is reduced by stalk rot and they are 
prone to lodging. If more than 10% of plants 
exhibit stalk rot symptoms, then harvesting that 
field should be a priority over other fields that 
are at less risk in order to reduce the chance of 
plant lodging and the potential for yield loss.   
There are several fungi that are common in 
our production fields that can cause stalk rot 
diseases.  Some of the most common stalk rot 
diseases this year are listed below: 
 
• Charcoal rot is one of the few diseases that 
are more common during drought 
conditions, and so, is more likely to affect 
non-irrigated crops.  The disease is 
characterized by the presence of many 
minute black round structures inside the 
stalk that can give it a gray to black 
appearance (hence the name).  In addition, 
the fungus that causes charcoal rot, 
Macrophomina phaseolina, has a wide host 
range and can cause the same disease in 
several crops, including soybean, sorghum, 
and alfalfa.  
 
• Fusarium stalk rot is especially common 
during damp conditions, but may occur 
anywhere, including in irrigated fields this 
year.  The pathogen, Fusarium 
verticillioides, can sometimes be visible as 
white fungal growth on the outside of stalks 
at the nodes.  Eventually, the disease may 
cause discoloration of the inside of stalks to 
pink or salmon. 
 
• Anthracnose stalk rot can also cause a leaf 
disease and is a common cause of top rots in 
corn.  In more advanced stages the disease 
can cause the development of black lesions 
visible on the outside of the stalk and is 
caused by the fungus Colletotrichum 
graminicola.   
 
Management 
 
Usually, there is nothing to be done to stop 
stalk rot development once it is identified in the 
field.  In most cases, stalks will continue to 
degrade over time further weakening them.  But, 
you can work to minimize your losses by 
identifying which fields have the worst stalk rot 
diseases and adjust the harvest order of those 
fields.  Consider harvesting those fields that are 
heavily impacted by stalk rots first to minimize 
losses after lodging.   
 
More Resources 
 
For more information on stalk rot diseases 
of corn, see the UNL Extension publications: 
 
Corn Disease Profiles II:  Stalk Rot Diseases 
http://www.ianrpubs.unl.edu/sendIt/ec1868.pdf 
 
Common Stalk Rot Diseases of Corn 
http://www.ianrpubs.unl.edu/sendIt/ec1898.pdf 
 
Crop Watch  
http://cropwatch.unl.edu/ 
 
 If you are in doubt about the identity of a 
disease or cause of another plant problem, you 
may submit a sample to the UNL Plant and Pest 
Diagnostic Clinic (P&PDC) for diagnosis.  For 
more information about these and other plant 
diseases or for submission forms for the P&PDC 
and submission instructions, visit the Plant 
Disease Central website at: 
http://pdc.unl.edu/ 
 
 
 
 
 
 
134  2013 Proceedings : Crop Production Clinics


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