Alison Robertson and Gary Munkvold, Department of Plant Pathology; Charles Hurburgh, Department of Agricultural and Biosystems Engineering
Very wet conditions in October 2009 and early snowfalls in November resulted in several thousand acres of corn left standing through the winter in Iowa. Considering the grain quality issues that ended the growing season, concerns were raised regarding the quality of corn left standing over the winter.
To address these concerns, samples of ears were collected from 72 fields throughout Iowa in March 2010. Ears were visually assessed for ear rot severity. After shelling, test weight, moisture, protein, oil, starch and density were determined before grain was ground and tested for deoxynivalenol (DON), zearalenone (ZEA) and fumonisins (FUM) using GIPSA-approved commercially available antibody-based lateral flow strip tests.
Ear rot severity (percentage of ear covered with mold), physical characteristics and mycotoxin contamination were compared with ear samples collected in October 2009 from 27 arbitrarily selected Iowa fields. These fields were part of the 2009 Iowa Hail Damage Grain Quality Survey and were considered representative of undamaged corn grain at the end of the 2009 growing season.
Mean ear rot severity among standing corn fields ranged from 0.2 to 83.8 percent (Table 1). Ear rot severity in standing corn (24.0 percent) was statistically greater than ear rot severity in October 2009 (3.3 percent). The predominant ear rot in standing corn was Cladosporium, followed by Fusarium and Gibberella at low levels, which is similar to ear rots present on corn in October 2009.
Not surprisingly, range in test weight of the standing corn was similar to that of corn in October 2009, and grain moisture was significantly lower in standing corn (18.4 percent) compared with grain moisture in October 2009 (24.4 percent) (Table 1).
Low levels of fumonisin (0.1 ppm), DON (0.9 ppm) and zearalenone (0.72 ppm) were detected in grain from standing corn and these levels of mycotoxins were not statistically different from those detected in grain sampled in October 2009 (Tables 1).
Grain that remained in the field actually fared better than grain stored in bins over the winter. Although severity of Cladosporium ear rot was high, most growers reported that "the mold blew off in the combine" and grain quality was good. These findings may create viable alternatives to ground piles for wet corn volumes beyond dryer capacity at elevators.
We thank ISU Extension field agronomists for collecting ear samples, and growers who allowed us to sample their fields. We also thank Agribusiness Association of Iowa, ISU College of Agriculture and Life Sciences, and Iowa State University Extension who provided funding to cover costs associated with this survey.
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 firstname.lastname@example.org. Gary Munkvold is an associate professor of plant pathology and seed science endowed chair in the Iowa State University Seed Science Center with research and teaching responsibilities in seed pathology. He can be reached at (515) 294-7560 or by email at email@example.com. 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 firstname.lastname@example.org.