Hail Damaged Corn – Risk of Molds and Mycotoxins? 

Paul Esker, Joe Lauer, and Dan Undersander Extension Plant Pathology, Extension Corn Agronomist, and Extension Forage Agronomist UW-Madison and UW-Extension

In late July, there was a significant hail event in Wisconsin, primarily located in the southwestern portion of the state (Fig. 1). At that time, the corn crop was at approximately the R1 (silking) growth stage, but ranging from pre-VT (pre-tasseling) to R1. The hail event led to extensive bruising on the ear, husks, and stalks, however, the severity of the hail event varied from field to field. While some fields had finished pollinating, with bruising on ears, others had not yet started the pollination process and ears were unaffected.

Since that time we have received numerous questions regarding the risk of mold and/or mycotoxin development in fields damaged by hail. The simplest answer is that we cannot predict that either mold growth or mycotoxin development will occur in these fields since there are numerous factors that must be considered. Also, the occurrence of field molds does not necessarily mean that there will be mycotoxin development. However, monitoring of fields and sampling and testing for specific mycotoxins can improve understanding of the risk of contamination.

Corn for Grain or Silage? Concern for possible mycotoxin development increases the longer corn remains in the field. The highest risk for mycotoxin contamination would be in corn for grain, followed by high moisture corn, and lastly corn for silage. Additionally, increased risk for stalk rots is likely for heavily bruised plants.

What to Look For?Walking hail affected fields at the Lancaster ARS on 31 August, there was some early evidence of ear rots, including Fusarium or Gibberella ear rot. Fusarium ear rot typically begins where kernels have been damaged and will be white to pink or salmon-colored in appearance (Robertson and Munkvold 2009). Gibberella ear rot is different in that it is typically not associated with damaged kernels and will be a pink mold that starts at the tip of an ear. It should be noted that the field where these observations were made has had a history of Gibberella. Aspergillus ear rot is also associated with damaged kernels and will have powdery olive green appearance. As a reminder, evidence of the mold on the ear does not mean that there is mycotoxin present.

Mycotoxins: Currently, there are 400-500 known mycotoxins, which are produced by fungi. Production of mycotoxins can occur in both the field and in storage, although it is thought that most contamination occurs in the field (Payne 1999). When mycotoxin contamination can occur is also dependent on the type of mycotoxin. While most aflatoxin contamination would occur in the field, mycotoxins produced by Penicillium would occur in silage, especially if fermentation is poor.

Mycotoxin development is highly dependent on the environment, factors that may cause wounding on the plant, or can occur when resource demand is high or resources are limiting. Three key environmental components for mycoxtoxin contamination are temperatures above freezing, moisture above 20%, and oxygen are required (Gotlieb 2004). In storage, the risk of mycotoxin contamination can be reduced with proper drying or ensiling conditions, however, there is a risk of contamination occurring at the end of silage use, where the original infection occurred in the field (Richard et al. 2007).

• Fusarium mycotoxins: These mycotoxins include deoxynivalenol (DON; produced by several species of Fusarium, including F. graminearum), zearalenone (F. graminearum), and fumonisin B1 and T-2 (multiple species of Fusarium). Of these mycotoxins, DON is the most common. In silage, DON does not appear to have a significant effect, however, in grain, production of DON is favored by grain moisture of 21% or more and temperatures from 21-29ºC. It is thought that rumen microorganisms are also able to degrade DON to less toxic form. 
• Aflatoxin: This toxin is produced by two species, Aspergillus flavus and A. parasiticus. Aflatoxin is globally very important, since it is listed as a carcinogen for humans. However, development of aflatoxin is typically favored by hot and dry conditions.
• Penicillium mycotoxins: In silage, P. roqueforti is a common fungus. This organism is a saprophyte that grows well in low oxygen and acidic environments. There are multiple toxins produced by P. roqueforti, including, PR toxin, roquefortin C, patulin, and mycophenolic acid. While the effect of these toxins on dairy cattle is not well known, proper harvest timing and ensiling can reduce the risk of toxin development.

Recommendations: Continue to monitor hail-affected fields closely. Harvesting on the early side of the optimum moisture range may help reduce the risk for mold and/or mycotoxin development. Corn grown for grain would normally be harvested between 25% to 20 % moisture. For corn grown for silage, we recommend using silage drydown days to help estimate harvest timing. The proper harvest moisture for the storage structure varies (i.e. bunker = 70% to 65% while concrete stave = 65% to 60%), but ensiling on the wetter side of these ranges can reduce the risk of mycotoxin development. This is in part because the anaerobic conditions and low pH should arrest development of the fungi that require an aerobic environment.

Sampling for mycotoxins in corn silage should occur just prior to ensiling, while sampling corn for grain can be done prior to harvest by collecting ears at random throughout the field. It is recommended to sample at least 25 ears (Robertson and Munkvold 2009) since that will provide a better estimate of the entire field.

Laboratories that test for mycotoxins are listed in A3646, Pest Management in Wisconsin Field Crops and this is available at: http://learningstore.uwex.edu/Pest-Management-in-Wisconsin-Field-Crops2009-P155C37.aspx

Useful Resources

Gotlieb, A. 2004. Mycotoxins in silage: A silent loss in profits. (http://www.uvm.edu/pss/vtcrops/?Page=articles/Mycotoxins.html, Accessed 1 September 2009).

Kuldau, G. A. Managing mycotoxins in Northeast silages. (http://128.118.11.160/dairynutrition/documents/kuldau.pdf, Accessed 30 August 2009).

Payne, G.A. 1999. Mycotoxins and mycotoxicoses. Pages 47-49 in: D.G. White (Ed.) Compendium of Corn Diseases, Third Edition. APS Press, St. Paul, MN.

Rankin, M., and Grau, C. 2002. Agronomic considerations for molds and mycotoxins in corn silage. Focus on Forage 4(1): 1-4. (http://www.uwex.edu/ces/crops/uwforage/Mycotoxins.htm, Accessed 30 August 2009).

Richard, E., Heutte, N., Sage, L., Pottier, D., Bouchart, V., Lebailly, P., and Garon, D. 2007. Toxigenic fungi and mycotoxins in mature corn silage. Food and Chemical Toxicology 45: 24020-2425.

Robertson, A., and Munkvold, G. 2009. Risk of mycotoxins associated with hail damaged corn. Integrated Crop Management News, Iowa State University – University Extension (http://www.extension.iastate.edu/CropNews/2009/0818robertsonmunkovld.htm, Accessed 30 August 2009).