Four ways to get ahead of ear rots and mycotoxins

Ear rots and moldy grain are annual concerns in the U.S. and Canada in both harvested grain and corn for silage. Ear rots are some of the most important diseases to look for because they not only decrease yield and grain quality, but several can also produce mycotoxins. Mycotoxins are nonliving toxic compounds produced by ear rot fungi during infection and colonization. Mycotoxins contaminate grain, making it difficult or impossible to sell or use as livestock feed This article summarizes the most important things about ear rots and mycotoxins and how to minimize their impact in harvested grain and silage.

1. What ear rots should I look for?

Ear rot prevalence and severity depend on harvest date, hybrid susceptibility, and local environmental conditions during reproductive growth stages and through grain fill and harvest. 

There are currently four major ear rots that impact corn, three of which produce mycotoxins (italics):

• Aspergillus ear rot (Fig. 1)— aflatoxin

• Diplodia ear rot — no mycotoxins currently reported in the U.S. or Canada

• Fusarium ear rot — fumonisins

• Gibberella ear rot (Fig. 2) — deoxynivalenol (DON/vomitoxin) and zearalenone

Several minor ear rots also occur that have less impact on grain and yield. However, they may cause issues in storage, or if grain is used in specialty feed markets, such as horse feed:

• Cladosporium ear rot — no mycotoxins currently known

• Nigrospora ear rot — no mycotoxins currently known

• Penicillium ear rot — ochratoxin

• Trichoderma ear rot (Fig. 3)— trichothecenes

Scouting is the best practice to manage grain affected by ear rots and mycotoxins. Before harvest, scout several locations across the field and pull husks back completely to examine the entire ear. If 10 percent or more of the corn samples are moldy, the field should be scheduled for an early harvest. In general, ear rot fungi will continue to grow and spread (and produce mycotoxins) until grain moisture is below 15 percent.

2. What causes ear rots?

Ear rots are fungal diseases and each ear rot is caused by a different fungus. All ear rot fungi infect ears during silking and grain fill, but environmental conditions that favor each ear rot vary. For example, hot, dry conditions at silking favor Aspergillus ear rot, but wet conditions during and after silking favor Diplodia and Gibberella ear rots. Anything that damages corn kernels, such as insect feeding, bird damage, or hail, can also increase ear rot risk. The Crop Protection Network (CPN) publication Ear Rots CPN-2001 describes the environments conducive to ear rot development based on the fungi involved, and the crop production practices that increase risk of ear rot development. 

3. What are mycotoxins?

Mycotoxins are nonliving chemical compounds produced by ear rot fungi. Mycotoxins are regulated by government agencies to ensure humans and animals are not harmed by the negative effects of mycotoxin-contaminated grain and silage. Specific action and advisory levels for mycotoxins in grain and silage for livestock consumption can be found in the CPN publication Ear Rots CPN-2001. Answers to many of the frequently asked questions about mycotoxins can be found in the CPN publication Mycotoxin FAQs CPN-2002.

4. How do I manage grain or silage affected by ear rots and mycotoxins?

If there are concerns about the quality of grain or silage prior to, or after harvest, send a sample to be tested by a mycotoxin-testing facility. Obtaining a representative grain or silage sample for testing is crucial because mycotoxin levels can vary significantly between contaminated kernels. These contaminated kernels are often unevenly distributed within a grain cart, trailer, or silage mass, which can affect the accuracy and reliability of testing results. Information about how to obtain a representative sample of grain or silage, as well as certified testing laboratories which test for mycotoxins can be found in the CPN publication Grain and Silage Sampling and Mycotoxin Testing CPN-2003.

In severe cases, the overall mycotoxin concentration in harvested grain can be reduced by cleaning the grain to remove broken grain (fines), foreign materials, and lightweight moldy kernels. Store harvested moldy or mycotoxin-contaminated grain separately from clean grain, and dry to 15 percent moisture or lower to reduce moisture content. Since mycotoxins are highly stable, methods such as heating, freezing, roasting, or chemical treatments cannot reliably reduce mycotoxin levels within kernels. Coring bins of affected grain can help remove additional fines and foreign materials. During grain or silage storage, regular monitoring of grain and silage moisture levels to ensure they remain below 15 percent can help prevent fungal regrowth and grain-to-grain spread in the bin or silage mass. 

Acknowledgements

Authors

Albert Tenuta, Ontario Ministry of Agriculture, Food and AgriBusiness; Kiersten Wise, University of Kentucky; Alison Robertson, Iowa State University; Daren Mueller, Iowa State University; and Adam Sisson, Iowa State University.