Albert Tenuta, Ontario Ministry of Agriculture, Food and Rural Affairs; Kiersten Wise, University of Kentucky; Alison Robertson, Iowa State University; Daren Mueller, Iowa State University; Ethan Stoetzer, Iowa State University
Ear rots and moldy grain have been observed in harvested grain, corn for silage, and corn that has yet to be harvested across the U.S. and Canada. Ear rots are some of the most important diseases to look for because they decrease yield and grain quality and several produce mycotoxins. Mycotoxins are nonliving toxin compounds produced by these fungi during infection and colonization. These chemical compounds contaminate grain, making it difficult or impossible to sell or use as livestock feed in the current marketing system. This article will review the most important things to understand about ear rots and mycotoxins and how to minimize their impact in harvested grain.
1. What ear rots should I look for?
There are several ear rots observed across the U.S. and Canada, and prevalence and severity will depend on harvest date, hybrid susceptibility, and local environmental conditions.
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 — none currently reported in the U.S. or Canada
- Fusarium ear rot — fumonisins
- Gibberella ear rot (Fig. 2) — deoxynivalenol (DON/vomitoxin) and zearalenone
Several minor rots also occur that have less impact on grain and yield. However, they may cause issues in storage, or if used in specialty feed markets, such as grain for horse feed:
- Cladosporium ear rot — none currently known
- Nigrospora ear rot — none 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 greater than 10 percent 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.
Figure 1. Aspergillus ear rot is an olive-green, powdery mold frequently found at the tip of the ear.
Figure 2. Gibberella ear rot is a pinkish mold that generally begins at the ear tip.
Figure 3. Trichoderma ear rot is a dark green mold on or between kernels and can cause kernels to sprout on the ear.
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 risk of ear rot development. 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 the ear-rot fungi. Mycotoxins in grain are regulated to ensure that humans and animals are not harmed by the negative effects of mycotoxin-contaminated grain and silage. Specific action 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 to be tested is important because the levels of mycotoxins vary greatly among contaminated kernels and these kernels are often irregularly dispersed in a grain cart, trailer, or silage mass. Information about how to get a representative sample of grain or silage, as well as certified testing laboratories that can test for mycotoxins can be found in the CPN publication Grain and Silage Sampling and Mycotoxin Testing CPN-2003.
In severe cases, you can reduce the overall mycotoxin concentration in harvested grain 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. Mycotoxins are extremely stable and heating, freezing, roasting, or treating with chemicals cannot reliably reduce mycotoxin levels within kernels.Coring bins of affected grain will also reduce fines and foreign materials. During grain or silage storage, monitor grain and silage moisture to ensure it stays below 15 percent to restrict fungal re-growth and grain-to-grain spread in the bin or silage mass.