The Food and Agriculture Organization of the United Nations (FAO) has estimated that more than 25% of the global food crop is contaminated with mycotoxins, but the origin of this value is unclear, and research suggests that up to 60-80% of crops have detectable levels of mycotoxins (Eskola et al., 2019).  While measuring the economic impact is difficult and varies year-to-year, the FAO has estimated that mycotoxins can have up to a $5 billion impact in the US and Canada alone.  Economic losses accrue from costs associated with management (prevention, sampling & analysis, mitigation), losses in crop yields, decreased crop value, as well as effects in animals and humans. Costs to livestock producers can show up in a variety of ways ranging from reduced nutritional value of feeds, increased production costs, impaired immunity, decreased growth rates, as well as increased veterinary care and treatment costs.

As we look ahead to corn harvest this fall, we will explore some of the factors that can impact disease development and mycotoxin production during the lifecycle of the plant.  Mycotoxin formation can occur in the field during crop growth, after harvest, during storage, and all the way through feed out. Many factors influence the production of mycotoxins, but we will highlight three common indicators of stress (environmental conditions, crop health, and insect damage) that can contribute to the presence of mycotoxins at harvest.

Environmental Conditions play a major role in the development of disease and mycotoxin production. Weather variation across the country is a key contributor to regional patterns of mycotoxin contamination. Temperature and moisture content are crucial to mold growth and why different climates tend to support different types of molds. Stress situations ranging from drought to excess rainfall increase plant susceptibility to mold colonization and mycotoxin production. Corn is especially at risk of infection during silking. This year much of the Corn Belt has experienced hot, dry conditions during pollination. Such conditions favor Fusarium ear rot (associated with fumonisins) and Aspergillus ear rot (associated with aflatoxins). Deoxynivalenol (DON aka “vomitoxin”) and zearalenone (ZEN) are associated with Gibberella ear rot which is favored by high moisture around silking (Munkvold, 2003). Although much talk has revolved around hot and dry weather recently, some areas have experienced wet conditions and should keep potential for DON and ZEN in mind this harvest. Droughtmonitor.unl.edu/ is a useful tool for tracking current conditions in your area.

Additionally, wind can create greensnap and lodging events, while hail can create lesions that damage the plant, making it a more favorable host for mycotoxin-producing molds.  Monitoring weather events for sources of stress can help identify areas at risk for mycotoxin development.  Interactivehailmaps.com is a great resource for monitoring hail events and there are many publicly available wind maps that can help illustrate potential areas of damage to aid in identifying areas with possible mycotoxin contamination.

Crop Health is another good indicator of general plant stress or lack thereof throughout the growing cycle.  This planting season got off to a late start with wet conditions across much of the country through the spring.  The May 31^st USDA crop progress report indicated that on average 86% of the corn was planted, which was only 1% point behind the 5-year average.  While growers seem to have caught up to the historical average, the delay in planting can be see with 61% of the corn emerged compared to a 5-year average of 68%.  Some states like Minnesota show an even more exaggerated discrepancy with 42% of the crop emerged compared to 72% over the past 5 years. Late planting can also push harvest windows later, resulting in crops standing in the field when weather conditions are favorable for mycotoxin accumulation. While numerous environmental factors contribute to plant health over the course of a growing season, USDA’s plant condition ratings can be a good source of insights for potential mycotoxin pressures in the fall.

Foliar diseases also play a role in crop health. Some leaf diseases caused by fungi include Gray Leaf Spot, Northern Corn Leaf Blight, Common Rust, Southern Rust, Anthracnose, and Tar Spot. Although not associated with mycotoxin-producing molds, such foliar diseases stress the plant, can be detrimental to grain yields, and increase susceptibility to molds that do produce mycotoxins. Additionally, several of the troublesome ear rot causing fungi can also lead to stalk rot. Depending on the timing of disease, mycotoxins may be present in various parts of the corn plant beyond the ear which is relevant to those harvesting corn silage. Scouting fields for the various diseases will help identify disease pressure and guide timely and appropriate management tactics that can boost plant health.

Insect Damage, both to the ear and other parts of the plant, can create an environment where fungi can thrive, giving way to mycotoxin production. In addition to creating lesions prone to fungal assault, there is evidence that insects can carry fungal spores and further infection by spreading disease. Looking at insect pressure maps can provide some insight into potential areas that may see higher mycotoxin loads this fall.  Insectforecast.com monitors common corn insects for pressure and migration and can highlight areas to keep an eye on for potential insect damage. Corn Rootworm and Western Bean Cutworm are starting to appear across the country this year. Ear feeding by Western Bean Cutworm can damage corn kernels and increase susceptibility to fungal disease.  The good news is that pressure for this pest is relatively low but showing some hot spots in the Mid-Plains and Great Lakes regions. Corn Rootworm pressures are high across much of the Midwest, and while it is not as common, this pest can contribute to colonization of Fusarium fungi in the plant, elevating the chance of fumonisins to appear. Various other insects including stink bugs and beetles have been tied to increased mycotoxin concentrations through damage and spread of spores.

As the corn crop approaches maturity, these are some key factors to keep an eye on as indicators of an elevated risk for mycotoxins in your area.  Knowing where your grain is sourced from can provide potential insight into mycotoxin contamination patterns. Visual inspection alone is not a reliable indicator of mycotoxins, so screening your grain is another important step in understanding the level of contamination present in your feed inputs.  Rapid test kits are available that can be administered locally and quickly to help inform your operation of the mycotoxin pressures in your feed ingredients. Submitting samples for analysis to a mycotoxin service lab is another option to screen feeds. If you would like to learn more about the services and mitigation options dsm-firmenich offers, including the first and only FDA-approved product for degradation of fumonisins in swine and poultry feed, our sales and technical teams would be happy to discuss options to minimize the financial impact mycotoxins can have on your operation through testing and addressing risk in your operation.