What Mycotoxins Should We Expect Following an Interesting Growing Season? (Part 2)

North America has experienced a variety of weather events over the course of the 2023 growing season. Twenty-three separate billion-dollar weather and climate disasters have been recorded through the month of August in the United States, making 2023 the most active year on record for such events with four months remaining and events like Tropical Storm Hilary in Southern California and the Southern/Midwestern drought are still under review. Not all these events occurred during the growing season or in areas which are key to corn production, but this statistic highlights the tumultuous weather and climatic conditions the country has faced. Disease pressures in crops are strongly influenced by weather conditions. Monitoring weather and other stressors such as insect pressure during the growing season and throughout harvest can provide insights to new crop yields and quality, including mycotoxin contamination. 

As noted in the previous article, multiple factors influence the development of fungal diseases and potential for mycotoxin production. Table 1 provides an overview of the major factors which can affect mycotoxin contamination. Often, we see regional differences in mycotoxin contamination profiles because different climates support different types of molds and different molds can produce different types of mycotoxins. Additionally, anything that stresses the plant increases the risk for mold colonization and subsequent mycotoxin production. 

Figure 1. Overview of major factors that influence mycotoxin contamination.


Agronomic Practices

Stress Conditions

Other Factors


Crop rotation



Precipitation / moisture content


Excess rainfall / flooding


Relative humidity

Planting / harvest date or timing

Damage to plant

  • Insect

  • Hail

  • Wind

  • Wildlife

Oxygen availability

Water activity


Other diseases

Genetics (hybrid / variety)


Pest control

Weed pressure

Soil type



Crop density

Storage conditions

Corn is especially at risk to ear rot-associated fungal pathogens around silking. According to the United States Department of Agriculture (USDA) National Agricultural Statistics Service (NASS) Crop Progress and Condition Report, silking began late in June and extended through mid-August, with the majority of silking occurring in July (Figure 2).

Figure 2. Progress excerpt from USDA NASS Crop Progress and Condition: Corn in United States, 2023 Report, October 1, 2023. Most of the silking occurred during the month of July.

The National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (NCEI) website provides maps which track temperature and precipitation across the US.3 Although many parts of the Corn Belt experienced a period of dry, warmer than typical weather immediately following planting, many areas picked up timely precipitation into July and August, reaching near average or above average rainfall during those months and more moderate temperatures in some places during silking. A pocket of heat brought record temperatures across the Plains, Midwest, and South later in August and extended into September, leading to widespread warmer and drier weather again. During this time, drought conditions expanded or intensified in areas such as the Northern Tier, Upper Midwest, Southern Plains, and Southeast.1 As we head into October, forecasts show many areas of the Corn Belt will continue to be drier and warmer than typical through the middle of the month which should allow harvest to begin and continue in many areas without much delay. However, more seasonable temperatures and potentially wetter weather are expected as fall progresses.

Figure 3. NOAA National Centers for Environmental Information Divisional Average Temperature Ranks May-July 2023 (Period 1895-2023), August 4, 2023.3 Many of the top corn producing states have experienced at least above average temperatures during much of the 2023 growing season while parts of the eastern Corn Belt were near or below average.

Figure 4. NOAA National Centers for Environmental Information Divisional Precipitation Ranks May-July 2023 (Period 1895-2023), August 4, 2023.3 Many of the top corn producing states have experienced below average to much below average precipitation throughout much of the 2023 growing season.

In addition to temperature and precipitation anomalies, other stressful weather-related occurrences including strong winds and hail events, predispose plants to infection by mycotoxigenic molds as noted in Figure 1. Using data extracted from NOAA’s National Weather Service Storm Prediction Center Local Storm Reports4 database, the frequency of significant wind and hail events in the top 13 corn producing states (representing 90% of US corn production) are summarized for the period of May through September each year from 2019 to 2023 in Figures 5 and 6. The taller the bar is on the graphic, the greater the number of significant events. States experiencing an increased number of strong wind events during that timeframe for 2023 vs. 2022 include Illinois, Kansas, Kentucky, Missouri, Nebraska, and Ohio (Figure 5). States which had an increased number of significant hail events over that period of 2023 vs. 2022 include Iowa, Illinois, Indiana, Kansas, Kentucky, Missouri, Nebraska, Ohio, and South Dakota (Figure 6). For the most part, the central portion of the Corn Belt has had fewer extreme deviations in temperature and precipitation this year, but significant wind and/or hail events have occurred and can increase the risk for mycotoxins in crops even if the area has not experienced other weather anomalies.

Figure 5. Significant wind events which occurred May through September, 2019-2023. Six of the 13 states represented on the map have had a greater number of significant wind events this year vs. last year, with states like Kansas and Missouri experiencing the greatest increase in number of events.

Figure 6. Significant hail events which occurred May through September, 2019-2023. Nine of the 13 states represented on the map have had a greater number of significant hail events this year vs. last year, with states like Indiana, Kansas, Missouri, and Nebraska seeing the greatest jump in number of events.

An additional factor to consider is insect pressure as these pests can create stress for plants and enhance entry of mycotoxin-producing molds through damage or lesions. Additionally, insects can act as vectors which spread mold spores. The InsectForecast5 website is a great resource to use to monitor pest pressures in your area.

Foliar diseases also play a role in crop health, but diseases such as Tar Spot, Gray Leaf Spot, Southern Rust, and Northern Corn Leaf Blight, although of fungal origin, are not directly associated with the production of mycotoxins. Although not a primary risk for mycotoxins, such foliar diseases stress the plant and open the door for secondary disease by molds that can produce mycotoxins. Risk for such foliar diseases is variable across the Corn Belt this year, but Bayer Crop Science has Corn Disease Risk Maps on their website6 and can help provide some insight to disease pressures in your area. Scouting fields to determine disease pressure can guide timely and appropriate management tactics that can boost plant health, which may help limit risk of mycotoxins, even if management strategies (i.e., fungicide application) do not directly address mycotoxin-producing fungi. Supporting plant health and stalk integrity is beneficial, especially as crops stand in the field later into the harvest season as weather conditions may deteriorate and compromise the plant prior to harvest.

Believing that we can accurately predict what mycotoxin contamination patterns will look like in all bushels of corn that will be harvested this fall is absurd. Too many factors influence disease occurrence and contamination patterns, and those factors vary tremendously across the US and over time, resulting in an excessive number of potential combinations and outcomes. However, we’re willing to shake the magic 8 ball and see what insights we can harness from all the information that was presented in this article. In general, we believe that the “outlook is not so good” and there is a high likelihood for mycotoxins to be present in potentially challenging levels in the 2023 crop based on conditions which occurred over the course of the growing season. However, with harvest just under way in many top corn producing states, we suggest that you “ask again later” as our annual mycotoxin survey accrues data to better characterize what mycotoxin occurrence and contamination patterns truly look like in the 2023 corn crop.

Figure 7 outlines a few of our general predictions. DISCLAIMER: the following predictions are based on available information at the time of writing this article. We cannot guarantee contamination will follow these predictions, but check back in future issues of The Digest to see what contamination patterns look like according to the annual dsm-firmenich mycotoxin survey as harvest progresses and feeding of 2023 corn ingredients commences.

Figure 7. General mycotoxin predictions for 2023 US corn crop.


Potential Mycotoxins

Traditional Areas at Risk (Including 2023)

Additional Areas to Be Alert

Hot, dry weather / drought conditions

Aflatoxins, Fumonisins

Across the South (south of I-70)

Upper Midwest (Minnesota, Wisconsin, Iowa, Eastern Dakotas) and generally further north

Excess moisture, moderate temperatures

Trichothecenes (including Deoxynivalenol aka “vomitoxin”, T-2 Toxin, & related metabolites), Zearalenone

Can be widespread, but frequently found throughout the Midwest, Great Lakes region, and into the Northeast

Mid-Atlantic region and areas affected by late season tropical storms

Hail, wind, insect, wildlife, etc. damage

All (Fumonisins especially associated with insect damage); also influenced by general weather conditions in area

Variable year-to-year

Missouri, Kansas, Nebraska, Texas, Colorado, South Dakota

Keep in mind that single stressors increase the risk of mycotoxin contamination, but combinations of stressors, even when occurring individually at low to moderate levels, can enhance risk for mycotoxins that much more. It’s difficult to calculate and assess an aggregate stress level that incorporates all the factors that have been reviewed in this article. Despite this, understanding what stressors occurred in your area can help provide guidance as to what mycotoxin(s) to be on the lookout for and how frequently new crop feeds should be screened following harvest.

If you would like to submit samples for mycotoxin analysis to better understand risk in your feeds, contribute samples to the annual mycotoxin survey, or are curious to learn more about the analytical services dsm-firmenich offers, please contact your dsm-firmenich account manager. 


  1. Falconer, R. (2023, September 12). NOAA: 2023 worst year on record for billion-dollar disasters. AXIOS. Retrieved October 4, 2023, from https://www.axios.com/2023/09/12/disasters-weather-climate-record-2023-noaa 
  2. United States Department of Agriculture. (2023, October 1). 2023 Crop Progress and Conditions: Corn in United States, 2023. USDA National Agricultural Statistics Service. Retrieved October 4, 2023, from https://www.nass.usda.gov/Charts_and_Maps/Crop_Progress_&_Condition/2023/index.php
  3. National Oceanic and Atmospheric Administration. (n.d.). Climate Monitoring National Maps. NOAA National Centers for Environmental Information. Retrieved October 5, 2023, from https://www.ncei.noaa.gov/access/monitoring/us-maps/
  4. National Oceanic and Atmospheric Administration. (2023, October 5). Severe Weather Event Summaries. NOAA National Weather Service. Retrieved October 5, 2023, from https://www.spc.noaa.gov/climo/online/
  5. Migration Map. InsectForecast. https://www.insectforecast.com/migration-map/
  6. Bayer Crop Science United States. Corn Disease Risk Maps. Bayer Crop Science. https://www.cropscience.bayer.us/articles/bayer/corn-disease-risk-maps

Published on

23 October 2023


  • Poultry
  • Swine
  • Ruminants
  • Mycotoxins

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