Zum Inhalt
Zur Hauptnavigation
  • Mycotoxin Risk
  • Mycotoxins
  • Mycofix
  • Mycotoxin Risk
  • Mycotoxins
  • Mycofix

How Heavy Rains and Floods Contribute to Mycotoxin Contamination

Heavy precipitation, such as that faced by parts of Europe in 2021, can mean a higher risk of contaminants in corn (maize), wheat and other grains.

Bettina Behler-WoechtlWolfgang Schweiger

In Brief

• Extreme weather events will become more frequent in future due to climate change.
• Heavy rain events during critical periods of plant development increase the risk of fungal infection and mycotoxin production.
• Testing for mycotoxins and other contaminants is even more important if crops were exposed to moist conditions or flooding.
• If the harvest is contaminated, mycotoxin deactivation products with proven efficacy can counteract negative effects of mycotoxins.

European situation in 2021

Several European countries including Germany, Belgium and the Netherlands were subject to heavy rain leading to disastrous floods in July 2021.

Floodwater contaminates harvests with heavy metals, dioxins, polychlorinated biphenyls (PCBs) and pathogenic bacteria. Often, alternative use or disposal of respective batches is necessary, as contamination may exceed maximum contents of undesirable substances in feeding stuff (listed in ANNEX I of Directive 2002/32/EC). In such extreme cases, the harvest is spoiled and must be discarded.

Crops that do not have to be discarded but experienced strong rainfalls and soil wetness during critical periods as flowering or ripening may be suitable for animal feed. However, fungal crop contamination and mycotoxin production may present additional risks to animals.

Flooded maize field
Flooded maize field. Depending on respective local legislative, crops from flooded fields need to be withdrawn.

Fungal infection and mycotoxin production on the field

In temperate regions the field fungi Fusarium spp. are a main concern. They infect the developing crop on the field. Trichothecenes, zearalenone and fumonisins are types of mycotoxins that accumulate in the maturing kernels.

High moisture increases risk of infection particularly during three periods:

  1. flowering
  2. ripening
  3. delayed harvest

Spores dormant in plant debris on the soil can reach the flowering ears via splash water. Thus, rain increases the risk of fungal infection. Additionally, as the plant matures, ongoing moist conditions lead to higher disease pressure and higher toxin levels.

High moisture during flowering

Corn (maize) flowers between July and August in Europe, being earliest in southern countries and latest in the Northwest of the continent. While Mediterranean regions were exposed to high temperatures and minimal precipitation, Central Europe from France to Romania received abundant rain in July, with major flooding events in Germany, Austria, Belgium, the Netherlands and Switzerland. The individual timing of corn silking partly coincides with these events. This contributes to a higher risk of infection of maize with Fusarium fungi. The BIOMIN mycotoxin prediction tool uses weather forecasts during the European growing season to estimate the probable levels of mycotoxin contamination in the current harvest.

Corn cob with Fusarium ear rot.
Corn cob with Fusarium ear rot. In this case, infection with Fusarium is visible. Kernels without visible fungal infection can still contain mycotoxins.

Consequences of delayed harvest

In general, earlier harvest results in lower concentrations of mycotoxins.  If fields are impassable,  timely harvest is impossible and mycotoxins produced by field fungi accumulate. A delay of harvest of one month resulted in a 10 to 25 times higher contamination of wheat with deoxynivalenol and zearalenone (Edwards and Jennings, 2018).

Mycotoxin production in storage

In Europe, mycotoxins produced by field fungi dominate, but production of mycotoxins in storage also occurs. In the cool and moist conditions of Northern European, Ochratoxin A production by Penicillium verrucosum occurs during storage (Magan and Aldred, 2006). Ongoing production of fumonisins in stored moist maize in France has been reported (Cahagnier et al., 1995).

It is important to achieve and keep a moisture content of 14% or below in stored crops to avoid fungal growth and mycotoxin formation. If it is necessary to harvest in a moist condition, drying of crops needs to be performed. Farmers need to keep time between harvest and drying as short as possible (Cahagnier et al., 1995).

Tips for crop storage:

  • Keep crop moisture content at 14% or below

  • Dry crops if needed

  • Minimize time between harvest and drying

  • Use organic acids to prevent mold growth and toxin production in storage

Testing and intervention

In times of heavy rains and flooding it is even more important to apply diagnostics to know the contamination of respective crops and identify potential problems. It is advisable to analyze crops exposed to the described conditions on the field at least for the most relevant mycotoxins within the group of trichothecenes (for example deoxynivalenol) as well as for zearalenone and fumonisins. Additionally, testing for Ochratoxin A may be advisable in case of suboptimal storage conditions in some regions.

The Mycofix® range of mycotoxin deactivators counteracts the negative effects of mycotoxins. Your local BIOMIN representative will gladly support you to identify the most effective and cost-efficient solution for your operation.


Edwards, S. G., & Jennings, P. (2018). Impact of agronomic factors on Fusarium mycotoxins in harvested wheat. Food Additives & Contaminants: Part A, 35(12), 2443-2454.

Magan, N., & Aldred, D. (2005). Conditions of formation of ochratoxin A in drying, transport and in different commodities. Food Additives and Contaminants, 22(s1), 10-16.

Cahagnier, B., Melcion, D., & Richard‐Molard, D. (1995). Growth of Fusarium moniliforme and its biosynthesis of fumonisin B1 on maize grain as a function of different water activities. Letters in Applied Microbiology, 20(4), 247-251.