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Implementation of best management practices – at planting, during harvest, storage, and through feeding out – can help reduce the risk of mold growth and mycotoxin production in crops and feeds, but some factors influencing those events are beyond our control, such as weather conditions. Additionally, limitations exist in different production systems and locations as to what agronomic practices may be utilized.
Both the molds that produce mycotoxins and the plants they infect are living organisms that can adapt and adjust to challenges over time. Many factors influence mold growth and mycotoxin formation including temperature, moisture content, oxygen levels, and physical damage to the crop. Stress factors, including drought or excessive rainfall, can increase plant susceptibility to mold colonization and mycotoxin formation. Due to the many “moving parts” involved in the development of mycotoxins, complete prevention of contamination is difficult, especially since mycotoxins can be produced while the plant is in the field or once the feed is in storage.
Many factors in the crop production environment influence the risk of mycotoxin contamination, but infection with a mold capable of producing mycotoxins is the first step. Prevention of fungal infection is key but is difficult to ensure because of the complexity of dealing with living organisms. Plus, some factors are uncontrollable, such as weather conditions.
Research has investigated what agronomic practices influence fungal infections and mycotoxin production in a variety of crops. Varied results have been reported for many of these factors. Some suggested actions need implemented prior to planting to reduce plant susceptibility to molds while additional practices are advised during plant growth to keep crops healthy. Harvest practices and storage management also influence the risk of contamination in feeds.
Anything that stresses the plant will make it more susceptible to infection including drought conditions (or excessive rainfall), hail damage, insect or wildlife damage, high crop density, and competition with weeds. Many of the agronomic decisions are inter-related and may provide direct or indirect means of protection from mold colonization and mycotoxin formation.
Certain corn hybrids have resistance to specific fungal infections including different types of ear rot caused by particular mold species. Some hybrid resistance mechanisms are based on physiological characteristics while others are based on morphological characteristics (e.g., tight and longer husks to protect ears). Choosing a hybrid that is well-suited for local growing conditions such as climate, soil, and pest pressures to optimize the crop reaching maturity and can limit harvest delays which lowers mycotoxin risk. Additional hybrid considerations like drought tolerance should also be considered based on the area’s climate and soil. An earlier planting date for corn has been shown to reduce risk across a range of locations in the US for several toxins. This may be due to several factors including promoting pollination and grain fill when insect activity is low (fumonisins) and prior to heat stress (aflatoxins). Planting date can influence harvest date as well. Additional considerations for crop yield should also be considered when looking at both planting and harvest dates.
Crop rotation and tillage practices are important as most mycotoxin-producing fungi survive in crop residues, but both cultural practices have additional reasons supporting their implementation beyond the potential to limit mycotoxin contamination such as reducing soil erosion, improving soil fertility, and increasing crop yields. Many mycotoxin producing molds are saprophytes which means they can obtain the nutrients they require from dead and decaying organic material. Therefore, leaving organic matter like corn stubble in the field when implementing no-till or even low-till practices provides a desirable environment for mold spores to live and thrive. The molds will be present when the next crop is planted, leaving the new crop exposed with an increased risk of disease.
Crop rotation can be useful for reducing the carryover risk of Fusarium diseases. Various species of Fusarium molds can produce mycotoxins such as deoxynivalenol (DON aka “vomitoxin”, zearalenone (ZEN), and fumonisins (FUM)). Corn followed by another crop of corn the next year presents the biggest risk. Unfortunately, many cereal crops are susceptible to infection by the same Fusarium species that produce DON and ZEN in corn (though much less susceptible to FUM producing Fusarium). Therefore, corn in sequence with wheat or barley can result in Fusarium infections and elevated DON and ZEN levels despite rotation. Rotation with less susceptible crops such as soybeans has been shown to limit carryover of these fungal infections and limit mycotoxin levels, even when no-till was implemented.
Some data suggests that crop rotation and tillage type are more influential on DON and ZEN producing mold species than those that produce aflatoxins and FUM. Gibberella ear rot is related to DON and ZEN in corn and is associated with cool, wet weather during silking as well as heavy rainfall late in the season. The mold spores associated with this fungal infection are typically spread over short distances through splash up during rain. The FUM-producing disease Fusarium ear rot is linked to insect damage and warm, humid conditions are associated with FUM production. Aspergillus ear rot is associated with dry conditions and high temperatures as well as insect damage. Both Fusarium and Aspergillus ear rot causing mold spores can be spread via the wind (and potentially via insects, birds, and wildlife) over long distances, so neighboring fields can be a source of contamination. This is likely why crop rotation and tillage practices have not been as effective at reducing these fungal infections and their corresponding mycotoxins.
The depth that crop residues are incorporated into the soil can influence mold presence in soil and mycotoxin levels in crops. One study investigating tillage type utilized in wheat fields saw a 10-fold increase in DON levels when low-till was practiced instead of plowing. Moldboard plowing reduced the number of Fusarium species isolated from soil more so than chisel plowing and rotary tilling. That study also saw a greater reduction in the mold spore count when crop debris was pushed further into the soil. Although differences in the occurrence of the Fusarium molds which produce DON were seen between tillage practices, there was no correlation to the DON levels in the grain detected in that study. Due to the complex nature of mold growth and mycotoxin production, differences in mycotoxin levels are not always observed when different tillage practices are used. It is clear, however, that crop residues left on and near the soil surface can harbor mold spores and potentially lead to future fungal infections and mycotoxin contamination including DON, ZEN and FUM in subsequent crops.
Many factors influence the occurrence of fungal plant diseases and production of mycotoxins, so consideration for agronomic practices prior to and following planting as well as proper harvest and storage practices through feeding out are needed to help limit mycotoxin contamination. Much goes into a comprehensive mycotoxin risk management program. Monitoring of mycotoxin levels in feeds is a valuable tool to understand potential risks to animal health and productivity and is useful because implementation of best management practices cannot guarantee prevention of mycotoxin development at some point in the feed production cycle. Contact your DSM Animal Nutrition & Health representative if you have questions about mycotoxin risk management on your farm.
20 February 2023
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