Perspectives - Spring 2018 - 34

Another challenge is that mycotoxins occur at very low concentrations-parts per
million (ppm) and parts per billion (ppb).
Such low levels make detection difficult,
especially when there are "hotspots" within large quantities of feed. Care is needed
when collecting feed for analysis in order
to obtain representative samples and reliable results.
Agronomic Considerations
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 control because of the
complexity in dealing with living organisms-and some factors are uncontrollable,
such as weather conditions. Research with
a variety of crops has investigated what agronomic practices can help to reduce fungal
infections and subsequent mycotoxin production. Varied results have been reported
for many of these factors and management
practices. Some suggested actions need to
be implemented prior to planting in an effort to reduce plant susceptibility to molds
while additional practices are advised
during plant growth to keep crops healthy.
Harvest practices and storage management
are important to maintain clean feeds.
Pre-Planting Factors:
* Hybrid selection
* Crop rotation
* Tillage practices
* Seed treatment with fungicide
* Planting date
* Planting density
Post-Planting Factors:
* Irrigation
* Weed management
* Insect management
* Fungicide application in the field
* Weather conditions during harvest
* Harvest date
Anything that stresses the plant will make
it more susceptible to infection by molds.
This includes drought conditions (or excessive rainfall), insect or wildlife damage,
mechanical 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, such as ear rot
caused by specific mold species. Some hybrid resistance mechanisms are based on
physiological characteristics while others
are based on morphological characteris34

Perspectives Magazine

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tics (e.g., tighter and longer husks to provide ears protection from insect damage).
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 the prevention of harvest delays 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 U.S. 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 of these
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 able
to be saprophytes, which means they can
get the nutrients they require from dead and
decaying organic material. Therefore, leaving organic matter like corn stubble and
roots in the field with utilization of no-till
or even low-till practices provides a desirable environment for mold spores to live
and thrive. The molds are present when the
next crop is planted, leaving the new crop
exposed and increasing the risk of disease.
Crop rotation can be useful for reducing
the carryover risk of Fusarium diseases.
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 increased
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 fumonisins. 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 fun-

gal 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 that 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.
Summary
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 Phoenix Feeds
and Nutrition representative if you have
questions about mycotoxin risk management on your farm.


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Perspectives - Spring 2018

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