There is often a misperception that forage management starts in the bunker or silo. However, when I get the question, “Why does our silage have such extreme levels of yeast and mold counts?” my first instinct is to review the growing conditions in the field. As spring approaches, the planning and decisions that affect next year’s feed quality should begin now.
From field to feed, the growing season, paired with various management practices, can have substantial impacts on crop health. Considerations starting at the ground level with soil health all the way to crop residue from previous years can have an impact on silage quality and hygiene. Understanding some of the stressors that contribute to persistent fungal life cycles is valuable when making management decisions for crop residue, manure application and inoculant use at harvest and feedout.
Field stressor: Last year’s crop
What remains in the field?
At the end of harvest, many fields are left covered with corn residue. This residue can be beneficial as organic matter and as a layer of protection for the soil. However, it is also an advantageous environment for fungus and mold to grow.
There are numerous different fungi that can overwinter on corn residue. Leaf blights and foliar disease are both common fungi that will try to use last year’s field residue as an apartment until they move in on new crops emerging through the soil.
Field stressor: Manure application
How much manure was applied, and when?
While manure is an essential fertilizer, it can also host bacteria and disease, compounding the risks of what new crop health could look like. The interaction between when manure is applied on fields and environmental factors such as temperature, humidity and rainfall heavily influences mold growth.
Warm, wet conditions are particularly conducive to both fungal growth and mycotoxin production. The University of Nebraska – Lincoln Institute of Agriculture and Natural Resources gives these recommendations for manure application and quality:
- Manure can increase the soil's moisture retention, creating a favorable environment for mold growth. High moisture levels in the soil and around plants encourage fungal proliferation, particularly in humid climates or poorly drained fields.
- Applying manure close to planting or harvesting times can increase the risk of mold contamination by introducing spores during critical crop growth stages.
- Properly composted manure has fewer viable fungal spores than raw or partially decomposed manure. Composting can reduce the risk of mold introduction and later mycotoxin production.
Field stressor: Weather
How are crops responding to the weather?
As we move into the growing season, we naturally hope for adequate amounts of sunshine and rainfall during the right times. The reality is we are often faced with the occasional occurrence of a hailstorm or other disease-promoting weather events. Cool, wet conditions, late silage harvest and extreme weather events are environmental factors that can promote mold development. Attempting to suppress some of these risks is challenging, if not almost impossible.
Two considerations could include the correct application and timing of fungicide, which has been shown to reduce the risk of fungal development alongside the selection of hybrid or resistant varieties upon planting. These are just one part of the equation when preventing challenges throughout the growing season.
Opportunity for adjustments at harvest
Reviewing risk throughout the growing season allows for the opportunity to adjust harvest practices prior to silage season. While utilizing the common drydown days for checking moisture in preparation for chopping, I also recommend sending a sample to a laboratory at this stage to establish a baseline of mold and yeast counts. These laboratory results could encourage the use of a different inoculant choice to enhance the fermentation or feedout desired.
As harvest begins, having awareness of the crop condition and health alongside precise harvest plans will help manage some of the risks discussed thus far. All silage will ferment naturally, but challenges brought in from the field will jeopardize this process. These challenges could lead to elongated fermentation time, with the consequence of bound-up protein due to excessive heat damage throughout this lengthened time. If there are heightened risks of yeast or mold presence from preliminary screening, an appropriate inoculant or acid selection is encouraged. If not used, one could see the potential for heating in forages upon feedout, and that heating could reduce intake.
These preliminary, preharvest numbers are a baseline for what we want to help control during fermentation. Having the ideal fermentation environment, including adequate chop length and kernel processing, dense packing and quick covering with an oxygen-excluding barrier, can help prevent those yeast and mold counts from exploding. The most critical factor in fermentation is the moisture of the crop. If forages are chopped too dry, the natural amount of lactic acid bacteria coming in on those plants has been reduced and therefore restricts fermentation. If forages are chopped excessively wet, we have magnified our risks for a clostridial fermentation, resulting in a high level of butyric acid in the fermented forage.
Silage is an energy-dense feed that makes up a substantial portion of rations. When it is compromised by fungi and mold in the field, we run the risk of sick cattle and economic losses from lower production. Getting the best value at feedout starts by understanding the common stressors affecting the corn plant in the field.
