Managing the Challenging 2018 Corn Crop through Feed out

John Goeser, Ph.D., PAS, and Diplomate ACAN Rock River Laboratory

John Goeser, Ph.D., PAS, and Diplomate ACAN Rock River Laboratory

Regardless of growing location, the 2018 corn crop faced a myriad of disruptions throughout the growing season and harvest. Now that 2018 is almost completely behind us, corn silage is off the fields, and corn grain is mostly off (seems that some is in ‘cold storage’ at the moment), we’ve taken numerous questions about not only the challenges that we experienced during growth, but also the challenges that could be lurking in the silos, bunkers, bags, and piles.

To set the stage, at the beginning of 2017, Vomitoxin (DON) levels with 2016 harvested feeds were generally above dietary limits (on average between all regions of the US). Then the 2017 crop came in relatively clean, and mycotoxin loads dropped. With the new 2018 crop, we’ve seen these numbers creep back up well above average (See Graph 1: Vomitoxin). Dr. Damon Smith, known virtually as the Badger Crop Doc, has addressed how one might reduce vomitoxin levels in corn silage in his recent video, ‘Mycotoxins and corn earn rot’ here: https://youtu.be/uM8m-Fvo4U4. However, vomitoxin is just the tip of the iceberg when it comes to the challenges Rock River Laboratory has received calls about, and we’d like to address the rest of those Frequently Asked Questions (FAQs), as well as those asked of Dr. Damon Smith, University of Wisconsin-Madison Plant Pathology Associate Professor and UW Extension Specialist.

Graph 1: Vomitoxin

Q: What toxins have been observed most prevalently in the 2018 corn crop?

Record rainfall, delayed harvest, and new fungal plant pathogens have contributed to the vast number of feed hygiene concerns this year. We are recognizing mycotoxins produced by some of these fungi, including Vomitoxin & Zearalenone trending up from Minnesota to Pennsylvania.

Smith has also shared, “I have mostly seen vomitoxin issues in my neck of the woods. Gibberella ear rot combined with wet weather led to high levels of vomitoxin.” He goes on, “You can have several mycotoxins of concern with a single disease.”

Don't panic though; identify and prioritize opportunities for improving the hygiene of the feed through management and storage. For better or for worse, many growers and farms are experiencing similar outcomes.

Q: Are some hybrids better than others when it comes to growing and harvesting years like this?

“Hybrids vary for different disease issues. The trouble this season was that there were so many to deal with - some were good on one disease, while not so good on others,” explains Dr. Smith. “I would select hybrids rated better on the harder to control issues, such as ear rots and stalk rots. Fungicides can be used on foliar issues more readily and that decision can be made in-season. So, look for good ear and stalk rot ratings and go from there.”

As I’ve learned from Dr. Smith, hybrid resistance is key. Genetic impact on nutritive quality is also substantial, in some cases even up to 50 percent of phenotype. Crop scouting and management are also important to reduce disease issues and subsequent mycotoxin problems.

Dr. Smith echoes, “Crop scouting is key, as is paying attention to weather. If it’s hot and dry, diseases are less of an issue. Cooler and wetter weather creates the issues like we’ve seen this season.”

Growers should develop their own custom hybrid plots to monitor yield, disease resistance and quality on their own fields. I recommend assessing digestible tons per acre (which is a good yield measure), with seed costs and disease resistance, in a partial budget to make decisions.

Going forward, hybrid selection will likely be even more of a balancing act. Historically, it’s consisted of a yield versus quality discussion. Now, though, we need to balance disease resistance with yield and with Neutral Detergent Fiber Digestibility (NDFD) or quality metrics.

“Lignin is a defense for disease,” says Dr. Smith. “Unfortunately, there might be a tradeoff with stalk integrity and issues with rots and accumulation of mycotoxins by fungi that produce them in stalk portion of plant. The choice of hybrid will be a huge balancing act.”

Q: What about tar spot’s repercussions? Can it overwinter and what can we do to prevent it?

“We don't believe tar spot directly leads to mycotoxin issues, but it can reduce feed quality by inducing abnormally fast dry down,” explains Dr. Smith.

He recommends a QoI+DMI, or SDHI+DMI, or QoI+SDHI+DMI fungicide to get decent control of tar spot, but warns that timing the application of such fungicides to most closely coincide with the start of the epidemic, is key. But he also suggests planning ahead when choosing varieties. “Look for resistant varieties in hybrid trials. Most are not very resistant, but some partial resistance might be available. Despite some resistance, fungicide application may be needed, and timing of application will be an issue. You will also need something more than a straight DMI or QoI fungicide.”

Dr. Smith shares that, “cool 30-day temperatures and high 30-day average humidity is a good indicator of tar spot onset. If the average 30-day temperature is less than 71 degrees F, combined with a humidity average above 75 percent for the month, tar spot is likely.”

“The evidence is good that tar spot can overwinter, and we will likely see it again,” suggests Dr. Smith. “As far as how bad, it’s hard to say. It will depend on weather conditions and if those conditions coincide with corn at susceptible growth stages.”

Dr. Smith’s lab is currently working on a tar spot model, and have put together a video, ‘Tar Spot: What We Know and What We Don’t Know’: https://youtu.be/uLygYjMkXQE.

Q: What are the biggest issues you've seen to date with the current corn crop?

Our main concern at this point is silage that is too dry, has high wild yeast counts, and less than ideal stability. Low NDFD levels and mycotoxin concerns are secondary, but very real.  Unfortunately, there is no ‘one size fits all' cure to all of these issues.

“The longer the corn sat in the field, the longer it had to accumulate potential vomitoxin or other mycotoxins from ear rot issues,” observes Dr. Smith. “Other ear rots could be present. For instance, further south of Wisconsin, Fumonisin mycotoxin may be of concern. This is caused by Fusarium ear rot, not Gibberella ear rot.

He recommends continuing to test, so you know what you have.

The multitude of issues may be additive. Some dairies are recognizing lesser feed conversion efficiency, meaning less milk per pound of feed. In such cases, either the immune system takes up energy, or digestion capacity is limited. Echoing Dr. Smith, identification through testing is important to then prioritize next steps.

Q: Can fungicides help for ear and stalk rot? What about mycotoxins?

“In years where pressure isn't overwhelming, they can be useful,” shares Dr. Smith. “In 2017 we saw good reduction of vomitoxin using fungicide.” (See Graph 2 of Ear Rot vs. Vomitoxin)

Graph 2: Ear Rot vs. Vomitoxin

However, Dr. Smith goes on to explain that in 2018, the situation was challenging as the weather was conducive for the fungi. Success with fungicide wasn't as good, but there were some reductions on some hybrids. (See Table A of DON levels)

Table A: DON levels

Q: What should I test for in the 2018 corn crop now that it’s harvested?

From Minnesota to Pennsylvania, I recommend staying on top of crop dry matter. Then focus on routine forage analysis. Check NDFDs as fiber seems to be slower this year. After that, priority analysis should include mold and yeast, followed by vomitoxin if the grower is suspicious of it.

Growers in the Great Plains, and the southern and western states avoided the challenges the eastern US endured. Those who experienced drought should check ash levels.  "Normal" corn silage should be in the three to five range. Greater than five to six is "high", and could contaminate the feed, creating poor feed hygiene.

Q: What can I do to ‘clean up’ corn with high loads of vomitoxin?

I’ve learned from Professor Lon Whitlow, roasting won't help, however, cleaning chaff, etc. will.

“Mycotoxins are very stable and resist heating, freezing, roasting, etc.,” explains Dr. Smith. “In grain, cleaning well and drying quickly help stop accumulation. In silage, good fermentation is pertinent.” Learn more about mycotoxin stability in this resource from the Badger Crop Doc: https://t.co/sy1070V9vl.

Q: How will this year's silage fermentation be affected by the molds, higher dry matter, and general crop stress?

Excessive rains excited wild yeast and microbes and delayed harvest, ultimately leading to a drier crop that won’t pack as well. I’m expecting a slower fermentation, curing, and some feed stability issues. My three recommendations for dealing with these antinutritional factors includes keeping oxygen out, keeping the tires on, and ensuring all edges are sealed. Detailed management items like this can go a long way.

Q: Feed was warm when we harvested and saw challenges, but winter is here and the temperatures have dropped. Do we still have to worry about the bugs?

High yeast loads, which cause heating, are likely present but not dead. They are dormant in refrigeration weather, so growers should be prepared for warmer temperatures and what they may bring in this sector (See Graph 3: Yeast).

Graph 3: Yeast

Q: If corn silage looks OK but I send it in for analysis, what are some non-visible challenges you might recommend to analyze for, or I might find via analysis?

There is so much present in silage that isn’t visible to the human eye, including living microbes (mold and yeast), mycotoxins (i.e. Vomitoxin), alcohols, and biogenic amines (fermentation products). All of these and more can affect animal health.

While the corn crop has proved to challenge us in 2018, it has also brought problems to the surface to be addressed, solved, and continue growth in our management understanding. While our industry will remain diligent in researching for better means to manage and avoid such challenges in the future, growers can also feel better prepared for 2019 having endured, and learned from the 2018 crop.

The author can be contacted at [email protected] and at the website www.rockriverlab.com

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