Disease and Mycotoxin Considerations for Corn Silage Harvest In Wisconsin

/in , , , , , , , , /by

Damon Smith, Extension Field Crops Pathologist, Department of Plant Pathology, University of Wisconsin-Madison

We are quickly approaching that time of year where we will see silage choppers working the 2024 corn crop. This means it is time to understand overall crop health and how diseases might be affecting the crop so that you can make the best silage product you can.

Overall, the corn crop in Wisconsin looks good. Yes, I can find some sort of disease in any field I visit, but I would say for the most part, most fields that were planted relatively on time, and didn’t experience early-season flooding, have a decent crop. With that said, we need to monitor the crop closely as we approach harvest as foliar disease issues can sneak up quickly as cool, wetter weather moves in near the early fall harvest.

Foliar diseases such as southern rust, tar spot, gray leaf spot (GLS), and northern corn leaf blight (NCLB) can be problematic for silage production. Not only do these diseases lead to a reduction in overall silage quality, they can force the plant to scavenge carbohydrates in the stalk which can result in standability issues and lodging. These diseases can also influence whole plant moisture making harvesting at optimal moisture difficult. If silage is harvested at sub-optimal moisture, then packing the bunker properly can be a challenge which can lead to slow fermentation and continued growth of aerobic organisms like fungi. This can indirectly lead to an increase in mycotoxins and “mold” issues from these aerobic fungi.

Tar spot and silage harvest

Tar spot of corn has been an issue on silage corn in Wisconsin since 2016. In fact, the first finding of tar spot was on corn for silage that year. Since 2016 the largest and most consistent impacts happen on corn for silage vs. corn for grain. Yes, tar spot can result in significant grain losses, but tar spot can also affect the overall plant in other ways such as loss in dry-matter yield (Fig. 1) and whole plant moisture contents well below optimal, making bunker-packing a significant issue. In recent work in Wisconsin, we see significant dry-matter yield reductions when tar spot severity on the ear leaf reaches over 10% at the time of chopping. This can result in as much as 15% reduction in yield, with these impacts dramatically increasing at severity levels of 20% or more on the ear leaf (Fig. 1). If tar spot (or any foliar disease) is moving quickly in your silage crop, you might consider chopping a bit earlier to reduce dry-matter yield losses and to try to optimize whole plant moisture, prioritizing good bunker management. If moisture at chopping is not prioritized, then subsequent storage issues such as mold and mycotoxin concerns can arise indirectly, due to poor bunker management. This brings us to Gibberella ear and stalk rot in silage corn.

Figure 1. Impact of tar spot severity on the ear leaf at harvest time compared to dry-matter yield in whole-plant chopped silage corn.

Gibberella and silage harvest

Gibberella ear rot is caused by Fusarium graminearum (a.k.a. Gibberella zea). The same pathogen can cause Gibberella crown and stalk rot in corn. We have observed both diseases on silage corn in Wisconsin in recent years. Our environment here in the Great Lakes region makes a perfect place for this pathogen to cause these diseases. In addition to the damage that the pathogen can cause, the fungus can also produce various mycotoxins, most importantly deoxynivalenol (DON or Vomitoxin). Our laboratory has conducted quite a bit of research recently trying to understand where in the plant DON accumulates. In detached plant part experiments, we have noted that DON can accumulate in both the stalk and ear portions of the plant, AND that these two phases of accumulation are not linked to each other (Chibuogwu et al., 2024). The fungus can infect these parts separately at different times during the season and the subsequent accumulation of DON can happen differentially in the stalks vs. the ears. This is partially why you can go out to the field and scout for ear rot and not see a lot of infection (moldy ears), but still have high DON levels at chopping time. Some of that DON is likely accumulating in the stalks.

We have also been following the fate of DON in silage harvested and chopped from a brown midrib (BMR) hybrid and a dual-purpose hybrid that were grown in the field and treated with fungicides at white silk (R1). We chopped the plants in each plot and then used mini-silos (polyethylene bags vacuum-sealed using a commercial grade vacuum packer) to conduct a time-course experiment following DON levels in the mini-silos (Chibuogwu et al. 2025). In all cases we saw DON levels generally increasing in the first 30 days after chopping (Fig. 2). They then leveled off and became stable at 60, 90, and 120 days after chopping. Some of this increase could be due to oxygen still in the system during the first 30 days after chopping. DON-producing fungi are aerobic and continue to consume some of the minute levels of oxygen still in the system, thereby still producing DON. However, this likely only explains some of the DON levels we detected.

Figure 2. DON concentration of chopped field-grown silage corn over time of ensiling.

There are also “masked” or conjugated forms of DON that are detectable in routine DON analyses. One such conjugate is DON-3-glucoside (D3G). D3G can be produced by fungi or during a plant’s attempt to protect itself from the toxicity of DON. Either way, D3G is not detectable in routine test and must be tested for specifically. We investigated our samples further during the first 30 days of ensiling and found that the level of D3G at harvest, explained a significant level of the DON recorded in samples after 30 days of ensiling. This is to say that D3G present at harvest, is likely metabolized in the first 30 days of ensiling releasing DON and resulting in higher DON levels 30-days later (Fig 3). Again, this relationship only partially explains why DON increases in silage during the first 30 days of storage. The full explanation is likely due to both metabolization of D3G and continued fungal respiration leading to an increase in DON at feed out compared to when it was packed in the bunker.

Figure 3. Relationship of DON-3-Glucoside (log) at harvest and DON concentration after 30 days of ensiling.

The Take Home

So, what are we to do with all of this information? Well, knowledge is power. You need to balance foliar disease management with Gibberella/DON management when making high-quality silage in Wisconsin. Diseases like tar spot are the new normal. As you prepare to harvest, it is a good idea to get out in the field and see how bad the foliar disease is and how much ear rot you are seeing. You will want to prioritize harvest on fields showing more disease. In fields where there are high levels of tar spot, southern rust, or NCLB, monitor moisture carefully and try to chop to optimize moisture. Concentrate on good bunker hygiene and spend time packing the material as best you can, focusing on getting as much oxygen out of the system as you can. If a corn crop becomes too dry to make good silage, you might consider harvesting it for high-moisture grain to try to circumvent bigger issues that could arise at feed out, by making less than ideal silage. Finally, it is important to test for DON frequently and understand what you are dealing with. You want to start with the lowest levels of DON coming from the field that you can. DON will likely increase in the bunker no matter how well you pack it. Thus, starting with the lowest levels at harvest will help keep final levels of DON below critical thresholds. Moving forward, mycotoxin testing in corn should include not only DON but also for conjugates of DON that can be metabolized back to DON and increase the final DON concentration during ensiling.

Have a safe and productive silage harvest season!

Citations

Chibuogwu, M.O., Groves, C.L., Mueller, B., and Smith, D.L. 2024. Effects of fungicide application and corn hybrid class on the presence of Fusarium graminearum and the concentration of deoxynivalenol in ear and stalk parts of corn (Zea mays) used for silage. Plant Disease. https://doi.org/10.1094/PDIS-12-23-2662-RE.

Chibuogwu, M.O., Reed, H., Groves, C.L., Mueller, B., Barrett-Wilt, G., Webster, R.W., Goeser, J., and Smith, D.L. 2025. Influence of hybrid class and ensiling duration on deoxynivalenol accumulation and its derivative deoxynivalenol-3-glucoside while ensiling corn for silage. Plant Disease. https://doi.org/10.1094/PDIS-06-24-1166-RE.

Corn Stalk Rots and Ear Rots: A Double Whammy for Wisconsin Corn Farmers Again this Year

/in , , , , , /by

Damon L. Smith, Associate Professor and Extension Field Crops Pathology Specialist, University of Wisconsin-Madison

John Goeser, Adjunct Assistant Professor, Department of Dairy Science, University of Wisconsin-Madison and Animal Nutrition Director, Rock River Laboratory, Inc

Figure 1. Anthracnose stalk rot of corn.

The 2019 growing season is the third year in a row where we are going to end with many challenges for Wisconsin farmers. The excessively wet weather is challenging the last of corn silage harvest, and grain harvest has barely started in much of the state. Couple this with wet weather, delayed planting, and plant stress most of the season and there is a double whammy of stalk rot and ear rot issues to contend with this fall.

What is the Primary Stalk Rot Issue in Wisconsin?

Anthracnose stalk rot (Fig. 1) has been readily apparent for Wisconsin corn growers this season. Anthracnose stalk rot is typically worse in fields in a corn-on-corn rotation, and/or no-tilled, and planted to a susceptible hybrid. Reports and observations of lodging are starting to come in. In addition, to anthracnose stalk rot, we are also seeing Gibberella stalk rot picking up . This stalk rot seems to be showing up in late-planted corn-situations and especially wet fields. This isn’t surprising given the weather conditions and level of plant stresses from compaction, slow accumulation of growing degree day units, and foliar pathogens. Impending frost in much of the state this weekend will also end the growing season, meaning that plants already damaged by stalk rot will shut down. The clock starts ticking on what can be done and lodging becomes a considerable concern.

Frosted corn for silage will begin drying at a faster and constant rate, regardless of kernel or plant maturity. The primary aim for frosted corn meant for the silo becomes achieving an ideal moisture content for ensiling. With whole-plant corn silage, the ideal moisture range is 63 to 68% however with frost damaged or killed corn, achieving this dry matter for the entire crop may prove impossible.  Actively monitor moisture during harvest and segregate the crop if moisture dips below 55%, to avoid silage storage and stability issues later on. 

What should I do if I have a field with stalk rot?

In fields where stalk rot is an issue, HARVEST AS EARLY AS POSSIBLE to avoid yield losses from lodging. Silage corn fields should also be chopped as soon as possible, monitoring moisture and being sure to take extra care in packing the bunker. Delaying harvest for grain corn will increase the likelihood of lodging which will increase harvesting issues. Once conditions dry enough to allow combines to run, fields with higher levels of stalk rot and/or lodging should be prioritized for harvest.

What should I do about stalk rot for next season?

Management of of any of the stalk rots is multi-faceted. First, choose hybrids with the best resistance available. Hybrids that also have good resistance to foliar diseases will also offer an advantage when managing stalk rot, as foliar disease can stress corn plants and lead to increased risk of stalk rots like anthracnose stalk rot. Cultural practices such as crop rotation and tillage to manage surface residue can also help. Other practices that reduce plant stress such as balanced fertilization, proper planting population, providing suitable drainage, and using well adapted hybrids for your location will reduce the risk of anthracnose stalk rot.

Fungicides are not recommended for managing stalk rots, directly. However, we have observed better standability of corn in years with heavy foliar disease pressure, where fungicides have been applied.  This makes sense, because controlling heavy foliar disease allows the plant to continue to produce carbohydrates through photosynthesis. When heavy foliar disease pressure is left unchecked, corn plants can scavenge the stalks for resources predisposing corn plants to stalk rot diseases and a loss in stalk integrity.  

What corn ear rots and mycotoxins should I watch out for?

Figure 2. Diplodia ear rot (2 ears on the left) and Gibberella ear rot (2 ears on the right) of corn. Photo Credit: Craig Grau.

With all the wet weather, several ear rots have appeared in corn around much of the state. Ear rots caused by fungi in the groups Diplodia (Fig 2.), Fusarium, and Gibberella (Fig. 2) will be the most likely candidates to watch for as you begin harvest.  Fusarium and Giberrella are typically the most common fungi on corn ears in Wisconsin.  This group of fungi not only damage kernels on ears, but can also produce toxins called mycotoxins.  These toxins (fumonisins and vomitoxin) can threaten livestock that are fed contaminated grain. Thus grain buyers actively test for mycotoxins in corn grain to monitor mycotoxin levels to be sure they are not above certain action levels established by the U.S. Food and Drug Administration (FDA).

The FDA has established maximum allowable levels of fumonisins in corn and corn products for human consumption ranging from 2-4 parts per million (ppm).  For animal feed, maximum allowable fumonisin levels range from 5 ppm for horses to 100 ppm for poultry. Vomitoxin limits are 5 ppm for cattle and chickens and 1 ppm for human consumption.

Diplodia ear rot is not as common in Wisconsin. This disease is often more severe in years where dry weather precedes silking, followed by wet weather immediately after silking. Diplodia ear rot does not produce mycotoxins. While this disease does not result in mycotoxin accumulation, it can cause grain yield loss and quality issues.

For more information about ear rots and to download a helpful fact sheet produced by a consortium of U.S. corn pathologists, CLICK HERE.

 

How do I reduce mycotoxin risks at harvest?

Before harvest, farmers should check their fields to see if moldy corn is present. Sample at least 10-20 ears in five locations of your field. Pull the husks back on those ears and observe how much visible mold is present. If 30% or more of the ears show signs of Gibberella or Fusarium ear rot then testing of harvested grain is definitely advised. If several ears show 50-100% coverage of mold testing should also be done. Observe grain during harvest and occasionally inspect ears as you go. This will also help you determine if mycotoxin testing is needed.

If substantial portions of fields appear to be contaminated with mold, it does not mean that mycotoxins are present and vice versa. Remember, Diplodia ear rot does not produce mycotoxins. However, if you are unsure, then appropriate grain samples should be collected and tested by a reputable lab.  Work with your corn agronomist or local UW Extension agent to ensure proper samples are collected and to identify a reputable lab. If tests show high levels of mycotoxins in grain, that grain SHOULD NOT BE BLENDED with non-contaminated corn.

For more information on mycotoxins and to download a fact sheet, CLICK HERE.

Helpful information on grain sampling and testing for mycotoxins can be found by CLICKING HERE.

For a list of laboratories that can test corn grain for mycotoxins, consult Table 2-16 in UW Extension publication A3646 – Pest Management in Wisconsin Field Crops.

 

How should I store corn from fields with ear rots and mold?

If you observe mold in certain areas of the field during harvest, consider harvesting and storing that corn separately, as it can contaminate loads; the fungi causing the moldy appearance can grow on good corn during storage.  Harvest corn in a timely manner, as letting corn stand late into fall promotes Fusarium and Gibberella ear rots.  Avoid kernel damage during harvest, as cracks in kernels can promote fungal growth.  Also, dry corn properly as grain moisture plays a large role in whether corn ear rot fungi continue to grow and produce mycotoxins.  For short term storage over the winter, drying grain to 15% moisture and keeping grain cool (less than 55F) will slow fungal growth. For longer term storage and storage in warmer months, grain should be dried to 13% moisture or less. Fast, high-heat drying is preferred over low-heat drying. Some fungi can continue to grow during slow, low-heat drying. Also, keep storage facilities clean.  Finally, mycotoxins are extremely stable compounds: freezing, drying, heating, etc. do not degrade mycotoxins that have already accumulated in grain. While drying helps to stop fungal growth, any mycotoxins that have already accumulated prior to drying will remain in that grain. The addition of acids and reducing pH can reduce fungal growth but will not affect mycotoxins that have already accumulated in harvested grain.

For wet corn, earlage, snaplage or corn silage, promote optimal fermentation to preserve and stabilize the feed for dairy or beef cattle. As mentioned above, mycotoxin presence will not be alleviated, however stabilizing the crop can ensure the issue won’t worsen. Seal the crop as quickly as possible after harvest and use a research proven bacterial inoculant, acid or chemical preservative to stabilize the crop quickly after sealing. Monitor bag, bunker, and pile silo plastic for holes throughout the year and seal those you find quickly. Seal the ends and/or edges with added weight to minimize air infiltration into the silage or grain.

For more information on properly storing grain and to download a fact sheet on the subject, CLICK HERE.

 

What impact will ear and stalk rot have on my cows? 

Ear and stalk rots do not equate to animal health issues, however mycotoxins or wild yeast contamination which may be produced by or accompany ear and stalk rots can affect rumen health and digestion. As described above, manage the crop to the best of your ability from harvest through storage. Upon feed out, introduce heavily ear and stalk rot-laden feeds slowly into the ration. Test the suspicious crop for mold, yeast and vomitoxin content as you begin feeding it and closely monitor dry matter intakes and animal health. 

If animal health issues or contaminant levels for yeast and mycotoxin are recognized, consult with your nutrition and veterinary advisor as to the best plan of attack. Dilute the suspicious feed to a lesser amount if possible or consider research backed nutritional additives which can lessen yeast or mycotoxin impact on health. 

 

References

This article is an adaptation of the following resource:

Smith, D.L. 2016. Corn Stalk Rots and Ear Rots: A Double Whammy for Wisconsin Corn Farmers. 

 

 

What to Expect from Stalk Rot and Mycotoxins in Severely Diseased and Damaged Corn

/in , , , , , , /by

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Corn is looking pretty rugged in many areas of the Wisconsin corn belt. Areas in southern, southwestern, and south-central Wisconsin have experienced major foliar disease epidemics including the new disease, tar spot. Areas in eastern, east-central, and south-central Wisconsin have also seen heavy flooding and storm damage in corn fields. We have seen fields severely diseased, experiencing stalk rot, lodged, flooded – you name it, it has been a challenging finish to a season that had much promise.

How is tar spot affecting stalk integrity?

Figure 1. Stalks lodged due to reduced stalk integrity.

For corn foliar diseases such as northern corn leaf blight (NCLB) and gray leaf spot (GLS), it is well known that high severity can lead to stalk integrity issues. As foliage is damaged, less photosynthetic capacity is available from the leaves to produce carbohydrates for the plant. To fill an ear of corn, carbohydrates are needed from somewhere. In corn where the foliage is significantly damaged, the stalks become a considerable source to fill out the ear (a sink for nutrients). This leaves the stalk tissues devoid of carbohydrates leading to cell death and subsequent colonization of the stalk by fungal pathogens who are taking the opportunity to feed on a weak stalks. Thus, it isn’t uncommon to see stalk rots like Gibberella stalk rot, Fusarium stalk rot or Anthracnose stalk rot at higher incidence where high foliar disease pressure was observed (Fig.1). Where you find stalk rots, you often find root rots caused by the same pathogens. Root rot and stalk rot often go hand-in-hand.

Other causes for loss in stalk integrity can include large ears (nutrient sinks) that the plant can’t fill out, without using some of the stalk resources. In 2018 we saw many fields where the crop was moving through growth stages quickly and setting what appeared to be good yields. However, weather conditions changed midseason, with wet weather and more cloud cover, combined with nitrogen issues in some fields. This led to large ears that needed to be filled out, with again, limited photosynthetic capacity. The stalks were scavenged for carbohydrate, leaving them, again, with limited integrity.

Figure 2. An entire field lodged due to significant stalk rot

Now throw in some tar spot. Yet, another foliar disease that can limit photosynthetic capacity of the corn plant. We have observed many fields with significant stalk integrity issues. Whether just tar spot, or tar spot combined with GLS, NLCB, and/or stalk scavenging just for carbohydrates – stalks are in bad shape in many areas of Wisconsin. This is resulting in significant lodging issues in many fields, especially those hit with bad storms over the last several weeks (Fig. 2). Harvesting fields with low stalk integrity early will be key to protect yield potential. Conduct a “pinch” test or “push” test to determine which field have lower stalk integrity. Simply pinch stalks or push stalks to a 30 degree angle. Those plant that are soft and easily pinch or don’t pop back up after pushing, have stalk integrity issues. If 30-50% or more of these plants are identified with stalk integrity problems, they should be harvested first, to prevent yield losses from lodging.

What about tar spot, lodged corn, and mycotoxins?

Mycotoxins have not been implicated in the organisms reported to cause tar spot in Latin America. However, that doesn’t mean that other organisms that cause mycotoxins might not be present on harvested grain or silage. As plants dry down they can no longer actively fight fungal infection. We have looked at many brown and drying leaf samples from corn plants with tar spot. We do find many other fungal organisms, including Fusarium-organisms, which can produce mycotoxins. So while tar spot itself may not lead to mycotoxins, opportunistic fungi that colonize secondarily may result in elevated mycotoxin levels.

In addition, corn that has lodged and is in contact with the wet and saturated ground is at risk of being colonized by organisms that produce mycotoxins. Many of the known mycotoxin-producing fungi are found in the soil and on residue on the surface of the soil. If lodged corn is in contact with the ground and there is good moisture, it is possible that the ear and plant are being colonized and mycotoxins are being produced. So while your combine might be able to pick a plant up and harvest the ear, beware that it might be heavily colonized with organisms that produce mycotoxins. If taking corn for silage, lodged plants run the risk of significant hygiene issues in the bunker, including mycotoxins issues.

Where else can mycotoxins come from?

Figure 3. Diplodia ear rot on an ear of corn.

Corn ears don’t have to touch the ground to be infected with ear-rot fungi, they can also be colonized by ear-rot fungi through the silks. Given the kind of crazy year we have had, ear rot might be a significant concern in fields that saw erratic weather this season. Ear rots caused by fungi in the groups Diplodia (Fig. 3), Fusarium, and Gibberella will be the most likely candidates to watch for as you begin harvest.  Fusarium and Giberrella are typically the most common fungi on corn ears in Wisconsin.  This group of fungi not only damage kernels on ears, but can also produce mycotoxins.  The toxins of main concern produced by these organisms are fumonisins and vomitoxin and can threaten livestock that are fed contaminated grain.  Thus grain buyers actively test for mycotoxins in corn grain, and feed managers monitor silage for mycotoxin levels to be sure they are not above certain action levels established by the U.S. Food and Drug Administration (FDA).

The FDA has established maximum allowable levels of fumonisins in corn and corn products for human consumption ranging from 2-4 parts per million (ppm).  For animal feed, maximum allowable fumonisin levels range from 5 ppm for horses to 100 ppm for poultry. Vomitoxin limits are 5 ppm for cattle and chickens and 1 ppm for human consumption.

For more information about ear rots and to download a helpful fact sheet produced by a consortium of U.S. corn pathologists, CLICK HERE.

How do I reduce mycotoxin risks at harvest?

Before harvest, farmers should check their fields to see if moldy corn is present. Sample at least 10-20 ears in five locations of your field. Pull the husks back on those ears and observe how much visible mold is present. If 30% or more of the ears show signs of Gibberella or Fusarium ear rot then testing of harvested grain is definitely advised. If several ears show 50-100% coverage of mold testing should also be done. Observe grain during harvest and occasionally inspect ears as you go. This will also help you determine if mycotoxin testing is needed.

If substantial portions of fields appear to be contaminated with mold, it does not mean that mycotoxins are present and vice versa. For example, Diplodia ear rot does not produce mycotoxins. However, if you are unsure, then appropriate grain samples should be collected and tested by a reputable lab.  Work with your corn agronomist or local UW Extension agent to ensure proper samples are collected and to identify a reputable lab.

For more information on mycotoxins and to download a fact sheet, CLICK HERE.

Helpful information on grain sampling and testing for mycotoxins can be found by CLICKING HERE.

For a list of laboratories that can test corn grain for mycotoxins, consult Table 2-16 in UW Extension publication A3646 – Pest Management in Wisconsin Field Crops.

How should I store corn from fields with ear rots and mold?

If you observe mold in certain areas of the field during harvest, consider harvesting and storing that corn separately, as it can contaminate loads; the fungi causing the moldy appearance can grow on good corn during storage.  Harvest corn in a timely manner, as letting corn stand late into fall promotes Fusarium and Gibberella ear rots.  Avoid kernel damage during harvest, as cracks in kernels can promote fungal growth.  Also, dry corn properly as grain moisture plays a large roll in whether corn ear rot fungi continue to grow and produce mycotoxins.  For short term storage over the winter, drying grain to 15% moisture and keeping grain cool (less than 55F) will slow fungal growth.  For longer term storage and storage in warmer months, grain should be dried to 13% moisture or less. Fast, high-heat drying is preferred over low-heat drying. Some fungi can continue to grow during slow, low-heat drying. Also, keep storage facilities clean.  Finally, mycotoxins are extremely stable compounds: freezing, drying, heating, etc. do not degrade mycotoxins that have already accumulated in grain. While drying helps to stop fungal growth, any mycotoxins that have already accumulated prior to drying will remain in that grain. The addition of acids and reducing pH can reduce fungal growth but will not affect mycotoxins that have already accumulated in harvested grain.

For more information on properly storing grain and to download a fact sheet on the subject, CLICK HERE.

References

Munkvold, G.P. and White, D.G. Compendium of Corn Diseases, 4th Edition. APS Press.

In addition, This article is a compilation of the following previously written resources:

Smith, D.L. 2016. Wisconsin Late-Season Corn Disease Update. /2016/09/07/wisconsin-late-season-corn-disease-update/.

Smith, D.L. and Mitchell, P. D. 2016. Wet Wisconsin: Moldy Corn and Crop Insurance. http://ipcm.wisc.edu/blog/2016/09/wet-wisconsin-moldy-corn-and-crop-insurance/.

 

 

Corn Stalk Rots and Ear Rots: A Double Whammy for Wisconsin Corn Farmers

/in , , , /by

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Figure 1. Anthracnose stalk rot symptoms in a cut corn stalk.

Figure 1. Anthracnose stalk rot symptoms in a cut corn stalk.

The 2016 growing season is going to end with many challenges for Wisconsin farmers. The excessively wet weather has slowed or ended harvest of corn silage and grain harvest has barely started in much of the state. Couple this with warm and wet weather is August and we have a double whammy of stalk rot and ear rot issues to contend with this fall.

What is the Primary Stalk Rot Issue in Wisconsin?

Anthracnose stalk rot (Fig. 1) has been a major concern for Wisconsin corn growers this season. Anthracnose stalk rot is typically worse in fields in a corn-on-corn rotation, and/or no-tilled, and planted to a susceptible hybrid. We have observed several fields with significant lodging and wind damage where anthracnose stalk rot has advanced quickly (Fig. 2). In other fields lodging has been minimal, but some anthracnose stalk rot can be found. In addition, to stalk rot anthracnose, we have also observed Fusarium stalk rot and Gibberella stalk rot. The occurrence of these stalk rots has been much less than that of anthracnose stalk rot.

Figure 2. Corn field with considerable lodging due to anthracnose stalk rot.

Figure 2. Corn field with considerable lodging due to anthracnose stalk rot.

Why did stalk rots start so early in 2016?

The late onset of northern corn leaf blight (NCLB) this season likely contributed to increased stalk rot this season. It has been documented that late season increase in leaf blight diseases, such as NCLB, can cause increased stress that leads to higher levels of stalk rot. Also, ears were large and yield potential appeared high this season. These large yield potentials may have led to increased scavenging of resources from stalks leading to more stalk stress. These stress issues, combined with excessively moist and mild conditions, likely led to the occurrence of higher levels of stalk rot in 2016.

What should I do if I have a field with stalk rot?

In fields were stalk rot is an issue, harvest as early as possible to avoid yield losses from lodging. Delaying harvest will increase the likelihood of lodging which will increase harvesting issues. Once conditions dry enough to allow combines to run, fields with higher levels of stalk rot and/or lodging should be prioritized for harvest.

What should I do about stalk rot for next season?

Management of anthracnose stalk rot (and for any of the stalk rots) is multi-faceted. First, choose hybrids with the best resistance available. Hybrids that also have good resistance to foliar diseases will also offer an advantage when managing stalk rot, as foliar disease can stress corn plants and lead to increased risk of anthracnose stalk rot. Cultural practices such as crop rotation and tillage to manage surface residue can also help. Other practices that reduce plant stress such as balanced fertilization, proper planting population, providing suitable drainage, and using well adapted hybrids for your location will reduce the risk of anthracnose stalk rot.

Fungicides are not recommended for managing anthracnose stalk rot. Attempts to use fungicides to manage anthracnose stalk rot often result in high variability and little translation to a yield advantage. In 2015 we conducted a corn fungicide trial where anthracnose stalk rot was detected at harvest. While higher levels of stalk rot were observed, and some treatments did lead to a significant reduction in stalk rot severity, no differences in lodging or yield were identified among the treatments. To view results of this 2015 trial, click here and scroll down to pages 2 and 3.

What corn ear rots and mycotoxins should I watch out for?

Figure 1. Moldy growth on a corn ear caused by the Diplodia ear rot fungus.

Figure 3. Moldy growth on a corn ear caused by the Diplodia ear rot fungus.

With all the wet weather late in the 2016 season, several ear rots have appeared in corn around much of the state. Ear rots caused by fungi in the groups Diplodia (Fig. 3), Fusarium, and Gibberella (Fig. 4) will be the most likely candidates to watch for as you begin harvest.  Fusarium and Giberrella are typically the most common fungi on corn ears in Wisconsin.  This group of fungi not only damage kernels on ears, but can also produce toxins called mycotoxins.  These toxins (fumonisins and vomitoxin) can threaten livestock that are fed contaminated grain.  Thus grain buyers actively test for mycotoxins in corn grain to monitor mycotoxin levels to be sure they are not above certain action levels established by the U.S. Food and Drug Administration (FDA).

The FDA has established maximum allowable levels of fumonisins in corn and corn products for human consumption ranging from 2-4 parts per million (ppm).  For animal feed, maximum allowable fumonisin levels range from 5 ppm for horses to 100 ppm for poultry. Vomitoxin limits are 5 ppm for cattle and chickens and 1 ppm for human consumption.

Figure 4. Symptoms and signs of Gibberella ear rot of corn.

Figure 4. Symptoms and signs of Gibberella ear rot of corn.

Diplodia ear rot (Fig. 5) is not as common in Wisconsin. However, the weather pattern this season was favorable for occurrence of this disease. This disease is often more severe in years where dry weather precedes silking, followed by wet weather immediately after silking. Diplodia ear rot does not produce mycotoxins. While this disease does not result in mycotoxin accumulation, it can cause grain yield loss and quality issues.

For more information about ear rots and to download a helpful fact sheet produced by a consortium of U.S. corn pathologists, CLICK HERE.

Figure 5. Signs and symptoms of the Diplodia ear rot fungus inside a split corn ear.

Figure 5. Signs and symptoms of the Diplodia ear rot fungus inside a split corn ear.

How do I reduce mycotoxin risks at harvest?

Before harvest, farmers should check their fields to see if moldy corn is present. Sample at least 10-20 ears in five locations of your field. Pull the husks back on those ears and observe how much visible mold is present. If 30% or more of the ears show signs of Gibberella or Fusarium ear rot then testing of harvested grain is definitely advised. If several ears show 50-100% coverage of mold testing should also be done. Observe grain during harvest and occasionally inspect ears as you go. This will also help you determine if mycotoxin testing is needed.

If substantial portions of fields appear to be contaminated with mold, it does not mean that mycotoxins are present and vice versa. Remember, Diplodia ear rot does not produce mycotoxins. However, if you are unsure, then appropriate grain samples should be collected and tested by a reputable lab.  Work with your corn agronomist or local UW Extension agent to ensure proper samples are collected and to identify a reputable lab.  If tests show high levels of mycotoxins in grain, that grain SHOULD NOT BE BLENDED with non-contaminated corn.

For more information on mycotoxins and to download a fact sheet, CLICK HERE.

Helpful information on grain sampling and testing for mycotoxins can be found by CLICKING HERE.

For a list of laboratories that can test corn grain for mycotoxins, consult Table 2-16 in UW Extension publication A3646 – Pest Management in Wisconsin Field Crops.

How should I store corn from fields with ear rots and mold?

If you observe mold in certain areas of the field during harvest, consider harvesting and storing that corn separately, as it can contaminate loads; the fungi causing the moldy appearance can grow on good corn during storage.  Harvest corn in a timely manner, as letting corn stand late into fall promotes Fusarium and Gibberella ear rots.  Avoid kernel damage during harvest, as cracks in kernels can promote fungal growth.  Also, dry corn properly as grain moisture plays a large roll in whether corn ear rot fungi continue to grow and produce mycotoxins.  For short term storage over the winter, drying grain to 15% moisture and keeping grain cool (less than 55F) will slow fungal growth.  For longer term storage and storage in warmer months, grain should be dried to 13% moisture or less. Fast, high-heat drying is preferred over low-heat drying. Some fungi can continue to grow during slow, low-heat drying. Also, keep storage facilities clean.  Finally, mycotoxins are extremely stable compounds: freezing, drying, heating, etc. do not degrade mycotoxins that have already accumulated in grain. While drying helps to stop fungal growth, any mycotoxins that have already accumulated prior to drying will remain in that grain. The addition of acids and reducing pH can reduce fungal growth but will not affect mycotoxins that have already accumulated in harvested grain.

For more information on properly storing grain and to download a fact sheet on the subject, CLICK HERE.

References

This article is a compilation of the following previously written resources:

Smith, D.L. 2016. Wisconsin Late-Season Corn Disease Update. /2016/09/07/wisconsin-late-season-corn-disease-update/.

Smith, D.L. and Mitchell, P. D. 2016. Wet Wisconsin: Moldy Corn and Crop Insurance. http://ipcm.wisc.edu/blog/2016/09/wet-wisconsin-moldy-corn-and-crop-insurance/.

Wisconsin Late-Season Corn Disease Update

/in , , , , /by

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Figure 1. Anthracnose stalk rot symptoms in a cut corn stalk.

Figure 1. Anthracnose stalk rot symptoms in a cut corn stalk.

NCLB and Anthracnose Stalk Rot

As corn silage harvest has begun and the corn grain crop is finishing, there have been some disease issues of note in Wisconsin. Northern corn leaf blight (NCLB) activity has picked up quickly over the last several weeks. This is due to the fact that the weather has become much cooler and has remained wet. These conditions are favorable for the fungus. You will remember that NCLB was observed very early this season. See my previous post on this topic by clicking here.The hotter and dryer weather we saw mid-season was not only good for corn growth, but it kept the NCLB pressure minimal during the critical time of silking and pollination. As stated in the fourth edition of the “Compendium of Corn Diseases” (Carson, 2016) direct yield losses from NCLB are typically minimal if infection is moderate or delayed until 6 weeks after silking. Therefore, the expected direct yield loss from NCLB in Wisconsin in 2016 is expected to be low, due to its late onset.

Figure 2. Corn field with considerable lodging due to anthracnose stalk rot.

Figure 2. Corn field with considerable lodging due to anthracnose stalk rot.

Certainly, there are other issues to consider with this late onset of NCLB. Dry-down will be accelerated. If you have a considerable epidemic in silage corn, then it would be advisable to try to chop as quickly as possible or consider taking the crop as high-moisture corn. Another issue to consider is the fact that a late-season NCLB epidemic can increase the risk for stalk rot issues. We have observed earlier than typical onset of anthracnose stalk rot this season (Fig. 1). Anthracnose stalk rot has been observed in many fields, with a range in severity dependent on the hybrid resistance and field history. Fields in a corn-on-corn rotation, and/or no-tilled, and planted to a susceptible hybrid are at high risk of severe symptoms. We have observed several fields with significant lodging and wind damage where anthracnose stalk rot has advanced quickly (Fig. 2). In other fields lodging has been minimal, but some anthracnose stalk rot can be found.

Management of anthracnose stalk rot is multi-faceted. First, choose hybrids with best resistance available. Hybrids that also have good resistance to foliar diseases will also offer an advantage when managing stalk rot, as foliar disease can stress corn plants and lead to increased risk of anthracnose stalk rot. Cultural practices such as crop rotation and tillage to manage surface residue can also help. Other practices that reduce plant stress such as balanced fertilization, proper planting population, providing suitable drainage, and using well adapted hybrids for your location will reduce the risk of anthracnose stalk rot. Finally, in fields were stalk rot is an issue, harvest as early as possible to avoid yield losses from lodging.

Fungicides are not recommended for managing anthracnose stalk rot. Attempts to use fungicides to manage anthracnose stalk rot often result in high variability and little translation to a yield advantage. In 2015 we conducted a corn fungicide trial where anthracnose stalk rot was detected at harvest. While higher levels of stalk rot were observed, and some treatments did lead to a significant reduction in stalk rot severity, no differences in lodging or yield were identified among the treatments. To view results of this 2015 trial, click here and scroll down to pages 2 and 3.

Bacterial leaf streak – A new disease of corn in the U.S.

Bacterial leaf streak (BLS) of corn has recently been reported for the first time on corn in the U.S. The first reports were in Nebraska with subsequent reports coming in from other states in the U.S. corn belt including Iowa, Illinois, Colorado, and Kansas. Efforts are underway in Wisconsin to monitor for the disease. As of this writing, BLS has not been found in Wisconsin. However, survey and scouting efforts are continuing, to monitor for this disease.

Bacterial leaf streak is caused by a bacterium named Xanthomonas vasicola pv. vasculorum. Very little is understood about this disease on corn, as it is so new. This pathogen presents no risk to humans or animals and there is little evidence to suggest that it will have an adverse effect on corn yield and quality. You can click here to read the USDA APHIS Statement on Xanthomonas vasicola pv. vasculorum. To learn more about the disease and to watch a video by Dr. Tamra Jackson-Ziems at the University of Nebraska CLICK HERE. Helpful information and hints on initially diagnosing BLS can be found HERE.

If you suspect that you have BLS in your corn crop in Wisconsin, leaf samples of corn plants can be sent in a sealed plastic bag with NO added moisture to the University of Wisconsin Plant Disease Diagnostic Clinic (PDDC). Information about the clinic and how to send samples can be found by CLICKING HERE.

References

Esker, P. 2016. Anthracnose stalk rot: in “Farmers Guide to Corn Diseases” Edited by: K. Wise, D. Mueller, A. Sisson, D. Smith, C. Bradley, and A. Robertson. APS PRESS.

M.L. Carson. 2016. Northern Corn Leaf Blight: in “Compendium of Corn Diseases, Fourth Edition.” Edited by: G.P. Munkvold and D.G. White. APS PRESS.

 

Disease Considerations for Soybean and Corn Harvest

/in , , , , , , /by

Damon L. Smith – Extension Field Crops Pathologist, University of Wisconsin

As the fall is approaching and crop harvest plans are being made, it is important to continue to assess disease issues in corn and soybean. These assessments aren’t being made in order to make plans for in-field management, but to potentially improve the quality of grain that is harvested.

Some Diseases to Consider in Corn at Harvest

Figure 1. Gibberella stalk rot on corn. Severe stalk rot on the left and less severe stalk rot on the right.

Figure 1. Gibberella stalk rot on corn. Severe stalk rot on the left and less severe stalk rot on the right.

Now is the best time to begin scouting corn for stalk rot issues and also fungal ear rot potential. Diseases such as Anthracnose stalk rot and Gibberella stalk rot are becoming apparent in corn.  Inspect the stalks integrity on the outside.  Be sure to squeeze the outside of the stalk to gauge the potential severity of the rot on the inside of the stalk.  Cut a few stalks from diverse areas of the field to see how rotted stalks might be. In figure 1, the stalk on the left has a severe case of Gibberella stalk rot, while the stalk on the right is far less rotted.  The more severely rotted stalks are, the more likely they will lodge.  Therefore timely harvest is important. Growers should target harvest on fields with severe stalk rot before fields that have less stalk rot, in order to minimize harvest losses due to lodging.

Figure 2. Diplodia ear rot.

Figure 2. Diplodia ear rot.

Ear rots can also be an issue at harvest time. Fusarium ear rot, Gibberella ear rot, and Diplodia ear rot (Fig. 2) are just a few that can damage corn in Wisconsin. Ear rots are becoming evident in some corn I have scouted in the last week or so.  It will be critical to check fields in the next several weeks in order to make decisions on what fields to harvest first.  Harvest priority should be placed on fields with a high level of ear rot.  As corn stands late into the fall, certain ear rot fungi can continue to grow, damage ears, and cause increases in mycotoxins in grain. The quicker these fields dry and can be harvested, the more likely the losses due to ear rot and mycotoxin accumulation can be minimized.

Soybean Disease Considerations at Harvest

Figure 3. Sclerotia of the white mold fungus inside a soybean stem.

Figure 3. Sclerotia of the white mold fungus inside a soybean stem.

In Wisconsin, the main disease to consider when making harvest plans in soybean is white mold. White mold is present in some soybean fields in the state and has caused considerable damage in a few of those fields. Remember that the white mold fungus not only causes stem blight and damage, but also causes the formation of sclerotia (fungal survival structures that look like rat droppings) on and in soybean stems (Fig. 3). These scelrotia serve as the primary source of fungal inoculum for the next soybean crop. They also get caught in combines during harvest. These sclerotia can then be spread in combines to other fields that might not be infested with the white mold fungus.  Therefore, it is important to harvest non-infested soybean fields first, followed by white mold-infested fields, to be sure the combine does not deposit any residual sclerotia in the non-infested fields.  If this is not an option and you must harvest white mold infested fields before non-infested fields, be sure to clean the combine between fields.

For more information about white mold management in soybean you can click here and scroll down to “white mold” or watch a video by clicking here.