Updated! Fungicide Resistance Management in Corn, Soybean and Wheat in Wisconsin

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

Richard Proost, Regional Agronomist, University of Wisconsin-Madison, Nutrient and Pest Management Program

Mimi Broeske, Senior Editor, University of Wisconsin-Madison, Nutrient and Pest Management Program

Updated for 2020! Fungicides are important tools for managing plant diseases in corn, soybean, and wheat. Unlike insecticides and herbicides that are used to kill insects and weeds, fungicides act as a barrier to protect healthy plant tissues from infection by fungi.  But resistance to fungicides can become a real problem if not managed well. This 8 page publications has background information about resistance, reviews the relevant FRAC codes, management guidelines and has two significantly updated, handy tables that list fungicides by FRAC code and registered crop.

You can download a PDF version of “A3878 – Fungicide Resistance Management in Corn, Soybean and Wheat in Wisconsin” by clicking here!

Wisconsin Winter Wheat Disease Update – May 6, 2020

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

Brian Mueller, Assistant Field Researcher, Department of Plant Pathology, University of Wisconsin-Madison

The Badger Crop Docs have started scouting wheat in south-central Wisconsin over the past few days. In general the crop needs some heat and is moving slow. However, the overall health looks good.

The mild winter of 2019/2020 was needed as a lot of the wheat was planted late and into less than ideal conditions last fall, due to the extremely wet weather. The mild winter spared stands that weren’t well established, including some of our own research plots. Most fields we have been in are still tillering.

No visible disease is present in any of the fields we have scouted. However, it will be important to keep visiting fields and scout. Also be sure to pay attention to local extension and follow our blog to keep up to speed on any developments as we move forward. The biggest disease concerns for Wisconsin wheat will be stripe rust and Fusarium head blight. You will want to be prepared to manage these diseases if they should become problematic. You can keep track of the status of these diseases nationally by visiting the Stripe Rust Ag Monitor and the Fusarium Head Blight Risk Tool The key to managing both diseases is to catch them before they arrive. Both of these resources can be used to help you anticipate the arrival of these diseases in your field. Continue to check back here regularly for more reports and scout, scout, scout!

Sporecaster Smartphone App Updated for 2020

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

Roger Schmidt, Nutrient and Pest Management Program, University of Wisconsin-Madison

The Sporecaster smartphone app for predicting white mold epidemics in soybean has been updated for 2020. The new version is now available for download, or has been updated on your phone if you have automatic updates turned on. Updates include modifications internally and also a change on the user interface. These modifications were made based on feedback from users and our own internal testing over the winter of 2019/2020.

The most substantial changes include modifications to how we handle weather internally. The modifications were made to improve accuracy of the prediction when using GPS-referenced weather data. We also added the ability for the user to now adjust the action threshold for each individual location. This can be done based on your prior knowledge of severity at that location or the amount of risk you feel comfortable with. If you don’t know how severe past epidemics have been, then we suggest leaving the action threshold at its default.

We have also assembled several short YouTube videos describing the changes made for 2020 and also a bit about the science behind the app. The new version (version 1.35) of the Sporecaster app can be downloaded for the iPhone on the App Store here and the Android version can be downloaded from Google Play here.

Check back to badgercropdoc.com often during the season as we will also provide white mold updates on risk and commentary. Also follow us on Twitter @badgercropdoc for the latest in-season updates for field crops in Wisconsin. Don’t forget to subscribe to the Wisconsin Crop Manager for valuable crop updates.

2019 Wisconsin Field Crops Pathology Fungicide Tests Summary Now Available

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

Brian Mueller, Assistant Field Researcher, Department of Plant Pathology, University of Wisconsin-Madison

Each year the Wisconsin Field Crops Pathology Program conducts a wide array of fungicide tests on alfalfa, corn, soybeans, and wheat. These tests help inform researchers, practitioners, and farmers about the efficacy of certain fungicide products on specific diseases. The 2019 Wisconsin Field Crops Fungicide Test Summary is now available. These tests are by no means an exhaustive evaluation of all products available, but can be used to understand the general performance of a particular fungicide in a particular environment. Keep in mind that the best data to make an informed decision, come from multiple years and environments. To find fungicide performance data from Wisconsin in other years, visit the Wisconsin Fungicide Test Summaries page. You can also consult publication A3646 – Pest Management in Wisconsin Field Crops to find information on products labeled for specific crops and efficacy ratings for particular products. Additional efficacy ratings for some fungicide products for corn foliar fungicidessoybean foliar and seed-applied fungicides, and wheat foliar fungicides can be found on the Crop Protection Network website.

Mention of specific products in these publications are for your convenience and do not represent an endorsement or criticism. Remember that this is by no means a complete test of all products available.  You are responsible for using pesticides according to the manufacturers current label. Some products listed in the reports referenced above may not actually have an approved Wisconsin pesticide label. Be sure to check with your local extension office or agricultural chemical supplier to be sure the product you would like to use has an approved label.  Follow all label instructions when using any pesticide. Remember the label is the law!

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

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. 



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. 



Soybean Disease Considerations As the 2019 Harvest Approaches

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

Shawn P. Conley, Professor and Extension Soybean and Small Grains Agronomy Specialist, University of Wisconsin-Madison 

As the days get shorter and the temperatures start to cool, soybean harvest is on everyone’s minds. As the crop is maturing and beginning the early stages of drydown, calls about diseases are starting to come in. In the southern third of the state most of the calls have centered on sudden death syndrome or SDS. To the north, most questions pertain to Sclerotinia stem rot or white mold. Below we will discuss SDS in some detail and provide a brief update on the white mold situation as well as elaborate on seed decay issues that we should pay attention to as we begin harvest.

Scout for Sudden Death Syndrome (SDS)

Figure 1. Symptoms of sudden death syndrome on soybeans

The first noticeable symptoms of SDS (Fig. 1) are chlorotic (i.e., yellow) blotches that form between the veins of soybean leaflets. These blotches expand into large, irregular, chlorotic patches (also between the veins), and this chlorotic tissue later dies and turns brown. Soon thereafter entire leaflets will die and shrivel. In severe cases, leaflets will drop off leaving the petioles attached. Taproots and below-ground portions of the stems of plants suffering from SDS, when split open, will exhibit a slightly tan to light brown discoloration of the vascular (i.e., water- conducting) tissue. The pith will remain white or cream-colored. In plants with advanced foliar symptoms of SDS, small, light blue patches will form on taproots and stems below the soil line. These patches are spore masses of the fungus that causes the disease.

Figure 2. Symptoms of BSR in soybean stems compared with a healthy soybean stem in the center.

Foliar symptoms of SDS can be confused with those of brown stem rot. However, in the case of brown stem rot (BSR), the pith of affected soybean plants will be brown (Fig. 2). In addition, roots and lower stems of plants suffering from BSR will not have light blue spore masses.

Once symptoms of SDS are evident, yield losses are inevitable. Yield losses can range from slight to 100%, depending on the soybean variety being grown, the plant growth stage at the time of infection and whether or not SCN is present in a field. If SDS occurs after reproductive stages (R5 or R6) impact on yield is usually less compared to the development of SDS at flowering, which can lead to substantial yield losses. When SCN is present, the combined damage from both diseases can be substantially more than the sum of the damage expected from the individual diseases.

SDS is caused by the soilborne fungus, Fusarium virguliforme (synonym: F. solani f. sp. glycines). F. virguliforme can overwinter freely in the soil, in crop residue, and in the cysts of SCN. The fungus infects soybean roots (by some reports as early as one week after crop emergence), and is generally restricted to roots as well as stems near the soil line. F. virguliforme does not invade leaves, flowers, pods or seeds, but does produce toxins in the roots that move to the leaves, causing SDS’s characteristic foliar symptoms.

SDS cannot be controlled once plants have been infected. Foliar fungicides have NO effect on the disease. Recently a new seed treatment has been identified that has efficacy against SDS. The active ingredient fluopyram can be found in the seed treatment iLeVo and is rated “very good” in multi-state trials. Other methods of control include using SDS-resistant varieties whenever possible in fields with a history of the disease; however, keep in mind that SDS-resistant varieties with maturity groups suitable for Wisconsin and other northern regions (groups I and II) can be limited. If SDS and SCN are both problems in the same field, planting an SCN-resistant soybean variety may also be beneficial in managing SDS. Do not delay planting soybeans to avoid symptoms of SDS.  In Wisconsin, it has been demonstrated that the benefits to yield when planting early outweigh the benefits of reduced SDS symptoms if planting is delayed. Improve soil drainage by using tillage practices that reduce compaction problems. Rotation, while useful in managing other soybean diseases, does not appear to significantly reduce the severity of SDS. Even after several years of continuous production of corn, F. virguliforme populations typically are not reduced substantially. Research from Iowa State University has shown that corn (especially corn kernels) can harbor the SDS pathogen.

For more information CLICK HERE to download a full color fact sheet on SDS. A short video on SDS can also be viewed by CLICKING HERE.

Know Where White Mold is in 2019

Figure 3. White Mold in a Soybean Field

Symptoms of white mold (Fig. 3) are becoming pretty apparent in some parts of central and northern Wisconsin. White fluffy growth (mycelium) is readily evident over the last week while weather has been humid and wet. Incidence in the northern half of the state is high in some fields. Fields in the northeast and northwest corridors of the state seem to be hardest hit, but severity is highly variable from one field to the next.  This is likely due to a combination of variety and micro-environments that can influence the disease. Most of the soybean crop is at the R6 growth stage, with some earlier maturing fields are almost through R7 or have made it to R8. Now the question is how much soybean yield might I lose from white mold?

Research has demonstrated that for every 10% increase in the number of plants that are infected with white mold at the R7 growth stage, you can expect between 2 to 5 bushels of yield loss. Thus, fields with low levels (say 3% incidence) will likely experience no detectable yield loss while fields with 20% incidence could lose as much as 10 bushels per acre.

What should I do if I see white mold in my soybean field now?

The first step is to get out and survey your fields for white mold. It is a good idea to determine how much white mold you have in your fields, so you can make some educated harvest decisions. One way to move white mold from one field to the next is via combines. You could clean your combine between each field, but this can be time consuming. So by determining which fields have no white mold and which fields have the most white mold, you can develop a logical harvest order by beginning your harvest on fields with no white mold and working your way to the heavily infested fields. This will help reduce spread of the white mold fungus to fields that aren’t infested. You can also make some decisions on your rotation plan and future soybean variety choices based on these late season observations.

If you would like to learn more about white mold and management of this disease, CLICK HERE to download a fact sheet from the crop protection network. You can also watch a short video about white mold by CLICKING HERE.

Watch for Phomopsis Seed Decay at Harvest

Figure 4. Severe Phomopsis seed decay. Photo Credit: Craig Grau, University of Wisconsin-Madison.

If you remember the 2018 harvest season, you are probably having nightmares right now. Extended rainy periods in October significantly delayed harvest and subjected the standing soybean crop to significant seed decay issues. Watch out for rainy periods during the 2019 harvest. If we end up in these wet patterns again in 2019, we could have a repeat of poor seed quality going into 2020. 

What does Phomopsis seed decay look like?

The fungus that causes Phomopsis seed decay (Fig. 4) can infect soybean plants early in the season and colonize pods and infect seeds near, or at maturity. Infected seed will often be shriveled or undersized and can have a white or chalky appearance. If pods are opened in the field a white cottony “mold” (different than that of white mold) can be observed. Infected seed can pass the Phomopsis seed decay fungus on in seedlings of the next soybean crop. Therefore, it is important to identify Phomopsis seed decay especially in soybean-seed fields.

What conditions are favorable for Phomopsis seed decay?

Warm and wet weather during pod fill and maturity favor the development of Phompsis seed decay. The conditions have been prevalent in areas of Wisconsin in 2019, especially where planting was delayed. Soybean varieties that mature early are also more prone to Phompsis seed decay. Other stresses such as nutrient deficiencies or virus infections can also increase the occurrence of Phompsis seed decay. Infested seed is a likely source of Phompsis seed decay, however, the fungus can survive on soybean debris and certain weeds like velvetleaf.

How should I handle soybeans with Phomopsis seed decay?

Scout fields before harvest to get an idea of how much Phomopsis seed decay you might have in a field. Scout multiple plants in at least 5 locations in a field, opening pods to determine if Phomopsis seed decay is present. In fields where Phomopsis seed decay is observed, harvest should be prioritized as soon as combines can enter the field. Seed infected with the Phomopsis seed decay fungus will continue to rot in the pod until they are harvested.

How should I manage Phomopsis seed decay in the 2020 soybean crop?

Soybean seed producers should try to clean seed to achieve less than 20% damaged seed in a seed lot. Multiple cleaning steps might be needed to achieve this level. While testing germination now is recommended, remember that testing germination again next spring and potentially just prior to delivery will also help you to understand the germination rate and determine if other management strategies need to be employed such as fungicidal seed treatments.

Seed treatments can help improve the germination rate of seed damaged by Diaporthe. However, you will need more than metalaxyl or mefonoxam active ingredients in your seed treatment. Metalaxyl and mefonoxam are good against Phytophthora and Pythium, but not effective against other organisms, like Diaporthe. Seed treatments with Phomopsis on the label have an additional fungicide (either a DMI or SDHI). Table 3-8 of the publication A3646 – Pest Management in Wisconsin Field Crops has a table of some of the seed treatments with Phomopsis on the label. Also available, as stated above, is the seed treatment efficacy table from the Crop Protection Network (CPN). You can download that publication by clicking here.

As farmers begin to look forward to the 2020 growing season we also recommend that you double check the percent germination on every seed lot prior to planting and adjust your seeding rates accordingly. Here are our recommendations for soybean seeding rate based on yield potential and white mold risk: The Soybean Seeding Rate Conundrum.

An Additional Phomopsis Seed Decay Resource

A fact sheet about Pod and Stem blight and Phomopsis seed decay has been developed by a consortium of soybean extension pathologists. You can download that fact sheet by clicking here.

Corn Disease and Nutritive Value Considerations for the 2019 Silage Harvest

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

The 2019 silage corn harvest is finally starting to ramp up in Wisconsin. With the excitement of finally getting into the field comes the need to be aware of the corn disease situation this season. As most of you will remember, the 2018 field season was an extreme challenge when it came to making quality corn silage in Wisconsin. Foliar diseases of corn, forced the plants to lose photosynthetic capability pre-maturely, resulting in cannibalization of stalks for carbohydrates to fill ears. Loss in stalk integrity meant extreme lodging, not to mention that is was a struggle to find optimum moisture in any field. Throw in frequent rains, and trying to chop on time to achieve quality fermentation was nearly impossible in 2018. The consequences of the challenging season are still being felt with poor quality, wild yeast issues, and higher than typical mycotoxin loads. So what does 2019 look like?

Foliar Disease of Silage Corn in 2019 

Compared to 2018, the foliar disease situation has been less significant in 2019. However, there are still some important diseases to consider as you prepare for harvest. Statewide, gray leaf spot did appear early again this season. However, unseasonably cool weather kept this disease relegated to the lower canopy. For most fields we have visited, gray leaf spot will likely be of little impact on yield and feed quality this year. 

Figure 1. Tar spot on a leaf of corn located in Arlington, WI on August 7, 2019. Photo Credit: Hannah Reed, University of Wisconsin-Madison.

The flipside of the cooler weather meant that tar spot (Fig. 1) has become an issue again this year. Tar spot is favored by persistent temperatures between 60 and 70 F and high relative humidity averaging above 75% for a 30-day period. Periods of extended leaf wetness further facilitate increase and spread. We have been right in the ideal growth zone for the pathogen that causes tar spot since the first part of August. Over the last month, tar spot has been found in many areas of the state (CLICK HERE to view the latest national map for tar spot confirmations), leading to the 4th straight field season where this disease has impacted silage corn. While the disease has moved in later this season, compared to 2018, it is moving quickly. Tar spot can kill leaves prematurely, or reduce photosynthetic capacity. 


Figure 2. Northern corn leaf blight on corn.

Northern corn leaf blight (NCLB; Fig. 2) can also be readily found in the upper canopy in some fields in 2019. This disease has historically been a more significant problem on silage hybrids, increasing when the weather is cool and the humidity high. Depending on the severity and interaction of both NCLB and tar spot, these diseases can influence whole plant moisture levels and also cause stalk-cannibalization, leading to increased risk for lodging. As you prepare to chop silage, scout fields to understand the severity of foliar disease levels along with whole plant moisture and kernel maturity. Fields with the highest levels of foliar disease should be closely monitored for whole plant moisture and prioritized for harvest first. Then work your way to those fields with less visible disease.       

Ear rots and mycotoxins of silage corn in 2019 

Figure 3. Gibberella ear rot on corn.

In 2018, corn production in Wisconsin was also plagued by high levels of Gibberella ear rot (Fig. 3) and high levels of deoxynivalenol (DON or vomitoxin) in finished grain and silage. Remember that vomitoxin is a secondary metabolite produced by the fungus that causes Gibberella ear rot. We believe that 2019 will be another year with high levels of Gibberella ear rot and vomitoxin levels. Weather has been wet, especially during silking on late-planted fields in 2019. This increases the risk of Gibberella ear rot. Furthermore, the fungus that causes Gibberella ear rot can cause Fusarium head blight (FHB or scab) in wheat. Vomitoxin can also accumulate in wheat grain resulting in unusable grain, or grain subjected to dockage at the elevator. The 2019 wheat season saw high levels of FHB in winter wheat, with subsequent reports of high levels of vomitoxin. Anecdotal reports of very high DON levels have been reported in wheat straw harvested in 2019. This situation further substantiates the possibility that corn might also be hit hard with Gibberella this year. When scouting fields, pull back some husks to see if there is visible ear rot. Note these fields where high levels of severity exist. Also, check fields for lodging and assess stalk integrity. The fungus that causes Gibberella ear rot can also cause Gibberella stalk rot. We also know that from some preliminary research, vomitoxin can accumulate in the stalk portions of the plant in addition to the ears. Fields with high levels of ear rot and/or stalk rot should be prioritized for harvest first. You might also consider keeping silage from these higher-severity fields separate from other fields you harvest. Also consider testing for nutritive quality and mycotoxin load as you chop silage, so you know how much vomitoxin is present and potentially from which fields. Information on testing grain and silage can be found by clicking here. An additional list of testing labs can be found in A3646-Pest Management in Wisconsin Field Crops in table 2-16. Remember that mycotoxins like vomitoxin are very stable. They cannot be removed by heating or freezing. When storing corn grain for long periods of time, we recommend drying grain down to 13%. This will help stop the continued growth of the fungus that can cause vomitoxin and reduce any subsequent accumulation of the mycotoxin. In silage corn production, harvesting at optimum moisture and packing the bunker and inducing fermentation and anaerobic conditions as quickly as possible will limit any further growth of the fungus and any additional accumulation of vomitoxin.

If you sprayed silage corn with fungicide in 2019, this might help reduce the levels of foliar disease, ear rot, and vomitoxin levels. However, it will not “cure” the situation nor is it anywhere near perfect. Research in 2018 demonstrated that fungicides could reduce disease levels, but in a year when weather conditions were conducive for ear rot and vomitoxin accumulation expectations needed to be lowered. In 2018 certain fungicide programs had the capability of reducing vomitoxin levels by 50% or more, but that still meant that a lot of the silage made was still considered unacceptable for feeding due to high vomitoxin levels. Remember that hybrid choice, in addition to treating with fungicide, can play an important role in how much vomitoxin is present and the nutritive value of the finished feed.

What are the impacts of poor silage quality and mycotoxin accumulation? 

Animal nutritionists have observed many impacts of mycotoxin and microbial growth challenges in animals, including dairy cattle. Performance and health issues can range from milk fat or milk protein percentage decreases, to decreased milk production and all the way on up to feed refusal, intestinal or gut hemorrhaging, and death. For this reason, nutritionists have devised guidelines for dietary limits of some mycotoxins to reduce harm to the animal. Dr. John Goeser has assembled the “Mycotoxin Guidelines and Dietary Limits” fact sheet to help producers better understand the potentially harmful toxin levels in the total diet (DM). You will see in that chart that for vomitoxin (DON), the suggested total mixed ration (TMR) concern limit is just 0.5 to 1.0 ppm for dairy cattle. The fact sheet also provides a helpful formula to understand the contribution of toxin in a particular component of feed, relative to the total diet.

Also recognize microbial growth (mold, yeast and negative bacteria) challenges will increase with wetter conditions. Both mycotoxin load and microbial contamination need to be checked if performance or health appear challenged for your herd. Start by checking the TMR and then work backward from there with your advisory team.

We are expecting a prolonged harvest this year due to unprecedented planting growing conditions earlier this season. As discussed previously, step up your crop scouting efforts to optimize harvest this year. Consider using the approach discussed in this recent Hoard’s Dairyman HD Intel newsletter to be proactive and stay in control this harvest.

The Take-Home

  1. Spend some time scouting fields for foliar, ear, and stalk disease. Prioritize harvest for fields with high disease severity.
  2. Be proactive. Consider testing corn silage for mycotoxins, specifically vomitoxin, a couple times as your farm begins harvest. If results come back greater than expected, consider increasing frequency so you know what you are dealing with before silage is ensiled.
  3. Consider keeping fields with high disease levels and/or high vomitoxin levels segregated from better feed. 
  4. Take time to target optimum harvest moisture and packing conditions to shorten time to anaerobic conditions and fermentation.
  5. Keep oxygen out of the silo. After the silo, bunker, pile, or bag have been sealed, continue watching for holes or leaks on a regular basis and repair damaged plastic or seams. 

Should I Be Applying Fungicide to My Fall Forage Oat Crop?

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

Shawn Conley, Extension Soybean and Small Grains Agronomist, Department of Agronomy, University of Wisconsin-Madison

Figure 1. Crown rust on an oat leaf. Photo Credit: Craig Grau, University of Wisconsin-Madison.

Record prevent-plant acres and lack of on-farm forage has pushed WI farmers into trying alternative cropping systems in 2019. A record number of late planted oats have been planted with the intension of being used as a forage. Oats, planted the first week of August can be expected to produce 2.5 to 3 t DM/a in an average year.  Coblentz, USDA Dairy Forage Research Center, found that a late-maturing forage cultivar (ForagePlus) produced maximum annual yields ranging from 2 to 3.5 t DM/a.  Because the forage cultivar matured slowly it was better able to respond to sometimes erratic late-summer precipitation. These oat types mature later and produce more tonnage of quality forage.  In addition, fall planted oat is higher in forage quality than spring planted oats.  Research at the University of Wisconsin by Albrecht found that maturation of summer-sown (August) oats was delayed, resulting in 10 to 15% less neutral detergent fiber (NDF), 18% greater digestibility, and 250% more water soluble carbohydrate than spring-sown oat. With all of the cool wet weather in 2019 and lush plant tissue, these oats are likely to be challenged with crown rust. The question being posed today is should farmers be spraying these fall forage oats with a fungicide?

We are being up front here…we don’t have any empirical data to speak from so this our best educated GEUSTIMATE. The oat crown rust pathogen (Puccinia coronataf. sp. avenae) can quickly overcome genetic resistance in oat grain varieties. That means that certain varieties have better partial resistance than others, which can result in differences in yield and quality parameters in years when crown rust is significant. Examples of these differences can be found below:

It is important to know the level of resistance to crown rust that your variety has. This might dictate how often you scout in order to make your fungicide spray decision.

When it comes to fungicide efficacy, many products are very effective against oat crown rust. Haugen et al. at North Dakota State University conducted fungicide evaluations on oat for grain in 2014-2016. In all years fungicide was applied at flag leaf emergence. Products used included Headline®, Priaxor®, Tilt®, and Quadris®. In the 2015 and 2016 data, normalized difference vegetation index (NDVI) was recorded to measure quality of the vegetative portions of the plant. In all cases fungicide improved the NDVI scores relative to the control. Not surprisingly, a corresponding increase in yield was observed relative to the higher NDVI scores in the fungicide-treated oats. While these data are from oats for grain, it highlights the fact that fungicide can indeed protect oat plants from crown rust and delay disease development, resulting in greener, healthier vegetative plant parts.

When making the decision to apply fungicide on oats for forage, it appears that there are several products which are effective for controlling crown rust. Given the current farm economy, it might be good to find a product that is cheap, yet effective, to keep the cost of this input low. Several of the strobilurin only fungicides are labeled for control of rust in oats for forage. These include Headline® and Quadris®. Others might be available, however, read the labels very carefully. Be sure that oats for forage or hay is indicated on the label. Also be sure you know what the pre-harvest interval (PHI) is for the product you choose.  Some of these products cannot be harvested for 7, 14, or more days after application for forage. Additional fungicide options may be found in A3646, Pest management in Wisconsin Field Crops. Again, read any labels VERY carefully to be sure that the product can be used for oats for hay and forage.

Given the upward limitations of forage yield ~2 to 3.5 t DM/a it is difficult to know what dry matter differences we can expect; however, the most likely benefit of a fungicide application on forage oats would be in forage quality. Given the market prices and lack of cash flow in agriculture right now if a grower chose to do this practice a lower cost product that was efficacious on the oat crown rust would be the best choice.

Author Note: Mention of product names above is not an endorsement for that product.

2019 Pest Management Update Meeting Series Announced

The schedule for the 2019 Wisconsin Pest Management Update meeting series has been set. Presentations will include agronomic pest management information for Wisconsin field and forage crops. Speakers include Mark Renz and Rodrigo Werle, weed scientists, Damon Smith, plant pathologist, and Bryan Jensen, entomologist.

The format will be the same as in recent years. Meetings will either be in the morning or afternoon on November 4-8, 2019. Simply choose a day/location to attend with each meeting running 3 hours. Note that several locations and contacts have changed since 2018 (marked with * in the meeting flier). Please read the informational flier carefully and make sure you contact the appropriate person at your desired location.

2019 Pest Management Update Highlights:

Integrated Pest Management Updates in corn, soybeans, alfalfa, and small grains: Update on new products and/or use of existing products as well as brief highlights of the 2019 pest situations in each crop.

Please make your reservation with the host contact at least one week prior to the scheduled meeting date.

Three hours of Certified Crop Advisor CEU credits in pest management are requested for each session.

To download a PDF of the flier, CLICK HERE.

Tar Spot Now Confirmed in Wisconsin in 2019

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

Hannah Reed, Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin-Madison 

Brian Mueller, Assistant Researcher, Department of Plant Pathology, University of Wisconsin-Madison 

Figure 1. Corn IPM PIPE tar spot occurrence map as of August 7, 2019.

Tar spot has been found on corn in plots established to monitor for the disease in Arlington (Columbia Co.) and Lancaster (Grant Co.) WI (Fig. 1). In both cases the disease was present on hybrids known to be susceptible. At the Arlington location disease was found in just one small area of the field. Tar spot coverage was low to moderate on a few leaves (Fig. 2). Microscopy was used to observe ascospores from stromata, thus confirming the tar spot fungus (Fig. 3).

Figure 2. Tar spot on a leaf of corn located in Arlington, WI on August 7, 2019.

Tar spot was very hard to find in the Lancaster location. However, it was observed on several plants in one monitoring plot. In each case only 1-2 spots were observed.

What does this mean for you?

Figure 3. Asci and Ascospores of the tar spot fungus.

This means it is time to get back out and scout corn fields for tar spot. If you have had a history of tar spot and you know that you have a hybrid that is more susceptible and there is a large amount of infested residue, then you should monitor this situation closely. If tar spot is observed and you are irrigating or have had frequent rain, monitor this situation very closely. Tar spot seems to progress quickly in irrigated environments. Remember, that the window of opportunity to treat with a fungicide can pass rapidly as this disease can move quickly. Protecting this ear leaves before R3 can be important for preserving yield. There are many products that have demonstrated decent efficacy toward tar spot. You can find our 2018 fungicide test summaries by CLICKING HERE and scrolling down to pages 2-7. Work with your local extension personnel if you need help diagnosing the disease or need advice on spraying fungicides.