2023 Wisconsin Fungicide Test and Disease Management Summary Now Available!

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Brian Mueller, Researcher II, UW-Madison, Plant Pathology

Damon Smith, Professor and Extension Specialist, UW-Madison, Plant Pathology

Each year the Wisconsin Field Crops Pathology Program conducts a wide array of fungicide and disease management 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 and how to pair them with other disease management strategies. We hope you find this report useful in making decisions for the 2024 field season.

The 2023 Wisconsin Field Crops Fungicide Test and Disease Management Summary is available by clicking here. 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 fungicides, soybean 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!

Fungicide For Field Crops Information Page Updated

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

 

The Fungicide for Field Crops Information webpage on the Badger CropDoc website has now been updated! The update includes links to the latest fungicide efficacy tables from the Crop Protection Network as well as several updated fact sheets from UW Integrated Pest and Crop Management Program. Many fungicide application decisions will be made over the next month or so. Even if you are already familiar with fungicides and how they work, a little refresher might be helpful as you make product and application decisions. If you aren’t familiar with fungicides or how to use on field crops, this page covers the basics with lots of useful information.

Timely Wheat Disease Management Video Series and Wheat Fungicide Information

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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

Winter wheat in Wisconsin is finally starting to move along in growth stages. Warmer weather is helping to increase tillering. As wheat begins to move through growth stages, diseases and disease management will begin to be of concern. To assist in making wheat disease management decisions in Wisconsin, we have developed a 3-video series on the subject. Each video talks about making fungicide application decisions at the critical growth stages in for management in Wisconsin. The video series can be found below:

For information about fungicides and fungicide efficacy for winter wheat diseases, you can check out the “Fungicide Efficacy for Control of Wheat Diseases” fact sheet on the Crop Protection Network Website. Fact sheet A3878 – Fungicide Resistance Management in Corn, Soybean, and Wheat in Wisconsin has also been updated and available by CLICKING HERE.

Local data from fungicide efficacy trials in Wisconsin are also available on the Wisconsin Fungicide Test Summary Page. These trials date back to 2013 with the latest data from 2019. Be sure to scroll all the way through the documents as the wheat trials generally are listed toward the end of the documents.

Finally, don’t forget to get out and Scout, Scout, Scout to best make your in-season wheat disease management decisions!

2017 Field Crop Fungicide Efficacy Tables Now Posted

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

Northern Corn Leaf Blight symptoms on a corn leaf.

The 2017 fungicide efficacy tables are now posted for foliar diseases of corn, soybeans, and small grains. New this year is an added efficacy table for fungicides effective against seedling diseases of soybean. You can access these tables by clicking directly on the links imbedded in this page or by clicking on the Fungicide Information tab above, and scrolling down the page to find the tables. The efficacy ratings are generated based on independent, University efficacy trial data from across the U.S. If you can’t find a particular product on the table, it is likely that it isn’t commonly used, or there isn’t enough data to confidently generate an efficacy rating. Remember to follow all label recommendations attached to the fungicide container. The label label is the law!

Northern Corn Leaf Blight Positively Identified in Wisconsin in 2016

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

I was hoping that I would write this article later in the year. But it has happened relatively early for us. We have positively confirmed northern corn leaf blight (NCLB) on field corn at about the V7-V8 growth stage near Janesville, WI this week. This is a bit early for us, however, not entirely surprising given the levels of residual inoculum from the fungus that causes NCLB left from 2015 in many fields and the cool wet conditions we have had this spring. The situation has been similar to that in Iowa. Dr. Alison Robertson also reported the first find of NCLB in southeast Iowa this week. While this find is relatively early for Wisconsin, I don’t think the world is going to come to an end. Patience will be key over the next couple of weeks. I’ll explain why folks should be cautious in making management decisions below.

Figure 1. Northern Corn Leaf Blight symptoms on a corn leaf.

Figure 1. Northern Corn Leaf Blight symptoms on a corn leaf.

What is the Organism that Causes Northern Corn Leaf Blight (NCLB)? 

A fungus called Setosphaeria turcica (synonym: Exserohilum turcicum) causes NCLB (Fig. 1). The fungus loves it wet and cool. The fungus is most active when wet weather coincides with temperatures between 65 F and 80 F. During these conditions, the fungus will readily make microscopic spores (called conidia) inside the symptomatic areas of leaves and those spores (Fig. 2) will get splashed onto more leaves. Therefore, the disease typically moves form the lower canopy, up the corn plant as the season progresses. When temperatures get above 80 F and it is dry, growth and spread of the fungus slows dramatically. Remember the disease triangle?  It takes three things for a plant disease to occur – susceptible plants, fungal inoculum present near those susceptible plants, and favorable weather. Early this season, all three legs of the triangle were present. We have lots of residual inoculum left from 2015, we have lots of corn planted again in many fields that had corn last year, and we had cool rainy conditions early on this season. However, as we think about the disease triangle moving forward, and look at forecasts over the next 7-10 days, weather is not going to be conducive for the NCLB fungus. Temperatures are forecasts to be above 80 F and there isn’t much rain in site. Without the weather component of the triangle, fungal growth, spread, and subsequent disease development will be halted.

Figure 2. A photo-micrograph of spores produced by the NCLB fungus.

Figure 2. A photo-micrograph of spores produced by the NCLB fungus.

What should I do About Managing NCLB in 2016?

Farmers and consultants should start actively scouting corn fields in Wisconsin and keep track of disease and disease development. Remember, that while the disease is manifesting early, it is currently affecting leaves that will be in the lower canopy of the plant and are not responsible for a large portion of grain yield. While I hate talking about threshold levels for managing disease, it can be helpful in your decision making process to know what might be severe disease. While scouting look in the lower portion of the canopy. If some symptoms are present in the lower canopy, make a visual estimation of how frequent (percentage of plants with lesions) NCLB is in a particular area and how severe (how much leaf area is covered by NCLB lesions.  The lower leaves aren’t responsible for much yield accumulation in corn, but spores produced in NCLB lesions on these leaves can be splashed up to the ear leaves where disease can be very impactful. So by scouting the lower canopy and getting an idea of how much disease is present, you can “predict” what

Figure 3: A computer simulation of 5% NCLB severity on a corn leaf.

Figure 3: A computer simulation of 5% NCLB severity on a corn leaf.

might happen later on the ear leaves to make an informed spray decision. The other consideration you should make while scouting is the resistance rating that the hybrid has for NCLB. If it is rated as resistant, then NCLB severity might not be predicted to get very severe, while in a susceptible hybrid, NCLB might be present on 50% or more of plants at high severity levels. Note however, that even if a hybrid is rated as resistant, it can still get some disease. Resistance isn’t immunity! If NCLB is present on on at least half the plants and severity is at least 5-10% and weather is forecast to be rainy and cool, a fungicide application will likely be needed to manage the disease. So what does 5% leaf severity look like? Figure 3 is a computer generated image that shows 5% of the corn leaf area with NCLB lesions. You can use this image to train your brain to visually estimate how severe the disease might be on a particular leaf. As for fungicide choice and timing, I consider that further below.

When Should I Spray and What Should I Spray?

While it might seem tempting to spray fungicide now (between the V6-V8 growth Stages) because of NCLB, remember that the disease will likely slow due to the hot dry weather pattern we are about to encounter. I would encourage you to be patient and save your fungicide spray until as close to tassel (VT growth Stage) as you can. Over the last several years corn pathologists in the U.S. corn belt have conducted fungicide application timing trials on corn for grain. Programs included various products, but applications focused on an early (V5-V8) timing, a VT-R2 timing, or a combination of V5-V8 plus a VT-R2 application (two fungicide applications). Over a 6 year period and well over 1,500 observations, the average yield gain when using fungicide at V5-V8 alone was 1.9 bu/acre, while that at the VT-R2 timing was 4.7 bu/acre, and 5.6 bu/acre for the two-pass program. Now consider the price of corn and the fungicide cost. Figure 4 is a breakeven table for fungicide cost compared to corn price. You will see that I have called out a couple of possibilities depending on the price of your fungicide. If we consider the price of corn grain to be somewhere between $3 and $4 and the cost of a fungicide to be in the $10 to $14 range, you can see from the table that you would need 2.5 to 4.7 bu/acre of additional corn grain in the treated fields, over not treating, to cover the cost of fungicide. Considering these numbers, and the nationwide average bushel return when using fungicide at various corn growth stages, you can see that the VT application timing for fungicide seems to make the most sense.

So what about fungicide application on corn in Wisconsin? We have compiled a 3-year dataset where we have looked at return on investment when using fungicide in fields where little disease was active (< 5% NCLB ear-leaf severity) or where diseases active (>5% NCLB ear-leaf severity). When NCLB was active, we found that there was a positive yield response when using fungicide about 74% of the time with an average yield gain of 5.4 bushels per acre (Figure 5). When disease activity was low, that positive yield response dropped to just 32% with little gain over zero bushels (Figure 5).

How about the return on investment in the current corn market? If we consider the current corn pricing and a fungicide cost of $10 to $14, Figure 6 shows that in Wisconsin a positive return on investment (ROI) occurs about 50-65% of the time when disease is active on ear-leaves (Figure 6). When disease is not active, the odds of positive ROI drop to just 12% – 20%. For a full discussion and explanation, I would encourage you to watch this video about corn disease and fungicide applications in Wisconsin.

Also be aware that in some cases, application of fungicide in combination with nonionic surfactant (NIS) at growth stages between V8 and VT in hybrid field corn can result in a phenomenon known as arrested ear development. The damage is thought to be caused by the combination of NIS and fungicide and not by the fungicide alone. To learn more about this issue, you can CLICK HERE and download a fact sheet from Purdue Extension that covers the topic nicely.

For information on fungicide efficacy for NCLB you can consult fungicide efficacy trial data in Wisconsin BY CLICKING HERE. You can also consult the National Corn Disease Working Group fungicide efficacy table that was recently updated. The fungicide efficacy table can be found BY CLICKING HERE.

Summary

While it is earlier than normal to see NCLB in Wisconsin, I would encourage people to be patient in managing this disease with fungicide. Remember that conditions are going to be hot and dry over the next 1 – 2 weeks, which will dramatically slow the progress of NCLB. Also, considering that the best response out of a fungicide application seems to be between VT-R2, and the issues with fungicide plus NIS application between V8 and VT, I would suggest holding off for any fungicide applications until closer to VT. With the price of corn grain comparatively lower than in years past, one application of fungicide is about all that Wisconsin farmers can afford, therefore I would maximize that application and apply it as close to the VT growth stage as you can. As you approach that growth stage, continue scouting and consider if the disease is active. If it isn’t active and the weather pattern continues to be hot and dry, a fungicide application may not be needed at all.

Corn Diseases of 2015 and Should I Spray Fungicide?

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

The phone has been ringing a lot lately and the primary questions are:

  • What corn diseases should I be concerned with this year in Wisconsin?
  • Should I spray a fungicide? And If so, what product and timing?

Lets start with the first question. As far as foliar disease issue, I think we need to scout closely for northern corn leaf blight (NCLB) in Wisconsin. The Midwest is already seeing high levels of this disease and it is showing up in the lower canopy in corn fields in southern Wisconsin. Remember, that this disease can be easily confused with Goss’s wilt. Earlier this season I wrote a post about differentiating these two diseases. I encourage you to revisit that post as a refresher. In addition to NCLB, our scouting has revealed a second foliar disease present in the lower and mid-canopy of the corn crop. That second disease is eyespot. Lets talk about NCLB and eyespot in a little greater detail.

Figure 1. NCLB Lesions on a corn leaf

Figure 1. NCLB Lesions on a corn leaf

Northern Corn Leaf Blight (NCLB): The most diagnostic symptom of NCLB is the long, slender, cigar-shaped, gray-green to tan lesions that develop on leaves (Fig. 1).  Disease often begins on the lower leaves and works it way to the top leaves.  This disease is favored by cool, wet, rainy weather, which has seemed to dominate lately. Higher levels of disease might be expected in fields with a previous history of NCLB and/or fields that have been in continuous and no-till corn production. The pathogen over-winters in corn residue, therefore, the more residue on the soil surface the higher the risk for NCLB.  Management should focus on using resistant hybrids and residue management.  In-season management is available in the form of several fungicides that are labeled for NCLB. However, these fungicides should be applied at the early onset of the disease and only if the epidemic is expected to get worse.

Figure 2: A computer simulation of 5% NCLB severity on a corn leaf.

Figure 2: A computer simulation of 5% NCLB severity on a corn leaf.

While I hate talking about threshold levels for managing disease, it can be helpful in your decision making process to know what might be severe. While scouting look in the lower portion of the canopy. If some symptoms are present in the lower canopy, make a visual estimation of how frequent (percentage of plants with lesions) NCLB is in a particular area and how severe (how much leaf area is covered by NCLB lesions.  The lower leaves aren’t responsible for much yield accumulation in corn, but spores produced in NCLB lesions on these leaves can be splashed up to the ear leaves where disease can be very impactful. So by scouting the lower canopy and getting an idea of how much disease is present, you can “predict” what might happen later on the ear leaves to make an informed spray decision. The other consideration you should make while scouting is the resistance rating that the hybrid has for NCLB. If it is rated as resistant, then NCLB severity might not be predicted to get very severe, while in  a susceptible hybrid, NCLB might be present on 50% or more of plants at high severity levels. Note however, that even if a hybrid is rated as resistant, it can still get some disease. Resistance isn’t immunity! If NCLB is present on on at least half the plants and severity is at least 5-10% and weather is forecast to be rainy and cool, a fungicide application will likely be needed to manage the disease. So what does 5% leaf severity look like? Figure 2 is a computer generated image that shows 5% of the corn leaf with NCLB lesions. You can use this image to train your brain to visually estimate how severe the disease might be on a particular leaf. As for fungicide choice and timing, I consider that further below.

Figure 3. Eyespot symptoms on a corn leaf.

Figure 3. Eyespot symptoms on a corn leaf.

Eyespot: Eyespot typically first develops as very small pen-tipped sized lesions that appear water-soaked.  As the lesions mature they become larger (¼ inch in diameter) become tan in the center and have a yellow halo (Fig. 3).  Lesions can be numerous and spread from the lower leaves to upper leaves. In severe cases, lesions may grow together and can cause defoliation and/or yield reduction. Eyespot is also favored by cool, wet, and frequently rainy conditions.  No-till and continuous corn production systems can also increase the risk for eyespot, as the pathogen is borne on corn residue on the soil surface.  Management should focus on the use of resistant hybrids and residue management.  In-season management is available in the form of fungicides. Severity has to reach high levels (>50%) before this disease begins to impact yield. I often have eyespot present in my corn trials each year as we plant into continuous corn and use no-till. However, we typically do not see yield reductions from this disease even in non-sprayed plots. When scouting, note the disease and keep track of the severity. Again, fungicides should be applied early in the epidemic and may not be cost effective for this disease alone.

What fungicide should I spray and should I spray at all? My question is what are you trying to do? Control a disease or simply boost yield? Fungicide should be used as a tool to control a disease and preserve yield. There is no silver bullet fungicide out there for all corn diseases. However, there are many products which work well on a range of diseases. The Corn Fungicide Efficacy table lists products that have been rigorously evaluated in university research trials across the country. You can see there are several products listed that perform well on both NCLB and eyespot. So obviously, if a disease is present and you are trying to control the disease, you might expect more return on your investment, compared to simply spraying fungicide and hoping that there might be a yield increase.

Paul et al. (2011) conducted research to investigate the return on investment (ROI) of using fungicide at low and elevated levels of disease. Data from 14 states between 2002 and 2009 were used in the analysis. They looked at 4 formulations of fungicide products across all of these trials. I won’t go into detail about all products, but will focus on one here, pyraclostrobin. This is the active ingredient in Headline® Fungicide. In all, 172 trials were evaluated in the analysis and Paul et al. found that on average there was a 4.08 bu/acre increase in corn grain yield when pyraclostrobin was used. So there does appear to be some increase in yield with the use of fungicide, but in our current market, will this average gain cover the fungicide application?

Figure 4. Break-even scenarios for corn when foliar fungicide was applied.

Figure 4. Break-even scenarios for corn when foliar fungicide was applied.

The suggested application rate for Headline® Fungicide is 6 to 12 fl oz/acre. My latest cost sheets indicate that at the 6 fl oz/acre rate, the cost of the product alone would be about $20/acre. Note that this does not include the custom applicator cost. This is a variable expense that would need to be added in to get an accurate ROI for your operation. Today we can estimate that we might sell corn grain somewhere between $4 and $5 per bushel. We can then use the cost of the fungicide product and the price of grain to figure out how many bushels of corn we need to make in the crop that would be treated with pyraclostrobin vs. non-treating. Figure 4 is a table with various corn prices along the vertical axis and fungicide costs per acre along the horizontal axis. The cells indicate the bushels of corn per acre needed to break even when using a fungicide at the corresponding cost and corn grain sale price. Using the above scenario, we see that with corn priced between $4 and $5 per acre and a fungicide application cost of $20/acre, we would need to gain 4-5 bushels per acre when using Headline® Fungicide in the current corn market. Obviously these calculations are for just one product, but you can do the same for your farm and fungicide program and use the table to figure out what break-even yield gain you will need to cover your costs.

What are the odds of getting that 4 to 5 bushel per acre yield gain when using Headline® Fungicide? Paul et al. went further and calculated the probability of return at various corn prices and fungicide costs. They did separate analyses for foliar disease severity less than 5% and greater than 5%. In our current corn market with around $4/bu corn prices and a cost of Headline® Fungicide at $20/acre, Paul et al. found that at low foliar disease levels (<5% severity) the odds of a positive ROI using the fungicide would be around 50%. The odds of a positive ROI improve if disease severity is greater than 5%. In their calculations with higher levels of disease (>5% severity), the odds of a positive ROI would be between 60% and 70%. The morale of this story is that if you are going to use fungicides on corn, they should be targeted toward fields that will have, or are at risk, for disease!

So what about fungicide application timing? Over the last several years corn pathologists in the U.S. corn belt have conducted fungicide application timing trials on corn for grain. Programs included various products, but applications focused on an early (V5-V8) timing, a VT-R2 timing, or a combination of V5-V8 plus a VT-R2 application. Over a 5 year period and nearly 1,500 observations, the average yield gain when using fungicide at V5-V8 alone was 1.4 bu/acre, while that at the VT-R2 timing was 4.4 bu/acre, and 4.7 bu/acre for the two pass program. In Wisconsin in 2013, the best gain in yield when using fungicide was at the VT application timing with almost 10 bu/acre over the non-treated. In 2014, we saw the opposite, with an average loss of grain yield at the VT timing of around 10 bu/acre. In Wisconsin, we see that yield gain in fungicide trials is highly variable and depends on the hybrid and weather for that particular season. You can check out results of the fungicide trials and the performance of various products over the last two years by visiting my Fungicide Test Summaries page and viewing the results in the 2013 and 2014 reports.

Finally, be aware that in some cases, application of fungicide in combination with nonionic surfactant (NIS) at growth stages between V8 and VT in hybrid field corn can result in a phenomenon known as arrested ear development. The damage is thought to be caused by the combination of NIS and fungicide and not by the fungicide alone. To learn more about this issue, you can CLICK HERE and download a fact sheet from Purdue Extension that covers the topic nicely. Considering that the best response out of a fungicide application seems to be between VT-R2, and the issues with fungicide plus NIS application between V8 and VT, I would suggest holding off for any fungicide applications until at least VT.

Summary

As we approach the critical time to make decisions about in-season disease management on corn, it is important to consider all factors at play while trying to determine if a fungicide is right for your corn operation in 2015. Here is what you should consider:

1) Corn hybrid disease resistance score – Resistant hybrids may not have high levels of disease which impact yield.

2) Get out of the truck and SCOUT, SCOUT, SCOUT – Consider how much disease and the level of severity of disease present in the lower canopy prior to tassel.

3) Consider weather conditions prior to, and during, the VT-R2 growth stages – if it is cool and wet, disease may continue to increase in corn and a fungicide application might be necessary. If it turns out to be hot and dry, disease development will stop and a fungicide application would not be recommended.

4) Consider your costs to apply a fungicide and the price you can sell your corn grain – Will you gain enough out of the fungicide application to cover its cost?

5) Hold off with making your fungicide application in Wisconsin until corn has reached the VT-R2 growth stages – The best foliar disease control and highest likelihood of a positive ROI will occur when fungicide is applied during this timing when high levels of disease are likely.

6) Be aware that every time you use a fungicide you are likely selecting for corn pathogen populations that will become resistant to a future fungicide application – Make sure your fungicide application is worth this long-term risk. To learn more about fungicide resistance, you can CLICK HERE to download a UW Extension fact sheet.

Other Resources

Wisconsin Field Crops Fungicide Information Page 

Diseases Showing up in Iowa Corn, 2015

UNL CropWatch: Worn Disease Update

References

White, D.G., editor. 2010. Compendium of Corn Diseases. APS Press.

Paul, P. A., Madden, L. V., Bradley, C. A., Robertson, A. E., Munkvold, G. P., Shaner, G., Wise, K. A., Malvick, D. K., Allen, T. W., Grybauskas, A., Vincelli, P., and Esker, P. 2011. Meta-analysis of yield response of hybrid field corn to foliar fungicides in the U.S. Corn Belt. Phytopathology 101:1122-1132.

Time to Start Looking for Corn Diseases in Wisconsin

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Figure 1. NCLB Lesions on a corn leaf

Figure 1. NCLB Lesions on a corn leaf

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

The 2014 field season was a bit of a challenge for corn growers in Wisconsin, to say the least. We had poor growing conditions, which made for a lot of challenges including diseases. On the top of that list in Wisconsin was Northern Corn Leaf blight (NCLB). A close second was Goss’s Wilt.  Already in 2015, states like Iowa and Nebraska have already reported both diseases on corn. This is among the earliest reports of both diseases in many years. In Wisconsin, we haven’t seen either of these yet, but given the weather patterns recently, I think it is only a matter of time.

For many folks, identification of these two diseases can be challenging. Many are confused by the subtleties of each disease “signature.” Diagnosis is critical in making your management decisions properly. Obviously, the best way to properly diagnose any plant disease problem is to send a sample to the Plant Disease Diagnostic Clinic. A sample can be sent by following their helpful sample guidelines, which can be found by clicking here. In addition to sending a diagnostic sample, there are some signs and symptoms that can be identified in the field, to help get you closer to diagnosing the right disease. Here are some helpful details for each disease.

Figure 2. Foliar symptoms of Goss's wilt on a corn leaf. Photo Credit: Larry Osborne, Bugwood.org.

Figure 2. Foliar symptoms of Goss’s wilt on a corn leaf. Photo Credit: Larry Osborne, Bugwood.org.

Northern Corn Leaf Blight (NCLB): NCLB is caused by a fungus called Exserohilum turcicum. The most diagnostic symptom of NCLB is the long, slender, cigar-shaped, gray-green to tan lesions that develop on leaves (Fig. 1).  Disease often begins on the lower leaves and works it way to the top leaves.  This disease is favored by cool, wet, rainy weather, which has seemed to dominate lately. Higher levels of disease might be expected in fields with a previous history of NCLB and/or fields that have been in continuous and no-till corn production. The pathogen over-winters in corn residue, therefore, the more residue on the soil surface the higher the risk for NCLB.  Management should focus on using resistant hybrids and residue management.  In-season management is available in the form of several fungicides that are labeled for NCLB. However, these fungicides should be applied at the early onset of the disease and only if the epidemic is expected to get worse. Often the best time to apply fungicides to field corn to maximize the benefits is near the VT/R1 growth stage. However, if NCLB is visible on leaves earlier than this time, a fungicide might be beneficial at those earlier stages. The only way to determine this is to scout frequently and keep an eye on the disease situation in your corn crop.

If you elect to control NCLB with fungicides, you might consider taking a look at my page on FUNGICIDE INFORMATION. This page talks about fungicide use in general and also includes the Corn Fungicide Efficacy Table. You will find products listed with good efficacy toward NCLB on this table.

Additional NCLB Information

Purdue University – https://www.extension.purdue.edu/extmedia/BP/BP-84-W.pdf

Iowa State University – http://www.extension.iastate.edu/CropNews/2014/0714Robertson.htm

Figure 3. "Freckles" on a corn leaf with Goss's wilt. Photo credit: Larry Osborne, Bugwood.org.

Figure 3. “Freckles” on a corn leaf with Goss’s wilt. Photo credit: Larry Osborne, Bugwood.org.

Goss’s Wilt: Goss’s wilt is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis. First visual symptoms usually appear as gray or yellow stripes on leaves that tend to follow the leaf veins (Fig. 2). Often “freckles”, or brown or green irregular spots, can be observed within the leaf lesions (Fig. 3). Freckles are an excellent diagnostic symptom to confirm Goss’s wilt. Vascular tissue, husks, and kernels can sometimes take on an orange hue. Occasionally, bacterial ooze or dried ooze can be observed on symptomatic leaves. Fungicides do not work for Goss’s wilt, because this is caused by a bacterium, not a fungus. Management is preventative for Goss’s wilt. Choose hybrids with the best possible resistance, manage excessive amounts of corn surface residue, and rotate crops. The longer the rotation between corn crops, the better. There are some foliar products being marketed for the control of Goss’s wilt, but no efficacy data are currently available.

Additional Goss’s Wilt Information

University of Nebraska – http://pdc.unl.edu/agriculturecrops/corn/gosswilt

Purdue University – https://www.extension.purdue.edu/extmedia/bp/BP-81-W.pdf

Corn Diagnostics Quick Guide: Many of you likely attended the 2014 Pest Management Update Series and obtained the corn diagnostics quick guide sheet to help differentiate between Goss’s wilt and NCLB. I have again attached it to this post for download as a PDF. This is a quick guide to help you differentiate the diseases in the field. Remember, the only way to definitively differentiate the diseases is to send a sample to the diagnostic clinic. Get out there and SCOUT, SCOUT, SCOUT!

 

Fungicide Efficacy Tables Updated For 2015!

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2015 Corn Fungicide Efficacy Table

2015 Corn Fungicide Efficacy Table

The corn, soybean, and small grains fungicide efficacy tables have been updated for the 2015 field season. The efficacy tables reflect efficacy ratings from a group of land grant extension pathologists from around the country. These ratings are based on unbiased, university efficacy trials over multiple years and locations. Not all products labeled for a particular crop are included on the table. This is because some products are relatively new and not enough data is available for the scientists to make a reliable rating. These tables do not reflect any advertising or endorsement of any product. These data are merely for your information as you work on developing your disease management plans for the 2015 grain cropping season. The tables can be found and downloaded as a PDF by clicking on the FUNGICIDE INFORMATION page and scrolling down. Or you can click here for the CORN table, SOYBEAN table, or SMALL GRAINS table.