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.

Wisconsin Mid-Season Corn Disease Update – August 2, 2019

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

The Tar Spot Situation

Figure 1. Tarspotter risk predictions for the state of Wisconsin on August 2, 2019.

Figure 1 shows the calculated risk from Tarspotter for August 2, 2019, for various locations in Wisconsin. As you can see, the present risk remains very low for most of the state. Continued warm and dry conditions have kept the risk low in Wisconsin. Tar spot is favored by persistent temperatures between 60 and 70 F and high relative humidity averaging above 75% for a 30-day period. We continue to scout fields in southern and southwestern WI and continue to find no tar spot in our travels. Tar spot has been observed now in multiple counties in Illinois, Indiana, and Michigan, along with one county in Iowa (Fig. 2). Continued dry weather is expected to keep this disease at non-existent or low levels in Wisconsin for the next couple of weeks.

Other Corn Diseases To Watch in Wisconsin

Figure 2. Corn IPM PIPE tar spot occurrence map as of August 2, 2019.

We continue to frequently find gray leaf spot (GLS) on corn. This disease is going to be problematic on some hybrids and in certain environments in Wisconsin. We are seeing GLS on ear leaves and severity is increasing. Remember, if you are going to spray fungicide, the idea is to spray preventatively before the disease reaches the ear leaves. Continue to scout fields and look in the lower canopy and watch movement of the pathogen and disease symptoms up the canopy. Optimal fungicide application timing if disease is progressing will be between VT and R3. See my previous article about making the fungicide spray decision.

Figure 3. Common rust on Corn. Photo Credit: Daren Mueller, Iowa State University, Bugwood.org

Southern rust has also been on our minds recently in Wisconsin. The disease is is caused by the fungus Puccinia polysora. Symptoms of southern rust are different from common rust (Fig. 3) in that they are typically smaller in size and are often a brighter orange color (Fig. 4). Pustules of southern rust also typically only develop on the upper surface and will be be more densely clustered. Favorable conditions for southern rust development are similar to those for common rust. high humidity and temperatures around 80F encourage disease development. However, very little free moisture is needed for infection to occur. Southern rust is typically a late-arriver in Wisconsin. When it does move in, it is usually in the southern and south-western portions of the state. Spores of this fungus have to be blown up from tropical regions or from symptomatic fields in the southern U.S. The fungus can not overwinter in Wisconsin. While southern rust epidemics can be rare events in Wisconsin, the disease can be serious when it occurs. In addition, when it occurs close to sinking, yield loss from the disease can be high. Thus, close monitoring of forecasts and scouting are needed to make timely in-seaosn management decision.

Figure 4. Southern rust on corn. Photo Credit: Emmanuel Byamukama, South Dakota State University, Bugwood.org

Currently the Corn Southern Rust iPIPE map is showing numerous confirmed cases of southern rust to our south, including an observations in a far northern Illinois county (Fig. 5). No confirmed cases have been identified in Wisconsin. However, close attention should be paid to this disease in 2019 as the confirmed cases this year have been earlier than in the past. This could mean that conditions are ripe for movement of southern rust inoculum into Wisconsin.

Management of Southern Rust

Figure 4. Corn IPM PIPE southern rust occurrence map for August 2, 2019.

Traditionally resistance was used to manage southern rust. However, in 2008 a resistance-breaking race of the southern rust fungus was confirmed in Georgia. Thus, most modern hybrids are considered susceptible to southern rust. Rotation and residue management have no effect on the occurrence of southern rust. The southern rust fungus has to have living corn tissue in order to survive and can not overwinter in Wisconsin. Fungicides are typically used to control southern rust in parts of the U.S. where this is a consistent problem. Efficacy ratings are also available for fungicides against southern rust on the Corn Fungicide Efficacy Table. Should southern rust make its way to Wisconsin prior to the “milk” (R3) growth stage in corn, it could cause yield reductions. Growers and consultants should scout carefully through the R3 growth stage and be sure to properly identify the type of rust observed. If you need assistance in identifying rust on corn, 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.

Other Useful Resources about Rusts on Corn

Purdue Extension Fact Sheet – Common and Southern Rusts of Corn

Video by Dr. Tamra Jackson-Ziems of the University of Nebraska – Identifying Rust Diseases of Corn

Wisconsin Soybean White Mold Update – August 1, 2019

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

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

Figure 1. Sporecaster predictions for selected non-irrigated locations in Wisconsin for August 1, 2019.

Figure 1 illustrates the calculated risk of white mold for select Wisconsin locations for non-irrigated soybeans, as determined by Sporecaster for August 1, 2019. This means that if soybeans are flowering and the area between rows is filled in more than 50%, risk is mostly low for the presence of apothecia and subsequent white mold development at this point in the season. Figure 2 illustrates calculated risk for the same locations for irrigated soybeans planted to 30-in row spacing. As you can imagine, risk is even higher for irrigated soybeans planted to 15-in rows.

Mild and dry conditions recently have pushed the risk down dramatically in non-irrigated fields. The UW Field Crops Pathology Team continues to scout white mold locations for apothecia. We have only observed apothecia in irrigated fields in the Hancock area.

I’m Ready To Spray, What Should I use?

Figure 2. Sporecaster predictions for selected irrigated locations with soybeans planted to 30″ row-spacing in Wisconsin for August 1, 2019.

If the canopy has met threshold, soybeans are flowering, and your Sporecaster risk is high, then a fungicide might be warranted. If you have decided to spray soybeans for white mold, what are the best products to use? Over the last several years we have run numerous fungicide efficacy trials in Wisconsin and in conjunction with researchers in other states. Applications should be targeted during the R1-R3 growth stages in soybean. Research has shown that applications outside these growth stages, are often less effective. In Wisconsin, we have observed that Endura applied at 8 oz at the R1 growth stage performs well. We have also observed that the fungicide Aproach applied at 9 fl oz at R1 and again at R3 also performs comparably to the Endura treatment. Other fungicide options also include Omega and Proline. You can view results of past fungicide evaluations for Wisconsin by CLICKING HERE. If you would like to run tailored estimations of return on investment for various fungicide programs, you can use another smartphone application called Sporebuster.

Helpful Smartphone Application Links

Sporecaster

  1. Click here to download the Android version of Sporecaster. 
  2. Click here to download the iPhone version of Sporecaster.
  3. Here is a helpful video if you would like some tips on how to use Sporecaster. If you would like some advice on how to interpret the output, we have created an additional short video on this subject.

Sporebuster

  1. Click here to download the Android version of Sporebuster.
  2. Click here to download the iPhone version of Sporebuster.
  3. Here is a video on how to use Sporebuster and interpret the output.

Other White Mold Resources

  1. To watch an in-depth video on white mold management, CLICK HERE.
  2. To find more information and download a fact sheet on white mold from the Crop Protection Network, CLICK HERE.

Wisconsin Corn Tar Spot and General Disease Update – July 18, 2019

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

Figure 1. Tarspotter risk predictions for the state of Wisconsin on July 19, 2019.

Figure 1 shows the calculated risk from Tarspotter for July 19, 2019, for various locations in Wisconsin. As you can see, the present risk has dropped substantially over the past week, leaving much of the state at low risk. The drop is due to the high temperatures and drier conditions. Tar spot is favored by persistent temperatures between 60 and 70 F and high relative humidity averaging above 75% for a 30-day period. We have also scouted fields in southern and southwestern WI and have not found tar spot in our travels.

Gray Leaf Spot, Common Rust, and Northern Corn Leaf Blight, Oh My!

Figure 2. Gray leaf spot on a corn leaf.

While scouting we have observed other foliar diseases of corn, including gray leaf spot (GLS: Fig. 2), common rust (Fig. 3), and northern corn leaf blight (NCLB; Fig. 4). Out fo these three, GLS has been the most consistent to find in fields we have visited. In Grant Co., GLS has made its way to the mid-canopy of some corn planted no-till in a field that had corn last season. It will be important to keep an eye on GLS and NCLB over the next couple of weeks. These two disease can become yield limiting if they reach the ear leaf of corn at high severity levels before the R3 corn growth stage. Scouting to determine the number of plants showing symptoms and the severity will be important in determining if a fungicide application at the tasseling growth stage is needed. Right now I’m most concerned about GLS and NCLB in field corn in Wisconsin, while keeping an eye out for tar spot.

What Should I Spray, and When Should I Spray for Corn Foliar Diseases In Wisconsin? Fungicide should be used to preserve yield and reduce disease level. 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 2019 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 GLS along with efficacy against tar spot. 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.

Figure 3. Common rust on a corn leaf.

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 over not treating across a range of environments. But in our current market, will this average gain cover the fungicide application? Today’s corn future price for September has a bushel of corn at $3.76.

Let’s Take a Closer Look at Corn Fungicide Return on Investment (ROI): While most of the early work on fungicide use in corn has focused on Headline® Fungicide, much of the industry has transitioned to using multi-mode-of-action products. These would be products mostly containing strobilurin (QoI) and triazole (DMI) fungicides in the same jug. Products such as Headline AMP® or Quilt Xcel® would fall into this category. These combination products have also been fairly consistent in response in my fungicide trials. You can find summaries of these trial results here. If we consider using Quit Xcel® at 10.5 fl oz or Headline AMP® at 10.0 fl oz, the list pricing of the product alone ranges from $15/acre (Quit Xcel®) to $22/acre (Headline AMP®). If the fungicide will be flown on with an aircraft, that cost will likely add nearly $15/acre to the application. Thus, fungicide plus application would range from $30/acre to $37/acre. If we can sell corn at $3.76 per bushel then we would need to preserve 8 bu/acre to nearly 10 bu/a in yield over not treating to break even! In a recent analysis of corn yield data where DMI+QOI products were applied at the tasseling period across the entire corn belt, the average yield preservation over not treating was 7.20 bu/a. This average projection is short of the 8 bu/a minimum we would need in the scenario above. However, the probability of preserving yield in the 8-10 bu/a range in this range is estimated to be 25% – 50%. This means that if we apply Quit Xcel® at 10.5 fl oz or Headline AMP® at 10.0 fl oz aerially, we will only break even 25% – 50% of the time with corn priced at $3.76 per bushel. If we can sell our corn for a better price or make the applications cheaper, then the odds will improve, but probably not climb above 70% even under the best case scenario. We do know that in Wisconsin, the odds of breaking even do improve if NCLB or GLS are active and increasing during the tasseling period. Get out there and scout!

Figure 4. Northern corn leaf blight on a corn leaf.

So What About Fungicide Application Timing? We can investigate this question over the U.S. corn belt using the same dataset. Applications focused on an early (V6) timing, a VT-R2 timing, or a combination of V6 plus a VT-R2 application. Let’s again focus on the QoI+DMI products. Based on observations across the corn belt the V6 timing averaged almost 3 bu/a of preserved yield over not treating. The VT application resulted in nearly 8 bu/a in preserved yield, while the two-pass program only offered a little over 8 bu/a. Clearly the higher average yield preservation occurs using a single application of fungicide at the VT-R2 timing. Wisconsin data has been consistent with this observation. Thus it is recommended that a single application of fungicide be used around the VT-R2 growth stages, when NCLB or GLS are active and increasing on or near the ear leaves.

What About Silage Corn and Ear Rot? When it comes to ear rot control and reducing the accumulation of mycotoxins in grain or silage corn, fungicide application should be made when white silks are out. Spores of fungicide that generally cause mycotoxin issues in the grain portion of corn will infect the plant through silks. Thus, apply fungicides during silking or with 5 days after silking starts, can be beneficial. Note though that if the goal is to target mycotoxin production and reduce deoxynivalenol (DON) accumulation in the grain portion of the plant, Products containing a DMI should be used. Like winter wheat, the application of some QoI-containing fungicides can increase DON accumulation in the grain portion of corn plants. Some work has been done using Proline® to control Fusarium ear rot. This DMI only product has shown promise in reducing ear rot and DON accumulation in the grain portion of the corn plant and has a label for suppressing Fusarium ear rot in Wisconsin. Performance of some additional products in Wisconsin in a 2018 silage corn trial can be viewed by CLICKING HERE and scrolling down to pages 4 and 5.

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 2019. Here is what you should consider:

1) Corn hybrid disease resistance score for NCLB and GLS – 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 weather is conducive for NCLB or GLS, 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 needed.

4) Consider your costs to apply a fungicide and the price you can sell your corn grain – Will you preserve enough yield 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. See fact sheet A3878 below for more information.

Other Resources

Video: Disease Management in Low-Margin Years (fast forward to 10:00 for corn information)

Fact Sheet: A4137 – Grain Management Considerations in Low-Margin Years

Fact Sheet: A3878 – Fungicide Resistance Management in Corn, Soybeans, and Wheat in Wisconsin

References

Munkvold, G.P. and White, D.G., editors. 2016. Compendium of Corn Diseases, Fourth Edition. 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.

Wise, K., Mueller, D., Sisson, A., Smith, D., Bradley, and Robertson, A., editors. 2016. A Farmer’s Guide to Corn Diseases. APS Press.

Wisconsin Soybean White Mold Update – July 18, 2019

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

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

Figure 1. Sporecaster predictions for selected non-irrigated locations in Wisconsin for July 18, 2019.

Figure 1 illustrates the calculated risk of white mold for select Wisconsin locations for non-irrigated soybeans, as determined by Sporecaster for July 18, 2019. This means that if soybeans are flowering and the area between rows is filled in more than 50%, risk ranges from low to medium for the presence of apothecia and subsequent white mold development. Figure 2 illustrates calculated risk for the same locations for irrigated soybeans planted to 30-in row spacing. As you can imagine, risk is higher for irrigated soybeans planted to 15-in rows.

Extremely warm temperatures over the last week have pushed the risk down dramatically in non-irrigated fields. The UW Field Crops Pathology Team continues to scout white mold locations for apothecia. We have been unable to find apothecia at all locations we have visited over the last week.

I’m Ready To Spray, What Should I use?

Figure 2. Sporecaster predictions for selected irrigated locations with soybeans planted to 30″ row-spacing in Wisconsin for July 18, 2019.

If the canopy has met threshold, soybeans are flowering, and your Sporecaster risk is high, then a fungicide might be warranted. If you have decided to spray soybeans for white mold, what are the best products to use? Over the last several years we have run numerous fungicide efficacy trials in Wisconsin and in conjunction with researchers in other states. In Wisconsin, we have observed that Endura applied at 8 oz at the R1 growth stage performs well. We have also observed that the fungicide Aproach applied at 9 fl oz at R1 and again at R3 also performs comparably to the Endura treatment. Other fungicide options also include Omega and Proline. You can view results of past fungicide evaluations for Wisconsin by CLICKING HERE. If you would like to run tailored estimations of return on investment for various fungicide programs, you can use another smartphone application called Sporebuster.

Helpful Smartphone Application Links

Sporecaster

  1. Click here to download the Android version of Sporecaster. 
  2. Click here to download the iPhone version of Sporecaster.
  3. Here is a helpful video if you would like some tips on how to use Sporecaster. If you would like some advice on how to interpret the output, we have created an additional short video on this subject.

Sporebuster

  1. Click here to download the Android version of Sporebuster.
  2. Click here to download the iPhone version of Sporebuster.
  3. Here is a video on how to use Sporebuster and interpret the output.

Other White Mold Resources

  1. To watch an in-depth video on white mold management, CLICK HERE.
  2. To find more information and download a fact sheet on white mold from the Crop Protection Network, CLICK HERE.

Wisconsin Soybean White Mold Update – July 11, 2019

Figure 1. Sporecaster predictions for selected non-irrigated locations in Wisconsin for July 11, 2019.

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

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

Figure 1 illustrates the calculated risk of white mold for select Wisconsin locations for non-irrigated soybeans, as determined by Sporecaster for July 11, 2019. This means that if soybeans are flowering and the area between rows is filled in more than 50%, risk ranges from medium to high for the presence of apothecia and subsequent white mold development. Figure 2 illustrates calculated risk for the same locations for irrigated soybeans planted to 30-in row spacing. As you can imagine, risk is higher for irrigated soybeans planted to 15-in rows.

The UW Field Crops Pathology Team has started scouting white mold locations for apothecia. Overall, apothecia have not been observed at most locations, due to the fact that soybean canopies have not filled in to threshold. At only one location were we able to find apothecia and this location had met the canopy threshold. Remember, canopy closure is critical in calculating the probability of apothecial presence and subsequent white mold risk.

I’m Ready To Spray, What Should I use?

Figure 2. Sporecaster predictions for selected irrigated locations with soybeans planted to 30″ row-spacing in Wisconsin for July 11, 2019.

If the canopy has met threshold, soybeans are flowering, and your Sporecaster risk is high, then a fungicide might be warranted. If you have decided to spray soybeans for white mold, what are the best products to use? Over the last several years we have run numerous fungicide efficacy trials in Wisconsin and in conjunction with researchers in other states. In Wisconsin, we have observed that Endura applied at 8 oz at the R1 growth stage performs well. We have also observed that the fungicide Aproach applied at 9 fl oz at R1 and again at R3 also performs comparably to the Endura treatment. Other fungicide options also include Omega and Proline. You can view results of past fungicide evaluations for Wisconsin by CLICKING HERE. If you would like to run tailored estimations of return on investment for various fungicide programs, you can use another smartphone application called Sporebuster.

Helpful Smartphone Application Links

Sporecaster

  1. Click here to download the Android version of Sporecaster. 
  2. Click here to download the iPhone version of Sporecaster.
  3. Here is a helpful video if you would like some tips on how to use Sporecaster. If you would like some advice on how to interpret the output, we have created an additional short video on this subject.

Sporebuster

  1. Click here to download the Android version of Sporebuster.
  2. Click here to download the iPhone version of Sporebuster.
  3. Here is a video on how to use Sporebuster and interpret the output.

Other White Mold Resources

  1. To watch an in-depth video on white mold management, CLICK HERE.
  2. To find more information and download a fact sheet on white mold from the Crop Protection Network, CLICK HERE.

Wisconsin Corn Tar Spot Update for July 11, 2019 – Frass Happens!

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

Figure 1. Tarspotter risk predictions for the state of Wisconsin on July 11, 2019.

Figure 1 shows the calculated risk from Tarspotter for July 11, 2019, for various locations in Wisconsin. Figure 2 shows the risk for locations in southern and south-central Wisconsin. As you can see, the present risk remains generally high for tar spot development in all locations examined. However, risk percentages have dropped over the last week, for the most part. The continued elevated risk is due to the fact that the humidity was high over the last weekend, despite warmer temperatures. As temperatures climb and conditions remain dry, expect risk to decline. Tar spot is favored by persistent temperatures between 60 and 70 F and high relative humidity averaging above 75% for a 30-day period.

Frass Happens!

Figure 2. Tarspotter risk predictions for southern Wisconsin on July 11, 2019.

That’s right folks, frass or bug poop is a common reality in corn fields. With all of the hype concerning tar spot, it has gotten folks out scouting corn. This is a good thing. However, we have received many samples in our diagnostic clinic that were submitted for tar spot confirmation. So far, these have all been confirmed to be insect frass or bug poop (Fig. 3). We have also scouted fields in Dane co., Walworth Co., Grant Co., and Lafayette Co. and have not observed tar spot in any fields visited. We have seen lots of insect frass though.

How can you tell if it is bug poop and not tar spot? Use a little spit or some water from a water bottle. Wet the leaf and lightly rub.  Bug poop will come off, tar spot will not. In addition, tar spot spots will be raised and can be felt when you rub your finger across the black spot. Frass generally won’t feel like it is raised. Continue to scout and send samples. It is always better to get a confirmation, before you spray. If it is nothing to worry about, you can save the trip and the money!

The Current Recommendation

Figure 3. Insect frass (a.k.a bug poop) on the surface of a corn leaf. Photo Credit: Roger Schmidt.

While weather continues to be mostly conducive for tar spot, evaluate the likelihood that tar spot might develop in your field. Remember, if you have no history of the disease, then the likelihood of local inoculum being present is low. Saving the fungicide application for as as close to tassel or white silking periods will be the best option resulting in the highest return on the fungicide investment. If you have a history and you know you have a susceptible hybrid coupled with a no-till situation, then the risk is higher and you need to evaluate the economics of doing an application of fungicide as early as V6. Remember, if you do a V6-V8 application of fungicide, conditions could stay conducive later in the season for tar spot. Those early applications will “burn out” by the time the tasseling period rolls around. So if you do put a fungicide spray on at V6, you might have to come back at VT with another application to protect plants during the reproductive phase, should we stay in favorable conditions for tar spot. Keep an eye on the weather and keep scouting!

More Tar Spot Information

  1. Tar spot Fact sheet
  2. Short Tar Spot Video
  3. Tar Spot Webinar 
  4. Corn Fungicide Efficacy Table

Don’t let Fusarium Head Blight Keep You Down – Prepare Now to Harvest Those Scabby Wheat Fields

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison
Shawn P. Conley, Extension Soybean and Small Grains Agronomist, University of Wisconsin-Madison

Figure 1. FHB on some wheat heads. Note the bleached and reddened appearance of infected kernels.

Fusarium head blight (FHB) or scab has been observed at moderate to high levels in some Wisconsin winter wheat fields this season. Incidence and severity have been variable by location, susceptibility of the wheat variety, and if a fungicide was applied at or shortly after anthesis. Generally, we have observed more FHB in the southern and south-central wheat growing areas of the state, but it can be found just about everywhere we have visited this year. It is important to scout your maturing wheat crop and consider how much damage from FHB might be in a field as you prepare for harvest. While FHB can cause direct yield loss, the fungus that causes this disease can also produce deoxynivalenol (also known as DON or vomitoxin). Assessing wheat fields now can assist you in determining how much vomitoxin might be expected at harvest. However, it is possible to find high levels of vomitoxin in finished grain, even if FHB levels where low.

What does scab look like? Diseased spikelets on an infected grain head die and bleach prematurely (Fig. 2).  Healthy spikelets on the same head retain their normal green color.  Over time, premature bleaching of spikelets may progress throughout the entire grain head.  If infections occur on the stem immediately below the head, the entire head may die.  As symptoms progress, developing grains are colonized causing them to shrink and wrinkle.  Often, infected kernels have a rough, sunken appearance, and range in color from pink or soft gray, to light brown. As wheat dries down, visual inspection of heads for scab will become more difficult.

Figure 2. Fusarium head blight of winter wheat

Why is identifying scab important? Scab identification is important, not only because it reduces yield, but also because it reduces the quality and feeding value of grain.  In addition, the FHB fungus may produce mycotoxins, including DON or vomitoxin, that when ingested, can adversely affect livestock and human health.  The U.S. Food and Drug Administration has set maximum allowable levels of DON in feed for various animal systems, these are as follows: beef and feedlot cattle and poultry < 10ppm; Swine and all other animals < 5ppm. In addition, local grain elevators test for DON and discount loads of grain for unacceptable levels of the mycotoxin. Be sure to check with your local elevator about their thresholds for docking grain and discount schedule based on the level of DON detected BEFORE you bring a load for delivery.

What should I do to prepare for wheat harvest?

  1. Scout your fields now to assess risk. Wheat is maturing rapidly. As maturity progresses it will be increasingly difficult to assess the incidence and severity of the infection. Understanding a field’s risk will help growers either field blend or avoid highly infected areas so entire loads are not rejected.
  2. DO NOT spray fungicide now. Research has demonstrated that the window of opportunity to manage FHB with fungicides is at the beginning of anthesis and only lasts about 7 days. Applications later than 7 days after the start of anthesis are not effective in controlling FHB. In addition, most fungicide labels do not allow a pre-harvest interval (PHI) suitable for a late application on wheat. Any application now would be off-label.
  3. Adjust combine settings to blow out lighter seeds and chaff. Salgado et al. 2011 indicated that adjusting a combine’s fan speed between 1,375 and 1,475 rpms and shutter opening to 90 mm (3.5 inches) resulted in the lowest discounts that would have been received at the elevator due to low test weight, % damaged kernels, and level of the mycotoxin deoxynivalenol (DON; vomitoxin) present in the harvested grain.
  4. Know your elevators inspection and dockage procedure and discount schedule (each elevator can have a different procedure and discount rate).
  5. Scabby kernels does not necessarily mean high DON levels and vice versa. For example, in a 2014 fungicide evaluation very low visible levels of FHB were observed for all treatments. However, when the finished grain was tested for DON, significant levels were identified for all treatments. Be sure to test and know what levels of DON are in your grain even if you didn’t see a high level of visible disease. Also, don’t assume that because a fungicide was used, there will be no DON.
  6. DON can be present in the straw so there is concern regarding feeding or using scab infected wheat straw.  DO NOT use straw for bedding or feed from fields with high levels of scab (Bissonnette et al., 2018; Cowger and Arellano, 2013). If in doubt, have the straw tested for DON levels.
  7. Do not save seed from a scab-infected field. Fusarium graminearum can be transmitted via seed. Infected seeds will have decreased growth and tillering capacity as well as increased risk for winterkill.
  8. Do not store grain from fields with high levels of scab.  DON and other mycotoxins can continue to increase in stored grain.
  9. Harvest in a timely fashion to minimize elevator discounts and balance dockage due to FHB. Click here to read about some recent research on optimizing harvest timing in winter wheat.
  10. For more information on Fusarium head blight click here.

References

  1. Bissonnette, K.M., Kolb, F.L., Ames, K.A., and Bradley, C.A. Effect of Fusarium head blight management practices on mycotoxin accumulation of wheat straw. Plant Dis. 102:1141-1147.
  2. Cowger, C., and Arellano, C. 2013. Fusarium graminearum infection and deoxynivalenol concentrations during development of wheat spikes. Phytopathology 103:460-471.
  3. Salgado, J. D., Wallhead, M., Madden, L. V., and Paul, P. A. 2011. Grain harvesting strategies to minimize grain quality losses due to Fusarium head blight in wheat. Plant Dis. 95:1448-1457.

Wisconsin Corn Tar Spot Update – July 3, 2019

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

Figure 1. Tarspotter risk predictions for the state of Wisconsin on July 3, 2019.

Figure 1 shows the calculated risk from Tarspotter for July 3, 2019, for various locations in Wisconsin. Figure 2 shows the risk for locations in southern and south-central Wisconsin. As you can see, the present risk remains generally high for tar spot development in all locations examined. This is due to the fact that the weather continues to be relatively wet and humid for the past 30 days across the entire state. Tar spot is favored by persistent temperatures between 60 and 70 F and high relative humidity averaging above 75% for a 30-day period. We have been right in the zone for conducive conditions for this disease.

We have also spent the last few days scouting corn in Walworth Co., Grant Co., and Lafayette Co. Some of these fields are planted to known tar spot-susceptible hybrids and planted in fields with a history of the disease. We have been unable to find any symptoms of tar spot. Fields generally look disease free with just a bit of Anthracnose, which is common this time of year.

The Recommendation

Figure 2. Tarspotter risk predictions for southern Wisconsin on July 3, 2019.

While weather continues to be conducive for tar spot, evaluate the likelihood that tar spot might develop early in your field. Remember, if you have no history of the disease, then the likelihood of local inoculum being present is low. Saving the fungicide application for later in the season might be a better option. If you have a history and you know you have a susceptible hybrid coupled with a no-till situation, then the risk is higher and you need to evaluate the economics of doing an application of fungicide as early as V6. Remember, if you do a V6-V8 application of fungicide, conditions could stay conducive later in the season for tar spot. Those early applications will “burn out” by the time the tasseling period rolls around. So if you do put a fungicide spray on at V6, you might have to come back at VT with another application to protect plants during the reproductive phase, should we stay in favorable conditions for tar spot. Keep an eye on the weather and keep scouting!

More Tar Spot Information

  1. Tar spot Fact sheet
  2. Short Tar Spot Video
  3. Tar Spot Webinar 
  4. Corn Fungicide Efficacy Table