Wisconsin Corn Tar Spot Update – July 29, 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

No new county level first-detects of tar spot in Wisconsin have been added to the national tar spot map this week (Fig. 1). This week we are seeing just a a handful of new counties added in the Midwest corn belt. Note that all county level confirmations for 2020 are in areas where the disease has been previously reported.

Figure 1. Corn IpmPIPE tar spot confirmations for U.S. Counties as of July 29, 2020. Grey shading indicates past confirmation in the county. Orange shading indicates a positive confirmation for 2020. Yellow shading indicates a probable positive.

Figure 2. Tar Spot risk for various locations in Wisconsin for July 29, 2020.

Figure 2 shows the calculated risk from Tarspotter (our smartphone prediction tool for tar spot) for July 29, 2020, for various locations in Wisconsin. The action threshold for high risk is 75% using the updated Tarspotter model for 2020. As you can see, the present risk has continued to decline overall for the entire state with the exception of the far Northwest, where there is not a history of tar spot. Continued dryer and warm weather is less conducive for the development of tar spot, thus we see the risk continuing to decline. So while we can find tar spot in handful of fields, progress of the disease is slow. Remember, tar spot is favored by persistent temperatures between 60 and 70 F and high relative humidity averaging above 75% for a 30-day period, accompanied by extended periods of leaf wetness caused by dew, rain, or irrigation events. The newest Tarspotter tool captures all of these aspects and balances these in the calculations of risk in the map above.

The Recommendation

Tassels and silks have been out in the southern portion of the state. We are now in the tail-end of the window of opportunity for a fungicide application if you feel the risk for disease, including tar spot, is warranted. While tar spot is slow to develop, we have seen gray leaf spot (GLS) developing in the lower canopy and moving up. We continue to also scout for southern rust, but have had no confirmations of this disease so far in Wisconsin.

Do some scouting and check weather reports. If it is dry in your area and has been hot, then no disease may be present. You might be able to hold off on that fungicide application. If it has been humid and rainy and you have some disease present in the lower canopy, then a fungicide application might be warranted. Now is the critical time to pay attention to disease development and make a final fungicide spray decision. See my previous post for more information about making the decision to spray fungicide on corn.

More Tar Spot Information

  1. Tar Spot Fact sheet (Updated for 2020!)
  2. Short Tar Spot Video
  3. Tar Spot Webinar 
  4. Corn Fungicide Efficacy Table

Wisconsin Corn Tar Spot Update – July 14, 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

Last week brought our first detect of tar spot in Wisconsin for the 2020 field season. This week we are seeing more counties being added now in Iowa and Indiana, with some additional non-confirmed reports from southwest Wisconsin. Figure 1, show the location of the confirmed detections, which are all in the previously recorded range of the tar spot pathogen.

Figure 1. Corn IpmPIPE tar spot confirmations for U.S. Counties as of July 14, 2020. Grey shading indicates past confirmation in the county. Orange shading indicates a positive confirmation for 2020.

Figure 2. Tar Spot risk for various locations in Wisconsin for July 14, 2020.

Figure 2 shows the calculated risk from Tarspotter (our smartphone prediction tool for tar spot) for July 14, 2020, for various locations in Wisconsin. Figure 3 shows the risk for locations in southern and south-central Wisconsin. The action threshold for high risk is 75% using the updated Tarspotter model for 2020. As you can see, the present risk is elevated in much of the southern and southwestern portion of the state, the areas where reports are coming in. This is due to the fact that the weather continues to be relatively wet and humid for the past 30 days with decent rainfall. Cooler conditions this week are also contributing to the rising risk. Tar spot is favored by persistent temperatures between 60 and 70 F and high relative humidity averaging above 75% for a 30-day period, accompanied by extended periods of leaf wetness caused by dew, rain, or irrigation events. The newest Tarspotter tool captures all of these aspects and balances these in the calculations of risk in the map above.

The Recommendation

Figure 3. Tar spot risk for the southern and south-central zones of Wisconsin for July 14, 2020.

Tassels are starting to peek or are out in the southern portion of the state. We are now in the window of opportunity for a fungicide application if you feel the risk for disease, including tar spot, is warranted. Do some scouting and check weather reports. If it is dry in your area and has been hot, then no disease may be present. You might be able to hold off on that fungicide application. If it has been humid and rainy and you have some disease present in the lower canopy, then a fungicide application might be warranted. See my previous post for more information about making the decision to spray fungicide on corn.

More Tar Spot Information

  1. Tar Spot Fact sheet (Updated for 2020!)
  2. Short Tar Spot Video
  3. Tar Spot Webinar 
  4. Corn Fungicide Efficacy Table

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.

2017 Wisconsin Field Crops Pathology Fungicide Tests Summary Now Available

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

This report is a concise summary of pesticide related research trials conducted in 2017 under the direction of the Wisconsin Field Crops Pathology program in the Department of Plant Pathology at the University of Wisconsin-Madison.  We thank many summer hourlies and research interns for assisting in conducting these trials.  We would also like to thank Carol Groves, Jaime Willbur, Megan McCaghey, Cristina Zambrana-Echevarria, Bryan Jensen, John Gaska, Adam Roth and Shawn Conley for technical support.

Mention of specific products in this publication are for your convenience and do represent an endorsement or criticism.  This by no means is a complete test of all products available.  You are responsible for using pesticides according to the manufacturers current label.  Follow all label instructions when using any pesticide.  Remember the label is the law!

To download the current report, or past reports visit the SUMMARIES page by clicking here.

2015 Wisconsin Field Crops Pathology Fungicide Tests Summary Now Available!

Results of the 2015 Wisconsin Field Crops Pathology Fungicide Tests are now available. You can download a PDF copy by CLICKING HERE or by clicking on the Summaries tab at the top of the page. Also available is a 2015 special report describing first year results of testing fungicide on reduced-lignin alfalfa. That report can also be found on the Summaries page or you can download it by CLICKING HERE.

Wisconsin Winter Wheat Disease Update – June 24, 2014

Figure 1.  FHB Risk Map for June 24, 2014

Figure 1. FHB Risk Map for June 24, 2014

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

I have spent the last several days rating winter wheat variety trials and fungicide trials at the Arlington Agricultural Research Station in Arlington, Wisconsin, Columbia Co.  Wheat in this area is mostly in the mid-to-late milk stage.

Leaf rust was observed at low levels in border rows and plots not sprayed with fungicide.  Incidence (number of plants with symptoms) in some plots is near 50%.  However, severity (area of leaf covered by rust pustules) on flag leaves is low at 5% or less.  At this stage impact on yield by leaf rust will likely be low and fungicide sprays to control the disease at this stage are NOT recommended.

Septoria/Stagopsora leaf blotch was also observed on lower leaves of most plots.  Very few plots had leaf blotch symptoms on the flag leaves, and if they did, severity was in the 5% range. Impact on yield by leaf blotch at this location will be low.  Again, fungicides are NOT recommended on winter wheat at this growth stage.

Very little Fusarium head blight (scab) has been observed on winter wheat from Arlington, Wisconsin on up through to Chilton, Wisconsin. Currently the Fusarium Head Blight Prediction Center (http://www.wheatscab.psu.edu) is predicting moderate to high risk for head blight for much of the state of Wisconsin (Fig. 1).  Winter wheat in much of the state is likely past flowering now, and thus the window of opportunity to treat for head blight has passed. However, some late-planted barley may be emerging from the boot at this time and this is the window of opportunity to control scab on barley, especially with the risk being moderate to high.

If a fungicide is warranted for control of scab on barley, products such Prosaro, Caramba, or similar that contain triazole active ingredients can offer suppression of scab and reduce deoxynivalenol (DON) accumulation in harvested grain.  These products should be applied within a week from the beginning of flowering for reasonable control.  Products containing strobilurin fungicides should be avoided after heading.  Research has demonstrated that levels of DON can be higher after treatment with strobilurin products after heading.

Wisconsin Soybean Disease Update – June 19, 2014

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

Soybean planting has finally finished up for our research program.  We planted our last, late planting date trial this week.  Soybeans around the state have emerged and are at the VC or early V1 stage.  Several diseases have been noted already this year in soybeans.

Figure 1. Septoria brown spot on a soybean seedling.

Figure 1. Septoria brown spot on a soybean seedling.

With all of the rain we have been seeing early symptoms of Septoria brown spot (Fig. 1).  This is a common disease of soybean in Wisconsin and is caused by the fungus Septoria glycines.  While scouting a field near Fond du Lac this week, we observed the characteristic purple-brown lesions (Fig. 2) caused by this fungus, on the unifoliate leaves of soybean plants.  This isn’t unusual considering the moderate temperatures and frequent heavy rain.  The spores of this fungus are typically rain splashed from old soybean debris, to the growing plants.  Septoria brown spot is usually not considered a yield limiting disease, but in certain cases, it has been attributed to significant yield loss.  This is usually the case where a susceptible variety is grown in a location conducive to the disease and rain is frequent and heavy.  In a situation like this, fungicides might be required during the reproductive phase of growth to preserve yield. However, most of the time, Septoria brown spot is observed early in the season and again late in the season during periods of heavy rainfall and does not affect yield.  I suspect, once the rain subsides a bit, this disease will also subside.  However, growers and consultants should keep an eye on it just in case it does not.  To learn more about Septoria brown spot, visit the brown spot information page by clicking here.

Figure 2. Purple-brown lesions characteristic of early Septoria brown spot symptoms.

Figure 2. Purple-brown lesions characteristic of early Septoria brown spot symptoms.

Reports of seedling diseases are also starting to roll in as a result of the very wet conditions and frequent rainfall.  Pythium damping off and root rot is a likely culprit in many of these fields. Cool wet soil conditions at planting and during seedling emergence favor this disease.  There are many species of Pythium that can infect soybean and soybean pathologists are currently conducting a study to identify these species.  An informative pocket guide has been developed.  You can download a PDF version of the pocket guide by clicking here.  You will note that management focuses on adjusting planting date and using seed treatments to protect against infection by Pythium species. Foliar fungicide application is NOT recommended for this disease.

Other seed and seedling diseases might also be plaguing soybeans with all of the wet weather.  Other pathogens include Rhizoctonia and Phytopthora.  To learn more about other seed and seedling issue of soybean in Wisconsin, click here and scroll down to “seedling diseases.” You will find helpful resources pertaining to many of the common seedling issues.  Also for specific information on Phytopthora root and stem rot of soybean, you can download a UWEX fact sheet by clicking here.

Growers and consultants should scout soybeans for disease frequently during this cool wet weather.  Hopefully the rain will subside soon.  Some dry weather will help slow down the advancement of many soybean diseases.

Wisconsin Winter Wheat Disease Update – June 6, 2014

FHB Update for Wisconsin - June 6, 2014

FHB Update for Wisconsin – June 6, 2014

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

Winter wheat in the southern portion of Wisconsin is heading and will be flowering in the next few days. This is a critical time to control Fusarium head blight (scab). Currently the Fusarium Head Blight Prediction Center (http://www.wheatscab.psu.edu) is predicting low risk for head blight for most of the state of Wisconsin.  Rain is forecast for this weekend and early next week.  This may increase the risk for head blight, so growers and consultants should watch the weather and the FHB Prediction Center carefully if their wheat is flowering.

Areas of the state also have malting barley and risk for FHB can be high if conditions are favorable during barley head emergence.  Timing of fungicide application should occur as the head is emerging to protect open flowers if the weather is conducive for FHB.

If a fungicide is warranted for control of scab, products such Prosaro, Caramba, or similar that contain triazole active ingredients can offer suppression of scab and reduce deoxynivalenol (DON) accumulation in harvested grain.  These products should be applied within a week from the beginning of flowering for reasonable control.  Products containing strobilurin fungicides should be avoided on wheat that has headed.  Research has demonstrated that levels of DON can be higher after treatment with strobilurin products after heading.

No rust or powdery mildew has been observed in wheat that I have looked at.  Reports from area extension personnel and consultants also confirm these observations. Wheat appears to be relatively disease free in much of the state this year.

Hot Off the Press! New Pythium Root Rot in Soybean Scouting Card

A new Pythium root rot in soybean scouting card has been developed by research and extension soybean pathologists in the North Central region.  The describes risk and symptoms of Pythium root rot and how to scout for the disease.  Management recommendations are also included in this short and concise pamphlet.  CLICK HERE TO DOWNLOAD A PDF VERSION OF THIS SCOUTING CARD.

Disease Profile: Ergot

Ergot 1A new disease profile was recently posted describing signs and symptoms of Ergot of rye, wheat, and other grasses and consequences of the disease.  Click here to download a PDF of the disease profile.