The 2019 edition of our annual report on applied research in field crop disease and insect management can be downloaded at the following link: https://uofi.box.com/v/2019PestPathogenARB
Each year, University of Illinois plant pathologists and entomologists produce a summary of the applied research we have conducted to inform disease and insect management practices in Illinois. This information provides a non-biased, third-party evaluation of control tactics such as pesticides and resistant varieties for use in corn, soybean, and wheat.
The 2019 report includes information on the following topics:
- Surveys of insect pests and soybean cyst nematodes
- Control evaluations for diseases of corn, soybean, and wheat (including southern rust, tar spot, fusarium head blight, and more)
- Evaluations of Bt trait packages and soil insecticides in corn and foliar insecticides in soybean (including western corn rootworm, bean leaf beetle, dectes stem borer, and others)
For questions about the guide, please contact:
Nick Seiter, Field Crop Entomologist | email@example.com
Nathan Kleczewski, Field Crop Plant Pathologist | firstname.lastname@example.org
Last year we started a project focusing on determining origins of Phyllachora maydis, the causal agent of tar spot of corn, in the United States. As part of this project, we need to collect Phyllachora species from different hosts and areas. Today I went for a lunchtime walk and was able to find Phyllachora spp. on four different grass hosts. Note the large, somewhat raised stroma that follow the veins on most occasions. They can have halos around them as well. If you are walking fields, gardens, parks and happen to come across any putative Phyllachora, please send leaves and seed heads to the UIUC plant diagnostic clinic
Phyllachora stroma following the veins, which is somewhat typical for the genus. N. Kleczewski
Phyllachora spp. on a senesced grass. N. Kleczewski
Phyllachora spp. with halos around stroma. N Kleczewski
at S-417 Turner Hall, 1102 S.Goodwin Ave. Urbana, IL 61801 ATTN Tar spot survey. We really can use your help in this regard!
Nathan Kleczewski- Extension Plant Pathologist UIUC
Tar spot was a minor nuisance in Illinois this year, with many areas only affected to a mild degree. Why did we see less tar spot in 2019 and what does this mean for 2020? Click here to read the new article posted on the Illinois Field Crop Disease Hub.
Corn producers in parts of the state are nearing the point in time where they are thinking about fungicide applications to their fields. In a recent post on my blog I discussed tar spot and also mentioned a recent publication that shows that a single fungicide application at the VT/R1 growth stage has the greatest chance of providing the producer with a return on their investment. Click here for access to this article.
Nobody knows your farm history and yields better than you do. That is why running the numbers yourself and thinking about your past experiences can help you determine how likely you are to break even or make a profit using various programs under your specific situation.
To calculate how much yield needs to be protected to break even at a given application cost (fungicide cost plus application costs) and commodity price:
yield protected (bu/A) = application cost ($/A) / corn price ($/bu).
This formula can be used to help you determine the amount of protected yield and commodity price needed to break even and see a return on your investment.
For example, to see how much yield would need to be protected by a fungicide to pay for the cost of a $26/ A total application cost at a $4.50 per bu grain price:
yield protected = ($26.00 per A )/ ($4.50 per bu) = 5.8 bu/ A
the same situation but a program that costs $30 per A =
($30.00 per A)/($4.50 per bu) = 6.7 bu per A.
Below is a table of the potential protected yields needed to break even at a few different commodity prices and total application costs.
Knowing your application costs for 1 or 2 trips and product, and estimating the commodity price, what sort of yield response will you need? Have you seen this sort of yield response on your field before or not? Has this response been fairly consistent? Knowing this information can be very useful in selecting fungicide programs for your specific fields.
Corn leaf samples from LaSalle county have been positively identified by the University of Illinois Plant Clinic to be infected with Tar Spot Phyllachora maydis. Commercial Agriculture Extension Educator Russ Higgins found the disease while field scouting. The fungal leaf blight was identified in numerous northern Illinois and northern Indiana counties in 2015.
Tar Spot has distinctive signs and symptoms. The fungal fruiting body, called an ascomata, looks like an actual spot of tar on the leaf. Lesions are black, oval to circular. They can be small flecks of about 1/64” up to about 5/64”. The lesions can merge together to produce an affected area up to 3/8”. If you run your finger across the leaf you will feel tiny bumps.
Picture 1. Distinctive black fruiting bodies of Tar Spot on corn leaf 2016. Photo courtesy of Russ Higgins, University of Illinois Extension
Prior to 2015, Tar Spot was known to occur only in cool humid areas at high elevations in Latin America. Tar Spot can form a complex with another fungus. The 2 fungi that cause ‘Tar Spot disease complex’ on corn are Phyllachora maydis and Monographella maydis. When Monographella maydis is in association with Phyllachora maydis the complex has been demonstrated to cause economic yield losses in Latin America. Phyllachora maydis alone is not known to significantly reduce yield. When the two are in combination a distinctive symptom is seen. The black Tar Spot will be surrounded by a tan lesion so the two together resemble a ‘fish-eye’.
Other pathogens may be confused with Tar Spot, especially the overwintering teliospore (black) phase of corn rust. Also, there are many fungi, called saprophytes that feed on dead corn tissue and form black splotches on the leaves.
To date only one of the pathogens, Phyllachora maydis, has been found in IL in 2015 and 2016, and IN in 2015. If you suspect Tar Spot please submit a sample to The University of Illinois Plant Clinic. We are cooperating with USDA-APHIS-CAPS to get a comprehensive idea of distribution in the state. Illinois producers can participate at no cost, see how at this link https://uofi.box.com/s/bizu6oz3re35v9boif784nz4zvy85gjc
Tar spot confirmed: Announced by the Illinois Department of Agriculture today. Corn leaf samples from 3 northern Illinois counties have been confirmed positive for the fungus Phyllachora maydis by Megan Romby National Plant Pathologist with the USDA Animal Plant Health Inspection Service in Beltsville, MD. Positive counties in Illinois are LaSalle, DeKalb and Bureau. The samples were collected from commercial fields by Monsanto breeders and pathologists and sent to Dr. Kiersten Wise in response to her inquiry for samples and distribution information of the Tar spot pathogen. Dr. Wise and Purdue Plant Clinic director Gail Ruhl initially identified the pathogen which is new to the United States 1 ½ weeks ago and submitted confirmation samples to the USDA http://extension.entm.purdue.edu/pestcrop/2015/Issue24/ . Upon receipt of the Illinois samples, they diagnosed the fungus, contacted us at the University of Illinois Plant Clinic and submitted the Illinois samples to the USDA for confirmation at our request.
Scouting for the disease has been active in Illinois. Jennifer Chaky , Pioneer Plant Diagnostic Clinic, also has samples from Bureau County diagnosed with Tar spot and we have additional LaSalle county samples from our University of Illinois Extension Agronomist in Northern IL, Russ Higgins.
Figure 1. Symptoms of Tar spot on corn leaves in LaSalle County, IL. Note that orange rust pustules are also present on this leaf. Photo courtesy of Russ Higgins University of Illinois Extension
Tar spot has distinctive symptoms. The fungal fruiting body, called an ascomata, really does look like a spot of tar on the leaf. Lesions are black, sunken oval to circular. They can be small flecks of about 1/64” up to about 5/64”. The lesions can merge together to produce an affected area up to 3/8”. If you run your finger across the leaf you will feel tiny bumps.
Figure 2. Microscopic view of fruiting structure of Tar spot from Bureau County, IL. Photo courtesy of DuPont Pioneer Diagnostician, Jennifer Chaky
Prior to the Indiana finding, Tar spot was known to occur only in cool humid areas at high elevations in Latin America. There are actually 2 fungi that cause Tar spot disease on corn Phyllachora maydis and Monographella maydis. While Monographella maydis is known to be able to cause economic yield losses in Latin America, Phyllachora maydis is not known to significantly reduce yield. Other pathogens may be confused with Tar spot, especially the overwintering teliospore (black) phase of corn rust. Also, there are many fungi, called saprophytes that feed on dead corn tissue and form black splotches on the leaves.
To date only one of the pathogens, Phyllachora maydis, has been found in IN and IL. If you suspect Tar spot please submit a sample to the University of Illinois Plant Clinic. We would like to get a comprehensive idea of distribution in the state. For more information on tar spot of corn, please see the USDA-ARS Diagnostic Fact Sheet: http://nt.ars-grin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Phyllachoramaydis