Tarspot in corn continues to be the hot topic in our field crops this season. I put together a brief update on what we know based on this seasons observations, which can be found by clicking this link.
Hybrid resistance is a key component for managing many plant pathogens. To access a new sheet on hybrid response to tar spot in corn click the following link: Corn Hybrid Response to Tar Spotfin.docx.
We are currently rating multiple variety trials in affected areas across states to generate more hybrid-specific data. More information will be available soon.
Tar spot is a relatively new disease in corn. It was first described in Illinois and Indiana in 2015, and was first located near DeKalb. Tar spot has been detected to some degree in Northern Illinois each year since. However, typically infections are sparse and the disease does not come in until later in the season. Consequently, yield loss due to this disease has been minimal, and the disease mostly considered an oddity.
However, in parts of Latin America, where the disease is known as Tar Spot Complex, severe yield losses can occur. In this case, two pathogens are involved. One fungus produces the black tar spots we typically see, and another produces toxins that can cause varying degrees of foliar blight and necrosis. Our colleagues at CIMMYT in Mexico are currently working on identifying the toxins involved and how they may relate to virulence. It is important to note that there is very little known about tar spot complex, how the pathogens interact with oneanother, the epidemiology of the disease, and how the pathogens interact with their corn host. In addition, it is possible that this disease may act differently in Midwest production systems, as hybrid genetics, production practices, and environments differ from those in Latin America.
This season we have seen this disease take off in Northern Illinois, as well as Southern Wisconsin, Michigan, and parts of Indiana. Symptoms vary from from the traditional black raised bumps, to bumps with necrotic fisheye lesions, to spots on leaves that blight and drydown. Some fields have light infection, whereas others have over 30% leaf severity through the highest leaf of the hybrid. Early this summer, prior to this outbreak, we started working with colleagues in other states and CIMMYT to better understand the tar spot pathogens and improve our abilities to detect and manage this disease if needed. One item that we need for this project are samples. If you have fields with symptoms of tar spot, particularly those with necrosis associated with the lesions, please send care of Dianne Plewa at the University of Illinois Plant Disease Clinic. The website with address and contact information is located at the following address: https://web.extension.illinois.edu/plantclinic/ Please include the county of origin, if a fungicide was applied, and the hybrid, if possible.
In addition, we are working to assess potential variety response and yield impacts of this disease. If you would like to participate in the effort, please contact me at 217-300-3253 or email me at firstname.lastname@example.org. I also can be reached on Twitter @ILplantdoc
Physoderma brown spot and node rot is a disease that has been increasing in incidence in the Midwest over the past 5-10 years. We observed this disease frequently during scouting trips throughout the state conducted in late July. Recently, we have been receiving more reports of this disease and questions pertaining to it’s impact on the crop and management. I recently wrote an article on this disease and management recommendations on the Illinois Field Crop Disease Blog. Click HERE to access the article.
Scout those fields!
Many people have asked about the need to make a fungicide application for frogeye leaf spot on soybeans this season. I have posted a new article on the Illinois Field Crop Disease Blog which reviews this pathogen, how it works, and some new tools that may help you with these important decisions. Find the article by clicking here.
The University of Illinois Extension will host the Ewing Demonstration Center Agronomy Field Day on Thursday, July 26, 2018 at 9 a.m. Every growing season presents challenges to production, and this year is no exception! We are happy to host this summer field day to share with local growers current, ongoing agronomy research in southern Illinois, including cover crop trials on corn and soybeans, nitrogen management in corn, weed management in soybean, and our continuous no-till field, now in its 50th year of continuous no-till production.
We are highlighting our 50th year of continuous no-till production in our field day this year. This no-till trial area was established in 1969 by George McKibben, the “Father of No-Till”, long-time agronomist and researcher at the Dixon Springs Ag Center in southern Illinois. This plot has been cropped utilizing no-till production of corn and soybeans ever since. The “zero-till” system as it was first called, was researched to “save the soil” that was lost over the many years of intensive tillage required to raise grain crops on the sloping hills of southern Illinois with the planting equipment available at the time.
In honor of this milestone, we will have the original “zero-till planter” on display. This planter was modified and built in the early 1960s at the Dixon Springs Ag Center and used there and also at the Ewing Demonstration Center and other research sites. The demonstrated success of this zero-till planter and production system was one of the inspirations that led companies like Allis-Chalmers and John Deere to start engineering and producing no-till planting equipment. Also, joining us for the field day will be Donnie Morris, retired farm mechanic and engineer who built this planter, along with other retired Extension advisors and educators that worked at the Ewing Demonstration Center over the years.
The topics to be discussed at Field Day include:
Looking Back at 50 Years of Continuous No-till
- Current and Retired Staff, University of Illinois
Insect Management in Corn and Soybean
- Nick Seiter, Research Assistant Professor, University of Illinois
What We Have Learned After 48 Years of Continuous No-till
- Ron Krausz, Manager SIU Belleville Research Center
- Sarah Dintelmann, Undergraduate Assistant ,Weed Science, SIU
Managing Cover Crops in Corn and Soybean
- Nathan Johanning, Extension Educator, University of Illinois
Intro to Corn Genetics: Why is Sweet Corn Sweet?
- Talon Becker, Extension Educator, University of Illinois
Please join us for Agronomy Field Day to help celebrate this milestone in crop production! The field day is free and open to anyone interested, and lunch will be provided. Certified Crop Advisor CEUs will also be offered (Soil & Water – 2.0; IPM – 0.5, Crop Management – 0.5). The Ewing Demonstration Center is about 20 minutes south of Mt. Vernon located at 16132 N. Ewing Rd; Ewing, IL 62836, on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road. Watch for signs.
To help us provide adequate lunch and materials, please RSVP to the University of Illinois Extension Office in Franklin County at 618-439-3178 by Tuesday, July 24. For additional information on the field day, contact Marc Lamczyk at the Franklin County office or email@example.com.
Today we received reports of Tar spot appearing in corn grown in Illinois. We are currently studying tar spot of corn in the United States, and are requesting that any CCA, producer, or ag professional that encounters this disease, even if outside of Illinois, please send samples to Diane Plewa at the University of Illinois Plant Diagnostic Clinic.
S-417 Turner Hall, 1102 S.Goodwin Ave.
Urbana, IL 61801
Please note “Tar spot study” on the sample.
We are at that time in the season where many people will be making final decisions regarding fungicide applications in soybeans and corn. I wrote an article with tips and other items to consider when making fungicide decisions and on farm trials on the Illinois Field Crop Disease Blog, which can be found by clicking HERE.
With the storm that moved through the state the past week, it is not surprising that we are seeing more seedling diseases in soybeans. In many cases Rhizoctonia has been identified as the causative organism, alone or in combination with other soil issues such as compaction. Rhizoctonia is one of the most common and problematic seedling issues for soybean producers in Illinois, and can cause significant yield losses due to stand reduction and reduced plant growth. In addition to killing germinating and emerging seedlings, Rhizoctonia can produce stem cankers. Cankers are sunken lesions that are
typically located at or near the soil line, although sometimes they can extend a couple of inches up the lower stem. Large cankers can severely reduce the translocation of water and nutrients up the stem, causing the plant to wilt and potentially die. Affected plant tissues tend to appear reddish-brown and will have a corky, almost dry-rotted look to them. Rhizoctonia typically appears in patches, and is most problematic when soils are moist and warm. Seed treatments with active ingredients that are effective for Rhizoctonia can be effective for reducing early infections. However, these products are only effective for the first week or two after planting, and are unlikely to impact disease occurring later in crop development. Varieties differ in their tolerance, but there is no resistance to Rhizoctonia.
Another pathogen that we may start to see more of in the upcoming days is Phytophthora. Phytophthora lesions on stems are black to brown and extend from the roots up the lower stem of the plant. Margins are not as defined as in Rhizoctonia-infected plants, and lesions are soft and mushy. Phytophthora is a water mold and is favored by wet, saturated soils. When soils are saturated and warm, the overwintering structure of this pathogen germinates, producing another structure that releases small spores into soil solution. These spores have tails, or flagellae, that propel the spores in the water. Then, the spores sense gradients in chemicals from plant roots to locate and infect root systems. A video of these spores in action can be found by clicking here. Phytophthora tends to be found in low lying, poorly drained areas of the field.
Management of Phytophthora starts with the selection of a resistant variety. There are two types of resistance available for management of Phytophthora, race-specific (Rps) and partial. Race specific is similar to a door that will completely block specific types of Phytophthora from infecting plants. However, some individuals contain a key that allows them to open that door and infect roots. Thus, if a variety with an Rps gene (door) is planted into a field with a Phytophthora population that is comprised of individuals able to overcome (key) that resistance, you may still see significant infection. The most common Rps genes are Rps1a, Rps1c, Rps1k, Rps3a, and Rps 6. Although many varieties only have a single Rps gene, some have multiple, or stacked Rps genes. Partial resistance acts like bouncers guarding the stage at a concert. They provide some resistance to all populations of Phytophthora, but some disease, typically less and developing at slower rates, can be caused (rowdy fans who eventually jump on stage, only to be pulled off soon thereafter). Partial resistance is not expressed until later in plant development, typically after V1, and therefore are not effective for managing early infections. Like Rhizoctonia, seed treatments can provide benefits early in the season. It is important to realize that Phytophthora is not a true fungus, but an oomycete, and therefore seed treatments must contain oomycete- specific active ingredients (e.g. metalaxyl, mefanoxam, ethaboxam).
Now is the time that seedling diseases of soybeans will start to be apparent. Indeed, we have started to see more images of soybeans that may have symptoms of seedling disease. However, it is important to understand that seedling diseases are complex, and a simple picture often is not sufficient to adequately diagnose the issue. I wrote a more extensive of seedling diseases of soybean on the Illinois Field Crop Disease Blog, which can be accessed here