Corn Disease Update - Tar Spot

May 17, 2016

By Angie Peltier

Figure. Raised, black ascoma characteristic of tar spot of corn (photo source: Russ Higgins, University of Illinois Extension).

Last September tar spot, a corn disease that had not been previously found in the continental US, was confirmed in corn samples collected in Indiana and in several northern Illinois counties.This disease occurred late enough in the growing season that yield loss was not of concern, but many questions remained. Before its 2015 Midwestern appearance, tar spot was only found on corn grown under very humid conditions in Latin America and Puerto Rico. This disease, caused by the fungus Phyllachora maydis, is characterized by leaf lesions that contain raised, black structures called ascoma. Ascoma resemble small drops of tar (Figure) and house reproductive structures called perithecia which produce ascospores. These ascospores can cause additional infections during the growing season.

In addition to P. maydis, a fungus called Monographella maydis can be found in tar spot lesions in Mexico. In Mexico, it is the two fungi working as part of the tar spot 'complex' that result in significant leaf damage and yield losses. University of Illinois Plant Clinic staff members were unable to isolate M. maydis from any of the Illinois tar spot lesions.

P. maydis was not expected to survive the northern Illinois winter as similar to the rust pathogens, it is an obligate parasite and requires living plant tissue to survive. University of Illinois personnel set out to test these expectations through survival observations. In October, extension commercial agriculture educator Russ Higgins collected symptomatic leaves from a late-planted corn trial at the former Northern Illinois Agronomy Research Center. In order to easily recover the leaves in the springtime, they were placed in mesh bags. The bags were staked to either the soil surface or buried 3 to 5 inches deep to expose the leaves to conditions that would mimic either no-till or fall tillage, respectively. In April, after the leaves experienced the northern Illinois winter, they were recovered and delivered to the University of Illinois to the plant pathology lab of Dr. Santiago Mideros. Researchers were unable to observe live perithecia or ascospores under a microscope. Provided that (similar to in its home in Mexico) this pathogen is not able to survive the winter on any of the perennial grasses in or near corn fields in Illinois, this preliminary survival study suggests that farmers may have one less disease to worry about in 2016.

If you suspect that you have tar spot in your corn in 2016, please send a sample to the University of Illinois Plant Clinic.

Source: illinois.edu

Video: Seeing the Whole Season: How Continuous Crop Modeling Is Changing Breeding

Plant breeding has long been shaped by snapshots. A walk through a plot. A single set of notes. A yield check at the end of the season. But crops do not grow in moments. They change every day.

In this conversation, Gary Nijak of AerialPLOT explains how continuous crop modeling is changing the way breeders see, measure, and select plants by capturing growth, stress, and recovery across the entire season, not just at isolated points in time.

Nijak breaks down why point-in-time observations can miss critical performance signals, how repeated, season-long data collection removes the human bottleneck in breeding, and what becomes possible when every plot is treated as a living data set. He also explores how continuous modeling allows breeding programs to move beyond vague descriptors and toward measurable, repeatable insights that connect directly to on-farm outcomes.

This conversation explores:

• What continuous crop modeling is and how it works

• Why traditional field observations fall short over a full growing season

• How scale and repeated measurement change breeding decisions

• What “digital twins” of plots mean for selection and performance

• Why data, not hardware, is driving the next shift in breeding innovation As data-driven breeding moves from research into real-world programs, this discussion offers a clear look at how seeing the whole season is reshaping value for breeders, seed companies, and farmers, and why this may be only the beginning.