Tar Spot Of Corn: What To Know And New Research

by: Dan Quinn and Darcy Telenko, Purdue University

Due to its relatively recent U.S. discovery and its ability to cause significant production and economic losses, tar spot is often a topic of angst and anxiety amongst corn farmers and agronomists in Indiana. For example, a severely infected field can reach yield losses upwards of 60 bushels per acre! Yield losses are often a result of reduced photosynthetic capacity (green leaf area) of the corn plant during grain fill resulting in poor grain fill, kernel abortion, and reduced kernel weight. In addition, severe infection can reduce corn stalk integrity and cause significant lodging later in the season. Tar spot was first confirmed in northwest Indiana in 2015 and the first significant yield-reducing event of the disease was observed in 2018. Similarly, severe outbreaks and large areas of infection of this disease were observed in Indiana in 2021. Tar spot is caused by the fungus known as Phyllachora maydis and can be identified by small, raised black and circular spots present on corn leaves, stalks, and husks (Figure 1). These black and circular spots are known as fungal fruiting structures called stromata, each of which can produce thousands of spores. Overall, tar spot infection and severity can vary based on environmental conditions, the total amount of the pathogen present in the field, and corn hybrid chosen.

What Conditions Cause Tar Spot? Continue reading

Xyway Corn Fungicide Trial

Knox County Xyway Trials

Taking stand counts at our Xyway plot – Great looking field of corn!

 

 

A Special Thanks to Ed & Vicki Piar!!

 

The goal of this study is to determine corn’s response to an at-plant soil application of flutriafol (Xyway™) fungicide. Information from this trial will be used to improve corn disease management recommendations for growers throughout the state.

Vomitoxin Research 2022 – Plot #4

Knox County Vomitoxin Research Station #4 Installed – Thanks to Dr. Pierce Paul and Crew!

A Special Thanks to Braddock Farms – Jim and Susan Braddock!!

 

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots. Corn from fields with this disease issue may need to be tested for potential contamination.

The goal of this Statewide research project is to develop a prediction model that will allow producers to take corrective action based upon a weather prediction model to prevent plant infections.

40 of these research stations are scattered throughout West-Central Ohio.

Vomitoxin Research 2022 – Plot #3

Knox County Vomitoxin Research Station #3 Installed – Thanks to Dr. Pierce Paul and Crew!

A Special Thanks to Clark Farms – Tom and Nate Clark!!

 

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots. Corn from fields with this disease issue may need to be tested for potential contamination.

The goal of this Statewide research project is to develop a prediction model that will allow producers to take corrective action based upon a weather prediction model to prevent plant infections.

40 of these research stations are scattered throughout West-Central Ohio.

Vomitoxin Research 2022 – Plot #2

Knox County Vomitoxin Research Station #2 Installed – Thanks to Dr. Pierce Paul and Crew!

 

A Special Thanks to David and Emily Mitchem!!

 

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots. Corn from fields with this disease issue may need to be tested for potential contamination.

The goal of this Statewide research project is to develop a prediction model that will allow producers to take corrective action based upon a weather prediction model to prevent plant infections.

40 of these research stations are scattered throughout West-Central Ohio.

Vomitoxin Research 2022 – Plot #1

Knox County Vomitoxin Research Station #1 Installed – Thanks to Dr. Pierce Paul and Crew!

 

A Special Thanks to Sassafras Hill Farms – Nate McKee and Skyler Epler!!

 

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots. Corn from fields with this disease issue may need to be tested for potential contamination.

The goal of this Statewide research project is to develop a prediction model that will allow producers to take corrective action based upon a weather prediction model to prevent plant infections.

40 of these research stations are scattered throughout West-Central Ohio.

Early Season Wheat Diseases and Fungicides

By: Dr. Pierce Paul, OSU Extension

The wheat crop in Ohio is now between early boot (Feekes 10, in the south) and approaching Feekes 8 (flag leaf emergence) in northern counties. Cooler-than-usual conditions over the last few weeks have slowed the crop down considerably, but as temperatures increase, the crop will advance through several growth stages over a relatively short period. Cool conditions have also kept foliar diseases in check, but Septoria, and to a lesser extent, powdery mildew are still showing up in some fields. Septoria tritici leaf spot is favored by cool, wet conditions similar to those experienced over the last several weeks. It usually shows up first on the lower leaves as yellowish flecks that later develop into irregularly-shaped, brownish-gray lesions, with easily-seen dark-brown to black spots (called pycnidia) in the center. Cool temperatures and high relative humidity are also required for the development of powdery mildew. Typical symptoms of powdery mildew are whitish fungal growth (pustules) on the surface of leaves and stems. If the variety is susceptible and conditions continue to be favorable, a fungicide application may be warranted to prevent both diseases from reaching the flag leaf before grain-fill.

Septoria tritici leaf spot on wheat – note the black dots (pycnidia) inside the lesion.

Most of the fungicides commonly used on wheat are rated as very good or excellent against Septoria and good or very good against powdery mildew. See the attached chart for fungicide options and efficacy. Remember,

Powdery mildew on wheat leaf – as the name suggests, note the powdery, white pustules.

always read and follow the labels when making an application. For both diseases, a single application between Feekes 8 and Feekes 10 would be sufficient to protect the flag leaf and minimize yield loss. However, applications made at these early growth stages will not provide adequate control of late-season diseases like head scab and Stagonospora glume blotch. So, you should scout fields before making your fungicide application decisions. If powder mildew and Septoria levels are low as the crop approaches heading (Feekes 10.5), you may be better off waiting to treat fields at anthesis (Feekes), as this will help to suppress head scab, which is still the most damaging and important disease of wheat in Ohio, while at the same time provide very good control of Septoria, powdery mildew, and late-season diseases such as Stagonospora and rust.