Notice: Using Internet Explorer may cause some issues with loading dynamic content such as Cash Bids. Please use a modern browser such as Edge, Firefox, or Chrome.

Dynamic Weather Icon for Today's Forecast
Weather N/A

Tar spot in corn – is it coming to Ontario?

08/19/2020
Tar spot in corn – is it coming to Ontario?

Written by Mark McKerrall
Crop Sales Specialist
AGRIS Co-operative – Thamesville
Wanstead Farmers Co-operative


Tar spot in corn is caused by the fungal pathogen Pyllachora maydis. The disease is prevalent in Mexico and other Central and South American counties, as well as the Caribbean.  In the Latin America region, Pyllachora maydis and Monographella maydis co-infect corn plants to cause the tar spot complex.

 Tar spot was first confirmed on field corn in the United States in 2015 in northwestern Indiana and north-central Illinois, and as of 2019 the disease has been found in Florida, Illinois, Indiana, Iowa, Michigan, Ohio and Wisconsin. So far, tar spot in the U.S. is only caused by P. maydis, as M. maydis has not been detected on symptomatic plants.
 
Since tar spot was detected in the U.S. it has caused varying amounts of damage. In 2018 when early infection (R5), occurred tar spot caused severe lodging and yield losses of 20-60 bu/ac. Yield loss was associated with an early, rapid senescence that led to reduced ear size and poor grain fill. However very late detection of the disease in some fields that very same year resulted in no yield loss. The single pathogen P. maydis tar spot complex does not seem to have same severe yield loss potential as the multi pathogen complex present in Latin America.

TarSpot_D_Malvick.png

Tar spot appears as small, raised, black spots scattered across the upper and lower leaf surfaces. These spots are ascomatum (fungal fruiting structures). Tan to brown lesions with dark borders surrounding ascomatum can also develop. These are known as “fisheye” lesions.


The keys to managing tar spot is hybrid resistance, residue management, crop rotation and fungicide applications.

Hybrid resistance testing is in its infancy as tar spot is relatively new to the U.S. and presently there are no resistant hybrids available. Some hybrids are more tolerant then others.

Residue management is only moderately effective as tar spot is both residue borne and wind borne. The bottom is that if you are practicing conservation tillage/no-till, there is no reason to return to conventional tillage systems.
Similarly, a corn/soy crop rotation is unlikely to have much of an effect on tar spot as these fields were just as severely impacted in 2018 as the corn on corn acres. 

There are numerous fungicides labeled for tar spot suppression. However, tar spot ramps up reproduction and symptom development rapidly so timing of application is critical. Multiply applications are usually not cost effective. A single timely application (R1-R3) multiple mode fungicide application is your best option.

The last thing to remember is this disease is heavily impacted by weather. Just because you have severe tar spot one season does not mean you are going to have it the following year. If you had tar spot before and your corn is heading into VT with a forecast of heavy persistent rains you may want to consider a fungicide application.

The concern in our trading area is there are tar spot infected fields as close by as Michigan. Remember tar spot is both residue borne and wind borne so it is possible it could show up in Ontario sometime in the future. If you have any questions or concerns please contact your local AGRIS or Wanstead Farmers Crop Sales Specialists. 

Sources: Ref: Purdue.edu/extension, Illinois farmdoc Extension

Your choice regarding cookies on this site:

We use cookies to optimize site functionality and give you the best possible experience.
Privacy Policy

Your choice regarding cookies on this site:

We use cookies to optimize site functionality and give you the best possible experience.