Eagle Ag Consulting

"Revenue Based Agronomy"

Tar Spot- Moving West

In February Damon Smith, Wisconsin Corn Specialist presented the findings of a survey conducted last fall for tar spot in WI corn fields.  Their findings were that they estimate 97% of corn fields in the state have the overwintering inoculum.  He said it’s not a matter of if, but when for 2022.  Tar spot was identified in SE Minnesota and as far east as Martin County-Fairmont in 2021.  Tar spot is a devastating disease that just showed up in Illinois a few years ago and keeps expanding its footprint in all directions across the corn belt.  Timing of infection is the key as the later in the season it occurs, the less yield impact.  Wisconsin research showed a yield loss of 40-60 bu/acre based off of severity.  Some of our newest and top yielding hybrids are very susceptible and so we need to keep a close eye out this summer.  Corn breeders are racing to find hybrids that are more tolerant like they have done for Goss Wilt but it takes a few years to find these hybrids and get them ramped up into the pipeline for us to use.  Growers in Wisconsin and Michigan that had inoculation early last year reported 80 bushels plus losses when not treated.  Many of those areas required 2 applications of fungicide to obtain maximum yield.  Because tar spot is so new, researchers don’t know how it will respond to the drier conditions as it moves west.  For now, summer scouting is the key to catch it early before significant damage is done.

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