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Dry weather conditions limiting the spread of tar spot disease

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TIPPECANOE COUNTY, Ind. (WLFI) — The month of August will be an important month for farmers.

After dealing with drought conditions in July, everything is in mother natures hands right now.

“The big thing for the state of Indiana is that we haven’t had the best corn and soybeans that we’ve seen in the last couple of years,” said Purdue Extension Corn Specialist, Dan Quinn. “Looking at last week’s USDA crop report we’re sitting at about 46% good to excellent for the state of Indiana and that’s behind states like Illinois, Ohio and Iowa. Those are states where a lot of corn is produced.”

Quinn says there are a few reason why Indiana’s corn crop is behind.

“Because of both the delay in planting and the drought, we had a lot of really dry conditions especially here in Tippecanoe County,” said Quinn. “We had a lot of drought stricken corn that really knocked-back some of those condition ratings.”

Towards the end of July, the state of Indiana received some much-needed rain. Quinn says it came at a critical time.

"With the corn across the state we’re getting into the most critical stages of that corn plants life,” said Quinn. “It’s in pollination so you can see the tassels when you drive by corn fields in the state and when those tassel comes out, that corn plant is moving into those reproductive stages.”

Quinn says crops are looking a little better due to the rain we received.

“I’ve kind of got one word from a lot of farmers because I do a lot of meetings with a lot of farmers around the state, and I’ve asked them ‘how’s your crop looking?’,” said Quinn. “Really in the last week or so a lot of them just tell me one word and it’s ‘better’ so the fact that the crop is getting better that’s good that we caught some of that moisture.” 

However Assistant Professor Extension Field Crop Pathologist at Purdue University, Darcy Telenko, says the dry conditions in July had another impact on Indiana's corn crop. 

“So far this year tar spot has been quiet,” said Telenko. “Last year when we had a rally bad epidemic is started early, so we started it around July 4 with our first finds and it just continued to build from that.”

Telenko says she just found the first tar spot case at the end of July.

“Right now it’s still really hard to find, “said Telenko. “So that means the disease is starting a little later in the season, which means we don’t have a long period to protect the corn like we had last year when we had a lot of yield loss because of the disease.”

Telenko says there's a reason why tar spot has had a delayed start this year.

 “So the environment is the big key factor of how bad a disease will happen in each crop and each disease each season,” said Telenko. “Tar Spot needs a long period of leaf wetness and so those last couple of weeks where we were really dry and lacking water, I think we slowed it down.”

Last year Tar Spot disease was found in all but 10 counties in Indiana, but it's off to a slow start this year.

“I’m less worried about it than I was in 2021,” said Telenko. “2021 when we found it on July 3 that was really early; it was two weeks earlier than we had found it in previous years.”

Telenko says the disease can live on debris from the previous year, so once a field has tar spot it will likely have it again.

“We know that the inoculum is there,” said Telenko. “But again it’s the weather conditions that is going to dictate how fast it ramps up in that crop canopy.”  

Quinn is hopeful the month of August will bring favorable weather conditions to help crops thrive.

“Any stress that comes in during this time period, even consecutive cloudy days, drought, nutrient deficiencies and disease can impact that corn crop pretty significantly,” said Quinn. “So it’s good that we’ve caught some moisture.”

However, Telenko and her team will continue to monitor fields for tar spot moving forward.

She says moisture can create the perfect condition for tar spot to take off. 

"These mornings with these long dews are the perfect environment for the disease to take off," said Telenko. "It's just delayed it's start, which is good news that maybe it wont be as bad when it comes in, but we know it'll be here by the end of the season. It just hasn't started as early as it had last year."

Telenko encourages farmers to continue scouting their fields and send samples to be tested.

“We have Indiana Corn Marketing money to support those samples and it’s free of charge to send those leaves in and we can diagnosis them,” said Telenko. “If you think you have Tar Spot please reach out to me and we can help inform others that the disease is active in their area.”


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