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Iowa fields need a stretch of dryer, cooler weather

By James Grob, jgrob@charlescitypress.com

Terry Basol said the expression “knee high by the Fourth of July” is an old tale, and in northern Iowa the corn is usually much higher by Independence Day.

“Most often we are a lot taller than ‘knee high,’” he said. “It depends on the variety, but on average the corn is 6 or 7 feet tall by now.”

The Iowa State University Extension and Outreach crop specialist, who works out of Nashua, said the warmer growing season has spurred increased corn growth this year.

“It’s got everything it needs,” Basol said. “Some farmers got their corn in early enough that it’s 7 feet tall now.”

This after what was a remarkably rainy June in Iowa. According to the National Weather Service, Charles City recorded the wettest June on record, with nearly 12 inches of rain. The normal is 5.26 inches. Just over 6 inches fell in 2017.

“I’d believe it. It seems like we’ve had a tremendous amount of rainfall,” Basol said.

Basol said the rainy conditions have not had a huge impact on the corn and soybeans crop — at least not yet.

“We always say, ‘soybeans don’t like wet feet,’” he said. “We’d like to see it dry for the soybeans to feel better.”

Northern Iowa has not seen nearly the flooding as other parts of the state have.

“The storms that have rolled across the state over the past couple of weeks have brought needed moisture to some areas, but unfortunately we have also seen significant flooding in other parts of the state,” Iowa Secretary of Agriculture Mike Naig said last week in the weekly crop report. “Many areas could use a few days of dry weather to allow fields to dry out so farmers can spray.”

Basol said he hasn’t seen a lot of washed-out fields in this part of Iowa, but knows there are some.

“Around Rockford and some other places, the flooding has ruined some spots,” Basol said. “These guys need to talk to their insurance agents and figure out what they want to do about that.”

According to the USDA report for Iowa last week, topsoil moisture levels rated 1 percent very short, 5 percent short, 68 percent adequate and 26 percent surplus. Subsoil moisture levels rated 3 percent very short, 9 percent short, 66 percent adequate and 22 percent surplus.

Heavy rainfall left many fields and pastures ponded. In south central Iowa the subsoil moisture supplies rated adequate to surplus increased to 46 percent; the highest percentage in these categories since July 2017.

“I hate to say we need dry weather, because you never want it too dry,” Basol said. “Ideally, we need some dryer weather and temperatures in the mid-80s over the next few weeks. That would be perfect.”

The corn is at a precarious stage right now, and Basol said fields don’t need too much more rain or heat.

“We already have some corn that’s starting to tassel — if it hasn’t tasseled yet, it’s getting close — so we need to keep the stress levels down,” Basol said. “We don’t want a lot of stress on the corn right now.”

According to last week’s USDA crop report, 7 percent of the corn crop has silked, a week ahead of both last year and the five-year average. Seventy-eight percent of the corn crop was rated in good to excellent condition.

Twenty-one percent of the soybean crop has bloomed, four days ahead of last year and six days ahead of the average. Seventy-six percent of the soybean crop was rated in good to excellent condition.

“The soybeans will be OK — they just need to dry out and recoup,” said Basol.

The warmer weather is usually favorable to the corn crop, Basol said, but he has seen some diseases develop this year, with the unusually hot and wet weather. Basol said corn in parts of Iowa will be very susceptible to Physoderma brown spot and node rot.

Physoderma brown spot and node rot risk increases when warm and excessively wet conditions result in water pooling in the whorl, and occurs during the early vegetative stages of corn growth. A fungus produces spores that swim through water in the whorl and infect the corn tissue.

Given the recent large amounts of rain, coupled with the warm temperatures, the disease is more likely to occur this summer.

“We usually see a little of that every year, but this year it’s more pronounced,” Basol said.

Warm temperatures and relative humidity greater than 90 percent favor gray leaf spot development as well. The fungus survives in corn residue and spores are spread by wind and splashing rain. Hybrid susceptibility and weather conditions strongly influence disease development.

“Farmers need to make sure they’re scouting their fields real well, especially if we keep having these weather conditions,” Basol said. “They just need to stay on top of it.”

Gray leaf spot can be locally severe but not cause widespread damage throughout a region. For corn that was planted late, there is usually an increased risk for disease that could result in higher levels of infection and potential yield loss, Basol said.

“Those are some of the things that have popped up due to environmental conditions and warmer temps and moisture,” he said. He added that with the wet weather, some farmers have also seen nitrogen deficiency.

“With all the rainfall, it makes sense,” he said. “Some growers have been applying some supplemental nitrogen to help out.”

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