DES MOINES, Iowa — Iowa Department of Natural Resources (DNR) officials have been fielding calls this spring from nearly 1,000 residents reporting cases of sickly oak tree leaves, likely caused by drifting farm chemicals coupled with changing weather.

 

“The reports are from many rural and community landowners throughout Iowa,” said Paul Tauke, DNR forestry bureau chief and state forester, about the damaged condition of the leaves, commonly known as oak tatters. “The IDNR is still collecting the sites and based on the current map (at the department), the majority of the reports are in central and southeast Iowa.”

Tauke said DNR found trace levels of acetochlor (an herbicide) in both rainwater and on tattered leaf tissue, which led to a greenhouse experiment where oaks were tattered using acetochlor at a 3-gram rate. “That is 1/1000th the field application rate; however, that rate isstill higher than of what we find in the rainwater. This is an area that would require further research.”

In 1961, the Iowa General Assembly designated the oak as the official state tree, which is also the nation’s official tree, according to the Iowa State University forestry extension office.

So far, the reports have been isolated to only Wright and Buchanan counties, said Gretchen Paluch, Iowa Department of Agriculture and Land Stewardship (IDALS) pesticide bureau chief. “The incident reports filed with the IDALS pesticide bureau involve cases of pesticide misuse and, at this time, the bureau does not specifically track cases by tree species, type or disease,” she explained.

Paluch said the bureau had two incident reports, which mentioned oak tatters, covering the period of fiscal years 2014-17. “One investigation is still open; the other investigation documented glyphosate and 2,4-D residues on vegetation.”

Mark Vitosh, DNR District 12 forester based in Iowa City, told Radio Iowa the oak tatters residents have reported were likely from a type of herbicide used by corn and soybean growers.

He’s known about the problem for 20 years, but said weather patterns have made 2017 a bad year for oak trees, adding the trees can usually recover from the condition.

“Our concern is, if this would happen in multiple years, year after year, that’s heavy defoliation,” he said. “It can cause stress, which can induce other insects and other things to attack them.”

He said most of the callers thought insects or diseases were damaging the leaves and that oak tatters have been spotted in both rural and urban areas.

“In the spring when they were usually an inch to 2 inches long, the edges would turn purple and kind of whitish,” he said. “I come back seven days later, and that tissue would be falling off. Insects don’t do that and diseases don’t do that.”

Officials with Monsanto, which makes chloroacetanilide herbicide products cited in studies, told the Des Moines Register it hasn’t received any complaints and wasn’t immediately familiar with research on it, so did not comment. A 2004 University of Illinois study found a strong correlation between oak tatters  and the drift of chloroacetanilide herbicides, particularly in white oaks.

“Winter injury, frost, insect attack and herbicide drift were all thought to be possible causes of leaf tatters,” researchers wrote. “We hypothesized that leaf tatters on white oak was due to herbicide drift from herbicide applications onto corn and soybean fields.”

The study stated tatters had also been reported in Illinois, Indiana, Michigan, Minnesota, Missouri, Ohio and Wisconsin.

A 2008 study in Iowa by the DNR and ISU forestry experts reported 11 million pounds of acetochlor and metolachlor (both in the chloroacetamide group of herbicides) were applied in Iowa in 2005, and showed similar correlations to oak tatters.

Tivon Feeley, DNR forest health program leader, told the Register he’s seeing a lot of oak tatters this year because a warm February and a cold March slowed oak leaf development. He said the leaves emerged at the time when the chemicals were at peak ambient levels. The number of complaints filed with the DNR this year is higher than prior years, although not at a record level.

The DNR reports the problem of oak tatters annually to the USDA Forest Service, which monitors issues with tree health, Feeley said. USDA officials said they hear more reports from Iowa than other Midwest states.

Vitosh told the Associated Press the state of Iowa has seen a significant decline in white oak trees over the last five years, and the tatters may be contributing to that decrease. Tauke said the current funding level to DNR forestry has prevented it from doing much tree leaves research.

In addition, DNR doesn’t have regulatory authority over herbicide usage or application, which currently rests with the IDALS pesticide bureau, Tauke said. “We intend to continue to take calls from landowners and provide diagnosis of tree insect and disease issues,” he said. “If oak tatters is diagnosed, we will inform landowners of the suspected causes of the tatters and what to expect in terms of their tree re-leafing later in the growing season.”

According to IDALS, when claiming an accident, incident or loss due to aperson’s use of a pesticide, the claimant must file an incident report within 60 days of the alleged date that damages occurred. If a growing crop is alleged to have been damaged, the report must also be filed before 25 percent of the crop is harvested.