Tony Singh recently has become concerned about damage to his oak trees, possibly caused by herbicide "drift" from neighboring farm fields.

Several years ago, he noticed that leaves on some of his white oaks would shrivel in spring, as though something ate the green matter and left the veins.

"When leaf emergence and spraying coincide, it affects the white oaks," he says.

He contacted the Iowa Department of Agriculture, which sent a representative who took samples and determined that the leaves did contain traces of acetochlor and atrazine.

But that does not prove those herbicides caused the damage, according to Chuck Ackermann, chief of the pesticide bureau of the Iowa Department of Agriculture and Land Stewardship, which investigates reports of pesticide misapplication.

A second flush of leaves comes through, but repeated years of stress taxes the health of trees, Singh said.

Research into oak tatters and the link to certain herbicides has been conducted at the University of Illinois and is ongoing at Iowa State University and the University of Nebraska.

The current theory is that oak tatters is caused by the transfer of farm chemicals from crops to trees; so far, foresters have not found any links to insects or other diseases, according to Tivon Feeley, the forest health program leader for the Iowa Department of Natural Resources Bureau of Forestry.

"It appears that acetochlor, a herbicide used to control weeds, volatilizes after being applied on agricultural fields, and it is possible that these vapors are then blown into nearby trees and forested areas; another possibility is that wind could be carrying acetochlor-covered soil particles into these areas," according to the bureau's website.

"Though a tree's susceptibility to tatters may vary from year to year, one thing is certain: Exposure to tatters for many successive years can lead to serious decline or mortality," the website states.

Researchers at Iowa State are looking into starch levels and photosynthetic rates as well as the possibility of damage to oak roots, Feeley said.