DES MOINES, Iowa (AP) – Nearly 1,000 Iowa residents have contacted a state agency about sickly oak tree leaves, and officials say the problem was likely caused by farm chemicals and made worse by weather fluctuations.

Iowa Department of Natural Resources district forester Mark Vitosh tells The Des Moines Register that little can be done to stop the deterioration of the oak leaves besides stopping the use of herbicides. The condition, called leaf tatters, causes leaves to appear as if they’ve been eaten down to the veins.

Department forest health program leader Tivon Feeley says there have been more oak tatters this year because the leaves emerged at the same time chemicals were at peak ambient levels. U.S. Department of Agriculture Forest Service officials say Iowa makes more reports about sickly oak trees than other Midwest states.