Oak leaf miners
Defoliation of white and bur oaks over large areas of Region I by the gregarious oak leaf miner, Cameraria cincinnatiella , were reported during the months of August and September. It was common in Otter Tail, Becker and Mahnomen Counties. Oak leaf miners are the larvae of tiny moths that appear pale and silvery with bronze colored patches on their wings. While caterpillars of the solitary oak leaf miner feed singly, forming irregular blotch-like mines just below the upper epidermis, larvae of the gregarious leaf miner feed together (as many as 20) forming large irregular shaped mines. The leaves appear rusty or brownish by mid-September and fall off the tree prematurely. Winter is spent in the larval stage in leaves on the ground. There are two or more generations per year.
Recommendation. Leaves should be raked and destroyed in the fall to help reduce the overwintering population for the next year. Chemical control is often not practical and would have to be applied when the adults emerge in the spring. Natural enemies usually keep hardwood leaf miners from becoming a concern.