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Solitary oak leafminers causing leaf disfiguration throughout the county
Oak leaf
Solitary oak leafminers are damaging leaves of white oak trees throughout the county.

Part of what we do on the Agriculture and Natural Resources side of UGA Extension is detective work. Today, I’ll give you an inside look as the Forsyth County Extension ANR team solves a trending plant pathology mystery.

We started the week at the Extension office with several concerned client calls and emails about sudden eruptions of leafspots on their oak trees. 

Photographs emailed to us showed oak leaves covered with numerous round, whitish spots on the upper surface. After three weeks without rain, however, a diagnosis of fungal leafspots didn’t quite fit the situation.

Plus, the fungus the spots most closely resembled, Tubakia, is a late summer pathogen that tends to affect red oaks. It’s mid-spring, and all the photos we received were of white oaks. 

Simple oak identification tip: White oaks have rounded leaf lobes. Oaks in the red and black family group have sharp, bristle-pointed lobes.

Under the circumstances of season, plant species, and weather conditions, some type of gall seemed more likely. There are many different oak galls caused by insects and fungus. 

To make a diagnosis, we needed more information than photos could provide. We needed a physical specimen to examine.

Solitary oak leafminers
Oak leaf damage we seeing this week is caused by solitary oak leafminers, the larva of a tiny moth. -Micrograph by Beverly Adams.

Since the alarming pathology seemed to be widespread, I scouted the trees behind the Extension office hoping to find a white oak showing similar signs. 

Sure enough, I was able to collect leaves with similar tan and white blotches from two different varieties of white oaks. On close examination of one spot, we saw something moving inside. 

“Leafminer,” proposed ANR Educator Shannon Kennedy. A good lead. Leafminer larvae eat plant tissue between the upper and lower surfaces of the leaf, creating tunnels or blotches of detached epidermis that lacks the green color of chlorophyll.

After cutting open a leaf blotch, ANR Program Assistant Beverly Adams captured a living specimen under the microscope. 

Comparing her micrograph to images of leafminers that affect oaks, I identified the leaf-delving insect as a solitary oak leafminer, the minute larva of the microlepidoptera Cameraria hamadryadella. 

Rather than laying eggs en masse, this tiny moth anchors her eggs one-by-one to the upper surface of white oak leaves, ensuring that each larva benefits from the food available its own leaf mine. Hence the “solitary” designation in its name. 

Had we not disturbed this little leafminer – and presuming it escaped becoming food for another of nature’s wild wonders – it would have spun a delicate cocoon and pupated inside it until it was ready to emerge from both cocoon and leaf as a miniscule adult moth. Two generations per year are possible. Late season larvae enter dormancy and overwinter in fallen leaves.

We seem to be experiencing a heavy infestation in the county this spring, but it’s not necessarily a cause for worry. Trees may drop heavily damaged leaves and replace them with new leaves. Pesticide treatments are not recommended for managing leafminers, but raking up and destroying leaf litter is an effective control measure to reduce populations in subsequent years. 

If you have plant pathology or insect identification questions, contact Forsyth County Extension at 770-887-2418 or 

UGA Extension strives to translate the science of life for use in everyday living. Forsyth County Extension is supported by the University of Georgia, Forsyth County Board of Commissioners, Forsyth County Board of Education, and United Way of Forsyth County.