Ron Wilson

Ron Wilson

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Leaf Blotches on Aesculus: Don’t Make a Quick-Draw Diagnosis - Buggy Joe

The fungus, Guignardia aesculi, produces the disease called Guignardia Leaf Blotch of Aesculus. It’s common on buckeyes and horsechestnuts in Ohio with early symptoms appearing around this time of the year.




The disease symptoms are generally described as zonate lesions on the leaflets that are often surrounded by a yellow, chlorotic halo. The lesions are initially small, reddish brown, and often bounded by the leaf veins.



As the summer progresses, the lesions expand to become large, dark brown blotches. Heavily infected trees may appear scorched as the brown leaf blotches envelop entire leaflets.




In 2020, I came across obvious reddish-brown lesions on a yellow buckeye (Aesculus flava) in southwest Ohio. My quick-draw diagnosis was the lesions were symptoms of Guignardia. However, as I zoomed in with my camera to take some pictures, some of the blotches “suddenly morphed” into something that didn’t fit with Guignardia. 



Question #6 in our “20 Questions on Plant Diagnostics” is “What Exactly Do You See?” What exactly I saw through my camera viewfinder was that the upper leaflet surface on some of the necrotic areas appeared wrinkled like the tissue was pulling away from the leaf, as if it was delaminating.



My observation produced a complete metamorphosis of my diagnosis. Leaf tissue delamination is the calling card of a leafminer. This was not Guignardia.


Of course, the images below show that Guignardia should never be eliminated without a second look to separate the blotch-like symptoms produced by a leafminer from the leaf blotch symptoms of Guignardia, and vice versa. The mix-messaging with having two look-a-like problems occurring on the same leaflets at the same time raises the importance of answering the question, “What exactly to you see?




I’ve been revisiting the yellow buckeye annually since my diagnostic U-turn. The leafminer feeds just beneath the upper leaf epidermis. It’s why I observed the wrinkling of the necrotic tissue in 2020. Also, unlike Guignardia leaf blotch, there’s little evidence on the underside of the leaflet of the blotch on the upper leaf surface created by leafminer activity.




The leafmining activity is very different from some of our more common leafminers like the Boxwood Leafminer midge fly (Monarthropalpus flavus, family Cecidomyiidae), Hawthorn Leafminer sawfly (Profenusa canadensis, family Tenthredinidae), and Yellow Poplar Weevil (Odontopus calceatus, family Curculionidae). These leafminers produce “blotch mines” by tunneling between both the upper and lower leaf surfaces causing both leaf surfaces to delaminate.





Mining just beneath the upper leaf epidermis is commonly associated with moths belonging to the family Gracillariidae. These and other small moths are called “microlepidoptera” which is not a taxonomic group but a nod to their diminutive size. 


Indeed, removing the paper-thin upper epidermis revealed a moth caterpillar. The leafmines commonly contained silk filaments which also point to a caterpillar rather than a beetle or midge fly.





Another common feature of leaf mines produced by microlepidopteran leafminers is the occurrence of circular structures within the leafmines. The structures may be pupation chambers or used for other purposes. These structures are very apparent in the mines of the Poison Ivy Leafmining moth (Cameraria guttifinitella).





The image below was taken this past Tuesday and shows that the leafmining caterpillars on yellow buckeye are pupating. The pupa was originally located in an aforementioned circular structure and bounded by silk; however, the wind rolled the pupa to one side as I was taking the picture.



I have not been able to find an identification for the microlepidopteran leafmining moth on yellow buckeye. Perhaps it’s a new species, or it’s a species that’s been described but it has not yet been connected to Aesculus. This is not uncommon given that moth species are primarily described based on adults.


A paper published in 2019 describes a new leafmining caterpillar found in China tunneling the leaves of Chinese buckeye, Aesculus chinensis. The authors named it Caloptilia aesculi, family Gracillariidae. It may be a tantalizing lead.


I’ve been observing the activity of the yellow buckeye leafmining moth since 2020. I’ve also found small populations on wild horsechesnut trees.



Although the leafmines produced by the caterpillars are readily apparent, I’ve never seen the damage rise to a level that would threaten the overall health of the tree. So, I consider the moth more of an oddity rather than a serious pest.





Selected References

Boggs, J., E. Draper, and J. Chatfield. 2017. 20 Questions on Plant Diagnosis, Ohio State University Extension Fact Sheet, PLPATH-GEN-3. Digital Access:


Liao, C., Ohshima, I. and Huang, G., 2019. A new leaf-mining moth, Caloptilia aesculi, sp. nov.(Lepidoptera: Gracillariidae: Gracillariinae) feeding on Aesculus chinensis Bunge (Hippocastanaceae) from China. Zootaxa4586(3), pp.586-600. Digital Access to Abstract:

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