I am trying to grow a scarlet buckeye in my front yard (his name is Bucky), and something I don't understand is happening to the leaves. I bought Bucky from the Arbor Day Foundation and planted him in the autumn of 2018, whereupon the above-ground portion promptly died. I was thinking of trying again when the autumn of 2019 rolled around, but to my surprise, that spring he put up a three-inch shoot next to his dead stick and put out a spray of half a dozen leaves. He never got any bigger that year, but he seemed healthy enough until something started blighting his leaves. This got worse over the summer until they fell off in early autumn, but they left behind an apparently healthy little shoot. This survived the winter and, this year, has been taking off like gangbusters. However, I'm noticing that the leaf blight is coming back. Can anyone help me identify what's happening here? I've been spraying down the leaves with a copper fungicide under the assumption it's some sort of fungal infection, but if it's something else that I should be treating differently, I'd obviously like to know. Any help would be greatly appreciated.

You can show us your whole plant. You can show us more than one leaf and a component leaflet.

You can tell us where you are growing this plant, and the soil and moisture conditions. What other plants are in the nearby vicinity, as well as on adjoining properties? Are there other Buckeye plants in the neighborhood?

The first alarm bell went off when you noted that you acquired this plant from The Arbor Day Foundation. While TADF has an excellent mission, they are less than stellar in their plant identification and distribution. You don't always get what you thought you were getting.

I can see that you have a Buckeye (Aesculus sp.) of some sort, but I wouldn't be absolutely confident that you have a Red/Scarlet Buckeye. Also, many members of Aesculus sp. are fraught with susceptibility to leaf blotch, leaf spot, Anthracnose infections, and powdery mildew. If you must know what leaf malady you have - and cease unnecessary pesticide treatments - then collect a leaf sample and submit it to your local Cooperative Extension Service for diagnostics. Otherwise, you are just waving chemicals around.

All that said: I have grown many taxa of Aesculus here at the Valley since 1990.

Aesculus glabra - several seedlings
Aesculus flava - more than a dozen seedlings, several 20' tall
Aesculus parviflora - innumerable seedlings, dating to 1990, centerpiece of my front yard
Aesculus parviflora var. serotina - half a dozen plants, one 12' x 12'
Aesculus parviflora var. serotina 'Rogers' - one large 25' year old specimen
Aesculus pavia - more than a hundred seedlings; six parent plants, many self-seeded individuals
Aesculus turbinata - one plant, approaching 2" caliper
Aesculus x carnea - two seedlings, now 8' tall and in third flowering year

EVERY PLANT can have from time to time some sort of leaf malady. None are fatal, though they can be seasonally unattractive. That is part and parcel of the plant. I could show you images of how fantastic Red Buckeye can be, grown under regular intense loving care in perfect conditions. I can show you images of how fantastic Red Buckeye can be, grown under live-and-let-live general neglect here at the Valley. Self-sown seedlings seem to flower in their third year. Ones I grew in containers performed similarly.

To get what you think you are getting: grow your own. Buckeye seeds are extremely easy to grow, and generally are produced in abundance on healthy trees. This is how I procured almost all my plants here. If you know where a flowering tree is, go visit it in the fall (September is average ripening date in the Ohio River valley) and collect the seeds as the husks split. They should be sown quickly, or refrigerated to keep from drying and losing viability. Buckeye seeds will form a root radicle in the fall, and then form a stem sprout come spring. You can watch this happen in a clear food storage bag in your fridge.

If you don't have a tree at the ready to collect from, visit a park, botanic garden, arboretum, any number of cemeteries - or ask here if anybody knows where one is in your neck of the woods. Collect as many seeds are you are allowed to, and distribute the excess successes that you don't want or have room for.