This does not look like the symptoms of verticillium wilt. But, one way to check for the potential of it being present is to cut into a stem and look for vascular streaking. If vascular streaking is present I suggest taking several twigs 6-10 inches long showing symtpoms into the Oklahoma County Extension Center to be sent to the OSU disease lab for diagnostics.

With that said, and knowing it was recently planted, I believe it is more of an establishment issue than a disease. How was the tree planted? How much water and method of watering is being applied/used?

When planting, the hole should be 2-3 times wider than the root ball, but no deeper than the root ball. Planting too deep can lead to problems. We do not recommend using amendments in the hole when planting; depending on the amendment and how much is used, that can cause more problems than it does good. The root ball should be kept moist, but not wet. Digging down about 6-10 inches next to the root ball occasionally to check soil moisture to determe if it really needs more water is better than a set schedule. A regular watering schedule may not be efficient or could lead to overwatering, depending on the method. Checking the soil several inches deep near the root ball occasionally is a better method. If roots are brown and slimy you may have root rot occuring.

I also noticed the bamboo pole used for training and protection during shipping is still attached. I recommend removing that immediately as it does not really serve a purpose anymore.

For additional assistance please feel free to contact the Oklahoma County OSU Extension Center - https://extension.okstate.edu/county/oklahoma/.

This looks like it could be a foliar disease. I suggest taking some samples into the extension office, they can send them in for diagnosis to determine which disease it might be so we can provide an accurate treatment recommendation. However, this late in the season it is not worth spraying anything to control it since it is not affecting the overall health of the tree and they will be falling off soon anyway. The best thing to do at this point is to collect and destroy falling leaves, especially this autumn, then be prepared to treat next spring.