Thank you for your question and for the photos!  While all of the things you asked about are possibilities, I think water may be more likely.  The tree appears young, and we've had a hot summer with some very hot days.  How old is the tree?  How often do you water, and how much water is applied each time?  Have you applied any fertilizers, and if so, what kind and when?  Have you seen any evidence of insects on the tree (which are the primary means of spreading bacterial leaf scorch)?  Sorry for all the questions, but your answers will help us rule out some possibilities and hone in on the most likely cause of these symptoms.

Hello Jeff, I am not sure of the exact age of the trees (there are two). My guess is they are about 5-7 years old and we planted them two years ago in the landscaping strip next to the sidewalk. They have been irrigated by the automatic system for 10 minutes each morning and I don't know what the output of those sprinklers might be. In addition to the automatic irrigation I apply 5 gallons of water once or twice a week directly to each tree. This directly applied water includes a low rate (1/3 cup per 32 gallons) addition of "Age Old Bloom" which is a liquid 5-10-5 fertilizer that also has some micronutrients. Early in the growing season I applied some conventional 16-16-16, maybe 1/2 cup spread around the tree near the drip line and watered in. I have not seen any insects, my assumption was that the tree may have been infected at the nursery though I did not see any symptoms last year. Thank you for your answer!

I think the issue is related to too much water.  Daily watering by irrigation systems is too much for many plants, including lawns.  My general recommendation is every other day for lawns, which need about 1.5 inches per week during summer, so that amounts to about 0.5 inches every other day.  If you move to that schedule, the ginkgo should tolerate the schedule just fine.  The good news is that it is deciduous, and fall is upon us, so the bad looking leaves soon will be dropping.

Regarding the fertilizer, 16-16-16 once in the spring about the time you see the buds starting to open should be sufficient.  Weekly watering with the 5-10-5 probably won't hurt anything at the rate you're diluting it, but it isn't necessary.