So I can't figure out what would only affect one of the shoots like this, though it looks like either a nutrient deficiency or overabundance. The only fertilizer I've used is Espoma Plant-tone, which I sprinkled on the soil surface as directed about a month ago. It's possible that I sprinkled it a little thicker in some spots than others, though I made an effort to do it uniformly.
Here are a couple shots showing the affected leaves, and a growing tip for comparison:
And here's a shot just to show the setting: