I planted some Emerald blueberry bushes over at my mom's house and now one is having some problems. It was doing well and putting out lots of new growth this spring, then I noticed these brown marks on the leaves. I inspected the plant closely and I didn't see any insects of evidence of insect damage. Can anyone help me with this.

It is in the ground, gets sun for about half a day, soil is amended with peat, and I don't believe my mom has fertilized this plant at all (so I don't think it is fertilizer burn).

I am wondering if it is a fungus? Just in case, I sprayed it with some wettable sulfur.