Big Push for Blueberry Kush!!!

First establish if it's a fungus and what type then deal with it accordingly... and remember the only thing you want growing is the things that make Up the plant

looks like discoloration... not powder. not consistent enough to be a leaf tunneler... Looks like an ugly, early leaf.. probably grow out of it. you've got a hint of tip burn, but otherwise the leaves look healthy. Did some fertilized water drip on that leaf, maybe?