Black/brown spots on leaves - underfed?

[StickyFingrs707]

I have a Blueberry Cookies clone by Medicine Man growing outdoors at the moment. It’s in its final month of flower right now and as of a week or so ago I started noticing deep brown/black spots along the edges of the fan leaves that were still yellowing. The majority of the affected leaves are fans that are midway up the plant. Almost none at the bottom and only a select few toward the top. Only one new growth leaf has been affected on a cola.
The stems of a few of them have been purple somewhat, but not all. I noticed purple leaf tips too, not sure if genetics.The veins are all turning yellow/white with the rest of the leaf when they die off though.

I have accidentally fed with 1 or 2 tablespoons of flower instead of 1/2 cup (DUH) of the GreenGro lineup since the start, so I’m hoping she is just really hungry. I recently started with Flower Finisher and GreenAmino/HiBrix products from the lineup too.

Let me know if you guys think this is something more serious. Thanks.

 

[StickyFingrs707]

I’m almost 100% sure this is a potassium deficiency, hopefully from being underfed. I’ll report later in the season with the results.

 

[StickyFingrs707]

Update: definitely was a deficiency. As soon as I started feed her proper amounts of flowering food the spots quit appearing. I supplemented with a bit of K from the earth juice lineup as well and it did the trick. She got hungry for N about mid September too so just dosed her with the Grow again. All is looking well. Trichome stalks are turning purple and some of the leaves are turning purple in large spots too, so assuming it’s genetics.