Help! Leaves turning brown!

Hello, I'm having some trouble figuring out what's the issue for my plants, started with a northern highly blueberry shrub, every couple of days I get about four leaves turning brown just like in the image and they turn brown really quickly. (Takes about a day for half the leaf to go brown, down the midrib)

I've tried these in the past two months:

• keeping the plant leaves dry placed in a ventilated area just in case it was fungal.
• Reducing watering to only water when soil is try to avoid overwatering and underwatering.
• increasing amount of fertilizer slightly to ensure plant has sufficient nutrition
• Neem oil sprays to remove pests

Today, I found a similar leaf on my garden mint that's exhibiting the same brown patch on the tip of the leaf, worried it will start spreading.

Has anyone experienced something similar?