My blueberry bushes this year seem to be producing less fruit. I started fertilizing them (lightly) once a week.The plant began producing more leaves and looked healthy, then all of the sudden the leaves started showing black veins in them.
What Do I Do if My Blueberry Leaves Start Showing Dark Veins on the Leaves
Certified GKH Gardening Expert
It sounds like you may be overfertilizing. Most of the time, fertilizers like that only need to be applied every few months. It would be best if you follow manufacturer's recommendations regarding application.
At this time, I would recommend having your soil tested to see where the levels are before applying any more.