If symptoms appear on new leaves, the problems could related to iron, zinc, manganese, copper, boron, calcium, or sulfur.
Deficiency: this will first show on younger leaves, they will yellow. this resembles calcium deficiency. stunted growth, discoloration, death of growing tips. buds will stop forming. tip of shoots will die. stems/petioles will brittle. leaves will curl, and die. dead spots develop between veins, and leaves will become thick. boron is not absorbed with too much potassium. a lack of boron can lead to rot/fungus. can also cause severly hollowed stems. (fast fact: boric acid can be purchased at pharmacies for fungus treatment, as well as for jewelers to remove salts/oils from their work before they apply the torch to them. its kills bacteria, and can even be used in your laundry as a weak bleach!... the more you know....)
A boron deficiency is often marked by a graying of the plant as well as an appearance of burnt leaves.
Growing shoots turn grey or die. Growing shoots appear burnt. Treat with
one teaspoon of Boric acid (sold as eyewash) per gallon of water.
These pictures show a boron deficiency in different stages.