That looks like a calcium deficiency IMO. Plants don't absorb calcium very well below a pH of 6 with the exception of gypsum. If you have a chelated liquid/powdered calcium product you can foliar spray it and that will help in quick time. I use liquid Biomin Calcium for foliar feeding. Also I'd top dress some form of liming product, e.g. fine powder calcium carbonate and gypsum. The lime should help bring the pH up over time and the calcium in the gypsum should be available immediately.