looks nutritionally marginal? Is your root zone mulched?

It might be nutritional, or cultural (too much/little water, pH issue, .....), natural senescence (aging), or it might be typical. It's common for foliage of fruiting trees to go chlorotic while fruits are forming, then return to normal as fruits mature and slow development. If the soil is sandy, which it appears to be, suspect a N and/or K deficiency. Your best bet is to have the soil professionally analyzed, with recommendations for what amendments to add. When you guess, you could easily be supplying nutrients already represented in the soil adequately, and an excess (toxicity) has as much potential to be limiting as a deficiency.

Al