We found a spray of seaweed around the time when the fruit bud is at the early green cluster stage helps the rosette of leaf that surrounds the cluster. These are the leaves that will be feeding the blossom as it develops. It gets all the micro nutrients into the leaf as well as a good burst of nitrogen just when it’s needed most.
After that, any time dureing the growing season when you feel the tree could be coming under stress......drought...cold...heavy crop etc.
Also near to harvest it can make sure that the fruit itself has the best chance of going into store with all its nutrients in place.
Like all sprays...refrain from spraying once the bloom has started to open until 80% petal fall. Any sprays....even plain water..can effect pollination by damaging the viability of the pollen during this period.