White resin or powder on conifer needles
I believe this is actually crystallized sap which formed on and around the bud as the bud opened up and new leafs emerged.

Note that some coniferous trees have a powdery coating as part of the leaf itself, continuing on throughout the life of the leaf. Blue spruce is a good example of this, as its dark green needles appear blue/gray due to a waxy coating the needles. This wax can be easily scraped off the leaf.