In mature trees I'd suggest you consider slowing down a gear to get a higher volume of spray and better penetration into the tree canopy. If you elect to slow up, remember to recalibrate so you don't inadvertently overdose on the rate. This crawler generation could last for a two to three weeks. It may require two cover spray applications to control this generation. I encourage you to spray infested blocks as soon as you can.
Crawlers are the only stage of the life cycle that can be readily controlled.
Do not use diazinon on blocks with fruit , as there is a risk of damage to the fruit finish. Spraying the crawlers is important. Once the scale set up and secrete coverings, they are immune to cover spray insecticides. Don't make a permethrin spray because you have early peaches where PHI prevents you from using Imidan.