Actually this is an insect. This is white prunicola scale, one of the hard scales. Scales are insects that have a hard covering (like a shell) that protects them when they are adults. What you see are their coverings.
When their eggs hatch, crawlers come out that are not protected, so that's a good time to spray them. Two things to do now:
In June, spray the crawlers with insecticidal oil or insecticidal soap.
Before you spray, take a stiff brush (not metal) and scrub all the infested trunk and branches that you see (and can reach) covered with scale. This will knock some off, but also scrape off the coverings of many so that the spray is more effective on adults as well as crawlers.
You can also treat for crawlers in mid-July, mid-August and September.
Read through our webpage on hard scale, with photos of prunicola scale, for more tips and help: https://extension.umd.edu/hgic/topics/armored-hard-scale-trees-and-shrubs
Thank You. Is this what is effecting the fruit as well?
That looks like brown rot, which is very common if not controlled with precisely timed spray management.
Tree fruits in general are challenging to grow well in our area due to the weather and common pests and diseases to which we are prone.
Tree fruits with pits are termed 'stone fruits'. Here is our page on them, including links to common problems and how to best care for them, including management of diseases and pests, etc: https://extension.umd.edu/hgic/topics/stone-fruit-peaches-cherries-plums-apricots-nectarines