Dear Mr. Richards,

Your tree looks to be infested with Kuno scale, a species of soft scale insect. Learn more (focus on soft scale info) here:
http://ucipm.ucdavis.edu/PMG/PESTNOTES/pn7408.html
http://ucipm.ucdavis.edu/PMG/PESTNOTES/pni7408-3b.html
http://ucipm.ucdavis.edu/PMG/E/I-HO-EKUN-AD.007.html

The best way to manage these pests will be to :

• exclude ants, since ants harvest honeydew from soft scales and therefore protect them from their natural enemies...once ants are excluded with a sticky barrier, or managed using ant bait stations, the scale insects will be readily attacked by parasites and predators
• apply a horticultural oil during dormancy or when scle crawlers are active (you can use double-sided sticky tape on either side of the mature scales to determine when the first instar 'crawlers' are walking around...this is when oil sprays will have the largest effect

You may improve the size and quality of your fruit simply by providing adequate irrigation and nutrition and by following proper maintenance guidelines.

You can get more information and face-to-face help at your county's Master Gardener Help Desk:
http://ccmg.ucanr.edu/Ask_Us/

Best regards,
Andrew