California red scale crawlers emerge about 550 degree days (biofix in March, lower developmental threshold of 53^oF) after the first flight of males.  As you can see on the CRS degree day web page, Kern county passed that point last week, Tulare County crawlers are emerging this week and Fresno scale crawlers are soon to emerge.  The first or second crawler generations are the best times to treat with most insecticides, because crawlers are most sensitive at this stage.

See the UC IPM Guidelines for Citrus for more information on treatments.