Crop loss—of 20% or more—from the splitting of Navel oranges is no new problem. The trouble has plagued orange growers the world over and the general opinion seems to be that internal pressure develops within the fruit—probably as a result of extreme changes in moisture content associated with certain weather and soil moisture conditions—which ruptures the rind at the weakest point, the navel opening. Once started, the split usually expands rapidly dividing the fruit into two or more segments.

Weather data obtained from Citrus Grove Rejuvenation weather stations operated by Joseph R. Orlando, Technician in Horticulture, University of California, Riverside.