The DA reading indicates the level of chlorophyll (green color) in the mesocarp of the fruit, just below the skin. As the fruit ripens, chlorophyll degrades and DA readings decline accordingly. Starch index, fruit firmness and, to some degree, Brix values, are used either alone or in combination to determine the harvest date for most commercial apple varieties. Generally speaking, fruits for CA should be harvested at starch index (3-5), firmness (> 16 lb), and DA reading (0.60). For fresh consumption, fruits at starch index (5.5-7), firmness (13-16 lb), DA reading (0.35) and Brix (12-14%) would be ready for harvest.
Starch iodine test was conducted on Sep 1, 2020, for 19 apple cultivars grown at the AHS Jr. AREC, Winchester, VA. Starch values were estimated according to the Cornell starch index (1-8). The recipe for the starch iodine test was described in a previous post (( https://blogs.ext.vt.edu/tree-fruit-horticulture/2012/08/23/harvest-maturity-resources/)
Sherif M. Sherif, Assistant Professor of Horticulture at Virginia Tech, School of Plant and Environmental Sciences, AHS Jr. Agricultural Research and Extension Center
595 Laurel Grove Road, Winchester, VA 22602 Tel. 540-232-6035, Email: firstname.lastname@example.org