Leaf Zonal Chlorosis

Zonal chlorosis resembles leafhopper damage, but is not caused by leafhoppers (Rosenberger et al., 2001). It occurs earlier in the season on non- or lightly-bearing trees, and is associated with light crop loads. Abnormally large starch grains may cause chloroplast disruption and chlorosis.

References

• Chen, L.S. and L. Cheng. 2004. CO2 assimilation, carbohydrate metabolism, xanthophyll cycle, and the antioxidant system of 'Honeycrisp' apple leaves with zonal chlorosis. J Amer Soc. Hort Sci. 129:729-737.
• Snyder-Leiby, T.E. and S. Wang. 2008. Role of crop load in chloroplast ultra-structure and zonal chlorosis, a physiological disorder in 'Honeycrisp' apple trees. HortScience 43:1819-1822.
• Cheng, L. and T. Robinson. 2009 Presentation at NY Apple Growers conference Honeycrisp Leaf Chlorosis: Causes and Mitigation