Greenhouse experiments were conducted to determine effects of spirea aphid, Aphis spiraecola Patch, feeding and nitrogen fertilization on net photosynthesis (Pn), total chlorophyll content (Tchl), and greenness (Gn) of apple leaves. One-year-old apple trees grown in pots were infested with spirea aphid. Spirea aphid reduced Pn at various levels of infestation, and the reduction persisted after aphid removal. Pn rates decreased with increasing accumulation of sooty mold. Gn and Tchl were reduced by spirea aphid feeding. Chlorophyll concentrations obtained by methanol extraction technique were linearly related to Gn values obtained with a SPAD leaf greenness meter for both infested and control leaves and for sooty mold and control leaves. Four nitrogen (N) rates were applied to trees in the second year. Pn and Gn were correlated with aphid-day accumulations at each N rate. Pn increased linearly with increasing Gn. Pn and Gn were positively related to N rates. Decrease in Tchl helps to explain the reduction in Pn. Pn may be related to Tchl, but leaf age, nutritional status, and other parameters may influence the results. Callose accumulation at the phloem sieve plates in response to aphid feeding was observed but to a lesser degree than for other aphids reported on apple and pecan leaves.
