The relationship between SPAD-501 meter readings (SPAD) and total chlo- rophyll content (TCHL) was evaluated for 'Delicious' apple (Malus domestica Borkh.) leaves grown in various environments. Regression models were developed between SPAD and TCHL for each of six separate experiments and were evaluated for statistical coincidence. SPAD was linearly related in a positive manner to TCHL in five of the six experiments; however, models differed between experiments, particularly between field- and greenhouse-grown trees. Thus, the relationship between SPAD and TCHL must be determined for each experiment. The SPAD-501 portable leaf greenness meter (Minolta Corp., Ramsey, N.J.) non- destructively measures leaf greenness. A positive linear relationship has been dem- onstrated between SPAD measurements and total extracted chlorophyll (TCHL) for a range of plant species (Yadava, 1986; Marquard and Tipton, 1987). These studies indicated the need to develop separate relationships for each plant species and individual meter. Our preliminary studies with the SPAD sug- gested that the relationship between SPAD and TCHL may vary within a species, de- pending on the growing conditions. The ob- jective of this study was to evaluate the influence of various growing conditions on the relationship between the SPAD and TCHL for apple leaves. 20, and 40 mg N/tree per week) and three ERM populations (0, 1000, and 2000 mite days/leaf). The experimental designs were randomized complete blocks with two and six single-tree replicates per treatment in 1987 and 1988, respectively. Field; mite population (Expts. 3 and 4). In Apr. 1987, 40 2-year-old 'Redchief De- licious'/MM.111 trees were planted at a spacing of 2 × 3 m at the Virginia Poly- technic Inst. and State Univ. Horticultural Research Farm. Trees were grown according to standard recommendations, except ERM populations were allowed to develop on 20 randomly selected trees, while the remaining trees were kept mite-free. Mite populations were monitored weekly on one leaf per tree, and mites were removed or added to main- tain mite levels of ≈ 0 and 3000 mite days/ leaf on 20 trees per treatment. The experi- ment was repeated in 1988. In each experiment, following accumula- tion of desired mite levels, three SPAD mea- surements (37.8 mm 2 total measurement area) were averaged per leaf to represent one ob- servation. Immediately following SPAD measurement, four disks per leaf (1.2 cm 2