13. Olsen, K.L. and G.C. Martin. 1980. Influence of apple bloom date on maturity and storage quality of ‘Starking Delicious’ ap- ples. J. Amer. Soc. Hort. Sci. 105:183-186. 14. Patten, K.D. and E.L. Proebsting. 1986. Effect of different ar- tificial shading durations and natural light intensities on fruit quality of ‘Bing’ sweet cherry. J. Amer. Soc. Hort. Sci. (In press) 15. Pemberton, H.B. 1983. A study of photoperiod, endogenous ABA and growth dynamics in the development of evergreen azalea floral buds. PhD Diss., Univ. of Minnesota, St. Paul. 16. Proebsting, E.L. and H.M. Mills. 1981. Effects of season and crop load on maturity characteristics of ‘Bing’ cherry. J. Amer. Soc. Hort. Sci. 106:144-146. 17. Roberts, R.H. 1917. Winter injury to cherry blossom buds. Proc. Amer. Soc. Hort. Sci. 14:105-110. 18. Robinson, T.L., E.J. Seeley and B. Barritt. 1983. The effect of light environment and spur age on ‘Delicious’ apple fruit size and quality. J. Amer. Soc. Hort. Sci. 108:855-861. 19. Sullivan, D.T. 1965. The effect of time of bloom of individual flowers on the size, shape and maturity of apple fruits. Proc. Amer. Soc. Hort. Sci. 87:41^-6. 20. Westwood, M.N., L.P. Batjer, and H.D. Billingsley. 1967. Cell size, cell number, and fruit destiny of apples as related to fruit size, position in cluster, and thinning method. Proc. Amer. Soc. Hort. Sci. 72:85-91. J. Amer . Soc . Hort . Sci . 111(3):360-363. 1986. Effect of Different Artificial Shading Times and Natural Light Intensities on the Fruit Quality of ‘Bing’ Sweet Cherry K. D. Patten1 and E.L. Proebsting Irrigated Agriculture Research and Extension Center, Washington State University, Prosser, WA 99350-0030 Additional index words. Prunus avium, fruit color, fruit firmness, soluble solids, pruning, fruit set Abstract. Limbs of ‘Bing’ cherries (Prunus avium L.) were shaded with neutral density shade structures to reduce light levels to 10-15% full sun. Three placement times were used: a) petal fall to pit hardening (PF-PH), b) pit hardening to harvest (PH-H), and c) petal fall to harvest (PF-H). Shaded limbs had reduced fruit set, and fruit color and soluble solids were less in comparison to fruit from unshaded limbs. Fruit from shaded limbs were smaller than unshaded for the first 2 harvests, but for the last 2 harvest dates, fruit shaded from PF-PH or PF-H were larger. The time to reach dark red maturity was delayed 5 days by shading from PF-PH or PH-H and 12 days by shading from PF-H. When compared at equal color maturities, fruit from unshaded limbs were firmer than those from shaded limbs. In a study using natural shade, the relationship of fruit color and soluble solids to the percentage of full sun (FS) was logarithmic, with both variables dramatically reduced at light levels below 10-15% FS. Neither fruit weight nor firmness were related to the percentage of FS. Mature sweet cherry trees may have low light levels in a high percentage of the total canopy. To modify tree shape and or- chard design, the relationship between fruit quality and radiation must be known. In apples, the most positive relationship between light and fruit quality is usually for soluble solids (7, 14, 17), followed by fruit size (14, 17). Because low light reduces size and delays horticultural maturity, fruit firmness in apple is negatively cor- related with light (7, 14). Light is not required for anthocyanin pigmentation in high-coloring strains of ‘Delicious’ (14), but is required for ‘McIntosh’ (7, 10), other strains of ‘Delicious’ (7, 17), and peaches (15). Seeley et al. (17) suggested that there is a threshold light limit below which no red color develops in apples. Lakso (10) and Morgan et al. (11) have reported that this relationship for apples was curvilinear. Compared to apples, sweet cherries have a short growth and maturity period, and fruit color will develop at low light levels. Consequently, only limited extrapolations from apples to cherries can be made. Most research on effects of reduced light levels on fruit qual- Received for publication 29 Apr. 1985. Scientific Paper No. 7115, Washington State Univ. College of Agriculture Research Center. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. Present address: Texas A&M Univ. Agriculture Research and Extension Cen- ter, Overton, TX 75684. ity has been limited to whole-season shading effects as opposed to shading during a particular phase of fruit growth. In apples, the young fruits are not strong sinks (1). Fruit set and/or fruit size was decreased by early competition with vegetative shoots (3), reduced early spur leaf area (3), or low early season solar radiation (2). The early season competition for assimilates may be particularly important in cherries, where fruit growth and development occur entirely concomitant with vegetative growth. In sour cherries, reduction of light to 36% full sun reduced flower bud formation (4, 5), while reduction of light to below 10% full sun caused embryo abortion and fruit drop (6). The effect of shading on cherry fruit appears to be a result of de- creased production of assimilates by the leaves. Total occlusion of light from just the fruit by using an aluminum foil wrap increased fruit size (16). The purpose of this study was to determine the effects of different artifical shading times and natural light intensities on the fruit quality of ‘Bing’ cherries. Materials and Methods Study 1—artificial shade. Fiberglass-covered (structo-glass white 1.41 kg-m-2) neutral density shading shelters (14, 17) were placed over limbs of ‘Bing’ cherry trees planted in 1973 on prunus mahaleb rootstocks. Shaded and unshaded limbs used in this study all originated below 1.5 m height on the trunk and were fairly comparable in diameter, vigor, and crop density 360 J. Amer. Soc. Hort. Sci. 111(3):360-363. 1986.