Mature ‘McIntosh’, ‘Empire’, and ‘Golden Delicious’ apple trees (Malus domestica Borkh.) were sprayed with simulated acid rain solutions in the pH range of 2.5 to 5.5 at full bloom in 1980 and in 1981. In 1981, weekly sprays were applied at pH 2.75 and pH 3.25. Necrotic lesions developed on apple petals at pH 2.5 with slight injury appearing at pH 3.0 and pH 3.5. Apple foliage had no acid rain lesions at any of the pH levels tested. Pollen germination was reduced at pH 2.5 in ‘Empire’. Slight fruit set reduction at pH 2.5 was observed in ‘McIntosh’. The incidence of russetting on ‘Golden Delicious’ fruits was ameliorated by the presence of rain-exclusion chambers but was not affected by acid rain. With season-long sprays at pH 2.75, there was a slight delay in maturity and lower weight of ‘McIntosh’ apples. Even at the lowest pH levels no detrimental effects of simulated acid rain were found on apple tree productivity and fruit quality when measured as fruit set, seed number per fruit, and fruit size and appearance.
Received for publication February 12, 1982. Approved by the Director of the New York State Agricultural Experiment Station as Journal Paper No. 3411. This work supported in part by a subcontract from the EPA-NADP Acid Precipitation Program (EPA Cooperative Agreement #CR806912-01-0 with North Carolina State University).
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Present address: Statewide Air Pollution Research Center, Univ. of California, Riverside, CA 92521.
Present address: Agricultural Research & Education Center, Univ. of Florida, 700 Experiment Station Rd., Lake Alfred, FL 33850.
The authors gratefully acknowledge the technical assistance of R. E. Melious, R. C. McMinn and K. M. Stone and thank Warren Knapp for providing local precipitation chemistry data.