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A chill unit model was developed for ‘Starkrimson Delicious’ (Malus domestica Borkh.) apples grown under the wide range of temperature and elevations in North Carolina. The model relates air temperature to effective chill units and predicts rest completion for North Carolina-grown apples more accurately than previously reported models. The model proposes a broader range of effective temperatures and incorporates a greater negative effect when temperatures exceed 21°C for rest. According to the model, 1200 chill units are required to break rest of apple buds. Growing degree hours correlated with each apple bud developmental stage, as well as from projected date of rest completion to full bloom, were determined using various base temperatures.

Gibberellin A4A7 (GA4-7) and benzyladenine (BA) were applied to ‘Starkrimson Delicious’ apples from 1969 through 1972. In initial tests, GA4-7 + BA (50 to 200 ppm each) increased fruit length, fruit wt and length/diam ratio (L/D) but did not alter diam or fruit color. Firmness and seed numbers were reduced only at 200 ppm. At concn above 50 ppm flower initiation was substantially reduced. Concentrations of 25 ppm were as effective as 50 ppm but concentrations below 25 ppm were not effective. To be most effective, these materials must be applied between full bloom and petal fall. In general, a single application was more effective than split applications. Repeated annual applications of 50 ppm resulted in continued good response and no adverse effects. In one of the 4 years tested, fruit set but not commercial crop, was significantly reduced by applications of GA4-7 + BA. Air blast applications were as effective as hand gun applications even when the amount of spray mixture/acre was substantially reduced. The average fruit weight response in all experiments reported was 12 and 20% at 25 and 50 ppm, respectively. The improved fruit shape and increased fruit mass could justify the use of GA4-7 + BA in apple producing areas where post bloom temp conditions reduce “typiness”.

`Fuji' apples (Malus domestica Borkh.) were harvested at three maturities for three consecutive seasons. Fruit firmness, soluble solids concentration, starch—iodine index (SI), and internal ethylene concentration were measured at harvest. Fruit were stored in 0 °C air storage for 8 months. Fruit firmness and other maturity indices were measured monthly during storage. Using a stepwise regression procedure, harvest maturity indices were used to predict firmness after air storage. When all maturity indices measured were represented in the model, R2 = 0.29, 0.34, and 0.26 at 4, 6, and 8 months, respectively. Use of only SI and fruit firmness in the model gave R2 values of 0.25, 0.29, and 0.24 for 4, 6, and 8 months, respectively. Although R2 values were low, they were highly significant. The model using fruit firmness and SI resulted in the best fit. Thus, an equation was developed using months of air storage, firmness, and SI at harvest. Actual firmness values correlated fairly well with predicted firmness values, usually within ≈5 N. On Washington apples, predicted values were 4.3 and 3.7 N too low compared to actual firmness values after 3 or 5 months' storage. In 1993, when predicted and actual firmness values were compared for Pennsylvania apples, predicted values ranged from 2.6 to 8.3 N too high after 3 months' storage, depending on harvest date. In 1994, Pennsylvania fruit stored 4 months had predicted values 0.5 N too high to 6.3 N too low, depending on harvest date. It may be possible to develop and refine models for an apple variety that would be applicable to several regions.