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Costanza Zavalloni, Jeffrey A. Andresen, and J.A. Flore

A simulation model for determining flower bud phenological stages and fruit growth as a function of daily maximum and minimum temperatures was developed for `Montmorency' sour cherry (Prunus cerasus L.). The models were developed and tested with observations collected in the three major sour cherry production areas in Michigan located in northwestern, western central, and southwestern sections of the lower peninsula. Observations of flower bud phenology and fruit diameter were collected at 3- to 7-day intervals, in spurs and terminal shoots across multiple years. Nonlinear equations using accumulation of growing degree-days (base 4 °C) as an independent variable were fitted to observed flower bud phenological stages and fruit diameter, expressed as percentage of final fruit diameter. Simulated bud phenology stages were in agreement with observed data. Mean differences of simulated vs. observed dates of early phenological stages in the three production areas were between 4 and 1 days for side green and near 0 days for tight cluster, while during later stages (e.g., first bloom and full bloom) mean differences ranged from -2 to 0 days. Means differences of predicted fruit diameter were in the range of 0 to -3 days. Needing only daily temperature data, these simulation models have potential applicability in improving the timing and efficiency of management decisions related to crop phenology, such as pest control, fertilization, and irrigation.

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Nader Soltani, J. LaMar Anderson, and Alvin R. Hamson

`Crimson Sweet' watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plants were grown with various mulches and rowcovers and analyzed for relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), leaf area index (LAI), and crop growth rate (CGR). Spunbonded polyester fabric (SB-PF) and perforated polyethylene film (PCP) rowcovers generally showed greater mean RGR, SLA and CGR than spunbonded polypropylene polyamide net (SB-PP), black plus clear combination plastic mulch and black plastic mulch alone. Plants on mulches and under rowcovers showed significant increases in RGR, NAR, and SLA over plants grown in bare soil. Carbon dioxide concentration inside the transplanting mulch holes was nearly twice the ambient CO, concentration. Growth analysis of sampled watermelon plants during early stages of development under various treatments was predictive of crop yield. Plants under SB-PF and PCP rowcovers produced the earliest fruit and the greatest total yield. An asymmetrical curvilinear model for watermelon growth and development based on cardinal temperatures was developed. The model uses hourly averaged temperatures to predict growth and phenological development of `Crimson Sweet' watermelon plants grown with and without rowcovers. Early vegetative growth correlated well with accumulated heat units. Results indicate a consistent heat unit requirement for the `Crimson Sweet' watermelon plants to reach first male flower, first female flower and first harvest in uncovered plants and plants under rowcovers. Greater variability was observed in predicting date of first harvest than first bloom.

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Joseph M. Caprio and Robert D. Snyder

The within-station performance of the most accurate phenological model in each of three classes of hourly models was compared for the ability to predict flowering dates of common purple lilac (Syringa vulgaris L.). For the three model classes used, day-only, solar thermal unit (STU), and 24-hour interpolations were made between three threshold temperatures and five effective temperature exponents. The most accurate within-station model for each of the three model classes, all having a threshold temperature of 5C, were: (T - 5)1.54 day-only, (T - 5)1.26 R0.5 STU, and (T - 5)1.70 24-hour, where T = temperature and R = solar radiation. These three models and the corresponding three linear temperature exponent models were then compared for among-station performance using 10 sites in the western United States. The most accurate model for the among-station analyses was the (T - 5)1.0 day-only model. The two STU models did not perform as well as the two day-only and the two 24-hour models.

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P. W. Robinson, M. V. Mickelbart, and M. L. Arpaia

Measurements of flowering, yield, vegetative and root growth were begun in Spring 1992 to establish a phenological model for `Hass' avocado. Although rootstock (Thomas', Topa Topa', Duke 7' and `D9') did not affect the timing or intensity of bloom, differences in yield were observed. Flowering occurred in March - April in both years, although the intensity of bloom in 1993 was drastically reduced due to an extremely heavy 1992-93 crop. Vegetative flushes occurred in April (following bloom) and July in both years. In 1993, however, cumulative growth was ca. 10-fold greater. Rootstock did not affect the timing or intensity of vegetative growth in either year. In both years, vegetative growth preceded root growth. In 1992, there were no differences detected in the timing or intensity of root growth related to rootstock. In 1993, however, the `Topa Topa' rootstock produced more roots throughout the growing season. The timing and intensity of root growth during the spring flush were similar in both years. During Fall 1993, root growth rates, however, were consistently higher than those observed in 1992. Additionally, while root growth ceased in November 1992, roots have continued to grow through January 1994.

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Carolyn DeMoranville, Irving DeMoranville, and Tom Bicki

Cold tolerance of cranberry (Vaccinium macrocarpon Ait.) flower buds (spring) and fruit had previously been investigated for the cultivars Early Black (EB) and Howes (H), leading to predictors of cold tolerance based on appearance of the buds (size and growth) and fruit (color). We studied these cultivars along with `Ben Lear' (BL) (buds only) and `Stevens' (S) using controlled temperatures to determine the accuracy of predicting cold damage. BL was the least cold-tolerant cultivar in early spring, both BL and S were less tolerant than EB and H during budbreak (-2.8C vs. -3.9C) and elongation (-2.8C vs. -1.4C), and all survived any exposure to -1.4C. EB fruit were tolerant of -5C once maximum color was achieved and 2 weeks later would tolerate short exposures to -6.5C or less. H fruit developed deep tolerance (below 6.5C) by November in only 1 year out of 2. S fruit were least tolerant: -5C for short periods at M maturity. The phenological model used to predict cold tolerance of flower buds was 48% accurate in our trials, generally overestimating bud tolerance, particularly for BL and S. EB fruit showed more tolerance than predicted, H less.

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Arthur Q. Villordon, Don R. La Bonte, Nurit Firon, Yanir Kfir, Etan Pressman, and Amnon Schwartz

phenological models for optimizing storage root formation. Literature Cited Artschwager, E. 1924 On the anatomy of sweet potato root with notes on internal breakdown J. Agr. Res. 23 157 166 Belehu, T. Hammes, P.S. Robbertse, P.J. 2004 The origin and structure

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Bradley S. Sladek, Gerald M. Henry, and Dick L. Auld

. 41 133 138 Zavalloni, C. Andresen, J.A. Flore, J.A. 2006 Phenological models of flower bud stages and fruit growth of ‘Montmorency’ sour cherry based on growing degree-day accumulation J. Amer. Soc. Hort. Sci. 131 601 607

Open access

Andrés Javier Peña Quiñones, Melba Ruth Salazar Gutierrez, and Gerrit Hoogenboom

time for four grapevine cultivars Intl. J. Biometeorol. 59 1771 1781 Zavalloni, C. Andresen, J.A. Flore, J.A. 2006 Phenological models of flower bud stages and fruit growth of ‘Montmorency’ sour cherry based on growing degree-day accumulation J. Amer

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Penelope F. Measham, Audrey G. Quentin, and Nicholas MacNair

.A. 2006 Phenological models of flower bud stages and fruit growth of ‘Montmorency’ sour cherry based on growing degree-day accumulation J. Amer. Soc. Hort. Sci. 131 601 607

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Arthur T. DeGaetano

Proebsting, E.L. Jr Mills, H.H. 1978 Low temperature resistance [frost hardiness] of developing flower buds of six deciduous fruit species J. Amer. Soc. Hort. Sci. 103 192 198 Rea, R. Eccel, E. 2006 Phenological models for blooming of apple in a mountainous