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

over time (°C·d −1 ), a simple regression analysis was conducted in which LT 10 was the dependent variable and the number of days after the branch segments were placed in the chamber (DAC) was the independent variable. Degree-day calculation. A similar

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Arthur Villordon, Christopher Clark, Don Ferrin, and Don LaBonte

crops, the most common approach used for harvest scheduling is based on the relation of harvest date with accumulated degree days often in combination with other factors ( Everaarts, 1999 ; Perry et al., 1997 ). Well-characterized degree day

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Diane E. Dunn, Janet C. Cole, and Michael W. Smith

The objective of this study was to determine the most advantageous time to collect cuttings of Chinese pistache, a commonly recommended ornamental shade tree that is difficult to propagate by cuttings. In 1993, calendar date and degree days (daily mean temperature -7.2C) were used to estimate an appropriate cutting time. The greatest percentage of rooted cuttings occurred in male cuttings harvested on 13 May 1993 (397 degree days) and treated with 17,500 mg·liter-1 IBA or in male cuttings harvested on 20 May 1993 (482 degree days) and treated with either 8750 or 17,500 mg·liter-1 IBA. In 1994, cutting time was associated with calendar days, degree days, and morphology. The most rooted cuttings (44%) were from green softwood cuttings taken on 9 May 1994, which was 380 degree days from orange budbreak using a threshold temperature of 7.2C. Orange budbreak was characterized by separation of the outer bud scales such that the orange, pubescent inner bud scales were visible. Cuttings taken on 9 May 1994 and treated with 8750 mg·liter-1 IBA produced the most primary and secondary roots and the longest primary roots per cutting. Male Chinese pistache cuttings should be collected from green softwood or red semi-softwood stems when about 380 to 573 degree days have accumulated after orange budbreak. Chemical names used: indolebutyric acid (IBA).

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Thibault Nordey, Elias Shem, and Joel Huat

seedling growth rates vary with temperature. It would, therefore, be interesting to assess the accuracy of degree-days, a common indicator of plant phenology, to predict seedling development ( Bonhomme, 2000 ; Brisson et al., 2003 ; Jones et al., 2003

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Matthew L. Richardson and Dewey M. Caron

Various instruments and contract services can be used to calculate degree-days. This study compared instruments and services to the Wescor Biophenometer, an instrument used by cooperators of the Southeast Pennsylvania IPM Research Group (SE PA IPM RG) throughout Delaware and southeastern Pennsylvania for 10 years. Instruments evaluated in the study were the Wescor Biophenometer Datalogger, Avatel HarvestGuard, Avatel Datascribe Junior, Davis Weather Monitor II, Accu-Trax, and the HOBO H8 Pro Temperature Data Logger. The services were SkyBit and national weather data. Different combinations of instruments and services were used at three locations in Pennsylvania and four locations in Delaware over a 2-year period. We checked the degree-day accumulation of each instrument and service weekly and made statistical comparisons among the instruments and services at each site. To further construct a comparison of the instruments, we noted distinctive qualities of each instrument, interviewed the manufacturers, and received feedback from SE PA IPM RG members who used the instruments. We evaluated the instruments' algorithms, durability, cost, temperature sampling interval, ease of use, time input required by the user, and other distinctive factors. Statistically, there were no significant differences in degree-day accumulations between the Biophenometer, Harvest-Guard, Datascribe, Weather Monitor II, Skybit, or weather service data. However, cost and time required to access/interpret data and personal preference should be major considerations in choosing an instrument or service to measure degree-days.

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Gil Simmons and Bill B. Dean

Carrot (Daucus carota) L.) seed quality is affected by the environment in which it matures. Substantial differences in germination from year to year and from field to field have been recognized for many years for umbelliferae seed. Part of the explanation for low germination appears to be the harvest of immature seed. Data was collected for two years, from fields of the cultivars Chantenay and Nantes. Approximately 550 growing degree days were accumulated from anthesis until maturity for seed from the primary umbel. Growing degree days were calculated using a 10°C base temperature and without truncating for temperatures in excess of 35°C. Secondary, tertiary, and quaternary umbel seed maturity sequentially followed primary umbel seed. Secondary and tertiary umbels produced approximately 80 percent of the total seed yield while the primary and quaternary umbels produced approximately 20 percent. Seed maturity was determined by measuring the germination rate. Immature seed germinate at a slower rate than mature seed. The implications of these results for obtaining high quality carrot seed will be discussed.

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Darrell Sparks

A modification of the chilling and heating model for pecan budbreak was used to describe the interactive effects of chilling and heating on the date of first entry of the pecan nut casebearer (PNC; Acrobasis nuxvorella Neunzig) into the pecan [Carya illinoinensis (Wangenh.) K. Koch] fruit. Selected data from unpublished and published sources were used to construct the model. Base temperatures of 9.4 and 13.9C for chilling and heating, respectively, provided the best fit (r 2 = 0.981) for the model used to predict PNC activity. An inverse relationship [1/Y = 0.0037259(1 – 0.1e–0.0028069x – 574.9638969)] was found between chilling (1 Dec. through February) and heating (beginning 1 Feb.) degree-days accumulated until entry of first-generation PNC into the pecan fruit. This model can be used to predict entry of first-generation PNC larvae into fruit over a range of geographic and climatic conditions and pecan genotypes. Model validation using 1994 data from two sites in Texas suggests precision is sufficient to use the model as a guide in managing nut casebearer control.

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Mathieu Ngouajio and Jeremy Ernest

In temperate regions, the vegetable growing season is short and plastic mulches are usually left in the field for an entire year when used for double cropping. This work was conducted to study the effect of weathering on the physical, optical, and thermal properties of plastic mulches during double cropping. The design was a randomized complete block with four replications. The mulches were black, grey, infrared transmitting brown (IRT-brown), IRT-green, white, and white-on-black (co-extruded white/black). Tomato was grown the first year and cucumber the following year. The grey mulch degraded substantially during double cropping (only 40% of bed was covered the second year) and showed an increase in light transmission and a decrease in heat accumulation (degree-days). The black, whiteon-black, white, IRT-brown, and IRT green mulches showed less degradation with 93%, 91%, 85%, 75%, and 61% soil cover, respectively. However, their soil warming ability was significantly reduced. These mulches could be used for double cropping to suppress weeds and to reduce inputs associated with plastic purchase, laying, and disposal. However, they may not provide adequate soil warming early in the season for the second crop.

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Maria A. Macias-Leon and Daniel I. Leskovar

.min), and average (T.avg) temperature; Maximum (RH.max), minimum (RH.min), and average (RH.avg) relative humidity; Daily light integral; and cumulative precipitation. Cumulative degree-days (CDD) calculation. Cumulative degree-days at each sampling date were

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Roberto G. Lopez and Erik S. Runkle

The vegetatively propagated `Fire Kiss' clone of the hybrid Zygopetalum Redvale orchid has appealing potted-plant characteristics, including fragrant flowers that are waxy lime-green and dark maroon with a broad, three-lobed, magenta and white labellum. We performed experiments to quantify how temperature influenced leaf unfolding and expansion, time from visible inflorescence to flower, and longevity of individual flowers and inflorescences. Plants were grown in controlled-environment chambers with constant temperature set points of 14, 17, 20, 23, 26, and 29 °C and an irradiance of 150 μmol·m-2·s-1 for 9 h·d-1. As actual temperature increased from 14 to 25 °C, the time to produce one leaf decreased from 46 to 19 days. Individual plants were also transferred from a greenhouse to the chambers on the date that an inflorescence was first visible or the first flower of an inflorescence opened. Time from visible inflorescence to open flower decreased from 73 days at 14 °C to 30 days at 26 °C. As temperature increased from 14 to 29 °C, flower and inflorescence longevity decreased from 37 and 38 days to 13 and 15 days, respectively. Data were converted to rates, and thermal time models were developed to predict time to flower and senescence at different temperatures. The base temperature was estimated at 6.2 °C for leaf unfolding, 3.5 °C for time to flower, and 3.7 °C for flower longevity. These models could be used by greenhouse growers to more accurately schedule Zygopetalum flowering crops for particular market dates.