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Nancy L. Schulte, Edward J. Timm and Galen K. Brown

`Redhaven' peaches [Prunus persica (L.) Batsch] were dropped onto several impact surfaces to determine impact conditions that initiate bruising. After impact, the peaches were tested for flesh firmness and sorted into firm, soft, and very soft groups for bruise analysis. The drop height that did not bruise decreased as fruit softened. The peach shoulder area bruised most easily. A drop of only 8 mm onto a hard surface initiated bruising on a soft peach, whereas a Poron 15250 cushion could protect the peach for a ≤85-mm drop. Impact damage threshold estimates were developed for the three flesh firmness conditions. The threshold estimates and impact history information collected by an instrumented sphere can be used to develop handling equipment design and operation guidelines that essentially avoid impact bruises on peaches.

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Fabio Orlandi, Carlo Sgromo, Tommaso Bonofiglio, Luigia Ruga, Bruno Romano and Marco Fornaciari

calculated using 13 different threshold temperatures (TT) from 3 to 15 °C. The meteorological data: minimum, maximum temperatures (°C), and rain (mm), were surveyed from 15 meteorological stations of the national agrometeorological network located near the

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Donna A. Marshall, James M. Spiers and Kenneth J. Curry

-susceptible cherries. They concluded that water uptake thresholds at which fruit split was a major factor explaining the split susceptibility difference in cherry cultivars. Lane et al. (2000) added that a cultivar difference causally related to splitting

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Freddy Mora, Cristóbal M. Concha and Carlos R. Figueroa

, 2014 ; Santos et al., 2011 ). Threshold models have been reported to be useful for the genetic evaluation of categorical traits ( Sorensen et al., 1994 ), enabling the estimation of genetic parameters, including heritability and genetic correlations

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C.C. Shock, E.B.G. Feibert and L.D. Saunders

Onion (Allium cepa L., `Great Scott') was grown on silt loam soils and submitted to four irrigation thresholds (-25, -50, -75, and -100 kPa) in 1992 and six irrigation thresholds (-12.5, -25, -37.5, -50, -75, and -100 kPa) in 1993 and 1994. Irrigation thresholds (soil water potential measured at 0.2-m depth) were used as criteria to initiate furrow irrigations. Onions were evaluated for yield and grade after 70 days of storage. In 1992 and 1994, total yield, marketable yield, and profit increased with increasing irrigation threshold. In 1993, total yield increased with increasing irrigation threshold, but marketable yield and profit were maximized by a calculated threshold of -27 kPa due to a substantial increase of decomposition during storage with increasing threshold.

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J.F. Karlik, P.B. Goodell and G.W. Osteen

Spider mites [including Tetranychus pacificus McGregor (Pacific mite) and T. turkestani Ugarov & Nikolski (strawberry mite)] are the most important invertebrate pests of the roses (Rosa hybrida) grown in Kern County, Calif. (the major production area in the United States). However, sampling methods and treatment thresholds have been subjective. A rapid presence–absence field sampling method has been developed, and treatment thresholds for mites have been evaluated based on the method. Roses exhibit a higher tolerance for spider mite populations than previously thought.

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Marvin Pritts, Mary Jo Kelly and Greg English-Loeb

The strawberry bud weevil (Anthonomus signatus Say; clipper) is considered to be a serious early-season pest in perennial matted row strawberry (Fragaria ×ananassa Duchesne) plantings in North America. Adult females damage flower buds in early spring by depositing an egg in the bud, then clipping the bud from the pedicel. Action thresholds are low (two clipped buds/meter of row) because pest managers and growers have assumed that one clipped flower bud results in the loss of one average-sized fruit. Fields with a history of clipper damage are often treated with insecticides during the first period of warm weather that coincides with inflorescence development, without scouting for clipped buds or evaluating damage. We examined 12 strawberry cultivars and found that most can compensate for a significant amount of flower bud loss, provided that the loss occurs early in the development of the inflorescence. A new threshold is proposed in which the potential loss of fruit per inflorescence is considered, along with the total number of severely damaged inflorescences. We believe that in most circumstances and with most cultivars, clipper injury will remain below the damage threshold.

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J. Caron, H.L. Xu, P.Y. Bernier, I. Duchesne and P. Tardif

In nursery plant production, optimum water use is important to maintain productivity and make this production environmentally sound. Water should be supplied when it becomes difficult to extract for the plant, at a bulk soil water potential threshold value that may vary with environmental conditions, species and substrate properties. The objective of this study was to determine the threshold value at which availability of water rapidly drops for three newly developed substrates to be used in the production of Prunus ×cistena. Xylem water potential and potential at the soil-root interface were used as indices of water availability and were compared with bulk soil water potential. Water was easily available (no drop in xylem or soil-root interface water potential) from container capacity down to a bulk soil water potential of about-10 kPa when xylem water potential was used as an indicator and -8 kPa when the soil-root interface water potential was chosen as the indicator. No significant differences in the threshold values were found between substrates, consistent with the absence of differences in the substrate physical properties. The differences in water availability among substrates were consistent with an observed difference in salt content. The important variability observed in the threshold suggests that plant based measures may be preferred to soil based measures in assessing water availability in artificial mixes.

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Darrell Sparks

The modified Mitscherlich plant growth model was used to quantify the threshold leaf Zn level influencing nut yield and vegetative growth, on an orchard basis, for pecan [Carya illinoinensis (Wangenh.) C. Koch]. Four indices of tree performance, including percentage of trees without deficiency symptoms, vegetative growth, nut yield, and trees without deficiency symptoms plus nut yield, were analyzed with regard to leaf Zn concentration. Data available from published and unpublished sources on any single performance index were combined for mathematical modeling. The threshold value for leaf Zn was determined to be ≈50 μg·g-1 for these tree performance indices. Thus, nut yield and vegetative growth in an orchard will be reduced with a leaf Zn concentration below ≈50 μg·g-1, but will not be affected above this value.

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John M. DeLong, Robert K. Prange, Jerry C. Leyte and Peter A. Harrison

HarvestWatch is a new chlorophyll fluorescence (F)-based technology that identifies the low-oxygen threshold for apple (Malus × domestica) fruit in dynamic low-O controlled atmosphere (DLOCA) storage environments [e.g., <1% oxygen (O2)]. Immediately following harvest, `Cortland', `Delicious', `Golden Delicious', `Honeycrisp', `Jonagold' and `McIntosh' fruit were cooled and loaded into 0.34 m3 (12.0 ft3) storage cabinets. A static controlled atmosphere (CA) regime of 1.5% O2, 1.5% carbon dioxide (CO2) and 3 °C (37.4 °F) [0 °C (32.0 °F) for `Delicious' and `Golden Delicious'] was established for the control fruit, while the low-O2 threshold was identified by a spike in the fluorescence parameter, Fα, as the O2 levels in the DLOCA cabinets were lowered below 1%. The DLOCA storages were then maintained at O2 levels of 0.1% to 0.2% above the threshold value for each cultivar, which returned Fα to prethreshold signatures. Quality measurements following 5 to 9 months of storage and a 7-day shelf life of 20 °C (68.0 °F), showed that the HarvestWatch fruit were generally firmer, had no incidence of superficial scald in `Cortland' and `Delicious' apples, and did not accumulate fermentative volatile compounds. The HarvestWatch system permits rapid, real-time measurements of the status of stored apple fruit in ultra low-O2 environments without the inconvenience of breaking the room's atmosphere. Our results indicate that HarvestWatch facilitates what may be the highest possible level of fruit quality retention in long-term, low-O2 apple storage without the use of scald-controlling or other chemicals before storage.