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Abstract

Infrared (IR) thermometry has not been extensively applied in deciduous tree fruit production to determine water use. The objectives of this study were to a) examine IR measurement techniques for evaluating canopy temperatures in peach [Prunus persica (L.) Batsch.] trees; b) evaluate a foliage-minus-air temperature- (Tc – Ta) based diffusion equation for vapor flux used to predict tree water use; and c) measure the Tc – Ta response of irrigated peach trees over a range of air vapor pressure deficits. The mean Tc – Ta for a tree was similar for readings made from the canopy sides (horizontal orientation of the IR thermometer) or canopy tops (vertical orientation). Peach tree water use from weighing lysimeters was predicted within 9.4% ± 3% using the diffusion equation for vapor flux. Tc – Ta for irrigated peach trees was related to the air vapor pressure deficit (VPD). Data are presented to show that stomatal response to VPD does alter the Tc – Ta nonstressed baseline for peach at VPD > 2 kPa.

Open Access
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Abstract

Antitranspirant sprays of 5 film-forming materials were compared on mature Citrus sinensis (L.) Osbeck cv. Valencia trees for film persistence and reduction of fruit weight loss after harvest. These materials were also sprayed on young ‘Pineapple’ (C. sinensis) or ‘Valencia’ orange trees growing in 7.6 liter containers on which weight loss was subsequently measured for 48-hour periods after watering. Spray solutions of equal or known film-forming ingredients (solids content) of 1 to 4% (weight/weight) were applied and compared. Plantgard film did not significantly increase the leaf epicuticular coating nor did it reduce fruit weight loss or young tree water use. Mobileaf, Vapor Gard, Nu-Film-17, and Wilt Pruf NCF did result in heavier leaf coatings and less fruit weight loss than the controls. Mobileaf and Vapor Gard reduced potted tree water use. Some loss of effectiveness and coating thickness occurred 5 months after application, but only a small nonsignificant change in effectiveness occurred during the first 2 months after application. Mobileaf and Vapor Gard appeared to give the best antitranspirant protection for the initial 2 months and Vapor Gard for 5 months.

Open Access

Abstract

The relative ozone sensitivities of a 7-parent diallel set of petunia hybrids were compared with their rates of ozone absorption, rates of transpiration, ascorbic acid concentrations, and shoot and root weights. Ozone sensitivity was highly correlated with both ozone and water vapor diffusion resistance, but not with ascorbic acid concentration or shoot-root ratio.

Open Access

productivity, contrary to the assertion of Blum (2005) . Environmental effects on WUE include the response to the abiotic environmental effects of vapor pressure deficits (VPD), photosynthetically active radiation ( PAR ), and water deficits in addition to

Free access

were provided when the integrated light intensity reached 0.20 mol·m −2 ·h −1 or after 60 min, whichever occurred first. A vapor-pressure deficit of 0.3 kPa was maintained by the injection of steam or fine mist (Humidifan Turbo XE; Jaybird

Free access

; Brown and Morra 1997 ; Gao et al. 2021 ; Kim et al. 2020 ; Ren et al. 2018 ; Vandicke et al. 2020 ). However, at 25 °C, AITC is an oily substance with very low vapor pressure; therefore, it has a low tendency to disperse in the soil ( Almasri et

Open Access

This study examined the effects of high humidity (>95%) and airflow on fresh peach [Prunus persica (L.) Batsch.] quality. Peaches were stored in high airflow at 98%, 88%, and 67% relative humidity (RH) (6, 5.6, and 4.3C, respectively) and negligible airflow at 100%, 95%, and 81% RH (6, 5.6, and 4.3C, respectively). Fruit weight loss, penetrometer force, impact variables, and bruise occurrence from a single 15-cm drop impact were measured over 20 days of storage. Fruit stored at a low vapor pressure deficit had a lower rate of weight loss, with drop impact values characteristic of firmer fruit than fruit stored at higher vapor pressure deficits. High airflow increased weight loss and decreased fruit firmness, but had only a secondary effect on localized humidity. Penetrometer force and bruise occurrence were less sensitive than drop impact variables in detecting differences in fruit firmness due to treatments.

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Abstract

Antitranspirants (‘Vapor Gard’ and ‘Wilt Pruf’) effectively controlled powdery mildew on Hydrangea macrophylla Thunb. and Lagerstroemia indica Nana. A 2% antitranspirant emulsion was sufficient to suppress the pathogen’s development without causing visible phytotoxic effect or plant growth inhibition. The antitranspirants were as effective, and in some cases more effective (‘Vapor Gard’), than the systmic triazole fungicide ‘Tilt’ in controlling the disease. Hydrangea and dwarf Lagerstroemia (crapemyrtle) are grown commercially as flowering pot plants. Disease-free plants are required. Powdery mildew (Erisiphe polygoni DC) often causes severe damage on greenhouse-grown hydrangea. This fungus usually appears 1st on the lower leaf surface, where it produces a white, loose, cottony mycelium. Yellowish or purple-white blotches with mycelium also can be observed on the upper surface of the leaf. When the disease develops under favorable environmental conditions, the symptoms cover not only the entire leaf surface but also the bud clusters and flowers (11). Various fungicides control powdery mildew under greenhouse conditions.

Open Access

Abstract

The effects of air temperature and leaf-to-air vapor pressure deficit (VPD) on the gas exchange behavior, i.e., net CO2 exchange rate (NCER) and dark respiration rate, transpiration, leaf diffusive conductance to water vapor, water use efficiency (WUE), and xylem pressure potential of Schefflera arboricola Hayata ‘Compacta’ were examined under conditions of adequate substrate moisture in a controlled environment growth chamber. The optimum temperature for NCER was around 25°C at a photo-synthetic photon flux density (PPFD) of 450 μmol s-1m-2 and an ambient CO2-concentration of about 350 cm3.m-3. With increasing VPD, transpiration increased while leaf diffusive conductance as well as leaf temperature decreased. Due to humidity induced stomatal closure, WUE expressed per unit of VPD also decreased. Changes in VPD did not significantly affect NCER and xylem water potential.

Open Access

Abstract

Various storage treatments were imposed on cut douglas-fir Christmas trees to measure drying relative to the damage threshold ψ of −3.5 MPa. In a greenhouse (day/night 16°/10° ± 5°C, RH 70-95%), cut douglas-fir dried to −3.5 MPa in 4 days. Overhead irrigation under these conditions maintained ψ about − 3.2 MPa for 9 days. Outdoors (day/night 672° ±9°), ψ declined to a range of −2.5 to −3.0 MPa depending on the weather. Overhead irrigation outdoors maintained ψ between −1.0 to −2.5 MPa. The antitranspirants tested did not reduce the rate of water loss significantly in the greenhouse. Outdoors, ψ of Vapor Gard-treated trees was similar to the irrigated trees, but Vapor Gard caused serious cosmetic defects. None of the other antitranspirants tested reduced moisture loss outdoors.

Open Access