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Nitrogen fertilizer rates and timings were reexamined for potatoes (Solanum tuberosum L.) under sprinkler irrigation with scheduling by soil water potential. Four potato cultivars were grown on a silt loam soil in eastern Oregon in 1992, 1993, and 1994. Potatoes were submitted to six treatments: four N fertilizer rates (0, 135, 200, and 270 kg·ha-1) and two split application treatments (67 kg·ha-1 applied three times, and 40 kg·ha-1 applied five times). The crop was irrigated when the soil water potential at 0.2-m depth reached -60 J·kg-1. No more than the accumulated evapotranspiration was replaced at each irrigation. Over 3 years, the cultivars had similar responses to N rates and N timing. In 1992, following alfalfa, tuber yield was not responsive to N fertilization. In 1993 and 1994, following wheat, tuber yield was maximized by N at 211 and 175 kg·ha-1. Split applications of the N fertilizer did not increase tuber yield in any year. In 1993 and 1994, the highest tuber specific gravity was obtained with no N fertilization. Nitrogen rates above the optimum resulted in darker frying tubers in 1992 and 1993. The N rates maximizing tuber yield in this study were lower than the rates recommended in the university fertilizer guides.
Four potato (Solanum tuberosum L.) varieties were grown under four season-long sprinkler irrigation treatments in three successive years (1992-94) on silt loam soil in eastern Oregon. The check treatment was irrigated when soil water potential (SWP) at the 0.2-m depth reached -60 J·kg-1 and received at most the accumulated evapotranspiration (Etc) to avoid exceeding the water-holding capacity of the top 0.3 m of soil. The three deficit irrigation treatments were irrigated when SWP at the 0.2-m depth reached -80 J·kg-1 and had the following percent of the accumulated Etc applied at each irrigation: 1) 100%, 2) 70%, and 3) 70% during tuber bulking with 50% thereafter. Based on regression of applied water over 3 years, potatoes lost both total and U.S. No. 1 yields when irrigations were reduced. Based on regression on applied water, when irrigation was reduced gross revenues declined more than production costs, resulting in a reduction in profits. Leaching potential, as determined by the SWP treatments, was low for all treatments. The results of the study suggest that deficit irrigation of potatoes in the Treasure Valley of Oregon would not be a viable management tool, because the small financial benefits would not offset the high risks of reduced yields and profits from the reduced water applications.
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.
Abstract
Cuts were generally more prevalent on mechanically harvested peaches than on those hand harvested, although they were usually within acceptable limits. Bruise development during storage was variable and often not significantly higher on machine harvested fruit than on those hand harvested. Fruit position within bulk bins appeared to influence subsequent bruise development. A prototype portable dumper-sorter did not significantly increase fruit injuries. Providing fruit were of comparable maturity, injuries to postbloom regulator-treated fruit were comparable to those untreated. The development of rots during storage was the greatest source of unmarketable fruit and is regarded as the most serious problem related to the mechanical harvesting of peaches for fresh market.
Oil sprays increase the phytotoxicity of captan to apple foliage. The purpose of this study was to determine if oils increase the penetration of captan through leaf cuticles. Enzymatically isolated apple leaf cuticles were used as a model system to study captan penetration. A bioassay was developed using the inhibition of growth of Penicillium cyclopium on potato-dextrose agar as a measure of captan penetration through the cuticle. Captan penetrated through both surfaces, but significantly more penetrated through the abaxial cuticles than the adaxial cuticles. Increasing the captan concentration increased the captan penetration through the abaxial cuticle in a linear relationship. Captan penetration through the cuticle was increased by 63% when cuticles were treated with captan plus 1% emulsified soybean oil. Abaxial cuticles treated with captan plus emulsified soybean oil or with captan plus SunSpray Ultra-Fine oil had >125% greater captan penetration than cuticles treated with only captan. Cuticles treated with captan plus dormant oil (petroleum oil) had 220% more captan penetration than the captan only treatment.
Abstract
Examination of flowers of carrot (Daucus carota L.) using the scanning electron microscope revealed that some cytoplasmically male-sterile genotypes exhibit flower abnormalities that may be associated with reduced pollination and seed set. Such abnormalities, evident in many inbred lines, may carry over to the male-sterile F1 parents used to produce 3-way hybrids and probably affect insect pollinator activity.
Abstract
‘Green Ice’ is a green-fleshed muskmelon (Cucumis melo L.) adapted to the climatic conditions prevalent in the southeastern United States and is well-suited for both commercial and home garden production. It is a high-yielding ‘Honey Ball’-type muskmelon that produces round to oval, pale gray-green, medium-sized fruit that turn cream-colored and slip from the vine at maturity. The thick light-green flesh has a pleasing aroma and sweet flavor and is high in vitamin C. The vigorous plants are resistant to race 3 of powdery mildew [Spaerotheca fuliginea (Schlect ex Fr.) Poll.] and tolerant to most pests and environmental stresses of the region.
Bacteriophages specific to Xanthomonas campestris pv. pelargonii (Xcp), the causal agent of bacterial blight of geranium, Pelargonium ×hortorum L.H. Bailey, were isolated from soil and sludge samples from Florida, California, Minnesota, and Utah. Sixteen phages were evaluated for their potential to lyse 21 Xcp strains collected from around the world. The Xcp strains varied in their susceptibility to the phage isolates with 4 to 14 phages producing a lytic or highly virulent reaction. A mixture of five h-mutants was developed from phages that exhibited the broadest host-ranges and tested against the same Xcp strains. The h-mutant phage mixture lysed all 21 Xcp strains. Three experiments were designed to determine the efficacy of using a mixture of four h-mutant phages to control the spread of the bacterial blight pathogen on potted and seedling geraniums under greenhouse conditions. Plants surrounding diseased inoculated plants were treated with a phage mixture at 5 × 108 pfu/mL daily, biweekly, or triweekly, or treated with Phyton-27®, at 2.0 mL·L-1 every 10 or 14 days. In potted geraniums, daily foliar sprays of the phage mixture had reduced disease incidence and severity by 50% and 75%, respectively, relative to control plants after 6 weeks. In two plug experiments, the phage mixture applied daily also had reduced disease incidence and severity by 69% and 86%, and 85% and 92%, respectively, when compared with controls after 5 weeks. In all three experiments, disease incidence and severity were less for plants treated daily with phages than for those treated less frequently with phages or with Phyton-27®. Chemical name used: copper sulfate pentahydrate (Phyton-27®).
A mixture of host-range mutant (h-mutant) bacteriophages specific for tomato race 1 (T1) and race 3 (T3) of the bacterial spot pathogen, Xanthomonas campestris pv. vesicatoria (Doidge) Dye was evaluated for biological control of bacterial spot on `Sunbeam' tomato (Lycopersicon esculentum Mill.) transplants and field-grown plants for two seasons (Fall 1997 and Fall 1998). Foliar applications of bacteriophages were compared with similar applications of water (control) and of copper/mancozeb bactericides, the commonly used chemical control strategy for tomato seedling and field production. In 1997, the incidence of bacterial spot on greenhouse-grown seedlings was reduced from 40.5% (control) to 5.5% or 0.9% for bactericide- or bacteriophage-treated plants, respectively. In 1998, the incidence of bacterial spot was 17.4% on control plants vs. 5.5% and 2.7% for bactericide- and bacteriophage-treated plants, respectively, although these differences were not statistically significant at P ≤ 0.05. Applications of bacteriophages to field-grown tomatoes decreased disease severity as measured by the area under the disease progress curve (AUDPC) by 17.5% (1997) and 16.8% (1998) compared with untreated control plants. Preharvest plant vigor ratings, taken twice during each field season, were higher in the bacteriophage-treated plants than in either bactericide-treated plants or nontreated controls except for the early vigor rating in 1998. Use of bacteriophages increased total weight of extra-large fruit 14.9% (1997) and 24.2% (1998) relative to that of nontreated control plants, and 37.8% (1997) and 23.9% (1998) relative to that of plants treated with the chemical bactericides. Chemical names used: manganese, zinc, carboxyethylene bis dithiocarbamate (mancozeb).
Environmental factors such as rainfall may reduce the efficacy of foliar-applied soybean [Glycine max (L.) Merrill] oil in reducing pest mortality. Greenhouse studies were conducted to investigate the influence of rain on the retention of soybean oil and the influence of soybean oil and rainfall on surface morphology of apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] and peach [Prunus persica (L.) Batsch (Peach Group)] leaves and stems. `Contender' peach and `Golden Delicious'/Malling 27 apple trees were grown in 19 L pots in a greenhouse (23 ± 9 °C) and sprayed with soybean oil (1%) emulsified with the adjuvants Latron B-1956 or K1. Twenty-four hours after treatment, the trees were subjected to simulated rainfall of 0.0, 0.25, 1.25, or 2.54 cm. A negative linear relationship existed between rainfall and oil retention. Peach leaves receiving 0.25, 1.25, and 2.54 cm rainfall retained 81%, 38%, and 18% of the applied oil, respectively. Oil retention by apple leaves was also negatively related to rainfall. For both species, a negative linear relationship existed between oil retention on stems and rainfall. There was no effect of emulsifier on retention of 1% soybean oil after rain on apple leaves or on the retention of 8% to 11% soybean oil on the stems of apple and peach. Scanning electron microscopy revealed that epicuticular wax occurred as striations on apple and peach leaves. The wax morphology on peach and apple stems appeared as thin plates and platelets, respectively. The wax morphology of leaves and stems of both trees was not affected either by the soybean oil emulsions or rain. Both emulsions induced stomatal closure in leaves and peach stems, however, stomates opened after rainfall of 1.25 or 2.54 cm. The lenticels appeared to be unaffected by either emulsion. Results illustrate that rainfall of 2.54 cm washed off a major portion of the applied oil. Thus, respraying may be needed under natural climatic conditions with rainfall ≥2.54 cm to restore the efficacy of applied soybean oil.