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Curt R. Rom, Donn Johnson, Mark Den Herder, and Ron Talbert

Twelve apple orchards and an experimental orchard were evaluated in 2 years for weed population and diversity, primary pests (codling moth, oriental fruit moth, plum curculio and mites), primary diseases, soil water content, and 37 horticultural attributes describing tree growth, fruit growth, productivity, tree nutrition, and management intensity. Data were collected at 2 week intervals. The experimental orchard contained three apple cultivars grown in three orchard floor management systems.

Increased weed ground cover related to earlier and increased mite predator populations in trees, decreased pest mite-days, but reduced tree and fruit growth. Grass weed species appeared more detrimental to tree growth than broadleaf species. Tree training intensity was negatively related to canopy density, and incidence of pests and diseases. Reductions in fruit size and quality were more closely linked to weed competition, and earliness and degree of pest mite infestation than to crop load.

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Mengmeng Gu, James A. Robbins, and Curt R. Rom

One-year-old paper birch (Betula papyrifera Marsh.) seedlings were exposed to water deficit, ethylene, or inhibitors of ethylene action under greenhouse conditions to investigate ethylene's role in water-deficit stress-induced leaf abscission. Exposing well-watered and water-stressed paper birch to 20 ppm ethylene resulted in more than 50% leaf abscission after 96 h regardless of plant water status. However, application of a physiological level (1 ppm) of ethylene did not cause leaf abscission in either well-watered or water-stressed paper birch. Inhibitors of ethylene action (1ppm 1-methylcyclopropene or 0.1 mm silver thiosulfate) did not affect predawn water potential, gas exchange, or chlorophyll fluorescence. A significant increase in ethylene production was not detected in water-stressed paper birch before the onset of significant leaf abscission. Based on these observations, ethylene would appear to play a minor role in water-deficit stress-induced leaf abscission in paper birch.

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Curt R. Rom, R.A. Allen, K. Kupperman, and J. Naraguma

Three studies were established to compare spring (S) vs. autumn (F) N fertilizer applications on apple tree performance. The studies used newly planted trees, 4-yr-old trees, and 8-yr-old trees, fertilized with either ammonium nitrate or urea at 2 weeks after harvest (F) or at bud break (S). In the first 3 years growth in a newly planted orchard, time of fertilizer did not significantly affect tree height or TCSA. In the first cropping year, F fertilized trees had the greatest flower cluster number and bloom density but similar % set and yield compared to S fertilized trees. F fertilized trees in mature orchards studies tended to be shorter and have smaller TCSA increment after 3 yrs. Treatments did not affect bloom density, % set or total yield although spring fertilized trees had a greater % drop. Although spur leaves of F fertilized trees had greater N content at bloom, shoot leaves typically had lower N and Mn, and higher P, K, and Ca at 90 days after bloom compared to S treatment trees.

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Eric T. Stafne, John R. Clark, and Curt R. Rom

Net CO2 assimilation (A), evapotranspiration (ET), and stomatal conductance (g s) were determined in two experiments for 14 and 18 raspberry (Rubus sp.) genotypes, respectively, grown in 4-L containers and exposed to 35 °C daytime temperatures 2 weeks and 4 weeks after placement in growth chambers. Measurements were taken on two successive leaves on the same primocane between the third and seventh node (≈75% to 85% of full leaf expansion). In Expt. 1, selections from Louisiana exhibited higher A (3.10-5.73 μmol·m-2·s-1) than those from Oregon (0.50-2.65 μmol·m-2·s-1). In Expt. 2, the genotype × time interactions were nonsignificant, and time of measurement did not affect A or ET (P ≤ 0.05). Assimilation ranged from 2.08 to 6.84 μmol·m-2·s-1 and varied greatly among genotypes, indicating that diverse A levels exist at high temperatures in raspberry germplasm. NC 296, a selection of R. coreanus Miq. from China, and `Dormanred', a southern-adapted raspberry cultivar with R. parvifolius Hemsl. as a parent, had the highest A rates. Evapotranspiration and g s did not differ among genotypes. Average g s for all genotypes declined from 234 mmol·m-2·s-1 in week 2 to 157 mmol·m-2·s-1 in week 4. Our findings, coupled with plant performance under hot conditions, can be used to identify potential parental raspberry germplasm for breeding southern-adapted cultivars.

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Mengmeng Gu, Curt R. Rom, and James A. Robbins

Four birch taxa, Betulaalleghaniensis, B. davurica, B. nigra `Heritage', and B. papyrifera, were grown in a greenhouse and exposed to water deficit stress for 35 days. Daily water was withheld from the plants until the combined weight of each container and the plant was reduced to 40% of the control. Supplemental water was supplied to each container to maintain 40% of the initial combined weight. Predawn water potential, gas exchange, and abscised leaf area were measured daily during the first week and at 3-day intervals after the first week. Predawn water potential dropped to lowest value before the containers were rehydrated and remained low throughout the treatment period. Net CO2 assimilation (A), stomatal conductance (gs) and evapotranspiration (Et) of all taxa decreased significantly during the first week of water deficits. Changes in A and Et varied among taxa after the first week of water deficits. Water use efficiency (WUE = A/Et) of four birch taxa decreased to significant lower values than control in the first week that water was withheld, and then increased to significantly higher values than control. Gas exchange data were fit into 2- or 3-segmented linear model. The type and shape of the models, and the joint of each segment gave an indication of how the gas exchange responded to the long-term water deficit stress. At the end of the water deficit treatment, B. papyrifera had abscised most of its leaves and maintained a high A, while B. alleghaniensis maintained more leaves on the tree, but had a relatively low A.

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Zimian Niu, Dapeng Zhang, Jicheng Zhan, and Curt Rom

Influence of photosynthetically active radiation (PAR) microclimate in the canopy of four training systems [open-center with high trunk (OH); open-center with middle trunk (OM); open-center with low trunk (OL); and a traditional round canopy (RC)] on the growth, yield and fruit quality of apple were studied in the Beijing area. The results showed that: 1) the growth and yield potential were affected by canopy light microclimate. The average leaf chlorophyll content from OH, OM and OL systems was 12.3% to 18.1% greater than that from the RC system. Trees from OH, OM, and OL systems produced 84.2% to 89.7% of shoot forming flower clusters compared to only 47.3% to 50.9% of the RC shoots. Training system did not affect total yield of 8-year-old trees, but in 10-year-old trees the RC system had lower yields compared with open-center systems. 2) Fruit quality was also affected by canopy light microclimate. The average anthocyanin content in the skin of fruit from OH, OM, and OL systems was 35.9% to 46.1% higher than that from the RC system, but chlorophyll content from the OL system was higher than in the open-center systems. Meanwhile, the contents of TSS and esters in apple flesh from the open-center systems were significantly higher than that from the RC system. 3) When the relative value of PAR in canopy exceeded 33.8%, the growth index of trees (chlorophyll: return-bloom ratio) exceeded 66.6% and the fruit quality index (TSS × anthocyanin) exceeded 94.7%. When PAR was less than 20.6%, the growth index was under 37.2% and the fruit quality index was under 67.5%. PAR value was significantly correlated with the growth and fruit quality index in the four training systems, and the total canopy volume of higher PAR(exceeding 33.8%, relative value) from OH, OM, and OL systems was 37.1% to 45.0% greater than that from the RC system.

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Mengmeng Gu, James A. Robbins, Curt R. Rom, and Jason McAfee

Japanese beetle (Popilla japonica Newman) has caused severe damage on a wide range of horticultural crops since its first introduction to the Eastern United States from Japan in 1916. Leaves are skeletonized by adult beetles feeding in masses, which makes this insect damage easy to identify. In Arkansas, Japanese beetle was first trapped in Washington County in 1997 and has reached epidemic proportions in the most recent three years. Leaf skelotonization and feeding preference on eighteen birch accessions by Japanese beetle were recorded in 2003 and 2004. There was a wide range from no feeding (0% leaf skelotonization) to high feeding preference (89% leaf skelotonization). Betula utilis var. jacquemontii and B. papyrifera `Renaissance Upright' had highest preference. Betula pendula `Laciniata' had no feeding damage from Japanese beetle.

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Eric T. Stafne, John R. Clark, and Curt R. Rom

Leaf gas exchange of six red raspberry (Rubus idaeus L.) and one blackberry (Rubus L. subgenus Rubus Watson) genotypes growing in 12-L containers was measured at four temperatures (20, 25, 30, and 35 °C) once a month for 3 months in growth chambers by infrared gas analysis. Measurements were taken on three successive leaves on the same primocane between the third and seventh nodes (≈75% to 85% of full leaf expansion). The plants were grown in ambient (field) conditions except when measurements were taken. Maximum daily ambient temperatures rose as high as ≈37 °C during this period. Net CO2 assimilation (A), evapotranspiration (ET), and stomatal conductance (gs) were measured during June, July, and August. Significant differences (P ≤ 0.01) in A were found among the seven genotypes. 'Arapaho' blackberry displayed the highest mean A rate at all temperatures. Only in the raspberry cultivars Nova and Reveille did the rate of A drop significantly when temperature increased from 20 to 30 °C. 'Reveille' was also the only cultivar in which A significantly declined between 30 and 35 °C. The ET increased significantly over the four temperatures in four cultivars ('Arapaho', 'Heritage', 'Nova', and 'Southland'). The ET rate at 35 °C was higher for 'Arapaho' than for all other cultivars. 'Autumn Bliss', 'Dormanred', and 'Reveille' did not change significantly as the temperature rose from 20 to 35 °C. Stomatal conductance of 'Heritage' and 'Arapaho' did not change significantly between 20 and 35 °C, whereas that of 'Autumn Bliss' and 'Reveille' declined almost 50% when temperature increased to 30 or 35 °C.

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Eric T. Stafne, John R. Clark, and Curt R. Rom

Seven Rubus cultivars were evaluated at two locations in Arkansas, northwest (Fayetteville) and southwest (Hope), to evaluate plant growth differences under high and very high summer temperature conditions. Temperatures during the hottest month (July) averaged 34 °C and 38 °C for Fayetteville and Hope, respectively. Growth; leaf area and number; and fresh and dry weights of leaves, stems, and roots were measured on the containerized raspberry cultivars Autumn Bliss, Dormanred, Heritage, Nova, Reveille, and Southland and the blackberry cultivar Arapaho. Growth measurements included number of canes per plant, number of laterals per cane, cane length, node number, and internode length. Measurements were taken monthly from June through September. Leaf areas were done after all growth measurements were taken at both locations in September. Variation occurred among cultivars and locations for leaf area, fresh and dry weights, growth, and leaf number. Plant death occurred at the Hope location, with `Heritag', `Reveille', and `Southland' all having plant mortality, while `Dormanred' and `Arapaho', both southern-adapted cultivars, had the greatest fresh and dry weights. The Fayetteville location had no plant loss after initial emergence in spring, and this more moderate environment probably contributed to higher plant survival. Our data indicated that only `Dormanred' and `Arapaho' achieved adequate survival and growth in the very high temperatures of the Hope location, whereas other cultivars (Reveille and Southland) with some southern U.S.-adapted germplasm, showed poor adaptation to the environments of our study. Our findings reflect the impact of high heat on non-adapted germplasm and reveal information on adaptation levels needed for parental consideration in breeding for southern conditions.

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Hyun-Sug Choi, Curt R. Rom, Mengmeng Gu, and Jason McAfee

Seasonal variations of nutrient concentrations in soil and apple leaves, soil properties, weed density, and tree performance were observed for response to four groundcover managements systems: 1) mowed control; 2) plastic woven landscape fabric; 3) wood chip mulch; and 4) shredded commercial paper mulch. Soil sampled below the wood chip and shredded paper mulch treatments had higher NO3-N concentrations during the season. Soil below the shredded paper mulch had greater soil Ca, Na, and Zn than other treatments. Soil sampled below wood chip mulch had higher Mg and B. Leaf K was greater for trees grown with bark chip mulch than the other treatments. Overall, the seasonal patterns of N, P, and K decreased and had similar patterns as previously reported conventionally grown orchards. The leaf Ca and Mg increased during the season for all treatments. The concentration of other microelements had patterns similar among all treatments. Seasonal soil pH decreased during the season and was affected by treatments. During the season, water infiltration was faster into the soil covered with shredded paper mulch. The organic matter was greater in soil under the wood chip mulch at the 15-cm soil depth. Very little weed invasion occurred in the landscape fabric through August. Trees grown with shredded paper and wood chip mulch treatments had greater trunk cross-sectional area compared to trees grown under landscape fabric after 5 years; however, the latter treatment resulted in greater tree height, tree canopy spread, and fruit yield.