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Nicole Burkhard, Derek Lynch, David Percival, and Mehdi Sharifi

A 2-year study in Nova Scotia examined the effectiveness of thickly applied organic mulches as a method of weed control in highbush blueberries (Vaccinium corymbosum L.), and assessed weed and mulch impact on crop growth, leaf nutrient concentration, yield, and quality under organic production management. Mulches, applied in-row at 20-cm depth, included pine needles (PN), manure–sawdust compost (MC), and seafood waste compost (SC). Competition from weeds negatively affected crop growth and productivity, reducing canopy volume (16% to 38%), leaf nitrogen concentration and berry yields (up to 92%), number (up to 91%), and specific weight (up to 21%). Among mulches, PN proved to be the most effective in suppressing weed growth with 55% less and 73% less aboveground weed biomass compared with the control in 2005 and 2006, respectively, although PN productivity effects were much more modest. One year after application, PN lost some efficacy at suppressing weeds but was still superior to both composts. Distribution of weed species was substantially altered by mulch treatment. Both composts prevented some weed emergence (i.e., sheep sorrel), but weed seeds germinating in composts, especially SC, experienced prolific growth likely as a result of available nutrients in composts. No detrimental effects on short-term plant productivity were noted despite high C:N ratios of PN and MC (72:1 and 48:1, respectively). Plant vigor and yield were typically higher for compost mulch treatments, especially in weed-free subplots, and composts provided more complete fertilization reflected in increased leaf tissue elemental (NPK) composition. Fruit soluble solid (sugar) content was found to be significantly lower in PN and MC compared with SC, whereas total phenolic content was unaffected by mulches. Mulch application can improve organic highbush blueberry productivity by improving soil properties, nutrient availability, and weed suppression; however, precautions should be taken to avoid excess nutrient loading and weed seed contamination of mulches.

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Chris A. Martin and Dewayne L. Ingram

Thermal properties of pine bark: sand container media as a function of volumetric water content and effectiveness of irrigation as a tool for modulating high temperatures in container media were studied. Volumetric water and sand content interacted to affect container medium thermal diffusivity. Adding sand to a pine bark container medium decreased thermal diffusivity if volumetric water content was less than 10 percent and increased thermal diffusivity if volumetric water content was between 10 and 70 percent. Thermal diffusivity was greatest for a 3 pine bark : 2 sand container medium if volumetric water content was between 30 and 70 percent. Irrigation was used to decrease temperatures in 10-liter container media. Irrigation water at 26°C was more effective if 1) volumes equaled or exceeded 3000 ml, 2) applications were made during mid-day, and 3) sand was present in the container medium compared to pine bark alone. However, due to the volume of water required to lower container media temperatures, nursery operators should first consider reducing incoming irradiance via overhead shade or container spacing.

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Alfonso Hernández-Barajas, José Luis Vera-Medina, and Dr. Benito Alvarado-Rodriguez

During a two-year-period, a study was made in the field in order to know the ocurrence of aphids in the broccoli crop. It was possible to know that the total aphid population is higher in winter plantings where more than 240 aphids/plant were found Spring and fall plantings, in comparison, less than 20 aphids/plant were encountered. The species more common were the cabbage aphid (Brevicoryne brassicae L.), the most prevalent species in the crop, getting more than 80% of the population, and the green peach aphid (Myzus persicae Sulzer) with a little bit more than 17% of the total. The natural parasitism in all plantings was around 17%. By species, parasitism in B. brassicae was higher in springs (70% of the total) and fall plantings where the parasitic wasp Diaretiella rapa e (MacIntosh) was probably more active. The sane pattern was obtained for M. persicae, in which the parasitism was again higher in spring and fall plantings (20% of the total) and very low during the winter. Regarding leaf preference, a very defined pattern was found in the M. persicae than for B. brassicae.

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Nicole E. Burkhard, Derek H. Lynch, and David C. Percival

Within-row weed management of highbush blueberry (Vaccinium corymbosum L.) is reliant upon herbicide applications. However, in organic production, herbicides are typically not permitted and alternative methods must be used. The impact of thick (25-cm) mulch applications on weed pressure in an organic production system was initiated at a commercial operation in Nova Scotia, Canada, during 2005. A split-plot experimental design was used with five blocks (replications), six treatments, and five plants per split plot (cv. Duke). The whole-plot factor consisted of mulch/fertility treatments and included: i) control (no amendment); ii) ammonium sulphate fertilizer (30 kg·ha-1 N); iii) pelletized poultry manure (60 kg·ha-1 N); iv) pine needles (80 t·ha-1); v) horse manure and sawdust compost (550 t·ha-1); and vi) seafood waste compost (360 t·ha-1). The split-plot factor consisted of level of hand weeding (–/+). Weed control was assessed by sampling percent ground cover and weed shoot biomass in three 0.25-m2 quadrats in nonweeded subplots. Blueberry leaf N content, plant canopy volume, and berry yield (fresh weight and number) were recorded. The manure/sawdust compost and pine needle treatments had the lowest weed biomass and percent ground cover values, thereby providing the best weed control. Weed shoot biomass, blueberry leaf N, plant canopy volume, and berry yield were greatest in the seafood waste compost treatment. Results from this preliminary study indicate the potential of using these groundcover treatments to improve organic cultural management practices.

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James P. Mattheis

Ripening and development of physiological disorders and decay were assessed in ‘d’Anjou’ pear fruit after 1-methylcyclopropene (1-MCP) treatment and cold storage in air or controlled atmosphere (CA). Fruit were exposed after harvest to 0 or 12.6 μmol·L−1 1-MCP and then stored at 0.5 °C in air or 1, 3, or 5 kPa O2 with 0.5 kPa CO2. Pears were held poststorage at 20 °C for 7 days before analysis. 1-MCP fruit usually had higher hue compared with controls. Softening after removal from storage was delayed in 1-MCP fruit regardless of storage atmosphere; however, control fruit stored in air or CA ripened to below 23 N, a minimum value for consumer acceptance, after all storage durations. 1-MCP fruit stored in air, 3, or 5 kPa O2 softened in the outer cortex (fruit surface to 8 mm into the cortex) to below 23 N only after 9 m, however, only fruit stored in air softened to less than 23 N in the inner cortex (8 mm to coreline). 1-MCP treatment also delayed deformation in cortex tissue tensile strength (TTS); after six or more months, 1-MCP fruit TTS was lower compared with those for control fruit. After 9 m, 1-MCP fruit stored in air had TTS values similar to those of controls whereas values for fruit stored in CA increased with CA O2 concentration. Titratable acidity was higher in 1-MCP-treated fruit stored in air (6 m only) or 3 or 5 kPa O2 compared with controls. Superficial scald developed after 6 m on control fruit stored in air or 5 kPa O2 and on control CA fruit regardless of O2 concentration after 9 m. No 1-MCP fruit developed scald. The results indicate ‘d’Anjou’ pear ripening in response to 1-MCP is influenced by storage pO2 as well as storage duration, and at the 1-MCP treatment concentration used, softening to a consumer standard for firmness occurred only in fruit cold stored in air for 9 months plus a 7-day poststorage ripening period. These fruit had peel hue less than 100, and the yellow peel color may not be consistent with current market expectations.

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Thomas E. Marler and Mark A. Lander

101 WORKSHOP 13 (Abstr. 669–674) Long-term Recovery Dynamics of Perennial Species Following Tropical Cyclone Damage

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Alan L. Wright, Tony L. Provin, Frank M. Hons, David A. Zuberer, and Richard H. White

nutrient dynamics. Problems commonly associated with land compost application include nutrient accumulation in soil, leaching, and runoff. The long-term cycling of nutrients in compost-amended soils is dependent on compost quantity and quality in addition

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M. Lenny Wells

may result in overapplication of fertilizer. In addition, proper timing of N applications based on soil N dynamics and plant demand can play a large role in the efficient use of fertilizer N. The in situ soil core technique can be helpful in evaluating

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Rhuanito Soranz Ferrarezi, Marc W. van Iersel, and Roberto Testezlaf

dynamics and plant growth in a sensor-controlled subirrigation system. Our objectives were: 1) to automate a subirrigation system using capacitance-type soil moisture sensors to monitor and control substrate θ; 2) to evaluate short-term substrate θ dynamics

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Quanen Guo, Tianwen Guo, Zhongming Ma, Zongxian Che, Lili Nan, Yiquan Wang, Jairo A. Palta, and Youcai Xiong

secondary substances accumulated. Fruit trees are perennials and there is no disturbance in the growing soil. The distribution characteristics of their root system are different from that of cereals crops. In studying the temporal and spatial dynamics of