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L.W. Lass, R.H. Callihan, and D.O. Everson

Predicting sweet corn (Zea mays var. rugosa Bonaf.) harvest dates based on simple linear regression has failed to provide planting schedules that result in the uniform delivery of raw product to processing plants. Adjusting for the date that the field was at 80% silk in one model improved the forecast accuracy if year, field location, cultivar, soil albedo, herbicide family used, kernel moisture, and planting date were used as independent variables. Among predictive models, forecasting the Julian harvest date had the highest correlation with independent variables (R2 = 0.943) and the lowest coefficient of variation (cv = 1.31%). In a model predicting growing-degree days between planting date and harvest, R2 (coefficient of determination) = 0.85 and cv = 2.79%. In the model predicting sunlight hours between planting and harvest, R2 = 0.88 and cv = 6.41%. Predicting the Julian harvest date using several independent variables was more accurate than other models using a simple linear regression based on growing-degree days when compared to actual harvest time.

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Cayetana Schluter and Zamir K. Punja

, and the Science Council of British Columbia, G.R.E.A.T. Awards program. The authors acknowledge Don McKenzie, Tom Li, Eric Littley, and Chai-Na-Ta Ginseng Farms for making available plant materials and field locations. We also thank D. Wardle, M. Van

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Ute Albrecht and Kim D. Bowman

field location near Orlando, currently unaffected by HLB, was significantly larger, whereas seeds were smaller, which may have been the result of different environmental conditions. Surprisingly, the percentage of seeds belonging to the smallest weight

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Richard L. Hassell, Jonathan R. Schultheis, Wilfred R. Jester, Stephen M. Olson, and Gilbert A. Miller

Perfection, and Xite) were selected ( Table 1 ). In 2004, these cultivars were evaluated in field locations at northern Florida (Quincy), central South Carolina (Blackville), coastal South Carolina (Charleston), and eastern North Carolina (Kinston). Five

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Richard L. Hassell, Jonathan R. Schultheis, Wilfred (Bill) R. Jester, Stephen M. Olson, Donald N. Maynard, and Gilbert A. Miller

several companies ( Table 1 ). In 2004, 18 cultigens ( Table 1 ) were evaluated in field locations at southern Florida (Bradenton), northern Florida (Quincy), central South Carolina (Blackville), coastal South Carolina (Charleston), and eastern North

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Philip M. Sheridan and Richard R. Mills

permission to collect seed from the now federally endangered mountain sweet pitcher plant and to Bruce Bednar for field locations and John Hummer for use of plant material. The cost of publishing this paper was defrayed in part by the payment of page charges

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Kathryn S. Orvis and Irwin L. Goldman

Organosulfur compounds in onion extracts inhibit the aggregation of human blood platelets. Antiplatelet activity is important to human cardiovascular health. We hypothesized that modification of sulfur fertility may increase organosulfur compound concentration and thereby affect platelet inhibitory activity in onion. Four contrasting onion genotypes were grown at four sulfur levels in a hydroponic system in the greenhouse and in contrasting sulfur environments in seven field locations in Wisconsin, Oregon, and New York. The contrasting field sites were comprised of sandy soils with a mean sulfate level of 5.4 ppm and muck soils with a mean sulfate level of 20.3 ppm. Onions grown in field environments with increased soil sulfur concentrations had significantly higher antiplatelet activity (33% higher than sand-grown onions; P < 0.001). The greenhouse experiment was conducted in hydroponics with nutrient solutions containing four sulfur levels ranging from 0.8 mM to 15 mM sulfate. The 10-mM sulfur treatment resulted in onion bulbs with 10% higher antiplatelet activity over those grown in the 0.8-mM sulfur treatment (P < 0.06). These data suggest that sulfur concentration in nutrient solution and in soil may be directly responsible for the increased antiplatelet activity in onion extracts observed in this study.

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T.R. Roper, A.R. Krueger, C.J. DeMoranville, N. Vorsa, J. Hart, and A.P. Poole

Nitrogen fertilizer application is a universal practice among cranberry growers. Cranberries only use ammonium nitrogen sources. This study was undertaken to discover how quickly cranberries in the field would take up fertilizer-derived ammonium nitrogen. Ammonium sulfate labeled with 15N was applied in field locations in Oregon, Massachusetts, New Jersey, and Wisconsin. Samples of current season growth were collected daily for 7 days beginning 24 hours after fertilizer application. In all cases 15N was detectable in the plants from treated plots by 24 hours following application. Additional nitrogen was taken up for the next 3 to 5 days depending on the location. With the exception of Oregon, the maximum concentration of 15N was found by day 7. Oregon was the coolest of the sites in this research. To determine a temperature response curve for N uptake in cranberry, cranberry roots were exposed to various temperatures in aeroponics chambers while vines were at ambient greenhouse temperatures. The optimum temperature for N uptake by cranberry vines was 18 to 24 °C. This research suggests that ammonium fertilizers applied by growers and irrigated into the soil (solubilized) are taken up by the plant within 1 day following application. Soil and root temperature is involved in the rate of N uptake.

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E. Ryan Harrelson, Greg D. Hoyt, John L. Havlin, and David W. Monks

Throughout the southeastern United States, vegetable growers have successfully cultivated pumpkins (Cucurbita pepo) using conventional tillage. No-till pumpkin production has not been pursued by many growers as a result of the lack of herbicides, no-till planting equipment, and knowledge in conservation tillage methods. All of these conservation production aids are now present for successful no-till vegetable production. The primary reasons to use no-till technologies for pumpkins include reduced erosion, improved soil moisture conservation, long-term improvement in soil chemical and microbial properties, and better fruit appearance while maintaining similar yields compared with conventionally produced pumpkins. Cover crop utilization varies in no-till production, whereas residue from different cover crops can affect yields. The objective of these experiments was to evaluate the influence of surface residue type on no-till pumpkin yield and fruit quality. Results from these experiments showed all cover crop residues produced acceptable no-till pumpkin yields and fruit size. Field location, weather conditions, soil type, and other factors probably affected pumpkin yields more than surface residue. Vegetable growers should expect to successfully grow no-till pumpkins using any of the winter cover crop residues tested over a wide range in residue biomass rates.

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Douglas V. Shaw, John Hansen, and Greg T. Browne

One hundred-eighty six strawberry genotypes from the Univ. of California strawberry (Fragaria ×ananassa Duch.) breeding program were evaluated for resistance to Phytophthora cactorum Schroet. in trials conducted over 6 years; 60 of these genotypes were tested in 2 years or more. Mother plants of each genotype were grown in a propagation nursery beginning in June, and runner plants were set into soil infested with inoculum from a mix of four P. cactorum isolates in August or September of the same year. Runner plants of each genotype were harvested from the inoculated nursery, transferred to a fruiting field location, and evaluated for disease symptoms during the winter and spring following inoculation using a disease severity score. Significant variation for the disease severity score was detected due to years, genotypes, and their interaction. Differences among genotypes were responsible for 60.6% of the phenotypic variance, whereas years and year × genotype interactions contributed relatively little to this variance, 8.2% and 9.3%, respectively. A separate analysis conducted using a balanced subset of six cultivars that were present in all trial years detected variance components due to years and year × genotype interaction slightly smaller than those estimated for the complete trial, 5.0% and 3.9%, respectively. These results highlight the utility of the screening system and suggest that stable resistance to P. cactorum is obtainable in California strawberry breeding populations and production systems.