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L. Espinoza, C.A. Sanchez and T.J. Schueneman

Four field experiments were conducted during two production seasons to evaluate soil-test P fertilizer recommendations for celery (Apium graveolens var. dulce) produced on Histosols, which often are linked hydrologically to environmentally sensitive wetlands, and to evaluate band placement as a strategy for improving P fertilizer-use efficiency in celery in such areas. Phosphorus was applied (broadcast or banded) at 0,50, 100,150, and 200 kg P/ha. Broadcast P was surface-applied and disked into the soil ≈ 15 cm deep 1 day before planting. Banded P was applied 5 cm below the soil surface and 5 cm to the side of each celery row. Total above-ground mass, marketable trimmed yield of celery, and yield of the larger grade sizes increased with P rate in all experiments. Band P placement was not a viable strategy for improving P fertilizer-use efficiency for celery. However, our results indicate that previous soil-test-based P fertilizer recommendations for celery were too high for the cultivars grown currently, and improved P fertilizer-use efficiency can be obtained with revised soil-test calibrations.

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Clinton J. Steketee, Alfredo D. Martinez-Espinoza, Karen R. Harris-Shultz, Gerald M. Henry and Paul L. Raymer

Seashore paspalum (Paspalum vaginatum Swartz) is a warm-season turfgrass species primarily used on golf courses and athletic fields, and is often impacted by the disease dollar spot caused by Sclerotinia homoeocarpa F.T. Bennett. Dollar spot is the most common and economically important turfgrass disease in North America, and current management of this disease relies heavily on frequent fungicide applications. An alternate management strategy is host plant resistance, but a better understanding of the interactions between pathogen isolates and the host species is needed to effectively incorporate this resistance into elite seashore paspalum genotypes. The goal of this study was to gather host plant/isolate response data that could be used to develop an effective and efficient screening protocol for resistance to this important disease. Five genotypes of seashore paspalum (‘Aloha’, ‘SeaIsle 2000’, ‘SeaIsle 1’, ‘SeaIsle Supreme’, and 05-1743) varying in dollar spot resistance were inoculated with five isolates of S. homoeocarpa in repeated field studies during 2012 and 2013. Isolates used were from three warm-season and one cool-season turfgrass species. Inoculated plots were evaluated visually and using digital image analysis (DIA) for disease development over time and for number and area of infection centers at two rating dates each year. Statistical differences among the seashore paspalum genotypes and inoculation/isolate treatments were detected for area under the disease progress curve (AUDPC) values, number of infection centers, and infection center area. A significant interaction between seashore paspalum genotype and S. homoeocarpa isolate effects was not observed, indicating that host plant resistance genes are likely not isolate specific. Using this information, breeders should be able to use one highly virulent S. homoeocarpa isolate to screen for host plant resistance in seashore paspalum.