2004 Annual Report 4.What were the most significant accomplishments this past year? D. Progress Report: This report serves to document research that was conducted under a Specific Cooperative Agreement between ARS and Dr. Hannah Mathers, Ohio State University. Additional details of research can be found in the report for the parent CRIS 3607-21000-008-00D Develop New or Improved Methods of Hydroponic and Greenhouse Production and Pest Protection. In early June 2003 bare-root liners of four species of woody plants were placed into one-gallon containers, filled with a standard bark mix, using overhead irrigation practices and an Osmocote plus fertilizer, 5-6 month formulation applied at the medium rate. The four species used were Berberis 'Bailsel', Cornus alba, Spireae 'Goldmound', and Viburnum trilobum. In early October 2003, 240 plants per species will be sprayed at the 1X label rate with Surflan (Oryzalin), Barricade (Prodiamine), Pendulum (Pendimethalin), or Treflan (Trifluralin) using a GS CO2 sprayer on 16" centers, with 8002VS medium droplet nozzles spraying at 45-50 psi. Sixty plants will not receive herbicide applications. Plants will be evaluated for cold hardiness at two sampling dates during the overwintering period, January 15, 2004 and March 15, 2005. At each sampling date plants were frozen to five test temperatures in a Forma UltraLow Freezer: 0, -5, -10, -15 and -20 C. Plants were moved to a heated greenhouse and evaluated for regrowth one and two months after freezing. Regrowth was evaluated two ways by a visual rating score (0-5), where 0 represents a dead plant, and plant live height. An arc sine of square root transformation was preformed on the rated score data to test normality. Treatment effects were compared by analysis of variance (SAS© procedure General Linear Model. Fisher's least significance difference test was used to compare means. For combined sampling dates and evaluation times the main effects of species, freeze temperature, evaluation time and freeze date and the interactions of temperature X species, temperature X time, date X time and species X time were significant for plant live height. The main effects of treatment, species, freeze temperature, evaluation time and freeze date and the interactions of temperature X species, temperature X time, date X time, species X time and date X temperature were significant for the rated score data. Combined over sampling dates and evaluation times, Pendimethalin and Trifluralin significantly reduced the hardiness of the four species and their regrowth potential after overwintering. Prodiamine provided a significant increase in growth potential over the control and Oryzalin had no effect over the control on reduction of hardiness or regrowth. Significantly more plants died during the March sampling date versus the January sampling and regrowth potential was also significantly reduced for March versus January. More plants also died at the two-month evaluation time versus the one-month evaluation, indicative of root injury. Cornus alba was the hardiest plant material, followed by Berberis 'Bailsel', and Spireae 'Goldmound', which were not significantly different in hardiness, and Viburnum trilobum was significantly less hardy than the other three species. There were no significant interactions for treatment with any other variable for plant height or rated score meaning the treatments reduced hardiness and regrowth similarly over species, evaluation temperature, sampling time and evaluation date.