The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Monday, January 28, 2008
54
Competitiveness of Glyphosate-Resistant Alfalfa During Establishment
Marvin H. Hall1, Nick S. Hebrock1, Keith A. Diedrick2, and Justin M. Dillon1. (1) Crop & Soil Sciences, Penn State Univ., 116 ASI Building, University Park, PA 16802, (2) The Ohio State University, 428 West Liberty Street, Wooster, OH 44691
The cross pollinating and autotetraploid nature of alfalfa (Medicago sativa L.) combined with its relative intolerance to inbreeding creates challenges manipulating trait inheritance. Consequently, in the case of glyphosate [N-(phosphonomethyl) glycine] -resistant alfalfa, there are nulls (seeds that do not posses the resistant trait) within each bag of purchased seed. The relative competitive ability of null and resistant seedlings may be detrimental to alfalfa stand density if glyphosate application is delayed. The objective of this study was to determine if there are competitive differences between null and glyphosate-resistant alfalfa seedlings. Commercially available glyphosate-resistant alfalfa was seeded at 17 and 29 kg ha-1and then treated with glyphosate at the 3-4 trifoliolate-leaf stage or one-year after seeding. Seeding alfalfa at 29 kg ha-1 resulted in greater plant density but also greater plant mortality during the seeding year than seeding at 17 kg ha-1. Regardless of when glyphosate was applied, on average about 5 percent of the alfalfa seedlings died. We conclude that glyphosate-resistant and null alfalfa seedlings exhibited equal intraspecies competitiveness during seedling establishment. Consequently, delayed glyphosate application on glyphosate-resistant alfalfa and subsequent intraspecies competition does not increase the percent of glyphosate susceptible plants.