Factors affecting potential for Palmer amaranth (Amaranthus palmeri) suppression by winter rye in Georgia, USA

Authors: Webster, Theodore; SIMMONS, DANIELLE - University Of Georgia; CULPEPPER, A - University Of Georgia; GREY, TIMOTHY - University Of Georgia; BRIDGES, DAVID - Abraham Baldwin Agricultural College; Scully, Brian

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2016
Publication Date: 5/4/2016
Citation: Webster, T.M., Simmons, D.B., Culpepper, A.S., Grey, T.L., Bridges, D.C., Scully, B.T. 2016. Factors affecting potential for Palmer amaranth (Amaranthus palmeri) suppression by winter rye in Georgia, USA. Field Crops Research. 192:103-109. doi: 10.1016/j.fcr.2016.04.020.

Interpretive Summary: Herbicide resistant Palmer amaranth is the dominant weed management challenge of agronomic crops of the Southeast U. S. The small size of Palmer amaranth seeds provides an opportunity to use high-biomass cover crops and judicious use of herbicides as part of an integrated management system. Experiments were conducted to characterize Palmer amaranth suppression and light permeability from a range of rye biomass levels. In the absence of rye, there was approximately 80% Palmer amaranth emergence, while the highest rate of rye biomass prevented Palmer amaranth emergence. The highest level of rye biomass reduced the amount of light to 13% of full sunlight, while 5,370 kg/ha of rye caused a 50% reduction of light transmission; a similar level of rye biomass reduced Palmer amaranth emergence by 50%. Effective suppression of Palmer amaranth will depend upon the ability to produce high-biomass rye. Field experiments evaluated changes in planting date, seeding rate, and nitrogen application on rye biomass production. Maximum rye biomass in April occurred when rye was planted prior to middle-November. However, a 50% reduction in rye biomass resulted from middle-December planting of rye, providing growers with a short planting interval for high-biomass rye production. Additionally, rye seeding rate did not increase rye biomass accumulation indicating that delays in autumn sowing cannot be overcome with increased seeding rate. Finally, nitrogen fertilizer applied at planting consistently increased rye biomass production 23 to 33% relative to non-fertilized controls averaged over all planting dates. Additional research is needed to evaluate how repeated high-biomass cover crop systems affect weed management systems, other pest complexes, and soil moisture status in the sandy soils of the southeast Coastal Plain.

Technical Abstract: Herbicide resistant Palmer amaranth has rapidly become a dominant weed management issue in agronomic crops of the Southeast U. S. The small size of Palmer amaranth seeds, relative to other common weeds, provides an opportunity to use physical weed control through high-biomass, rolled cover crop mulches, in conjunction with herbicide tools. Experiments were conducted to characterize Palmer amaranth suppression and light permeability from a range of rye biomass levels. There was an inverse relationship between Palmer amaranth emergence and rye biomass that was described by a log-logistic regression model. In the absence of rye, there was approximately 80% Palmer amaranth emergence, while the highest rate of rye biomass prevented Palmer amaranth emergence. A log-logistic regression model also described the amount of photosynthetic active radiation transmitted through rye mulch in a greenhouse experiment. The highest level of rye biomass reduced the amount of light to 13% of full sunlight, while 5,370 kg/ha of rye caused a 50% reduction of light transmission; a similar level of rye biomass (P=0.93) reduced Palmer amaranth emergence by 50%. Effective suppression of Palmer amaranth will depend upon the ability to produce high-biomass rye. Field experiments evaluated changes in planting date, seeding rate, and nitrogen application on rye biomass production. Maximum rye biomass in April occurred when rye was planted prior to middle-November. However, a 50% reduction in rye biomass resulted from middle-December planting of rye, providing growers with a short planting interval for high-biomass rye production. Additionally, rye seeding rate did not increase rye biomass accumulation indicating that delays in autumn sowing cannot be overcome with plant density. Finally, nitrogen fertilizer applied at planting consistently increased rye biomass production 23 to 33% relative to non-fertilized controls averaged over all planting dates. Additional research is needed to evaluate how repeated high-biomass cover crop systems affect weed management systems, other pest complexes, and soil moisture status in the sandy soils of the southeast Coastal Plain.