Status of Amaranthus Species in Ohio Crop Production Thesis Presented in partial fulfillment of the requirements for the degree Master of Science in the Graduate School of The Ohio State University By Samantha N. Konkle, B.S. Horticulture and Crop Science Graduate Program The Ohio State University 2015 Thesis Committee: Dr. Mark M. Loux, Advisor Dr. Laura Lindsey Dr. Kristen Mercer Copyright by Samantha N. Konkle 2015 Abstract Studies were conducted in 2012, 2013, and 2014 with the objectives of: 1) Determining the frequency and distribution of horseweed (Conyza canadensis), giant ragweed (Ambrosia trifida), and three Amaranthus species, Palmer amaranth (Amaranthus palmeri), waterhemp (Amaranthus tuberculatus), and redroot pigweed (Amaranthus retroflexus), in Ohio soybean fields at the end of the growing season; 2) Determining the response of Ohio Amaranthus species to herbicide site of action groups 2, 9, and 14; and 3) Developing herbicide-based management strategies for herbicide-resistant redroot pigweed. A survey was conducted in 2012, 2013, and 2014 in 52 Ohio counties just prior to soybean harvest, and each soybean field encountered was assessed for infestation level of horseweed, giant ragweed, and Amaranthus species. Amaranthus species were the least frequent in comparison with horseweed and giant ragweed in all three years of the survey. Palmer amaranth was not observed on the survey in any of the three years, but seed samples were collected from growers and provided by agribusinesses. Waterhemp infestations were observed in four and ten fields in 2013 and 2014, respectively. Redroot pigweed infestations occurred in 34, 19, and 2 fields in 2012, 2013, and 2014, ii respectively. There was no pattern for the distribution of these infestations throughout the state. A greenhouse herbicide screen was conducted using Amaranthus species samples from the 2013 and 2014 surveys to determine response of populations to glyphosate (site 9), fomesafen (site 14), and imazethapyr (site 2). The experiment was conducted twice in 2013 and once in 2014. Results varied across the two 2013 experiments, as herbicides were more active in the second experiment than in the first. Redroot pigweed populations exhibited resistance to site 2 and 14 herbicides in all three experiments. Glyphosate resistance was inconsistent between the 2013 experiments, but was observed in 2014. Redroot populations also exhibited multiple resistance for sites 2 and 14 in 2013 and 2014, and three-way resistance occurred in the second 2013 and the 2014 experiment. Waterhemp populations were resistant to sites 2 and 9 in all experiments, but resistance to site 14 was less consistent. Multiple resistance also occurred in waterhemp populations. In 2013, this was seen only for sites 2 and 9, but in 2014, multiple resistance was seen for all combinations of site 2, 9, and 14. None of the three 2013 Palmer amaranth populations were glyphosate-resistant, but several 2014 populations were. All Palmer amaranth populations in all experiments showed resistance to site 2, and resistance to site 14 was inconsistent in 2013 but was also observed in the 2014 experiment. Three-way resistance and resistance to site 2 and 14 and site 9 and 14 were observed in the 2014 populations. Two field studies were conducted in 2013 and 2014 to assess control of redroot pigweed using a number of herbicides with residual activity, and compare control between currently available herbicide programs and prospective herbicide programs for iii new herbicide resistance traits. The results of the residual study showed the most effective late-season control with three-way herbicide mixes, while the least effective control was provided by 2,4-D and metribuzin applied individually or together. Preemergence treatments in the herbicide programs study mostly provided over 90% control at 21 DAT, but many treatments showed less control starting at 42 DAT. Several preemergence + EPOST and preemergence + LPOST treatments, including a preemergence application of pyroxasulfone + flumioxazin followed by various tank mixtures postemergence, provided 90% or greater late-season control. An advantage for either current herbicide programs or prospective herbicide programs was not observed in either study. iv Vita January 12, 1991 ................................................................... Born – Columbus, Ohio December 2012 ..................................................................... B.S. Agriculture, The Ohio State University January 2013 to present ........................................................ Graduate Research Associate, Department of Horticulture and Crop Science, The Ohio State University Field of Study Major Field: Horticulture and Crop Science Specialization: Weed Science v Table of Contents Abstract ......................................................................................................... ii Vita ................................................................................................................ v List of Figures ............................................................................................... viii List of Tables ................................................................................................ ix Chapter 1: Literature Review ........................................................................ 1 Chapter 2: Distribution characteristics of Ohio Amaranthus spp. Introduction ....................................................................................... 16 Objectives ......................................................................................... 17 Materials and Methods ...................................................................... 17 Results and Discussion ..................................................................... 19 Bibliography ..................................................................................... 22 Chapter 3: Assessment of herbicide resistance in Ohio Amaranthus spp. Introduction ....................................................................................... 31 Objectives ......................................................................................... 33 Materials and Methods ...................................................................... 33 Results and Discussion ..................................................................... 35 Bibliography ..................................................................................... 42 vi Chapter 4: Control of Redroot Pigweed Utilizing Current and Prospective Herbicide Technologies Introduction ....................................................................................... 49 Objectives ......................................................................................... 51 Materials and Methods ...................................................................... 51 Results and Discussion ..................................................................... 53 Bibliography ..................................................................................... 57 Thesis Bibliography ...................................................................................... 70 vii List of Figures Figure 2.1 All counties surveyed in 2012, 2013, and 2014 .......................... 23 Figure 2.2 Distribution of known Palmer amaranth and waterhemp populations in Ohio in 2012 ... ........................................................................................................... 28 Figure 2.3 Distribution of known Palmer amaranth and waterhemp populations in Ohio in 2013 ... ........................................................................................................... 29 Figure 2.4 Distribution of known Palmer amaranth and waterhemp populations in Ohio in 2014 ... ........................................................................................................... 30 viii List of Tables Table 2.1 Percentage of soybean fields infested by species in end-of-season survey of 52 Ohio Counties ........................................................................................................... 24 Table 2.2 Number of infestations from the survey by county and species for 2012, 2013, and 2014 .................................................................................................................... 25 Table 2.3 Number of populations collected/submitted for determination of herbicide resistance ................................................................................................................... 27 Table 3.1 Response of 2013 Amaranthus spp. population to herbicides in the greenhouse ........... ....................................................................................................................... 43 Table 3.2 Response of 2014 Amaranthus spp. populations to herbicides in the greenhouse ........... ....................................................................................................................... 45 Table 3.3 Percentage of 2013 Palmer, waterhemp, and redroot populations exhibiting resistance to site 2, 9, and 14 herbicides at 1X and 4X rates and populations exhibiting multiple resistance at 1X rates .................................................................................. 47 Table 3.4 Percentage of 2014 Palmer, waterhemp, and redroot populations exhibiting resistance to site 2, 9, and 14 herbicides at 1X and 4X rates and populations exhibiting multiple resistance at 1X rates .................................................................................