Phenology of five Palmer amaranth (Amaranthus palmeri) populations grown in northern Indiana and Arkansas

Authors: Spaunhorst, Douglas; DEVKOTA, PRATAP - University Of California; JOHNSON, WILLIAM - Purdue University; SMEDA, REID - University Of Missouri; MEYER, CHRISTOPHER - University Of Arkansas; NORSWORTHY, JASON - University Of Arkansas

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2018
Publication Date: 3/27/2018
Citation: Spaunhorst, D.J., Devkota, P., Johnson, W.G., Smeda, R.J., Meyer, C.J., Norsworthy, J.K. 2018. Phenology of five Palmer amaranth (Amaranthus palmeri) populations grown in northern Indiana and Arkansas. Weed Science. 66(4):457-469. https://doi.org/10.1017/wsc.2018.12.
DOI: https://doi.org/10.1017/wsc.2018.12

Interpretive Summary: This research focused on the influence of planting date (early-, mid-, and late-season) and population source (AR, IN, MO, MS, NE, and TN) on Palmer amaranth growth and reproduction. Individual plants from all five Palmer amaranth populations, listed by state abbreviation above, were planted in Arkansas and Indiana. All populations planted early- or mid-season at IN and AR grew to 196 and 141 cm or more in height, respectively. Palmer amaranth established later in the growing season did not grow beyond 168 and 134 cm at IN and AR, respectively. Early-season planted Palmer amaranth from NE grew to 50% of maximum height one to two weeks earlier than all other populations under IN conditions. In addition, the NE population planted early-, mid-, and late-season began to flower 5, 4, and 6 days earlier than all other populations, respectively. At both locations, Palmer amaranth biomass and seed production were correlated, given that larger plants produced more seeds. All populations established at IN produced fewer than 100,000 seeds plant-1; however, at AR all but one population produced greater than 117,000 seeds plant-1 when planted. At IN in 2013, Palmer amaranth planted early-season produced 43% more biomass than mid-season planted Palmer amaranth. At AR, Palmer amaranth planted early- versus mid-season produced 25% more biomass. However, late-season planted Palmer amaranth at AR produced 50% less biomass than early-season planted Palmer amaranth. No population planted at IN and AR produced more than 740 and 1,520 g plant-1 of biomass at the end of the growing season, respectively. Planting date influenced the distribution of male and female plants at IN, but not at AR. Palmer amaranth from IN and MS planted late-season had more male plants than female plants. Palmer amaranth introduced to northern IN from NE can produce up to 7,500 seeds plant-1 if emergence occurs in mid-July. The NE Palmer amaranth population appears to be highly competitive if introduced to northern IN due to a similar latitudinal range, but was least competitive when introduced to AR. Although Palmer amaranth originating from different locations can vary biologically, plants could survive and complete their life cycle when introduced to new environments.

Technical Abstract: Palmer amaranth is one of the most problematic weeds encountered in US cotton and soybean production, with infestations spreading northward. Recently, Palmer amaranth seed has been introduced to cropping areas across Indiana through contaminated feedstuffs and equipment. This research focused on the influence of planting date (early-, mid-, and late-season) and population source (AR, IN, MO, MS, NE, and TN) on Palmer amaranth growth and reproduction at two locations. All populations planted early- or mid-season at IN and AR measured 196 and 141 cm or more in height, respectively. Palmer amaranth height did not exceed 168 and 134 cm when planted late-season at IN and AR, respectively. Early-season planted Palmer amaranth from NE grew to 50% of maximum height 8 to 13 days earlier than all other populations under IN conditions. In addition, the NE population planted early-, mid-, and late-season achieved 50% inflorescence emergence 5, 4, and 6 days earlier than all other populations, respectively. At both locations, Palmer amaranth biomass and seed production were correlated, given that larger plants produced more seeds. All populations established at IN produced fewer than 100,000 seeds plant-1. At IN in 2013, Palmer amaranth planted early-season produced 43% more biomass than mid-season planted Palmer amaranth. At AR, Palmer amaranth planted early- versus mid-season produced 25% more biomass. However, late-season planted Palmer amaranth at AR produced 50% less biomass than early-season planted Palmer amaranth. No population planted at IN and AR produced more than 740 and 1,520 g plant-1 of biomass at 17 and 19 wk after planting, respectively. Planting date influenced the distribution of male and female plants at IN, but not at AR. Palmer amaranth from IN and MS planted late-season had male to female plant ratios of 1.3:1 and 1.7:1, respectively. Palmer amaranth introduced to northern IN from NE can produce up to 7,500 seeds plant-1 if emergence occurs in mid-July. The NE Palmer amaranth population appears to exhibit biological characteristics allowing it to be highly competitive if introduced to northern IN due to a similar latitudinal range, but was least competitive when introduced to AR. Although Palmer amaranth originating from different locations can vary biologically, plants exhibited environmental plasticity and could complete their life cycle and contribute to spreading populations.