What is 1000 grain weight of cotton crop?

What is 1000 grain weight of cotton crop?

Emergence Date Influences Growth and Fecundity of Palmer Amaranth in Cotton

Jason K. Norsworthy, Brandon W. Schrage, Tom L. Barber, and Lauren M. Schwartz*

J.K. Norsworthy, B.W. Schrage, and L.M Schwartz*, Crop, 

Soil, and Environmental Sciences, University of Arkansas, 

1366 West Altheimer Drive, Fayetteville, AR 72704; and T.L. 

Barber, Crop, Soil, and Environmental Sciences, University 

of Arkansas, 102 NE Front St. Suite 2, Lonoke, AR 72086 

*Corresponding author: lmschwar@uark.edu

ABSTRACT

Research was conducted in 2012 and 2013 in 

Fayetteville, AR to evaluate the impact of Palmer 

amaranth (Amaranthus palmeri (S.) Wats.) emer-

gence date on plant biomass, height, and seed 

production as well as the corresponding influence 

on cotton (Gossypium hirsutum L.) biomass and 

yield. Palmer amaranth was evaluated in the 

presence and absence of cotton and when emer-

gence was delayed in cotton (0, 2, 4, 6, 8, and 10 

wk). Seed production per plant was reduced by 

a greater extent in the presence of cotton, com-

pared to the absence of cotton. Palmer amaranth 

plants emerging 10 wk after cotton were able to 

produce on average 880 seed per plant, which is 

a sufficient amount to replenish a soil seedbank. 

The late-emerging plants competing with cotton 

were smaller in size than earlier emerging plants. 

Seed production in the presence of cotton was cor-

related with Palmer amaranth biomass produc-

tion (r2 = 0.63). Furthermore, the later-emerging 

cohorts responded to the presence of cotton by 

producing less biomass more so than a reduction 

in plant height with delayed emergence. This 

research shows that Palmer amaranth cohorts 

emerging as late as 10 wk after cotton emergence 

must be removed to prevent weed seed production.

Weed control has always been a crucial step 

in successful cotton (Gossypium hirsutum 

L.) production as problematic weed species, if 

not controlled, can effectively out-compete cotton 

What is 1000 grain weight of cotton crop?

for light, nutrients, space, and water. Cotton can 

require up to 8 wk of weed-free maintenance after 

planting to maximize yields; whereas corn (Zea 

mays L.) and soybean [Glycine max (L.) Merr.] 

require 2 to 4 wk (Buchanan and Burns, 1970). The 

release of glyphosate-resistant (GR) cotton in 1997 

enabled growers to make multiple POST glyphosate 

applications, controlling a broad spectrum of 

weeds without disrupting the growth of the crop 

(Funke et al., 2006). Ultimately, the availability 

of GR cotton prompted growers to widely adopt 

the technology because of cost savings, improved 

weed management, and simplicity of the system 

(Duke and Powles, 2009; Norsworthy et al., 2016). 

In 2000, after the loss of patent rights to glyphosate, 

the price of glyphosate decreased by 40% in the 

United States (U.S.) (Duke and Powles, 2009; 

USDA-NASS, 2006). The low price of glyphosate 

and its ability to control a broad spectrum of weed 

species with POST applications resulted in extensive 

use of the herbicide. Annual weeds having high rates 

of reproduction were a target for control, and sole 

use of the herbicide, especially early in the cropping 

season, resulted in immense selection for herbicide 

resistance (Nichols et al., 2009; Neve et al., 2011). 

Today, there are 32 GR weed biotypes worldwide and 

seven of these occur in Arkansas, of which Palmer 

amaranth is the most problematic in cotton (Heap, 

2015; Riar et al., 2013).

Palmer amaranth is a dioecious, summer annual 

capable of producing over 600,000 seed per female 

plant in the absence of competition (Keeley et al., 

1987). It is highly competitive with crops, having 

been found to reduce soybean yield 68% at densities 

of 10 plants m-2 (Klingaman and Oliver, 1994). In 

cotton, for every one Palmer amaranth per 10 m of 

row, yield was reduced 5.9 to 11.5% at two sites in 

Oklahoma (Rowland et al., 1999). Additionally, its 

rapid erect growth and allelopathic potential directly 

hinder the yield potential of cotton (Menges, 1987; 

1988). Palmer amaranth densities of 1 to 10 plants 

per 9.1 m-1 of row in cotton decreased crop canopy 

volume 35 and 45% by 6 and 10 wk after cotton 

emergence (WAE), respectively (Morgan et al., 

2001). Furthermore, light interception is considered 

to have the greatest impact on cotton canopy volume, 

biomass, and yield when soil moisture and nutrients 

are not limiting (Donald, 1958; Morgan et al., 2001). 

The rapid, erect growth of Palmer amaranth can re-

sult in individuals reaching over 2 m in height, leav

What is 1000 grain weight of cotton crop?

experience decreased lint yield via shading (Keeley 

et al., 1987; Rowland et al., 1999). The high level 

of Palmer amaranth interference with cotton results 

in the need for effective control, even to the point 

of complete elimination of escaped plants in cotton 

(Norsworthy et al., 2014).

New herbicide chemistry is limited as industry 

research and development efforts slowed following 

the release of GR crops (Norsworthy et al., 2012). 

While great attention has been focused on redevelop-

ing existing technologies, the use of integrated weed 

management (IWM) strategies has gained renewed 

attention. In 2012, best management practices 

(BMPs) were put forth to address the ever-increasing 

occurrence of herbicide-resistant weeds (Norswor-

thy et al., 2012). Understanding the biology of the 

targeted weed was noted as a critical component in 

designing resistance management strategies and is 

essential for modeling the evolution of herbicide re-

sistance. The BMPs to mitigate herbicide resistance 

encourage attention to weed biology and ecology; 

namely, weed growth, fecundity, and overall com-

petitiveness in a given crop (Bagavathiannan et al., 

2012). Weed fecundity and biomass are highly de-

pendent upon time of emergence relative to the crop, 

weed and crop density, and proximity of the weed 

to the crop (partially impacted by seeding rate and 

row spacing) (Clay et al., 2005; Knezevic and Horak, 

1998; Murphy et al., 1996). Previous research shows 

that as emergence date becomes later in the growing 

season, weed fecundity decreases (Clay et al., 2005; 

Knezevic and Horak, 1998). Continued exploration 

of weed biology and ecology benefits cotton produc-

ers striving to quantify the competitive interactions 

between cotton and Palmer amaranth within vary-

ing environments and agronomic scenarios (Clay 

et al., 2005; Gressel, 2011; Uscanga-Mortera et al., 

2007; Van Acker, 2009). Hence, the objective of this 

research was to determine to what extent biomass 

production, mature height, and fecundity of Palmer 

amaranth in cotton are affected by emergence date 

relative to the crop and the resulting effect on cotton 

biomass and seed cotton yield.

What is 1000 grain weight of cotton crop?

MATERIALS AND METHODS

In 2012 and 2013, a field experiment was con-

ducted at the Arkansas Agricultural Research and 

Extension Center in Fayetteville, AR, as a random-

ized complete block with a 2 x 6 factorial treatment 

structure with two levels of cotton (presence or 

absence) and six Palmer amaranth emergence dates. 

There were four replications. Cotton cultivar ‘PHY 

375 WRF’ (Dow AgroSciences, Indianapolis, IN) 

was planted at a 2-cm depth into a Leaf silt loam 

soil (Fine, mixed, active, thermic Typic Albaquults) 

(USDA-NRCS, 2015) with 34% sand, 53% silt, 

13% clay, 1.5% organic matter, and a pH of 6.9 at 

125,000 seed ha-1 and supplemented with over-head 

sprinkler irrigation to maintain optimal growing 

conditions. Planting occurred on 1 June 2012 and 

15 May 2013, using a four-row planter. The twelve 

treatments were grown in four-row plots on a 92-cm 

row spacing and 9.1 m plot length. Approximately 

20 Palmer amaranth seeds were hand-planted in 

close proximity to the inner two rows (< 13 cm from 

row center) of each four-row plots approximately 4 

d after seeding cotton in order for Palmer amaranth 

emergence to coincide with cotton emergence. Cot-

ton emerged on 5 June 2012 and 23 May 2013 and 

was shortly thereafter removed in one treatment of 

each of the six Palmer amaranth emergence dates 

(0, 2, 4, 6, 8, and 10 wk after cotton emergence). 

Removal of cotton in one-half of the plots allowed 

for the effect of cotton on Palmer amaranth to be 

assessed, accounting for the delayed emergence 

of cohorts after typical planting of cotton. Palmer 

amaranth seedlings were manually thinned to one 

plant per m-1 of row within 2 wk after emergence, 

resulting in a final density of 1.1 plants m-2 compet-

ing with the two innermost rows of cotton in each 

four-row plot.

What is 1000 grain weight of cotton crop?

A known glyphosate- and trifloxysulfuron-

resistant Palmer amaranth biotype was used, which 

allowed for use of glyphosate and trifloxysulfuron for 

control of unwanted weeds. Additionally, clethodim 

was used later in the growing season to remove 

grasses and some unwanted Palmer amaranth plants 

were hand-removed throughout the season to pro-

mote as close of a weed-free environment as possible. 

Only slight injury to Palmer amaranth was observed 

following any of the herbicide applications, and the 

plants had often fully recovered by 2 to 3 wks after 

treatment. All applications were made using a CO2-

pressurized backpack sprayer equipped with four 

TTI 110015 nozzles (TeeJet Technologies, Glendale 

What is 1000 grain weight of cotton crop?

Heights, IL) calibrated to deliver 187 L ha-1 at a 

pressure of 276 kPa and a walking speed of 4.8 kph.

Prior to cotton defoliation each fall, the height 

of three Palmer amaranth and three cotton plants in 

each plot was measured and aboveground biomass of

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