Nicholas Korres

A yellow nutsedge biotype (Res) from an Arkansas rice field has evolved resistance to acetolactate synthase (ALS) -inhibiting herbicides. The Res biotype previously exhibited cross resistance to ALS inhibitors from four chemical families (imidazolinone, pyrimidinyl benzoate, sulfonylurea, and triazolopyrimidine). Experiments were conducted to evaluate alternative herbicides (i.e. glyphosate, bentazon, propanil, quinclorac, and 2,4-D) currently labeled in Arkansas rice-soybean production systems. Based on the percentage of aboveground dry weight reduction, control of the yellow nutsedge biotypes with the labeled rate of bentazon, propanil, quinclorac, and 2,4-D was < 44%. Glyphosate (867 g ae ha-1) resulted in 68 and > 94% control of the Res and susceptible yellow nutsedge biotypes, respectively at 28 days after treatment. Dose response studies were conducted to estimate the efficacy of glyphosate on the Res biotype, three susceptible yellow nutsedge biotypes, and purple nutsedge. Based on the dry weights, the Res biotype was ≥ 5 and ≥ 1.3 fold less responsive to glyphosate compared to the susceptible biotypes and purple nutsedge, respectively. Differences in absorption and translocation of radiolabeled glyphosate were observed among the yellow nutsedge biotypes and purple nutsedge. The susceptible biotype had lesser 14C-glyphosate radioactivity in the tissues above the treated leaf and greater radioactivity in tissues below the treated leaf compared to the Res biotype and purple nutsedge. Reduced translocation of glyphosate in tissues below the treated leaf of the Res biotype could be a reason for the lower glyphosate efficacy in the Res biotype. No amino acid substitution that would correspond to glyphosate resistance was found in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene of the Res biotype. However, an amino acid (serine) addition was detected in the EPSPS gene of the Res biotype; albeit, it is not believed that this addition contributes to lower efficacy of glyphosate in this biotype.

A large-plot field experiment was conducted at Keiser, AR from fall of 2010 through fall of 2013 to understand to what extent soybean in-crop herbicide programs and postharvest fall management practices impact Palmer amaranth population density and seed production. The effect of postemergence-only (glyphosate-only) (POST) or preemergence (PRE) followed by (fb) POST (glyphosate or glufosinate) + residual herbicide treatments were evaluated alone and in combination with post-harvest management options of soybean residue spreading or soil incorporation, use of cover crops, windrowing with/without burning, and residue removal. Significant differences were observed between fall management practices on Palmer amaranth population density each fall. The use of cover crops and residue collection and removal followed by the incorporation of crop residues into soil were the most effective practices in lessening the Palmer amaranth population. In contrast, the effects of fall management practices on Palmer amaranth seed production were inconsistent among years. The inclusion of a PRE herbicide application into the herbicide program significantly reduced Palmer amaranth density and subsequent seed production each year when compared to the glyphosate-only program. Additionally, the glufosinate-containing residual program was superior to the glyphosate-containing residual program in reducing Palmer amaranth seed production. PRE fb POST herbicides resulted in significant decreases in the Palmer amaranth population density and seed production compared to POST application of glyphosate alone for all fall management practices, including the no-till practice. This study demonstrated that crop residue management such as chaff removal from the field, the use of cover crops, or seed incorporation during bed formation in combination with an effective PRE plus POST residual herbicide program is important for optimizing in-season management of Palmer amaranth and subsequently reducing the population density, which has a profound impact on lessening the risk for herbicide resistance and the consistency and effectiveness of future weed management efforts.

Amazon sprangletop is problematic weed of rice in the midsouthern USA. Two biotypes of this species from rice fields approximately 100 km apart in Louisiana were unaffected when sprayed with the labeled field rate of cyhalofop-butyl (314 g ai ha-1) in 2008. Dose response studies were conducted to confirm the level of resistance to cyhalofop-butyl over a range of doses. Cross-resistance to acetyl-CoA carboxylase (ACCase)-inhibiting herbicides from two different chemical families and multiple herbicide resistance to other mechanisms of action were evaluated. Sequencing using the Illumina Hiseq platform and ACCase gene sequencing revealed two different amino acid substitutions, Trp2027-to-Cys in the first resistant biotype and Asp2078-to-Gly in the second resistant biotype, within the CT domain of the ACCase gene. Two known amino acid substitutions confirmed resistance to cyhalofop-butyl and fenoxaprop-P-ethyl in resistant Amazon sprangletop biotypes. Asp2078-to-Gly amino acid substitution that was detected in one of the resistant biotypes did not result in cross-resistance to clethodim, an ACCase-inhibiting cyclohexandione herbicide which has endowed clethodim resistance in other weed species. Based on this research, both resistant Amazon sprangletop biotypes have evolved target-site resistance to the APP herbicides; yet, alternative herbicides are still active on these plant

Resistance to aryloxyphenoxypropionate herbicides in Amazon sprangletop: Confirmation, control, and molecular basis of resistance (PDF Download Available). Available from: https://www.researchgate.net/publication/296331009_Resistance_to_aryloxyphenoxypropionate_herbicides_in_Amazon_sprangletop_Confirmation_control_and_molecular_basis_of_resistance [accessed Apr 30, 2016].

Climate change is caused by the release of greenhouse gases in the atmosphere. Climate change will impact many activities, but effects on agricultural production could be acute. Estimates of annual damages in agriculture due to temperature increase or extended periods of drought will be more costly than damages in other activities. Yield losses are caused both by direct effects of climate change on crops and by indirect effects such as increased inputs in crop production for weed control of weeds. One possible solution to counteract the effects of climate change is to seek crop cultivars that are adapted to highly variable, extreme climatic conditions and pest changes. Here we review the effects of climate change on crop cultivars and weeds. Biomass increase will augment marketable yield by 8-70% for C3 cereals, by 20-144% for cash and vegetable crops, and by 6-35% for flowers. Such positive effects could however be reduced by decreasing water and nutrient availability. Rising temperature will decrease yields of temperature-sensitive crops such as maize, soybean, wheat, and cotton or specialty crops such as almonds, grapes, berries, citrus, or stone fruits. Rice, which is expected to yield better under increased CO2, will suffer serious yield losses under high temperatures. Drought stress should decrease production of tomato, soybean, maize and cotton. Nevertheless, reviews on C4 photosynthesis response to water stress in interaction with CO2 concentration reveals that elevated CO2 concentration lessens the deleterious effect of drought on plant productivity. C3 weeds should to respond more strongly than C4 types to CO2 increases through biomass and leaf area increases. The positive response of C3 crops to elevated CO2 may make C4 weeds less competitive for C3 crops whereas C3 weeds in C4 or C3 crops could become a problem, particularly in tropical regions. Temperature increases will mainly affect the distribution of weeds, particularly C4 type, by expanding their geographical range. This will enhance further yield losses and will affect weed management systems negatively. In addition, the expansion of invasive weed species such as itchgrass, cogongrass and witchweed facilitated by temperature increases will increase the cost for their control. Under water- or nutrient shortage scenarios, an r strategist with characteristics in the order S-C-R, such as Palmer amaranth, large crabgrass, johnsongrass and spurges will most probably prevail. Selection of cultivars that secure high yields under climate change but also by competing weeds is of major importance. Traits related with a) increased root:shoot ratio, b) vernalization periods, c) maturity, d) regulation of node formation and/or internode distance, e) harvest index variations and f) allelopathy merit further investigation. The cumulative effects of selecting a suitable stress tolerator-competitor cultivar will be reflected in reductions of environmental pollution, lower production costs and sustainable food production.

A survey was conducted in 2012 across 13 counties in the Eastern Arkansas-Mississippi Delta area on 489 randomly selected road sites to assess the distribution of the most commonly occurring arable weeds. Among the thirty six species recorded, Palmer amaranth, johnsongrass, large crabgrass, barnyardgrass, prickly sida, and broadleaf signalgrass were the top six weed species, occurring at 313, 294, 261, 238, 176, and 136 sites, respectively. Barnyardgrass, johnsongrass, and Palmer amaranth were present at 33.5, 31.5, and 30.6% of all sampling occasions (site × roadside topographical characteristic). Habitat preferences varied between weed species. Palmer amaranth, large crabgrass, and johnsongrass exhibited a preference for disturbed habitats as well as field shoulders. Conversely, barnyardgrass, yellow nutsedge, hemp sesbania, and giant ragweed exhibit a preference for moist environments similar to these found in roadside ditches. Herbicide use on roadsides is subject to many environmental regulations and public concerns that, in combination with the evolution of herbicide resistance, necessitate an effective plan for managing agronomically important weed species on Eastern Arkansas-Mississippi Delta roadsides.

The occurrence of 36 arable weed species across 13 counties in the Eastern Arkansas-Mississippi Delta area on 489 randomly selected road sites was surveyed in 2012. Palmer amaranth, johnsongrass, large crabgrass, barnyardgrass, prickly sida, and broadleaf signalgrass were the top six weed species, with occurrence noted at 313, 294, 261, 238, 176, and 136 sites, respectively. Factors found to affect weed occurrence along Mississippi Delta roadsides included topographical characteristics, weed species, ditch slope, road type, and nearby land use.
Amongst roadside topographical characteristics, road shoulder was found to strongly affect weed occurrence. In addition, paved and/or gravel road types with moderate roadside slope explained most of the variability of weed occurrence at each sampling site. Additionally, nearby arable land use affected weed occurrence more so than natural, residential, and pastoral land. Barnyardgrass, johnsongrass, and Palmer amaranth were 3.6 to 4.3 times more likely to occur than all other species identified. An effective weed management plan along Eastern Arkansas-Mississippi Delta roadsides should focus on road shoulder, adjacent arable land use, road type, and specific weed species (e.g. Palmer amaranth, johnsongrass, and barnyardgrass). The inclusion of these parameters in future weed control programs can be proved invaluable for preventing the spread of the herbicide-resistant Palmer amaranth, barnyardgrass, and johnsongrass.

Cover crops are becoming increasingly common in cotton as a result of glyphosate resistant Palmer amaranth; hence, a field experiment was conducted in 2009 and 2010 in Marianna, AR, with a rye cover crop used to determine its effects on the critical period for weed control in cotton. Throughout most of the growing season, weed biomass in the presence of a rye cover crop was lesser than that in the absence of a
rye cover crop. In 2009, in weeks 2 through 7 after planting, there was at least a twofold reduction in weed biomass in the presence of a rye cover compared to the absence of rye. In 2009, in both presence and absence of a rye cover crop, weed
removal needed to begin prior to 150 g m-2 of weed biomass or approximately 4 weeks after planting to prevent yield loss greater than 5%. Weed density was lower in 2010 than in 2009, so weed removal was not required until 7 weeks after planting, at which point weed biomass values were 175 or 385 g m-2 in the presence or absence of a cover crop, respectively.

The effects of intraspecific and interspecific competition on a wide range of winter wheat cultivars were investigated in two consecutive split plot field experiments. Significant reductions of grain yield at greatly reduced seed rates were observed in the first experiment, whereas increasing crop density up to 380 plants m-2 in the second experiment failed to produce a significant yield response due to compensation through increased ears and grains per plant at lower crop densities. Appreciable weed suppression and acceptable grain yield can be achieved at crop densities between 150 and 270 plants m-2• Reductions in final yield due to weed competition occurred in both experiments; 11.7 and 13.6% for the first and second experiment, respectively, with the onset of weed competition occurring from tillering in the first experiment and from stem elongation in the second.The possibility of enhancing crop competitiveness for weed suppression and improved grain yield is discussed.

In this paper, data mining techniques are coupled with internal daylight analytical tools. The aim is to examine the benefits of these techniques in assisting designers’ decision making and improving scalability and applicability of indoor daylight methods. Techniques were verified using lowest annual daylight factor values, resulting from the worst case scenario in Ecotect, for rooms in the Environmental Research

The need for new approaches in agricultural production such as these of integrated agricultural systems for food and energy production necessitates the rapprochement of these systems in terms of their environmental burden. This in combination with the importance of lignocellulosic materials for biofuel production makes the system under examination extremely complex. The feedstock production, transport, processing, and conversion of cellulosic materials have not been attempted to any real degree anywhere in the world; hence, a number of
sustainability issues related to energy inputs and environmental quality need to be examined. This highlights the importance of LCA as an important optimization tool. Nevertheless, the interactions and intra-, interrelationships necessitate a thorough study of the system under examination and a good knowledge of life cycle thinking.