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A putative glufosinate‐resistant Amaranthus palmeri population was reported in 2015 in Anson County, North Carolina. The results from dose–response assays conducted in the field suggested plants were surviving lethal rates of glufosinate. Dose–response assays conducted in the glasshouse determined the Anson County accession exhibited reduced susceptibility to glufosinate compared to three glufosinate‐susceptible populations. The LD50 values (210–316 g ai ha−1) for the Anson County population were always higher than the LD50 values (118–158 g ai ha−1) for the tested susceptible populations from the dose–response assays. Anson County plants that survived lethal glufosinate rates were reciprocally crossed with susceptible plants to create F1 genotypes and treated with a lethal rate of glufosinate (267 g ai ha−1; ascertained from glasshouse dose–response assay) to determine the distribution of injury and survival for each cross compared to a cross of susceptible parents. The distribution of injury was non‐normal for the crosses containing an Anson County plant compared to the cross with a susceptible parent. Survival was 68%–84% for crosses containing an Anson County plant, whereas the survival was significantly reduced to 35% for the susceptible plant cross. Chi‐square goodness of fit tests were used to test inheritance models to describe the responses of the genotypes. The resistant × susceptible crosses were best described with a heterozygous two loci with incomplete dominance model compared to the resistant × resistant cross that was best described with a heterozygous single locus with incomplete dominance model. The Anson County population has evolved resistance to glufosinate that is heritable and likely conferred by an oligogenic mechanism with incomplete dominance. [ABSTRACT FROM AUTHOR]

Management of herbicide‐resistant weeds can be improved by understanding the biology of resistant biotypes. While the majority of research has focused on female plants and seed production of Palmer amaranth (Amaranthus palmeri S. Watson) that are resistant to glyphosate, growth of male plants that are resistant to this herbicide has not been studied in detail. Additionally, interference of male versus female Palmer amaranth plants on cotton (Gossypium hirsutum) yield has not been reported. Plant height and biomass of male and female plants from a mixed population of glyphosate‐resistant (GR) and glyphosate‐susceptible (GS) plants was studied in North Carolina when grown season‐long with cotton. Palmer amaranth height was less for GR male plants compared with GS males and both GR and GS females. Biomass of Palmer amaranth female plants was twice that of male plants irrespective of glyphosate resistance. Cotton yield was affected similarly by Palmer amaranth regardless of either gender or glyphosate resistance status. The implications of shorter GR male plants on pollen dispersal and ramifications on management of glyphosate resistance are not known. Results from these trials did not address implications of the height of male plants on fitness of GR resistance. Nonetheless, the finding that GR male plants were shorter in the field than GS male plants warrants a new look at this topic. Similar reductions for cotton yield in presence of both GR and GS biotypes and genders suggest that current yield loss assessments and management decisions do not need to consider these variables in Palmer amaranth populations. Plain Language Summary: Understanding the biology of Palmer amaranth (Amaranthus palmeri S. Watson) plants that are glyphosate‐resistant and glyphosate‐susceptible can facilitate improved management of this weed in crops. Research in North Carolina found that glyphosate‐resistant male plants were shorter than glyphosate‐susceptible male plants. Cotton (Gossypium hirsutum L.) yield was affected the same regardless of gender or susceptibility to glyphosate even though female plants exhibited twice the biomass of male plants. Further research is needed to address the impact of shorter male plants that are glyphosate resistant on pollen movement and possible fitness of this weed associated with herbicide resistance. These results also indicate that management decisions for Palmer amaranth do not need adjustment based on gender or glyphosate resistance relative to interference with cotton yield. [ABSTRACT FROM AUTHOR]

Amaranthus tuberculatus (waterhemp) is a pervasive weed of the Mid‐west and ‐south United States and is not native to North Carolina but infestations in crop fields have been reported recently. Amaranthus tuberculatus has evolved resistance to seven herbicide groups and multiple herbicide‐resistant populations are common where the species is native. The reported A. tuberculatus infestations in North Carolina have not been controlled with herbicides but no formal herbicide resistance characterisation has been conducted to date. Glasshouse dose–response experiments were conducted to determine the susceptibility of a population collected from Surry County, North Carolina to commonly applied postemergence herbicides compared to a herbicide‐susceptible population collected from Story County, Iowa. The Surry County population survived labelled rates of imazethapyr, atrazine, glyphosate, fomesafen, and mesotrione; the Story County population was controlled with these herbicides. Further, 2,4‐D, dicamba, and glufosinate effectively controlled the Surry and Story County populations. Molecular sequencing assays were subsequently conducted to determine if altered target sites facilitated resistance in the acetolactate synthase (ALS), 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSPS), photosystem II (psbA), and protoporphyrinogen oxidase (PPX2) genes. The Surry County population carried a Trp574Leu and ∆Gly210 mutations in the ALS and PPX2 gene, respectively. No mutations that would confer resistance were found in the EPSPS or psbA gene for either population. The results of both experiments provide evidence that a five‐way herbicide‐resistant A. tuberculatus population has encroached North Carolina. More research is needed to determine the mechanisms of resistance to atrazine, glyphosate, and mesotrione. [ABSTRACT FROM AUTHOR]

Effective weed control is critical to growth and development of flue‐cured tobacco; however, current herbicide options are limited in commercial production. Field experiments were conducted from 2017 to 2018 to evaluate S‐metolachlor for use in flue‐cured tobacco weed management programs. Treatments included 10 herbicide programs: pretransplanted incorporated (PTI) applications of S‐metolachlor (1.07 kg a.i. ha–1) alone or in various combinations with sulfentrazone (0.18 kg a.i. ha–1), clomazone (0.84 kg a.i. ha–1), and pendimethalin (0.79 kg a.i. ha–1). S‐metolachlor and pendimethalin were also applied posttransplanting directed to row middles (POST‐DIR) following PTI applications of sulfentrazone + clomazone. A single posttransplanting over‐the‐top (POST‐OT) application of S‐metolachlor and a non‐treated control were included for comparison. The inclusion of S‐metolachlor in PTI herbicide programs did not improve weed control beyond the combination of sulfentrazone + clomazone. However, weed control after final harvest was improved by 8%, when S‐metolachlor was applied POST‐DIR. S‐metolachlor applied POST‐OT caused injury to tobacco plants (12%), although symptoms were transient with less than 2% visual injury 6 wk after transplanting. Due to increased weed control through harvest and the low injury potential, our results suggest that POST‐DIR applications of S‐metolachlor are the best fit for flue‐cured tobacco production when used in conjunction with recommended PTI herbicide programs. Core Ideas: Additional herbicides are needed for commercial tobacco production.S‐metolachlor may extend weed control through harvest when applied POST‐DIR 6 WAT.Visual injury may occur when S‐metolachlor is applied POST‐OT, but it may not reduce value. [ABSTRACT FROM AUTHOR]

Core Ideas: All of the 120 accessions of Palmer amaranth collected in the Coastal Plain of North Carolina were controlled by atrazine and dicamba applied at field use rates in the greenhouse.Reduced sensitivity among accessions was noted when S‐metolachlor and 2,4‐D were applied to Palmer amaranth at field use rates in the greenhouse.Additional research is needed to determine if reduced sensitivity of Palmer amaranth to S‐metolachlor and 2,4‐D is associated with evolved resistance. [ABSTRACT FROM AUTHOR]

Adequate weed control is important in protecting crop yield and allowing efficient harvest in North Carolina. Data in the literature are limited with respect to direct comparisons of weed control and yield across multiple crops. Research is also limited in terms of documenting the impact of weed control in one crop on weed populations in the crop planted the following season. Experiments were conducted in North Carolina to determine weed control and yield of corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] in the same experiment when herbicides were applied postemergence at different timings (Year 1) and to determine how weed control translated into weed populations and cotton yield the following year (Year 2). Herbicides were applied 2 or 6 wk after planting (WAP); 2 and 4 WAP; 4 and 6 WAP; and 2, 4, and 6 WAP. At Lewiston-Woodville, common ragweed (Ambrosia artemisiifolia L.) and Texas millet (Urochloa texana L.) were present. At Rocky Mount, Palmer amaranth (Amanthus palmeri S. Wats) and large crabgrass (Digitaria sanguinalis L.) were present. A single postemergence application of herbicide protected yield from weed interference in corn, whereas in most instances multiple herbicide applications were needed in cotton and to a degree in soybean. Weed densities in Year 2 in cotton were negatively correlated with weed control the previous year in corn, cotton, and soybean. Densities of common ragweed and Palmer amaranth 3WAP in Year 2 were higher in cotton when the preceding crop was cotton or soybean rather than corn when herbicides were not applied; no difference was noted when comparing cotton and soybean. In some instances, sequential applications of herbicides resulted in lower weed densities the following year in cotton. These results demonstrate the importance of timely, sequential herbicide applications for weed control in cotton and soybean and in some instances the positive benefits on weed populations the following year in cotton. [ABSTRACT FROM AUTHOR]

The high concentration of swine production in southeastern North Carolina generates public health concerns regarding the potential transport of pathogens from these production systems to nearby surface waters. The microbial source tracking (MST) tool, antibiotic resistance analysis (ARA), was used to identify sources of E. coli in a segment of Six Runs Creek in Sampson County, North Carolina. Among 52 water samples, fecal coliform (FC) counts averaged 272.1 ± 181.6 CFU/100 mL. Comparisons of isolates from water samples to an ARA library with an average rate of correct classification (ARCC) of 94.3% indicated an average of 64% and 27.1% of 1,961 isolates from Six Runs Creek were associated with lagoon effluent and cattle manure respectively. The potential for aerosol transport of bacteria during lagoon spray events, as well as, the potential for wildlife to serve as a vehicle of transport for bacteria from fields and lagoons to nearby surface waters should be investigated further. [ABSTRACT FROM AUTHOR]

Palmer amaranth (Amaranthus palmeri S. Wats.) is a highly competitive weed that can be difficult to manage in many cropping systems. Research to date has not quantified the growth and development of A. palmeri in a manner that allows direct comparisons across cropping systems. Research was conducted to compare the growth, development, and seed production of A. palmeri when competing with corn (Zea mays L.), cotton (Gossypium hirsutum L.), peanut (Arachis hypogaea L.), and soybean [Glycine max (L.) Merr.] when emerging with crops or emerging three weeks after crops emerge. Regardless of when A. palmeri emerged, seed production was greatest and similar in cotton and peanut and exceeded that of corn and soybean; seed production in soybean exceeded that of corn. However, seed production was approximately 10-fold greater when A. palmeri emerged with crops compared with emergence three weeks later. These results illustrate the importance of controlling weeds during the first three weeks of the season relative to contributions of A. palmeri to the weed seed bank and is the first report comparing seed production in presence of these crops in a manner allowing a statistical comparison of seed production and highlighting the importance of crop sequence for seed bank management. [ABSTRACT FROM AUTHOR]