Herbicides classified as synthetic auxins have been most commonly used to control broadleaf weeds in a variety of crops and in non‐cropland areas since the first synthetic auxin herbicide (SAH), 2,4‐D, was introduced to the market in the mid‐1940s. The incidence of weed species resistant to SAHs is relatively low considering their long‐term global application with 30 broadleaf, 5 grass, and 1 grass‐like weed species confirmed resistant to date. An understanding of the context and mechanisms of SAH resistance evolution can inform management practices to sustain the longevity and utility of this important class of herbicides. A symposium was convened during the 2nd Global Herbicide Resistance Challenge (May 2017; Denver, CO, USA) to provide an overview of the current state of knowledge of SAH resistance mechanisms including case studies of weed species resistant to SAHs and perspectives on mitigating resistance development in SAH‐tolerant crops. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Simple, reliable tools are needed by land managers to quantify establishment success when seeding or re-seeding pastures or rangeland. A frequency grid was designed to measure seedling or plant establishment success for a single species, mixtures of species, or single species of a mixture. The frequency grid is a metal frame containing 25 squares (5 x 5) or cells and can be made from concrete reinforcing sheets that have 15 x 15 cm squares. When used, the frequency grid is either randomly or systematically placed within a seeded area. The number of cells containing 1 or more seeded plants are counted. The grid is then flipped, end-over-end, and the counts are repeated. The process is repeated until a total of 100 cells have been counted per sampling location within a seeded area. Counts can be directly converted into frequency of occurrence or stand percentages by dividing the number of cells that contain a seeded plant by 100. The process can be repeated at several locations within a seeded area to characterize establishment success. Multiplying frequency of occurrence percentages by 0.4 provides a conservative estimate of plant density (plants m -2 ). A single measurement of 100 frequency grid cells can be taken in less than 5 minutes. The frequency grid is inexpensive to make, requires minimal training, permits rapid measurements, and provides a meaningful estimate of plant density. The frequency grid has been used to document herbicide efficacy and seeding rates for use in grassland establishment in the central Great Plains and should be easily adaptable for use in other geographic regions.Key Words: planting, rangeland, pasture, plant density, seedling counts Millions of hectares of land have been seeded to grasslands in the Great Plains and other western states. Additional land will likely be seeded in the future to convert marginal cropland to grasslands, upgrade existing seeded grasslands, and to restore degraded rangeland invaded by noxious weeds or damaged by fires. In addition, millions of hectares of pastures are periodically seeded in humid grassland areas worldwide. After each establishment attempt, the questions that managers must answer include: Was the seeding successful? Is the stand adequate for the intended purpose? If not, do only portions of the seeded area need to be planted again? Because of these questions, managers need tools to quantify the success of grassland plantings and not be forced to rely on visual evaluations.The goal of all grassland re-vegetation is to obtain an acceptable number of established plants of the desired, seeded species per unit of land (i.e., density) which is often expressed as plants m -2 . To be of most value, the plant density measurement also should provide an estimate of plant distribution over the unit area. Methods that have been developed to determine plant density and species composition in grasslands include density per quad- ResumenLos manejadores de tierras necesitan herramientas simples y confiables para cuantificar el éxito del estable...

The productivity and native species diversity of Great Plains grasslands have been substantially reduced by past management that facilitated the establishment of invasive exotic weeds and displacement of native species. Management strategies are needed to rapidly restore the productive capacity and biological diversity of these degraded grasslands. Critically important phases of the grassland restoration process are the reintroduction and establishment of native species. Weed interference is the primary constraint to successful establishment of native plants. The goal of our research is to develop strategies that use multiple technologies, including herbicides, to expedite grassland revegetation with native grasses and forbs. Imidazolinone herbicides (AC 263,333, imazapyr, and imazethapyr) were used successfully to improve establishment of native perennial grasses (big bluestem, switchgrass, little bluestem) and selected forbs (blackeyed-susan, purple prairieclover, Illinois bundleflower, trailing crownvetch, and upright prairie coneflower) on cropland and as components of a strategy to revegetate leafy spurge-infested rangeland with native tallgrasses. Imazethapyr at 70 or 110 g ai/ha applied at planting resulted in stands of big bluestem and little bluestem that were similar or superior to stands established where atrazine was applied. Seedling grasses were susceptible to imazapyr at two of three study sites. Imazapyr at 560 g ai/ha plus sulfometuron at 100 g ai/ha applied in fall was the optimum treatment for suppression of leafy spurge and exotic cool-season grasses and establishment of big bluestem and switchgrass on degraded rangeland sites. Establishment of selected forbs was improved by PRE treatment with AC 263,222 or imazethapyr at 70 g ai/ha. This research provides evidence that the imidazolinone herbicides can be important components of integrated weed management strategies designed to reverse deterioration of grasslands by reestablishing native species, improving grassland productivity, and decreasing the prevalence of exotic weeds.

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DNA-based molecular markers may provide information about introduced weedy species that would be useful in biological weed control efforts. Chloroplast DNA restriction fragment length polymorphisms (cpDNA RFLP) and random amplified polymorphic DNA (RAPD) analysis are two DNA-based marker techniques that can provide estimates of genetic variation in native and introduced populations of weedy species. Profiles provided by these techniques could furnish the necessary information to determine the geographic origins of introduced species and provide evidence for multiple introductions. Although DNA-based markers would not necessarily identify the genetic basis for host-pest compatibility, they would enable identification of specific host genotypes. Current criteria for selecting a weedy species as a target for biological control are primarily political and economic. The importance of genetic diversity and population structure in determining the vulnerability of plant populations to insects or diseases has not been fully appreciated. Estimates of genetic diversity based on DNA marker analysis could be used as one criteria for determining which plants are targeted for biological control. The success of biological weed control efforts has been limited by the high levels of genetic diversity occurring in target weed specks and the lack of biocontrol agent and target weed compatibilities. DNA-based markers may be used to increase our understanding of these factors and contribute to the success of biological weed control by helping to target the most vulnerable species and provide more realistic expectations of the potential for success given available resources.