Andrew G. Hulting

A comparative ecological risk assessment for herbicides used on spring wheat: the effect of glyphosate when used within a glyphosate-tolerant wheat system

Abstract Glyphosate-tolerant spring wheat currently is being developed and most likely will be the first major genetically engineered crop to be marketed and grown in several areas of the northern Great Plains of the United States. The public has expressed concerns about environmental risks from glyphosate-tolerant wheat. Replacement of traditional herbicide active ingredients with glyphosate in a glyphosate-tolerant spring wheat system may alter ecological risks associated with weed management. The objective of this study was to use a Tier 1 quantitative risk assessment methodology to compare ecological risks for 16 herbicide active ingredients used in spring wheat. The herbicide active ingredients included 2,4-D, bromoxynil, clodinafop, clopyralid, dicamba, fenoxaprop, flucarbazone, glyphosate, MCPA, metsulfuron, thifensulfuron, tralkoxydim, triallate, triasulfuron, tribenuron, and trifluralin. We compared the relative risks of these herbicides to glyphosate to provide an indication of the effect of glyphosate when it is used in a glyphosate-tolerant spring wheat system. Ecological receptors and effects evaluated were avian (acute dietary risk), wild mammal (acute dietary risk), aquatic vertebrates (acute risk), aquatic invertebrates (acute risk), aquatic plants (acute risk), nontarget terrestrial plants (seedling emergence and vegetative vigor), and groundwater exposure. Ecological risks were assessed by integrating toxicity and exposure, primarily using the risk quotient method. Ecological risks for the 15 herbicides relative to glyphosate were highly variable. For risks to duckweed, green algae, groundwater, and nontarget plant seedling emergence, glyphosate had less relative risk than most other active ingredients. The differences in relative risks were most pronounced when glyphosate was compared with herbicides currently widely used on spring wheat. Nomenclature: Bromoxynil; clodinafop; clopyralid; dicamba; 2,4-dichlorophenoxy acetic acid; fenoxaprop; flucarbazone; glyphosate; MCPA; metsulfuron; spring wheat; thifensulfuron; tralkoxydim; triallate; triasulfuron; tribenuron; trifluralin; spring wheat, Triticum aestivum L.

Target-site mutation associated with glufosinate resistance in Italian ryegrass (Lolium perenne L. ssp. multiflorum).

BACKGROUND Studies were conducted to elucidate the mechanism of glufosinate resistance in an Italian ryegrass population. RESULTS Glufosinate rates required to reduce growth by 50% (GR(50)) were 0.15 and 0.18 kg AI ha(-1) for two susceptible populations C1 and C2 respectively, and 0.45 kg AI ha(-1) for the resistant population MG, resulting in a resistance index of 2.8. Ammonia accumulation after glufosinate treatment was on average 1.5 times less for the resistant population than for the susceptible populations. The glufosinate concentrations (µM) required to reduce the glutamine synthetase (GS) enzyme activity by 50% (I(50)) were 31 and 137 for C1 and C2 respectively, and 2432 for the resistant population MG. One amino acid substitution in the plastidic GS2 gene, aspartic acid for asparagine at position 171, was identified in the resistant population. CONCLUSIONS This is the first report of glufosinate resistance in a weed species that involves an altered target site.

Management of Italian Ryegrass (Lolium perenne ssp. multiflorum) in Western Oregon with Preemergence Applications of Pyroxasulfone in Winter Wheat

Abstract Management of Italian ryegrass in cereal-based cropping systems continues to be a major production constraint in areas of the United States, including the soft white winter wheat producing regions of the Pacific Northwest. Pyroxasulfone is a soil-applied herbicide with the potential to control broadleaf and grass weed species, including grass weed biotypes resistant to group 1, 2, and 7 herbicides, in several crops for which registration has been completed or is pending, including wheat, corn, sunflower, dry bean, and soybean. Field experiments were conducted from 2006 through 2009 near Corvallis, OR, to evaluate the potential for Italian ryegrass control in winter wheat with applications of pyroxasulfone. Application rates of PRE treatments ranged from 0.05 to 0.15 kg ai ha−1. All treatments were compared to standard Italian ryegrass soil-applied herbicides used in winter wheat, including diuron, flufenacet, and flufenacet + metribuzin. Visual evaluations of Italian ryegrass and ivyleaf speedwell control and winter wheat injury were made at regular intervals following applications. Winter wheat yields were quantified at grain maturity. Ivyleaf speedwell control was variable, and Italian ryegrass control following pyroxasulfone applications ranged from 65 to 100% and was equal to control achieved with flufenacet and flufenacet + metribuzin treatments and greater than that achieved with diuron applications. Winter wheat injury from pyroxasulfone ranged from 0 to 8% and was most associated with the 0.15–kg ha−1 application rate. However, this early-season injury did not negatively impact winter wheat yield. Pyroxasulfone applied at the application rates and timings in these studies resulted in high levels of activity on Italian ryegrass and excellent winter wheat safety. Based on the results, pyroxasulfone has the potential to be used as a soil-applied herbicide in winter wheat for Italian ryegrass management and its utility for management of other important grass and broadleaf weeds of cereal-based cropping systems should be evaluated. Nomenclature: Diuron; flufenacet; pyroxasulfone; metribuzin; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot; ivyleaf speedwell, Veronica hederifolia L.; wheat, Triticum spp.

Alleles Contributing to ACCase-Resistance in an Italian Ryegrass (Lolium perenne ssp. multiflorum) Population from Oregon

Abstract Acetyl-coenzyme A carboxylase (ACCase)–resistant Italian ryegrass is one of the most difficult-to-control weeds in United States wheat-production systems. Seed was collected from a suspected ACCase-resistant Italian ryegrass population in a winter wheat field with a history of ACCase-inhibitor herbicide use. This study investigated cross-resistance patterns in this Italian ryegrass population. Resistance was identified to the commercial dose of the ACCase herbicides pinoxaden, clethodim, sethoxydim, and clodinafop. Partial chloroplastic ACCase sequences revealed aspartate-to-glycine or isoleucine-to-asparagine substitutions at positions 2078 or 2041 in individuals of the resistant population. This is the first report, to our knowledge, of Asp-2078-Gly and Ile-2041-Asn substitutions in ACCase-resistant Italian ryegrass in the United States. Associating the occurrence of resistance alleles with resistance to specific active ingredients provides a better understanding of ACCase cross-resistance in Italian ryegrass and possibly options for its control. Nomenclature: Clethodim; clodinafop; pinoxaden; sethoxydim; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot LOLMU; winter wheat, Triticum aestivum L.

Multiple Pro197 ALS Substitutions Endow Resistance to ALS Inhibitors within and among Mayweed Chamomile Populations

Abstract Mayweed chamomile seeds were collected from six different fields across the Pacific Northwest. All populations (each collection site was considered a population) were suspected to have some level of acetolactate synthase (ALS) resistance. Greenhouse and laboratory studies were conducted to determine if these populations were resistant to three different classes of ALS inhibitors: sulfonylureas (SU), imidazolinones (IMI), and triazolopyrimidines (TP). A whole-plant dose–response and in vitro ALS activity studies confirmed cross-resistance to thifensulfuron + tribenuron/chlorsulfuron (SU), imazethapyr (IMI), and cloransulam (TP); however, resistance varied by herbicide class and population. Two ALS isoforms of the ALS gene (ALS1 and ALS2) were identified in mayweed chamomile; however, only mutations in ALS1 were responsible for resistance. No mutations were found in ALS2. Sequence analysis of the partial ALS gene identified four point mutations at position 197 (Pro197 to Leu, Gln, Thr, or Ser) in the resistant populations. This study demonstrates genotypic variation associated with cross-resistance to ALS inhibitors within and between populations. Nomenclature: Thifensulfuron + tribenuron; chlorsulfuron; imazethapyr; cloransulam; mayweed chamomile, Anthemis cotula L. ANTCO; wheat, Triticum aestivum L. TRZAX.

Postharvest kochia (Kochia scoparia) management with herbicides in small grains

Uncontrolled kochia plants that regrow after small-grain harvest can produce substantial numbers of seeds. An average of 4,100 seeds per plant were produced between harvest (late July to mid August) and the first killing frost (late September) at three locations in Montana. Field experiments were conducted to determine the optimal timing of postharvest herbicide applications to prevent kochia from producing viable seeds. Herbicide treatments were applied at three timings from late August to mid September. The most effective treatments were glyphosate (631 g/ha) and paraquat (701 g/ha) applied at the second application timing (late August to early September). These treatments reduced kochia seed production by 92% or greater at each site. Kochia regrowth by this time had sufficient leaf area for herbicide absorption, but few viable seed had been produced. Herbicide treatments at the first and third application timings were generally less effective and more variable in reducing kochia seed production. Sulfentrazone (157 g/ha) and 2,4-D (561 g/ha) were not as effective at reducing seed production as other herbicide treatments. Nomenclature: Glyphosate; paraquat; sulfentrazone; 2,4-D; kochia, Kochia scoparia (L.) Schrad. #3 KCHSC. Additional index words: Seed production. Abbreviations: AMS, ammonium sulfate.

Effects of Initial Seed-Bank Density on Weed Seedling Emergence during the Transition to an Organic Feed-Grain Crop Rotation

Abstract The transition period to certified organic production can present a significant weed management challenge for growers. Organic certification requires that prohibited fertilizers and pesticides must not have been used for 36 mo before harvest of the first organic crop. Understanding how organic management practices and initial weed seed-bank densities affect weed population dynamics during the transition period may improve weed management efficacy and adoption of organic practices. We examined how tillage systems (full or reduced) and cover crop species planted during the first transition year (rye or a mixture of timothy and red clover) affect the seedling densities of three common annual weed species, common lambsquarters, velvetleaf, and foxtail spp., during the 3-yr transition period. Weed seeds were applied in a one-time pulse at the beginning of the study at three densities, low, medium, and high (60, 460, and 2,100 seeds m−2, respectively), and cumulative seedling densities of each species were assessed annually. Treatment factors had variable and species-specific effects on weed seedling densities. In general, the full-tillage system, with an initial cover crop of timothy and red clover, resulted in the lowest density of weed seedlings following seed-bank augmentation. There was little consistent association between the initial densities of applied weed seeds in the weed seed bank at the start of the transition and weed seedling densities at the end of the transition period. This suggests that when multiple crop and weed cultural management practices are employed during the organic transition period, initial failures in weed management may not necessarily lead to persistent and intractable annual weed species management problems following organic certification. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; giant foxtail, Setaria faberi Herrm. SETFA; velvetleaf, Abutilon theophrasti Medik. ABUTH; yellow foxtail, Setaria glauca (L.) Beauv. SETLU; red clover, Trifolium pretense L.; rye, Secale cereal L.; timothy, Phleum pratense L.

Meeting the ‘multi-’ requirements in organic agriculture research: Successes, challenges and recommendations for multifunctional, multidisciplinary, participatory projects

Organic farming is one of the fastest growing agricultural sectors worldwide, and funds to support research and extension activities that address the needs of organic producers are becoming more widely available in the USA. Solutions to problems in ecologically complex systems, such as organic farming systems often exceed the expertise of individual investigators or single disciplines. Further, the complex nature of ecological and social interactions within systems-based agricultural research requires not only more emphasis on information exchange but also synthesis between multidisciplinary teams of academic researchers and organic farmers. Accordingly, federal grant agencies that support organic agriculture research increasingly require that projects encompass multiple academic disciplines, multiple functions (research, outreach, education), and the participation of stakeholders for the ultimate purpose of the integration of knowledge. Many researchers, educators and administrators at land grant universities (LGUs) remain inexperienced in multidisciplinary, multifunctional and participatory research. Using post-completion project interviews of the project investigators on an organic transition project, we identified eight factors that affected the integration of knowledge from a farmer advisory board and the conduct of our multidisciplinary, participatory organic transition project. The first five factors include shared values, balance in technical competence, institutional capacity for research, team capacity for problem solving and institutional resistance. The research team also identified three other factors that evoked confusion and divergence during the project, and include the ambiguity of power and control of knowledge, the proposed experimental plan and terms of team engagement. We considered participatory elements of the project according to Biggs’ linear typology of participation, but found more appropriate Neef and Neuberts position that a linear scale of participatory approach is an inadequate framework for helping agricultural scientists to decide on whether and in which phases they want to, can and should incorporate participatory elements into their research projects. From these findings, we conclude with critical issues for academic research and extension teams to consider during the development and before conduct of these types of projects. We also offer recommendations for LGUs and other research institutions, and funding organizations, to facilitate multidisciplinary, multifunctional, participatory research.

Characterization of multiple‐herbicide‐resistant Italian ryegrass (Lolium perenne spp. multiflorum)

BACKGROUND Multiple-herbicide resistance in Lolium perenne spp. multiflorum has evolved in many areas in Oregon. To manage the resistant populations, the resistance patterns must be determined. In this study, a population (CT) suspected to be resistant to sulfometuron and hexazinone was collected from a Christmas tree plantation. RESULTS The CT population is resistant to at least six herbicides with four different mechanisms of action: atrazine (>16-fold), diuron (2.4-fold), glyphosate (7.4-fold), hexazinone (3.1-fold), imazapyr (1.8-fold) and sulfometuron (>16-fold). Two mutations, Trp-591-Leu and Ser-264-Gly, were identified in the acetolactate synthase (ALS) and psbA gene respectively. No previously reported mutation in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene was found. Less shikimic acid accumulated in the CT plants than in the susceptible plants after treatment with glyphosate at 0.6 kg AE ha(-1) . CONCLUSION This study suggests that the multiple resistance patterns of Lolium perenne spp. multiflorum populations can be complex, but that chemical control options to manage these populations exist. These remaining chemical options should be integrated with non-chemical management strategies to slow the spread of multiple-resistant biotypes in agroecosystems.

Examining Shifts in Carabidae Assemblages Across a Forest-Agriculture Ecotone

ABSTRACT Northeastern U.S. farms are often situated adjacent to forestland due to the heterogeneous nature of the landscape. We investigated how forested areas influence Carabidae diversity within nearby crop fields by establishing transects of pitfall traps. Trapping extended across a forest-agriculture ecotone consisting of maize, an intermediate mowed grass margin, and a forest edge. Carabidae diversity was compared among the three habitats, and community and population dynamics were assessed along the transect. We used a principal response curve to examine and visualize community change across a spatial gradient. The highest levels of richness and evenness were observed in the forest community, and carabid assemblages shifted significantly across the ecotone, especially at the forest-grass interface. Despite strong ecotone effects, population distributions showed that some species were found in all three habitats and seemed to thrive at the ecotone. Based on similarity indices, carabid assemblages collected in maize adjacent to forest differed from carabid assemblages in maize not adjacent to forest. We conclude that forest carabid assemblages exhibit high degrees of dissimilarity with those found in agricultural fields and forested areas should thus be retained in agricultural landscapes to increase biodiversity at the landscape scale. However, ecotone species found at forest edges can still noticeably influence carabid community composition within neighboring agricultural fields. Further studies should determine how these shifts in carabid assemblages influence agroecosystem services in relation to ecosystem services observed in fields embedded in an agricultural matrix.