Imazamox-resistant wheat varieties carry the Imi1 allele, which confers resistance to the imidazolinone (IMI) herbicide imazamox. This resistance trait allows the selective control of jointed goatgrass, a difficult-to-control winter annual grass weed. Allele movement between IMI-resistant wheat and jointed goatgrass may occur via hybridization and backcross events. Hybrids (F1) of IMI-resistant wheat and jointed goatgrass were identified in 2008 in a commercial wheat field in Eastern Oregon. In 2009 and 2010, surveys were conducted in Eastern Oregon to determine the prevalence of the Imi1 allele in wheat × jointed goatgrass hybrids. Using polymerase chain reaction assays we detected the presence of the Imi1 allele. A total of 128 sites were surveyed over the 2 yr. Of 1,548 plants sampled, 1,100 were positive for the Imi1 alelle and of those, 1,087 were heterozygous and 13 were homozygous for the allele. We assessed hybrid yield components and how these components varied across the sampled sites. The association between the proportion of IMI-resistant hybrids and the area or management practice in the commercial fields was determined. Nonagricultural sites or production of IMI-resistant wheat in consecutive years were two factors associated with a greater proportion of IMI-resistant hybrids. Our results demonstrate that the Imi1 allele is moving from IMI-resistant wheat to jointed goatgrass, producing resistant hybrids and backcross plants. This is the first report of natural occurrence of IMI-resistant backcross plants in commercial wheat fields. Therefore, it is important to implement field management practices that reduce IMI-resistant hybrid production and to effectively manage nonagricultural areas with jointed goatgrass infestations to prevent introgression of the IMI-resistance allele.

Experiments were conducted in the greenhouse and field to investigate differential tolerance among tall, pitted, red, entireleaf, and ivyleaf morningglory species to DPX-PE350. Tall morningglory in the greenhouse was more tolerant of DPX-PE350 at 7 and 14 g ai ha-1 applied POST than were other species of morningglory. Increased tolerance of tall morningglory also was observed under field conditions with DPX-PE350 applied PRE and POST. Adjuvants did not increase biomass reduction of tall morningglory by DPX-PE350 applied POST.

Adoption of soybean that is resistant to 2,4-D will result in more use of glyphosate plus 2,4-D premixes and tank mixtures. Preliminary whole-plant greenhouse assays confirm most Palmer amaranth populations found in Indiana are glyphosate-resistant (GR), and some biotypes exhibit tolerance to 2,4-D amine. Dose–response experiments were conducted to determine the level of glyphosate resistance and 2,4-D amine tolerance in four Palmer amaranth biotypes. A premix formulation of glyphosate plus 2,4-D choline was also evaluated. The R1, R2, and R3 biotypes were 31- to 66-fold more resistant to glyphosate (R:S ratio) than the S1 biotype based on the herbicide dose to cause 90% mortality (LD90). The maximum POST rate of the premix formulation of Enlist Duo® labeled in ‘Enlist®’ soybean is 2,195 g ae ha−1. When separated by active ingredient, the maximum POST rate of Enlist Duo® is equivalent to 1,141 and 1,054 g ae ha−1 of glyphosate and 2,4-D choline, respectively. In the absence of glyphosate, the maximum rate of 2,4-D (1,054 g ae ha−1) in the premix formulation of Enlist Duo® controlled S1, R2, and R3 biotypes, but failed to control all plants from the R1 biotype. Estimates for LD90 showed the R1 biotype was 3-fold more tolerant than the S1 biotype to 2,4-D amine. However, no plants survived the 1,155 g ae ha−1 (600 g ae ha−1 of glyphosate plus 555 g ae ha−1 2,4-D) treatment with the premix formulation of glyphosate plus 2,4-D choline. Overall, results from this experiment suggest GR Palmer amaranth that also exhibits increased tolerance to 2,4-D amine will be difficult to control with glyphosate or 2,4-D alone, but can be controlled POST with Enlist Duo® at lower than labeled field rates (1,618 to 2,195 g ae ha−1).

Herbicide resistance has become a major topic of international research in weed science, with a steady stream of presentations and papers on various aspects of the biology of herbicide resistant weeds. Diverse sources—including WSSA—have generated an equally steady stream of recommendations for preventing and managing herbicide resistance. The situation in the field, however, continues to deteriorate, with new cases of herbicide resistant weeds being reported at an increasing rate. We know what to do, but why aren't we doing it?

Hazelnut (Corylus avellana L.) is a native shrub on the steep slopes of the mountains and on the plains in the Black Sea coast of Turkey. Turkey is the world’s largest hazelnut producer and exporter, followed by Italy, Spain, the United States, and Greece. Within the scope of this project, a number of surveys were conducted in Turkey to understand the impact of a glyphosate ban on hazelnut production and the economy. Sixty farm surveys were conducted within the Black Sea region, and those data were used as primary information sources. Databases of institutions, theses, academic reports, and published articles were used as secondary data sources to determine the possible effects of a glyphosate ban on Turkish hazelnut production and economy. One of the most important findings of the study was that agricultural business and employment sustained by hazelnut production constitute a significant part of the rural economy. Tillage and mechanical strategies remain as the most sustainable alternative methods for controlling weeds. A potential glyphosate restriction may increase the demand for labor due to a higher need for mechanical strategies. The cost of these alternative methods are 80% more compared with glyphosate weed control systems. The benefit–cost model predicted that, in the case of no glyphosate use, total hazelnut production would decrease by 12% to 21% due to inefficient weed control. A glyphosate ban would result in a reduction in Turkish gross domestic product. Yearly, an average of US$2 billion in revenue is obtained from hazelnut exports, and this number corresponds to 1.37% of Turkey’s annual export value. The glyphosate ban would cause a US$240 to US$420 million loss in hazelnut export value and reduce production by 66 to 115 million kg. Global demand for hazelnut is believed to be on the increase, and world production depends largely on Turkey.

Attempts to discover new active ingredients and target sites within the aromatic pathway have resulted in the synthesis of potent enzyme inhibitors, but no herbicides. As an aid in identifying a new target for inhibitor design and screening, we have determined the mode of action of a compound (6-methyl anthranilate) that exhibits noncommercial levels of herbicidal activity. Our evidence suggests that 6-methyl anthranilate is converted in vivo, by traversing the tryptophan biosynthetic sequence, to 4-methyl tryptophan, which inhibits anthranilate synthase. Inhibitors synthesized by design and those found by target-based screening converged on analogs of tryptophan and anthranilate. None, however, was more herbicidal than 6-methyl anthranilate.

Nitrogen (N) inputs have been found to exert strong influence on leaf stoichiometry in natural ecosystems, but there are few studies investigating the effects of N in agroecosystems. Using a 5-yr fertilization experiment in rice fields, we examined the effects of N inputs on leaf stoichiometry of one crop, rice (Oryza sativa L.), and its four common weeds, barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], Monochoria korsakowii Regel and Mack, alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.], and Japanese mazus [Mazus pumilus (Burm. f.) Steenis], and further evaluated whether and how straw return mediates these effects. We found that rice and weed leaf nitrogen:phosphorus:potassium (N:P:K) stoichiometry exhibited divergent responses to N fertilizer. Weed leaf N:P:K stoichiometry was not sensitive to low (120 kg N ha−1) and regular (240 kg N ha−1) N inputs, but rice plants were, with significantly increased leaf N concentration and N:P and N:K ratios. The opposite trend was found for high N inputs (360 kg N ha−1). Rice leaf N concentration [N] did not increase further, and N:P ratios even decreased, whereas E. crus-galli and M. korsakowii had significantly increased [N] and N-related stoichiometry. We also found that the positive effects of regular N inputs on rice leaf N:P and N:K ratios were significantly dampened by straw return, but the positive effects on N:P ratios in M. pumilus leaves were enhanced by straw return. Compared with weeds, rice leaves contained low elemental concentrations across fertilization levels at grain-filling stages. These results indicate that rice has a lower N requirement than weeds at grain-filling stages, and the N supply should be managed at a relative low level to reduce the nutrient acquisition and competitive abilities of weeds. From a stoichiometric perspective, this study highlights the importance of N management in combination with straw return in controlling weeds and increasing the nutrient-use efficiency of crops.

Plants of Zebrina pendula L., Phaseolus vulgaris L., Sorghum halepense (L.) Pers., and Chenopodium album L. were sprayed with a solution containing herbicide (sodium 2,4-dichlorophenoxyacetic acid or sodium 2,2-dichloropropionic acid), surfactant (sodium dioctylsulfosuccinate), and fluorescent tracer (sodium pyrenetrisulfonate). In most instances plants having stomata relatively open absorbed more tracer (based on UV observation) and more herbicide (based on injury and growth responses) than those with stomata relatively closed. Differences, however, were less than those expected from studies using detached leaves, probably from poorer control of stomatal aperture in intact leaves. There was good agreement between degree of opening and tracer uptake.

Field studies at three locations across Nebraska showed that 2,3,6-trichlorobenzoic acid (2,3,6-TBA) leached readily into the soil profile. The herbicide was lost from the surface soil much more readily in central and western Nebraska than in eastern Nebraska even though rainfall was about twice as much at the last location. Volatilization was suggested as a possible reason for this loss of 2,3,6-TBA. There was a definite, but not complete, loss of 2,3,6-TBA from the three soil profiles between May 1960 and September 1961. Soybeans proved to be an acceptable bioassay plant for this herbicide in soil at 2,3,6-TBA concentrations of ½ to 2 ppmw.

As the seeds of leafy spurge (Euphorbia esula L.) increase in age after fertilization, their color changes from yellow to yellow with brown tips, to brown ends with a narrow yellow band, to brown with an orange band, and to a reddish-brown seed, followed in order by brown, gray-brown, gray, and finally, mottled. The last four are viable; the others are not. Mowing of leafy spurge to prevent viable seed production must be done before seeds have turned brown. Brown seeds appeared 10 to 13 days after fertilization depending upon seasonal conditions.

The fungus Scopulariopis brumptii Salvanet-Duval (MSU 42018) was isolated from a soil sample collected from the rhizosphere of a potted asparagus plant. When cultured 7 days in A-9 broth medium, the organism produced compounds phytotoxic to seeding dicotyledonous weeds (via foliar application) and to Chlamydomonas reinhardtii Dangeard. Three herbicidal metabolites, 3-hydroxybenzyl alcohol, 2-methylhydroquinone, and (+)-epiepoformin, were isolated by column and thin-layer chromatography (TLC) and structures confirmed by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic reasonance spectroscopy (NMR), and mass spectrometry (MS). Of the three compounds, (+)-epiepoformin was the most active, providing complete control of redroot pigweed and 88% control of white mustard when applied at 4.4 kg/ha.

Crown bud, tiller, and rhizome development was studied in 10 quackgrass biotypes at two stages (three-to four- and seven- to eight-leaf stages) of development to determine if differential development of these structures influenced control with sethoxydim and haloxyfop. There was a differential response among the 10 biotypes to both sethoxydim and haloxyfop at both stages of development. The biotypes differed in the number of crown buds, tillers, and rhizomes that formed at both stages of development. In the three- to four-leaf stage, the biotypes with the greatest number of crown buds were the most difficult to control. These results suggest that in the susceptible stage (three-to four-leaf) the quackgrass biotypes with the least number of crown buds will be the easiest to control; however, by the time all the biotypes reach the seven- to eight-leaf stage even the biotypes with the lowest number of crown buds have enough crown buds that they become difficult to control with either sethoxydim or haloxyfop.

Enzymatically isolated mesophyll cells of soybean [Glycine max (L.) Merr. ‘Kino’] and cotton (Gossypium hirsutum L. ‘Stoneville 1613 glandless’) were used to study the effects of three surfactants, I = ‘Sterox SK’ (polyoxyethylene thioether), II = ‘Renex 36’ (polyoxyethylene-6-tridecylether), and III = ‘WSCP’ [polyoxyethylene (dimethylimino) ethylene (dimethylimino) ethylene dichloride] alone or in combination with two herbicides, D-497 (1,1-dimethyl-4,6-diisopropyl-5-indanylethyl ketone) and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) on cell permeability, photosynthetic 14CO2 fixation and cellular ultrastructure. Greatest amount of efflux of 14C-labeled material from soybean cells was caused by III, whereas other surfactants or herbicides produced only slightly higher effluxes than the controls. Mixtures of oryzalin-I or -II were the only combinations that enhanced efflux in soybean cells above that of cells treated with the surfactant or herbicide alone. However, on cotton cells all surfactants and oryzalin caused considerable leakage but no synergistic effects. Sugars were the predominant compounds leaked from the treated and control cells. Disorganization of all cellular membranes was caused by III whereas I and II disrupted only the chloroplast grana-intergrana thylakoids, causing abnormal grana. Herbicidal damage to the cell ultrastructure was minimal. Cells treated with combinations of surfactants and herbicides produced only those ultrastructural symptoms that the individual chemicals caused when applied alone. Photosynthetic CO2 fixation was inhibited in both cotton and soybean cells treated with surfactants and (or) herbicides. Interference with membrane integrity, either directly by interaction with membranes or indirectly by interference with cellular energy generating systems that maintain membrane integrity is the postulated mode of action of these surfactants and herbicides.

To determine if cell damage could account for chlorsulfuron inhibition of assimilate transport, the ultrastructure of companion cells and surrounding mesophyll cells was examined following chlorsulfuron treatment. Six hours after treatment of canola leaves, thylakoids in companion cells were swollen and chloroplast structures in mesophyll cells were disorganized. Three days after treatment, the treated leaves contained more starch granules in companion cells than corresponding control leaves, presumably as a result of reduced assimilate export. We conclude that the inhibition of assimilate export in chlorsulfuron-treated canola leaves is associated, at least in part, with the ultrastructural changes described, particularly those in companion cells.

Greenhouse experiments were conducted to determine the effects of drought stress length and relief on velvetleaf growth and bentazon efficacy with crop oil concentrate (COC) and 28% urea ammonium nitrate (UAN). Drought stress caused leaf water and osmotic potentials to decline linearly over time. Leaf water potential ΨL) declined 0.02 and 0.08 MPa day−1 for velvetleaf subjected to −0.03 and −0.4 MPa soil water potential (ΨP), respectively. Osmotic potential (ΨO) declined 0.02 and 0.21 MPa day−1 for velvetleaf subjected to −0.03 and −0.4 MPa ΨP respectively. Bentazon did not reduce drought-stressed compared to non-drought-stressed velvetleaf dry weight 21 d after treatment with either COC or no adjuvant but did decrease dry weight with UAN. Reduced velvetleaf dry wights in drought-stressed velvetleaf compared to non-drought-stressed velvetleaf could not be accounted for by increased bentazon penetration in the drought-stressed plants. Rewatering velvetleaf subjected to 7 d of −0.4 MPA ΨP caused them to be more sensitive to bentazon than velvetleaf subjected to −0.03 MPa ΨP except when UAN was the adjuvant.

The goal of this research was to determine whether crop management practices could substitute for a herbicide for managing mixed populations of green and yellow foxtail in hard red spring wheat. Crop yield and foxtail growth were measured in two years of field research in North Dakota. Spring wheat yields were as great or greater when early seeding date or 2× seeding rate were substituted for POST diclofop3 at 0.75 kg ai ha−1 for managing foxtail in spring wheat. Yield of spring wheat competing with foxtails was greater for the high seeding rate (2× = 270 kg ha−1) than both the normal (1× = 130 kg ha−1) and low (0.5× = 70 kg ha−1) seeding rates for early or middle seeding dates, but not for the late seeding date. For both early and middle seeding dates, wheat yield at the 2×seeding rate without diclofop was equal to or greater than that of the 1× seeding rate with diclofop. Late-seeded wheat did not yield well in competition with dense foxtail stands for any treatment combination. Early and middle seeding dates favored the relative increase of green foxtail over yellow foxtail in wheat, whereas late seeding favored yellow foxtail over green foxtail. Economic analysis demonstrated that early seeding date was the most critical factor in determining the stochastic dominance of treatments without diclofop over treatments with diclofop. Seeding rate was much less important than seeding date in determining the ranking of treatments in stochastic dominance analysis.

Two field experiments were conducted to examine the competitive effect of common cocklebur and sicklepod in soybean. Factors examined included sap flow of both the weed and the crop, as well as the traditional parameters of weed and crop growth and crop yield. The intent was to determine to what extent competitive effects could be attributed to differential water utilization. In the first study, soybean planted at 20 plants m−1 row was infested with either sicklepod at 10 plants m−1 row or common cocklebur at two plants m−1 row. Sicklepod reduced soybean sap flow and yield 53 and 49%, respectively. Common cocklebur reduced soybean sap flow and yield 31 and 38%, respectively. Within a weed species, weed-induced yield and sap flow reductions were comparable, indicating that water deprivation was the primary detriment that these weeds inflicted on soybean. Individual common cocklebur plants were 3.9 times more competitive than sicklepod with respect to reducing soybean yield. However, sap flow of individual common cocklebur plants was only 1.4 times more than that of sicklepod, indicating that water deprivation was not the only causal factor in weed-crop competition. In the second experiment, sicklepod was planted in soybean (fixed density) and clipped to either half the height, same height as soybean, or left unclipped, in an attempt to simulate herbicide-induced stunting. Clipping sicklepod had a positive effect on soybean sap flow and yield. Thus, the benefits of reduced weed competition were achieved without killing sicklepod.

Experiments were conducted to evaluate the occurrence and significance of release of herbicide through subterranean parts of nicosulfuron-treated johnsongrass. In a bioassay, the rooting medium of johnsongrass treated foliarly with 50 or 100 μg nicosulfuron plant−1 was inhibitory to the radicle elongation of sorghum and corn indicating the increased toxicity of the rooting medium of nicosulfuron-treated johnsongrass. The study with 14C-nicosulfuron indicated a basipetal translocation of foliarly applied nicosulfuron in johnsongrass to its roots/rhizomes and also into the rooting medium. By 30 DAT, around 23% of the 14C-label absorbed by johnsongrass was found exuded into the rooting medium. Radiochromatogram scans of thin layer chromatography plates of rooting medium indicated unmetabolized nicosulfuron as the major 14C-labeled compound (56%). The study also revealed a subsequent uptake of exuded 14C by corn roots sharing the medium. On the whole, the amount of 14C-label recovered from untreated corn amounted to 4.3% of the total applied to johnsongrass. In another experiment, the presence of nicosulfuron in the rooting medium was detrimental to corn growth. Reductions in corn growth occurred at concentrations of 10−8 M nicosulfuron or greater in the rooting medium. The sensitivity of corn to root uptake was attributed to greater accumulation of nicosulfuron at a faster rate in the growing parts.

Field horsetail shoots were severed from the rhizomes and grown hydroponically with and without shade (40 and 190 μmol m–2 s–1 photosynthetic photon flux) under six different nutrient regimes, by using nutrient solutions with different amounts of nitrogen (N) and potassium (K) (6/42 mmol L–1 N; 7/15/24 mmol L–1 K). Nutrients were supplied daily with the same volumes for the six different nutrient solutions at exponentially increasing rates corresponding to a maximum relative growth rate (RGR) of 12.5% from days 0 to 31 and 6% from days 32 to 48. RGR was calculated for the highest N and K rate. Photosynthetic rate and stomatal conductance to water vapor were determined on day 48, then the plants were harvested. The fresh weight (FW) and dry weight (DW) of different plant components were determined. Shade completely inhibited growth of tubers and fertile shoots and drastically reduced RGR, average aerial shoot height, and DW of shoots and rhizomes. N supplied at the high rate to unshaded plants increased the growth of all parts or the plant except fertile shoots and tubers. No effects of K were detected at the low N rate, whereas at the high N rate, K significantly increased total DW and belowsurface DW. RGR never exceeded 10% d–1. In the unshaded treatments, the K concentration was higher in aerial shoots, 150 to 240 μmol g–1 FW, than in belowsurface organs, 30 to 90 μmol g–1 FW. Shoot growth was significantly reduced at shoot K concentrations below 150 to 210 μmol g–1 FW, and root growth was significantly reduced at root K concentrations below 30 to 50 μmol g–1 FW. K significantly increased maximum net photosynthetic rate, 10 μmol CO2 m–2 s–1, at light saturation, 1,300 μmol m–2 s–1, in unshaded plants, whereas it reduced the light compensation point and respiratory losses of CO2 in darkness. It is concluded that field horsetail is a typical sunny habitat species with a rather high K demand.

The fact that quackgrass may occasionally escape control by the herbicide glyphosate is thought to result from the wide range in growth rate and sink activity among rhizome buds, especially in older portions of the rhizome. To study growth of rhizome structures, we supplied whole plants with 14CO2 throughout a 10-h light period and determined the amount of labeled carbon accumulated by the end of the subsequent 14-h night. Growth of rhizome structures during this 24-h period was estimated by determining their growth rate coefficients: the amount of labeled carbon accumulated per unit of carbon present in the structure. Growth rate coefficients generally were high for the rhizome tip that is enclosed in a sheath and the adjacent bud and rhizome segment, with values decreasing rapidly in a basipetal direction. However, extensive differences in the level and pattern of assimilate accumulation among rhizome structures were observed as rhizome development continued. Glyphosate accumulation generally paralleled the level of assimilate accumulation even though the range among rhizome structures for both increased with rhizome age. As a result of the increased variability among buds, some of the older buds will accumulate only a small, perhaps sublethal, amount of glyphosate and this may explain the tendency of the buds in older regions to escape control by glyphosate.