Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) affected oats and alfalfa in Nebraska planted the year following application to sorghum. No carry-over of 2-chloro-N,N-diallylacetamide (CDAA) + trichlorobenzyl (TCBC) was detected in oats and alfalfa. Intertillage of sorghum did not decrease herbicide residue.

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.

Monuron [3–(p–chlorophenyl)–1,1–dimethylurea] is reported to be a potent inhibitor of the Hill reaction by Cooke and Wessels and van der Veen. It is reported to be 125 times as active as phenylurethan [ethyl–N–phenylcarbamate] in inhibiting the Hill reaction. Diuron [3–(3,4–dichlorophenyl)–1,1–dimethylurea] is 2500 times as active as phenylurethan as a Hill reaction inhibitor. Monuron and diuron have been used in photosynthetic studies. There are no reports in the literature indicating a difference in the mode of action of these compounds.

The effects of sublethal and lethal levels of 3-(3,4-dichlorophenyl)-l-methoxy-l-methylurea (linuron) on the uptake of 32P and 45Ca were tested on tomato (Lycopersicum esculentum Mill., var. Kokomo) and parsnip (Pastinaca sativa L., var. Harris Model). Both levels of foliage-applied linuron stimulated the uptake of 32P from nutrient culture solution and its translocation to the leaves. The increased 32P in the leaves of the treated tomato plants was found in the inorganic phosphate fraction. Incorporation of the label in the phospholipid and nucleic acid fractions was decreased slightly. Linuron inhibited uptake and translocation of 45Ca in both plants.

Broom snakeweed achene dispersal was monitored by placing surface-level traps outwards in the cardinal directions from 12 plants and collecting the achenes weekly or biweekly from September 1993 until seeds were no longer retained by the plants after 42 wk. About 50% of the achenes dispersed between October and December. Especially high numbers of achenes were dislodged during periods of intense winter winds and rains, with 78% of the seed placed into the east tray and 86% falling within 50 cm of the parent plant. Achene production averaged 3,928 (± 1,146) per plant in 1993 and 2,036 (± 987) per plant in 1994. Achenes collected over time directly from the inflorescence and achenes stored in nylon packets on the soil surface averaged 82% viability during fall and winter. Achene viability declined rapidly in late spring, and few remained viable before the next seed crop. Greenhouse experiments compared the influence of water application interval and water amount on broom snakeweed germination and seedling survival. Treatments consisted of 4 water intervals: daily, 5-d, 10-d, and 15-d intervals; and 4 water amounts: field capacity (1/1 fc), 3/4 fc, 1/2 fc, and 1/4 fc. Germination was 52% at daily 1/1 fc, and no seed germinated at daily 1/4 fc. Data suggest that optimum germination occurs when soils are maintained at a minimum soil matric potential (Ψm) > −180 kPa for at least 4 d. Optimum Ψm for seedling survival appears to range between −300 and −900 kPa, while seedling mortality would generally be expected with a Ψm of > −1800 kPa.

Chemicals that stimulate germination of curly dock seed (Rumex crispus L. # RUMCR) and urediniospores of curly dock rust [Uromyces rumicis Schum. (Wint.)], an obligate parasite of this weed, were studied and compared. Methyl salicylate, benzyl cyanide, and benzonitrile were the best stimulators of germination of curly dock seed. The compounds tested were most effective at concentrations ranging from 250 to 1000 μl/L. A 500 μl/L concentration of methyl salicylate caused 99% of the curly dock seed to germinate. Exposure to volatiles from 10 μl methyl salicylate or octyl cyanide for 16 to 24 h was required for maximum stimulation of curly dock seed germination in 10 days. Benzonitrile, methyl-2,4-dihydroxybenzoate, 3-cyanophenol, 2-heptanone, and benzaldehyde were the most effective of 45 compounds tested on urediniospores of curly dock rust. Benzonitrile was most active of 19 compounds tested on both seed and spores. Benzyl cyanide, 4-methoxybenzonitrile, benzaldehyde, and methyl 2,4-dihydroxybenzoate also were active on both propagules.

Horseweed is a winter annual weed that has evolved resistance to multiple herbicide modes of action in 11 countries worldwide. A paraquat-resistant horseweed population in an Ontario orchard that was being managed by a rotation of herbicides began to show increased tolerance to the herbicide linuron. Experiments were conducted in the greenhouse to compare the response of this population and several paraquat-susceptible populations to linuron, diquat, and oxyfluorfen. Plants were sprayed with a range of doses of each herbicide when they were from 5 to 10 wk old, and the ED50, or dose at which shoot dry weight was reduced by 50%, was estimated. There was a sevenfold difference in the ED50 values of the paraquat-resistant and -susceptible populations in response to diquat and a threefold difference in response to linuron. The response to oxyfluorfen was age dependent. The ratio of resistance to susceptible ED50 values was estimated as 57 for 5-wk-old plants and 11 for 8-wk-old plants in response to oxyfluorfen. Ten-week-old plants from both populations showed no response to oxyfluorfen at rates up to 4.8 kg ai ha−1.

In greenhouse studies, overhead watering or subsurface irrigating soil can cause fluctuating moisture content, as can treatments such as surface application of residue used in cover crop research. This paper introduces a method of capillary mat subirrigation that maintained soil moisture at about field capacity for 16 d while no moisture could be detected after 6 d in soil placed under similar conditions that was not irrigated. In another study, subirrigation eliminated differences in soil moisture due to the presence of surface-applied residue and moisture supplied by hand watering from overhead was apparently removed from subirrigated treatments, which never differed in soil moisture content.

Field and greenhouse experiments were conducted to determine the effect of herbicides on napiergrass growth and control. In greenhouse experiments, hexazinone, glyphosate, and imazapic were applied POST, and carbon dioxide (CO2) assimilation was measured with the use of an open-flow gas-exchange system up to 22 d after treatment (DAT). Carbon dioxide assimilation was reduced to zero, indicating plant death, for hexazinone- and glyphosate-treated napiergrass by 2 and 12 DAT, respectively. Imazapic-treated napiergrass CO2 assimilation declined to a constant rate by 22 DAT, but never reached zero. Field studies at Chula and Ty Ty, Georgia, evaluated herbicides for napiergrass control. Herbicide treatments included autumn-only applications, autumn followed by spring applications, and spring-only applications. All autumn-applied treatments exhibited regrowth in the spring. Plants were not affected by cold winter temperatures. A spade tillage treatment was implemented in January 2010, but was not effective in controlling napiergrass. Spring treatments included split applications of autumn treatments and spring-only treatments of glyphosate, glyphosate plus sethoxydim, and imazapyr. Sequential autumn and spring treatments containing glyphosate at both locations failed to eradicate napiergrass. Imazapyr applied spring achieved 94% plant injury by 34 DAT, and indicated potential napiergrass control. Greenhouse results indicated multiple modes of action could be effective in reducing napiergrass growth, but were inconsistent with field results. Further field studies are needed to derive conclusive methods of napiergrass control.

Hydrilla is one of the most serious aquatic weed problems in the United States, and fluridone is the only U.S. Environment Protection Agency (USEPA)–approved herbicide that provides relatively long-term systemic control. Recently, hydrilla biotypes with varying levels of fluridone resistance have been documented in Florida. One susceptible and five fluridone-resistant biotypes of hydrilla varying in resistance levels were maintained in 950-L tanks under ambient sunlight and day-length conditions from September 2004 to September 2005 in absence of fluridone. Because fluridone is an inhibitor of the enzyme phytoene desaturase (PDS), the gene for PDS (pds) was cloned from fluridone-susceptible and -resistant hydrilla biotypes. Somatic mutations in amino acid 304 of hydrilla PDS are known to confer herbicide resistance. We determined pds sequence from these hydrilla biotypes at planting and 12-mo after planting. Two independent mutations at the arginine 304 codon of pds were found in the resistant hydrilla plants. The codon usage for arginine 304 is CGT, and a single point mutation yielding either serine (AGT) or histidine (CAT) was identified in different resistant hydrilla biotypes. There were no differences at codon 304 in the PDS protein of any hydrilla biotype 12-mo after planting. Several other mutations were also found in resistant pds alleles, though their possible role in herbicide resistance is unclear.

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.

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.

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).

Requirements for germination and rate of juvenile root and shoot elongation of 23 medusahead (Taeniatherum asperum (Sim.) Nevski) selections were investigated in relation to osmotic stress. These were compared with the germination and elongation characteristics of other grasses. Aqueous solutions of different osmotic pressures were obtained by dissolving polyethylene glycol in water. Successive 4-bar increases in osmotic pressure markedly reduced medusahead germination until germination terminated at 16 bars. Other grass species exhibited higher germination than medusahead under osmotic stress. Medusahead juvenile root and shoot elongation under low and moderate osmotic pressure exceeded all other species tested.

Invasive species face new selective pressures and low genetic variation caused by genetic bottlenecks and founder effects when they are introduced into novel environments. Epigenetic variation may help them to cope with these problems. Mile-a-minute (Mikania micrantha Kunth) is a highly invasive exotic weed that has seriously damaged biodiversity and agricultural ecosystems. We first adopted methylation-sensitive amplified polymorphism (MSAP) markers to investigate epigenetic variation of 21 M. micrantha populations in southern China, and further explored the effects of environmental factors on population epigenetic differentiation by correlating epigenetic and climate and soil data. Adaptive epiloci positively correlated with climate/soil variables were identified. Minimum temperature of the coldest month and mean temperature of the coldest quarter were considered as decisive factors for its distribution. Climate is presumed to play a relatively more important role than soil in shaping the adaptive epigenetic differentiation in M. micrantha. Under ongoing global warming, populations of M. micrantha are predicted to expand northward. In addition, the weed also presented higher epigenetic variation compared with genetic variation. Leaf shape variation was detected related to methylation-state change at the population level.

Investigations of smooth crabgrass growth and fenoxaprop-ethyl retention, foliar penetration, translocation, and metabolism were conducted at various soil moisture levels using a polyethylene glycol (PEG) semipermeable membrane system. The activity of fenoxapropethyl was significantly reduced at higher levels of moisture stress and this antagonistic effect was greater with increased duration of water deficit following herbicide application. Fenoxaprop-ethyl spray retention decreased linearly (23% total reduction) as soil matric potential (Ψm) decreased from −0.01 to −0.1 MPa. Foliar penetration and translocation of 14C-fenoxaprop-ethyl applied on the third true leaf were not affected by level or duration of moisture stress. Only 2% of the absorbed radioactivity was translocated out of the treated leaf for each moisture stress level and duration. As the soil Ψm decreased (−0.01 to −1.0 MPa) the relative levels of fenoxaprop-ethyl increased by 76 and 65% after a 48- and 96-h postapplication moisture stress period, respectively. In contrast, fenoxaprop acid decreased by 59 and 44% after 48 and 96 h of moisture stress, respectively. The relative level of fenoxaprop acid was linearly correlated to the antagonistic effect on shoot dry weight. These results suggest that decreased spray retention and, particularly, alterations in fenoxaprop-ethyl metabolism contribute to reduced fenoxaprop-ethyl activity observed in moisture-stressed smooth crabgrass.

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?

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.