Paraquat was the most successful nonselective herbicide in Korea due to its rapid herbicidal activity. However, its high mammalian toxicity, frequent self-poisoning incidents, and a lack of effective antidotes led to a paraquat ban in Korea in 2012. Therefore, this review was conducted to revisit the toxicological profile of paraquat and to investigate the impacts of the paraquat ban on human health and agriculture in Korea. A review of toxicological information reconfirmed that paraquat is highly acutely toxic to humans, and ingestion, inhalation, or dermal administration of the herbicide can cause severe clinical signs and inevitably lead to death by respiratory failure. In Korea, the paraquat ban immediately decreased the suicide rate due to pesticides (mainly paraquat) by 46.1%, resulting in a 10% decrease of the total suicide rate. However, this also led to an increase in suicide attempts with other poisons such as carbon monoxide, suggesting that suicide attempts and rates of suicide by poisoning depend on not only the toxicity of the poison but also the accessibility of the poisoning agents. In agriculture, paraquat was quickly replaced by other nonselective herbicides such as glufosinate and glyphosate. Thus, the paraquat ban did not have a significant impact on agricultural practices but influenced the nonselective herbicide market; the use of glufosinate was higher than use of glyphosate due to glufosinate’s rapid herbicidal activity, which is similar to that of paraquat. Though the paraquat ban can be considered as a national strategy to lower suicide rates, the increase in suicide attempts with other poisons suggests that multilateral efforts are required for not only keeping suicidal agents away from people but also minimizing motives for suicide.

Studies were conducted to determine the effect of interference between tropic croton (Croton glandulosus) and cotton (Gossypium hirsutum) on plant growth and productivity. Tropic croton height was not affected by weed density, but cotton height decreased with increased weed density 10 wk after planting. Tropic croton biomass per plant was not affected by weed density, but total weed biomass per meter of crop row increased with weed density. Cotton lint yield decreased linearly 2 kg ha−1 with each gram increase in weed dry biomass per meter of row. Percent yield loss–density relationship was described by the rectangular hyperbola model. Estimated coefficients A (maximum yield loss) and I (yield loss per unit density as density approaches zero) were 129.6 ± 42.2 and 35.6 ± 8.0%, respectively, when asymptotic iterations were based on least sums of squares. When A was constrained to 100% yield loss, I was 42.5 ± 5.1%. Results indicated that tropic croton was less competitive with cotton than many weeds but represents an economic threat to cotton growers.

Multiple cases of ALS inhibitor-resistant weed biotypes are reported for many species, including wild mustard. The physiological extent and molecular basis of resistance to ALS inhibitors was compared in four biotypes of wild mustard from western Canada: a sulfonylurea (SU)-resistant (R) biotype from Manitoba detected in 1992; an SU (ethametsulfuron)-R biotype from Alberta detected in 1993 (metabolism-based resistance); an SU-R biotype from Manitoba detected in 2002; and a SU- and imidazolinone (IMI)-R biotype from Saskatchewan detected in 2002. Herbicide dose-response experiments confirmed that the two Manitoba biotypes were resistant to the SU herbicides ethametsulfuron and tribenuron : thifensulfuron mixture, whereas the Saskatchewan biotype was resistant to both SU herbicides and to imazethapyr, an IMI herbicide. Sequence analysis of the ALS gene detected target site mutations in three of the four R biotypes, with amino acid substitutions Pro197 (CCT) to Ser (TCT) [Domain A of the gene] in the two SU-R Manitoba biotypes and Trp574 (TGG) to Leu (TTG) [Domain B] in the Saskatchewan biotype. The Alberta SU-R biotype had the same ALS nucleotide and amino acid sequence as the susceptible population at these two positions. Two heterozygous individuals [Trp574 (Tt/gG)] were detected in the Saskatchewan biotype, and genetic segregation for nucleotide bases and resistance phenotype was consistent with single gene control. Nucleotide variation in neutral regions of the ALS gene varied with biotype, with no variation in the two Manitoba biotypes, two variants in the Saskatchewan biotype, and 16 neutral nucleotide polymorphisms (0.9%) in the Alberta biotype. The occurrence of at least three different ALS inhibitor-R biotypes in this important weed species is likely to impact negatively on the use of ALS inhibitors, such as the IMIs, and serves as a warning for strict implementation of herbicide rotations to prevent or delay the evolution and spread of such populations.

Using a modified in vivo nitrate reductase assay, all photosynthetic inhibitors tested were shown to effectively block light-dependent nitrite reduction in green leaf tissue. Nitrate reduction continued so that nitrite accumulated. Nitrite, vacuum infiltrated into leaf tissue, disappeared linearly with time when incubated in the light. Nitrite, vacuum infiltrated with a photosynthetic inhibitor, did not disappear but accumulated to even higher levels. The degree of inhibition of nitrite reduction was a function of herbicide concentration and time of incubation.

Organic agricultural systems increase the complexity of weed management, leading organic farmers to cite weeds as one of the greatest barriers to organic production. Integrated Weed Management (IWM) systems have been developed to address the ecological implications of weeds and weed management in cropping systems, but adoption is minimal. Organic agriculture offers a favorable context for application of IWM, as both approaches are motivated by concern for environmental quality and agricultural sustainability. However, adoption of IWM on organic farms is poorly understood due to limited data on weed management practices used, absence of an IWM adoption metric, and insufficient consideration given to the unique farming contexts within which weed management decisions are made. Therefore, this study aimed to (1) characterize organic weed management systems; (2) identify motivations for, and barriers to, selection of weed management practices; and (3) generate guiding principles for effective targeting of weed management outreach. We surveyed Midwestern organic growers to determine how specified psychosocial, demographic, and farm structure factors influence selection of weed management practices. Cluster analysis of the data detected three disparate, yet scaled, approaches to organic weed management. Clusters were distinguished by perspective regarding weeds and the number of weed management practices used. Categorization of individual farms within the identified approaches was influenced by primary farm products as well as farmer education, years farming, and information-seeking behavior. The proposed conceptual model allows weed management educators to target outreach for enhanced compatibility of farming contexts and weed management technologies.

Some species of the genus Echinochloa are troublesome weeds in rice fields. The taxonomy of this genus leads to confusion in many cases due to its great morphological diversity. Because of the differential sensitivity to the herbicide quinclorac shown by Echinochloa spp., it was necessary to assess the botanical and molecular characterization of this weed. Echinochloa colonum, E. oryzoides, and E. oryzicola were very susceptible to quinclorac treatment; by contrast, E. crus-galli and E. hispidula showed some degree of natural tolerance. Physiological and molecular results agreed with the botanical classification of the genus Echinochloa in Flora Europea. The importance of these results is due to yield losses produced by the infestation of Echinochloa and the need for a strategy for Echinochloa management depending on the distribution of the Echinochloa species.

The use of electrolytic conductivity as a measure of cell membrane disruption was tested on buckwheat (Fagopyrum esculentum Moench. cv. ‘Tokyo’) plants which had been sprayed with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. All treatments which resulted in tissue damage caused significant increases to the solutions where the discs were floated for measurement. The highest conductivity measurement (most membrane disruption) was obtained from paraquat. The highest concentration for each herbicide gave higher conductivity measurements than lower concentrations. A difference in the pattern of conductivity change induced by the two chemicals implies a different mode of action for each.

Black nightshade (Solanum nigrum L.) planted in the field at monthly intervals from March through October at Shafter, California, began to emerge in March when soil temperatures at a depth of 5 cm reached 17C. With the exception of August plantings, emergence remained constant for all plantings. Average weights of plants of May, June, and July plantings at 12 weeks were 60% greater than March and August plantings and 30% greater than April plantings. Plants began flowering 7 to 9 weeks after planting for the March through June plantings and 5 to 6 weeks after planting for the July through September plantings. Killing frosts in November prevented black nightshade planted in October from flowering. Black nightshade planted in April through July produced an average of 1000 berries/plant, which was 40 to 95% greater than those planted in March, August, and September. Seed production ranged from 20000 to 30000 seed/plant for the May through July plantings, and 600 to 8000 seed/plant for the March, April, August, and September plantings.

Seedlings of barnyardgrass, green foxtail, and yellow foxtail emerged from seeds as deep as 5 inches in Sagemoor fine sandy loam. The number of emerged seedlings from depths of 4 to 5 inches decreased in the order of decreasing seed weights; yellow foxtail, barnyardgrass, green foxtail. Few seedlings developed in the field from seeds on the soil surface. Seedling emergence in spring or greenhouse seedings was greatest from the most shallow depths (½ or 1 inch) and decreased regularly as depth of planting increased. An autumn seeding gave maximum emergence at 1½ inches, possibly because some seeds sown shallower may have germinated in short warm periods but were killed by subsequent freezing.

Annual bluegrass control was reduced following 7 yr of continuous fall application of dinitroaniline (DNA) herbicides. Annual bluegrass control was < 40% on two fairways in year eight following prodiamine applied at 1.1 kg ai ha−1. In dose–response studies conducted in growth chambers, this annual bluegrass population exhibited 105-fold resistance in shoot growth to prodiamine compared with a known susceptible population. A 6.4-fold resistance to prodiamine was found when comparing annual bluegrass root growth to the known susceptible biotype. Spring-applied oxadiazon did not affect shoot or root growth between annual bluegrass biotypes. Equivalent levels of control were attained with pronamide. The presence of DNA-resistant annual bluegrass, in addition to previously confirmed triazine-resistant biotypes on North Carolina golf courses, indicates a need for resistance management strategies to be integrated into golf turf management practices.

Leaf-cover area is a widely required plant development parameter for predictive models of weed growth and competition. Its assessment is performed either manually, which is labor intensive, or via visual inspection, which provides biased results. In contrast, digital image processing enables a high level of automation, thereby offering an attractive means for estimating vegetative leaf-cover area. Nonetheless, image-driven analysis is greatly affected by illumination conditions and camera position at the time of imaging and therefore may introduce bias into the analysis. Addressing both of these factors, this paper proposes an image-based model for leaf-cover area and biomass measurements. The proposed model transforms color images into an illumination-invariant representation, thus facilitating accurate leaf-cover detection under varying light conditions. To eliminate the need for fixed camera position, images are transformed into an object–space reference frame, enabling measurement in absolute metric units. Application of the proposed model shows stability in leaf-cover detection and measurement irrespective of camera position and external illumination conditions. When tested on purple nutsedge, one of the world's most troublesome weeds, a linear relation between measured leaf-cover area and plant biomass was obtained regardless of plant developmental stage. Data on the expansion of purple nutsedge leaf-cover area is essential for modeling its spatial growth. The proposed model offers the possibility of acquiring reliable and accurate biological data from digital images without extensive photogrammetric or image-processing expertise.

Goosegrass is a problematic summer annual weed in cotton, soybean, and corn production in the southern United States. Glyphosate is labeled for POST control of goosegrass in glyphosate-resistant (GR) cotton, soybean, and corn production. A population of goosegrass in west Tennessee not controlled by glyphosate was examined in greenhouse and laboratory studies. At 21 days after treatment (DAT), a glyphosate-susceptible (SS) biotype was controlled > 90% with glyphosate at rates greater than 210 g ae ha−1. Comparatively, the GR biotype was only controlled 12% at 210 g ae ha−1. Using goosegrass control data, I50 values for GR and SS biotypes were 868 and 117 g ae ha−1, susceptibility, resulting in a resistance factor (RF) of 7.4. Treatment with glyphosate at 210 g ae ha−1 reduced fresh weight biomass of the SS biotype to 5 g per pot compared to 36 g for the GR biotype. A total of 3,360 g ae ha−1 glyphosate was required to reduce fresh weights of the GR biotype to ∼5 g per pot. Using fresh and dry weight biomass data, I50 values for the GR biotype were 3 to 10 times greater than the SS biotype. On each date from 1 to 6 DAT the SS biotype accumulated higher concentrations of shikimate than the GR biotype. Future research should evaluate strategies for managing GR goosegrass with alternative modes of action. To prevent the spread of resistance, additional research evaluating programs for managing glyphosate-susceptible goosegrass in GR crops is also warranted.

Diclofop-resistant Italian ryegrass is a major weed problem in wheat production. This study aimed to determine the resistance pattern of diclofop-resistant Italian ryegrass accessions from the southern United States to the latest commercialized herbicides for wheat production, pinoxaden and mesosulfuron, and to other acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibitors. Twenty-nine of 36 accessions were resistant to the commercial dose of diclofop. The majority (80%) of diclofop-resistant accessions were also resistant to clodinafop. Of 25 diclofop-resistant accessions, 5 were resistant to pinoxaden. All accessions tested were susceptible to the commercial dose of clethodim and sethoxydim. The cross-resistance pattern of diclofop-resistant Italian ryegrass to other ACCase inhibitors was 20% for pinoxaden and none with clethodim or sethoxydim. One accession was resistant to mesosulfuron but not to diclofop. This mesosulfuron-resistant accession was cross-resistant to sulfometuron but not to imazamox. All diclofop-resistant accessions tested were susceptible to ALS inhibitors, mesosulfuron, sulfometuron, and imazamox. Therefore, diclofop-resistant Italian ryegrass in Arkansas can be controlled with imazamox (in Clearfield wheat) and can mostly be controlled with mesosulfuron and pinoxaden. It could also be controlled by other selective grass herbicides in broadleaf crops.

Johnsongrass [Sorghum halepense (L.) Pers.] regrowth was used as an index for penetration and translocation of dalapon (2,2-dichloropropionic acid) with and without adjuvants under different environmental conditions. Johnsongrass control with dalapon at 1.12 kg/ha without surfactant decreased as air temperature increased from 16 to 27 to 38 C. Plants at 16 and 27 C with 100% relative humidity (RH) were more susceptible to dalapon without surfactant than were plants at 35% RH. The presence of 1% surfactant in dalapon solutions increased johnsongrass control above that of dalapon alone at 27 and 38 C regardless of RH. Adding 1% surfactant and maintaining plants at 100% RH and 38 C resulted in significantly less johnsongrass control than that at 35% RH and 38 C. The addition of 0.1 M KH2PO4 to mixtures of dalapon + surfactant restored effectiveness at 100% RH and 38 C. Dalapon applied without surfactant was more injurious to johnsongrass grown with 40% soil moisture than with 25% soil moisture regardless of air temperature or RH. When plants were maintained at 27 or 38 C with 25% soil moisture, 0.1 M KH2PO4 + surfactant was more beneficial than surfactant alone in increasing dalapon toxicity to johnsongrass. At 40% soil moisture, johnsongrass control with dalapon + 1 % surfactant was not improved with the addition of KH2PO4 regardless of air temperature.

The objective of this study was to investigate the resistance level of Japanese foxtail to haloxyfop, an acetyl coenzyme A carboxylase (ACCase; EC 6.4.1.2)–inhibiting herbicide. Eleven biotypes were collected from oilseed rape fields in different areas in Jiangsu and Anhui provinces where haloxyfop had been continuously applied for various periods. Biotypes were assessed by two different methods, a seed bioassay and whole-plant assay, to identify the most resistant and susceptible biotypes for further studies on the activity of the target enzyme ACCase. A good correlation was obtained between the two different bioassay methods. The Jurong and Chuzhou biotypes were the most resistant and susceptible biotypes, respectively, whereas the other nine biotypes showed variable and relatively low degrees of haloxyfop resistance. Furthermore, target-site enzyme sensitivity results confirmed that the Jurong biotype was resistant to haloxyfop with a concentration of herbicide causing 50% inhibition of ACCase activity (IC50) of 9.19 µM, whereas the IC50 of the susceptible biotype (Chuzhou) was 0.76 µM, giving a resistance index of 12.

Studies were conducted to determine the extent of full and partitioned interference of two nutsedge species with tomato. For full interference, the crop and the weed were transplanted in the same container. For belowground interference, tomato and either weed species were grown in the same container, but the canopies were separated. For aboveground interference, tomato and nutsedges were grown in separate containers placed adjacently, whereas for the no-interference treatment, tomato and nutsedge plants were grown in individual containers. Full interference by yellow nutsedge was more detrimental to tomato shoot dry weight accumulation (34% reduction) than was full interference by purple nutsedge (28% reduction). Belowground interference by purple nutsedge reduced tomato shoot dry weight (18%) more than did aboveground interference (9%). Yellow nutsedge interference above- or belowground reduced tomato shoot dry weight to a similar extent (19%). The belowground interference of both nutsedges with tomato resulted in deficient concentrations of nitrate in the sap of tomato (> 18% reduction). The growth of purple nutsedge was influenced more strongly by tomato shading than by belowground interference from the crop, whereas yellow nutsedge growth was equally affected by tomato above- and belowground. According to these results, shoot dry weight accumulation in tomato was affected to the same extent by belowground interference from purple and yellow nutsedge, and the higher effect of full interference by yellow nutsedge may be attributed to increased aboveground competition between tomato and yellow nutsedge.

Results of studies with microorganisms suggest that 5-bromo-3-isopropyl-6-methyluracil (isocil) does not interfere appreciably with pyrimidine metabolism. Instead the uracil herbicides studied appear to act in higher plants as inhibitors of photosynthesis. Strong inhibition of the Hill reaction of isolated chloroplasts by substituted uracils was noted (I50 of 2.7 × 10−6 M for isocil). Exogenously supplied carbohydrates partially nullified toxicity symptoms in intact barley plants growing in the presence of inhibitory concentrations of isocil.

Field experiments were conducted in 2016 and 2017 in Champaign County, IL, to study a waterhemp [Amaranthus tuberculatus (Moq.) J. D. Sauer] population (CHR) resistant to 2,4-D and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-, photosystem II–, acetolactate synthase (ALS)-, and protoporphyrinogen oxidase–inhibiting herbicides. Two field experiments were designed to investigate the efficacy of very-long-chain fatty-acid (VLCFA)-inhibiting herbicides, including a comparison of active ingredients at labeled use rates and a rate titration experiment. Amaranthus tuberculatus density and control were evaluated at 28 and 42 d after treatment (DAT). Nonencapsulated acetochlor, alachlor, and pyroxasulfone provided the greatest PRE control of CHR (56% to 75%) at 28 DAT, while metolachlor, S-metolachlor, dimethenamid-P, and encapsulated acetochlor provided less than 27% control. In the rate titration study, nonencapsulated acetochlor controlled CHR more than equivalent field use rates of S-metolachlor. Subsequent dose–response experiments with acetochlor, S-metolachlor, dimethenamid-P, and pyroxasulfone in the greenhouse included three multiple herbicide–resistant (MHR) A. tuberculatus populations: CHR-M6 (progeny generated from CHR), MCR-NH40 (progeny generated from Mclean County, IL), and ACR (Adams County, IL), in comparison with a sensitive population (WUS). Both CHR-M6 and MCR-NH40 are MHR to atrazine and HPPD, and ALS inhibitors and demonstrated higher survival rates (LD50) to S-metolachlor, acetochlor, dimethenamid-P, or pyroxasulfone than ACR (atrazine resistant but HPPD-inhibitor sensitive) and WUS. Based on biomass reduction (GR50), resistant to sensitive (R:S) ratios between CHR-M6 and WUS were 7.5, 6.1, 5.5, and 2.9 for S-metolachlor, acetochlor, dimethenamid-P, and pyroxasulfone, respectively. Values were greater for MCR-NH40 than CHR-M6, and ACR was the most sensitive to all VLCFA inhibitors tested. Complete control of all populations was achieved at or below a field use rate of acetochlor. In summary, field studies demonstrated CHR is not controlled by several VLCFA-inhibiting herbicides. Greenhouse dose–response experiments corroborated field results and generated R:S ratios (LD50) ranging from 4.5 to 64 for CHR-M6 and MCR-NH40 among the four VLCFA-inhibiting herbicides evaluated.

Timing of weed emergence and seed persistence in the soil influence the ability to implement timely and effective control practices. Emergence patterns and seed persistence of kochia populations were monitored in 2010 and 2011 at sites in Kansas, Colorado, Wyoming, Nebraska, and South Dakota. Weekly observations of emergence were initiated in March and continued until no new emergence occurred. Seed was harvested from each site, placed into 100-seed mesh packets, and buried at depths of 0, 2.5, and 10 cm in fall of 2010 and 2011. Packets were exhumed at 6-mo intervals over 2 yr. Viability of exhumed seeds was evaluated. Nonlinear mixed-effects Weibull models were fit to cumulative emergence (%) across growing degree days (GDD) and to viable seed (%) across burial time to describe their fixed and random effects across site-years. Final emergence densities varied among site-years and ranged from as few as 4 to almost 380,000 seedlings m−2. Across 11 site-years in Kansas, cumulative GDD needed for 10% emergence were 168, while across 6 site-years in Wyoming and Nebraska, only 90 GDD were needed; on the calendar, this date shifted from early to late March. The majority (>95%) of kochia seed did not persist for more than 2 yr. Remaining seed viability was generally >80% when seeds were exhumed within 6 mo after burial in March, and declined to <5% by October of the first year after burial. Burial did not appear to increase or decrease seed viability over time but placed seed in a position from which seedling emergence would not be possible. High seedling emergence that occurs very early in the spring emphasizes the need for fall or early spring PRE weed control such as tillage, herbicides, and cover crops, while continued emergence into midsummer emphasizes the need for extended periods of kochia management.

Weed control in organic onion production is often difficult and expensive, requiring numerous cultivations and extensive hand weeding. Onion safety and weed control with mustard seed meal (MSM) derived from Sinapis alba was evaluated in greenhouse and field trials. MSM applied at 110, 220, and 440 g m−2 severely injured onions and reduced onion stand by 25% or more when applied from planting to the one-leaf stage of onions in greenhouse trials. MSM derived from mustard cultivars ‘IdaGold’ and ‘AC Pennant’ reduced plant dry weight of redroot pigweed with an effective dose that provided 90% weed control (ED90) of 14.5 and 3.2 g m−2, respectively, in greenhouse trials, whereas the ED90 of MSM from a low-glucosinolate cultivar ‘00RN29D10’ was 128 g m−2, suggesting that glucosinolate content and ionic thiocyanate (SCN−) production contribute to phytotoxicity of MSM. In field trials, weed emergence, onion injury, and onion yield were recorded following single or three sequential applications of MSM from 1.1 to 4.5 MT ha−1 beginning at the two-leaf stage of onions in 2008, 2009, and 2010. By 8 wk after treatment (WAT), onion injury following MSM sequential applications was 10% or less in all 3 yr. Combined over 2008 and 2009, 48 and 68% fewer weeds emerged 3 WAT with MSM at 2.2 and 4.5 MT ha−1, respectively. In 2010, MSM at 2.2 and 4.5 MT ha−1 reduced the number of weeds emerged 4 WAT by 91 and 76%, respectively. MSM treatment did not significantly affect onion yield or size in 2008 and 2009, but in 2010 onion total yield was reduced by 29% by three sequential applications of MSM at 2.2 MT ha−1. MSM has potential to be used as a weed-suppressive amendment in organic production systems, but the risk of crop injury is substantial.