The chlorinated phenoxyalkylcarboxylic acids are extremely valuable in affording a solution to many weed problems. On the other hand, the use of such herbicides may create problems since many crop or ornamental plants which are very sensitive to the phenoxy herbicides may be growing in close proximity to crops or areas in which treatments with such herbicides seems desirable. In the South, cotton may be planted adjacent to crops such as rice, sugarcane or corn or in areas bordering woods, highways or railways. On such areas, the application of phenoxy herbicides may solve the problem of weed control; however, they may create a new problem by causing injury to cotton.

The logarithmic, or variable-dosage, sprayer described by Pfeiffer, Brunskill, and Hartley (4) for use in experimental field plot studies appears to offer a means of materially reducing the time and space required to conduct field evaluations of herbicides in horticultural crops. The experiments described herein were conducted to determine the conditions necessary for the successful use of the sprayer in evaluations of this type.

In a preliminary experiment young oat plants which grew in culture solution containing 0.05 ppmw of 2–chloro–4,6–bis (ethylamino)–s–triazine (simazine) for 60 hours were injured but not killed. The objective of the experiment reported here was to study the relations among (a) the concentration of simazine in the culture solution, (b) the concentration of simazine in the oat plant, and (c) the reduction in weight of plants following treatment.

The table briefly summarizes research findings involving the translocation of organic herbicides and certain selected growth regulators in higher plants. Gibberellic acid, indoleacetic acid, naphthaleneacetic acid and other “on-herbicide” growth regulators are for the most part not listed except when used in experiments with the more generally accepted herbicides. For tabular information on translocation of auxins and other growth substances, the reader is referred to the Handbook of Biological Data, mentioned later. Information in the table is based on techniques which primarily utilize foliar application and for the most part does not include application via root system, injection, or bark application. As a consequence, most substances listed may be assumed to be transported predominantly in the phloem, but in numerous cases the compounds also move into the xylem.

The wild oat developed along with man's early agricultural activities, adapted to his artificial environments and accompanied him in his migration, to become a major problem in grain growing areas of Europe, Asia, Australia and North America. Manson's survey revealed approximately 61 million acres of cultivated land infested with wild oats in western Canada. At the present time, the weed infests most soils in the black and transition black-grey soil zones and medium- to fine-textured soils in the dark brown soil zone. In the brown soil zone, wild oats are usually confined to fine-textured soils or to depressional areas. “Moderate” infestations reduced barley yields by 15.5 percent and flax yields by 79.4 percent during a four-year period. Severe infestations may occasionally produce as many as 900 to 1,000 plants per sq m, in which case they are “turned under” since competition from such an infestation makes crop production impractical.

Greenhouse evaluation of 30 s-triazine compounds indicated that several of them were suitable for pre-emergence weed control in Lee soybeans. The s-triazines least toxic to soybeans generally contained either methoxy or methylmercapto substituents but most of these were highly toxic to crabgrass (Digitaria sanguinalis (L.) Scop.). Soybeans were more tolerant to ethylamino substituted s-triazines than to isopropylamino derivatives. Chloro derivatives were generally toxic to soybeans. Proplyamino, allylamino, methoxypropylamino, ethoxy, trichloromethyl, and amido substitutions had much less effect on soybean selectivity than those previously mentioned.

Field evaluation of several s-triazines, preemergence, confirmed the tolerance of soybeans to 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne), 2-ethylamino-4-isopropylamino-6-methylmercapto-s-triazine (ametryne), and 2-isopropylamino-4-methylamino-6-methylmercapto-s-triazine (norametryne) at rates that provided adequate weed control.

Treatment interactions affecting endemic populations of annual grass and broadleaf weeds, corn rootworm larvae (CRW), corn earworm (CEW), European corn borer (ECB), and common rust in sweet corn were investigated in three field studies near Arlington, WI, in 1996 and 1997. In all environments, weed biomass was affected only by the weed control treatments with cultivation resulting in the highest weed biomass. Corn root damage was affected only by the CRW insecticide treatments in the early- and late-planted environments in 1997 (E97 and L97). Both weed control and ear insect (CEW and ECB) control treatments affected corn ear damage by CEW and ECB. In E97 and L97, more insect ear damage occurred in plots with 1× herbicide treatments than in cultivation treatments. In L97, the ear insect treatment decreased ear damage 55% compared to untreated plots. The interaction between ear insect and weed control treatments affected the number of CEW found per 10 ears in L97. The interaction between hybrid rust and weed control treatments influenced common rust severity in all environments. A hybrid rust by CRW by ear insect treatment interaction also affected common rust severity in E97 and L97. ‘Jubilee’ hybrid (rust-susceptible) corn treated with both insecticides had greater common rust severity than nontreated Jubilee corn. Sweet corn yield was affected most by weed control in all environments, with the lowest yields occurring in cultivated plots. Sweet corn yield did not differ between the 1× and ⅓× herbicide treatments in all environments. The interaction among hybrid rust by CRW by ear insect treatments also affected yield in E97 and L97. An important component of this interaction was the CRW treatment, as sweet corn yield was higher in treated than nontreated plots. The interactions in this study indicate that the best chances for developing comprehensive thresholds for sweet corn pests in the Midwest are for CEW, ECB, and common rust.

Germinable seeds were non-existent below 4 inches in the undisturbed soils used for cranberry bed development. Seeds were found at greater depths in manipulated soils. The seed in the vines used for planting was a major factor in the infestation of a properly scalped bed. Movement of seeds in water caused an infestation of a weed-free bed. The highest movement of seeds per acre-inch of water flow occurred in September, next highest in October and third highest in April. A relatively weed-free planting was maintained through one season by fumigating the soil for seed eradication, erecting a fine mesh screen exclosure to prevent weed invasion by flood water, and washing the vines prior to planting.

Foliar and soil herbicidal treatments were made on creosotebush (Larrea tridentata (DC.) Cov.), tarbush Flourensia cernua DC.), and whitethorn (Acacia constricta Benth.) near Tombstone, Arizona, from 1957 to 1964. All herbicides were most effective when applied approximately 30 days after initiation of the summer rainy season. The herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were about equal in effectiveness, but the relative susceptibility of the individual shrubs to the herbicides varied with treatment conditions. The acetic form of 2,4,5-T generally was more effective than the propionic; propylene glycol butyl ether, iso-octyl, and tetrahydrofurfuryl esters more effective than pentyl. Foliar applications of 4-amino-3,5,6-trichloropicolinic acid (picloram) were most effective on whitethorn, intermediate on creosotebush, and least effective on tarbush. The most effective soil herbicidal treatments were 3-phenyl-1,1-dimethylurea (fenuron) and 3-(p-chlorophenyl)-1,1-dimethylurea (monuron). In general, effective control of dominant Chihuahuan Desert shrubs required 2 to 4 lb/A of 2,4-D or 2,4,5-T, 14 to 1 lb/A of picloram, or 2 lb/A of fenuron or monuron.

One of the main limiting factors for high yields of flooded rice (Oryza sativa L.) is the presence of weeds, especially herbicide-resistant weeds. The aim of this study was to evaluate the association of weed management practices adopted by flooded rice farmers in the state of Rio Grande do Sul (RS), Brazil, with grain yield. For this purpose, 324 interview surveys were administered to farmers who supplied information about the history of weed management and yields. The answers to the survey indicated that weedy rice (Oryza sativa L.) and Echinochloa spp. were the most important weeds that occurred in flooded rice areas in RS. Advanced growth stage of weeds and inadequate environmental conditions such as air temperature and relative humidity were listed as the main reasons for low weed control efficacy. Farmers achieved greater rice yields when they adopted rice–soybean [Glycine max (L.) Merr.] (9,140 kg ha−1 average yield) and herbicide site of action rotations (8,801 kg ha−1 average yield) along with tank mixes (8,580 kg ha−1 average yield) as specific management practices for resistant weed control. The use of glyphosate with residual herbicides in a tank mix in the rice spiking stage is the main factor related to greater yields. The postemergence applications and their relationship to delaying of flooding in rice is a factor that reduces rice yield when no spiking glyphosate application was made. Identification of the most important weeds in terms of occurrence and knowledge of the main agronomic practices adopted by farmers are essential so that recommendations for integrated management practices can be adopted in an increasingly accurate and sustainable manner in flooded rice areas in southern Brazil.

Previous research has shown that strip-tillage (ST) systems conserve soil, reduce production costs, and save time for growers compared with intensive-tillage systems. In contrast to these well-documented benefits, we have limited information on weed community dynamics and management risks in ST corn (Zea mays L.) production systems in the northern Corn Belt. Therefore, we conducted research in 2015 and 2016 to characterize weed community composition, emergence patterns, and aboveground productivity in an ST corn/no-tillage (NT) soybean [Glycine max (L.) Merr.] rotation that was established in 2007 compared with a long-term intensive-tillage chisel-plow (CP) continuous-corn system. Fifteen or more weed species were identified in nontreated quadrats in each cropping system in each year. Common lambsquarters (Chenopodium album L.) was the most abundant weed species across systems and years. Chenopodium album densities were similar between CP and ST corn phases and were approximately 2-fold greater compared with the NT soybean phase. Other abundant weed species occurred at much lower densities than C. album. In each year, cumulative emergence of nontreated weed communities was described best by a logistic function in each cropping system. Maximum weed community emergence was greater in CP corn than ST corn phases in 2015, but did not differ in 2016. In the ST corn phase, most (about 75%) weed community emergence occurred in the in-row (tilled) zone compared with the between-row (nondisturbed) zone. Total late-season weed shoot biomass did not differ between nontreated CP and ST corn phases in either year, with C. album accounting for >85% of total weed biomass in these phases. These results suggest that weed community composition, total emergence, and productivity were similar between CP and ST corn phases after 10 yr. Our findings, coupled with previous research that showed favorable agronomic performance and greater soil conservation associated with the long-term ST corn/NT soybean system, suggest that production risks are no greater than a CP corn system, while processes that underpin ecosystem services are enhanced. These results provide strong evidence to support grower adoption of ST practices as an alternative to intensive tillage.

Weeds are often spatially aggregated in maize fields, and the level of aggregation varies across and within fields. Several annual weed species are present in maize fields before postemergence herbicide application, and herbicides applied will control several species at a time. The goal of this study was to assess the spatial distribution of multispecies weed infestation in maize fields. Ground-based imagery was used to map weed infestations in rain-fed maize fields. Image segmentation was used to extract weed cover information from geocoded images, and an expert-based threshold of 0.102% weed cover was used to generate maps of weed presence/absence. From 19 site-years, 13 (68%) demonstrated a random spatial distribution, whereas six site-years demonstrated an aggregated spatial pattern of either monocotyledons, dicotyledons, or both groups. The results of this study indicated that monocotyledonous and dicotyledonous weed groups were not spatially segregated, but discriminating these weed groups slightly increased the chances of detecting an aggregated pattern. It was concluded that weeds were not always spatially aggregated in maize fields. These findings emphasize the need for techniques allowing the assessment of weed aggregation prior to conducting site-specific weed management.

A goosegrass [Eleusine indica (L.) Gaertn.] population uncontrolled by paraquat (R) in a vegetable production field in St. Clair County, AL, was collected in summer 2019. Research was conducted to assess the level of resistance of the suspected resistant population compared with three populations with no suspected paraquat resistance (S1, S2, and S3). Visual injury at all rating dates and biomass reduction at 28 d after treatment (DAT) of S populations occurred exponentially to increasing paraquat rates. S biotypes were injured more than R at 3 DAT, with biomass recovery at 28 DAT only occurring at rates <0.28 kg ha−1. Plant death or biomass reduction did not occur for any rate at any date for R. Paraquat rates that induced 50% or 90% injury or reduced biomass 50% or 90% compared with the non-treated (I50 or I90, respectively) ranged from 10 to 124 times higher I50 for R compared with S and 54 to 116 times higher I90 for R compared with S biotypes. These data confirm a paraquat-resistant E. indica biotype in Alabama, providing additional germplasm for study of resistance to photosystem I electron-diverting (PSI-ED) resistance mechanisms.

In the transition zone, turfgrass managers generally utilize the dormancy period of warm-season turfgrass to apply herbicides for managing winter annual weeds. Although this weed control strategy is common in bermudagrass [Cynodon dactylon (L.) Pers.], it has been less adopted in zoysiagrass (Zoysia spp.) due to variable turfgrass injury during post-dormancy transition. Previous research reported that air temperature could affect weed control and crop safety from herbicides. Growth-chamber studies were conducted to evaluate zoysiagrass response to glyphosate and glufosinate as influenced by three different temperature regimes during and after treatment. A field research study was conducted at four site-years to assess the influence of variable heat-unit accumulation on zoysiagrass response to seven herbicides. In the growth-chamber study, glufosinate injured zoysiagrass more than glyphosate and reduced time to reach 50% green cover reduction, regardless of the rate, when incubated for 7 d under different temperature levels. When green zoysiagrass sprigs were incubated for 7 d at 10 C, the rate of green cover reduction was slowed for both herbicides; however, green cover was rapidly reduced under 27 C. After treated zoysiagrass plugs having 5% green cover were incubated at 10 C for 14 d, glyphosate-treated plugs reached 50% green cover in 22 d, similar to nontreated plugs but less than the 70 d required for glufosinate-treated plugs. Zoysiagrass response to glyphosate was temperature dependent, but glufosinate injured zoysiagrass unacceptably regardless of temperature regime. Diquat, flumioxazin, glufosinate, and metsulfuron + rimsulfuron injured zoysiagrass at 200 or 300 growing-degree days at base 5 C (GDD5C) application timings, but foramsulfuron and oxadiazon did not injure zoysiagrass regardless of GDD5C. The relationship of leaf density to green turf cover is dependent on zoysiagrass mowing height, and both metrics are reduced by injurious herbicides. Research indicates that glufosinate injures zoysiagrass more than glyphosate, and the speed and magnitude of herbicide injury generally increase with temperature.

Glufosinate is an effective postemergence herbicide, and overreliance on this herbicide for weed control is likely to increase and select for glufosinate-resistant weeds. Common assays to confirm herbicide resistance are dose–response and molecular sequencing techniques; both can require significant time, labor, unique technical equipment, and a specialized skillset to perform. As an alternative, we propose an image-based approach that uses a relatively inexpensive multispectral sensor designed for unmanned aerial vehicles to measure and quantify surface reflectance from glufosinate-treated leaf disks. Leaf disks were excised from a glufosinate-resistant and glufosinate-susceptible corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] varieties and placed into a 24-well plate containing eight different concentrations (0 to 10 mM) of glufosinate for 48 h. Multispectral images were collected after the 48-h incubation period across five discrete wave bands: blue (475 to 507 nm), green (560 to 587 nm), red (668to 682 nm), red edge (717 to 729 nm), and near infrared (842 to 899 nm). The green leaf index (GLI; a metric to measure chlorophyll content) was utilized to determine relationships between measured reflectance from the tested wave bands from the treated leaf disks and the glufosinate concentration. Clear differences of spectral reflectance were observed between the corn, cotton, and soybean leaf disks of the glufosinate-resistant and glufosinate-susceptible varieties at the 10 mM concentration for select wave bands and GLI. Leaf disks from two additional glufosinate-resistant and glufosinate-susceptible varieties of each crop were subjected to a similar assay with two concentrations: 0 and 10 mM. No differences of spectral reflectance were observed from the corn and soybean varieties in all wave bands and the GLI. The leaf disks of the glufosinate-resistant and glufosinate-susceptible cotton varieties were spectrally distinct in the green, blue, and red-edge wave bands. The results provide a basis for rapidly detecting glufosinate-resistant plants via spectral reflectance. Future research will need to determine the glufosinate concentrations, useful wave bands, and susceptible/resistant thresholds for weeds that evolve resistance.

Flumioxazin has recently (2010) been registered for aquatic use for control of hydrilla and other noxious invasive aquatic plant species. Due to the rapid degradation of flumioxazin, especially in high pH water, some hydrilla research trials have produced less than desirable results with rapid plant regrowth. Therefore, laboratory experiments were conducted to evaluate the influence of pH on flumioxazin's effect on photosynthesis. Flumioxazin applied at concentrations ≥ 200 µg ai L−1 in high (9.0) pH water and ≥ 100 µg L−1 in low (6.0) pH water required 68 to 123 h to reduce photosynthesis by 50% (ET50). The effect of 400 µg L−1 flumioxazin on photosynthesis of apical hydrilla tips was also compared at low (20 µmol m−2 s−1), medium (170 µmol m−2 s−1), and high (400 µmol m−2 s−1) light levels at pH 9.0. Low light–treated tips were still photosynthetic at approximately 73% of the nontreated control plants 168 h after treatment. Low light–treated hydrilla required an estimated 303 h to achieve a 50% reduction in photosynthesis, while high light plants only required 99 h. Chlorophyll content of hydrilla was reduced as flumioxazin concentration was increased from 100 to 1,600 µg L−1. These data indicate that flumioxazin activity on hydrilla photosynthesis is influenced by herbicide concentration, water pH, and light intensity.

The abundance of weedy rice (Oryza sativa L.) in the soil seedbank was estimated in 2011 in Italian rice (Oryza sativa L.) fields with different histories of imidazolinone-resistant Clearfield® rice varieties (CL), non-Clearfield® varieties (NCL), and planting methods. A model was used to predict weedy rice seedbank dynamics over time under different control strategies. Soil samples were taken from 50 rice fields cultivated with CL varieties consecutively for 0, 1, 2, or 3 yr, and weedy rice seedbank data were used in a model considering eight scenarios: (A) rice monoculture with CL and NCL varieties in alternate years; (B) 2 yr of CL, followed by 1 yr with NCL; (C) 3 yr of CL followed by 1 yr of NCL; (D) rice monoculture with only CL; (E) rice monoculture with only NCL; (F) 2 yr of CL followed by 1 yr of rotation with another crop (CR), and then by an additional year with NCL; (G) 1 yr of CR followed by 2 yr of CL, and then by 1 yr of NCL; (H) 2 yr of CR followed by 2 yr of CL. The weedy rice seedbank exceeded 1,000 seeds m−2 in the surveyed fields with no significant differences between rice planting methods. Highest densities were found in fields cultivated for 1 yr with CL varieties. Simulations indicated that where CL varieties were used in rice monoculture, the susceptible weedy rice seedbank was gradually reduced, producing a depletion after 17, 13, 11, and 9 yr in scenarios A, B, C, and D, respectively. The weedy rice seedbank increased in NCL monoculture (E) and declined significantly in crop rotation scenarios (F, G, H). The simulations indicated that the introduction of crop rotation is crucial for obtaining a relatively fast reduction of weedy rice seedbank and delaying the evolution of herbicide-resistant populations.

Silvex, [2-(2,4,5-trichlorophenoxy)propionic acid], impregnated (20% ae) on clay granules, applied at a rate as low as 20 lb/A ae gave excellent control of well-rooted alligatorweed [Alternanthera philoxeroides (Mart.) Grieb] growing in less than 18 inches of water. The 2-ethylhexyl ester of silvex was more effective than the potassium salt. Silvex was not effective on floating-mat alligatorweed or in water over 18 inches deep.

In the past 10 years, phenomenal advances have been made in the regulation of plant growth by organic compounds including some now used as herbicides. The introduction of new chemicals, new weed-control techniques, such as pre-emergence treatment, and low gallonage application are among the most important recent developments in the use of organic compounds for weed control. It is estimated that losses caused by weeds on farms have now reached 5 billion dollars annually, and at present well over 30 million pounds alone of the phenoxy compounds, 2,4–dichloro, 2,4,5–trichloro-, and 2–methyl–4—chlorophenoxyacetic acids (2,4–D, 2,4,5–T and MCP) are being used for herbicidal purposes to help combat these losses (9). The most recent of these three compounds to appear on the market in this country as an active ingredient in herbicidal formulations is 2–methyl–4–chlorophenoxyacetic acid. The chief claim made for its use as a herbicide is that it is less injurious to certain grasses, cereal crops and legumes and more effective on certain weeds than 2,4–D. Fertig (4) concludes that MCP is slower in action and definitely less injurious to legumes, and Crafts (3) cites a number of investigators who have shown that MCP is more selective than 2,4–D, particularly where clover, flax and other crops having leaves hard to wet are concerned. High specificity of the compound is indicated by numerous reports in the literature; Robinson's (8), on the effectiveness of MCP in selective weed control, is one example. However, from recent recommendations (1), there appears to be some disagreement on the use of MCP, indicating need for further testing and experimentation with the compound and its derivatives. MCP as sold may contain up to 40% of impurities by weight, some of which, according to Hansen (6), may have toxic properties.

Field and greenhouse experiments evaluated interactions of soil-applied insecticides and imazaquin and imazethapyr on growth and development of cotton. Imazaquin and imazethapyr were applied PPI at 0 to 6 and 0 to 16 g ae ha−1, respectively, in the greenhouse (plus a no-insecticide control), and 0 to 72 g ha−1 in the field in combination with aldicarb, disulfoton, and phorate (without a no-insecticide control) applied in the seed furrow. Cotton shoot fresh weight in the greenhouse experiment decreased linearly as herbicide rates increased. Greater reductions in shoot fresh weight were noted with imazaquin than with imazethapyr. Compared with no insecticide, the methylcarbamate insecticide aldicarb and the organophosphate insecticides disulfoton and phorate did not affect cotton response to either herbicide. In the field, cotton injury increased while stand, yield, and maturity decreased as herbicide rates increased. Delayed maturity was due to a lower percentage of bolls produced on sympodia from main stem nodes four to nine. Imazaquin caused greater injury, greater reductions in stand, greater delays in maturity, and lower yields than did imazethapyr. Earlier maturity was noted with aldicarb-treated cotton. Compared with aldicarb, disulfoton and phorate did not alter cotton response to imazaquin or imazethapyr.