Optimum herbicide use is a key factor affecting the success of any integrated weed management strategy. The main objective of the current study was to implement a method based on spectrometer measurements for the in situ evaluation of herbicide efficacy and the detection of potentially herbicide-resistant weeds. Field trials were conducted in Greece between 2018 and 2020 in several durum wheat fields (Triticum durum Desf.). In all trials, the overall effect of herbicide application on the recorded Normalized Difference Vegetation Index (NDVI) values (at 1 and 2 wk after treatment [WAT]) was significant (P ≤ 0.001). For the majority of the surveyed fields, low NDVI values were recorded after 2,4-D application and a mixture of clopyralid + florasulam from 1 WAT, suggesting their increased efficacy. In several cases, the application of pyroxsulam + florasulam resulted in significant NDVI reductions at 2 WAT. As observed at the end of the growing seasons, the herbicides that reduced NDVI resulted in lower weed biomass. Strong correlations were observed between weed aboveground biomass and NDVI (2 WAT). In particular, R2 values were 0.8234 to 0.8649, 0.8453, 0.8595, 0.8149, and 0.8925 for the Aliartos, Thiva, Domokos, Larissa, and Orestiada fields, respectively. The overall effects of herbicide application on wheat grain yield were also significant (P ≤ 0.001). Pot experiments confirmed that the high NDVI values in some cases could be attributed to the presence of herbicide-resistant weeds. For instance, the resistance indices of two accessions of catchweed bedstraw (Galium aparine L.) to mesosulfuron-methyl + iodosulfuron-methyl-sodium ranged between 9.7 and 13.2, whereas one sterile oat [Avena sterilis L. ssp. ludoviciana (Durieu) Gillet & Magne] accession was 8.8 times more resistant to fenoxaprop-p-ethyl than a susceptible one. The present study is targeted at making a significant contribution toward establishing cause–effect relationships and presenting a useful tool for developing more effective weed management practices in more arable crops and under different soil and climatic conditions.

Nutsedge tubers germinated readily in soil treated with EPTC. However, growth was suppressed and emergence delayed, the delay depending on the rate of application. EPTC at 12 and 16 pounds per acre with 8 and 12 weeks exposure was very effective in killing nutsedge tubers as indicated by tuber germination and condition of tubers that did not germinate.

The granular formulation of EPTC killed highly significantly more nutsedge tubers than the emulsifiable formulation. Repeat applications of EPTC were significantly better in terms of tubers killed than single applications of the same rate of the herbicide. Thorough incorporation of EPTC to a depth of 5 inches of mechanical means was significantly more effective than incorporation by leaching.

Molecular assays are often implemented by weed scientists for detection of herbicide-resistant individuals; however, the utility of these assays can be limited if multiple mechanisms of evolved resistance exist. Waterhemp resistant to protoporphyrinogen oxidase (PPO)– inhibiting herbicides is conferred by a target-site mutation in PPX2L (a gene coding for PPO), resulting in the loss of a glycine at position 210 (ΔG210). This ΔG210 mutation of PPX2L is the only known mechanism responsible for PPO-inhibitor resistance (PPO-R) in waterhemp from five states (Illinois, Indiana, Iowa, Kansas, and Missouri); however, a limited number of populations have been tested, especially in Illinois. To verify the ubiquity of the ΔG210 in PPO-R waterhemp populations in Illinois, a previously published allele-specific PCR (asPCR) was used for the detection of the ΔG210 mutation to associate this mutation with phenotypic resistance in 94 Illinois waterhemp populations. The ΔG210 mutation was detected in all populations displaying phenotypic resistance to lactofen (220 g ai ha−1), indicating the deletion is likely the only mechanism of resistance. With evidence that the ΔG210 mutation dominates PPO-R waterhemp biotypes, molecular detection techniques have considerable utility. Unfortunately, the previously published asPCR is time consuming, very sensitive to PCR conditions, and requires additional steps to eliminate the possibility of false negatives. To overcome these limitations, a streamlined molecular method using the TaqMan® technique was developed, utilizing allele-specific, fluorescent probes for high-throughput, robust discrimination of each allele (resistant and susceptible) at the 210th amino acid position of PPX2L.

Herbicide mobility in soils was compared by three laboratory methods. The Rf values calculated from soil thin-layer chromatography correlated closely with those obtained from soil thick-layer chromatography (r = 0.96). Herbicides leached slightly further in slotted column chromatography as compared with the other methods. The working hours required to conduct a study with each method were in the increasing order of thin-layer, thick-layer, and column chromatography. However, the thin-layer method required the longest waiting times, followed by the column and thick-layer chromatography. If radioactive herbicides are not available or obtainable, the thick-layer chromatography is simplest and quickest. The relative mobility of herbicides studied was fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] > napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] > terbutryn [2-(tert-butyl-amino)-4-(ethylamino)-6-(methylthio)-s-triazine] > trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Less herbicide mobility was observed in heavier soil than in sandy soil.

Common waterhemp seeds were collected from two Missouri soybean fields where biotypes were not controlled by acifluorfen. Plants grown from these seeds were tested for resistance to the diphenyl ether herbicides acifluorfen and lactofen. Resistance to susceptibility (R/S) ratios, calculated as the ratio of the dose required to inhibit dry weight accumulation by 50% (GR50) in resistant plants to that for susceptible plants, were 9.5 and 11 for the Meadville biotype and 28 and 44 for the Bethel biotype exposed to acifluorfen and lactofen, respectively. Electrolyte leakage assays determined that light-induced lipid peroxidation by acifluorfen was greatest on a control population (Bradford), intermediate for the Meadville biotype, and lowest for the Bethel biotype. Levels of the photodynamic pigment protoporphyrin IX (Proto) accumulating in leaf disks exposed to acifluorfen were much lower in the resistant biotypes than in the susceptible wild type, and the level of Proto accumulation was significantly correlated to the degree of membrane disruption. Although the binding of acifluorfen to protoporphyrinogen oxidase in chloroplasts may have been altered in the resistant biotypes, the molecular and biochemical factors involved in the mechanism of resistance remain to be fully characterized. However, this study establishes that the physiological basis for the evolved resistance to diphenyl ethers in common waterhemp rests on the reduction of Proto accumulation.

Competition between wild buckwheat (Polygonum convolvulus L.) and flax (Linum usitatissimum L.) was studied in field experiments at various North Dakota locations and in a controlled environment chamber in relation to soil moisture, soil fertility, light, wild buckwheat density, flax seeding rate, and length of the competition period. In the field, flaxseed yield losses caused by competition were lowered by increasing the flax seeding rate and by early wild buckwheat removal. Fertilizer increased flaxseed yield losses at the high seeding rate and generally doubled wild buckwheat dry matter production. Flax dry matter was reduced by competition at the lower seeding rates. The field and controlled environment studies indicated that competition occurred mostly in the root zone. In the latter study, wild buckwheat was a better competitor than flax on a dry weight basis and the dry weights appeared to be related to nitrogen uptake. Wild buckwheat utilized water for growth more efficiently than flax.

Field studies were conducted at four locations in North Carolina in 1998 and 1999 to evaluate the use of the Herbicide Application Decision Support System (HADSS™) for weed management in nontransgenic, bromoxynil-resistant, and glyphosate-resistant cotton. Weed management systems included trifluralin preplant incorporated (PPI) plus fluometuron preemergence (PRE) or no soil-applied herbicides. Postemergence (POST) options included bromoxynil, glyphosate, or pyrithiobac early POST (EPOST) followed by (fb) MSMA plus prometryn late postemergence–directed (LAYBY) or herbicide recommendations given by HADSS. Glyphosate-resistant systems provided control equivalent to or better than control provided by bromoxynil-resistant and nontransgenic systems for smooth pigweed, Palmer amaranth, large crabgrass, goosegrass, ivyleaf morningglory, and fall panicum. Trifluralin PPI fb fluometuron PRE fb HADSS POST provided equivalent or higher levels of weed control and yield than trifluralin PPI fb fluometuron PRE fb bromoxynil, glyphosate, or pyrithiobac EPOST fb MSMA plus prometryn LAYBY. The trifluralin PPI fb fluometuron PRE fb HADSS POST systems controlled large crabgrass at Goldsboro and fall panicum better than HADSS POST-only systems in nontransgenic cotton. Cotton yield and net returns in the glyphosate-resistant systems were always equal to or higher than the nontransgenic and bromoxynil-resistant systems. Net returns were higher for the soil-applied fb HADSS POST treatments in 8 of 12 comparisons with HADSS POST systems without soil-applied herbicides. Early-season weed interference reduced cotton lint yields and net returns in POST-only systems.

Developing ecological principles applicable to invasive plant management is central to implementing sustainable strategies. We tested portions of a potentially useful successional-based management framework to further our understanding of the relationship between disturbance and colonization during revegetation of invasive weed-dominated grasslands. We hypothesized (1) intermediate wheatgrass density and biomass would be greatest at highest seeding rates, (2) control and tillage procedures that increase the availability of safe sites would increase wheatgrass abundance, and (3) spotted knapweed density and biomass would be lowest in treatments with highest wheatgrass density and biomass. Treatments included three disturbance levels: (1) no disturbance, (2) application of glyphosate, and (3) fall tillage. Colonization treatments were seeding intermediate wheatgrass of 0, 500, 2,500, and 12,500 seeds m−2. Treatments were factorially applied in a randomized complete-block design with four replications at each of two sites located in Montana. Density and biomass of intermediate wheatgrass and spotted knapweed were sampled in 1997 and 2001. At both sites, seeding 2,500 or 12,500 seed m−2 increased wheatgrass density over that of the nonseeded control in 1997. The highest seeding rate produced almost three times as many wheatgrass plants as 2,500 seeds m−2 that year. By 2001, only the highest seeding rate produced wheatgrass densities greater than that of the nonseeded control at Bozeman. Seeding rates higher than 500 seeds m−2 yielded greater wheatgrass biomass than the nonseeded control with or without either tillage or glyphosate. At the highest seeding rate, tillage or glyphosate doubled intermediate wheatgrass biomass compared with no disturbance. Spotted knapweed generally had lower biomass where intermediate wheatgrass density and biomass was highest. One approach to rehabilitation is to design disturbances that favor desired species and then use high seeding rates that overwhelm the pool of available propagules and occupy a high percentage of safe sites.

Knowledge of environmental factors influencing demography of weed species will improve understanding of current and future weed invasions. The objective of this study was to quantify regional-scale variation in vital rates of giant ragweed and common sunflower. To accomplish this objective, a common field experiment was conducted across seven sites between 2006 and 2008 throughout the north central U.S. maize belt. Demographic parameters of both weed species were measured in intra- and interspecific competitive environments, and environmental data were collected within site-years. Site was the strongest predictor of belowground vital rates (summer and winter seed survival and seedling recruitment), indicating sensitivity to local abiotic conditions. However, biotic factors influenced aboveground vital rates (seedling survival and fecundity). Partial least squares regression (PLSR) indicated that demography of both species was most strongly influenced by thermal time and precipitation. The first PLSR components, both characterized by thermal time, explained 63.2% and 77.0% of variation in the demography of giant ragweed and common sunflower, respectively; the second PLSR components, both characterized by precipitation, explained 18.3% and 8.5% of variation, respectively. The influence of temperature and precipitation is important in understanding the population dynamics and potential distribution of these species in response to climate change.

Three facets of the phytotoxicity of disodium methanearsonate (DSMA) incorporated in soils were studied in seven greenhouse experiments. Growth of cotton planted immediately after incorporation of DSMA in Bosket silt loam was reduced significantly by herbicide concentrations of 50 to 80 ppmw. Toxicity appeared to decrease with time, particularly during the first 16 weeks after incorporation. DSMA incorporated in Bosket silt loam at 120 ppmw did not inhibit significantly the growth of cotton planted 32 weeks later. The addition of phosphorus to two silt loam soils increased the toxicity of DSMA to cotton. The incorporation of 50 ppmw of DSMA in Bosket silt loam inhibited rice growth by 75%, soybeans by 39%, oats by 12%, corn and cotton by 10%, and wheat by 0%. Rice growth was not affected in Dubbs silt loam or Sharkey clay by DSMA at concentrations as high as 100 ppmw.

Carfentrazone-ethyl absorption, translocation, and metabolism was determined in Glycine max, Zea mays, and Abutilon theophrasti. Glycine max absorbed greater than 90% of applied carfentrazone-ethyl within 2 h after treatment (HAT) when nonionic surfactant (NIS) or crop oil concentrate (COC) were included in the treatment solution. The addition of 28% urea ammonium nitrate (UAN) did not improve carfentrazone-ethyl absorption in G. max, but in Z. mays and A. theophrasti, UAN combined with NIS or COC increased the rate of carfentrazone-ethyl absorption. Carfentrazone absorption in A. theophrasti 2 HAT was 70% when UAN was combined with NIS or COC compared to 40% with NIS or COC alone; however, 24 HAT, absorption with NIS and COC were similar to treatments with UAN. Carfentrazone-ethyl did not translocate from the treated leaf to other plant parts in Z. mays and only small amounts of radiolabeled product were detected in the rest of the shoots of A. theophrasti (5%) and G. max (12%). Herbicide metabolism in Z. mays and G. max was greater than in A. theophrasti. All three species converted carfentrazone-ethyl to its phytotoxic metabolite carfentrazone-chloropropionic acid; therefore, the parent molecule was considered to be the sum of the ethyl ester and its hydrolysis product. Estimated half-lives of carfentrazone in Z. mays, G. max and A. theophrasti were 1, 7, and 40 h, respectively. The rate of carfentrazone metabolism corresponded to plant sensitivity (sensitivity to carfentrazone: Z. mays<G. max<<A. theophrasti); however, rapid absorption and translocation of carfentrazone may reduce the tolerance of G. max.

The herbicide 2,6-dichlorobenzonitrile (dichlobenil) was quite persistent in cranberry bogs. The chemical was not readily leached downward in the soil nor carried from the bog by flood water but was recovered primarily in the upper 4 in of the soil. Chemical residue analysis demonstrated a greater quantity of herbicide was present than indicated by a bio-assay test. Most of the herbicide is believed to be held ineffective by the organic matter in the soil.

Field experiments were conducted at four locations in the Central Pacific region of Costa Rica between 1994 and 1996 to determine suitable tactics for integrated control of propanil-resistant junglerice in rain-fed rice. Stubble incorporation within 3 mo after rice harvest did not affect the density of junglerice that emerged with the crop at the beginning of the rainy season at any location. However, the elimination with glyphosate of the first junglerice seedling population emerging before rice planting consistently reduced the in-crop infestation of junglerice and resulted in increased grain yields. The positive effect of eliminating the first junglerice flush remained even after the in-crop treatments were applied and lasted after rice harvest. Substitution of the two customary applications of propanil (3.8 kg ha−1 each) with a single application of pendimethalin (0.75 to 1.5 kg ha−1), preemergence or early postemergence, also reduced junglerice infestation and improved grain yield. Both propanil, in mixture with the synergist piperophos, and quinclorac controlled propanil-resistant junglerice and increased grain yields. Control of the initial junglerice population and improved in-crop weed management can serve as the basis for integrated management of herbicide-resistant junglerice in rain-fed rice.

UHF energies (45 to 730 j/cm2, 2450 MHz) were applied to irrigated and non-irrigated soils in the field just before planting of cantaloupe (Cucumis melo L., var. reticulatus Naudin) and onion (Allium cepa L.) to study the influence of UHF energy on plant growth. London rocket (Sisymbrium irio L.) and sunflower (Helianthus annuus L.) were controlled with 180 j/cm2 of UHF energy applied after seed had imbibed water from soil. These species and ridgeseed spurge (Euphorbia glyptosperma Engelm.), redroot pigweed (Amaranthus retroflexus L.), common purslane (Portulaca oleracea L.), and Japanese millet [Echinochloa frumentacea (Roxb.) Link.] were controlled with 360 j/cm2 (0.0048 kmph) regardless of seed or soil moisture. London rocket and sunflower were not controlled by several soil-incorporated herbicides. UHF energy had no deleterious effects on the growth of cantaloupe or onion and tended to increase the yields above those of the hand-weeded vegetables. Phytotoxic UHF radiation penetrated 7.5 and 10 cm in irrigated and non-irrigated soil, respectively, at 360 j/cm2. Soil temperature after UHF treatment increased with increasing UHF energy levels and decreasing soil moisture and depth.

Field bindweed and Russian knapweed were grown from seed or rhizome segments under 520, 325, or 236 μmol·m–2 · s–1 photosynthetic photon flux density (PPFD) to determine vegetative and reproductive response. Flower production in both species declined with decreasing light level. Leaf area of field bindweed decreased as light level decreased, but Russian knapweed leaf area increased as light intensity decreased from 520 to 325 μmol·m–2 ·s–1 PPFD or from 520 to 236 μmol·m–2 ·s–1. Dry matter of shoots, roots, and rhizomes of field bindweed grown from seed declined as light level decreased, but the only response of plants grown from rhizome segments was complete inhibition of rhizome production. Dry matter of Russian knapweed shoots and roots in plants grown from seed or rhizome segments decreased as light decreased. In both species the total PPFD was more important than whether low or high light level occurred first.

The effect of hydration (priming) treatment on dormancy release in annual ryegrass seeds from two populations was investigated. Hydration duration, number, and timing with respect to after-ripening were compared in an experiment involving 15 treatment regimens for 12 wk. Seeds were hydrated at 100% relative humidity for 0, 2, or 10 d at Weeks 1, 6, or 12 of after-ripening. Dormancy status was assessed after each hydration treatment by measuring seed germination at 12-hourly alternating 25/15 C (light/dark) periods using seeds directly from the hydration treatment and seeds subjected to 4 d postpriming desiccation. Seeds exposed to one or more hydration events during the 12 wk were less dormant than seeds that remained dry throughout after-ripening. The longer hydration of 10 d promoted greater dormancy loss than either a 2-d hydration or no hydration. For the seed lot that was most dormant at the start of the experiment, two or three rather than one hydration event or a hydration event earlier rather than later during after-ripening promoted greater dormancy release. These effects were not significant for the less-dormant seed lot. For both seed lots, the effect of a single hydration for 2 d at Week 1 or 6 of after-ripening was not manifested until the test at Week 12 of the experiment, suggesting that the hydration events alter the rate of dormancy release during subsequent after-ripening. A hydrothermal priming time model, usually used for modeling the effect of priming on germination rate of nondormant seeds, was successfully applied to dormancy release resulting from the hydration treatments.

Seed production of weedy species of Setaria in crops of Zea mays and Glycine max was studied for 2 yr in western Minnesota and eastern South Dakota. Viable seed production was curvilinearly related to panicle length. A 100-mm-long panicle of S. pumila, S. faberi, and S. viridis produced 129, 323, and 851 viable seeds, respectively. Values were consistent across years, crops, and herbicide treatments. Frequency distributions of panicle lengths of all panicles within a population closely followed nonlinear Weibull functions and were stable across years and crops but not species or herbicide treatment. Positive skewness of these distributions decreased, and median panicle size (mm) increased, in the following order: S. viridis (41), S. pumila (52), and S. faberi (78). Postemergence herbicides applied at full label rates increased skewness and reduced median panicle size (to 11 mm) and seed production of S. viridis. Skewness lessens the reliability of using average panicle size as a measure of seed production for the entire population. However, integration of panicle size–frequency and panicle size–fecundity relationships provided estimates of the number of seeds per panicle that were more representative of the population than the statistical average panicle. These estimates were 52, 242, and 246 seeds per panicle for S. pumila, S. viridis, and S. faberi, respectively. Multiplication of these values by panicle densities generated seed production estimates that were similar to actual counts of seeds. Setaria seed production tended to be higher in Z. mays than in G. max only because of higher plant and panicle densities. Early-maturing panicles tended to be larger than those maturing later, but seed viability generally was stable across maturity times.

A segment of the debate surrounding the commercialization and use of glyphosate-resistant (GR) crops focuses on the theory that the implementation of these traits is an extension of the intensification of agriculture that will further erode the biodiversity of agricultural landscapes. A large field-scale study was initiated in 2006 in the United States on 156 different field sites with a minimum 3-yr history of GR-corn, -cotton or -soybean in the cropping system. The impact of cropping system, crop rotation, frequency of using the GR crop trait, and several categorical variables on seedbank weed population density and diversity was analyzed. The parameters of total weed population density of all species in the seedbank, species richness, Shannon's H′ and evenness were not affected by any management treatment. The similarity between the seedbank and aboveground weed community was more strongly related to location than management; previous year's crops and cropping systems were also important while GR trait rotation was not. The composition of the weed flora was more strongly related to location (geography) than any other parameter. The diversity of weed flora in agricultural sites with a history of GR crop production can be influenced by several factors relating to the specific method in which the GR trait is integrated (cropping system, crop rotation, GR trait rotation), the specific weed species, and the geographical location. Continuous GR crop, compared to fields with other cropping systems, only had greater species diversity (species richness) of some life forms, i.e., biennials, winter annuals, and prostrate weeds. Overall diversity was related to geography and not cropping system. These results justify further research to clarify the complexities of crops grown with herbicide-resistance traits to provide a more complete characterization of their culture and local adaptation to the weed seedbank.

Requirements for germination of 23 medusahead (Taeniatherum asperum (Sim.) Nevski) selections were investigated in relation to temperature and afterripening requirements, and were compared with the germination characteristics of other grasses. Medusahead germinated best at 10 to 15 C. Germination percentages were markedly lower at 20 and 25 C. Unlike medusahead, germination of all competing or replacement species tested was markedly decreased at lower temperatures (10 C). Above 15 C, medusahead selections had strong afterripening requirements which decreased over time. Shortly after maturity, medusahead caryopses germinated only at low temperatures (10 and 15 C). Germination temperatures became less dominant after a 180-day afterripening period.

Seed production was studied near Lincoln, Nebraska for musk or nodding thistle (common names used for large-flowered species of Carduus – C. macrocephalus Desf., C. nutans L., C. thoermeri Weinm.). Four levels of seed maturity were studied from separate groups of plants with the heads harvested at the full-bloom stage, 2 days after full bloom, 4 days after full bloom, and at full maturity. The first heads to bloom (terminal) averaged about 1000 seeds/head and the last to bloom (lateral branches near the base of the plant), ca. 125. Plants produced only 26 good quality seeds/plant when the heads were all clipped at the full-bloom stage, but the plants with heads allowed to go to maturity produced 3580 of the good quality seeds/plant. Plants with heads clipped at 2 and 4 days after full bloom produced 72 and 774 good quality seeds, respectively.