Six crop species were irrigated with water that contained up to several times more glyphosate [N-(phosphonomethyl)glycine] than would be expected in irrigation water as a result of spraying ditchbank vegetation. In June or July 1976, sugarbeets (Beta vulgaris L.), alfalfa (Medicago sativa L., ‘Vernal’), grain sorghum [Sorghum bicolor (L.) Moench], field beans (Phaseolus vulgaris L., ‘Pinto’), tomatoes (Lycopersicon esculentum Mill., ‘Roza’), and squash [Cucurbita moschata (Duch.) Duch. ex Poir.] were sprinkler-irrigated with water that contained glyphosate at 0, 0.02, 0.22, or 2.2 ppmw. These concentrations were applied continuously for 8 h to make total applications of 0, 0.01, 0.1, and 1.1 kg/ha, respectively. No injury symptoms developed in any of the crop plants. Yields of treated crops were equal to those produced by untreated plants.

Ragweed parthenium (Parthenium hysterophorus L. #3 PTNHY) growing at six localities between 28°46′N and 13°O'N latitudes in India produced polymorphic ray achenes that varied in size and weight. Frequency of small achenes (1.9 to 2.2 mm) was higher at lower latitude (13°O'N) and that of large achenes (2.5 to 2.8 mm) at higher latitude (28°46′N). Achene weight was positively correlated with its germination percentage. Large-heavy achenes showed better germination than small-light ones.

Experiments were conducted to determine 14C absorption and translocation by oat (Avena sativa L. ‘Lyon’) foliarly treated with 14C-sethoxydim {(2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one)} and various additives. Safflower (Carthamus tinctorius L.), soybean [Glycine max (L.) Merr.], linseed (Linum usitatissimum L.), and sunflower (Helianthus annuus L.) oil all similarly increased foliar absorption and translocation of 14C more than palm oil (Elaeis quineensis Jacq.) but less than petroleum oil, when applied without an emulsifier. An emulsifier in the oil additive tended to enhance 14C absorption and translocation more in soybean oil than petroleum oil so that 14C absorption and translocation were similar with both oils containing emulsifiers. Absorption and translocation of 14C tended to increase more with an increase in emulsifier concentration in soybean oil than in petroleum oil but not beyond 15% with either oil. Percentage of 14C absorbed and translocated from 14C-sethoxydim applied to oats increased as the amount of soybean oil applied increased from 2.3 to 4.6 L/ha, but the increase was less for sethoxydim at 0.87 kg ai/ha than at 0.03 or 0.17 kg ai/ha.

Interest in using crop competitiveness as an integrated weed management tool is increasing. Our objective was to describe traits that could be sources of the competitiveness we previously observed in grain sorghum grown in association with shattercane, which is a common annual weed and a close relative of the crop. Such information could aid in developing management practices for cultivated sorghum to improve its competitiveness with weeds. A bioassay was conducted to compare emergence of the crop and the weed in the greenhouse, and vegetative growth was monitored for 31 d in a within-row competition study. Results described a crop that competed well with the weed and other crop plants and agreed with studies showing that relative time of emergence influenced competitiveness. The mechanism by which grain sorghum emerged before the weed was a by-product of domestication that reduced glumes surrounding the wild-type seeds. This could be shown experimentally by hulling shattercane seeds, which then emerged almost as quickly as the grain sorghum. When planted in the grain sorghum row, shattercane plants from hulled seeds decreased the number of leaves and the root mass of the crop. Similarly, the time between emergence of the crop and emergence of shattercane was lessened by planting shattercane seeds early, and this increased the leaf number of the weed and shoot mass of the crop. It might be possible to increase weed suppression in grain sorghum by using management practices, such as more equidistant crop planting patterns that exploit the competitiveness already present, but which is being lost to interactions among crop plants.

Garden huckleberry, a member of the Solanaceae family and a close relative of black nightshade, is an exotic plant introduced from Africa. Information on garden huckleberry response to a new environment and to herbicides is useful for determining the potential of this species to become an invasive weed, predicting the potential range of this species in the United States, and developing an optimum garden huckleberry management program. Germination and survival of garden huckleberry seed, as affected by environmental factors, were studied under greenhouse and controlled-environment growth chamber conditions. Garden huckleberry seed became viable between 2 and 3 wk after anthesis and was nondormant when separated from fresh berries. Garden huckleberry seed was not photoblastic and germinated equally well under both a 14-h photoperiod and continuous darkness. Seed germinated at constant temperatures from 17 to 35 C, with optimum germination between 22 and 30 C. Germination of garden huckleberry seed markedly declined as the osmotic potential of the germination medium decreased. The optimum pH for germination of garden huckleberry was between 5 and 9. Paraquat, dicamba, and bromoxynil provided excellent garden huckleberry control (95 to 100%); atrazine and glyphosate were more phytotoxic (90%) than imazamox (80%); and acifluorfen and foramsulfuron gave inadequate control.

Competition between crops and weeds may be stronger at the root than at the shoot level, but belowground competition remains poorly understood, due to the lack of suitable methods for root discrimination. Using a transgenic maize line expressing green fluorescent protein (GFP), we nondestructively discriminated maize roots from weed roots. Interactions between GFP-expressing maize, common lambsquarters, and redroot pigweed were studied in two different experiments with plants arranged in rows at a higher plant density (using boxes with a surface area of 0.09 m2) and in single-plant arrangements (using boxes with a surface area of 0.48 m2). Root density was screened using minirhizotrons. Relative to maize that was grown alone, maize root density was reduced from 41 to 87% when it was grown with redroot pigweed and from 27 to 73% when it was grown with common lambsquarters compared to maize grown alone. The calculated root : shoot ratios as well as the results of shoot dry weight and root density showed that both weed species restricted root growth more than they restricted shoot growth of maize. The effect of maize on the root density of the weeds ranged from a reduction of 25% to an increase of 23% for common lambsquarters and a reduction of 42 to 6% for redroot pigweed. This study constitutes the first direct quantification of root growth and distribution of maize growing together with weeds. Here we demonstrate that the innovative use of transgenic GFP-expressing maize combined with the minirhizotron technique offers new insights on the nature of the response of major crops to belowground competition with weeds.

The loss of 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) and 1-butyl-3-(3,4-dichlorophenyl)-1-methylurea (neburon) from an aquatic situation was studied. Appreciable loss of herbicides did not occur until 8 and 16 weeks after application of neburon and monuron, respectively. Periods of loss at an accelerated rate followed until approximately 50% of the herbicides disappeared. Further loss was observed but at a steadily decreasing rate. Approximately 15% of the monuron and 39% of the neburon remained after 128 weeks. More monuron was found in water than in soil during the first 32 weeks. After 32 weeks, most of the monuron was found in the soil and was largely in the top 4 in. The largest fraction of neburon was recovered from the soil and soil surface during all 128 weeks. Monuron moved down in the soil more readily than neburon.

Movement of 2-chloro-N-isopropylacetanilide (propachlor) from a granule to the soil was classified as horizontal, below the granule, above the granule, and into an area within a 3-ppmw contour. The influence of depth of placement, moisture content, temperature, relative humidity, and exposure time on each of the movement classifications was determined. Horizontal movement increased as the temperature, moisture, and exposure time increased. Propachlor tends to move down into the soil under dry conditions and up when the soil is moist. The size of the soil area that contained 3 ppmw was greater for granules placed in the soil than for granules placed on the surface. The size of the area increased as the moisture increased.

As early as 1946, a limited study conducted in Oregon (5) showed big sagebrush (Artemisia tridentata Nutt.) to be susceptible to the sodium salt of 2,4–D. Cornelius and Graham (3) stated that big sagebrush was highly susceptible or hypersensitive to 2,4–D. Kissinger, Hull and Vaughn (7), reporting on experiments conducted at the Beaver Rim area near Lander, Wyoming, found that the isopropyl and amyl ester of 2,4,5–T consistently gave higher kills for a given amount of chemical. One pound acid equivalent (hereafter referred to as pounds acid) of 2,4,5–T usually gave somewhat higher kills than two pounds acid equivalent of 2,4–D.

Since the work of Cox and Cates in 1912, it had been shown repeatedly that weeds growing in competition with crops decrease yields. These results lead to the general assumption that weeds are detrimental anytime, including a fallow period for moisture conservation. In fact many farmers in the Great Plains area still plow during the winter or when there are no weeds to promote a “dust mulch” for moisture conservation even though this practice has been shown to be of little value. Recent research has shown that where runoff is prevented and weed control is adequate during the fallow period, type of tillage or amount of mulch does not greatly affect moisture storage in the Southern Great Plains. Finnell stated that on the heavy soils of the Southern Great Plains 65.8 percent of the rainfall was evaporated, 13.5 percent was runoff, 2.7 percent was lost in tillage operations and 18.0 percent was stored in the soil.

Common ragweed (2n=36), giant ragweed (2n = 24), and their reciprocal F1 hybrids (2n = 30) were analyzed for a number of traits. Hybrids of the type giant ragweed♀ × common ragweed♂ were obtained via immature embryo culture. The analyses revealed a surprising contribution of the pollen parent for features such as biomass, leaf area, and specific leaf area. Leaf morphology, however, was similar to the maternal parent. One plant, originating from crosses of the type common ragweed♀ × giant ragweed♂, developed abnormally and cytological analysis revealed the presence of 24 chromosomes in its somatic cells. Probably this plant had an androgenetic origin.

Triquetrous murdannia is an annual weed commonly found in rice fields in China. Laboratory and screenhouse experiments were carried out to determine the effect of light, temperature, osmotic and salt stress, seed burial depth, amount of rice residue, and depth of flooding on seed germination and seedling emergence of triquetrous murdannia and to evaluate the response of this weed to commonly available POST herbicides in China. Germination was greater than 93% under a wide day/night temperature range of 20/10 to 30/20 C in the light/dark regime. The time to onset of germination decreased as temperature increased. Germination was slightly stimulated when seeds were placed in light/dark conditions compared with seeds placed in the dark. The osmotic potential and NaCl concentration required for 50% inhibition of maximum germination were −0.5 MPa and 122 mM, respectively. The highest germination (68%) was observed from seeds sown on the soil surface, but decreased with increasing burial depth. Only 7% of seedlings emerged from a depth of 4 cm, and no seedlings emerged from seeds buried deeper than 6 cm. Seedling emergence decreased from 93 to 35% with increasing quantity of rice residue (1 to 6 103 kg ha−1) applied on the soil surface. Seedling emergence was reduced by 40, 48, 64, and 70% at flooding depths of 1, 2, 4, and 6 cm, respectively, for the seeds sown on the soil surface. Fluroxypyr and MCPA herbicides provided 100% control of triquetrous murdannia at the 2- to 6-leaf stages; however, to achieve 100% control with bispyribac-sodium, MCPA+bentazone or MCPA+fluroxypyr, herbicides had to be applied by the 4-leaf stage. The results of this study could help in developing more sustainable and effective integrated weed management strategies for the control of triquetrous murdannia in rice fields in China.

Acetolactate synthase (ALS) –inhibitor resistance has been recently documented in a yellow nutsedge biotype in Arkansas rice production, with a target-site mutation resulting in an amino acid substitution from Trp574 to Leu. Preliminary observations have indicated that the resistant biotype showed distinct phenotypic characteristics. Two greenhouse experiments were conducted on the resistant biotype in comparison with three susceptible standards (1) to understand differential growth habit and spatial distribution, and (2) to characterize shoot emergence pattern and seedling vigor. The resistant biotype exhibited a drastically different growth habit with secondary and tertiary basal bulbs emerging away from the parent shoot, resulting in a wider spatial distribution and ground coverage compared to the very compact growth habit of susceptible biotypes. Unlike the susceptible biotypes, the rhizomes developing into tubers were not often connected to the primary basal bulb, but were originating randomly from daughter shoots. The resistant biotype produced an extensive subterranean network of rhizomes and basal bulbs, with wider root spread and distribution compared to the susceptible biotypes. The growth habit of the resistant biotype appeared to be intermediate between yellow and purple nutsedges. Further, the resistant biotype showed a considerably delayed emergence pattern with relatively high levels of tuber dormancy. Although the resistant plants exhibited low early-growth seedling vigor and biomass production compared to the susceptible biotypes (perhaps because of smaller tubers), final aboveground biomass production was greater than that of susceptible biotypes. The overall growth habit and phenotype of the resistant biotype may provide a competitive advantage over adjacent species through the ability to occupy niches and gain improved access to critical resources. The distinct growth pattern may also mean that tillage should not be relied upon for control because it can assist further spread by disconnecting and displacing the chains of rhizomes.

The mitotic-inhibiting herbicide pronamide controls susceptible annual bluegrass (Poa annua L.) pre- and postemergence, but in some resistant populations, postemergence activity is compromised, hypothetically due to a target-site mutation, lack of root uptake, or an unknown resistance mechanism. Three suspected pronamide-resistant (LH-R, SC-R, and SL-R) and two pronamide-susceptible (BS-S and HH-S) populations were collected from Mississippi golf courses. Dose–response experiments were conducted to confirm and quantify pronamide resistance, as well as resistance to flazasulfuron and simazine. Target sites known to confer resistance to mitotic-inhibiting herbicides were sequenced, as were target sites for herbicides inhibiting acetolactate synthase (ALS) and photosystem II (PSII). Pronamide absorption and translocation were investigated following foliar and soil applications. Dose–response experiments confirmed pronamide resistance of LH-R, SC-R, and SL-R populations, as well as instances of multiple resistance to ALS- and PSII-inhibiting herbicides. Sequencing of the α-tubulin gene confirmed the presence of a mutation that substituted isoleucine for threonine at position 239 (Thr-239-Ile) in LH-R, SC-R, SL-R, and BS-S populations. Foliar application experiments failed to identify differences in pronamide absorption and translocation between the five populations, regardless of harvest time. All populations had limited basipetal translocation—only 3% to 13% of the absorbed pronamide—across harvest times. Soil application experiments revealed that pronamide translocation was similar between SC-R, SL-R, and both susceptible populations across harvest times. The LH-R population translocated less soil-applied pronamide than susceptible populations at 24, 72, and 168 h after treatment, suggesting that reduced acropetal translocation may contribute to pronamide resistance. This study reports three new pronamide-resistant populations, two of which are resistant to two modes of action (MOAs), and one of which is resistant to three MOAs. Results suggest that both target site– and translocation-based mechanisms may be associated with pronamide resistance. Further research is needed to confirm the link between pronamide resistance and the Thr-239-Ile mutation of the α-tubulin gene.

Weeds contribute to biodiversity and a wide range of ecosystem functions. It is crucial to map different weed species and analyze their physiological activities. Remote sensing techniques for plant identification, especially hyperspectral imaging, are being developed using spectral response patterns to vegetation for detection and species identification. A library of hyperspectral images of 40 urban weed species in northeast China was established in this study. A terrestrial hyperspectral camera was used to acquire 435 hyperspectral images. The hyperspectral information for each weed species was extracted and analyzed. The spectral characteristics and vegetation indices of different weeds revealed the differences between weed species in the cities of northeast China and indirectly characterized the growth and physiological activity levels of different species, but could not effectively distinguish different species. Five methods—first derivative spectrum (FDS), second derivative spectrum (SDS), standard normal variate (SNV), moving averages (MA), and Savitzky-Golay (SG) smoothing—were used to pretreat the spectral curves to maximize the retention of spectral characteristics while removing the influence of noise. We investigated the application of a convolutional neural network (CNN) with terrestrial hyperspectral remote sensing to identify urban weeds in northeast China. A CNN classification model was established to distinguish weeds from the hyperspectral images and demonstrated a test accuracy of 95.32% to 98.15%. The accuracy of the original spectrum was 97.45%; SNV had the best accuracy (98.15%) and SG was the least accurate (95.32%). This provides a baseline for understanding the hyperspectral characteristics of urban weed species and monitoring their growth. It also contributes to the development of a hyperspectral imaging database with global applicability.

For the control of wild garlic in Missouri in comparison with 2,4-dichlorophenoxyacetic acid (2,4-D) during 1954–1960, 3-amino-1,2,4-triazole (amitrole), sodium 2,2-dichloropropionate (dalapon), maleic hydrazide (MH), 2,3,6-trichlorophenylacetic acid (fenac) and 2,3,6-trichlorobenzoic acid (2,3,6-TBA) were effective. 2,3,6-TBA alone was more effective than 2,4-D. The toxicity of 2,3,6-TBA was increased by addition of a wetting agent. Heavy spot treatments of wild garlic with 2,3,6-TBA killed the established plants, but did not eradicate wild garlic because of sprouting of dormant bulbs.

Carinata (Brassica carinata A. Braun) is a potential crop for biofuel production, but the risk of injury resulting from carryover of soil herbicides used in rotational crops is of concern. The present study evaluated the carryover risk of imazapic and flumioxazin for carinata. Label rates of imazapic (70 g ai ha−1) and flumioxazin (107 g ai ha−1) were applied 24, 18, 12, 6, and 3 mo before carinata planting (MBP). The same herbicides were applied preemergence right after carinata planting at 1X, 0.5X, 0.25X, 0.125X, 0.063X, and 0X the label rate. When either herbicide was applied earlier than 3 MBP, there was no difference in plant density compared with the nontreated control. Carinata damage was <25% when flumioxazin or imazapic was applied at least 6 MBP in Clayton, NC (sandy loam soil), while in Jackson Springs, NC (coarser-textured soil and higher precipitation), at least 12 MPB were needed to lower plant damage to <25%. Preemergence application of 0.063X each herbicide decreased plant density by 40%, with damage reaching >25%. Quantification of herbicide residues in both soils showed that imazapic moved deeper in the soil profile than flumioxazin. This was more evident in Jackson Springs, where 0.68, 3.52, and 7.77 ng of imazapic g−1 soil were detected (15- to 20-cm depth) when the herbicide was applied at 12, 6 and 3 MBP, respectively, while no flumioxazin residues were detected at the same soil depths and times. When residues were 7.78 and 6.90 ng herbicide g−1 soil in the top 10 cm of soil for imazapic and flumioxazin, respectively, carinata exhibited at least 25% damage. Rotational intervals to avoid imazapic and flumioxazin damage to carinata should be between 6 and 12 MBP depending on soil type and environmental conditions, with longer intervals for the former than the latter.