The herbicides, S-ethyl hexahydro-1 H-azepine-l-carbothioate (molinate) applied preemergence and 3′,4′-dichloropropionanilide (propanil) applied as a contact spray at several dates, were evaluated for control of barnyardgrass (Echinochloa crusgalli (L) Beauv.) in water-seeded rice (Oryza sativa L., var. Caloro) flooded continuously to a shallow (3 inch) depth. Propanil applied when barnyardgrass had 6 to 9 inches of leaves exposed gave higher yields than earlier or later applications. Molinate gave the best barnyardgrass control when it was applied as a granule, incorporated, and applied onto dry soil. Molinate controlled the three major phenotypes of barnyardgrass. Germinating barnyardgrass seed were severely inhibited in growth by molinate concentrations greater than 0.3 ppm while germinating rice seed were not inhibited until the concentrations were greater than 5 ppm. Low concentrations of molinate stimulated shoot growth of both rice and barnyardgrass.

African turnipweed (Sisymbrium thellungii O. E.Schulz) is an emerging problematic broadleaf weed of the northern grain region of Australia. Laboratory experiments were conducted to evaluate the effects of temperature, light, salinity, pH, seed burial depth, and the amount of wheat crop residue on germination and emergence of two Australian S. thellungii weed populations (population C, cropped area; population F, fence line). Both populations behaved similarly across different environmental conditions, except in the residue study. Although the seeds of both populations of S. thellungii could germinate under complete darkness, germination was best (~95%) under light/dark conditions at the 20/10 C temperature regime. Both populations of S. thellungii germinated over a wide range of day/night temperatures (15/5, 20/10, 25/15, and 30/20 C). Osmotic stress had negative effects on germination, with 54% seeds (averaged over populations) able to germinate at −0.1MPa. Complete germination inhibition for both populations was observed at −0.8MPa osmotic potential. Both populations germinated at sodium chloride (NaCl) concentrations ranging from 50 to 100 mM, beyond which germination was completely inhibited. There were substantial reductions in seed germination, 32% (averaged over populations) under highly acidic conditions (pH 4.0) as compared with the control (water: pH 6.4). Seed germination of both populations on the soil surface was 77%, and no seedlings emerged from a burial depth of 1 cm. The addition of 6 Mg ha−1 of wheat (Triticum aestivum L.) residue reduced the emergence of the C and F populations of S. thellungii by 75% and 64%, respectively, as compared with the control (no residue). Information gathered from this study provides a better understanding of the factors favorable for germination and emergence of S. thellungii, which will aid in developing management strategies in winter crops, especially wheat, barley (Hordeum vulgare L.), and chick pea (Cicer arietinum L.).

If decision-aid software models of weed emergence and growth are ever to help producers better time weed management, these models must be able to predict perennial weed shoot emergence from vegetative propagules. In this research, Cirsium arvense shoot emergence from adventitious root buds in spring was modeled using degree-day heat sums. Fractional C. arvense shoot emergence was best modeled as a logistic dose–response function of degree-day heat sum as follows: Y = 1.108/(1+[X/488.344]−5.161) where Y = fractional C. arvense shoot emergence (0 to 1) and X = heat sum in degree-days above 0 C after day 91 of the year (April 1) with an upper limit of 800 degree (C) days (r2 = 0.83). This empirical model was validated by graphing observed vs. model-predicted C. arvense shoot emergence using two independently gathered data sets, one of C. arvense emergence in autumn chisel-plowed Triticum aestivum (r2 = 0.82) and the other in no-till fallow (r2 = 0.63). The model slightly overestimated emergence at low fractional emergence (< ∼7% at 0.1 fractional emergence) and underestimated emergence at high fractional emergence (10 to 20% at 0.8 to 1.0 fractional emergence). Below an emergence fraction of 0.8, the model adequately estimated observed emergence to within about 10% of the predicted regression line. Using the model, about 1% and 80% of C. arvense shoots should emerge from adventitious root buds after a heat sum accumulates of about 197 and 587 C d, respectively, starting from day 91 of the year. Consequently, farmers should begin monitoring C. arvense patches for emergence and height growth after about 197 C d accumulate and expect to control C. arvense before about 587 C d accumulate, which is when about 80% of shoots have emerged.

Sugar beets (Beta vulgaris L., var. MSU 126 × 5460) were treated with 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone (pyrazon) applied to the soil. The pyrazon was labeled with either 3H in the phenyl ring, or with 14C at the 4 and 5 positions of the pyridazinone ring. The disappearance of pyrazon and the appearance of metabolites in the soil and shoots were examined 1, 2, 4, 6, 8, 12, and 16 weeks after treatment. The total recoverable radioactivity decreased with time, but there was a greater loss of 3H-labeled compounds than 14C-labeled compounds from the soil. Thin-layer chromatography of the soil and shoot extracts revealed the presence of one metabolite in the soil and three metabolites in the plant. By co-chromatography with known pyrazon derivatives and by comparison of the labeling (14C, 3H, or both), the metabolites in the shoot were identified as N-(2-chloro-4-phenyl-3(2H)-pyridazinone)-glucosamine (hereinafter referred to as N-glucosyl pyrazon), 5-amino-4-chloro-3(2H)-pyridazinone (hereinafter referred to as ACP), and ACP-complex. The other moiety in the ACP-complex was not identified. The metabolite in the soil was identified as ACP, and was detectable 2 weeks prior to its appearance in the shoot, suggesting that it was absorbed from the soil.

Six herbicides were applied at 3, 9, and 27 lb/A to the soil in forests of three types in Puerto Rico. The forests differed in soil type, amount and pattern of rainfall, and species composition. Defoliation occurred slowly, but the correlation between percentage defoliation and plants killed was significant at the 1% level of probability. Some defoliation was evident 1 month after treatment and increased slowly during the next 6 to 8 months. The most effective herbicide was 4-amino-3,5,6-trichloropicolinic acid (picloram). Generally, 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 2-methoxy-4,6-bis(isopropylamino)-s-triazine (prometone), and 5-bromo-3-sec-butyl-6-methyluracil (bromacil) were less effective than picloram. Both 2,3,6-trichlorophenylacetic acid (fenac) and 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) were ineffective. Defoliation was greatest and more plants were killed in the driest site.

One year after treatment, fenac was the most persistent herbicide in the soil. Herbicides were found to a 36 to 48-in depth within 3 months after application.

Herbaceous and woody seedlings were present at all sites within 18 months after herbicide application. There was no definite relationship between herbicidal treatment and secondary succession, except that the number and frequency of successional species were greater on plots having the highest percentage of defoliation.

Threehorn bedstraw is an important dicotyledonous weed of winter crops in southern Australia, which can be difficult to control in some field crops. Knowledge of the germination ecology of this weed would facilitate development of effective weed control programs. Seed germination in the laboratory was greater for seeds that after-ripened while buried in the soil relative to those that after-ripened on the soil surface. The timing of greatest seed germination in the laboratory was found to coincide with the period of low temperature in the field. Seed germination of threehorn bedstraw was moderately sensitive to salt stress but moderately tolerant to osmotic stress. Seeds of threehorn bedstraw germinated over a broad range of pH from 4 to 10. No seedlings emerged from seeds placed on the soil surface. Maximum seedling emergence occurred at depths of 1 to 2 cm (89 to 91%) and declined at greater depths.

Quackgrass is a problematic agricultural weed in the temperate zones of the world and is difficult to control without herbicides or intensive tillage. However, it may be possible to control quackgrass with less environmental impact by combining multiple low-intensity control methods. A pot experiment was conducted in July to October 2012 and repeated in June to September 2013 to investigate the effect of rhizome fragmentation, competition from white clover, shoot-cutting frequency, and cutting height on quackgrass. Rhizome fragmentation was expected to result in more, but weaker, quackgrass shoots that would be more vulnerable to shoot cutting and competition. However, by 20 d past planting, rhizome fragmentation did not change the total number of quackgrass shoots per pot, because an increase in main shoots was offset by a decrease in tiller numbers. Rhizome fragmentation did not reduce quackgrass biomass acquisition during the experimental period. Although rhizome fragmentation did reduce total fructan content, it did not enhance the effect of clover competition, shoot-cutting frequency, or shoot-cutting height. Clover competition by itself reduced quackgrass shoot numbers by 72%, rhizome biomass by 81%, and belowground fructan concentration by 10 percentage points, compared with no competition. The more frequently quackgrass shoots were cut, the less biomass quackgrass acquired, and a high shoot-cutting frequency (each time quackgrass reached 2 leaves) resulted in a lower belowground fructan concentration than a low shoot-cutting frequency (at 8 leaves). However, in pots without competition, a higher shoot-cutting frequency resulted in more quackgrass shoots. A lower shoot-cutting height (25 mm) had more impact when shoot cutting was more frequent. In conclusion, rhizome fragmentation did not reduce the number of quackgrass shoots or rhizome biomass, but competition from white clover, a high shoot-cutting frequency, and a low shoot-cutting height strongly suppressed quackgrass biomass and fructan acquisition.

Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations by such species are common in no-till production fields in the midwestern United States of Indiana, Ohio, and Illinois. The objective of this research was to determine the influence of crop rotation and winter annual weed management on winter weed growth, SCN population density, and crop yield. Two crop rotations (SS and soybean–corn rotation) and six winter annual weed-management systems (autumn-applied herbicide, spring-applied herbicide, autumn + spring applied herbicides, autumn-seeded Italian ryegrass, autumn-seeded wheat, and a nontreated check) were evaluated in long-term, no-tillage systems at West Lafayette, IN, and Vincennes, IN. In the fourth and fifth years of these experiments, the 2-yr corn–soybean rotation generally resulted in increased soybean yield, decreased winter annual weed growth, and reduced SCN population density compared with SS. Autumn or spring herbicide applications or both were a more effective option than cover crops at reducing winter annual weed density. Cover-crop systems generally did not differ from the nontreated check in winter weed density. Between years three and five, winter annual weed SCN hosts in nontreated check plots increased approximately threefold to levels as high as 102 and 245 plants m−2 at West Lafayette, IN, and Vincennes, IN, respectively, which are infestation levels at or above those commonly observed in production fields. However, controlling winter annual weeds did not influence crop yields or SCN population density. The results of these studies suggest that winter weed management, even at the high levels of weed infestation present in these studies, appears to have little value as a tool for SCN management in corn and soybean production systems in the midwestern United States.

Weeds are a fundamental component of agroecosystems and, if not appropriately managed, can cause severe crop yield losses. New perspectives on weed management are required, because current approaches, such as herbicide application or soil tillage, have significant environmental and agronomic drawbacks. We propose the concept of “neutral weed communities,” which are weed communities that coexist with crops and do not negatively affect crop yield and quality compared with weed-free conditions. Management practices that promote neutral weed communities can enable reduced use of herbicides and soil tillage while enhancing ecosystem services and biodiversity. We report scientific evidence of neutral weed communities and survey ecological explanations for why different weed communities have different effects on crop production. We also propose two weed management approaches for attaining neutral weed communities. The first approach aims to maximize weed biodiversity using traditional approaches such as cropping system diversification and integrated weed management. Higher weed biodiversity is associated with lower dominance of competitive weed species that reduce crop yield. The second approach relies on modern tools such as robots and biotechnology to manipulate the density of specific weed species. This approach can remove highly problematic species and minimize niche overlap between the weeds and crops. Given the complexity of interactions among crops, weeds, and other components of the agroecosystem, we highlight the need for multidisciplinary research to illuminate mechanisms that determine the neutrality of weed communities.

The implementation of site-specific weed management requires information about weed cover and decision support systems to determine weed cover thresholds and concomitant herbicide rates. Although it is possible to create accurate weed cover maps over large areas, weed cover thresholds have generally been evaluated using tedious weed density counts. To bridge this gap between weed cover obtained by machine vision and the concept of economic threshold, crop advisers specializing in weed scouting were asked to evaluate over 2,500 weed cover images (2 m by 3 m) and determine if a given image would require herbicide application or not. Using the area under the “receiver operating characteristic” curve method, an optimal weed cover threshold was established. The derived economic thresholds ranged from 0.06 to 0.31% weed cover contingent on the level of tolerance of the expert adviser. Although this threshold seems low, it is comparable with economic threshold values based on weed density.

The adsorption of nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and oxyfluorfen [2-cholor-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] from aqueous solution by muck soil, and by kaolinite and bentonite saturated with hydrogen or calcium ions, was studied using 14C-labeled herbicides. Both compounds were readily adsorbed from solution by muck soil and Ca- and H-Al-bentonite but only slightly by Ca- and H-Al-kaolinite. Very little of the adsorbed compounds was desorbed after four extractions with distilled water. A bioactivity study using sorghum seedlings (Sorghum bicolor L. ‘RS610′) was conducted with the herbicides in a silica sand medium amended with 1% (w/w) of the various adsorbents. The herbicides were strongly inactivated by muck soil but there was very little inactivation by the clays. There was essentially no movement of either herbicide through 5-cm columns of a silt loam soil and a fine sand soil.

It has been only in comparatively recent years that any appreciable work has been conducted on equipment for the application of chemicals in the soil. Most of the early work was devoted primarily to methods of applying anhydrous ammonia and liquid solutions as fertilizers. In most of this work the principal injection tool consisted of a chisel-type applicator that released the chemical at a single point in the soil. In recent years, investigators have attempted to devise efficient and uniform methods of subsurface distribution. Hedman and Turner reported on a chisel-type applicator equipped with a “fishtail” to give more lateral spread to anhydrous ammonia. Arya and Pickard studied the effect of high pressures and velocities on the application of anhydrous ammonia, which was also single-point injection. Certain problems associated with the application of fungicides and herbicides in the soil have been discussed by Owen and Becker and Costel.

Propham (Isopropyl carbanilate) at 10-5 M concentration does not inhibit DNA synthesis nor does it reduce the number of dividing cells. It does, however, induce a number of abnormal mitotic figures. At higher concentrations (10-3 M) propham inhibits DNA, RNA, and protein synthesis as well as stopping entry of cells into mitosis and causing those which divide to be aberrant. DNA and RNA synthesis are not inhibited for approximately 3 hr, while protein synthesis is reduced within 1 hr. The metabolic inhibitory effect of propham is reversible at least in roots treated for 8 hr. The most likely mode of action of propham is the inhibition of certain mitotic specific proteins, or possibly some kind of protein binding function as has been suggested in the literature.

The metabolic fate of root-applied, carbonyl-labeled, 14C-3-(3-chloro-4-bromophenyl)-1-methoxy-1-methylurea (hereinafter referred to as chlorbromuron) was investigated in tolerant corn (Zea mays L., var. N.J. 9) and susceptible cucumber (Cucurbita sativus L., var. Marketer) in a time-course study. The major metabolite found in corn shoots and roots was the nonphytotoxic 3-(3-chloro-4-bromophenyl)-1-methoxyurea. Evidence of “binding” was found in both shoots and roots of corn. No evidence was found for the metabolism of chlorbromuron in cucumber; however, some binding occurred in both shoots and roots.

Antidotes were evaluated under greenhouse conditions for their ability to prevent injury to corn and sorghum from imazethapyr. Corn was more tolerant to imazethapyr and more effectively protected from imazethapyr toxicity than sorghum. Naphthalic anhydride (NA)3, CGA 92194, or flurazole treatment of corn seed reduced plant injury from preemergence applications of imazethapyr. Corn injury from postemergence applications of imazethapyr was decreased by seed treatment with NA or CGA 92194. Sorghum injury from preemergence applications of imazethapyr was not reduced by seed treatment with the antidotes. NA treatment of sorghum seed was the most effective antidote treatment for decreasing injury from postemergence applications of imazethapyr but the level of sorghum protection was much less than that achieved with corn. Corn seedlings grown from NA-treated and untreated seed absorbed equal amounts of 14C into the roots from nutrient solution containing 14C-imazethapyr. The NA-treated corn plants translocated less of the absorbed 14C to the shoots than the untreated plants. NA treatment of corn seeds increased the rate of imazethapyr conversion to soluble metabolites 2-and 10-fold in the corn seedling roots and shoots, respectively. The increased rate of imazethapyr metabolism in corn following NA seed treatment may be responsible for the protection from imazethapyr toxicity.

Efficacy of atrazine [2-chloro-4-(ethylamino-6-(isopropylamino)-s-triazine] applied preemergence to no-tillage and conventional-tillage corn (Zea mays L.) was studied in the field for 2 yr at two locations. Other variables examined were lime treatments, atrazine rates, and acid-forming (NH4NO3) vs. nonacid-forming (NaNO3) nitrogen fertilizers. Mean surface soil pH levels during the growing season were higher with no-tillage than conventional tillage, because of the retention of lime in the surface in no-tillage vs. mixing it with the soil in conventional tillage, but there was no consistent increase in atrazine efficacy or longevity in one system over the other. Liming significantly increased atrazine efficacy and longevity in both no-tillage and conventional-tillage systems. Increased rates of atrazine increased weed control and longevity of the herbicide. Use of NaNO3 as a nitrogen source resulted in increased atrazine efficacy and longevity as compared with use of NH4NO3 during the first year, which was relatively dry, but had no effect during the second year, which was relatively wet.

Field experiments were conducted to study the feasibility of using trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] for the selective control of johnsongrass [Sorghum halepense (L.) Pers.] from rhizomes and seed in soybeans [Glycine max (L.) Merr. ‘Lee’]. Both herbicides were incorporated into the soil at 0.56 to 3.36 kg/ha with two disk cultivations immediately after application. Most effective johnsongrass control on Dundee silty clay loam (sicl) followed treatments of nitralin or trifluralin at 1.68 to 3.36 kg/ha, but 2 years or more of continuous treatment were required for acceptable control. Trifluralin at 1.12 and 2.24 kg/ha on Sharkey clay and at 0.56 to 2.24 kg/ha on Bosket fine sandy loam (fsl) provided better average johnsongrass control over a 2-year period than nitralin at the same rates, but soybean yields after both herbicides at the same rates were equal. Immediate incorporation of trifluralin or nitralin in all three soils at 1.12 to 2.24 kg/ha for 2 successive years effectively controlled johnsongrass from rhizomes without soybean injury and with greatly increased soybean yields.

Laboratory and field experiments were conducted to determine the effects of several environmental factors on seed germination and seedling emergence of the invasive weed, apple of Peru. The anatomy of the seed was also investigated in this study. The anatomy of the seed is similar to that of an eggplant (Solanum melongena L.) seed. The seed is albuminous, and consists of a seed coat, endosperm, and an embryo. The seed coat, which consists of both outer and inner integuments, is relatively thick. Fresh and dry stored seeds exhibited strong dormancy. Hot water treatment did not affect the seed germination in the light, but significantly (P < 0.05) reduced the germination rate in the dark. Dry-heat treatment had no significant effect on seed germination in the dark, but it significantly (P < 0.05) increased the germination rate in the light. Cold stratification alone did not influence seed germination under constant temperature (25 C) but affected it under alternating temperature (25–15 C). However, a combination of warm and cold stratification produced significant (P < 0.05) germination in the dark as well as in the light. In addition, the effect of warm stratification followed by cold stratification was more pronounced in the dark than in the light. Gibberellin A3 (GA3) (10–3 and 10–4 M) treatments significantly (P < 0.05) increased the seed germination rate compared with that of the control. Emergence rate was maximum for seeds placed on the soil surfaces; no seedling emergence occurred when seeds were placed at a depth of 5 cm.

Certain sulfonylurea (SU) herbicides are used to remove overseeded cool-season species from bermudagrass. The effects of nitrogen (N) on the efficacy of a new SU herbicide, flazasulfuron, have not been determined. Field and laboratory studies were conducted in 2008 and 2009 evaluating the efficacy of flazasulfuron for control of overseeded perennial ryegrass contaminated with annual bluegrass. Flazasulfuron was applied at rates of 4.4, 8.8, and 17.5 g ha−1 alone, and in between sequential applications of N fertilizer at 73 kg N ha−1. N was granularly applied immediately prior to herbicide treatment and 4 wk later. In both years, the level of annual bluegrass control with flazasulfuron and two applications of N at 73 kg N ha−1 was significantly greater than following treatment with flazasulfuron alone. This response was observed for all application rates of flazasulfuron on every rating date. The level of annual bluegrass control with flazasulfuron at 4.4 g ha−1 and two applications of N at 73 kg ha−1 was greater than flazasulfuron at 17.5 g ha−1 alone each year. No significant differences in perennial ryegrass control were observed for flazasulfuron with and without N fertility. In laboratory studies with annual bluegrass, treatment with N fertilizer at 73 kg N ha−1 increased translocation of 14C flazasulfuron (and any potential metabolites) from treated annual bluegrass leaves to other shoot tissues by 18% at 1 h after treatment and 22% at 4 h after treatment compared to plants not treated with N fertilizer. This increase in translocation may explain the increased level of annual bluegrass control observed in the field.

Leaf cytoarchitecture was evaluated by light microscopy and scanning electron microscopy, and cell viability was monitored by fluorescence after treatment of velvetleaf with defined concentrations and droplet sizes of formulated glyphosate and blended tallowamine surfactant. In response to droplets of formulated glyphosate larger than in field sprays but useful for studying structural change, we observe that the leaf epidermis thins and flattens within 1.5 h, the epidermal, mesophyll, and vascular cells at the contact site exhibit localized cytolysis by 6 h, and cytolysis and pycnosis remain restricted to the contact site at 24 h. Using endogeneous fluorescence as a marker for nonviable cells, it was determined that cellular changes are directly correlated with droplet size and that the changes are minimal after exposure to spray sizes and concentrations of formulated glyphosate and blended tallowamine typically used in the field. The results show that, at field use concentrations, the effect of formulated glyphosate and blended tallowamine on leaf cytoarchitecture is modest and localized but sufficient to allow herbicide entry.