Rosering gaillardia (Gaillardia pulchella Foug. # GAIPU) and other herbaceous broadleaf plants were effectively controlled for one season by sprays of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.1 kg ae/ha or glyphosate [N-(phosphonomethyl)glycine] at 1.1 kg ai/ha, or a 4:1 combination of 2,4-D and picloram (4-amino-3,5,6-trichloropicolinic acid) at 0.7 kg ae/ha applied in late March in the southern Rolling Plains of Texas. Production of perennial warm-season grasses increased 428, 480, 728, and 1440 kg/ha on a clay site 7 months after spraying with 2,4-D, 2,4-D plus picloram (4:1), atrazine [2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine], and glyphosate, respectively. Application of 4.4 kg ae/ha of dalapon (2,2-dichloropropionic acid) severely damaged perennial warm-season grasses. Annual cool-season grasses were effectively controlled with sprays of atrazine or glyphosate at 1.1 kg ai/ha or dalapon at 4.4 kg ae/ha. Texas wintergrass (Stipa leucotricha Trin. & Rupr.) production was greatest on rangeland treated with 2,4-D or 2,4-D plus picloram (4:1).

X-ray fluorescence analysis (XFA) is a new method for the spatial localization and quantification of herbicide residue on leaf surfaces. The distribution pattern of propanil (3′,4′-dichloropropionanilide) on the surface of prune (Prunus domestica L.) leaves sprayed to simulate drift is easily mapped using XFA. Residue distribution maps may be electronically enhanced. Enhancement does not qualitatively change the information content of the map when done with discretion.

Combinations of herbicides applied preplant incorporated and preemergence plus at layby were evaluated in corn (Zea mays L.) at three Nebraska locations in 1977 through 1980 for their effectiveness in providing season-long weed control. Pendimethalin [N-(1 -ethylpropyl) - 3,4-dimethyl - 2,6 - dinitrobenzenamine], pendimethalin + atrazine [2- chloro - 4 - (ethylamino) -6 - isopropylamino) -s- triazine ], metolachlor [2 - chloro - N - (2 - ethyl - 6 - methylphenyl) - N - (2 - methoxy -1 - methylethyl) acetamide], alachlor [2 - chloro -2′,6’ - diethyl - N- (methoxymethyl)acetanilide], cyanazine {2 -[[4 - chloro- 6 - (ethylamino) - s - triazin-2 - yl] amino] -2 -methylpropionitrile}, and cyanazine + atrazine were shown to be selective to corn and effective in controlling late - germinating weeds. Irrigated - corn yield was not increased by layby herbicide applications on the weed species and weed densities present in these experiments.

The effect of reduced water availability on glyphosate efficacy and adventitious shoot growth in male and female clones of Canada thistle was studied. Water availability was regulated with polyethylene glycol (PEG) in hydroponically grown plants or by withholding water from soil-grown plants. In hydroponic media, there was 50% more adventitious shoot growth from male plants than from female plants. Both PEG and foliarly applied glyphosate reduced the number of adventitious shoots, regardless of gender. In soil, the same number of adventitious shoots formed on untreated male and female plants. However, when glyphosate was applied to plants growing under dry conditions, there was 75% more adventitious shoot growth from males than females. Distribution of glyphosate was similar in male and female plants. Approximately 23% of applied 14C-glyphosate was transported throughout Canada thistle plants within 10 d of treatment regardless of gender or moisture condition. Gender differences in capacity for vegetative reproduction may alter the sex ratio of Canada thistle populations in the field following glyphosate application.

Field experiments were conducted with the recirculating sprayer (RCS) at Lincoln, Nebraska from 1974 through 1978. Different spray pressures, spray nozzles, and spray volumes with the RCS showed no significant differences in shattercane [Sorghum bicolor (L.) Moench] control or soybean [Glycine max (L.) Merr.] injury when herbicides were applied at three stages of weed growth. When shattercane was treated in a grain sorghum [Sorghum bicolor (L.) Moench] field, poor weed control and excessive crop injury occurred during treatment at the early growth stage as compared with treatments applied 2 weeks later. The final treatment date gave selective weed control in grain sorghum, but many of the shattercane heads had already developed viable seed. A weed-to-crop height differential of at least 45 cm resulted in maximum weed control with minimum crop injury. Common milkweed (Asclepias syriaca L.) control in soybeans varied considerably, but treatments giving over 80% control were glyphosate [N-(phosphonomethyl)glycine] at 1.1 to 4.5 kg/ha applied through the RCS. Other herbicides were less effective. Volunteer corn (Zea mays L.) was controlled selectively at 75 to 100% in soybeans with glyphosate or paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) when applied through the RCS. Shattercane was controlled 95 to 100% in soybeans with glyphosate at 3.4 kg/ha. Unless spray drift and splash can be prevented when using the RCS, glyphosate and paraquat will not give selective control when applied to weeds growing in grain sorghum. Glyphosate applied through the RCS, however, can be a selective method of controlling weed escapes in soybeans because soybeans are not as sensitive to glyphosate as is sorghum.

A considerable amount of scientific time has been spent defining Integrated Pest Management (IPM). The following is quoted from an Extension Committee on Organization and Policy publication (4): “Integrated Pest Management (IPM) is a system that utilizes all suitable pest control techniques and methods to keep pest populations below economically injurious levels. Each pest control technique must be environmentally sound and compatible with production and user objectives. Integrated Pest Management is more than chemical pesticide management. In many cases it includes biological, cultural, and sanitary control practices for all pest complexes.”

Effects of barban (4-chloro-2-butynl m-chlorocarbanilate) were investigated on the growth and metabolism of oat (Avena sativa L. ‘Victoria’) (susceptible) and wheat (Triticum aestivum L. ‘Ushio’) (tolerant) plants. Barban remarkably retarded the growth of oat seedlings but not that of wheat seedlings. Respiration and photosynthesis of both plant species were not inhibited. Protein and RNA synthesis of oat seedlings were remarkably inhibited even 1 day after the barban treatment, while the protein and RNA synthesis of wheat seedlings were inhibited less.

Detached leaves of Drummond's goldenweed [Isocoma drummondii (T. & G.) Greene] absorbed the potassium salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] from aqueous solutions more slowly than did sunflower (Helianthus annuus L.), and both species absorbed less of the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) than 2,4-D. However, there was no difference in absorption of the herbicides by Drummond's goldenweed leaves after 6 h of exposure to solutions containing 0.5% (v/v) surfactant. Attached Drummond's goldenweed leaves absorbed about 50% of available 2,4-D (diethylamine) and 25% of available picloram (potassium salt) within 5 days after spraying in the field during July or November. Herbicide accumulation in Drummond's goldenweed taproots after spray applications was generally slow, regardless of season, but translocation to taproots was substantially greater after application in November than after treatment in March or July. Accumulation of picloram in taproots was faster and more extensive than accumulation of 2,4-D. However, based on mortality at 6 months after treatment, both herbicides were translocated in quantities adequate for control. The greater effectiveness of picloram, despite its low foliar uptake, than 2,4-D is attributed to its greater mobility and root uptake in Drummond's goldenweed after broadcast sprays.

Experiments were conducted in an environmentally controlled growth chamber to determine the effects of temperature (10/5 or 21/7 C, day/night), soil moisture (7, 14, or 20%), timing (preemergence [PRE] or postemergence [POST]), and rate (9 or 18 g ai ha−1) of application on MON 37500 efficacy on Bromus secalinus L. and toxicity to Triticum aestivum L. MON 37500 reduced B. secalinus plant density an average of 40% but did not reduce T. aestivum density. PRE treatments reduced B. secalinus density 40% compared to 12% with POST applications when plants were grown at 10/5 C. Soil moisture level also influenced plant density, with 7.9 plants per pot when soil moisture was maintained at 7%, compared to 8.5 plants per pot with 14 or 20% soil moisture. MON 37500 reduced B. secalinus dry weight more at 18 g ha−1 than at the 9-g ha−1 rate when grown at 21/7 C, but no rate response occurred at 10/5 C. PRE applications of MON 37500 at 10/5 C decreased B. secalinus dry weight 22% more than PRE applications at 21/7 C or POST applications under either temperature regime. However, PRE applications of MON 37500 at 21/7 C decreased T. aestivum biomass an average of 16%, compared to 3% or less with other treatments. At 21/7 C, B. secalinus dry weight decreased 46% as soil moisture increased from 7 to 20%. Bromus secalinus was 10 to 12% less susceptible to MON 37500 when grown at 7% soil moisture at 10/5 C than when grown at the same temperature at 14 or 20% soil moisture. Triticum aestivum injury was greater at 20% soil moisture under each temperature regime.

Monosodium methanearsonate (MSMA) and arsenic acid (AA) were measured simultaneously in johnsongrass (Sorghum halepense (L.) Pers.) and cottonseed (Gossypium hirsutum L. ‘SJ-1’) by a bicolorimetric method. Tissues from plants sprayed with MSMA while growing and tissues with MSMA and AA added just prior to extraction were analyzed. Johnsongrass sprayed with MSMA solution at 11.2 kg/ha contained, on a dry weight basis, 423.0 ppmw of MSMA and 0.00 ppmw of AA at 7 days and 10.83 and 0.21 ppmw, respectively, after 54 days of regrowth. The cotton plants were sprayed twice to runoff with MSMA, first with 0.3 g/L and second with 1.2 g/L. Cottonseed from the sprayed cotton plants contained, on a dry weight basis, 2.45 ppmw of MSMA and 0.08 ppmw of AA after the first picking and 3.02 and 0.10 ppmw, respectively, after the second. Background levels of MSMA and AA were, respectively, on a dry weight basis, 0.63 and 0.02 ppmw in johnsongrass and 0.58 and 0.00 ppmw in cottonseed.

Field research was conducted in Nebraska to evaluate the efficacy of herbicides for the control of summer annual weeds in sorghum [Sorghum bicolor (L.) Moench.]. During 1976 to 1979, no-till plots treated with a mixture of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], and terbutryn [N-(1,1-dimethylethyl)-N′-ethyl-6-(methylthio)-1,3,5-triazine-2,4-diamine] yielded 33% more sorghum grain than plots receiving the same herbicides when a seedbed was prepared by disking. During 1981 to 1983, season-long weed control was obtained with acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl) acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], or terbutryn added to paraquat plus atrazine and metolachlor plus cyanazine plus paraquat applied 10 days prior to planting. The use of seed safeners did not increase sorghum yield.

Aerial herbicide treatments were made on a native stand of short-leaf pine (Pinus echinata Mill.) heavily infested with noncommercial oak (Quercus sp.), hickory (Carya sp.), and associated species in southeastern Oklahoma from 1957 through 1960. Two formulations of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were applied in May and September at 1½ lb/A annually in one, two, and three applications with the later two made a year apart. The most diameter growth for all sizes of pine measured occurred following May treatments. Late May aerial applications also were made with 2-(2,4-dichlorophenoxy) propionic acid (dichloroprop) and 2-(2,4,5-trichlorophenoxy) propionic acid (silvex). Silvex reduced pine cone development, seed fill, and germination.

Native grass growth was increased twice following good weed tree control. However, where dense short-leaf pine seedlings developed, the native grasses were smothered and volume of herbage decreased.

During recent years the increasing use of herbicides for the control of weeds in croplands has stimulated interest in the effect of these chemicals upon the soil microflora. In 1953 Hoover and Colmer (4) showed that the application of 2,4–D to Sharkey sugarcane soil in concentrations comparable to that used in the field had little effect upon the bacteria, actinomycetes, and fungi of this soil. Colmer (1), using the Winogradsky soil plaque technique which can serve to gauge the effect of herbicides upon the nitrogen-fixing genus Azotobacter in their natural habitat, found that field application rates were not harmful to A. chroococcum, and it was only when prohibitive rates of application of 2,4–D (400–600 ppm) were used that growth was markedly affected.

Synthetic seed banks are a useful tool for tracking how weed populations change over time. By sowing a known number of seeds of a given species within a quadrat with defined boundaries, an investigator can measure the number remaining and thereby calculate demographic rates (e.g., mortality). The alternative is to use in situ seeds and estimate their initial population density via sampling. To make a synthetic seed bank approach useful within an agricultural system subjected to soil disturbances such as tillage, one would need a way to account for seeds leaving the initial quadrat (i.e., a way to follow how the area encompassing the sown seeds changes over time). Without accounting for the change in location/extent of the synthetic seed bank, any field operation moving soil will create additional uncertainty in population size. Depending on the “aggressiveness” of specific field operations and the initial size of the quadrat, this effect might be negligible or so large as to be intractable. Here, we describe a method for following a synthetic seed bank over time using a “living boundary” of nondormant seeds, which effectively play the role of tracers used in the study of dynamics in other scientific disciplines. Study quadrats in East Lansing, MI, and Arlington, WI, were sown with giant foxtail and velvetleaf at a rate of 2,000 seeds m−2. The study quadrats were marked on the perimeter and diagonals using nondormant seeds of three marker species: kale, radish, and rye. The areas were then subjected to tillage and planting operations. Spatial coordinates of seedling locations for the marker and weed species were obtained through digital image processing. A nonparametric comparison of the spatial displacement of marker and weed species indicated that their empirical spatial distributions did not differ. The marker species quadrats described by the 50th, 90th, and 99th quantiles of movement contained all velvetleaf seedlings in Wisconsin, all velvetleaf seedlings in Michigan, and all giant foxtail seedlings in Michigan, respectively. The results suggest a simple rule for applying the method to field demography studies: after the original quadrat is deformed and seedlings have emerged, flag the polygon containing all marker seedlings to obtain the expanded quadrat containing the study weed population.

Typha angustifolia L. var. brownii (Kunth) Kronf., known as cumbungi in Australia and narrow leaved cattail in the U. S. A., is a deep rooted perennial widely distributed throughout the world. It occurs naturally in swamps and marshy areas and also in irrigation channels, where it may seriously impede the flow of water during the irrigation season. Various mechanical methods of control have beeen devised; the most successful consists of regular cutting and subsequent maintenance of 15 to 18 inches of water above the cut stalks. This method was successfully employed in the Murrumbidgee Irrigation Area of New South Wales for many years, but recently has been virtually discarded because of rising labour costs.

Once it has been determined that the primary mode of action of a herbicide is dependent upon entry into the plant through its roots, it becomes important to know what factors will influence its movement in the soil. The findings of Ennis (3, 4) and Baldwin, Freed, and Fang (1) that certain cereals absorb carbamates by means of their roots rather than through their leaves stimulated experiments to study the effects of various soil factors upon the persistence and movement of carbamates in the soil. Blouch and Fults (2) found that the effect of various soil types on the effectiveness of pre-emergence applications of CIPC to several crops was much less than the effect of soil structure and high levels of organic matter. Data presented by Ogle and Warren (9) indicated that organic matter may have considerable effect on inhibiting the movement of CIPC in the soil. They also emphasized that the herbicidal behavior of a chemical in soil cannot be predicted from a study of one soil type, since there appears to be an interaction between soil type and movement of the herbicide. Smith and Ennis (12) reported similar results and also found that oil solutions of CIPC were less mobile than aqueous solutions.

Tall fleabane [Conyza sumatrensis (Retz.) E. Walker] is commonly invasive in agricultural fields, reducing yield in various infested crops. The current study investigates the genetic diversity within and between a significant number of invasive C. sumatrensis biotypes in soybean fields in southern, southeastern, and midwestern Brazil, using microsatellites as molecular markers. High and low observed and expected heterozygosity estimated in microsatellite loci supported our hypothesis that different levels of genetic diversity may be detected within biotypes from different invaded fields. Analysis of a significant number of biotypes in several fields showed high and low genetic diversity not associated with geographic distribution, bottleneck effect, or susceptibility to glyphosate. A deficit of heterozygous plants, high genetic divergence, and moderate allelic transference were also observed. Allelic fixation was different in the different biotypes. The bottleneck effect was seen in biotypes with reduced genetic diversity and in biotypes with the highest genetic diversity. Data on genetic diversity, bottleneck effect, and glyphosate resistance showed contrasts in biotypes from nearby invaded fields. Our study showed different genetic diversity levels in biotypes from invaded areas under the same climatic conditions.

The adoption of dicamba-resistant cotton (Gossypium hirsutum L.) cultivars allows using dicamba to reduce weed populations across growing seasons. However, the overuse of this tool risks selecting new herbicide-resistant biotypes. The objectives of this research were to determine the population trajectories of several weed species and track the frequency of glyphosate-resistant (GR) Palmer amaranth (Amaranthus palmeri S. Watson) over 8 yr in dicamba-resistant cotton. An experiment was established in North Carolina in 2011, and during the first 4 yr, different herbicide programs were applied. These programs included postemergence applications of glyphosate, alone or with dicamba, with or without residual herbicides. During the last 4 yr, all programs received glyphosate plus dicamba. Biennial rotations of postemergence applications of glyphosate only and glyphosate plus dicamba postemergence with and without preemergence herbicides were also included. Sequential applications of glyphosate plus dicamba were applied to the entire test area for the final 4 yr of the study. No herbicide program was entirely successful in controlling the weed community. Weed population trajectories were different according to species and herbicide program, creating all possible outcomes; some increased, others decreased, and others remained stable. Density of resistant A. palmeri increased during the first 4 yr with glyphosate-only programs (up to 11,739 plants m−2) and decreased a 96% during the final 4 yr, when glyphosate plus dicamba was implemented. This species had a strong influence on population levels of other weed species in the community. Goosegrass [Eleusine indica (L.) Gaertn.] was not affected by A. palmeri population levels and even increased its density in some herbicide programs, indicating that not only herbicide resistance but also reproductive rates and competitive dynamics are critical for determining weed population trajectories under intensive herbicide-based control programs. Frequency of glyphosate resistance reached a maximum of 62% after 4 yr, and those levels were maintained until the end of the experiment.

Purple deadnettle is an obligate winter annual weed and an alternate host of soybean cyst nematode (SCN). Field experiments were conducted using microplots to determine (1) the effect of purple deadnettle planting date and (2) the effect of purple deadnettle removal time on SCN egg population density in continuous no-tillage soybean. A population change factor (PCF) to assess treatment effects on SCN population densities was calculated by dividing the SCN population density at each sampling time (Pf) by the initial population density before treatments were applied (Pi). In the planting date experiment, purple deadnettle seeded on October 3, 11, and 18 resulted in PCF values ranging from 7.28 to 11.41, which were three- to fivefold higher than the PCF values for the weed-free control or purple deadnettle seeded on September 6, 20, and 27. Self-thinning of purple deadnettle seeded in September may have resulted in higher levels of SCN mortality compared to later seeding dates. In the removal time experiment, purple deadnettle removal at 2 and 4 wk after emergence (WAE) resulted in PCF values of 1.19 and 1.54, respectively, which were similar to the PCF for the weed-free control. In contrast, PCF values for purple deadnettle removal times of 6 WAE or later ranged from 2.46 to 5.44. Field and greenhouse experiments provided evidence that completion of the SCN life cycle on purple deadnettle was prevented if the weed was removed before the accumulation of 380 soil degree days within the 5 to 30 C range. Results from the removal study also suggested that completion of the first SCN generation on purple deadnettle in the fall was the primary factor causing increases in egg population density, since PCF values did not continue to increase significantly beyond the 6 WAE removal time.