American burnweed is an increasingly common annual weed in wild blueberry fields in Atlantic Canada and Maine. Knowledge of seed dormancy characteristics and potential for this species to form persistent seedbanks in wild blueberry soils, however, is lacking. A series of experiments were therefore conducted to investigate potential mechanisms regulating American burnweed seed dormancy in wild blueberry fields. Seeds were dormant at maturity and did not germinate in dark or light under warm conditions. Cold moist stratification (CMS) at 4 C for 90 d followed by exposure to warm conditions (22/15 C day/night) and light caused >90% germination, and germination was generally maximized following 80 d CMS. Exogenous potassium nitrate applied as a 5% solution did not stimulate germination, but nearly all seeds (>95%) germinated following treatment with 200, 400, 600, or 800 ppm (w/v) gibberellic acid (GA3) solution. Physical removal of the seed coat or seed exposure to short durations of dry heat did not increase germination. Seed exposure to 1 s of direct flame increased germination, but germination was low relative to germination following CMS and treatment with GA3. Based on these results, we conclude that American burnweed seeds in wild blueberry fields exhibit non–deep physiological dormancy that is most readily broken by CMS and light or seed treatment with GA3. Seeds will likely be exposed to favorable conditions for breaking dormancy (cold temperatures and light) in wild blueberry fields due to lack of tillage and seed burial, indicating high potential for this weed species to proliferate in wild blueberry fields if not properly managed.

The control of undesirable woody plants is one of the biggest land management problems on non-crop land in the South. There are more than six million acres of pine sites in Louisiana alone that are in need of cull hardwood control (12). Large acreages of similar stands and sites are located in other southern states. Because of the competition for land and increased demand for raw materials, many landowners have realized the necessity of utilizing their land to the fullest extent.

Synthetic auxin herbicides were developed and commercialized 60 yr before their mode of action was definitively elucidated. Although evolution of resistance to auxinic herbicides proceeded more slowly than for some other herbicide chemistries, it has become a major problem in the dicotyledonous weeds of many cropping areas of the world. With the molecular characterization of the auxin perception and signaling pathway in the mid-2000s came a greater understanding of how auxinic herbicides work, and how resistance may develop in weeds subjected to repeated selection with these herbicides. In wild radish (Raphanus raphanistrum L.) populations in southern Australia, resistance to multiple herbicides, including synthetic auxins such as 2,4-D, has reduced the number of chemical control options available. The aim of this study was to determine whether compounds involved in auxin biosynthesis, transport, and signaling are able to synergize with 2,4-D and increase its ability to control 2,4-D–resistant R. raphanistrum populations. Although some mild synergism was observed with a few compounds (abscisic acid, cyclanilide, tryptamine), the response was not large or consistent enough to warrant further study. Similarly, alternative auxinic herbicides applied pre- or postemergence were no more effective than 2,4-D. Therefore, while use of auxinic herbicides continues to increase due to the adoption of transgenic resistant crops, nonchemical control techniques will become more important, and chemical control of 2,4-D–resistant R. raphanistrum should be undertaken with alternative modes of action, using mixtures and good stewardship to delay the development of resistance for as long as possible.

Seed retention, and ultimately seed shatter, are extremely important for the efficacy of harvest weed seed control (HWSC) and are likely influenced by various agroecological and environmental factors. Field studies investigated seed-shattering phenology of 22 weed species across three soybean [Glycine max (L.) Merr.]-producing regions in the United States. We further evaluated the potential drivers of seed shatter in terms of weather conditions, growing degree days, and plant biomass. Based on the results, weather conditions had no consistent impact on weed seed shatter. However, there was a positive correlation between individual weed plant biomass and delayed weed seed–shattering rates during harvest. This work demonstrates that HWSC can potentially reduce weed seedbank inputs of plants that have escaped early-season management practices and retained seed through harvest. However, smaller individuals of plants within the same population that shatter seed before harvest pose a risk of escaping early-season management and HWSC.

The design and use of a variable-dosage spraying machine for the experimental evaluation of herbicides has been reported by Pfeiffer et al. (1). This equipment sprays at constant volume while simultaneously diluting the spray mixture exponentially. The machine is composed of a series arrangement of diluent tank, concentrate tank, pump, and nozzles. The concentrate tank is equipped with a rapid mechanical agitator. The pump propels the spray liquid from the concentrate tank through the nozzles in the conventional manner. The liquid withdrawn from the concentrate tank is replaced by an equal volume of water or other diluent from the diluent tank. Thus the concentration of active ingredient in the spray decreases logarithmically with the volume of spray delivered. Since spray volume is constant with time, by moving the sprayer at constant speed, the rate of application of the active ingredient becomes a logarithmic function of distance along the plot. The machine is mounted on a four-wheel-drive light truck and draws power for the pump and agitator from the power take-off.

Virginia chain fern (Woodwardia virginica (L.) Smith) was controlled by 2,6-dichlorobenzonitrile (dichlobenil) in cranberry bogs on a St. Johns soil at Chatsworth, New Jersey, in experiments conducted during 1960, 1961, 1962, 1963, and 1964. The treatments were applied at emergence of the weed. Stalk counts of the fern were recorded the year following treatment. Excellent control was obtained at either 4 or 8 lb/A of dichlobenil. No re-growth occurred in subsequent years.

Weed problems in Alaska are relatively new because man's agricultural activities in this region have been limited until very recently to isolated clearings. These early clearings made by prospectors and homesteaders to produce feed for their stock also unintentionally served as increase plots for some troublesome weeds.

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

Treatments made at 2-week intervals on guava (Psidium guajava L.) with a 1:1 ratio of butoxyethanol esters of 2,4-dichlorophenoxyacetic acid:2,4,5-trichlorophenoxyacetic acid (2,4-D:2,4,5-T) have shown it to be more susceptible when treatments are made during the wet season than during the dry season. Greater susceptibility is related to a plant condition characterized by many new leaves but little or no terminal twig elongation. A similar pattern of defoliation response is caused by 2-methoxy-3,6-dichlorobenzoic acid (dicamba) and 2,3,6-trichloropicolinic acid (picloram) as by 2,4-D:2,4,5-T, but the period of maximum susceptibility based on defoliation percentages 1 year after treatment occurred later in the season.

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

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

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

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

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

Diquat (6,7-dihydropyrido[1,2-a:2’,1′-c] pyrazidiinium salt) was applied to several emergent, submersed, floating-leaved, and free-floating aquatic plants common in Central Illinois ponds. At relatively low rates, it was effective in controlling several submersed aquatic plants but not American pondweed, Potamogeton nodosus, and cabomba, Cabomba caroliniana. This herbicide also was effective on several common emergent species.

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

A system involving resting cells of Euglena gracilis provides a rapid and convenient test system for screening potential herbicides which act as inhibitors of chlorophyll synthesis. The system appears to distinguish between inhibitors of chloroplast formation, such as 3-amino-1,2,4-triazole, and inhibitors of chlorophyll formation per se, such as ethionine.

Portability is a very important feature of a sprayer for experimental plots on rangeland. The rockiness of many sites and the height and density of many weed stands, such as species of Artemesia, Chrysothamnus, Linaria, Alhagi, and Centaurea, preclude use of push-type sprayers mounted on wheels. Ries and Terry discuss the use of a portable small-plot sprayer but the capacity of their sprayer is not adequate for many situations. Range weed control research is often combined with reseeding and fertilization studies, and a sprayer with considerable capacity is needed for large plots. Swath widths of at least 10 feet are desirable.

In 1955, three British workers (2) described a variable dosage sprayer which was designed for large field plots. The original description did not attract much attention in the United States when it was first published, but the principles described therein are receiving more attention at the present time, both in this country and abroad (1).

One of the major problems in present-day soybean production is weed control. The increased interest in profitable soybean production in recent years has stimulated a demand for a satisfactory and economical means of chemical control to supplement cultural practices. The gradual shift from solid planting to row planting has practically eliminated the problem of weeds between rows, but it has not solved the critical problem of weed growth in the row.