The role of ethylene in kochia injury following the application of dicamba and other auxinic herbicides is not known. Experiments were conducted to evaluate kochia response to ethylene generated within plant tissue and to quantify ethylene emission from kochia following dicamba application to determine if ethylene production could be used to differentiate between dicamba-susceptible (S) and dicamba-resistant (R) kochia accessions. Dicamba at 0.28 kg ha−1 and fluroxypyr at 0.28 kg ha−1 caused severe stem and petiole twisting within 6 h of application, with S kochia exhibiting a greater level of epinasty than R kochia and fluroxypyr causing more epinasty than dicamba. Fluroxypyr provided similar control of S and R kochia, but dicamba provided less control of R kochia than S kochia. Ethylene evolution in S kochia from ethephon at 1.1 kg ha−1 and dicamba at 0.28 kg ha−1 was similar, approximately 70 ng (g fresh weight)−1 h−1. Elevated ethylene concentration from as much as 2 kg ha−1 ethephon did not produce epinastic symptoms or other plant response in S or R kochia. Ethylene evolution following dicamba application increased with time up to 48 h after application and with increasing dicamba rate up to 0.56 kg ha−1, which were the end points of the research. Ethylene evolution from the S accession was 2.5 times that of the R accession averaged across dicamba rates and harvest times. The greatest difference in ethylene evolution between S and R accessions occurred 24 h after treatment at 0.14 kg ha−1 dicamba, with S kochia producing ethylene at 470%, compared with R kochia.

Studies were conducted to determine the effects of scarification, temperature, osmotic potential, and pH on seed germination of buffalo gourd and to examine seedling emergence and establishment. Mechanical and chemical scarification did not increase germination compared to non-scarified seed. Seed germinated at constant temperatures in the dark from 15 to 37 C with optimum germination at 25 C. As osmotic potentials became more negative from −0.1 to −0.8 MPa, germination decreased from 77 to 53%. Germination increased from 15% at pH 2.2 to 90% at pH 8. Seedlings were able to emerge from depths as great as 12 cm, and plants younger than 19 d were not able to sprout from the roots when the shoots were removed.

Two winter wheat cultivars are known to differ in sensitivity to metribuzin: TAM W-101 (tolerant) and Vona (sensitive). Their reciprocal F1, reciprocal F2, and backcross populations were compared to determine the genetic expression of metribuzin sensitivity. TAM W-101 showed a much wider range of response to metribuzin than Vona with little overlap between the two distributions. Both sets of reciprocal F1 and F2 populations resembled Vona in metribuzin response, but the variances of maternal TAM W-101 populations exceeded those of maternal Vona populations. Genetic segregation in metribuzin response was expressed in TAM W-101/Vona F2 but not in Vona/TAM W-101 F2. The greater variability observed in the metribuzin-tolerant parent TAM W-101 and maternal TAM W-101 populations could not simply be interpreted as the result of differential sampling of male and female gametes from TAM W-101.

The 14C-AC 263,222 was foliar applied to common cocklebur, johnsongrass, peanut, sicklepod, and soybean in order to study translocation and metabolism characteristics in each species. Differential absorption of 14C-AC 263,222 between species was evident 4 h after application. At 48 h after application, sicklepod and peanut absorbed more 14C-AC 263,222 than johnsongrass, common cocklebur, or soybean. Translocation of 14C-AC 263,222 and its metabolites out of the treated leaves increased with time for all species. The 14C-AC 263,222 and its metabolites appear to be both xylem- and phloem-mobile based on patterns of movement. Absorption and translocation differences occurred between species; however, they did not appear to explain differential species response. Metabolism of 14C-AC 263,222 differed greatly among species. Common cocklebur metabolized less 14C-AC 263,222 than any other species 96 h after application. Johnsongrass and sicklepod metabolized 24 and 28% of the 14C-AC 263,222, respectively, 96 h after application. Peanut and soybean metabolized 76 and 62%, respectively, of the 14C-AC 263,222 96 h after treatment. The half-life of 14C-AC 263,222 was 1.1, 2.5, 7.7, 11.6, and 34.5 d in peanut, soybean, sicklepod, johnsongrass, and common cocklebur, respectively. Differential tolerance of species appears to be directly related to the half-life of AC 263,222 in the plant.

Pollen movement between individuals can increase the rate of herbicide resistance evolution by spreading resistance alleles within or between populations and by facilitating the rapid accumulation of resistance alleles within individuals. This study investigated the level of pollen-mediated gene flow between paraquat-resistant and paraquat-susceptible populations of the self-pollinated weed species hare barley. The experiment was conducted in both directions, from resistant to susceptible and susceptible to resistant, across 2 yr. To maximize the potential for pollen flow, individual plants were grown in a single pot. The level of gene flow was similar across years and between genotypes. The level of pollen-mediated gene flow ranged from 0.06 to 0.15%. Gene flow from resistant to susceptible plants was confirmed by demonstrating segregation for resistance in the progeny of suspected crosses. This study suggests that pollen-mediated gene flow will occur in this species at frequencies less than 0.16% and could assist the accumulation of resistance alleles within a population. These low levels of gene flow through pollen movement suggest that cross-pollination over larger distances would be unlikely and pollen movement probably does not contribute to gene flow between populations.

4–Chloro–2–butynyl N–(3–chlorophenyl)carbamate (S–847) has been reported to show promise for selective control of wild oats in wheat, barley, flax, sugar beets, and peas. This paper presents data on the influence of several treatment conditions on wild oat control.

The cotton-producing industry today faces a real challenge in its attempt to control weeds in cotton. It is a problem with many facets. Differences in weed species, topography, soil type, scale of operation, rainfall, and many other factors make it difficult to develop single practices that work satisfactorily across large areas of the Cotton Belt.

The mesquite tree (Prosopis spp.) has been invading southwestern ranges to an alarming degree during the last half century, and has become a serious competitor for available moisture and light with perennial grass—the principal forage of livestock in this area. Its distribution in Arizona, New Mexico, and Texas has been estimated at over 70 million acres. Of the three varieties of mesquite found in these States, velvet mesquite (P. juliflora var. velutina (Woot.) Sarg.) is essentially limited to Arizona, and is the most common variety found therein.

These herbicides at rates of .01 to .25 lb/A caused moderate to severe morphological effects on soybeans and significant yield reductions. Soybeans treated in the vegetative stage were injured more than those treated in the bloom stage. The herbicide 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) injured soybeans most followed by 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 2,4-dichlorophenoxyacetic acid (2,4-D), and 4-(2,4-dichlorophenoxy)-butyric acid (2,4-DB), in that order.

The quantities of chloroplast proteins and chlorophyll were lower in oat plants treated 6 days with 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) than in the controls. Radioactive amino acid incorporation into chloroplasts indicated that the reduced levels of protein resulted from reduced synthesis. Glucose improved the amino acid incorporation in the treated tissue, but still the rate was reduced markedly by the simazine treatment. An effect of simazine even in darkness on amino acid incorporation into chloroplasts was suggested by the data. Total ribonucleic acid (RNA) content and synthesis as measured by incorporation of p32 were altered by simazine treatments.

Laboratory photolysis rates of 2,4-D [(2,4-dichlorophenoxy)acetic acid], bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} in dilute aqueous solution were enhanced by the presence of adjuvants. Addition of 1.0% (v/v) petroleum oil concentrate (POC), 1.0% (v/v) soybean oil concentrate (SBOC), and 0.15% (v/v) emulsifier package (EP) enhanced herbicide photolysis rates more than addition of 0.15% (v/v) oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate). Bioassays showed that phytotoxicity of photolyzed herbicide solutions was negatively correlated with time of exposure to ultraviolet light. Addition of 0.85% (v/v) acetophenone to aqueous herbicide solutions containing 0.15% (v/v) oxysorbic strongly sensitized photodegradation of 2,4-D, and to a lesser extent, haloxyfop. Acetophenone had no effect on bentazon photolysis in the presence of oxysorbic. In another study, herbicides were dissolved in white mineral oil or once-refined soybean oil and exposed to ultraviolet light. After a 6-h exposure, there was 92% loss of haloxyfop in mineral oil and 36% loss in soybean oil. There was no difference between oils in affecting the photolysis rate of 2,4-D or bentazon.

The use of 2,4-dichlorophenoxyacetic acid (2,4-D) to control annual weeds such as pigweed (Amaranthus retroflexus L.) is common. Abundant evidence has been published to show that 2,4-D affects germination and subsequent seedling development. Allard et al. found that 2,4-D delayed germination and caused abnormalities in seedlings of 22 broadleaf and cereal species. Elongation of radicles was inhibited in mustard seedlings and in both non-dormant and embryo-dormant seeds as well as in seeds with impermeable seed coats. Germination can not only be delayed but can be inhibited, although at low concentrations of 2,4-D germination may be accelerated. Leachates produced by rainfall coming in contact with 2,4-D in soil were deleterious to seeds of flax and corn. To explore further the effects of 2,4-D on seeds, germination tests were made with scarified and nonscarified seeds of pigweed and on the effect on yield and germination of seeds harvested from pigweed plants that were sprayed with sublethal doses of 2,4-D in field plots.

Field studies in 1978 and 1979 evaluated the effectiveness of single and combination herbicide treatments in processing peas (Pisum sativum L.) and soybeans [Glycine max (L.) Merr.] for the control of wild proso millet (Panicum miliaceum L.). Eight treatments that included dinitroaniline herbicides controlled wild proso millet adequately through the entire growing season of the early-planted peas (approximately 60 days). Wild proso millet emergence and growth in untreated peas was suppressed by the early emergence, rapid growth, and high plant density of the drill-planted crop. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.8 kg/ha stunted pea growth and was the only treatment that reduced yields significantly. No herbicide treatment evaluated in soybeans controlled wild proso millet adequately for the entire growing season without reducing soybean growth and yield. Treatments containing dinitroaniline herbicides, which controlled wild proso millet in peas and resulted in good yield, did not perform similarly in soybeans.

In Israel, an intensive modern agriculture has developed under difficult ecological constraints. The climate is characterized by two distinct seasons – a cool, rainy winter and a hot, dry summer. In winter, there are often temporary excesses of rain, causing erosion and preventing regular cultivation of fields; and in summer the soil dries out, and intensive cropping is only possible with irrigation. However, water is scarce and rationed directly by maximizing irrigation efficiency, and indirectly by controlling weeds, which compete for soil moisture.

Preemergence applications of herbicides were evaluated for their effect on establishment of zoysiagrass (Zoysia japonica Steud.) with competition from either smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl. # DIGIS] or goosegrass [Eleusine indica (L.) Gaertn. # ELEIN]. When ‘Meyer’ and ‘Belair’ zoysiagrass plugs were grown in sand and treated in the greenhouse, none of the herbicides reduced root weight or length. When plugs were grown in a Sassafrass sandy loam, bensulide {O,O-bis(1-methylethyl)-S-[2-[(phenylsulfonyl)amino] ethyl] phosphorodithioate} and simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine) reduced root weight, and simazine reduced root length of Belair, but not Meyer. In smooth crabgrass-infested field plots, more stolons were produced from Meyer plugs treated with simazine, oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one}, and siduron [N-(2-methylcyclohexyl)-N′-phenylurea] than plugs treated with bensulide, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], or the untreated control. At the end of two growing seasons, metribuzin-treated plots had significantly less zoysiagrass than other plots. Oxadiazon, DCPA (dimethyl tetrachloroterephthalate), and siduron enhanced the field establishment rate where Meyer zoysiagrass was competing with high populations of smooth crabgrass.

A population model of itchgrass was developed for a typical corn–based cropping system in the Pacific coastal region of Costa Rica. Field experiments were conducted to quantify density-dependent seedling mortality and fecundity. Additional information required for the model was obtained from the literature. Effect of control methods on itchgrass density—including a leguminous cover crop (velvetbean), a preemergence herbicide (pendimethalin), and classical biocontrol with the head smut—alone and in combination, were investigated using the model. According to model results, the cover crop planted at high and low densities between corn rows was highly efficient, reducing the initial itchgrass density from 54 plants m−2 to 4 and 17 plants m−2, respectively. Associating velvetbean with corn solely in the first crop each year resulted in predicted itchgrass densities of 33 and 36 plants m−2 (at high and low cover crop planting densities, respectively). The improvement in corn yield from preemergence herbicide or biocontrol in addition to the cover crop was only modest. This indicated that if, in practice, the cover crop is as effective as predicted, an inexpensive control tactic such as biological control (provided that an infection rate of at least 50% can be achieved) should be given priority to prevent income losses.

Since the commercialization of herbicide-resistant (HR) crops, primarily glyphosate-resistant crops, their adoption has increased rapidly. Multiple herbicide resistance traits in crops such as canola (Brassica napus L.), corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] have become available in recent years, and management of their volunteers needs attention to prevent interference and yield loss in rotational crops. The objectives of this review were to summarize HR crop traits in barley (Hordeum vulgare L.), canola, corn, cotton, rice (Oryza sativa L.), soybean, sugarbeet (Beta vulgaris L.), and wheat (Triticum aestivum L.); assess their potential for volunteerism; and review existing literature on the interference of HR crop volunteers, yield loss, and their management in rotational crops. HR crop volunteers are problem weeds in agronomic cropping systems, and the impact of volunteerism depends on several factors, such as crop grown in rotation, the density of volunteers, management practices, and microclimate. Interference of imidazolinone-resistant (IR) barley or wheat volunteers can be a problem in rotational crops, particularly when IR crops such as canola or wheat are grown. HR canola volunteers are abundant in the Northern Great Plains due to high fecundity, seed loss before or during harvest, and secondary seed dormancy, and they can interfere in crops grown in rotation such as flax (Linum usitatissimum L.), field peas (Pisum sativum L.), and soybean. HR corn volunteers are competitive in crops grown in rotation such as corn, cotton, soybean, and sugarbeet, with yield loss depending on the density of HR corn volunteers. Volunteers of HR cotton, rice, soybean, and sugarbeet are not major concerns and can be controlled with existing herbicides. Herbicide options would be limited if the crop volunteers are multiple HR; therefore, recording the cultivar planted the previous year and selecting the appropriate herbicide are important. The increasing use of 2,4-D, dicamba, glufosinate, and glyphosate in North American cropping systems requires research on herbicide interactions and alternative herbicides or methods for controlling multiple HR crop volunteers.

The loss of herbicide options due to resistance and lack of new chemistries have delivered the realization that herbicides are a finite resource and weed control alternatives are desperately needed. In Australian conservation cropping, the only available alternatives suited to routine use are the recently introduced harvest weed seed control (HWSC) and the ever-present but undervalued crop competition. Target-neighbor design pot studies examined wheat (Triticum aestivum L.) competition effects on biomass and seed production of rigid ryegrass (Lolium rigidum Gaudin), wild radish (Raphanus raphanistrum L.), ripgut brome (Bromus diandrus Roth), and wild oat (Avena fatua L.). The influence of wheat competition on crop canopy distribution of weed biomass and seed production was also examined. At the current commercially targeted wheat density (120 plants m−2) weed biomass was reduced by 69%, 73%, 72%, and 49% and seed production by 78%, 78%, 77%, and 50% for L. rigidum, R. raphanistrum, B. diandrus, and A. fatua, respectively, when compared with no competition. These results highlighted the importance of uniform wheat crop establishment in minimizing the ongoing impact of weeds. Enhanced what competition (from 120 to 400 plants m−2) resulted in further smaller, but substantial, reductions in biomass (19%, 13%, 20%, and 39%) and seed production (12%, 13%, 17%, and 45%) for L. rigidum, R. raphanistrum, B. diandrus, and A. fatua, respectively. This enhanced competition also increased weed seed retention in the upper crop canopy (>40 cm) by 35% and 31% for L. rigidum and B. diandrus, respectively, but not for A. fatua and R. raphanistrum, for which weed seed retention was already >80% at the wheat density of 120 plants m−2. Enhanced wheat crop competition, then, has the dual effect of restricting the growth and development of L. rigidum, R. raphanistrum, B. diandrus, and A. fatua as well increasing the susceptibility of these weed species to HWSC.

The members of the genus Cuscuta (common name: dodder) are obligate holoparasitic plants that are found throughout the agricultural regions of the world. Of all of the species of dodder, field dodder (Cuscuta campestris) causes the most damage to crops. This species parasitizes the shoots of broadleaf plant crops and weeds. We conducted a series of field dodder seed germination tests in controlled-temperature chambers, in order to describe the effect of temperature on field dodder germination and develop a germination model based on the obtained data. The best fit was obtained when temperature data and time were transformed to thermal time using the beta-function model. The field dodder germination model can serve as a tool for knowledge-based predictions of germination and emergence timing, to allow for the implementation of effective mechanical and chemical management measures.

The selective properties of 5-amino-4-chloro-2-phenyl-3-(2H)-pyridazinone (pyrazon), a new herbicide for the control of weeds in sugar beets, were investigated. Common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and green and yellow foxtail (Setaria viridis (L.) Beauv. and S. glauca (L.) Beauv.) represented about 77% of the weeds emerging and developing with beets. The preemergence rate of 4 to 5 lb/A pyrazon satisfactorily controlled the two broadleaf weed species but was marginal in controlling foxtail. At 6 and 7½ lb/A, beet stands were reduced; however, because of the standard practice of overseeding, normal stands were possible and yields of roots and extractable sugar were unaffected. Preemergence applications of aqueous suspensions of pyrazon were more satisfactory than postemergence. The addition of miscible non-phytotoxic oils or adjuvants to aqueous mixtures greatly improved the postemergence activity of pyrazon. In spite of the occasional temporary beet injury, beets in the two to four-leaf stage seemed relatively tolerant to postemergence treatments. Control was excellent when weeds were treated in the seedling stage (i.e. between cotyledon and four true leaves).