Laboratory experiments were conducted to determine the fate of 14C-EPTC in a soil that had a history of vernolate application and exhibited accelerated degradation of carbamothioate herbicides compared to nonhistory soil. A very rapid mineralization of the herbicide to 14CO2 was evident in history soil, compared to nonhistory soil. The two soils did not differ in the amounts of the EPTC lost through volatilization or in the nonextractable radioactive fractions. Except for small quantities of EPTC-sulfoxide and sulfone, no other metabolites were detected. Degradation of 14C-EPTC, as determined by evolution of 14CO2 in history soil, was drastically inhibited following soil sterilization by means of autoclaving or gamma irradiation. Soil disinfestation by solarization, methyl bromide, or metham had a pronounced inhibitory effect during the first 6 days, but was less effective than sterilization. Treatment of a history soil with the fungicide 2-methoxyethylmercury chloride and dietholate strongly inhibited EPTC degradation, while thiram and fentin acetate had only short lasting effects. Cycloheximide, an antifungal antibiotic, had little effect on the degradation of EPTC while chloramphenicol, an antibacterial antibiotic, inhibited the herbicide degradation. These results indicate that accelerated degradation of EPTC is linked to the activity of soil microorganisms, e.g. bacteria, and can be controlled by sterilization and chemical treatments.

Wax filaments > 100 μm long on the epidermis of johnsongrass leaves and culms occurred only around the edge of costal cork-silica cell pairs and intercostal silica cells. Silica cells alternating with cork cells occurred in rows over veins. Solitary or occasionally paired cork-silica cells occurred between veins. The high silicon content of silica cells was verified with X-ray mapping of silicon. X-ray analysis also indicated that wax filaments contained silicon. Scanning electron micrographs (SEM) of dislodged intercostal silica cells showed that wax filaments emerged from an integument that surrounded the silica cell. It is theorized that at high ambient temperatures the silica gel in silica cells provides the localized cooling necessary to solidify liquid wax constituents as they are extruded onto the surface of the plant.

Twenty-six cultivars of tomatoes from several countries were divided into four metribuzin [4-amino-6-tert-butyl-3-(methylthio)-1,2,4-triazin-5(4H)-one] tolerance groups: tolerant, semi-tolerant, semi-susceptible, and susceptible. Early maturity and tolerance to metribuzin were correlated (r = −0.78) in the field experiment and (r = −0.72) in a sinking leaf-disc bioassay. New super early cultivars were especially sensitive to metribuzin. Chlorophyll a and b content were not highly correlated with tolerance to metribuzin. Metribuzin rates used for weed control are close to toxic concentrations for very early cultivars of tomatoes. Plants in the 9-leaf stage were less sensitive than plants in the 5- or 7-leaf stage. Metribuzin tolerance came at later stages in early maturing cultivars than in later maturing cultivars.

More 4-amino-3,5,6-trichloropicolinic acid (picloram) was detected in soil samples by soybean (Glycine max (L.) Merr., var. Ford) bioassay when the herbicide was applied in the fall than when it was applied in the spring to several pasture types. Downward movement was greater in sandy loam than in silty clay loam. Dissipation of picloram was greatest in the upper 12 inches regardless of soil type. More picloram was detected in the 24 to 36-inch depth from plots treated 1, 2, or 3 years before sampling than in plots sampled the year of treatment. This indicated downward movement into the subsoil.

A phenetic classification of 44 ecotypes of common purslane (Portulaca oleracea L.) produced 4 major groups: cool temperate; warm temperate to wet dry subtropic; humid subtropic to tropic; and cultivated. These groups were based on 36 plant characteristics; the ecotypes were collected from 18 countries and are representative of climates inhabited by common purslane. The cultivated group is comprised of robust forms which are raised for culinary purposes. For weed forms, plants of the cool temperate group were small, prostrate plants with size and growth habit increasing to maximum in the humid subtropic to tropic group.

Japanese foxtail is a grass weed in eastern China. This weed is controlled by fenoxaprop-P-ethyl, one of the most common acetyl-CoA carboxylase (ACCase)-inhibiting herbicides. Some Japanese foxtail populations have developed resistance to fenoxaprop-P-ethyl, owing to target-site mutations (amino acid substitutions) located within the carboxyl transferase domain of ACCase. In the present study, three mutations were detected in three fenoxaprop-P-ethyl–resistant Japanese foxtail populations: Ile-1781-Leu in JCJT-2, Ile-2041-Asn in JZJR-1, and Asp-2078-Gly in JCWJ-3. Two copies of ACCase (Acc1-1 and Acc1-2) were identified, but mutations were detected only in Acc1-1. The derived cleaved amplified polymorphic sequence (dCAPS) method detected these mutations successfully in Japanese foxtail. The mutation frequencies in JCJT-2, JZJR-1, and JCWJ-3 were approximately 98%, 92%, and 87%, respectively. Different cross-resistance patterns to ACCase inhibitors were found in the three resistant populations. JCJT-2 (Ile-1781-Leu) and JZJR-1 (Ile-2041-Asn) showed cross-resistance to haloxyfop-R-methyl, clodinafop-propargyl, and pinoxaden, but were susceptible to clethodim. JCWJ-3 (Asp-2078-Gly) showed cross-resistance to all tested ACCase-inhibiting herbicides.

Invasive winter annual grass infestations on rangeland accumulate large quantities of litter on the soil surface, as plants senesce yearly and decompose slowly. It has been speculated that winter annual grass litter can adsorb soil-active herbicides and reduce overall performance. Three experiments were conducted from 2017 to 2018 at the Colorado State University Weed Research Laboratory to evaluate interception and subsequent desorption of herbicides applied to litter from three invasive winter annual grass species with simulated rainfall. Imazapic, rimsulfuron, and indaziflam were applied to medusahead [Taeniatherum caput-medusae (L.) Nevski], ventenata [Ventenata dubia (Leers) Coss.], and downy brome (Bromus tectorum L.) litter at two amounts (equivalent to 1,300 and 2,600 kg ha−1). Rainfall was simulated at 3, 6, 12, and 24 mm at 0, 1, and 7 d after herbicide application. Herbicide concentration from the collected rainfall was measured using liquid chromatography–tandem mass spectrometry. At 2,600 kg ha−1, B. tectorum herbicide interception was 84.3%, while V. dubia and T. caput-medusae averaged 76% herbicide interception. There were no differences in desorption among the three litter types. Simulated rainfall at 0 d after application recovered 100% of the intercepted rimsulfuron and imazapic from B. tectorum litter, while recovery decreased to 65% with rainfall at 1 or 7 d after application. Only 54% of indaziflam could be recovered at 0 d, and recovery decreased to 33% when rainfall was applied at 1 or 7 d after application. Applying soil-active herbicides before forecasted rain or tank mixing with a POST herbicide to provide initial control could potentially increase the amount of herbicide reaching the soil and provide more consistent invasive winter annual grass control.

Resistance to glyphosate in hairy fleabane and horseweed is a problem in orchards and vineyards in California. Population genetic analyses suggest that glyphosate resistance evolved multiple times in both species, but it is unknown if resistance to other herbicides is also present. Two approaches of research were undertaken to further evaluate herbicide resistance in Conyza sp. in the perennial crop systems of California. In the initial study, the distribution of Conyza sp. in the Central Valley, using a semistructured field survey, was coupled with evaluation of the presence and level of glyphosate resistance in plants grown from field-collected seed. In a subsequent study, single-seed descendants representing distinct genetic groups were self-pollinated in the greenhouse and these accessions were evaluated for response to glyphosate and paraquat. Conyza sp. were commonly found throughout the Central Valley and glyphosate-resistant individuals were confirmed in all field collections of both species. The level of glyphosate resistance among field collections varied from 5- to 21-fold compared with 50% glyphosate resistance (GR50) of the susceptible, with exception of one region with a GR50 similar to the susceptible. When self-pollinated accessions from different genetic groups were screened, the level of glyphosate resistance, on the basis of GR50 values, ranged from 1.7- to 42.5-fold in hairy fleabane, and 5.9- to 40.3-fold in horseweed. Three accessions of hairy fleabane from different genetic groups were also resistant to paraquat (40.1- to 352.5-fold). One glyphosate-resistant horseweed accession was resistant to paraquat (322.8-fold), which is the first confirmed case in California. All paraquat-resistant accessions of Conyza sp. identified so far have also been resistant to glyphosate, probably because glyphosate resistance is already widespread in the state. Because glyphosate and paraquat resistances are found across a wide geographical range and in accessions from distinct genetic groups, multiple resistant Conyza sp. likely developed independently several times in California.

All land uses in eastern and southeastern Nebraska were infested to some extent with hemp dogbane (Apocynum cannabinum L.). The highest infestations were observed in oats (Avena sativa L.) and soybeans [Glycine max (L.) Merr.] and the lowest infestations were in alfalfa (Medicago sativa L.), pastures, and winter wheat (Triticum aestivum L.). Yield reductions from hemp dogbane infestations ranged from 0 to 10% in corn (Zea mays L.), 28 to 41% in soybeans, and 37 to 45% in sorghum [Sorghum bicolor (L.) Moench]. Emergence of hemp dogbane from crown roots occurred when the soil temperature was 17 to 19 C, during April in 1977 and 1978. Plants attained the bud stage within 4 to 7 weeks after emergence. Early flower, full bloom, and pod initiation occurred subsequently at about 1 week intervals. Seeds produced were first viable 10 weeks after full bloom. Root activity or regenerative capacity as measured by length and number of new shoots and roots produced at monthly intervals in the germinator showed a cyclic pattern. The highest activity occurred in the spring and late fall and lowest activity in summer and early fall. Protein levels in the roots ranged from 7 to 9% in the fall and spring to 4 to 5% during the summer. Percentage total nonstructural carbohydrates (TNC) ranged from 20 to 31% in lateral roots and 32 to 53% in crown roots, but there was not a consistent cyclic pattern of percentage TNC during the growing season.

The effect of quackgrass [Agropyron repens (L.) Beauv.] density and duration of interference on soybeans [Glycine max (L.) Merr.] was investigated in two studies. In the density study, the average reduction in soybean yield by quackgrass densities of 520 and 910 shoots/m2 was 19 and 55%, respectively. Quackgrass densities of 95 and 160 shoots/m2 did not significantly reduce soybean yields. The number of branches that produced pods, the number of pods and seeds per plant, and soybean height were reduced by the two highest densities. In 1980, quackgrass densities of 265 and 595 shoots/m2 reduced soybean leaf area and plant dry weight. Leaf area partitioning (LAP), leaf weight partitioning (LWP), and net assimilation rate (NAR) of soybeans were reduced by a quackgrass density of 595 shoots/m2. In the duration study, interference by a natural stand of quackgrass for 6 weeks, 8 weeks, and full-season decreased soybean yield an average of 11, 23, and 33%, respectively. Results from the duration study suggest that a selective postemergence herbicide for the control of quackgrass in soybeans would be beneficial if available.

CGA-43089 [α-(cyanomethoximino)-benzacetonitrile], CGA-92194 {α-[(1,3-dioxolan-2-yl-methyl)imino] benzeneacetonitrile}, and MON-4606 [5-thiazolecarboxylic acid, benzyl ester, 2-chloro-4-(trifluoromethyl)], applied as seed treatments at 1.25 g/kg seed, prevented yield losses in grain sorghum [Sorghum bicolor (L.) Moench.] in the field due to metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl)acetanilide] or acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide] applied at 1.7, 2.2 and 1.7 kg/ha, respectively. CGA-92194, applied at 0.8 g/kg seed, prevented yield reduction from metolachlor applied at 4.5 kg/ha. MON-4606 was more effective in protecting grain sorghum when applied as a seed treatment than when applied in the furrow with a clay or sand granule as carrier.

Tall fescue (Festuca arundinacea Schreb. ‘Kentucky 31′) drilled into a pasture infested with broomsedge (Andropogon virginicus L.) and fertilized with N, P, and K, eliminated broomsedge after 4 years. In a second experiment, fertilization with N, P, and K increased the density of Kentucky bluegrass (Poa pratensis L.), and broomsedge was gradually reduced over a 5-year period. Fertilization with P and K caused the density of legumes and grass to increase and broomsedge was nearly eliminated after 5 years. In both experiments the old growth of broomsedge was mowed each winter and cattle were then able to graze the new growth of broomsedge. Grazing may have aided in the elimination of broomsedge.

The leaching of α,α,α-trifluoro-2,6-dinitro-N,N,-dipropyl-p-toluidine (trifluralin) and 3,5-dinitro-N4,N4-dipropylsulfanilamide (oryzalin) with and without surfactants was studied in soil columns. In dry soil without surfactants leaching of trifluralin was less than that of oryzalin and did not amount to more than a few centimeters despite the use of light soil and large amounts of herbicide. In wet soil trifluralin leached more than twice as deep as in dry soil with the same amount of water. The addition of surfactants at a concentration of 2% of the spray volume increased both depth of water penetration and herbicide movement into the soil. The most pronounced effect of surfactants was the increase in movement of trifluralin in dry soil, but they also increased trifluralin movement in wet soil. There was no direct relationship between the ability of the surfactants to improve water penetration and their effects on leaching of the two herbicides. It was therefore concluded that increased leaching was due to an effect of surfactants on the sorption-desorption balance rather than on improved penetration of water. The improved movement of trifluralin into the soil as a result of surfactant action was also evident from another experiment in which surfactants increased the herbicidal activity of trifluralin sprayed preemergence on the soil surface.

During 1971 and 1972, 4,400 adults of Rhinocyllus conicus Froelich were introduced into southern California from Italy for the biological control of milk thistle [Silybum marianum (L.) Gaertner]. These flowerhead-infesting weevils were colonized at nine, and successfully established at five, widely separated locations. Field data on the incidence and increase of R. conicus at colonization sites are presented. Biotic mortality factors reported for R. conicus in southern California include predation of eggs by ladybird beetles (Hippodamia sp.) and of adults by snakeflies [Raphidia (Agulla) adnixa Hagen] and spiders, destruction of weevils in flower-heads consumed by cattle and rodents, and larval and pupal parasitism by pyomotid mites.

The application of the acetolactate synthase (ALS)–inhibiting herbicide metsulfuron on greenhouse- and field-grown black nightshade and greenhouse-grown ladysthumb resulted in progressive inhibition of the level of carbon dioxide (CO2) fixation, the relative quantum efficiency of electron transport through photosystem I (ΦPSI) and II (ΦPSII), and the leaf chlorophyll content. Photosynthetic-related measurements, measured 2 to 4 d after treatment (DAT) at photon flux densities of 400 to 500 μmol m−2 s−1, provided valuable information before the visual symptoms that first appeared at 7 to 10 DAT with the herbicide. Measurements of the quantum efficiency for electron transport by photosystem II and the loss in leaf chlorophyll content appeared to be two of the most practical parameters to use when designing an early detection method to assess the toxicity of metsulfuron. The use of chlorophyll fluorescence would require a comparison of steady-state ΦPSII measurements for control and treated plants, which could be realized by either measuring in time (before/after application) or space (treated/untreated patch).

Field experiments were conducted to study the competitive ability of green foxtail (Setaria viridis (L.) Beauv.) with wheat (Triticum aestivum L.) and the feasibility of using a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) for the selective control of green foxtail in wheat. Rates of 0.56 to 0.84 kg/ha of trifluralin gave 90 to 100% control of foxtail when growing in competition with wheat. Wheat tolerated rates of trifluralin up to 2.24 kg/ha, the maximum rate used, without injury or reduction in crop yield, when the herbicide was applied and incorporated to a shallow depth 1 day after seeding. A semidwarf and a tall variety of wheat were not affected by trifluralin treatments. Green foxtail had a relatively low competitive ability, and wheat plants suppressed foxtail to a marked degree under normal growing conditions. However, suppressed plants still produced sufficient seed to insure a dense infestation of foxtail plants in the succeeding year. Further, when wheat was grown under less competitive situations, green foxtail resulted in significant reductions in crop yield. It was concluded that green foxtail is an “opportunist-type” weed.

Teliospores of Sphacelotheca holci Jack. [= S. cruenta (Kuhn.) Potter] infected johnsongrass [Sorghum halepense (L.) Pers. # SORHA) systemically after inoculation of cut stems in greenhouse studies. A preliminary host range test in the greenhouse revealed that no infection occurred on four varieties of sorghum (S. vulgare L.) and three cultivars of sudangrass (S. Sudanese L.). Infected johnsongrass plants grown in the greenhouse exhibited reduced vegetative growth and altered morphological characteristics compared to healthy johnsongrass plants. The aboveground biomass and lateral rhizome expansion of smutted johnsongrass field transplants were significantly lower than that of uninfected plants. Significant correlations between fraction of johnsongrass stems infected and plant weight, and basal area of plants were observed in field studies. Corn (Zea mays L.) and alfalfa (Medicago sativa L.) grown in competition with johnsongrass, and johnsongrass infected with S. holci reduced the aboveground biomass and rhizome length of johnsongrass plants significantly, compared to that of uninfected johnsongrass plants grown alone in greenhouse studies. Uninfected johnsongrass plants also exhibited higher plant weight than infected plants when both were grown in competition with alfalfa, regardless of the alfalfa planting density in the greenhouse or when measured after 3 months in field trials.

The amount of free, unaltered (2,4-dichlorophenoxy) acetic acid (2,4-D) in resistant and susceptible plant species 1, 4, and 8 days after treatment was determined by three procedures. Centrifugation and chromatography of plant homogenates was a more reliable assay than trichloroacetic acid (TCA) precipitation or dialysis procedures. The foliar penetration of 14C-2-4-D and radioactivity which moved from roots into the growth media following foliar application of 14C-2,4-D varied from one plant species to another, but no general correlations with 2,4-D resistance was observed. The resistant burcucumber (Sicyos angulatus L.) and oats (Avena sativa L.) were not fatally injured primarily because unaltered 2,4-D was immobilized in the treated leaves and unaltered, free 2,4-D was reduced to nontoxic concentrations. The 2,4-D in susceptible cocklebur (Xanthium sp.) remained largely as free and mobile 2,4-D, and the treated plants were near death 8 days after treatment.

Experiments were conducted to determine the influence of nitrogen (N) fertility and winter wheat cultivars on weed infestations in a winter wheat-ecofallow sorghum-fallow rotation near North Platte, NE. Centurk 78 and Lancota winter wheat suppressed density and growth of barnyardgrass and green foxtail significantly more than Eagle winter wheat before and after wheat harvest. Increasing N rates applied to winter wheat decreased annual grass weed population and weed yields. However, 67 and 101 kg N ha−1 reduced winter wheat grain yields compared to 34 kg N ha−1. Plots treated at 2.8 plus 0.3 kg ai ha−1 of atrazine plus paraquat 31 d after wheat harvest had more barnyardgrass before grain sorghum planting in 1983 than plots treated 17 d after wheat harvest but the reverse was true for green foxtail after grain sorghum emergence in 1984. Increasing N rates from 34 kg ha−1 to 67 and 101 kg ha−1 in the previous wheat crop decreased weed density before and after grain sorghum planting. There was no advantage in weed control in the grain sorghum from applying N to winter wheat in the fall vs. spring.

Hemp dogbane is sensitive to fluroxypyr and tolerant to clopyralid. Absorption, translocation, and metabolism of clopyralid and fluroxypyr were studied in hemp dogbane to determine if differences in these processes could be responsible for differential sensitivity. In addition, the effect of growth stage on herbicide absorption and translocation was evaluated. The 14C-herbicides were applied to the adaxial side of a single leaf located near the midpoint of hydroponically cultured plants. Uptake of fluroxypyr was more rapid than clopyralid. At 72 h after treatment (HAT), fluroxypyr and clopyralid absorption was 62 and 38%, respectively. Clopyralid was much more mobile than fluroxypyr, with 75% of the absorbed 14C from 14C-clopyralid recovered outside the treated leaf compared to only 45% for fluroxypyr 72 HAT. Relative to fluroxypyr, a higher percentage of 14C-clopyralid recovered outside the treated leaf translocated acropetally, especially when plants were treated during the vegetative stage. Treatment during the early reproductive stage increased basipetal and reduced acropetal translocation relative to the vegetative stage. Neither herbicide was metabolized rapidly. Approximately 60 and 90% of the recovered 14C was attributable to unaltered fluroxypyr and clopyralid, respectively, 72 HAT. Some differences in absorption, translocation, and metabolism between clopyralid and fluroxypyr exist, but they cannot fully account for differential sensitivity of hemp dogbane to these two herbicides. Differences in activity at the target site may be responsible for differential activity of these herbicides on hemp dogbane.