Since isopropyl N-(3-chlorophenyl)carbamate (CIPC) is being recommended for use on a limited acreage to control barnyardgrass (Echinochloa species) in drilled rice, it was of interest to the author to investigate the mechanism of selectivity involved. Although a difference in sensitivity among graminaceous plants to isopropyl N–phenylcarbamate (IPC) and CIPC has been recorded, the author was unable to find any explanation for this difference. Observations in the field indicated that Echinochloa seedlings were killed regardless of the depth at which the seed was located; whereas, most rice seedlings escaped injury if the seed was planted sufficiently deep. There appeared to be, however, a difference in response among varieties of rice. The following investigation was initiated to explain the differential response among varieties; however, the conclusions were expanded to explain the selective mechanism for controlling barnyardgrass in rice. The data presented in this paper are representative of results obtained in a series of experiments on this subject.

In field, soil culture, and nutrient culture experiments, 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) increased percent total nitrogen in all species studied, whether resistant, intermediate, or susceptible to 1 lb/A of atrazine. However, nitrogen content per plant was either unaffected or decreased by these atrazine treatments. One lb/A of atrazine increased percent protein and nitrate nitrogen in most species studied. Atrazine susceptibility apparently was related to its effect on percent non-protein and ammonia in the species tested. One lb/A of atrazine had no effect on percent non-protein nitrogen and decreased percent ammonia nitrogen in resistant species but increased both fractions in intermediate and susceptible species. One lb/A of 2-hydroxy-4-ethylamino-6-isopropylamino-s-triazine (hereafter referred to as hydroxyatrazine), a degradation product of atrazine, had no consistent effect on any nitrogen fraction studied.

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.

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.

Glyphosate-resistant giant ragweed has been confirmed in several Midwestern states. In some cases, weed resistance to glyphosate has been shown to carry a fitness penalty. Previous research has found that a glyphosate-resistant giant ragweed biotype from Indiana with a rapid necrosis response to glyphosate displayed early, rapid growth in the absence of glyphosate, flowered earlier, but produced 25% less seed than a sensitive biotype, suggesting that there may be a fitness penalty associated with the rapid necrosis resistance trait. In Wisconsin, we have recently identified a giant ragweed accession with a 6.5-fold level of resistance to glyphosate that does not demonstrate the rapid necrosis response. Our objective was to determine the noncompetitive growth and fecundity of the resistant accession in the absence of glyphosate, relative to a sensitive accession from a nearby field border population. In greenhouse experiments, plant height, leaf area, and dry shoot biomass were similar between the resistant and sensitive accessions during vegetative growth to the onset of flowering. The instantaneous relative growth rate, instantaneous net assimilation rate, and instantaneous leaf area ratio also did not differ between accessions. However, fecundity of resistant plants (812 seeds plant−1) was greater (P = 0.008) than sensitive plants (425 seeds plant−1). The percentage of intact viable seeds, intact nonviable seeds, and empty involucres did not differ between resistant and sensitive accessions. These results indicate that resistance of this accession of giant ragweed to glyphosate has not affected its growth and development relative to a sensitive accession. The greater fecundity and similar viability of resistant plants relative to sensitive plants suggests that in the absence of selection by glyphosate, the frequency of the resistance trait for glyphosate may increase in the giant ragweed field population over time.

An isolate of Fusarium solani (Sud 96) obtained from infected Striga plants in Sudan and six other isolates from Japan were evaluated for their effects on Striga germination. Among all the isolates, only the one from Sudan demonstrated high inhibitory activity. Aqueous and organic solvent culture extracts, as well as fungus suspension, when mixed with GR24, a synthetic analog of the natural germination stimulant strigol, inhibited germination of conditioned Striga seeds. Fusarium solani (Sud 96) filtrates, from cultures grown on autoclaved rice, sorghum grains, and potato dextrose agar (PDA), were more effective in reducing Striga germination than those from cultures grown on wheat straw. A significant difference between rice compared to sorghum and PDA cultures only occurred at high dilutions (40-fold). Complete inhibition of germination occurred when F. solani (Sud 96) culture filtrates and GR24 were applied simultaneously. Filtrate treatments made 2, 4 and 6 h subsequent to treatment with GR24 were less inhibitory. Filtrate treatments applied 8 h or more following GR24 had negligible effects on germination. Chromatographic separation on a silica gel column indicated the presence of several compounds with high inhibitory activity.

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.

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.

Winter annual weeds protect the soil from erosion and retain nutrients during the winter; however, they can also act as a host for crop pests and pathogens and impede planting. Increased knowledge of the reproductive biology and the seed fate of winter annuals would be useful to improve management and crop productivity. The objectives of this research were to determine the recruitment biology of shepherd's-purse, henbit, common chickweed, and field pennycress, including seed production, dispersal, dormancy, and seedling emergence, based on growing degree days (GDD). Henbit was the least prolific of the four weeds studied, producing 800 to 40,000 seeds m−2 at naturally occurring densities; shepherd's-purse was the most prolific, producing 11,000 to 400,000 seeds m−2 with 40 to 230 plants m−2. Fifty percent seed rain occurred for henbit, common chickweed, shepherd's-purse, and field pennycress at 620, 790, 880, and 1300 GDDBase ,0C, respectively. Overall, seeds were dormant for all species at the time of dispersal. In 2 of 3 yr, dormancy of later-dispersed common chickweed decreased after 6 mo of storage at natural, fluctuating temperatures in the absence of water. The emergence patterns of the four species followed the Gompertz equation and were indicative of facultative winter annuals. The emergence patterns by rate were similar between henbit and common chickweed and between shepherd's-purse and field pennycress. Seed production, dispersal, dormancy, and seedling emergence were influenced by moisture; therefore, including a precipitation or soil moisture component into a GDD model (such as the use of hydrothermal time) would improve the accuracy of predicting winter annual reproduction, seed fate, and emergence.

A number of s–triazine derivatives have shown considerable promise for pre-emergence weed control. Activity and selectivity as influenced by structural differences between many derivatives have been discussed by Gysin. The phytotoxicity of some of these materials is greatly influenced by the characteristics of the soil to which the herbicides is applied. Although solubility may be important in the toxicities of the s-triazines, adsorption may be of equal or greater importance in the presence of high organic matter or high colloid content. In solution these factors may be eliminated so that a more accurate determination of phytotoxicity and physiological selectivity may be made. The most successful pre-emergence herbicides for shallow planted crops possess at least some physiological selectivity.

The effects of formulation on clomazone volatilization and transport through soil were studied. After 22 days of leaching under unsaturated flow in 49-cm long intact soil cores, greater clomazone movement was observed in Plainfield sand than in Cisne silt loam or Drummer silty clay loam soils. Soil clomazone concentrations resulting in injury to oats occurred throughout Plainfield soil cores but were restricted to the upper 14 cm of Cisne and Drummer soils. In addition, clomazone was detected in the leachate from Plainfield soil only. In a similar study with Plainfield sand cores, clomazone was less mobile than atrazine; encapsulation of the herbicides in starch granules did not affect clomazone movement but greatly decreased atrazine movement from the soil surface. Similarly, starch encapsulation did not affect bioavailability of clomazone but did reduce bioavailability of atrazine. In a laboratory study with continual air flow, volatilization of clomazone applied to the soil surface was reduced by encapsulation in starch and starch/clay granules. Clomazone volatilization was not affected by soil water content within a range of 33 to 1500 kPa water tension. Following soil saturation with water, clomazone volatilization from both liquid and granular formulations increased. Granule size appeared to have a greater impact than granule composition on clomazone volatilization.

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).

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.

Competitiveness of weeds that survive a PRE herbicide application (escaped weeds) might be altered because of herbicide injury. As a result, potential crop yield loss may be reduced. Field experiments were conducted at Ashland Bottoms, KS, in 2001 and 2002 and at Rossville, KS, in 2002. The objectives were to quantify corn growth and yield response to Palmer amaranth or velvetleaf competition, with or without isoxaflutole (0.03 kg ha−1) or flumetsulam (0.04 kg ha−1) application, and to determine seed production of Palmer amaranth or velvetleaf as affected by PRE herbicide. Palmer amaranth and velvetleaf densities ranged from 0 to 6 and 0 to 32 plants m−1 of corn row, respectively. At Ashland Bottoms in 2002, corn height at tasseling decreased with increasing Palmer amaranth (1.58 cm weed−1 m−1) and velvetleaf (1.32 cm weed−1 m−1) density when no herbicide was applied. With flumetsulam application, each increase in velvetleaf density reduced corn height by 0.4 cm. Escaped Palmer amaranth and velvetleaf were shorter than untreated plants at corn tasseling. At Rossville in 2002, Palmer amaranth that escaped isoxaflutole or flumetsulam application caused 13% corn yield loss (YL) at a density of 3 plants m−1. In contrast, corn YL from untreated Palmer amaranth at the same density was 30%. At Ashland Bottoms in 2002, velvetleaf that escaped flumetsulam caused 3% corn YL at a density of 3 plants m−1 compared with 38% YL caused by untreated velvetleaf at the same density. Seed production of Palmer amaranth was independent of density or herbicide treatment, whereas production of velvetleaf seed increased with density, with or without flumetsulam. The study showed that corn YL from both Palmer amaranth and velvetleaf that escaped a PRE herbicide was less than from untreated weeds, but seed production by escaped weeds was similar to that of untreated weeds.

Desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)] controlled wild mustard (Sinapsis arvensis L. ♯3 SINAR) and redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) more effectively than phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate). A synergistic interaction occurred with all tank-mix combinations of the two herbicides for wild mustard control, except combinations containing 0.71 kg ai/ha of desmedipham. The magnitude of the synergism decreased as the rate of desmedipham was increased and increased as the rate of phenmedipham increased. Both herbicides caused injury symptoms of leaf necrosis and height reduction to sunflowers (Helianthus annuus L.). Crop injury and sunflower heights were affected more by desmedipham than by phenmedipham. Injury effects were temporary and had no influence on sunflower yields.