Field soil studies with 14C-isopropalin (2,6-dinitro-N,N-dipropylcumidine) have demonstrated its biodegradability. None of the recognizable transformation products in soil accumulated beyond 4% of the amount of applied herbicide. After 15 months, approximately 25% of the applied isopropalin remained in soil, and less than 10% was observed after 28 months. Only negligible amounts of radioactivity were detected in crops grown in soil treated with the herbicide. Isopropalin and its recognizable transformation products were not detected in any of the plant tissues examined. Fractionation techniques indicated that the radioactivity was randomly distributed throughout the plant tissue.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} is used to control weedy grasses in red fescue (Festuca rubra L. # FESRU and F. rubra ssp. commutata), an important seed crop in Oregon. The sethoxydim rate required to reduce growth rate of 11 cultivars of red fescue and four cultivars of bentgrass (Agrostis tenuis Sibth. # AGSTE and A. stolonifera L. var. palustris # AGSST), a common contaminant in red fescue fields, by 50% (GR50) was determined in greenhouse and laboratory experiments. Field experiments compared only red fescue cv. ‘Pennlawn’ and bentgrass cv. ‘Penncross'. The GR50 values for Pennlawn red fescue in the field, the greenhouse, and the laboratory were 30 kg ai/ha, 15 kg/ha, and 5300 μM, respectively. Penncross bentgrass was approximately 400, 1400, and 12 900 times more susceptible than Pennlawn red fescue in the field, in the greenhouse, and in laboratory experiments, respectively. Plants were at different growth stages in the different experiments. The xylene and surfactant used as a solvent for the technical grade sethoxydim was as toxic to red fescue without sethoxydim as when sethoxydim was included. Cultivars of red fescue differed in their response to sethoxydim, but cultivars of bentgrass did not. The GR50's of other species tested in the greenhouse were >4 kg/ha for annual bluegrass (Poa annua L. # POAAN), 0.22 kg/ha for tall fescue (F. arundinacea Schreb. # FESAR), 0.37 kg/ha for downy brome (Bromus tectorum L. # BROTE), and 0.017 kg/ha for Italian ryegrass (Lolium multiflorum Lam. # LOLMU).

The relationship between herbicide injury and soybean [Glycine max (L.) Merr. ‘Amsoy 71’] yield response was studied under weed free conditions at three locations. Reduced crop vigor at early growth stages was not an adequate indicator of yield response. Yield reduction was greater when soybean stand was reduced by herbicides than when stand was reduced to the same level by hand thinning. Yield response was a function of the degree and persistence of crop vigor reduction in a reduced stand of soybeans.

Excised leaves of Canada thistle (Cirsium arvense (L.) Scop.) ecotypes and bean (Phaseolus vulgaris L., var. Red Kidney) metabolized 3-amino-l,2,4-triazole-14C (amitrole) to the same radiolabeled products, but they were produced at different rates as shown by thin-layer and paper chromatography. Bean leaves metabolized amitrole to a metabolic product (Unknown II) probably β-(3-amino-1,2,4-triazolyl-1-) α-alanine approximately three times taster than Canada thistle leaves, while Canada thistle converted Unknown II to another product (Unknown I) about 10 times faster than did bean. Thus Unknown II accumulated in bean, and Unknown I in Canada thistle. This reaction sequence in Canada thistle was evidently an irreversible consecutive first order reaction. A difference in the rate of metabolism was observed between susceptible and resistant ecotypes of Canada thistle.

Treatments with the herbicide 3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea (chlorbromuron) were combined with seed treatments with the insecticide, 2,2-dimethyl-2, 3-dihydrobenzofuranyl-7-N-methylcarbamate (carbofuran), to measure phytotoxic interaction effects on barley (Hordeum vulgare L. ‘Larker’) and corn (Zea mays L. ‘Michigan 400’). The combination synergistically reduced radicle length in barley seedlings and reduced the leaf area and dry weight of 7-day-old corn seedlings grown in sand culture. The chlorbromuron-carbofuran combination reduced net photosynthesis in barley and corn and increased respiration in barley. The 14C from 14C-chlorbromuron preferentially accumulated in barley and corn shoots. The carbofuran seed treatment resulted in a reduced level in barley shoots and corn roots but increased the accumulation of 14C in barley roots and corn shoots. The basis for this interaction appeared related to the increased accumulation of chlorbromuron in corn and barley shoots and reduced chlorbromuron metabolism.

Two methods of obtaining air samples were used over 4-month periods in 1976 and 1977 to quantitate trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) vapors arising from a silt loam. With the first method, only the air from an enclosure covering 0.37 m2 of soil was sampled. The second method used air probes to sample the air above the field. Rainfall and resultant soil moisture were related to trifluralin vaporization from field soil. Soon after trifluralin incorporation (0.84 kg/ha) and, while the soil was relatively dry, there was very little herbicide vaporization. Trifluralin vapors accumulated rapidly during a period in which several centimeters of rain fell, but with continued precipitation the vapor density declined. The influence of rainfall and resultant soil moisture upon vaporization became less apparent as the soil concentration of the herbicides declined. Less than 0.5% of the applied trifluralin was detected as vapors during each 4-month period.

Experiments were conducted from 1990 to 1994 to investigate the density-dependent effects of rhizome and seedling johnsongrass on the magnitude of full-season interference in field corn. Corn grain yield was decreased as rhizome johnsongrass density increased. A maximum density of 3 rhizome johnsongrass plants 9.8 m−1 of row was considered critical to avoid yield losses above 5% of full-season weed-free corn. Interference of johnsongrass plants originating from seed and growing at densities up to 128 plants 9.8 m−1 of row did not affect grain yield. Seedling johnsongrass plants growing at a constant density of 9.8 plants m−1 of row did not affect yield from corn planted at five densities.

Studies were conducted to determine lethal temperatures for Cyperus esculentus and Cyperus rotundus tubers using diurnal oscillations in soil temperature with maxima of 40, 45, 50, and 55 C and a minimum of 26 C. Growth of Cyperus spp. plants was faster at 40 C than at a constant temperature of 26 C. The 45 C treatment delayed Cyperus spp. emergence but was not lethal to tubers. Tuber mortality was 100% for both Cyperus spp. with the 50 and 55 C temperature regimes. Soil solarization with thermal-infrared-retentive (TIR) films resulted in higher soil temperatures than with a 30-μm low-density polyethylene (LDPE) clear film. With TIR films, greater proportions of emerged C. rotundus plants were killed by foliar scorching, and 6 wk of soil solarization was more effective at reducing C. rotundus density than with the LDPE film. Four weeks after film removal, the lowest level of control was obtained with the LDPE film. For C. rotundus tubers planted 5 and 10 cm deep, 62% control was obtained with the LDPE film, and it decreased to 32% with a 15-cm planting depth. The best residual control was 95 and 92% with the 75-and 100-μm TIR films, respectively. With the TIR films, there was no significant change in C. rotundus control with planting depth.

A Powell amaranth population suspected to be resistant (R) to linuron was discovered in a carrot field in Keswick, Ontario, Canada, in 1999. Dose–response analysis with different herbicides and DNA sequencing of the psbA gene encoding the D1 protein of photosystem II were done to confirm the resistance and identify its basis. A calculated resistance factor indicated a 12-fold increased resistance when linuron was applied to an R population compared with a susceptible (S) population. Moreover, the R population showed 6.4- and 3.1-fold greater resistance to two other phenylurea herbicides (diuron and monolinuron), 1.8- and 1.4-fold greater resistance to two triazine herbicides (metribuzin and prometryn), and 2.6-fold greater resistance to the triazinone metribuzin. R population was also cross-resistant to bentazon and bromoxynil when compared with S population, with a calculated resistance factor of 1.4 and 2.2, respectively. The partial nucleotide sequence of the psbA gene of R populations differed at two locations when compared with S populations. The first mutation coded for a Val219Ile substitution in the deduced amino acid sequence of the D1 protein, and the second mutation was silent and encoded for a proline at position 279 in both R and S populations. The Val219Ile substitution in the psbA gene is most likely the cause of this Powell amaranth population resistance to linuron and other PSII inhibitors. This is the first recorded instance of a Val219Ile substitution in an Amaranthus species.

In the present field study, the capability of Canada thistle to develop shoots from intact roots and root fragments at different soil depths was studied. The experiments were performed on four sites with high-density Canada thistle, with three or four replications per treatment. At each site, the soil in the plots was removed layer by layer (to 30 or 40 cm, depending on the site), within a 1 by 1-m quadrat, and spread out on a plastic sheet. All roots and other plant parts were removed, and the soil was either replaced without any root material (two sites), or the roots of the thistles were cut into 10-cm-long fragments and replaced into the source holes (two sites). The measured variables were shoot number and biomass. The number of shoots of Canada thistle decreased with increasing depth (P < 0.001) and increased with time. Additionally, the two factors interacted (P < 0.001) such that shoot development was slower from greater depths. Roots from ≤ 20 cm depth produced higher biomasses than did roots from below 20 cm depth. Replacement of root fragments did not affect the amount of biomass produced. It was concluded that the intact root system contributed considerably more to the total biomass produced by Canada thistle than did the root fragments in the upper soil layers.

Understanding weed–crop interactions is critical in predicting crop yield loss, but it is also important to understand how these interactions affect weed productivity. Therefore, research was conducted to characterize the weed relative leaf area and weed relative volume of several giant foxtail cohorts in soybean, and to assess weed density and cohort emergence time, weed relative leaf area, and weed relative volume as predictors of giant foxtail shoot biomass and fecundity. Giant foxtail cohorts emerged at VE (emergence), VC (cotyledon), V1 (first node), and V3 (third node) soybean growth stages and were thinned to densities of 0, 4, 16, 36, and 64 plants m−2. Based on weed density and cohort emergence time, the maximum shoot biomass per square meter or the maximum fecundity per square meter differed between years. In contrast, shoot biomass or fecundity per plant, as weed density approached zero, and the rate at which shoot biomass or fecundity decreased exponentially, as time increased, were similar between years. Based on the weed relative leaf area, the cohort effect on giant foxtail shoot biomass differed between years, whereas the cohort effect on giant foxtail fecundity was similar between years. Maximum giant foxtail shoot biomass per square meter or fecundity per square meter differed between years when estimated from weed relative leaf area. Based on the weed relative volume, the cohort effect on giant foxtail shoot biomass per square meter or fecundity per square meter was similar between years, as was the maximum giant foxtail shoot biomass per square meter or fecundity per square meter. The temporal stability of weed relative volume, used to describe giant foxtail shoot biomass or fecundity, may aid in improving bioeconomic weed management models.

Effects of seven herbicides and two herbicide formulations on the phytotoxicity of glyphosate {[N-(phosphonomethyl)glycine]} were studied in the greenhouse. All herbicide formulations tested reduced glyphosate toxicity; the degree of reduction among herbicides varied. Type of formulation did not alter the reducing effects of propazine [2-chloro-4,6-bis(isopropylamino)-s-triazine] or propachlor (2-chloro-N-isopropylacetanilide). Liquid formulations of cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] caused less reduction than the wettable powder formulations, but the liquid formulation of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] caused greater reduction than the wettable powder. Inert ingredients of the herbicide formulations were primarily responsible for reduced glyphosate toxicity.

Twelve different johnsongrass (Sorghum halepense L.) clones were selected from four different regions of the United States and were grown in the greenhouse. The johnsongrass clones grew differently depending upon the environment from which they were originally obtained, suggesting that geographical ecotypes of johnsongrass exist. The parameter of growth most closely correlated to the latitude from which the plants were obtained was the time required for floral initiation. Plants from a more northern latitude consistently flowered earlier than plants obtained from a more southern latitude. Differences in height, stem number, and the weight of rhizomes, shoots, and roots also supported the hypotheses that geographical ecotypes of johnsongrass exist. Susceptibility to dalapon (2,2-dichloropropionic acid) appeared not to be correlated to the latitude from which the plants were obtained.

Recently, several incidents of glyphosate failure on junglerice [Echinochloa colona (L.) Link] have been reported in the midsouthern United States, specifically in Mississippi and Tennessee. Research was conducted to measure the magnitude of glyphosate resistance and to determine the mechanism(s) of resistance to glyphosate in E. colona populations from Mississippi and Tennessee. ED50 (dose required to reduce plant growth by 50%) values for a resistant MSGR4 biotype, a resistant TNGR population, and a known susceptible MSGS population were 0.8, 1.62, and 0.23 kg ae ha−1 of glyphosate, respectively. The resistance index calculated from the these ED50 values indicated that the MSGR4 biotype and TNGR population were 4- and 7-fold, respectively, resistant to glyphosate relative to the MSGS population. The absorption patterns of [14C]glyphosate in the TNGR and MSGS populations were similar. However, the MSGS population translocated 13% more [14C]glyphosate out of the treated leaf compared with the TNGR population at 48 h after treatment. EPSPS gene sequence analyses of TNGR E. colona indicated no evidence of any point mutations, but several resistant biotypes, including MSGR4, possessed a single-nucleotide substitution of T for C at codon 106 position, resulting in a proline-to-serine substitution (CCA to TCA). Results from quantitative polymerase chain reaction analyses suggested that there was no amplification of the EPSPS gene in the resistant populations and biotypes. Thus, the mechanism of resistance in the MSGR population (and associated biotypes) is, in part, due to a target-site mutation at the 106 loci of the EPSPS gene, while reduced translocation of glyphosate was found to confer glyphosate resistance in the TNGR population.

The potential dispersal of Benghal dayflower seeds by mourning doves was studied in southern Georgia, U.S.A. The gut contents (both crop and gizzard) of mourning doves harvested in the autumn months were investigated to determine if mourning doves fed on Benghal dayflower and whether seeds can survive conditions in the bird gut. Research indicated that mourning doves fed selectively on Benghal dayflower with some harvested birds containing hundreds of Benghal dayflower seeds and capsules in their guts. Further, some seeds recovered remained highly viable. Germination rates in seeds taken from bird crops were similar to controls over the first 4 wk of germination and enhanced over control treatments during the latter 16 wk of a 20-wk germination study. Ultimately, seeds extracted from dove crops had 92% germination as compared to 80% for control seeds. Seeds extracted from dove gizzards had 45% germination, about half that of controls. Benghal dayflower seeds have a structurally reinforced seed coat that probably aids in survival of mechanical damage through bird intestinal tracts. Benghal dayflower seeds exposed to 1.0 M HCl treatment for 2 h had little loss in viability, successfully germinating after such treatment. When evaluating mechanisms for the eradication of Benghal dayflower from agricultural crops, consideration needs to be given to the large number of mourning doves and other bird species that visit cropland and potentially aid in its dispersal.

Hairy galinsoga [Galinsoga ciliata (Raf.) Blake] and smallflower galinsoga [G. parviflora Cav.] are widespread weeds in New York State. Freshly harvested achenes (seed) are not dormant and germinate in the field from early May until frost. Rate of germination but not final total percentage was stimulated by alternating temperature, with the fastest rate being at 30 C day and 20 C night and with a 16-hr photoperiod and 11,000 lux of light. Some seed in each seed-lot required light for germination. Both species were day-neutral with respect to flowering. Smallflower galinsoga produced its first flower after node seven and hairy galinsoga after node six on the main axis 6 to 8 weeks after germination. Decreasing light intensity 83% decreased fresh weight.

Velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH) grown under monoculture consistently exceeded velvetleaf intercropped with soybeans [Glycine max (L.) Merr. var. ‘Amsoy 71′] in leaf area, nodes with fully developed leaves, canopy width, branches, and number of capsules as early as 3, 3, 4, 5, and 8 weeks, respectively, after simultaneous emergence. Velvetleaf plants without soybean competition eventually developed over nine times the dry matter of velvetleaf intercropped with soybean. The only components of velvetleaf plants sampled which sometimes increased significantly when soybean was defoliated in a manner simulating damage caused by the green cloverworm (GCW) (Plathypena scabra F.) were leaf area, number of leaves, and number of main-stem nodes. Soybeans in Iowa are attacked by the GCW late enough in the growing season that velvetleaf surviving previous weed management efforts benefited only slightly.

This study provides the first phytochemical characterization of the morphologically identified natural hybrid Solidago×niederederi Khek compared with the native Solidago virgaurea and two invasive species, Canada goldenrod (Solidago canadensis L.) and giant goldenrod (Solidago gigantea Aiton). The phenolic compounds, namely, chlorogenic acid, rutin, isoquercitrin, hyperoside, and quercitrin, were detected in leaves and inflorescences by the high-performance liquid chromatography–photodiode array detector/ultraviolet (PAD/UV) method. All analyzed Solidago species contained all of the phenolic compounds investigated. The quantitative phytochemical differentiation among Solidago taxa was shown by principal component analysis. The results indicated that S. gigantea plants were characterized by significantly different quantities of phenolic compounds compared with three other Solidago taxa, which formed a separate cluster in the space of the principal component model, indicating the high similarity of their profiles. An additional multivariate analysis of the three species studied revealed a chemical gradient from S. canadensis to S. virgaurea with a slightly overlapping zone on the score plots presented by S.×niederederi and S. virgaurea accessions. The results showed that S.×niederederi was closely related to S. virgaurea. This result is suggestive of a hybrid origin with significant contributions from the native species. However, S.×niederederi was significantly different from its parental species with respect to chlorogenic acid and quercitrin in leaves and rutin with isoquercitrin in inflorescences. Conversely, samples indicating intermediate chemical composition between native S. virgaurea and invasive S. gigantea were not distinguished. The comparison of phenolic compound accumulation in Solidago plants supported the additional identification of the origin of S.×niederederi.

Prediction of the developmental stages of wheat and wild oats would be useful in order to: 1) correctly time the application of herbicides, and 2) accurately schedule research and cultural operations. The Haun developmental scale which numbers leaf development and describes floral development on the main stem of grasses was found to be suitable for describing the development of semidwarf wheat and wild oats in California. Haun developmental rates of wheat and wild oats were similar. Interference by wheat or wild oats in mixed cultures did not change the developmental rate of either species when grown with added nutrients and water. Degree days gave better correlations with development than calendar days when different planting dates, years, and locations were compared. A degree day model with a 5 C base temperature and a second-order polynomial expression gave accurate predictions of developmental stage, which correlated well with field data.

Four modes of competition were studied in relation to early development of common milkweed (Asclepias syriaca L.) alone and in competition with green foxtail [Setaria viridis (L.) Beauv], redroot pigweed (Amaranthus retroflexus L.), and sorghum [Sorghum bicolor (L.) Moench ‘RS-626’]. The three species were used to study the effect of no competition, light competition, soil competition, and light and soil (full) competition on common milkweed. Common milkweed height was significantly reduced by soil and full competition with the three species, while only green foxtail caused a significant reduction in height due to light competition. Shoot weight of common milkweed was significantly reduced by light, soil, and full competition by the three species. Reproduction percentage of common milkweed roots was most severely reduced by light and full competition from green foxtail and redroot pigweed. An environment conducive to the establishment of the perennial common milkweed from seed exists when annual weeds are removed by herbicides.