Field violet germination occurred during May to early July and again during September to November in Nova Scotia (N.S.), Canada. Germination occurred from October until early April in the North Carolina (NC) piedmont. Germination was stimulated by tillage. Seed collected in N.S. and in NC germinated optimally in the dark under a temperature regime of 15/5 C, on an 8/16 h thermoperiod. Germination at constant temperatures decreased with increasing temperatures, from 5 to 25 C. Seed collected in NC was capable of germinating at a higher constant temperature of 25 C than seed collected in N.S. Germination of seed collected in NC was partially inhibited by constant irradiance with a photosynthetic photon flux density of 100 μM m−2 s−1 (400 to 700 nm). Seed did not germinate when exposed to constant red or far-red irradiance.

Weed management strategies are needed for no-till soybean grown on clay soils. The effect of several weed management strategies on weed biomass, soybean yield, and gross return were evaluated in 1993, 1994, and 1995 on clay soils at two locations in southern Ontario. Soybean seeds were planted in narrow (19 cm) and wide (76 cm) rows with or without a rye cover crop. Herbicide treatments included glyphosate alone, glyphosate followed by imazethapyr + metribuzin applied PRE, and glyphosate followed by acifluorfen + bentazon applied POST. Two additional treatments with interrow cultivation were included in the wide-row soybean plots with glyphosate and glyphosate + PRE treatments. A nontreated check plot without rye was also included. Presence of a cover crop did not affect weed biomass or soybean yield. The glyphosate + broadcast PRE treatment provided the most consistent weed control both in narrow- and wide-row soybean. The weed control in this treatment ranged from 92 to 100%. The other treatments provided variable weed control across years and locations. The narrow- row plots with glyphosate + broadcast PRE treatment provided the most consistent soybean yields that were generally higher than the other treatments and ranged from 2,560 to 3,420 kg/ha. Soybean yields varied across locations and years in other treatments. Similar weed control and soybean yields were obtained with banded PRE herbicide + interrow cultivation and PRE treatments; however, herbicide use was 60% lower in banded PRE herbicide + interrow cultivation treatment. Narrow-row soybean averaged 27% higher gross returns than wide-row soybean for all broadcast herbicide treatments. Narrow-row soybean with PRE herbicide provided the highest gross returns. No-till soybean in narrow rows with preplant glyphosate and broadcast PRE treatment was the most risk-efficient weed management system on clay soils.

Soil moisture, relative humidity (RH), and the addition of bentazon were examined for effects on absorption and translocation of 14C-imazethapyr in common ragweed. When common ragweed was growing under conditions of low soil moisture (-300 kPa), absorption of 14C-imazethapyr was reduced from 51 to 42%. Translocation of 14C-imazethapyr was not affected by soil moisture. In the absence of bentazon, absorption and translocation of 14C-imazethapyr was similar at 65 and 85% RH 48 and 168 h after treatment. Bentazon decreased absorption of 14C-imazethapyr from 61 to 26% at 65% RH and from 65 to 57% at 85% RH 168 h after treatment. Bentazon decreased translocation of 14C-imazethapyr from 35 to 9% at 65% RH and from 30 to 21% at 85% RH when averaged over time. This reduction in the absorption and translocation of 14C-imazethapyr when bentazon was added may result in a reduction in common ragweed control compared to imazethapyr alone when RH is 65% or lower.

Crop response to carfentrazone–ethyl can be affected by environmental conditions. Field research was initiated to determine the effect of irrigation and light intensity prior to herbicide treatment on crop response to carfentrazone–ethyl. Wheat, corn, and soybean response was evaluated in 1996 and 1997, 2 yr that differed significantly in rainfall. It was difficult to distinguish differences in visible crop injury between irrigated and nonirrigated crops within the same year; however, injury was much higher in 1996 than in 1997. In 1996, the study area received timely rainfall prior to treatment of each crop, but in 1997, no precipitation was recorded during the treatment period. Overall, irrigated plants appear to be slightly more sensitive than nonirrigated plants. In contrast, crop injury was significantly higher in response to low light intensity prior to herbicide treatment. Soybean plants covered with 80% shade cloth for 5 d prior to carfentrazone–ethyl application were injured 24 to 41% more than nonshaded plants. Corn was relatively insensitive to either condition. Soybean plants were very sensitive to carfentrazone–ethyl and were highly influenced by both light intensity and irrigation. Wheat response to carfentrazone–ethyl was not influenced within 1 yr by irrigation, but injury in 1996 was four times higher than in 1997. Light intensity prior to treatment influenced wheat response to carfentrazone–ethyl, where shading before treatment increased visible injury in wheat, but by less than 10%. The risk of crop injury increases when carfentrazone–ethyl is applied to irrigated plants or to crops following several cloudy days.

Common cocklebur is an adaptable and competitive weed with variable morphology. To learn how the rate of net photosynthesis (Pn) by common cocklebur relates to traits that may influence competitiveness, we compared Pn, accumulation of biomass (shoot mass, root mass, and total plant mass), and total leaf area among six accessions of common cocklebur grown in a greenhouse. There were highly significant (P ≤ 0.01) differences among accessions for all measured traits. Correlations of each measure of biomass with total leaf area were positive and highly significant, but correlations of Pn with each biomass measure and with total leaf area were negative. The negative correlations were largely a result of relatively low biomass accumulation by the two accessions with the highest Pn. This contrasted with results from a previous experiment on field-grown common cocklebur plants, in which the correlation of Pn with shoot mass was positive (r = 0.64). Despite the negative Pn-to-biomass correlations in the greenhouse study, the rank among accessions for Pn in the greenhouse was nearly the same as with the field-grown plants (Spearman rank correlation r = 0.89). We conclude that the relative Pn rates among common cocklebur accessions grown in the greenhouse may be used to predict their relative Pn rates in the field, but relationships of Pn with biomass or leaf area observed in the greenhouse may not be a reliable indicator of relationships in the field.

Farmer observations and previous studies indicated that reductions in soybean yield caused by the soybean cyst nematode (SCN) are greater when other stresses, biotic or abiotic, are present. Also, it has been reported that the effect of SCN on soybean growth depended on factors such as soil pH, soil texture, and herbicides. Although postemergence herbicides may adversely affect soybean metabolism, acifluorfen can reduce SCN infection. The objective of the present study was to determine the main and interactive effects of SCN egg population density (SCND), soil pH, soil texture, and the application of the herbicides acifluorfen, glyphosate, and imazethapyr on early soybean growth. Greenhouse studies assessed different combinations of these factors for 65 d after planting. No interactions were observed for any of the main effects. Soil pH and texture did not affect soybean growth. SCND was the only main effect that explained soybean growth reductions. The effect of SCND on soybean growth was exhibited as 15–50% decreases of leaf area index (LAI) and dry weight in all cases, but reductions in plant height also were observed. No relationship between SCND and the number of SCN eggs recovered at the end of the experiment was observed. Herbicides did not reduce soybean growth, although acifluorfen consistently caused the highest soybean injury reaching 18–20% from 1–14 days after application (DAA). At 50 DAA, acifluorfen injury was negligible, and soybean LAI and dry weight did not differ from the nontreated control. These results indicated that the effect of SCN on soybean growth was not directly affected by the other evaluated main effects. Therefore, trends observed in the field that suggested interactions between those factors are likely the result of other factors not considered in the present study or to more complex relationships between factors analyzed in the present study and other elements present in the field.

Field and growth chamber experiments determined the efficacy of temporal glyphosate applications on velvetleaf. Glyphosate was applied postemergence to velvetleaf periodically before and during light and after dark. In 1999, glyphosate at 840 g ae/ha applied before sunrise and after midday provided 54 and 100% velvetleaf control, respectively. In 2000, glyphosate at 840 g/ha applied before sunrise, midday, and after sunset provided 69, 100, and 37% velvetleaf control, respectively. In the growth chamber, glyphosate at 840 g/ha applied before or after light reduced velvetleaf biomass 15 to 20% or 32 to 47%, respectively, and reduced velvetleaf height 24% or 45 to 54%, respectively. Velvetleaf control was consistently greater with glyphosate applications during light compared with dark, regardless of constant air temperature and relative humidity (growth chamber), dew absence or presence (field and growth chamber), or leaf blade orientation (growth chamber) with natural light–dark movements or a fixed horizontal position.

Information on jointed goatgrass caryopsis development is currently lacking in published literature. It is hoped that through a better understanding of jointed goatgrass caryopsis ontogeny more effective weed-management strategies will be developed. Greenhouse experiments were initiated in fall 2002 and 2003 and completed the following spring seasons. Jointed goatgrass plants were started from spikelets, vernalized for 8 wk at 4 C, and grown in a greenhouse. Treatments were the number of days after anthesis (DAA) that a spike was allowed to remain on the plant before harvesting and ranged from 2 to 34 DAA, in increments of 1 (2002) or 2 (2003) d. Individual spikes were divided at harvest into three sections: top, middle, and bottom, disarticulated from the rachis, placed into a germinator, and germination recorded each day. Goatgrass spikelets germinated as early as 2 DAA, although spikelets harvested <7 DAA had <3% germination for all spike sections and were extremely variable, especially for the middle and bottom sections. Time to germination was similar for all sections of the spike. Maximum average germination of the top section was 72% compared with 86% for the bottom and middle sections. Our data suggest that factors other than developmental rate (i.e., dormancy) may affect germination in sections of the spike. A second year of the experiment was conducted for validation. Model validation suggested that although trends were similar in both years, variation in germination response might be too great for accurate, predictive model construction. The early germination shown in this research demonstrates that control measures must be implemented earlier than previously prescribed to prevent jointed goatgrass reproduction.

Goosegrass is considered tolerant to quinclorac. The purpose of this study was to determine whether there was a stage of growth at which it was susceptible. Stage of growth studies with goosegrass were conducted that evaluated quinclorac activity at rates of 0, 1, 2, 4, 8, and 16 kg ai/ha applied with 1% (v/v) Merge spray adjuvant. Quinclorac application stages evaluated included preemergence and one- to two-leaf, four- to five-leaf, and one- to two-tiller stage. The effects of root uptake from postemergence applications were also evaluated by comparing treatments with and without a vermiculite soil barrier. Goosegrass was more susceptible to quinclorac when applied preemergence or early postemergence at the one- to two-leaf stage than at later more mature stages. The importance of root uptake on quinclorac activity was also observed, particularly at the four- to five-leaf stage, where the dose required to reduce growth 50% (GR50) in the absence of the soil barrier was 3.4 kg/ha vs. 16 kg/ha in the presence of a barrier. At the most advanced growth stage of one to two tillers, calculated GR50 values were greater than 16 kg/ha whether a soil barrier was present or not. The lowest calculated GR50 value of 2.7 kg/ha for the one- to two-leaf stage with no soil barrier was still approximately 3.5 times higher than the maximum labeled rate for turfgrass.

Several commercial and experimental adjuvants were evaluated for efficacy in enhancing activity and selectivity of quinclorac in two cultivars of canola and four turfgrass species. Weed species investigated included cleavers, annual sowthistle, large crabgrass, and goosegrass. Turfgrass species evaluated included Kentucky bluegrass, perennial ryegrass, tall fescue, and creeping bentgrass. A variety of adjuvant types were selected, such as a methylated seed oil (Sunit II), a petroleum-based crop oil concentrate, the silicone-based Sylgard 309, a cationic fatty amine ethoxylate surfactant (Frigate), and modified crop oils (Dash and Merge). Adjuvant efficacy was evaluated by calculating the quinclorac rate required to reduce plant growth 50% (GR50) based on rates applied at 0, 15.6, 31.2, 62.5, and 125 g ai/ha. For goosegrass, quinclorac rates evaluated were increased to 250, 500, 1,000, and 2,000 g ai/ha. All evaluated adjuvants provided similar enhancement of control for cleavers and annual sowthistle. Sylgard 309 was the least effective adjuvant for control of large crabgrass. Goosegrass was tolerant to quinclorac across the evaluated rate range regardless of adjuvant; therefore, GR50 values could not be determined. None of the adjuvants alone caused phytotoxicity to canola or any turfgrass species.

Postemergence-applied diuron effectively controls yellow woodsorrel in nursery crops grown in pine bark–based container substrate. Whether the phytotoxicity of diuron on yellow woodsorrel is exclusively the result of foliar activity or is partially the result of root-based activity has not been determined. Application in which diuron was allowed to contact both the foliage and the pine bark–based substrate provided 84% control as determined by shoot fresh-weight reduction relative to that of a nontreated control. Foliar-only and root-only applications provided 52 and 12% shoot fresh-weight reduction, respectively. Absorption and translocation of foliar-applied diuron by yellow woodsorrel was evaluated using radiotracer techniques. After 24 h, 86% of the applied diuron had been absorbed, and 76% of the amount applied remained in the treated leaflet, indicating minimal translocation. Diuron sorption by the pine bark–based substrate was evaluated using radiotracer techniques. After 3 h, less than 6% of applied diuron remained in the aqueous phase, indicating 94% sorption. Exposing yellow woodsorrel roots to diuron concentrations as low as 0.50 mg/L resulted in injury, and concentrations equal to or greater than 10 mg/L resulted in death. Calculations described herein indicate the concentration that probably would occur within the aqueous solution held within the substrate following a 1.12-kg ai/ha application is sufficient to be phytotoxic to yellow woodsorrel. Thus, root-based absorption is a contributing factor in the overall efficacy of postemergence-applied diuron in controlling yellow woodsorrel.

Photosystem II (PS II) inhibitors halt electron flow within the photosynthetic electron transport chain, thereby leading to increased oxidative stress. As a result, their addition to mesotrione, which inhibits carotenoid biosynthesis by inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), is complementary. Field and greenhouse experiments were conducted in 2002 and 2003 to investigate the joint action of POST mesotrione plus PS II inhibitor herbicide combinations. The joint action of mesotrione plus PS II inhibitors was investigated across five plant species, three PS II inhibitors, and two moisture environments to determine their influence on the joint action response. Rates of mesotrione evaluated ranged from 4.4 to 87.6 g ai/ha alone and in combination with reduced rates of atrazine, bromoxynil, and metribuzin. In the field, all combinations of mesotrione at 8.8, 17.5, and 35.0 g/ha plus atrazine, bromoxynil, or metribuzin were synergistic for necrosis 6 d after treatment (DAT) on sunflower. Addition of atrazine at 280 g/ha to mesotrione at 8.8 g/ha increased velvetleaf leaf necrosis by 18 to 47%. In the greenhouse, the addition of bromoxynil at 70 g/ha to mesotrione at 17.5 g/ha increased leaf necrosis by 23 to 34% and biomass reduction by 38 to 47%. Synergism on Palmer amaranth occurred similarly under both normal and dry moisture environments at application. Plant height at application was found to influence detection of synergism on the whole-plant level.

We examined the effect of a postemergence application of fluazifop-P on root uptake, translocation, and metabolism of 14C-terbacil in ‘Kent’ strawberry. Fluazifop-P had no effect on uptake of 14C-terbacil from a nutrient solution over 48 h, nor did it affect the proportional distribution of 14C-label in the plants. The 14C-label was readily translocated to the foliage where it tended to accumulate in vascular tissue. Fluazifop-P reduced the overall conversion of 14C-terbacil to metabolites by about 50%. Thin layer chromatography of methanol extracts of leaflets, petioles, crowns, and roots separated the 6-hydroxymethyl derivative, and several unidentified metabolites, including a major water-soluble metabolite at the origin. At least 50% of the latter could be converted to the 6-hydroxymethyl metabolite by β-glucosidase, but other metabolites could be separated in other solvent systems. The levels of metabolites were generally two- to threefold higher in plants treated with terbacil alone than in those pretreated with fluazifop-P. Therefore, we conclude that the interaction observed between these herbicides in the field results from fluazifop-P inhibiting detoxification of terbacil by strawberry.