A 3-yr study was conducted to establish if the presence of corn had an effect on the emergence patterns and total weed seedling density under growing conditions in southwestern Québec. Weed seedling emergence was monitored in permanent quadrats throughout the growing season in the presence and absence of growing corn. Common lambsquarters and barnyardgrass were prevalent in most site-years. The presence of corn did not affect the patterns of common lambsquarters and barnyardgrass emergence nor their total weed seedling density except in 1994. Corn canopy was probably not sufficiently developed to affect light levels or soil temperature needed for weed germination and, consequently, seedling emergence. In 1994, in the absence of corn, some soil crusting was observed on a fine-textured soil, and the total number of seedlings was reduced. The results of these weed emergence studies in corn can be extended to other crops growing with wide row spacing and relatively slow canopy closure similar to those of grain corn.

Research was conducted to evaluate structure–function relationships of citric acid esters that varied in alkyl chain number (mono-, di-, and tri-), ethylene oxide number (EO 4,7,9,25,35,52), and alkyl chain length (C8, C12/14, C16/18). Adjuvant efficacy was evaluated on two weed species for each of the four herbicides. The experimental adjuvants were applied with glyphosate and glufosinate on giant foxtail and common lambsquarters, imazamox on velvetleaf and common lambsquarters, and nicosulfuron on giant foxtail and large crabgrass. Adjuvant efficacy was weed and herbicide specific. EO number and alkyl chain length and number influenced adjuvant efficacy with the effectiveness of various combinations dependent on both herbicide and weed species. EO numbers as high as 52 were shown to be effective for glyphosate, glufosinate, and imazamox.

Common cocklebur is an adaptable species found in diverse environments. We grew 28 common cocklebur accessions from 14 states at Urbana, IL, to compare their growth, physiology, and morphology in a common environment to determine if regional control recommendations of specific biotypes might be practical. Accessions were evaluated for midseason and maximum heights and widths, flowering date, insect damage, and petiole color in 1998 and 1999. Weight of aboveground tissue, photosynthetic rate, stomatal conductance, chlorophyll content, and leaf and bur morphology descriptions were also taken in 1999. Midseason and maximum widths, midseason height, flowering date, and insect damage differed significantly based on the year of evaluation. The year by accession interaction was a significant source of variation for midseason and maximum heights and widths, flowering date, insect damage, and petiole color. Within each year, accessions differed significantly for all measured variables except maximum width in 1998 and stomatal conductance in 1999. Accessions from northern states usually flowered earlier, and flowering date was negatively correlated with latitude of origin (1998 r = −0.76; 1999 r = −0.60). Nevertheless, some of the earliest flowering accessions were from the southern states. Results from cluster analysis indicated that several accessions had phenotypes more similar to accessions from distant sites than to nearby accessions. We conclude that the accessions differ for traits that may affect weediness, but proximal accessions differ too frequently to recommend regional, biotype-specific control strategies.

The presence of volunteer canola is becoming a significant agro-ecological concern, given the large-scale use of herbicide-tolerant varieties in some areas. Our goal was to estimate the frequency and persistence of volunteer canola in Québec cropping systems by surveying fields that included a single canola crop since 1995. A survey was conducted in 131 fields in the main canola-growing areas of Québec: in the Saguenay-Lac Saint-Jean region and the Québec City–La Pocatière area. Volunteer canola plants were counted in 0.25-m2 quadrats every 10 m along a W pattern, and every 15 m along the margins of 88 fields. Volunteer canola plants were found in 90% of the fields surveyed and in a wide range of crops, including cereal, corn, and soybean. Average densities of 4.9 and 3.9 plants/m2 were found 1 yr after canola production in fields and field margins, respectively. Volunteer canola densities decreased significantly over time. However, volunteer plants were still present at low densities 4 and 5 yr after production. Dense stands of volunteer canola were found before postemergence herbicide application in no-till fields (9.8 ± 4.1 plants/m2), suggesting that, contrary to what was suggested in the literature, seeds could become dormant in no-till as well as in tilled systems. A small proportion of the volunteer canola plants observed in no-till fields near Québec City and Ottawa included plants that had overwintered, either originating from fall-germinated seedlings, harvested adult plants that had grown new leaves before the onset of winter, or spring regrowth from the base of unharvested adult plants from experimental plots. The presence and persistence of low densities of volunteer canola may not have been a cause of concern until now. However, producers should be made more aware of the potential short-and long-term problems associated with potential gene flow between different herbicide-tolerant canola (HT canola) varieties and also between HT canola and related weed species.

Reduction of weed competition using herbicides is critical to the successful revegetation of weed-infested rangeland. However, little is known about the influence of persistent broadleaf herbicides on the establishment of many desired grasses. The objective of this study was to determine the influence of various rates and times of application of picloram and clopyralid before seeding on two native and two nonnative grasses important to western United States rangeland. The study was conducted in 1997 and 1998 in Wyoming, Montana, and Washington. Five herbicide treatments (none, picloram at 0.14, 0.28, 0.56 kg ai/ha, clopyralid at 0.14, 0.56 kg ai/ha), three timings of herbicide application (44, 24, and 0 d prior to seeding[DPS]), and four grass species (Idaho fescue, bluebunch wheatgrass, crested wheatgrass, and pubescent wheatgrass) were factorially arranged in a randomized split-plot design with three blocks. The whole-plots were the seeded grass species, and the subplots were the herbicide treatments and timings of application. Treatments were performed in the spring of 1997. Treatment effects on grass vigor (1997) and biomass (1998) depended on grass species, herbicide and rate, and timing. Idaho fescue established at low densities, and it was not possible to determine the treatment effects. In general, crested and pubescent wheatgrass had higher vigor estimates and biomass than did bluebunch wheatgrass. Herbicide applied 24 or 44 DPS had less effect on grass vigor and biomass than did herbicide applied at seeding. Picloram at 0.28 and 0.56 kg/ha tended to reduce vigor and biomass more when compared with the 0.14 kg/ha rate and with both rates of clopyralid. On the basis of these experiments, applying picloram or clopyralid at rates as high as 0.56 kg/ha 24 d or more before seeding bluebunch wheatgrass, pubescent wheatgrass, or crested wheatgrass may allow effective weed control and long-term management through grass competition.

Catchweed bedstraw, common hempnettle, wild buckwheat, and wild oat are serious competitors to arable crops in many parts of the world where cutting implements may be used to control weeds. After cutting, regrowth may become a problem. In greenhouse experiments, weed species were cut at different stages of development (wild oat had two or three leaves, and the dicot weed species were 10 or 15 cm high) and at different heights aboveground (5 and 8 cm). Three weeks after sowing, biomass was measured and compared with that of uncut plants. Cutting height had a significant effect on the regrowth of all species. Common hempnettle was the most sensitive to cutting height followed by wild oat, wild buckwheat, and catchweed bedstraw. Increasing cutting height from 5 to 8 cm above the soil surface increased biomass production by 100 to 400% for all species. Cutting catchweed bedstraw at 8 cm resulted in larger biomass production than that of uncut plants (about 30%). For this species, weed control by cutting once in the growing season, 8 cm aboveground, may result in increased weed biomass production when compared with no cutting. The stage of development when the plants were cut did not have a significant effect on the regrowth ability of any of the species, probably because the two growth stages were relatively close in time.

Midwest growers rely heavily on agrichemical retailers and crop consultants for making pest management decisions. A survey was mailed to 793 fertilizer and agricultural chemical dealers in Illinois to help understand their basis for pesticide recommendations, sources of information, and water quality concerns. Survey response rate was approximately 55%, and results indicated that agrichemical retailers use several sources of information, including manufacturers, universities, and company training programs. Newsletters and fact sheets were recognized as the most useful types of university resources, whereas videos were deemed the least useful. Product effectiveness was identified by 85% of the respondents as being the most important factor affecting pesticide selection. Soil erosion was listed as the greatest threat to water quality. Filter strips and best management practices were suggested as being the most likely to succeed in protecting water quality.

Field studies were conducted in 1998 and 1999 to evaluate the response of seven cotton cultivars to CGA-362622 applied postemergence at 7.5 and 15 g ai/ha to three- to five-leaf cotton. The cultivars evaluated included Deltapine 51, Deltapine NuCotn 33B, Paymaster 1220 RR, Paymaster 1220 BG/RR, Stoneville bromoxynil-resistant 47, Stoneville 474, and Sure-Grow 125. At 1 to 2 wk after treatment (WAT), CGA-362622 at 7.5 and 15 g/ha injured all cotton cultivars 7 to 9% and 13 to 15%, respectively. Cotton injury symptoms included chlorosis and minor stunting. At 3 to 4 WAT, injury from CGA-362622 at 7.5 and 15 g/ha was 2 to 6% and 7 to 9%, respectively. Except for Paymaster 1220 RR, Deltapine NuCotn 33B, and Stoneville 474, all cotton cultivars were injured more by the higher rate than by the lower rate of CGA-362622. Injury was not visibly apparent 6 to 8 WAT. CGA-362622 at either rate had no effect on cotton lint yield.

Field experiments were conducted in 2000 and 2001 near Painter, VA, to evaluate the potential of sulfentrazone for use in potato. Sulfentrazone was applied at 0.11, 0.14, 0.21, and 0.28 kg ai/ha preemergence (PRE) alone or in combination with metolachlor or metribuzin, or at emergence (AT EMERG) of potato to simulate a delayed PRE application where the herbicide would come into contact with potato foliage. Potato injury from sulfentrazone PRE at rates of up to 0.21 kg/ha was generally similar to injury from metribuzin, metolachlor, or metribuzin plus metolachlor PRE. However, AT EMERG applications resulted in excessive injury that ranged from 60 to 86%. AT EMERG applications also caused decreased potato height and alterations in potato-flowering patterns. Sulfentrazone at either application timing controlled common lambsquarters at least 98% even at the lowest rates and was more effective than metribuzin or metolachlor alone. Higher rates of sulfentrazone (0.28 kg/ha) also controlled goosegrass and large crabgrass. However, sulfentrazone at 0.28 kg/ha controlled common ragweed only 58%. Total potato yield and grade with sulfentrazone PRE applications were similar to those of potato treated with metribuzin, metolachlor, or metribuzin plus metolachlor in both years. Potato injury from AT EMERG applications of sulfentrazone plus metolachlor decreased total potato yield and caused changes in the grade distribution of B-size, small A–size, and extra-large potato in 2000.

The sugarcane varieties ‘LCP 85-384’, ‘HoCP 85-845’, and ‘LCP 82-089’ were treated in the plant cane crop (first production year) with various combinations of azafeniden preemergence (PRE) at 0.56 or 0.84 kg ai/ha after planting in September/October, postemergence (POST) at 0.56 kg/ha in spring (March), and semidirected at 0.42 kg/ha after the final cultivation at layby in May. In the first ratoon crop (second production year) azafeniden was reapplied in spring and at layby. Herbicide programs were compared with the standard program of atrazine plus pendimethalin PRE after planting, POST applications of diuron plus pendimethalin in spring, and atrazine plus pendimethalin semidirected at layby. Crop injury was negligible for all herbicide treatments applied after planting. Azafeniden injured sugarcane 30 to 33% when applied POST in spring, and injury was most severe in plant cane and first ratoon HoCP 85-845 when they were considerably taller and had more foliage at application compared with the other varieties. Injury from azafeniden following layby application ranged from 9 to 19% in plant cane and first ratoon crops. Multiple applications of azafeniden during the plant cane and first ratoon years did not reduce stalk height, population, sugarcane yield, or sugar yield for any of the varieties when compared with the standard herbicide program.

Field experiments were conducted from 1994 through 1996 to evaluate the effects of imazapic applied postemergence (POST) at 0.05 and 0.07 kg ai/ha, imazethapyr applied preplant incorporated (PPI) or POST at 0.07 kg ai/ha, and metolachlor applied PPI at 1.7 kg ai/ha on yellow nutsedge control, nutsedge tuber density, and peanut yield. All herbicides controlled yellow nutsedge at least 75% after 3 yr. Imazapic at 0.05 and 0.07 kg/ha controlled yellow nutsedge more consistently than did imazethapyr or metolachlor. Imazethapyr applied POST controlled yellow nutsedge more effectively than did imazethapyr applied PPI. Yellow nutsedge tuber densities in herbicide-treated plots were 51 to 75% less than in untreated control plots. Plots treated with imazapic, imazethapyr applied POST, and metolachlor resulted in higher peanut yields than did untreated control plots.

Separate field experiments were conducted to evaluate weed control and cotton response to flumioxazin in North Carolina. Flumioxazin postemergence directed (PD) at 70 g ai/ha applied alone or mixed with glyphosate or MSMA completely controlled common lambsquarters, common ragweed, entireleaf morningglory, ivyleaf morningglory, Palmer amaranth, pitted morningglory, prickly sida, sicklepod, smooth pigweed, and tall morningglory 4 wk after treatment. Glyphosate at 1,120 g ai/ha controlled sicklepod and entireleaf, ivyleaf, pitted, and tall morningglory less than flumioxazin. Weed-free experiments were conducted to evaluate cotton injury, fresh biomass reduction, and yield response to flumioxazin at 70 g ai/ha preplant (PP) and two rates PD. Nine PP applications were made at various timings between 0 and 10 wk prior to planting. Cotton was stunted 12% initially, and midseason cotton biomass was reduced when flumioxazin was applied at planting in 1 yr. Flumioxazin did not injure 15- or 30-cm–tall cotton when applied PD at 36 or 70 g/ha. Cotton yield differed between years, but was not affected by various flumioxazin treatments compared with commercial standards and nontreated controls.

Glyphosate-resistant spring wheat is being developed and may soon be available to growers. Field experiments were conducted to examine the effect of various rates and application timings of glyphosate on the tolerance of glyphosate-resistant spring wheat and the level of weed control attained with glyphosate in wheat. Glyphosate-resistant wheat exhibited excellent tolerance to glyphosate applied at the one- to two- or four- to five-leaf stages at rates up to 1,780 g ae/ha, representing a fourfold safety margin to the proposed field use rate. Glyphosate at 445 g/ha reduced shoot biomass of green foxtail, wild oat, redroot pigweed, and wild mustard > 95% in glyphosate-resistant wheat in all years, but wild buckwheat biomass was only reduced 67 to 75% at doses up to 890 g/ha. Glyphosate applied in-crop at 667 g/ha reduced quackgrass biomass by 97 to 99%. Comparison of glyphosate with other spring wheat herbicides indicated that glyphosate provided similar or better in-crop control of several weed species. Yield of weed-infested glyphosate-resistant spring wheat responded positively to glyphosate in all years.

Purple starthistle is one of the numerous species of Centaurea that have been accidentally introduced to western North America where most have become pernicious noxious weeds. Purple starthistle is not nearly as widely distributed as its close relative, yellow starthistle, but it is more undesirable because of its growth characteristics and the number, length, and persistence of its spines. Purple starthistle reproduces only by seeds. Knowledge of the seed and seedbed ecology of weeds is important in all suppression strategies and especially for purple starthistle, which has potential biological control agents that suppress seed production. Our purpose was to determine the germination of purple starthistle seeds at a wide range of constant or alternating incubation temperatures from 0 through 40 C. The maximum observed germination ranged from 94 to 100%. Some germination occurred at least 75% or above of the 55 temperature regimes tested. Optimum germination, defined as not less than the maximum observed minus one-half of the confidence interval at the 0.01 level of probability, averaged 88 to 96%. Only one accession of purple starthistle had germination at what we classify as very cold seedbed temperatures. All accessions had near 50% germination at cold seedbed temperatures. Germination was highest at moderate seedbed temperatures and declined at warmer temperatures. The only constant incubation temperature that supported optimum germination was 20 C, and that was for only one accession. The only temperature regime that always supported optimum germination was 15/25 C (15 C for 16 h and 25 C for 8 h in each 24-h period).

At 14 d after treatment (DAT), glufosinate at 0.42 kg ai/ha controlled barnyardgrass and broadleaf signalgrass 85 and 86%, respectively. Antagonism occurred for barnyardgrass control with all mixtures of glufosinate at 0.42 kg/ha. At 14 DAT, no herbicide was superior to glufosinate at either rate when applied in mixture for the control of broadleaf signalgrass. Rice flatsedge control 7 DAT was 68 and 82% with glufosinate at 0.42 and 0.84 kg/ha alone, respectively. The addition of propanil and triclopyr enhanced rice flatsedge control over that with glufosinate alone at 0.42 or 0.84 kg/ha. At 7 DAT, all herbicide mixtures increased spreading dayflower control compared with a single treatment of glufosinate at 0.42 kg/ha. By 28 DAT, spreading dayflower control was less than 80% with all treatments. Rice injury was less than 15% with all treatments.

Field studies were conducted at three locations in North Carolina to evaluate clomazone preemergence (PRE) in glyphosate-tolerant cotton. Cotton was injured by fluometuron PRE at one location. Clomazone PRE controlled common ragweed, goosegrass, large crabgrass, and prickly sida better than trifluralin preplant incorporated (PPI). Trifluralin controlled Palmer amaranth better than clomazone. The addition of a late post-directed (LAYBY) treatment of cyanazine plus MSMA improved the control of goosegrass. Glyphosate at 0.8 kg ai/ha, used postemergence as needed, controlled tall morningglory and entireleaf morningglory at least 84%. Common ragweed was controlled with all herbicides, except trifluralin PPI. Prickly sida was controlled 94% or greater in glyphosate-containing systems. Cotton yields and net returns were similar for all glyphosate systems, regardless of soil-applied herbicides and LAYBY treatment options.

Field studies were conducted in 1995 and 1996 to investigate postemergence (POST) applications of rimsulfuron (12 g ai/ha) plus thifensulfuron-methyl (6 g ai/ha) in tank-mixtures with various acetolactate synthase (ALS)- and non–ALS-inhibitor herbicides for weed control in corn. Rimsulfuron plus thifensulfuron-methyl controlled giant foxtail and common lambsquarters at least 95% but did not control common ragweed. Rimsulfuron plus thifensulfuron-methyl tank-mixed with 20 g ai/ha primisulfuron-methyl, 17 g ai/ha CGA-152005 plus 18 g ai/ha primisulfuron, 18 or 36 g ai/ha halosulfuron-methyl, 18 g ai/ha nicosulfuron, or 280 g ai/ha dicamba controlled giant foxtail at least 89%, common lambsquarters at least 96% and, with the exception of the nicosulfuron combination, controlled common ragweed at least 88%. Rimsulfuron plus thifensulfuron-methyl tank-mixed with flumetsulam (26 g ai/ha) plus clopyralid (69 g ai/ha) plus 2,4-D (140 g ai/ha), atrazine (560 g ai/ha), 2,4-D (280 g/ha), or dicamba (308 g/ha) plus atrazine (588 g/ha) reduced the control of giant foxtail to less than 78% 26 d after treatment (DAT). Corn injury was less than 12% from rimsulfuron plus thifensulfuron-methyl and from mixtures of rimsulfuron plus thifensulfuron-methyl with other herbicides except when rimsulfuron plus thifensulfuron-methyl was mixed with flumetsulam plus clopyralid plus 2,4-D. This combination injured corn 26%. In these studies the appropriate tank-mix partners for rimsulfuron plus thifensulfuron-methyl were primisulfuron, CGA-152005 plus primisulfuron, and halosufluron-methyl.

Our objective was to maximize Canada thistle control and plant community diversity in a waterfowl production area administered by the U.S. Fish and Wildlife Service. We tested three rates (1.5, 3.0, and 4.5 ai/ha) of glyphosate applied during spring, summer, or fall using two application methods. The lowest rate of glyphosate decreased the Canada thistle density by about 30% relative to the control. Glyphosate applied in the fall decreased Canada thistle density below that of the control more consistently than when applied in spring or summer. Wick application generally resulted in less Canada thistle biomass than did broadcast application. Species richness was generally higher when glyphosate was wick applied, and all rates of this application method increased species richness when compared with the control. We recommend fall wick application of glyphosate at 1.5 kg ai/ha to control Canada thistle near the riparian areas. This application provided optimum Canada thistle control, while maintaining species richness important for waterfowl.

Sericea lespedeza is an invasive weed in the tallgrass prairies of the Southern Great Plains. Field experiments were initiated in 1995 at three locations in central Oklahoma to evaluate control of sericea lespedeza for several years after treatment with herbicide. Herbicide treatments included triclopyr at 560 and 840 g ae/ha, fluroxypyr at 210 and 560 g ae/ha, and metsulfuron at 13 and 21 g ai/ha applied at simple-stem (SS), branched-stem (BS), and flowering (FL) growth stages of sericea lespedeza. At all three locations, applications of triclopyr and fluroxypyr at the BS growth stage resulted in less than 4% of the pretreatment sericea lespedeza stem density remaining in the first growing season after treatment (GSAT). Metsulfuron applied at the FL growth stage resulted in 0 to 9% of the pretreatment stem density remaining in the first GSAT. Regardless of rate, triclopyr and fluroxypyr applied at the BS growth stage provided the most consistent long-term control of sericea lespedeza. Percentage of pretreatment stem density remaining with these treatments was 0 to 20% at two locations in the third GSAT, and 4 to 15% at one location in the fifth GSAT. Aboveground biomass yields of desirable grasses (bermudagrass, indiangrass, and little bluestem) at two locations were greater than that of the untreated check in the second and third GSAT in all herbicide treatments. But biomass yield of bermudagrass did not increase when sericea lespedeza was controlled at the location with eroded soil conditions.