Studies were conducted in 1999, 2000, and 2001 to evaluate broadleaf weed control in cotton with postemergence applications of bromoxynil and bromoxynil plus CGA 362622. Bromoxynil was applied at 280 and 560 g ai/ha, and CGA 362622 was applied at 0, 3.8, and 7.5 g ai/ha in a factorial treatment arrangement. Cotton injury 7 d after treatment (DAT) during the 3 yr was 11 to 35% with the herbicide mixtures, but injury did not exceed 2% 28 DAT when averaged over years. CGA 362622 plus bromoxynil controlled velvetleaf, smooth pigweed, common ragweed, and common cocklebur at least 77% 28 DAT. Control of morningglory species was at least 87% with herbicide combinations, except in 2001 when control was only 60% with 280 g/ha bromoxynil plus 3.8 g/ha CGA 362622. Bromoxynil also controlled jimsonweed, but CGA 362622 did not. Spurred anoda control pooled over years did not exceed 53% with bromoxynil or bromoxynil plus CGA 362622 mixtures. Cotton yields generally reflected the level of weed control from the herbicide treatments. In these studies, mixtures of CGA 362622 with bromoxynil controlled several broadleaf weeds better than did either herbicide alone.

Green and yellow foxtail seed production following harvest of spring wheat is a concern of producers in the northern Great Plains of the United States and the Prairie Provinces of Canada. Experiments were conducted in 1996 and 1997 in three tillage systems, no till (NT), chisel plow (CP), and moldboard plow (MP), at the University of Minnesota West Central Experiment Station, Morris, MN, to determine whether time of glyphosate application or tillage after spring wheat harvest could reduce postharvest foxtail seed production. In both years, hard red spring wheat was planted in late April and a packaged mixture of fenoxaprop and 2,4-D ester and MCPA ester was applied at a rate of 53 g and 81 g and 246 g ai/ha for grass and broadleaf weed control. Following spring wheat harvest, each main plot was subdivided into seven subplots, including an untreated control. One subplot was disked twice at 4 to 6 d after harvest (DAH) of spring wheat, and five other subplots had glyphosate (0.25 kg ai/ ha) applied on different days (1 to 31 DAH). Foxtail seeds were collected from the soil surface following first frost, and the number of green and yellow foxtail seeds were determined. Tillage immediately after spring wheat harvest eliminated foxtail plants, and no new foxtail seedlings emerged in either tilled or glyphosate-treated plots despite ideal postharvest conditions for foxtail germination and emergence in 1997. Most viable green foxtail seeds were consistently obtained in NT plots, whereas yellow foxtail seed production varied among tillage systems. Either tillage soon after spring wheat harvest or glyphosate application within 16 DAH reduced green and yellow foxtail seed production by greater than 70%.

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.

Organizer's comments: Systems inquiry represents an array of research-based problem-solving approaches. European experience with the pesticide debate suggests several simple messages contained in this paper. As weed scientists, we have everything to gain by considering a global sphere of views, practices, logic, experience, and message. Read this paper for the essence, the message, the systems thinking, the research framework, and the interface between society and weed science. Read it because science and society must communicate.

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.

Field studies were conducted in South Carolina to evaluate the herbicides acifluorfen, chlorimuron, and imazaquin for control of Palmer amaranth and smooth pigweed in soybean, when applied 3 wk after weed emergence. Palmer amaranth was more difficult to control than smooth pigweed. Compared to untreated controls, acifluorfen, chlorimuron, and imazaquin reduced Palmer amaranth and smooth pigweed biomass 78 and 96%, 80 and 98%, and 82 and 99% at 30 d after treatment (DAT), 60 DAT, and at soybean harvest, respectively. The high rate (140 g/ha) of imazaquin provided greater control of Palmer amaranth than other herbicide treatments at soybean harvest. Except for the 140 g/ha rate of imazaquin, inadequate control of Palmer amaranth resulted in lower soybean seed yields for all herbicide treatments than the weed-free control. However, all herbicides controlled smooth pigweed to provide soybean seed yields similar to the weed-free control.

Experiments were conducted at two locations in North Carolina from 1999 to 2000 to evaluate flumioxazin preplant (PP) for weed management in strip-tillage cotton planted in winter-wheat cover. Flumioxazin PP was evaluated at two rates alone and in mixture with two commonly used PP herbicides and one experimental PP herbicide. Flumioxazin PP at 71 or 105 g ai/ha tank mixed with the isopropylamine salt of glyphosate at 1.12 kg ai/ha, paraquat at 1.05 kg ai/ha, or the trimethylsulfonium salt of glyphosate at 1.12 kg ai/ha controlled common chickweed, common lambsquarters, common ragweed, Palmer amaranth, and smooth pigweed ≥ 96% 29 to 43 d after treatment (DAT). Both glyphosate formulations and paraquat alone provided ≥ 91% control of common chickweed and henbit 29 to 43 DAT, but control of common lambsquarters, common ragweed, large crabgrass, Palmer amaranth, and smooth pigweed was ≤50%. Treatments including flumioxazin injured cotton (≤ 5%) at one location. In all comparisons within a location, cotton treated with flumioxazin PP at 71 or 105 g/ha in mixture with either glyphosate formulation or with paraquat provided equivalent or higher yields than did cotton not treated with flumioxazin PP.

Field experiments were conducted to determine the critical period of weed interference in glyphosate- and glufosinate-resistant sugar beet, and to determine if PRE herbicides increased weed control or sugar beet root yield when glufosinate, glyphosate, or conventional POST herbicides were applied. Glyphosate- and glufosinate-resistant sugar beet root yields were reduced by up to 66 and 67%, respectively, when weeds remained all season in the weedy control treatment compared with yields when weed removal occurred as soon as the weeds were 2.5 cm tall, approximately 2 to 3 wk after planting (WAP). A critical period of weed interference did not occur in this research. The critical time of weed removal was approximately 8 WAP in 1998 and beyond 11 WAP in 1999. Weeds averaged 20 cm in height at 8 WAP and weed densities were greater in 1998 compared with 1999. The critical weed-free period for glyphosate- and glufosinate-resistant sugar beet was 4.5 to 5 WAP in 1998. In 1999, the critical weed-free period at the Michigan Sugar location was 1.5 WAP in glyphosate-resistant sugar beet, and 6.5 WAP in glufosinate-resistant sugar beet for the Michigan Sugar site. Glyphosate or glufosinate POST provided better weed control and resulted in greater sugar beet root yield compared with conventional POST herbicides when data were combined over PRE herbicide treatments. PRE herbicides improved the control of common lambsquarters and Amaranthus species in some of the site-years when data were combined over POST treatments, but sugar beet yield did not increase. Our research suggests that PRE herbicides will not be necessary in glyphosate- or glufosinate-resistant sugar beet. To avoid sugar beet yield loss, multiple POST applications of glyphosate or glufosinate will be needed until 6 to 9 WAP to prohibit yield loss from weeds emerging after the last POST application.

A johnsongrass population from a cotton field in northern Greece along with a population from the university farm (“Control”) were evaluated for resistance to the herbicide quizalofop; cross-resistance to cycloxydim, propaquizafop, and fluazifop (acetyl coenzyme A [CoA] carboxylase [ACCase]-inhibiting herbicides), and multiple resistance to nicosulfuron (acetolactate synthase [ALS]-inhibiting herbicides). In greenhouse experiments, the application of four times the recommended rates of quizalofop and propaquizafop to suspected resistant rhizomatous plants resulted in 4 and 5% growth reduction, respectively. However, the growth of suspected resistant seedlings was reduced by 54 and 28% after the application of two times the recommended rate of the same herbicides. In contrast, the application of quizalofop and propaquizafop at recommended rates on rhizomatous plants and seedlings of the Control population reduced their growth by 97 to 100%. Also, the growth reduction of both populations by the application of cycloxydim, fluazifop, and nicosulfuron at recommended rates ranged from 93 to 100%. In the field experiment, quizalofop and propaquizafop applied at four times the recommended rate reduced growth of the suspected resistant population by 9 and 18%, respectively, whereas the recommended rate of fluazifop gave a 94% growth reduction of this weed. The herbicide rate required for 50% growth reduction (GR50 ) values for rhizomatous plants of the suspected resistant population were 0.90 and 2.465 kg ai/ha for quizalofop and propaquizafop, respectively, whereas the corresponding GR50 values for the seedlings were 0.074 and 0.185 kg ai/ha. These results indicate that a johnsongrass population developed cross-resistance to quizalofop and propaquizafop, but did not evolve cross-resistance to cycloxydim and fluazifop or multiple resistance to nicosulfuron.

Field experiments were established to evaluate preemergence and postemergence herbicides for control of triazine-resistant smooth pigweed and common lambsquarters in no-till corn. When applied preemergence, alachlor in the microencapsulated formulation controlled smooth pigweed better than the emulsifiable concentrate formulation and better than either metolachlor or pendimethalin. These herbicides applied preemergence did not control common lambsquarters consistently. Pendimethalin controlled both triazine-resistant species when applied as a sequential treatment of a preemergence and an early postemergence application. Control of triazine-resistant smooth pigweed and common lambsquarters was excellent when dicamba was applied early postemergence in treatments containing alachlor, metolachlor, or pendimethalin applied preemergence and/or early postemergence. Thiameturon and CGA-131036 controlled triazine-resistant smooth pigweed with acceptable crop tolerance. Thiameturon also controlled common lambsquarters, but control was unacceptable with CGA-131036.

A rapid increase in the number of herbicides and herbicide mixtures registered for use in row crops has made herbicide selection difficult. WEEDS is a computer program that enables a weed management expert to build a list of recommended herbicides or herbicide mixtures based upon weed species, soil texture, and soil organic matter content. An example is given for soybeans.

Field experiments conducted in Texas at six locations from 1996 to 1998 evaluated peanut tolerance to imazapic applied postemergence. Imazapic at 71 g ai/ha was applied weekly from ground cracking to 56 d after ground cracking (DAGC). Visible injury 70 DAGC ranged from 0 to 40%. No reduction in canopy height, canopy width, yield, or grade was observed at harvest following any imazapic treatment.

Volunteer potato is becoming increasingly detrimental in potato production regions. We assessed methods to manage the weed in field corn with herbicides and arthropod herbivory. In greenhouse trials, new tuber production was reduced at least 95% in ‘Ranger Russet’, ‘Russet Burbank’, ‘Russet Norkotah’, and ‘Shepody’ potato varieties by mesotrione applied at 0.11 kg/ha. In field studies conducted near Paterson, WA, a single application of mesotrione at 0.07 or 0.11 kg/ha applied at the time of tuber initiation (mid-postemergence [MPOST]) controlled potato top growth 96 to 98% in 2002 and 2003. Mesotrione applied at earlier stages of potato growth, preemergence or early postemergence, controlled potatoes less than mesotrione applied MPOST. All herbicide treatments prevented yield loss in field corn compared with nontreated checks. Mesotrione reduced new potato tubers and tuber weight more than any other herbicide. Herbivory of volunteer potato by Colorado potato beetle reduced tuber number 21% and tuber density 23% in the absence of herbicides and appeared to further suppress the weed in combination with herbicides. Whereas treatments containing mesotrione were most effective against volunteer potato, arthropod herbivory supplemented weed suppression and may be an important component in reduced or low-input weed management systems.

Despite the abundance of common ragweed in crops and the potency of ragweed pollen as an allergen, pollen production in agricultural fields has hardly been evaluated. Our goal was to evaluate pollen and seed production of early- (i.e., plants missed by weed control) and late- (i.e., after weed control) emerging common ragweed growing in corn and soybean. Allocation and gender distribution were also evaluated. The experiment included 2 yr (2008, 2009), three competition treatments, two seeding/emergence dates, three densities, and four replicates. Competition treatments (main plots) included no crop or weeds (bare), corn, or soybean. Crops were glyphosate resistant. Subplots were seeded with common ragweed before or after glyphosate application at densities of 1 (4 m−2), 3 (12 m−2), or 6 (24 m−2) plants per plot. Ragweed plants were harvested in mid-October and measured (aboveground biomass, length of all male inflorescences, stem diameter, and seed production). Based on our estimates, mean (backtransformed from ln[x + 1]) pollen production values were: 6.25 (bare), 0.74 (corn), and 1.13 (soybean) × 108 pollen grains per ragweed. Biomass and diameter were good predictors of ragweed male and female fitness. Plant height was not correlated with maleness. In crops, ragweed gender distribution was shifted toward maleness. Estimations indicate early-emerging (June 18 to 23) ragweed produced three times more pollen than late (July 7 to 11) plants.

Field surveys were conducted across the Blacklands region of Texas during 2016 and 2017 to document the distribution of herbicide-resistant Lolium spp. infesting winter wheat production fields in the region. A total of 68 populations (64 Italian ryegrass, four perennial ryegrass) were evaluated in a greenhouse for sensitivity to herbicides of three different modes of action: an acetolactate synthase (ALS) inhibitor (mesosulfuron-methyl), two acetyl-coenzyme-A carboxylase (ACCase) inhibitors (diclofop-methyl and pinoxaden), and a 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitor (glyphosate). Herbicides were applied at twice the label-recommended rates for mesosulfuron-methyl (29 g ai ha−1), diclofop-methyl (750 g ai ha−1), and pinoxaden (118 g ai ha−1); and at the recommended rate for glyphosate (868 g ae ha−1). The herbicide screenings were followed by dose-response assays of the most-resistant ryegrass population for each herbicide at eight rates (0.5, 1, 2, 4, 8, 16, 32, and 64×), compared with a susceptible population at six rates (0.0625, 0.125, 0.25, 0.5, 1, and 2×). The initial screening and dose-response experiments were conducted in a completely randomized design with three replications and two experimental runs. Survivors (<80% injury) were characterized as highly resistant (0% to 20% injury) or moderately resistant (21% to 79%). Results showed that 97%, 92%, 39%, and 3% of the Italian ryegrass populations had survivors to diclofop-methyl, mesosulfuron-methyl, pinoxaden, and glyphosate treatments, respectively. Of the four perennial ryegrass populations, three were resistant to diclofop-methyl and mesosulfuron-methyl, and one was resistant to pinoxaden as well. Perennial ryegrass populations did not exhibit any resistance to glyphosate. Dose-response assays revealed 37-, 196-, and 23-fold resistance in Italian ryegrass to mesosulfuron-methyl, diclofop-methyl, and pinoxaden, respectively, compared with a susceptible standard. One Italian ryegrass population exhibited three-way multiple resistance to ACCase-, ALS-, and EPSPS-inhibitors. The proliferation of multiple herbicide–resistant ryegrass is a challenge to sustainable wheat production in Texas Blacklands and warrants diversified management strategies.

Jointed goatgrass is a problem weed in winter wheat production areas of the Great Plains. Winter wheat seeding rates are easily adjusted by the growers and influence competition by some weeds. Field experiments were initiated in Kansas, Nebraska, and Wyoming using winter wheat cultivars selected from leading adapted cultivars from each region to determine the effect of wheat plant density in the fall on jointed goatgrass competitiveness. Three winter wheat seeding rates (50, 67, and 84 kg seeds/ha) were used at Hays, KS, and Sidney, NE, and four seeding rates (33, 50, 67, and 101 kg seeds/ha) were used at Torrington and Archer, WY. An analysis of covariance model was fit with winter wheat fall plant density as the covariate. In 1996, winter wheat grain contamination (dockage) was reduced at the rate of about 6% for every 10 additional wheat plants/m2 above the threshold density of 70 plants/m2 at Archer, WY, and at the rate of about 0.5% for every 10 additional wheat plants/m2 above the threshold density of 110 plants/m2 at Hays, KS. At Hays the reduction occurred only with the semidwarf cultivar ‘Vista’. Increased wheat density reduced jointed goatgrass reproductive tillers in four out of six location–year combinations and biomass in two out of four location–year combinations. Despite the lack of a consistent reduction in jointed goatgrass competitiveness as the result of increased wheat density, increased seeding rates may be a good, low-cost, long-term investment as part of an integrated jointed goatgrass control program in winter wheat.

2,4-D is the most widely used herbicide for weed control in grain sorghum in northern Tamaulipas, Mexico. Crop injury caused by 2,4-D drift to nontarget crops commonly occurs because of prevailing high winds. Field experiments were conducted from 2001 to 2003 to evaluate an integrated weed management program in grain sorghum with alternative postemergence herbicides to 2,4-D at registered and reduced rates. Bromoxynil applied at 480 (registered rate), 360, and 240 g/ha provided excellent broadleaf weed control when adequate rainfall occurred. Prosulfuron at 14.2 g/ha applied broadcast without cultivation provided excellent weed control and sorghum yield comparable with 28.5 g/ha (registered rate). This treatment represented a 32% cost reduction and 50% reduction in herbicide input compared with prosulfuron applied at registered rate without cultivation, and 31% cost reduction compared with 2,4-D at the registered rate (590 g ae/ha) plus cultivation, considered the commercial standard.

Field experiments were conducted in 1998 and 1999 at two locations in Mississippi to determine weed control efficacy of postemergence soybean herbicides alone or following pendimethalin + imazaquin preemergence in glufosinate-tolerant soybean planted in 38- or 76-cm rows. Glufosinate applications controlled pitted morningglory better than conventional herbicide treatments, regardless of row spacing. Pendimethalin + imazaquin did not increase the efficacy of glufosinate on pitted morningglory. Pitted morningglory control was increased in narrow rows when compared to wide rows with all treatments. Sicklepod control ranged from 90 to 100% in narrow rows with glufosinate, regardless of rate. Residual herbicides alone controlled sicklepod 54%, regardless of row spacing. With grass species, two applications of 420 g ai/ha glufosinate controlled weeds 82 to 100%. Residual herbicides followed by 420 g/ha glufosinate controlled grass species 80% or more, regardless of row spacing. Hemp sesbania control ranged from 80 to 92% in 76- and 38-cm rows with one application of 560 g/ha glufosinate. Glufosinate at 420 g/ha used as sequential applications controlled hemp sesbania better than the conventional treatment in 76-cm rows. Residual herbicides in combination with glufosinate did not increase hemp sesbania control. There were no differences in yield due to row spacing at Stoneville in either year due to extremely dry growing conditions during pod set. At Starkville, two applications of 420 g/ha glufosinate resulted in higher yields than pendimethalin + imazaquin followed by 420 g/ha glufosinate in both years. Pendimethalin + imazaquin followed by 420 g/ha glufosinate increased yield in narrow rows compared to wide rows at Starkville in 1998.

Preemergence herbicides are commonly applied to nursery containers for control of annual weeds in the production of ornamental plants. Pine bark is a popular container growing medium because it is inexpensive, drains well, is easy to transport, and supports acceptable nursery crop growth. However, little is understood about leaching of herbicides through pine bark. The downward movement of these herbicides through container media may inhibit root growth in sensitive nursery crops and also reduce herbicidal efficacy. Four experiments were conducted at two different irrigation volumes to evaluate depth of pendimethalin movement in packed columns of pine bark and field soil. After 17.5 cm of water was applied over 7 d, pendimethalin moved downward into the 6 to 9-cm depth in 100% pine bark, whereas no movement was detected below the 0 to 3-cm depth in a Tetotum loam soil, as determined by a large crabgrass bioassay. Doubling the irrigation volume to 35 cm of water applied over 14 d did not significantly increase pendimethalin movement in pine bark or field soil. However, it did decrease pendimethalin persistence in the top 0 to 3-cm depth in pine bark. The pine bark had a higher cation exchange capacity than did the field soil. However, the physical characteristics of pine bark, a large volume of void space and low bulk density, resulted in higher hydraulic conductivity rates than in field soil. These factors may be the principal reasons that pendimethalin leached to a greater extent through pine bark than the field soil.

The effects of five soil fungi, endemic to the western United States, were evaluated for disease reaction, root dry weights and shoot dry weights on five grass species. The undesired grass, downy brome or medusahead, the perennial forage species, squirreltail or western wheatgrass, and winter wheat were susceptible to take-all. Downy brome, medusahead, squirreltail, and winter wheat were susceptible to crown rot. The desired grasses, squirreltail, western wheatgrass, and winter wheat, were susceptible to barepatch. Crown rot is adapted to dry soils and may be a potential biological control on downy brome and medusahead in the arid environment of the western U.S.