Sixteen applications of imazapyr and other herbicides were made to field bindweed from 1982 to 1986. Control with imazapyr was 89% or more 1 yr after treatment at 0.14 kg ai ha-1 when plants were growing vigorously at application. Only 1 of 16 applications of imazapyr at 0.56 kg ha-1 controlled less than 90% regardless of plant vigor. Control at 0.56 kg ha-1 was usually superior to that obtained with dicamba at 1.1 and 2.2 kg ae ha-1, and 2,4-D at 1.1 kg ae ha-1, as well as combinations of picloram with either 2,4-D or dicamba. All herbicides were less effective when applied to field bindweed with poor vigor. Winter wheat planted in the fall up to 122 days after application was injured 20 to 88% by imazapyr at 0.14 kg ha-1. Sorghum planted the next spring was injured 15% or less by imazapyr at 0.14 and 0.28 kg ha-1.

Dicamba, 2,4-D, picloram, and commercially available premixes of glyphosate plus 2,4-D or glyphosate plus dicamba were evaluated alone and in combination for field bindweed control in a winter wheat-fallow system in Colorado, Wyoming, Kansas, and Montana. Approximately one year after application, herbicide mixtures containing picloram at 0.14 or 0.28 kg ai ha-1 provided the best control. In five of seven locations, the control provided by picloram in herbicide mixtures was greater than the control provided by glyphosate plus 2,4-D, 2,4-D, or dicamba when these products were mixed with picloram. Glyphosate plus 2,4-D or glyphosate plus dicamba premixes, or 2,4-D added to dicamba were less effective for long-term control of field bindweed than mixtures containing 0.14 kg ai ha-1 or more of picloram. Under drought conditions in Kansas in 1988, picloram did not control field bindweed as well as in Colorado, Wyoming, or Montana where rainfall was normal.

Applications of isopropylamine glyphosate at 0.28, 0.56, 0.84, and 1.12 kg ae/ha in combination with the dimethylamine salts of 2,4-D or dicamba at 0.14, 0.28, 0.42, and 0.56 kg ae/ha produced additive or synergistic field bindweed control compared to the herbicides applied alone. Leaf and root growth was inhibited more from herbicide combinations than would be predicted from the effects of the chemicals applied alone at the same rate. The uptake of 14C from glyphosate into the treated leaf and its accumulation in roots increased when 2,4-D or dicamba was combined with the 0.28 kg/ha rate of 14C-glyphosate. The combination of 2,4-D or dicamba with a higher (0.84 kg/ha) 14C-glyphosate rate did not change total absorption of 14C from glyphosate. However, compared to 0.84 kg/ha of 14C-glyphosate applied alone, less 14C accumulated above the treated leaf and more accumulated in the roots when 2,4-D was added to the glyphosate. The combination of glyphosate with 2,4-D or dicamba generally resulted in both increased uptake of 14C from 2,4-D or dicamba and greater accumulation in the roots. The additive or synergistic field bindweed control observed from mixtures of glyphosate with 2,4-D or dicamba appeared to be due to greater accumulation of the herbicides in the roots.

Glyphosate plus 2,4-D at 0.3 + 0.5 or 0.4 + 0.7 kg ae ha-1 applied 31 to 1 d before seeding did not affect wheat yields or grain test weights, in field experiments in conventionally tilled and no-till winter wheat. In the conventionally-tilled system in each of two years and in the no-till system in a year with 48 mm rain within 7 d before wheat was seeded, picloram applied at 0.14 kg ai ha-1 from 31 to 1 d before seeding reduced crop yields by 7 to 8%. In the conventionally-tilled system in a year with only 2 mm rain within 7 d before wheat was seeded, 2,4-D at 3.4 kg ae ha-1 and dicamba at 0.14 kg ae ha-1 applied 30 to 1 d before seeding, reduced wheat yields by 7 and 4%, respectively. Grain test weights in both tillage systems were increased slightly by picloram at 0.14 kg ha-1, but were decreased slightly by dicamba at 0.14 kg ha-1, in the year with little rain before sowing. Test weights did not differ among herbicides or tillage systems in the year with significant rain a few days before seeding.

This research compared seven field bindweed control treatments to a check in a 3-yr winter wheat-sorghum-fallow rotation. Treatments included 3 wk intervals of sweep tillage combined with one or two annual applications of 2,4-D (tillage and 2,4-D). Two other treatments were the same as tillage and 2,4-D, except dicamba or a mixture of picloram and 2,4-D were applied once in October after wheat harvest. A fourth treatment was identical to tillage and 2,4-D, except imazapyr was sprayed immediately after harvest of wheat. Also, three no-tillage systems using glyphosate and 2,4-D at monthly intervals were supplemented with either dicamba, picloram and 2,4-D, or imazapyr the same as in treatments involving tillage and 2,4-D. The check was sweep tilled every 6 wk. All treatments controlled field bindweed in one rotation of two fallow periods and two crops. After control was accomplished, wheat and sorghum yields were about twice the check. Using 1995 costs and returns, profit for an owner-operator for the two fallow periods and two crops was $123 ha−1 for tillage and 2,4-D, compared to $19 ha−1 for the check. Tillage and 2,4-D supplemented with picloram or imazapyr were almost as profitable as tillage and 2,4-D. Because of high herbicide cost and low yields, no-tillage treatments lost money. Profits with a 33:67 owner-tenant rental agreement were $105 and $21 ha−1, respectively, for owner and tenant using tillage and 2,4-D. With no field bindweed control practice, the tenant lost $33 ha−1 and the owner made $51 ha−1.

The effect of glyphosate applied as a desiccant to field bindweed-infested alfalfa in the final year of seed production was examined in field experiments near Lovelock, NV. Glyphosate at 2.5 and 5.0 kg ae/ha flat fan applied was equal to and/or superior to dinoseb for desiccation of foliage, respectively. Alfalfa seed yield and quality following glyphosate treatment were similar to that of dinoseb-treated alfalfa. Glyphosate treatment reduced some alfalfa and field bindweed stands. A beneficial interaction between low-volume control droplet application (CDA) and glyphosate was not evident.

Two biotypes of field bindweed differing in their susceptibility to glyphosate were used to determine if diluent or carrier volume and additional surfactant could overcome differences in intraspecific response to glyphosate. In greenhouse studies, glyphosate (formulated product) was applied at 1.68 kg/ha in three diluent volumes (142, 189, and 237 L/ha), with and without 1 % (v/v) additional amphoteric surfactant. Nonparametric and ordinal categorical analyses indicated that field bindweed biotype, diluent volume, and surfactant significantly increased glyphosate phytotoxicity 7 DAT. Only biotype and volume were significant 21 DAT. The tolerant biotype was less injured at the 189 and 237 L/ha volumes than the susceptible biotype. Field bindweed injury was similar at a diluent volume of 142 L/ha for both biotypes. These greenhouse studies suggest that control of field bindweed may be improved with glyphosate by using low spray volume in concert with additional surfactant.

Weed data were collected over three tillage systems and two years in southwestern Ontario, in fields of corn, soybean, and winter wheat. Tillage systems involved soil inversion by moldboard plow, soil disturbance without inversion, and no tillage. The data were subjected to multivariate ordination techniques to determine if weed communities were associated with the different crops, tillage systems, or years. Crop, year, and tillage system all had significant effects on the weed community. Weed communities in corn and winter wheat were least similar; those in soybean were intermediate. Several grass weeds were more abundant in the drier of the two years. Some variation was related to tillage system but the effect of tillage was less than that of either crop or year.

To develop an understanding of how adjuvants might enhance glyphosate [N-(phosphonomethyl)glycine] activity, absorption and translocation of a polyethoxylated tallow amine amphoteric surfactant (MON 0818) were examined in field bindweed (Convolvulus arvensis L. # CONAR). Scanning electron microscopy did not reveal any physical disruption of the epicuticular waxes from spray applications of MON 0818, an oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate) surfactant, or glyphosate. Radioactive MON 0818 absorption was rapid during the first 6 h. Maximum absorption (84%) occurred by 24 h after application. Less than 3% of the applied radioactivity was recovered from the epicuticular wax of treated leaves. Movement of radioactivity away from the treated area was limited predominantly to movement within the treated leaf. Altering light intensity or humidity in which the plants developed before treatment did not influence MON 0818 absorption.

Field bindweed and Russian knapweed were grown from seed or rhizome segments under 520, 325, or 236 μmol·m–2 · s–1 photosynthetic photon flux density (PPFD) to determine vegetative and reproductive response. Flower production in both species declined with decreasing light level. Leaf area of field bindweed decreased as light level decreased, but Russian knapweed leaf area increased as light intensity decreased from 520 to 325 μmol·m–2 ·s–1 PPFD or from 520 to 236 μmol·m–2 ·s–1. Dry matter of shoots, roots, and rhizomes of field bindweed grown from seed declined as light level decreased, but the only response of plants grown from rhizome segments was complete inhibition of rhizome production. Dry matter of Russian knapweed shoots and roots in plants grown from seed or rhizome segments decreased as light decreased. In both species the total PPFD was more important than whether low or high light level occurred first.

Experiments were conducted under controlled environment and field conditions to evaluate the influence of growth stage and fluroxypyr dosage on control of field bindweed. In controlled environment studies fluroxypyr effectively controlled 8- to 12-leaf field bindweed. Shoot number, length, and dry weight, and root dry weight decreased as herbicide dose increased. The estimated ED50 (effective dose for 50% reduction) values for shoot and root dry weight were 50 and 33 g ai/ha, respectively. The ED50 for shoot length was 98 g ai/ha. Fluroxypyr was applied at rates from 0.2 to 0.4 kg/ha under field conditions to field bindweed at selected stages of growth. Regardless of herbicide dosage, fluroxypyr applied at the late flowering stage of growth controlled field bindweed better than when applied at the bud or early flower stage. Corn grain yield increased as a function of fluroxypyr dose in 1988 but not in 1987. Dry weight of roots and shoots of field bindweed harvested one year after treatment decreased with increasing rates of fluroxypyr. These studies demonstrate the potential of fluroxypyr for the control of field bindweed.

Field experiments were conducted in Oklahoma to evaluate the effect of three imidazolinone herbicides and metsulfuron on established field bindweed and hard red winter wheat followcrops. Imazapyr at 280 g ai ha-1 and imazethapyr at 560 g ai ha-1 controlled field bindweed from 78 to 100% for 48 wk, but imazaquin at 560 g ai ha-1, metsulfuron at 17.5 g ai ha-1, and 2,4-D plus picloram at 1120 plus 280 g ae ha-1 did not. Imidazolinone herbicides reduced forage and grain yield of wheat seeded 8 to 14 wk after herbicide application. Only imazapyr reduced grain yield of wheat seeded 15 mo after treatment.

Management of perennial weeds is a major concern in reduced-tillage cropping systems. Field research was conducted at Nashua, IA, from 1977 through 1990 to evaluate the long-term impacts of tillage and cropping patterns on perennial weed populations in corn and soybean production. Continuous corn and a corn/soybean rotation were conducted utilizing moldboard plow, chisel plow, ridge tillage, and no-tillage systems. The research area was free of established perennial weed species at the initiation of the experiment in 1977. Hemp dogbane was observed by 1980, with the greatest densities in no-tillage. By 1990, continuous corn had greater hemp dogbane densities with no-tillage than other tillage system by crop rotation treatments. American germander densities were not affected by tillage systems in 1980 and 1981, but by 1990, corn/soybean rotations had greater densities in moldboard plow than other tillage systems. Field bindweed developed primarily in the corn/soybean rotations with the greatest densities occurring in no-tillage. Greater and more diverse populations of perennial weeds developed in reduced-tillage systems than in the moldboard plow system. However, practices used to control annual weeds and environmental factors interacted with tillage to regulate perennial weed populations.

Field bindweed infests millions of hectares in the Great Plains greatly reducing productivity and value of land. The standard practice for field bindweed control is sweep tillage at 3 wk intervals combined with one or two annual 2,4-D) applications during the 14 mo fallow period in a winter wheat-fallow crop rotation. This was compared to tillage and 2,4-D in conjunction with dicamba or a mixture of picloram+2,4-D applied once during the first October of the first 14 mo fallow period. Also, three no-tillage systems were included using glyphosate+2,4-D at monthly intervals. Two of the treatments were supplemented with dicamba, or picloram+2,4-D as in the sweep tillage system. All treatments controlled field bindweed in two fallow periods and two winter wheat crops, and increased winter wheat yields to about twice the control. Sweep tillage at 3 wk intervals combined with 2,4-D resulted in $36 ha−1 profit for an owner-operator compared to $15 ha−1 loss with no herbicide or tillage treatment. On average no-tillage lost $35 ha−1. Other treatments, although controlling field bindweed, lost from 35 to $186 ha−1. To determine if long-term benefit after control was achieved, average yields for the area were used to calculate profits using normal farming practices. Profits were 136, 78, and $-50 ha−1, respectively, for sweep tillage and 2,4-D, no-tillage, and the untreated check. In a standard 33:67 owner-tenant rental, profits to the owner for the control period were 90, −33, and $43 ha−1, respectively for tillage and 2,4-D, no-tillage, and untreated check. The tenant lost from $24 to 69 ha−1 for the three systems indicating owners must modify rental agreements during a field bindweed control program.

Over 20 experiments comparing glyphosate [N-(phosphonomethyl)glycine], dicamba (3,6-dichloro-2-methoxybenzoic acid), fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], and 2,4-D [(2,4-dichlorophenoxy) acetic acid] for control of field bindweed (Convolvulus arvensis L. # CONAR) were conducted from 1976 to 1982 at various times of the year and different stages of weed growth. In three of the studies, 1.7, 3.4, and 5.0 kg ae/ha of glyphosate gave 54, 72, and 80% control, respectively, 1 yr after application. Control with glyphosate at 3.4, 2,4-D at 1.1, dicamba at 1.1, and fosamine at 13.7 kg ae/ha in the 20 studies was 71, 55, 57, and 73%, respectively, 1 yr after application. Glyphosate, 2,4-D, and fosamine gave good control at any time of the year if weed growth was lush. Dicamba gave good control anytime if growth was good and in the fall regardless of growing conditions. Control with mixtures of dicamba and picloram, picloram and 2,4-D, or glyphosate and picloram was higher than with the other herbicides. Dicamba at 1.1 kg/ha, applied after August caused some injury to wheat planted the same fall. Herbicide combinations with picloram at 0.28 kg/ha applied after June injured wheat planted in the fall.

Greenhouse experiments were conducted to determine effects of watering frequency, drought stress, and a combination of watering frequency and glyphosate on growth of field bindweed. Watering daily, twice weekly, or weekly to field capacity affected field bindweed grown from seed differently than plants grown from root runner segments. Shoot and root dry matter of plants grown from seed increased when plants were watered frequently but dry matter allocated to root runners did not change when plants were watered less frequently. Plants grown from root runner segments increased their shoot and root runner dry matter when watered frequently, but root dry matter was not affected by watering frequency. Plants grown from seed had highest regrowth when watered weekly and plants grown from root runner segments had higher regrowth when watered daily. Drought reduced survival rate and dry matter of surviving plants. Frequency of watering and whether plants began from seeds or root runner segments influenced glyphosate action on field bindweed. No regrowth was observed 6 months after 1.5 kg ai/ha of glyphosate was applied to plants that had been grown for 8 weeks under three different watering frequencies.

Absorption and translocation of glyphosate [N-(phosphonomethyl)glycine] with and without adjuvants were examined in field bindweed (Convolvulus arvensis L. # CONAR) to develop an understanding of the influence of selected adjuvants and environment before application on glyphosate activity. Light intensity and humidity during plant development resulted in differences in 14C-glyphosate absorption. When applied in water or with an oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate) adjuvant, an average of 9% of the glyphosate was absorbed in plants grown in high light intensity, low humidity (HLLH) before treatment, compared to an average of 21% in plants grown in low light, high humidity (LLHH) before treatment, respectively. Amounts of epicuticular wax on HLLH field bindweed were almost three times as great as on LLHH leaves and may explain absorption differences. No differences in glyphosate absorption were observed between glyphosate applied with oxysorbic or no adjuvant even though the oxysorbic adjuvant effectively reduces surface tension. Absorption was increased two- to threefold with a polyethoxylated tallow amine adjuvant (MON 0818) compared to no adjuvant. Unlike absorption without adjuvant or with oxysorbic adjuvant, there were few absorption differences in plants grown in different environments before application. Absorption continued for 24 to 36 h after application regardless of adjuvant. Reductions in MON 0818 concentration and subsequent necrosis resulted in increased movement of radioactivity away from the site of application.

Five presumed biotypes were identified among field bindweed (Convolvulus arvensis L. ♯3 CONAR) clones collected from a field population near Lafayette, IN. Consistent variations in leaf morphology, floral characteristics, and accumulation of shoot and root biomass were found between biotypes when grown in a controlled environment. The biotypes also differed in their flowering capacity. The earliest flowering biotype formed flowers 23 days before the latest and produced 19 times more flowers per plant, which indicated further differences in seed production potential between biotypes. Pollination studies helped to differentiate biotypes within the population and showed that the presumed biotypes were self-incompatible. Vegetative reproduction potential of the biotypes varied from 1.8 to 74.5% in the number of root buds that developed into shoots. The variability in growth and reproduction observed between these field bindweed biotypes may explain the survival and adaptability of a population of this weed as environmental conditions and control practices change.

Biotypes of field bindweed that vary in sensitivity to glyphosate were studied to determine the physiological or biochemical bases for these differences. Studies con ducted using whole plants and in vitro cultured shoots identified several potentially important differences between the most tolerant (biotype 4) and most susceptible (biotype 1) biotypes. Biotype 4 plants had greater 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (DAHPS) activity and higher concentrations of phenolic compounds, indicating greater shikimate pathway activity than biotype 1. This may reflect a higher growth ability of biotype 4, as observed in shoot cultures. 5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS) activity in whole plants increased in all parts of biotype 4 by 7 d after a glyphosate treatment of 1.1 kg ae ha−1, whereas activities in biotype 1 plants did not increase at any time. However, this may not be the only mechanism of glyphosate tolerance because EPSPS activity in cultured shoots of both biotypes increased equally in response to glyphosate, even though biotype 4 shoots were able to survive and grow on a glyphosate-containing medium that inhibited growth of biotype 1 shoots. We propose that multiple mechanisms operating at a cellular/metabolic level combine to enable biotype 4 to tolerate higher glyphosate rates than biotype 1.

Phomopsis convolvulus Ormeno, a fungus, reduced growth and regeneration of field bindweed under greenhouse environments. Field bindweed seedlings at the cotyledon stage were severely injured and killed (95% mortality) with 108 conidia/m2. Three- to five-leaf seedlings (2 weeks old) were controlled when inoculated with 109 conidia/m2 (70% mortality; 98 and 89% reduction in dry weight of aboveground biomass and roots, respectively). This inoculum density reduced aboveground and root biomass, and adversely affected regeneration of 4-week-old seedlings and established plants, but few plants were killed. In controlled-environment studies, two inoculations were superior (P = 0.02) to one inoculation in reducing foliage aboveground of well-established seedlings (4 weeks old). However, new shoots produced between the first and second inoculation treatments were less diseased than expected.