Laboratory photolysis rates of 2,4-D [(2,4-dichlorophenoxy)acetic acid], bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} in dilute aqueous solution were enhanced by the presence of adjuvants. Addition of 1.0% (v/v) petroleum oil concentrate (POC), 1.0% (v/v) soybean oil concentrate (SBOC), and 0.15% (v/v) emulsifier package (EP) enhanced herbicide photolysis rates more than addition of 0.15% (v/v) oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate). Bioassays showed that phytotoxicity of photolyzed herbicide solutions was negatively correlated with time of exposure to ultraviolet light. Addition of 0.85% (v/v) acetophenone to aqueous herbicide solutions containing 0.15% (v/v) oxysorbic strongly sensitized photodegradation of 2,4-D, and to a lesser extent, haloxyfop. Acetophenone had no effect on bentazon photolysis in the presence of oxysorbic. In another study, herbicides were dissolved in white mineral oil or once-refined soybean oil and exposed to ultraviolet light. After a 6-h exposure, there was 92% loss of haloxyfop in mineral oil and 36% loss in soybean oil. There was no difference between oils in affecting the photolysis rate of 2,4-D or bentazon.

The use of 2,4-dichlorophenoxyacetic acid (2,4-D) to control annual weeds such as pigweed (Amaranthus retroflexus L.) is common. Abundant evidence has been published to show that 2,4-D affects germination and subsequent seedling development. Allard et al. found that 2,4-D delayed germination and caused abnormalities in seedlings of 22 broadleaf and cereal species. Elongation of radicles was inhibited in mustard seedlings and in both non-dormant and embryo-dormant seeds as well as in seeds with impermeable seed coats. Germination can not only be delayed but can be inhibited, although at low concentrations of 2,4-D germination may be accelerated. Leachates produced by rainfall coming in contact with 2,4-D in soil were deleterious to seeds of flax and corn. To explore further the effects of 2,4-D on seeds, germination tests were made with scarified and nonscarified seeds of pigweed and on the effect on yield and germination of seeds harvested from pigweed plants that were sprayed with sublethal doses of 2,4-D in field plots.

The members of the genus Cuscuta (common name: dodder) are obligate holoparasitic plants that are found throughout the agricultural regions of the world. Of all of the species of dodder, field dodder (Cuscuta campestris) causes the most damage to crops. This species parasitizes the shoots of broadleaf plant crops and weeds. We conducted a series of field dodder seed germination tests in controlled-temperature chambers, in order to describe the effect of temperature on field dodder germination and develop a germination model based on the obtained data. The best fit was obtained when temperature data and time were transformed to thermal time using the beta-function model. The field dodder germination model can serve as a tool for knowledge-based predictions of germination and emergence timing, to allow for the implementation of effective mechanical and chemical management measures.

Field studies in 1978 and 1979 evaluated the effectiveness of single and combination herbicide treatments in processing peas (Pisum sativum L.) and soybeans [Glycine max (L.) Merr.] for the control of wild proso millet (Panicum miliaceum L.). Eight treatments that included dinitroaniline herbicides controlled wild proso millet adequately through the entire growing season of the early-planted peas (approximately 60 days). Wild proso millet emergence and growth in untreated peas was suppressed by the early emergence, rapid growth, and high plant density of the drill-planted crop. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.8 kg/ha stunted pea growth and was the only treatment that reduced yields significantly. No herbicide treatment evaluated in soybeans controlled wild proso millet adequately for the entire growing season without reducing soybean growth and yield. Treatments containing dinitroaniline herbicides, which controlled wild proso millet in peas and resulted in good yield, did not perform similarly in soybeans.

In Israel, an intensive modern agriculture has developed under difficult ecological constraints. The climate is characterized by two distinct seasons – a cool, rainy winter and a hot, dry summer. In winter, there are often temporary excesses of rain, causing erosion and preventing regular cultivation of fields; and in summer the soil dries out, and intensive cropping is only possible with irrigation. However, water is scarce and rationed directly by maximizing irrigation efficiency, and indirectly by controlling weeds, which compete for soil moisture.

Preemergence applications of herbicides were evaluated for their effect on establishment of zoysiagrass (Zoysia japonica Steud.) with competition from either smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl. # DIGIS] or goosegrass [Eleusine indica (L.) Gaertn. # ELEIN]. When ‘Meyer’ and ‘Belair’ zoysiagrass plugs were grown in sand and treated in the greenhouse, none of the herbicides reduced root weight or length. When plugs were grown in a Sassafrass sandy loam, bensulide {O,O-bis(1-methylethyl)-S-[2-[(phenylsulfonyl)amino] ethyl] phosphorodithioate} and simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine) reduced root weight, and simazine reduced root length of Belair, but not Meyer. In smooth crabgrass-infested field plots, more stolons were produced from Meyer plugs treated with simazine, oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one}, and siduron [N-(2-methylcyclohexyl)-N′-phenylurea] than plugs treated with bensulide, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], or the untreated control. At the end of two growing seasons, metribuzin-treated plots had significantly less zoysiagrass than other plots. Oxadiazon, DCPA (dimethyl tetrachloroterephthalate), and siduron enhanced the field establishment rate where Meyer zoysiagrass was competing with high populations of smooth crabgrass.

A population model of itchgrass was developed for a typical corn–based cropping system in the Pacific coastal region of Costa Rica. Field experiments were conducted to quantify density-dependent seedling mortality and fecundity. Additional information required for the model was obtained from the literature. Effect of control methods on itchgrass density—including a leguminous cover crop (velvetbean), a preemergence herbicide (pendimethalin), and classical biocontrol with the head smut—alone and in combination, were investigated using the model. According to model results, the cover crop planted at high and low densities between corn rows was highly efficient, reducing the initial itchgrass density from 54 plants m−2 to 4 and 17 plants m−2, respectively. Associating velvetbean with corn solely in the first crop each year resulted in predicted itchgrass densities of 33 and 36 plants m−2 (at high and low cover crop planting densities, respectively). The improvement in corn yield from preemergence herbicide or biocontrol in addition to the cover crop was only modest. This indicated that if, in practice, the cover crop is as effective as predicted, an inexpensive control tactic such as biological control (provided that an infection rate of at least 50% can be achieved) should be given priority to prevent income losses.

Since the commercialization of herbicide-resistant (HR) crops, primarily glyphosate-resistant crops, their adoption has increased rapidly. Multiple herbicide resistance traits in crops such as canola (Brassica napus L.), corn (Zea mays L.), cotton (Gossypium hirsutum L.), and soybean [Glycine max (L.) Merr.] have become available in recent years, and management of their volunteers needs attention to prevent interference and yield loss in rotational crops. The objectives of this review were to summarize HR crop traits in barley (Hordeum vulgare L.), canola, corn, cotton, rice (Oryza sativa L.), soybean, sugarbeet (Beta vulgaris L.), and wheat (Triticum aestivum L.); assess their potential for volunteerism; and review existing literature on the interference of HR crop volunteers, yield loss, and their management in rotational crops. HR crop volunteers are problem weeds in agronomic cropping systems, and the impact of volunteerism depends on several factors, such as crop grown in rotation, the density of volunteers, management practices, and microclimate. Interference of imidazolinone-resistant (IR) barley or wheat volunteers can be a problem in rotational crops, particularly when IR crops such as canola or wheat are grown. HR canola volunteers are abundant in the Northern Great Plains due to high fecundity, seed loss before or during harvest, and secondary seed dormancy, and they can interfere in crops grown in rotation such as flax (Linum usitatissimum L.), field peas (Pisum sativum L.), and soybean. HR corn volunteers are competitive in crops grown in rotation such as corn, cotton, soybean, and sugarbeet, with yield loss depending on the density of HR corn volunteers. Volunteers of HR cotton, rice, soybean, and sugarbeet are not major concerns and can be controlled with existing herbicides. Herbicide options would be limited if the crop volunteers are multiple HR; therefore, recording the cultivar planted the previous year and selecting the appropriate herbicide are important. The increasing use of 2,4-D, dicamba, glufosinate, and glyphosate in North American cropping systems requires research on herbicide interactions and alternative herbicides or methods for controlling multiple HR crop volunteers.

The selective properties of 5-amino-4-chloro-2-phenyl-3-(2H)-pyridazinone (pyrazon), a new herbicide for the control of weeds in sugar beets, were investigated. Common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.), and green and yellow foxtail (Setaria viridis (L.) Beauv. and S. glauca (L.) Beauv.) represented about 77% of the weeds emerging and developing with beets. The preemergence rate of 4 to 5 lb/A pyrazon satisfactorily controlled the two broadleaf weed species but was marginal in controlling foxtail. At 6 and 7½ lb/A, beet stands were reduced; however, because of the standard practice of overseeding, normal stands were possible and yields of roots and extractable sugar were unaffected. Preemergence applications of aqueous suspensions of pyrazon were more satisfactory than postemergence. The addition of miscible non-phytotoxic oils or adjuvants to aqueous mixtures greatly improved the postemergence activity of pyrazon. In spite of the occasional temporary beet injury, beets in the two to four-leaf stage seemed relatively tolerant to postemergence treatments. Control was excellent when weeds were treated in the seedling stage (i.e. between cotyledon and four true leaves).

Corn hybrids and inbreds were ranked for their relative tolerance to soil-incorporated clomazone, as assessed by the level of discoloration injury in the greenhouse. Inbred W117 was the most tolerant corn line tested. Some corn lines were affected similarly by clomazone. Inbred A619 was in the most susceptible group. Clomazone injury to A619 (susceptible) and W117 (tolerant) corn was similar when the clomazone rate was 10-fold greater on W117 than on A619. The distribution of corn lines on a sensitivity scale was of limited range; the distribution of hybrids on this scale was a single symmetrical peak. Changing the growth temperature or soil composition would change the absolute level of corn injury caused by a rate of clomazone but did not change the relative ranking of the corn lines in the test. A subset of the greenhouse-tested corn lines also was evaluated in several field locations. The tolerance of corn in a given field was highly (P<0.005) correlated with tolerance in the greenhouse; however, the absolute levels of injury differed among locations. The tolerance of- hybrids of known pedigree was highly (P<0.0002) correlated with the tolerance of the parent inbreds, indicating this trait was inherited.

A mixture of dimethyl sulfoxide (DMSO), glycerol, phytobland oil, and water (50:25:15:10, v/v) proved to be outstandingly effective as a carrier for water-soluble formulations of 4-amino-3,5,6-trichloropicolinic acid (picloram), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), and mixtures thereof. The carrier was selected after numerous experiments in which these and other adjuvants, used individually, gave at least some degree of herbicidal enhancement on velvet mesquite seedlings [Prosopis juliflora var. velutina (Woot.) Sarg.]. Maximum synergism between the carrier complex and herbicide occurred with the triethylamine salt of 2,4,5-T; relatively little influence on the butoxyethanol ester was observed. Picloram and 3,6-dichloro-o-anisic acid (dicamba) were intermediate in activity between the two phenoxy formulations.

Shoot and root growth of green foxtail [Setaria viridis (L.) Beauv. # SETVI] and yellow foxtail [Setaria lutescens (L.) Beauv. # SETLU] were compared under three moisture regimes under simulated field conditions in 1982 and 1983. An increase in water supply from 0.3 to 2.5 cm/week resulted in proportionately greater increases in the number of tillers and leaf area of green foxtail compared to yellow foxtail. In 1982, green foxtail produced approximately three times as many seed as yellow foxtail under all three water regimes, whereas under warmer conditions in 1983, green foxtail produced nearly six times as many seed as yellow foxtail under the highest water regime and more than 11 times under the lowest regime. By using a specially constructed periscope to observe root growth through clear plastic tubes implanted in the soil it was determined that the amount of available moisture had much less effect on root growth than on shoot growth of the two species. In 1982, green foxtail tended to produce more roots than yellow foxtail early in the season but as the plants matured no significant differences occurred between species. In 1983, no significant differences in total root length occurred between species at any growth stage. The roots of both species penetrated to a depth of nearly 60 cm, with the highest concentration of roots occurring at depths of 20 to 30 cm.

Field surveys were conducted during 1978 and 1979 to determine the abundance and distribution of weeds in fields seeded to barley, oats, spring wheat, and mixtures of barley and oats in various proportions in the province of Prince Edward Island. Using a stratified random sampling procedure, weeds were counted in 536 fields during the 2-yr survey period. The weed flora had a large number of species that occurred at high densities, probably due to the limited herbicide use on Prince Edward Island. The average total number of species (64), number of species per field (20), and weed density (253 plants/m2) were similar among the four crop types and the five Extension Districts of the province. Only 49 of the 77 species encountered during the survey were found in 5% or more of the fields. Low cudweed, corn spurry, and common lambsquarters were the most abundant species, occurring in more than 80% of the fields at a mean density higher than 33.4 plants/m2. Red sorrel, smartweed, common hempnettle, broadleaf plantain, and quackgrass were also found in 80% or more of the fields, but at a mean density from 14.4 to 16.5 plants/m2. The perennials accounted for 51% of the commonly occurring species, annual and biennial broadleaf species accounted for 43%, and annual grasses were a minor group with only 6% of the species.

This study was conducted to determine if field evaluations could be used to select insects for biological control of musk thistle. Host specificity and larval development of a weevil, Hadroplonthus trimaculatus, and a fleabeetle, Psylliodes chalcomera, were studied in field trials near Rome, Italy, in which insects were allowed free choice of several hosts. Natural populations of these two insects, which do not occur in North America, were exposed to North American species of Cirsium, Carduus, and selected crops. Adult insects and larvae on host plants were identified and counted on test plants from North America and native attraction plants. In addition to infesting musk thistle, weevil adults and larvae were recorded on flodman thistle, wavyleaf thistle, and spinosissimum thistle. Consequently, this insect was not suitable for introduction into North America. The fleabeetle would be satisfactory for biological control since no adults or larvae were recorded on Cirsium spp. or economic plants. These studies show that field trials are a valid method for identifying specific and nonspecific candidate insects for biological control of weeds.

The growth of green foxtail (Setaria viridis L. Beauv. ♯3 SETVI) and yellow foxtail [S. lutescens (Weigel.) Hubb. ♯ SETLU] in full sunlight, under 55 and 73% shade and within a wheat (Triticum aestivum L. ‘Neepawa’) stand, was compared in field experiments conducted over 3 yr. Shade resulted in a proportionately greater reduction in tiller number of yellow foxtail than of green foxtail. Plants growing in full sunlight produced up to five times more tillers than those growing in the crop. Averaged over the 3 yr, the two shade treatments reduced dry-matter accumulation of both species by 40% or more. The dry weight of plants within the crop was only about one-eighth of that of plants grown in full sunlight. Under both shade treatments and in the crop, yellow foxtail was consistently taller than green foxtail. Nevertheless, no differences in dry weight occurred between species under either shade treatment or in the crop. The results indicate that neither of the two species is distinctly more shade tolerant than the other, nor better adapted to compete with wheat.

Carbon-14-labeled glyphosate [N-(phosphonomethyl)glycine] was foliarly applied to ligustrum (Ligustrum japonicum Thunb.) and blue pacific juniper (Juniperus conferta Parl. ‘Blue Pacific’) at the following growth stages: cold acclimation, winter dormancy, budbreak, shoot elongation, and termination of the first flush of growth (shoot termination). At shoot elongation juniper plants absorbed 2% of applied 14C by 14 days after treatment (DAT). Applications at other growth stages resulted in no significant absorption of 14C by junipers. Within 7 DAT the amounts of radioactivity absorbed by ligustrum were significant and depended upon growth stage in the following order: budbreak < shoot termination < shoot elongation. Absorption by overwintered leaves occurred at budbreak but not at elongation or termination. Transport of absorbed 14C in ligustrum was primarily acropetal and occurred only in budbreak and flowering treatments. Differences in tolerance to glyphosate between juniper and ligustrum appear to be related to differential absorption. Seasonal differences in ligustrum tolerance also appear to be associated with differences in absorption. Although growth stage affected transport in ligustrum, differential transport does not appear to play a major role in seasonal influences on long-term glyphosate phytotoxicity.

Picloram release by leafy spurge roots, as affected by picloram rate, plant growth stage, and time intervals after treatment, was quantified under field conditions. Picloram was pipe-wick applied to leafy spurge in the vegetative, flowering, and seed-filling growth stages. Percent leafy spurge control was evaluated and picloram residues were determined in soil samples from 0- to 13-, 13- to 26-, and 26- to 39-cm depths taken 1, 2, and 3 weeks after treatment. Leafy spurge was controlled (frequently >85%) by all picloram concentrations applied, although control tended to increase as solution concentration increased. Picloram release from roots was greater from plants treated in the flowering and seed-filling stages than from plants in the vegetative stage. Picloram release from roots generally was correlated with application rate, averaging 490, 820, and 1420 ppbw in soil for the 30, 60, and 120 g ae/L application rates, respectively. Picloram release from roots occurred rapidly with 86% of the picloram detected in the 0- to 13-cm soil depth present by 1 week after treatment. Picloram was detected at all soil depths sampled, but over 84% was in the upper 13 cm and 8% was in both the 13- to 26- and 26- to 39-cm depths. Leafy spurge shoots emerged through a 7.5- and 15-cm depth of picloram-treated soil at concentrations up to 1000 ppbw within 14 to 21 days after the untreated control. Picloram soil residue had little effect on leafy spurge root growth.

A sinking leaf-disk technique enabled detection of differences among potato (Solanum tuberosum L.) varieties in herbicide tolerance within 24 hr. Susceptibility of varieties to field application of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5-(4H)-one] was correlated (r = 0.76∗∗) to the number of sunken disks in a metribuzin solution in a growth chamber with continuous light at 30 klux. Varieties that were very tolerant, very susceptible, or intermediate in tolerance to field application of metribuzin were generally in these same categories when evaluated by the sinking leaf-disk technique. Speed of this response was dependent upon herbicide concentration and solution temperature, but the varietal relationships did not change. It was necessary to use leaves of nearly the same age as determined by relative size and position on the plant. Other factors influencing results included plant growth stage, soil moisture, and atmospheric temperature. Results from the sinking leaf-disk test of winter-grown greenhouse plants of the same clones were correlated (r = 0.86∗) to estimated metribuzin injury to field-grown plants. This method, with adequate modification of technique, may have potential use for studying other plant species and other relationships between plants and photosynthesis-inhibiting herbicides.

Greenhouse and laboratory studies were conducted to determine the effect of atrazine on efficacy, absorption, translocation, and metabolism of primisulfuron applied to velvetleaf and giant foxtail. Efficacy of primisulfuron was reduced by 18 and 22% when applied at 20 and 40 g ai ha−1, respectively, in combination with 1.7 kg ai ha−1 atrazine to velvetleaf. Efficacy of primisulfuron was reduced by 15 and 16% when applied at 30 or 60 g ai ha−1, respectively, in combination with 1.7 kg ai ha−1 atrazine to giant foxtail. Foliar absorption of 14C-primisulfuron by either weed species was not affected by addition of atrazine to the treatment solution. Atrazine had no effect on metabolism of 14C-primisulfuron by either weed species. In the absence of atrazine, translocation of absorbed 14C from primisulfuron out of treated leaves of velvetleaf and giant foxtail averaged 19 and 29%, respectively, across sampling times. These values were reduced to an average of 9 and 16% in velvetleaf and giant foxtail, respectively, when 14C-primisulfuron was applied in combination with atrazine. The majority of translocated 14C from primisulfuron was transported acropetally in velvetleaf and basipetally in giant foxtail. Atrazine significantly reduced 14C translocation from primisulfuron to these meristematic sinks in both weed species. Reduced translocation was positively correlated with reduced control of these weeds when primisulfuron was tank mixed with atrazine.

Dimethyl tetrachloroterephthalate (DCPA) more severely inhibited growth of roots than shoots of corn (Zea mays L., var. WF9 X B37) and sorghum (Sorghum bicolor (L.) Moench., var. RS 610). Although roots of corn and sorghum were about equally susceptible to DCPA, corn shoots were much more tolerant than sorghum shoots when separately exposed. 14C-DCPA was absorbed by both shoot and root zones of corn and sorghum; however, only limited movement to other plant parts occurred. In contrast to the grass species, cucumber (Cucumis sativus L., var. Wis. SMR-15) roots were tolerant to DCPA. Hypocotyl length was reduced only when the shoot zone was exposed. 14C-DCPA absorbed by the shoot zone moved mainly acropetally. Root-absorbed 14C-DCPA tended to be accumulated there with only limited movement upward. Uptake by the hypocotyl of cucumber and movement of 14C-DCPA to foliage after emergence occurred readily, and pretreatment with unlabeled DCPA before emergence enhanced uptake.