The selective action of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) for the control of green foxtail (Setaria viridis (L.) Beauv.) in wheat (Triticum aestivum L.) was studied. Seedlings of both species, especially in the early stage of growth, were particularly susceptible to herbicide applied in the region of the coleoptile node. Selective control with trifluralin was possible, however, because of the morphological differences between the seedlings of the two species. Thus, the sensitive coleoptilar node area of green foxtail was located at a depth of less than 1 cm from the soil surface regardless of planting depth. The coleoptile node of wheat remained closely associated with the caryopsis. When a protective band of untreated soil was used to separate the caryopses from a 5-cm band of surface soil containing 1.12 ppmw of trifluralin, the shoot growth of wheat was normal. Much lower rates of trifluralin effectively controlled green foxtail, as surface or subsurface placement of a 1.3-cm layer of soil containing 1.12 ppmw of chemical above the foxtail caryopses completely inhibited shoot development. In addition to the differences in morphological development between the two species, the fact that green foxtail was considerably more susceptible to trifluralin than wheat was considered as an important factor contributing to the selective control.

Simulated rainfall less than 8 hr after postemergence application of bentazon (3-isopropyl-1H-2,1,3-benzothiadiazin-(4)3H-one 2, 2-dioxide) reduced its activity on velvetleaf (Abutilon theophrasti Medic.) and common cocklebur (Xanthium pensylvanicum Wallr.) in greenhouse studies. In field studies, simulated rainfall less than 24 hr after application reduced bentazon's activity on velvetleaf. on common cocklebur, bentazon's activity was reduced even if simulated rainfall was delayed for more than 24 hr after application. In greenhouse studies, spray adjuvants (vegetable or petroleum oil) were helpful in overcoming the detrimental effects of simulated rainfall. Greenhouse and field studies indicated that soybeans [Glycine max (L.) Merr.] could tolerate bentazon-oil adjuvant combinations.

Resistance to imidazolinone (IMI) herbicides has been incorporated recently into domesticated sunflower through conventional breeding methods. However, there are concerns regarding gene flow of the IMI-resistance trait to wild species and possible accompanying ecological consequences. Hybrids of domesticated sunflower with both common sunflower and prairie sunflower were created, with and without the imazamox-resistance trait. The relative fitness of imazamox-resistant (IMI-R) hybrids was compared with their imazamox-susceptible (IMI-S) counterparts. Greenhouse experiments were conducted to study the growth of IMI-R and IMI-S common and prairie sunflower hybrids under noncompetitive conditions. The photosynthesis rate of IMI-S prairie sunflower was slightly higher than that of IMI-R plants. However, relative growth rate, net assimilation rate, leaf area, and total dry weight were similar in IMI-R and IMI-S common and prairie sunflower, whereas plant height of IMI-S hybrid was greater than that of IMI-R common sunflower hybrids. A replacement series study was conducted under field conditions in 2001 and 2002 to evaluate the relative competitiveness of IMI-R and IMI-S common and prairie sunflower. IMI-R and IMI-S hybrids of both sunflower species were equally competitive. The results suggest that, in the absence of IMI herbicides, genes controlling IMI-R do not reduce or increase the competitive ability of either common or prairie sunflower. Therefore, if the IMI-resistant trait is incorporated in these species, the frequency of IMI-resistance genes is unlikely to decrease, even in the absence of IMI selection pressure.

Little published information is available related to seed germination and seedling establishment of Asia Minor bluegrass, a problematic grass weed in some regions of China. The objective of this study was to examine the effects of different environmental factors on Asia Minor bluegrass seed germination. The optimum temperature for germination was around 10 to 20 C, and more than 90% of seeds germinated under 20/10 and 25/15 C temperature regimes. Also, light and pH did not appear to have any effect on seed germination. Asia Minor bluegrass was sensitive to osmotic stress, but tolerant of NaCl. No seedlings emerged when seeds were buried 4 cm deep. The result suggested that Asia Minor bluegrass has the potential to spread into a large area in China. To prevent its spreading, measures such as soil cultivation can be used to limit seed germination from increased burial depth and/or nonselective herbicides can be applied to kill early-germinating weed seedlings in late summer.

Laboratory experiments were conducted to determine the effects of application factors and standing Triticum aestivum stubble on herbicide spray deposition and efficacy in a simulated no-till environment. Spray deposition on weeds was reduced in the presence of stubble, and deposition losses on Amaranthus hybridus were greater than those on Setaria faberi. Spray penetration through stubble was significantly enhanced with electrostatic charging of a fine hydraulic spray. The combination of 45 kV electrostatic charge and 50 cm nozzle spacing produced maximum spray deposition on weeds and resulted in a 96% and 345% increase in deposition on A. hybridus and S. faberi, respectively, compared to the uncharged controls. Deposit reduction from standing stubble was greater at travel speeds of 16 km h−1 (36 to 52%) than 8 km h−1 (9 to 38%). On a dry weight and plant density basis, weeds retained more spray than was retained by stubble, yet stubble, at average densities, was capable of capturing 9 to 12% of total applied spray dose per unit area. Bounce studies of individual droplets of water or imazethapyr plus adjuvant mixture demonstrated that T. aestivum straw had a general affinity for all spray droplets, exhibiting no rebound even for 800-µm water droplets. Setaria faberi foliage exhibited poor retention of droplets: both 350- and 800-µm water droplets as well as 800-µm droplets of imazethapyr plus adjuvant mixture rebounded. Only 350-µm herbicide mixture droplets were retained by S. faberi. Amaranthus hybridus retained all droplets. In broadcast spraying, British Crop Protection Council “Medium” quality sprays were poorly retained by S. faberi compared to “Fine” sprays, whereas A. hybridus retained both sprays equally well. However, imazethapyr spray deposits resulting from coarser sprays were more efficacious on S. faberi than fine spray deposits, a difference that was not observed for A. hybridus.

Ripgut brome is a difficult weed to manage in cereal crops of southern Australia because only a few herbicides can provide effective control in cereals. Knowledge of seed-dormancy mechanisms, germination ecology, and emergence behavior in the field could facilitate development of effective weed control programs for this weed species. Ripgut brome populations from cropping fields were found to possess much longer seed dormancy than that reported previously in the literature. Furthermore, some ripgut brome populations from cropping fields showed longer seed dormancy than those collected from adjacent noncropped fence lines. For example, all seeds of one of the populations from the fence line (SA-1F) germinated at 3 mo after maturity, whereas seeds from the cropping field at the same site (SA-1C) showed little germination (< 3%) even at 8 mo after maturity. These highly dormant ripgut brome populations from cropping fields were responsive to cold stratification, with germination increasing significantly after 2 to 14 d of exposure. Germination of dormant ripgut brome populations increased with addition of gibberellic acid (0.001 M GA3), particularly when lemma and palea had been removed. Ripgut brome populations from cropping fields (VIC-2C and SA-1C) showed strong inhibition of seed germination when exposed to light. These differences in seed dormancy among ripgut brome populations were also expressed in seedling emergence pattern in the field. The nondormant populations collected from fence lines showed high seedling establishment (> 80%) during autumn, which coincided with the planting time of winter crops in southern Australia. In contrast, five populations from cropping fields showed much lower seedling establishment (3 to 17%) before the time of crop planting. Delayed seedling establishment in populations from cropping fields could lead to less effective preseeding weed control and higher weed infestations in field crops. Results of this study also showed that the seedbank of these highly dormant ripgut brome populations can readily persist from one year to the next. Effective management of ripgut brome populations with long seed dormancy and increased seedbank persistence would require a major change in cropping systems used by the growers in southern Australia.

Absorption and translocation in both leaves and roots is less under low temperatures. Seasonal response of wheat to 2,4-D is conditioned by the stage of growth as well as environment. The response of wheat and downy bromegrass to triazine herbicides is seasonal, whereas the response to carbamate herbicides appears to be influenced by local environmental conditions at time of spraying. Physiological condition of fiddleneck is more important than age, i.e., plants in the rosette stage were always far more sensitive than bolting plants of the same age. Sensitivity to 2,4-D was greater at 26 C than at 10 C or 5 C at all stages of growth. Applications of certain metabolites, especially thiamin, increased the sensitivity of fiddleneck to 2,4-D at low temperatures.

Buds of locally collected yellow nutsedge (Cyperus esculentus L.) tubers are formed only at the six most apical nodes with a 1/3 phyllotaxy. The oldest bud is largest. Bud size grades to the small apical bud. Veins of the rhizome are continuous through the tuber to each bud, root, and leaf. Buds break dormancy in acropetal order, starting with the oldest bud. If the tubers and buds remain undisturbed, usually only two buds break dormancy and grow into shoots.

Laboratory studies were conducted to determine the effect of various factors on germination of dogfennel and yankeeweed. Dogfennel seed were found to be strongly photoblastic with no germination in the dark. Yankeeweed seed were moderately photoblastic, with 12% germination occurring in the absence of light Germination for both species increased in response to red light (650 nm), indicating phytochrome regulation. At the soil surface, dogfennel and yankeeweed emergence was 40 and 48%, respectively, but declined rapidly with increasing soil depths where dogfennel germination was lower than that of yankeeweed. Yankeeweed germination was 60 to 75% from 10 to 30 C while dogfennel germination was 45 to 70% between 15 to 30 C. Both species germinated over a broad range of pH (6 to 10) with the highest germination occurring at pH 8. Yankeeweed and dogfennel were moderately tolerant to water stress, but yankeeweed tolerated higher water stress than dogfennel. Both species germinated over a wide range of conditions, possibly enhancing adaptation to many diverse environments.

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 1 × 10−5 and 1 × 10−4 M increased the leakage of previously absorbed, 32P-labeled orthophosphate from the roots of onion (Allium cepa L.), a susceptible species, by 14 and 41 times the control values, respectively. A significant amount of 32P leaked from the roots of the moderately susceptible species, cotton (Gossypium hirsutum L. ‘DPL 61′) and cucumber (Cucumis sativus L. ‘Ashley′), whereas no significant loss of 32P occurred from two tolerant species, soybean [Glycine max (L.) Merr. ‘Bragg′] and corn (Zea mays L. ‘Pioneer 3369A′). At either 1 × 10−7 or 1 × 10−6 M, 1,8-naphthalic anhydride (NA) prevented 32P leakage from onion roots in the presence of 1 × 10−5 M metolachlor. High concentrations of NA [0.1% (w/v) suspensions], however, promoted 32P leakage and did not protect onion roots from the leakage induced by high concentrations (1 × 10−4 M) of metolachlor. Neither metolachlor nor alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], at 1 × 10−4 M, inhibited the uptake of acetate-2-14C or malonic acid-2-14C into excised cotton root tips or the incorporation of the precursors into lipids. Similarly, neither herbicide inhibited phospholipid synthesis by cotton root tips. Incorporation of 14C-choline chloride into phosphatidylcholine was not significantly inhibited by metolachlor.

Acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} and bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] were applied singly, in combination at various rates, with and without a crop oil concentrate to common lambsquarters (Chenopodium album L. # CHEAL), redroot pigweed (Amaranthus retroflexus L. # AMARE), jimsonweed (Datura stramonium L. # DATST), and velvetleaf (Abutilon theophrasti Medic. # ABUTH) grown in containers in the greenhouse and outdoors. Without crop oil concentrate, synergistic responses to the combinations were measured in common lambsquarters and velvetleaf. Antagonistic responses were measured in jimsonweed. Redroot pigweed response was antagonistic in the greenhouse and synergistic outdoors. The addition of a crop oil concentrate tended to mask the interactions. Crop oil concentrate also increased the droplet size for common lambsquarters, velvetleaf, jimsonweed, and redroot pigweed 53, 41, 28, and 27%, respectively. Neither herbicide at any rate or combination influenced droplet size. Radiolabeled studies showed reduced uptake of 14C-acifluorfen when bentazon was present in common lambsquarters and redroot pigweed by 15 and 10%, respectively. Radiolabeled bentazon uptake was reduced 3% in jimsonweed and increased 20% in redroot pigweed when acifluorfen was present.

Laboratory experiments were conducted to determine the effect of moisture stress on the absorption and translocation of 14C-labeled picloram (4-amino-3,5,6-trichloropicolinic acid), dicamba (3,6-dichloro-o-anisic acid), and glyphosate [N-(phosphonomethyl)glycine] within the Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] plants. The absorption and translocation of picloram and dicamba were unaffected by moisture stress. Absorption and translocation of glyphosate to the roots and apical meristem of Canada thistle was reduced by increasing moisture stress. Weekly differential irrigation of Canada thistle field plots during the summers of 1980 and 1981 established three soil moisture regimes averaging −6.6, −11.3, and −15.0 bars at the time of herbicide treatment. When Canada thistle control was evaluated 1 year after application of glyphosate, dicamba, and picloram at 2.5, 1.1, and 0.6 kg/ha, respectively, no differences in Canada thistle shoot control were found between moisture stress treatments.

Unicellular green algae were used as test organisms in experiments designed to provide an insight into the mode of action of 3-(m-trifluoromethylphenyl)-1,1-dimethylurea (fluometuron). Fluometuron suppressed the autotrophic growth of Chorella pyrenoidosa Chick (hereafter referred to as C. pyrenoidosa) and Euglena gracilis Klebs-strain ‘Z’ (hereafter referred to as Euglena) and the extent of inhibition was a function of herbicidal concentration. Euglena was less sensitive than C. pyrenoidosa. Treated cells contained less protein and chlorophyll than untreated cells, but the inhibitory effect of the herbicide on the algal growth was overcome when the organisms were grown heterotrophically. Fluometuron did not adversely influence respiration or the light-independent reactions that lead to the formation of chlorophyll or chloroplast precursors. It did interfere with the light-dependent or the greening process of chlorophyll synthesis and with photosynthetic oxygen evolution. Fluometuron appears to be selectively toxic to one or more light-mediated biochemical reactions required for the formation and function of photosynthetic pigments and organelles.

Atrazine is widely used to control broadleaf weeds and grasses in corn, sorghum, and sugarcane. Field persistence data published before 1995 showed that the average half-life of atrazine in soil was 66 d, and farmers expect to achieve weed control with a single application for the full season. However, reports of enhanced atrazine degradation in soil from fields that have a history of atrazine applications are increasing. A rapid laboratory assay was developed to screen soils for enhanced atrazine degradation. Soil (50 g) was placed in a 250 ml glass jar and treated with 7.5 ml of water containing atrazine (5 µg ai ml−1) and capped with a Teflon-lined lid. The assay was conducted at room temperature (25 C). Soil subsamples (1.5 to 3 g) were removed at 0, 1, 2, 4, 8, and 16 d after treatment and extracted with an equal weight of water (wt/vol). The atrazine in the water extract was assayed with high-pressure liquid chromatography (HPLC). The half-life of atrazine in soils with a history of use was ≤ 1.5 d, whereas the half-life in soils with no history of atrazine use was > 8 d. The advantages of this assay are (1) the ease of set up; (2) the rapidity of extraction, and (3) the simplicity of the quantification of the atrazine.

Growing crops that exhibit a high level of competition with weeds increases opportunities to practice integrated weed management and reduce herbicide inputs. The recent development and market dominance of hybrid canola cultivars provides an opportunity to reassess the relative competitive ability of canola cultivars with small-grain cereals. Direct-seeded (no-till) experiments were conducted at five western Canada locations from 2006 to 2008 to compare the competitive ability of canola cultivars vs. small-grain cereals. The relative competitive ability of the species and cultivars was determined by assessing monocot and dicot weed biomass at different times throughout the growing season as well as oat (simulated weed) seed production. Under most conditions, but especially under warm and relatively dry environments, barley cultivars had the greatest relative competitive ability. Rye and triticale were also highly competitive species under most environmental conditions. Canada Prairie Spring Red wheat and Canada Western Red Spring wheat cultivars usually were the least competitive cereal crops, but there were exceptions in some environments. Canola hybrids were more competitive than open-pollinated canola cultivars. More importantly, under cool, low growing degree day conditions, canola hybrids were as competitive as barley, especially with dicot weeds. Under most conditions, hybrid canola growers on the Canadian Prairies are well advised to avoid the additional selection pressure inherent with a second in-crop herbicide application. Combining competitive cultivars of any species with optimal agronomic practices that facilitate crop health will enhance cropping system sustainability and allow growers to extend the life of their valuable herbicide tools.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], and benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) were applied at two rates for five consecutive years (1966 through 1970) as soil-incorporated treatments to cotton (Gossypium hirsutum L. ‘Acala SJ-1’) before the preplanting irrigation. Repeated applications did not significantly affect stand or yield of cotton. Soil samples taken to depth of 120 cm showed that herbicide residues were confined to the tilled zone of soil (upper 30 cm), and about 80% of the residue was in the upper 15 cm of soil. The amount of herbicide residue found annually in the upper 15 cm of soil varied with herbicide and with season. Residues 15 months after final application had been reduced markedly, but were still sufficient to injure sensitive crops. Residues at 30 months had been reduced to innocuous amounts.

A charcoal barrier method was devised to prevent the movement of S-ethyl dipropylthiocarbamate (EPTC) in the soil in order to expose certain parts of the plant without exposing the rest of the plant. Exposing the roots of barley (Hordeum vulgare L., var. Blue Mariot), oats (Avena sativa L., var. California Red), barnyardgrass (Echinochloa crusgalli L. Beauv.), annual ryegrass (Lolium multiflorum Lam.), wheat (Triticum vulgare L.), rice (Oryza sativa L., var. Belle Patna), cotton (Gossypium peruvianum Cav.), and yellow nutgrass (Cyperus esculentus L.) caused more injury than shoot exposure, while shoot exposure caused slightly more injury than root exposure to Johnsongrass (Sorghum halepense Pers.), sorghum (Sorghum vulgare Pers., hybrid Amak R-10), and peas (Pisum sativum L.). Seed exposure caused severe injury in some plant species but not others. The results obtained by this method disagree with published reports which claimed that only shoot exposure to EPTC led to injury. In numerous experiments with barley seeds accurately planted in a vertical position in a ½-inch layer of charcoal between two 1-inch layers of soil, root exposure always injured the plants more than shoot exposure. Exposing all parts (seeds, roots, and shoots) to EPTC caused the most injury to barley followed by exposing only the seeds, a combination of roots and shoots, roots, and shoots in decreasing order of injury symptoms. Similar results were obtained with oats when the depth of the treated soil above or below the seed was 1 inch, but increasing this depth to 1.5 inches or more resulted in more injury by shoot exposure than root exposure. The importance of root exposure was confirmed using another method of testing in which only the roots were exposed to the herbicide in nutrient solutions. Concentrations as low as 1 ppm of EPTC applied to the roots in nutrient solutions inhibited shoot growth of oats, barley, sorghum, and corn, while the growth of the roots was enhanced in some cases.

A survey conducted in a seven-county region of eastern Oregon during the summers of 1998, 1999, and 2000 characterized the occurrence of jointed goatgrass × wheat hybrids and the features of weed infestations promoting hybridization. During the survey, 93 infested sites were visited with jointed goatgrass collected from 57 sites and hybrids collected from 45 sites. Thirteen collection sites were located in uncultivated areas. Observations of jointed goatgrass infestations in and around cropped fields suggested that jointed goatgrass successfully escapes control where weed populations persist in fencerows, access roads, scablands, draws, and roadsides. Most jointed goatgrass and hybrid populations were located in winter wheat fields but were also found in five spring grain fields. Of the 754 hybrid plants collected, 44% contained backcross seed. For all 3 yr, a 1% backcross hybrid seed–production rate was found. A parentage analysis of a subsample of the total hybrid collection showed that the majority were F1 hybrids and that jointed goatgrass was most often the female parent. This observational study has established that F1 hybrids are common in jointed goatgrass–infested wheat fields. Their capability for backcross seed production suggests the potential development of advanced backcross forms that resemble jointed goatgrass. The survey results offer valuable input for the risk assessment of gene flow potential between jointed goatgrass and herbicide-resistant wheat.

During 1967, field studies on the Holston River and in the laboratory produced evidence that excessive aquatic plant growths are not soley related to the presence of large amounts of nutrients in water. Factors contributing to growth were the amount of nutrients in sediments, water depth, and turbidity. Water depth and turbidity influence the amount of light which penetrates the water and is available for the growth of rooted plants.

Soybean plants exposed POST to 2,4-D can have reduced seed yield depending on the dose and time of exposure, but it is unclear how 2,4-D affects specific yield components. Objectives were to quantify soybean injury, characterize changes in seed yield and yield components of soybean plants exposed to 2,4-D, and determine if seed-yield loss can be estimated from visual assessment of crop injury. Ten rates (0, 0.1, 1.1, 11.2, 35, 70, 140, 280, 560, and 2,240 g ae ha−1) of 2,4-D were applied to Becks brand 342 NRR soybean at three soybean growth stages (V2, V5, or R2). The soybeans were planted near Lafayette, IN and Urbana, IL in 2009 and 2010 and near Fowler, IN in 2009. Twenty percent visual soybean injury was caused by 29 to 109 g ha−1 2,4-D at 14 d after treatment (DAT) and 109 to 245 g ha−1 at 28 DAT. Nonlinear regression models were fit to describe the effect of 2,4-D on seed yield and yield components of soybean. Seed yield was reduced by 5% from 87 to 116 g ha−1 and a 10% reduction was caused by 149 to 202 g ha−1 2,4-D at all application timings. The number of seeds m−2, pods m−2, reproductive nodes m−2, and nodes m−2 were the most sensitive yield components. Path analysis indicated that seeds m−2, pods m−2, main stem reproductive nodes m−2, and main stem nodes m−2 were the most influential yield components in seed-yield formation. Seed-yield loss was significant (P < 0.0001) and highly correlated (R2 = 0.95 to 0.99) to visual soybean injury ratings. A 10% seed-yield loss was caused by 35% soybean injury observed at 14 DAT, whereas a 10% seed-yield loss was a result of 40, 19, and 15% soybean injury observed at 28 DAT when soybean was exposed to 2,4-D at the V2, V5, and R2 growth stages, respectively.