Two species of invasive goldenrods, Solidago canadensis and Solidago gigantea, are spread over all territories ofLithuania. Solidago × niederederi, a putative hybridbetween S. canadensis and native Solidago virgaurea, was found in 27 populations mixed with the parentalspecies. This research represents the characterization of S. × niederederi in comparison to the other mentioned Solidago species, with the use of one-way analysis ofvariance (ANOVA), principal-components analysis (PCA), and discriminantanalysis of a large data set. Twenty quantitative, four qualitative, andfive ratio morphological and anatomical characteristics, pollen viability,and somatic chromosome numbers of the four Solidago specieswere studied with the aim to ascertain inter- and intraspecific variationand reliable features identifying S. × niederederi, and totest the hypothesized hybrid origin. The PCA of morphological and anatomicalcharacteristics showed the clear intermediate position of S. × niederederi compared to S. canadensis and S. virgaurea. The results showed that the mostinformative characteristics for the distinction of hybrids from parentalspecies are floral traits such as the lengths of the disc, ray florets, andinvolucre. The intermediate stomatal characteristics and sharply decreasedpollen viability discovered herein could potentially be used as anadditional discriminating character in Solidago hybrididentification and support the hybrid origin of S. × niederederi.

AlertInf is a recently developed model to predict the daily emergence ofthree important weed species in maize cropped in northern Italy (commonlambsquarters, johnsongrass, and velvetleaf). Its use can improve theeffectiveness and sustainability of weed control, and there has been growinginterest from farmers and advisors. However, there are two important limitsto its use: the low number of weed species included and its applicabilityonly to maize. Consequently, the aim of this study was to expand theAlertInf weed list and extend its use to soybean. The first objective was toadd another two important weed species for spring-summer crops in Italy,barnyardgrass and large crabgrass. Given that maize and soybean havedifferent canopy architectures that can influence the interrow microclimate,the second objective was to compare weed emergence in maize and soybean sownon the same date. The third objective was to evaluate if AlertInf wastransferable to soybean without recalibration, thus saving time and money.Results showed that predictions made by AlertInf for all five speciessimulated in soybean were satisfactory, as shown by the high efficiencyindex (EF) values, and acceptable from a practical point of view. The factthat the algorithm used for estimating weed emergence in maize was alsoefficient for soybean, at least for crops grown in northeastern Italy withstandard cultural practices, encourages further development of AlertInf andthe spread of its use.

Pseudomonas syringae pv. phaseolicola formulated with an organosilicone surfactant was tested as a potential bioherbicide for kudzu. Greenhouse studies were performed to determine the effect of kudzu plant age and leaf age on disease severity and growth of the bacterium in planta. Eight-week-old plants were more diseased 4 wk after spraying and had a higher potential for regrowth 7 wk after spraying than 12-wk-old plants. Young leaves developed water-soaked lesions earlier than older leaves and supported higher populations of bacteria. Data from field experiments at two separate locations indicated that single applications in late spring were as effective as multiple applications in early spring and were enhanced by repeat application. Three months after the beginning of the experiment, extensive regrowth occurred for all bioherbicide treatments and no differences were noted between treatments and the nontreated control.

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.

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.

A goosegrass biotype with suspected resistance to acetyl-CoA carboxylase(ACCase) inhibitors was identified in Georgia. The objectives of thisresearch were to evaluate the resistance level of this biotype to ACCaseinhibitors, efficacy of various herbicide mechanisms of action for control,and the physiological and molecular basis of resistance. In greenhouseexperiments, the rate of diclofop-methyl that reduced dry shoot biomass 50% (SR50) from the nontreated for the resistant (R) andsusceptible (S) biotypes measured 4,100 and 221 g ai ha−1,respectively. The SR50 for sethoxydim measured 615 and 143 g ai ha−1 for the R and S biotype, respectively. The R biotype wascross resistant to clethodim, fenoxaprop, and fluazifop. The R and Sbiotypes were equally susceptible to foramsulfuron, glyphosate, monosodiummethylarsenate (MSMA), and topramezone. In laboratory experiments, the twobiotypes had similar foliar absorption of 14C-diclofop-methyl.Both biotypes metabolized 14C-diclofop-methyl to diclofop acidand a polar conjugate, but the R biotype averaged ∼2 times greatermetabolism than the S biotype. Gene sequencing revealed an Asp-2078-Glysubstitution in the ACCase of the R biotype that has previously conferredresistance to ACCase inhibitors. A second mutation was identified in the Rbiotype that yielded a Thr-1805-Ser substitution that has been previouslyreported, but is not associated with ACCase resistance in other species.Thus, the Asp-2078-Gly substitution is the basis for resistance to ACCaseinhibitors for the R biotype. This is the first report of ACCase-inhibitorresistance in goosegrass from the United States and from a turfgrasssystem.

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.

Studies of the development and distribution of root systems of intraspecific and interspecific competition were conducted between soybean [Glycine max. (L.) Merr. ‘Lee 68′] and tall morningglory [Ipomoea purpurea (L.) Roth]. Tall morningglory at three plant densities and soybean were grown for 2 yr on a Taloka silt loam. The greatest density of soybean and tall morningglory roots grown under intraspecific competition was in the surface 12 cm and in the center of the row. Greater values of root length and density were during the dryer season. The largest fraction of total root length at a given date also was in the surface 12 cm and decreased with depth. The fraction at a given depth was a dynamic property of the root system during the growing season. When compared with the soybean root system, tall morningglory roots were found at deeper depths and had greater root densities. Little expansion of the soybean root system was found after initiation of the soybean reproductive phase. During this phase, the tall morningglory root system was increasing at a faster rate of growth than the soybean root system. The greatest density of roots grown under interspecific competition also was in the surface 12 cm and at the center of the row. These values were less than those found under intraspecific competition. Root distribution and development are dynamic functions of growth stage, planting density, and plant species.

Economic assessment of weed management strategies in rice is dependent upon a quantitative estimate of the yield impact of a given weed population. To assist rice producers in making such assessments, a mathematical model was developed to predict rice yield reduction as a function of weed density and duration of interference. The nonlinear empirical model was a unique 3-dimensional adaptation of the Richards equation with 4 parameters. Using published data, individual parameter values were fitted for each of 6 weed species interfering with either conventional or semi-dwarf statured rice cultivars. The functional form of the equation produced surfaces that were qualitatively consistent with available data and experience regarding rice-weed biology. Hence, predictions from the model should be useful and reliable in assessing the economic impact of weeds and in determining the feasibility of alternative weed control treatments for various field scenarios.

A rainfall simulator was used to evaluate the effects of washoff on 10 foliar-applied herbicides on johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in greenhouse experiments during 1983 and 1984 at Stoneville, MS. Time intervals between herbicide application and rainfall ranged from 20 to 240 min. Johnsongrass topgrowth control was equivalent to rain-free treatments using DPX-Y6202 {ethyl [2-[4-(6-chloro-2-quinozalinyl)oxy] phenoxy] propionate} at 0.03 and 0.06 kg/ha at time periods of 90 and 40 min between herbicide application and rainfall, respectively, at 28 days after treatment (DAT). A period of 120 min was required for johnsongrass control equivalent to rain-free treatments using sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.06 kg/ha, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} at 0.03 and 0.06 kg/ha, and cloproxydim {(E,E-2-[1-[[(3-chloro-2-propenyl)oxy] imino] butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 28 DAT. Neither glyphosate [N-(phosphonomethyl)glycine] and SC-0224 (trimethylsulfoniumcarboxy methylaminomethylphosphonate) at 0.45 and 0.99 kg/ha nor other selective herbicides at 0.03 and 0.06 kg/ha gave equivalent johnsongrass topgrowth control to rain-free treatments when rainfall occurred within 240 and 120 min, respectively.

Metabolism of C14-labeled and unlabeled atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) was studied in oats, soybeans, and beans (susceptible); cotton and peanuts (intermediate in susceptibility); and Johnsongrass, grain sorghum, and corn (resistant). Atrazine residues were found in all plants 11 days after a preemergence application of 1 lb atrazine/A. Methanol was found to be a better extraction solvent for atrazine and hydroxyatrazine than chloroform. Undegraded atrazine found in plants was roughly correlated with susceptibility, but atrazine absorption was not directly correlated with plant susceptibiliy. Radioactivity remaining in plant residue after methanol extraction likewise was not completely correlated with susceptibility. All plants converted some atrazine to hydroxyatrazine and the amount of hydroxyatrazine formed was somewhat correlated with resistance. The three resistant species converted at least twice as much atrazine to hydroxyatrazine as did the susceptible soybean and oats. Beans converted considerably larger amounts of atrazine than did other susceptible species.

Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations of such species have become common in no-till production fields in the Midwest. This research was conducted to determine the influence of herbicide- and cover-crop-based winter annual weed management systems and crop rotation on winter annual weed growth and seed production, SCN population density, and crop yield. Two crop rotations (continuous soybean and soybean-corn) and six winter annual weed management systems (a nontreated control, fall and spring herbicide applications, spring-applied herbicide, fall-applied herbicide, fall-seeded annual ryegrass, and fall-seeded winter wheat) were evaluated in no-tillage systems from fall 2003 to 2006 at West Lafayette, IN and Vincennes, IN. Fall or spring herbicide treatments generally resulted in lower winter annual weed densities than cover crops. Densities of henbit and purple deadnettle increased over years in the cover crop systems but remained constant in the herbicide systems. Averaged over sites and years, winter annual weed densities were nearly 45% lower in the spring than the fall due to winter mortality. Corn yield was reduced by the cover crops at West Lafayette but not Vincennes. Winter annual weed management system had no influence on soybean yield. SCN population density was reduced by including corn in the crop sequence but was not influenced by winter annual weed management. The density of weedy host species of SCN in the experimental area was relatively low (less than 75 plants m−2) compared to densities that can be observed in production fields. The results of these experiments suggest that inclusion of corn into a cropping sequence is a much more valuable SCN management tool than winter annual weed management. In addition, control of winter annual weeds, specifically for SCN management, may not be warranted in fields with low weed density.

Much research has been conducted on mesotrione activity on crops and weeds, but information is lacking in regards to the relative contribution of soil and foliar absorption of mesotrione. Three experiments conducted at Virginia Tech's Glade Road Research Facility in Blacksburg, VA, evaluated the effects of 50 and 90% relative humidity (RH) on the activity of mesotrione applied to foliage, soil, and soil plus foliage. Tall fescue injury ranged from 0 to 21% and was significant in 6 of 20 comparisons. Three of these injury events were caused by soil plus foliar applications, which were always more injurious than foliar only applications, which were more injurious than soil-only applications. Both application placement and RH significantly influenced smooth crabgrass responses to mesotrione. Smooth crabgrass phytotoxicity was lowest when mesotrione was applied only to foliage and highest when mesotrione was applied to soil and foliage. Increasing RH from 50 to 90% caused a 4- to 18-fold increase in plant phytotoxicity when mesotrione was applied only to foliage. By dissecting the plant canopy, it was noted at 14 d after treatment, when averaged over RH, that white leaves comprise 16% of leaves when only foliage was treated and 55 and 62% when applied to soil plus foliage and soil only, respectively. Furthermore, white tissue was found predominately in the two youngest leaves when mesotrione was applied to soil or both soil and foliage, but in older leaves when applied only to foliage. Data indicate mesotrione entering plants through soil travels quickly to growing points and has an equal or greater effect on plant phytotoxicity than foliar-absorbed mesotrione. In addition, foliar-absorbed mesotrione appears to increase in plants significantly with increasing RH, but does not move rapidly to growing points.

Glufosinate-resistant transgenic creeping and velvet bentgrass plants expressing a bar gene under the control of the maize ubiquitin promoter were inoculated separately with the fungal pathogens, Rhizoctonia solani and Sclerotinia homoeocarpa, before or after treatment with 560 mg L−1 of glufosinate at a rate of 0.56 kg ha−1. Application of the herbicide 3 h before or 1 d after fungal inoculation significantly reduced infection of these transgenic grasses by R. solani and S. homoeocarpa. Assessment of the in vitro antifungal activity of the herbicide showed that 336 and 448 mg L−1 glufosinate completely inhibited the mycelial growth of S. homoeocarpa and R. solani, respectively. The results suggest that the nonselective herbicide glufosinate may also be used to suppress the activity of some fungal pathogens in turf composed of these transgenic glufosinate-resistant creeping and velvet bentgrasses.

Microarray analysis was used to follow changes in gene expression coinciding with seasonal changes in the dormancy status of crown buds of field-grown leafy spurge. Known cold-regulated genes were induced, and numerous gibberellic acid–responsive genes were down-regulated during the transition from paradormancy to endodormancy. Genes involved in photomorphogenesis were induced during endodormancy. Also, ethylene signaling responses were observed during ecodormancy rather than endodormancy. These results provide additional insights into the signals regulating expression of several genes previously associated with transition from paradormancy to growth in root buds.

Factors influencing injury to oats from 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) residues in the soil were studied over a period of five years. Initial rate of triazine application was highly important with significant injury in about one-half of the trials on plots treated with 2 lb/A the year prior to planting oats, and on all plots treated at 4 lb/A. No material difference was found on plots treated with equivalent rates of atrazine and simazine. Granular preparations of atrazine left a residue that was more injurious than wettable powders. Disking the seedbed for oats, rather than plowing, resulted in greater injury. Cultivation of the corn between the rows after treatment did not influence the injury the following year. Soil type did not have a marked effect on injury in this study. Above-normal average mean air temperatures appeared to reduce injury the following year in some instances. Experiments initiated in years of abundant rainfall during April to October tended to have less injury the next year than experiments initiated in years when rainfall was limited.

Effects of a natural mixed stand of giant green foxtail [Setaria viridis var. major (Gaudin) Pospichel # SETVM] and fall panicum [Panicum dichotomiflorum Michx. # PANDI] on soybean [Glycine max (L.) Merr. ‘Union’ and ‘Essex′] biomass and seed yield were investigated during 1981, 1982, and 1983. Plots maintained weed free for 2 weeks after soybean emergence produced yields equal to those maintained weed free for the season despite any grass reinfestation. Grasses growing naturally with soybeans for 8 weeks after soybean emergence did not reduce crop yields. Weeds not removed after 8 weeks reduced soybean yields by decreasing the number of pods per plant. Under drought conditions, yield reduction due to grass competition did not occur until 12 to 16 weeks after soybean emergence. Hand-established densities of 1 grass plant/7.5 cm of crop row reduced soybean yield by 0 to 11%. Natural grass infestations reduced soybean yield by 21 to 41%.

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.

Experiments were conducted to determine 14C absorption, translocation, and metabolism by pitted morningglory (Ipomoea lacunosa L. # IPOLA) and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. # IPOHE] foliarly treated with 14C-acifluorfen [5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoic acid] or 14C-lactofen [(±)-2-ethoxy-1-methyl-2-oxoethyl-5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-dinitrobenzoate]. Seventy-one to 84% of applied 14 C-acifluorfen was recovered in leaf water wash of ivyleaf morningglory compared to 32 to 46% from pitted morningglory. Sixty-four percent of applied 14C-lactofen was recovered in leaf water wash 96 h after treatment in both morningglory species. Thirty-five to 37% more 14C from applied 14C-acifluorfen was found in pitted morningglory treated leaves than ivyleaf morningglory treated leaves. Less than 28% of applied 14C-lactofen was extracted from treated leaves of either morningglory species. Translocation and metabolism of 14C-acifluorfen and 14C-lactofen were minimal in both morningglory species.