bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact ofCeutorhynchus liturafeeding on root carbohydrate levels in Canada thistle (Cirsium arvense)
Authors: Hein Gary L. , Wilson Robert G.
Published: July 2006

Canada thistle is a serious perennial weed found throughout the northern regions of the United States and Canada. The weevil,Ceutorhynchus litura(F.), was first released in Canada in 1965 as a potential biological control agent for Canada thistle; however, its impact as a control agent has been sporadic. The objective of this study was to characterizeC. lituraimpacts on the carbohydrate profile in Canada thistle roots through the growing season and to evaluate the potential for this biological control agent in causing stress to Canada thistle. Field plots, infested withC. litura, were established and extensively sampled forC. liturainfestations. By samplingC. litura–damaged and undamaged Canada thistle shoots–roots through the season, we were able to establish the profile of free sugars and fructans in the roots and compare these levels to the presence and extent of insect damage. Levels of all free sugars and fructans were consistently found to be depressed in roots fromC. litura–damaged shoots early in the summer during and shortly after the larval feeding period.Ceutorhynchus liturafeeding in Canada thistle shoots appears to disrupt the movement of photoassimilates from leaves to roots. Late-season levels of free sugars and fructans indicate that roots do recover from these depressed levels, and in several instances, significant overcompensation occurred in the damaged roots. Measurement of free sugars and fructans to identify sublethal impacts of control tactics may allow the strategic combining of complementary tactics to maximize the impact of stresses on Canada thistle.
Herbicidal spectrum and activity of Myrothecium verrucaria
Authors: Anderson Kathleen I. , Hallett Steven G.
Published: July 2006

Myrothecium verrucaria, isolated from sicklepod, was investigated for bioherbicide potential against a wide range of economically important weed species from agronomic, pasture, and horticultural systems. A number of different weed species from a range of plant families were highly susceptible to sprays of crude preparations of the fungus. A small number of species, primarily monocots, were tolerant, showing no damage symptoms or insignificant effects on biomass. Symptoms developed very rapidly in susceptible hosts, suggesting the activity of toxins, several of which are known to be produced by Myrothecium spp. The activity of crude harvests of M. verrucaria was not diminished when they were filtered to remove fungal mycelium and spores. In contrast, washed conidia had relatively little impact on weed species. We conclude that the activity of M. verrucaria is primarily caused by the activity of metabolites produced by the fungus in culture and not due to infection by the fungus per se. Myrothecium verrucaria cultural preparations have extremely potent herbicidal properties, but given its ability to produce mammalian toxins, we caution against its use.
Compensatory responses of late watergrass (Echinochloa phyllopogon) and rice to resource limitations
Authors: Gibson Kevin D. , Fischer Albert J. , Foin Theodore C.
Published: July 2006

The development of optimal weed management strategies that rely, in part, on crop interference will require an understanding of how weeds compensate for limitations in above- and belowground resources. Trade-offs in the leaf morphology and biomass partitioning of rice and late watergrass were investigated under glasshouse conditions in 1999 and 2000. Both species responded to shade with increased height, reduced biomass, greater partitioning of biomass to leaves, and greater leaf area ratios. At the lowest light level (18% sunlight), plants of both species showed little response to nitrogen (N). However, height, tillers, biomass, and leaf area increased for plants grown at 50% and full sunlight as N increased from 0 to 224 kg N ha−1. Late watergrass exhibited more plasticity in specific leaf area and root weight ratio than rice in response to shade. This plasticity contributed to the ability of late watergrass to maintain a higher percent of its tillers and total dry weight than rice when sunlight was reduced by 50%. These results support the hypothesis that except at low light levels, limited N further reduces the growth of shaded late watergrass plants. Thus, weed management strategies that limit the plasticity of late watergrass by manipulating light and N availability are likely to be more effective than strategies that rely on manipulating a single resource.
Evolved resistance to acetolactate synthase–inhibiting herbicides in common sunflower (Helianthus annuus), giant ragweed (Ambrosia trifida), and shattercane (Sorghum bicolor) in Iowa
Authors: Zelaya Ian A. , Owen Micheal D. K.
Published: July 2006

Weed biotypes putatively resistant to acetolactate synthase (ALS)–inhibiting herbicides were reported by Iowa farmers from 1997 to 2001. Greenhouse studies confirmed cross-resistance to triazolopyrimidine sulfonanilide and sulfonylurea (SU) herbicides in giant ragweed from Scott County, IA (Werner Farm), which corresponded to resistance to susceptibility (R:S) GR50(50% growth reduction) ratios of 21 and 28 to cloransulam and primisulfuron + prosulfuron, respectively. At the enzyme level, this represented a 49- and 20-foldI50(50% enzyme inhibition) increase. Cross-resistance to imidazolinone (IMI) and SU herbicides was also observed in common sunflower from Cherokee, IA. Compared with a susceptible biotype, the resistant common sunflower biotype demonstrated GR50R:S ratios of 36 and 43 to imazethapyr and chlorimuron, respectively. Shattercane from Malvern, IA, was susceptible to nicosulfuron but was resistant to imazethapyr (GR50R:S ratio = 29). The woolly cupgrass biotypes from Union County, IA (Pettit Farm and Travis Farm), were reportedly resistant but were identified susceptible to both IMI and SU herbicides. Using an in vivo ALS assay, extractable endogenous 2,3-diketone concentrations ranged from 25 to 71 nmol g−1fresh weight for all species. Compared with susceptible biotypes, 2,3-diketone levels accumulated to at least twofold higher levels in treated resistant plants 120 h after herbicide application. Field history data suggested that resistance evolved independently in three environments where ALS-inhibiting herbicides represented an important component of the selection pressure.
Absorption and activity of foramsulfuron in giant foxtail (Setaria faberi) and woolly cupgrass (Eriochloa villosa) with various adjuvants
Authors: Bunting Jeffrey A. , Sprague Christy L. , Riechers Dean E.
Published: July 2006

Greenhouse and laboratory studies were conducted to examine the activity and foliar absorption of foramsulfuron in giant foxtail and woolly cupgrass with various adjuvants. Adjuvant selection was important for giant foxtail control. Foramsulfuron provided 90% or greater giant foxtail control with the addition of methylated seed oil (MSO) or MSO plus 28% urea ammonium nitrate (UAN). When a crop oil concentrate (COC) or a nonionic surfactant (NIS) was added to foramsulfuron, giant foxtail control was only 20%. However, when 28% UAN was added to COC or NIS, control was increased to 90 and 85%, respectively. Foramsulfuron absorption and control were closely related in giant foxtail. Foliar absorption of14C-foramsulfuron in giant foxtail ranged between 35 and 90% 24 h after treatment (HAT) depending on adjuvant selection. The rate of absorption was greatest when MSO plus 28% UAN was added to foramsulfuron and absorption was maximized 4 HAT. Foramsulfuron absorption in woolly cupgrass reached its maximum levels 2 HAT with all adjuvant combinations. Although the rate of foramsulfuron absorption was quicker in woolly cupgrass, absorption trends by adjuvants were similar to those in giant foxtail. Maximum absorption of14C-foramsulfuron in woolly cupgrass was 84% with the addition of MSO plus 28% UAN. However, even with high levels of absorption, woolly cupgrass control with foramsulfuron was poor and may be related to rapid metabolism to nonphytotoxic compounds.
Investigations into glyphosate-resistant horseweed (Conyza canadensis): retention, uptake, translocation, and metabolism
Authors: Feng Paul C. C. , Tran Minhtien , Chiu Tommy , Sammons R. Douglas , Heck Gregory R. , CaJacob Claire A.
Published: July 2006

The mechanism of glyphosate resistance in horseweed was investigated. Eleven biotypes of putative sensitive (S) and resistant (R) horseweed were obtained from regions across the United States and examined for foliar retention, absorption, translocation, and metabolism of glyphosate. Initial studies used spray application of14C-glyphosate to simulate field application. When S and R biotypes were compared in the absence of toxicity at a sublethal dose, we observed comparable retention and absorption but reduced root translocation in the R biotypes. S and R biotypes from Delaware were further examined at field use rates and results confirmed similar retention and absorption but reduced root translocation in the R biotypes. Application of14C-glyphosate to a single leaf demonstrated reduced export out of the treated leaf and lower glyphosate import into other leaves, the roots, and the crown in R relative to S biotypes. Examination of the treated leaf by autoradiography showed that glyphosate loading into the apoplast and phloem was delayed and reduced in the R biotype. Our results consistently showed a strong correlation between impaired glyphosate translocation and resistance. Tissues from both S and R biotypes showed elevated levels of shikimate suggesting that 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) remained sensitive to glyphosate. Analysis of tissue shikimate levels demonstrated reduced efficiency in EPSPS inhibition in the R biotypes. Our results suggest that resistance is likely due to altered cellular distribution that impaired phloem loading and plastidic import of glyphosate resulting in reduced overall translocation as well as inhibition of EPSPS.
Rice and red rice interference. I. Response of red rice (Oryza sativa) to sowing rates of tropicaljaponicaandindicarice cultivars
Authors: Estorninos Leopoldo E. , Gealy David R. , Talbert Ronald E. , Gbur Edward E.
Published: July 2006

Field experiments were conducted at the Rice Research and Extension Center at Stuttgart, AR, in 1997 and 1998 to evaluate the growth response of Stuttgart strawhull (Stgstraw) red rice to sowing densities of 0, 50, 100, and 150 kg ha−1of ‘Kaybonnet,’ ‘Guichao,’ and ‘PI 312777’ rice cultivars. PI 312777 produced a greater leaf area index and tiller density than Kaybonnet when grown with red rice. In 1997, Stgstraw seed yields were lower when grown with PI 312777 and Guichao than with Kaybonnet. The increased weed population in 1998 did not increase seed yield production of red rice when grown with the three rice cultivars. The Stgstraw red rice seed yield was reduced when grown with 50 kg ha−1rice when compared with its yield in monoculture and was reduced further when grown with 100 and 150 kg ha−1rice. These results demonstrate that red rice was more competitive when compared with the tropicaljaponicaKaybonnet than theindicaPI 312777. Despite its semidwarf stature, PI 312777 tended to suppress red rice more than did Guichao or Kaybonnet. The mechanisms responsible for this difference could be important keys to the effective use of weed-suppressive cultivars in reduced herbicide input systems.
Phylogenetic relationships among New MexicoAstragalus mollissimusvarieties andOxytropisspecies by restriction fragment analysis
Authors: Kulshreshtha Sanjeev , Creamer Rebecca , Sterling Tracy M.
Published: July 2006

The phylogenetic relationships within two major locoweed genera,AstragalusandOxytropis, and among varieties of woolly loco found in New Mexico were analyzed by comparing their chloroplastrpoC1 andrpoC2 gene sequences. Nucleic acids from locoweed species and varieties collected from different geographical locations in New Mexico were amplified using specific primer sets and subjected to restriction fragment analyses. Identity of the amplicons was confirmed by determining the 5′-end sequences from pea and woolly loco var.matthewsii. The amplified sequences from all samples were digested with 16 different restriction enzymes. Presence or absence of individual restriction fragments was scored as binary characters and used to develop a similarity coefficient matrix for cladistic analyses to determine the phylogenetic relationships. The target sequence was conserved, yielding 7% polymorphic data.Oxytropisspecies were monophyletic and, as expected, formed a clade distinct fromAstragalus. The average similarity coefficient among woolly loco varieties was very high (0.9733), but the varieties still separated into three different clades. The phylogenetic relationship among woolly loco varieties coincided with their geographic distribution but was unrelated to insect feeding preference.
Multiple herbicide resistance in a glyphosate-resistant rigid ryegrass (Lolium rigidum) population
Authors: Neve Paul , Sadler Jemma , Powles Stephen B.
Published: July 2006

Surviving rigid ryegrass plants were collected from a cropping field at Pindar, Western Australia (population WALR 50), after inadequate control by glyphosate applied at the normal field rate. Plants were grown to maturity in pots and seeds were collected. Glyphosate dose–response experiments with known susceptible and resistant control populations confirmed the resistant status of the WALR 50 population. The glyphosate rate resulting in 5% mortality (LD50) and GR50(the glyphosate rate required to reduce mean growth of individuals to 50% of the untreated control) values for this population were 1,069 and 217 g ae ha−1, respectively, corresponding to R:S ratios of 3.4 and 1.9 for mortality and growth. In addition, a novel root growth–based assay of glyphosate resistance was developed and validated, giving a root growth GR50R:S ratio of 3.4. A resistance profile was established by assessing population-level survival of WALR 50 after applications at recommended rates of a range of herbicides commonly used for rigid ryegrass control in Australia. High levels of resistance to the acetolactate synthase (ALS)–inhibiting sulfonylurea herbicides chlorsulfuron and sulfometuron, moderate resistance to the acetyl coenzyme A carboxylase (ACCase)–inhibiting herbicide diclofop, and low levels of resistance to the imidazilinone herbicide imazethapyr were found. More detailed dose–response experiments confirmed resistance to chlorsulfuron, sulfometuron, and diclofop. In vitro enzyme-inhibition studies demonstrated that ALS resistance in WALR 50 is due to an insensitive target enzyme and that ACCase resistance is due to a nontarget site–based mechanism. WALR 50 is the first glyphosate-resistant weed population with confirmed resistance to ACCase- and ALS-inhibiting herbicides.
Soybean canopy formation effects on pitted morningglory (Ipomoea lacunosa), common cocklebur (Xanthium strumarium), and sicklepod (Senna obtusifolia) emergence
Authors: Norsworthy Jason K.
Published: July 2006

Field studies were conducted in 2002 and 2003 to determine whether canopy formation influences pitted morningglory, common cocklebur, and sicklepod emergence in surface-tilled soybean. Each weed species was broadcast seeded before planting soybean in 19- and 97-cm-wide rows. Weed emergence beneath soybean was monitored after soybean emergence and compared with weed emergence in the absence of soybean (bareground treatment). Magnitude of daily diurnal soil temperature fluctuations diminished after soybean canopy formation, and light interception by soybean was positively related to the reduction in soil temperature. Canopy formation (50% light interception) occurred 16 to 17 d later in wide compared with narrow rows in both years. The red/far-red ratio of light available to seed on or near the soil surface was reduced from as much as 1.2 in full sunlight to less than 0.1 in the presence of a dense soybean canopy. Pitted morningglory emergence was not influenced by soybean canopy formation, whereas common cocklebur and sicklepod emergence were reduced as much as 33 and 68%, respectively. Although common cocklebur and sicklepod emergence diminished after soybean canopy formation, a small portion of the seedbank of both species emerged beneath the canopy. This research indicates that in a tilled system, emergence of some weed species is diminished by presence of an overlying canopy, but emergence does not completely cease with canopy formation. Late-season emergence of sicklepod and common cocklebur beneath a soybean canopy may contribute to replenishment of the soil seedbank, especially if these late-emerging cohorts are capable of surviving until the light environment is favorable for seed production.
Impact of integrated management systems on jointed goatgrass (Aegilops cylindrica) populations
Authors: White Anthony D. , Stahlman Phillip W. , Northam Francis E.
Published: July 2006

Research during the past several decades on jointed goatgrass management has focused on individual cultural practices rather than on multi- or interdisciplinary components. Field studies were conducted at Hays, KS, from 1997 to 2003 to evaluate the interaction of crop rotation, fallow weed management, and winter wheat variety on jointed goatgrass density. Extending a wheat–fallow (W–F) rotation to include grain sorghum or grain sorghum and sunflower reduced jointed goatgrass populations more than other cultural practices tested. Fallow treatments were equal in most years, but mechanical fallow resulted in increased jointed goatgrass emergence compared with chemical fallow under drought conditions. Winter wheat cultivars had little effect on jointed goatgrass populations. However, taller, more competitive varieties are favorable for jointed goatgrass control in an integrated management program. No specific combination of crop rotation, fallow weed management, and wheat variety consistently reduced jointed goatgrass density more than other combinations during multiple years.
Induced resistance—an innovative approach to manage branched broomrape (Orobanche ramosa) in hemp and tobacco
Authors: Gonsior Guido , Buschmann Holger , Szinicz Gundula , Spring Otmar , Sauerborn Joachim
Published: July 2006

This study indicates that induced disease resistance might be useful to control branched broomrape. Strains of the rhizosphere bacteria Pseudomonas spp. (Proradix®), salicylic acid derivates (Bion®), and extracts of the algae Ascophyllum nodosum L. (Goemar Fruton Spezial®) can decrease branched broomrape infection to 80%. Results suggest that agents working as elicitors for resistance in other plant–pathogen interactions by induced systemic resistance or by systemic acquired resistance also could reduce branched broomrape infestation. These findings suggest that activation of immune responses before infection of plants could be an innovative control method for parasitic weeds.
Soil microbial and nematode communities as affected by glyphosate and tillage practices in a glyphosate-resistant cropping system
Authors: Liphadzi Konanani B. , Al-Khatib Kassim , Bensch Curtis N. , Stahlman Phillip W. , Dille J. Anita , Todd Timothy , Rice Charles W. , Horak Michael J. , Head Graham
Published: July 2006

Field experiments were conducted at Ashland Bottoms in northeastern Kansas and at Hays in western Kansas in 2001, 2002, and 2003 to determine the response of soil microbial and nematode communities to different herbicides and tillage practices under a glyphosate-resistant cropping system. Conventional herbicide treatments were a tank mixture of cloransulam plusS-metolachlor plus sulfentrazone for soybean and a commercially available mixture of acetochlor and atrazine for corn. Glyphosate was applied at 1.12 kg ai ha−1when weeds were 10 or 20 cm tall in both corn and soybean. Soil samples were collected monthly at Ashland Bottoms during the growing period for soil microbial biomass (SMB) carbon determination. In addition, substrate-induced respiration (SIR) and BIOLOG substrate utilization were determined at the end of the growing season each year at Ashland Bottoms, and nematode populations were determined at the beginning and the end of the growing season at both sites. Direct effects of glyphosate rates on soil microbial and nematode communities were also studied in a controlled environment. Values for SMB carbon, SIR, and BIOLOG substrate utilization were not altered by glyphosate. Nematode community response to the glyphosate treatment was similar under both conventional tillage and no-till environments. Total nematode densities were similar with the glyphosate and conventional herbicide treatments. SMB carbon and BIOLOG substrate utilization did not differ between tillage treatments. Nematode densities were greater under conventional tillage than in the no-till system. This study showed that soil health when glyphosate was applied in a glyphosate-resistant cropping system was similar to that of cropping systems that used conventional herbicides.
Rice yield and quality as affected by cultivar and red rice (Oryza sativa) density
Authors: Ottis Brian V. , Smith Kenneth L. , Scott Robert C. , Talbert Ronald E.
Published: July 2006

Previous research has examined the extent to which red rice affects both yield and grain quality of cultivated rice. However, this research was conducted over 15 yr ago. Modern long-grain rice cultivars have the potential to produce yields above 10,000 kg ha−1; however, it is unknown whether modern rice cultivars sacrifice competitiveness to achieve higher yields, or if, in fact, they are more competitive. Field studies were conducted in 2002 and 2003 at the Southeast Research and Extension Center near Rohwer, AR, and at the University of Arkansas Pine Bluff Research Farm near Lonoke, AR, to investigate the effect of red rice density on interference between red rice and five rice cultivars (‘CL161’, ‘Cocodrie’, ‘LaGrue’, ‘Lemont’, and ‘XL8’). White rice yield reductions were between 100 and 755 kg ha−1for every red rice plant m−2. The hybrid rice, XL8, had higher yields than the conventional cultivars. Red rice contamination in milling samples increased linearly as a function of red rice density at Lonoke and Rohwer in 2003. Dockage for each cultivar was calculated on the basis of the relationship between red rice density and red rice contamination. Semidwarf Lemont was the most contaminated and hybrid XL8 the least contaminated by the various densities of red rice.
Seed burial by tillage promotes field recruitment of false cleavers (Galium spurium) and catchweed bedstraw (Galium aparine)
Authors: Reid Danielle J. , Van Acker Rene C.
Published: July 2006

False cleavers and catchweed bedstraw are problematic weeds of field crops in high-latitude regions of the northern Great Plains of North America. The abundance of these species has been increasing in areas of greater tillage intensity and frequency. Field experiments were established over 4 site-yr in Manitoba, Canada, and results indicated that the recruitment of false cleavers and catchweed bedstraw was strongly promoted by a single shallow tillage operation with a sweep cultivator in the spring. Percent recruitment levels in 2001 (pooled over sites) were 17 and 46% for the untilled and tilled treatments, respectively. In 2002, the percent recruitment levels for the untilled and tilled treatments, respectively, were 28 and 38% for the Komarno site and 13 and 28% for the Petersfield site. Only a few and minor differences in microsite conditions (soil temperature, soil moisture, and bulk density) resulted from the single spring tillage pass. The single tillage pass caused a significant relocation of simulated seeds (plastic beads) to below the soil surface and deeper into the soil profile (2–4 cm). Mean bulk density and volumetric soil moisture increased significantly with soil depth. The results of this study suggest that the positive effect of tillage on cleavers recruitment was not due to the effect of tillage on microsite conditions per se. Rather, the vertical redistribution of seed by tillage moved these seeds to a place in which the microsite conditions differed from those on the surface and were more favorable for recruitment. False cleavers and catchweed bedstraw recruitment is clearly promoted by tillage (even minor tillage) under field conditions, and farmers might be able to limit recruitment by limiting spring tillage.
Conservation cotton production in the southern United States: herbicide dissipation in soil and cover crops
Authors: Locke Martin A. , Zablotowicz Robert M. , Bauer Philip J. , Steinriede R. Wade , Gaston Lewis A.
Published: July 2006

Soil and surface residues from cotton field studies in Stoneville, MS (1994 through 1996) and Florence, SC (1995 through 1996) were sampled to evaluate effects of cover crop and tillage on herbicide dissipation. Mississippi treatments included tillage (conventional [CT]; none [NT]) and cover crop (ryegrass; none [NC]). South Carolina treatments included tillage (CT; reduced tillage [RT]) and cover crop (rye; NC). Fluometuron was applied preemergence (PRE) in both Mississippi and South Carolina, and norflurazon was applied PRE in Mississippi. Soils were sampled various times during the growing season (depths: 0 to 2 cm, 2 to 10 cm). Cover crop residues were sampled from RT or NT cover crop areas. Soil and cover crop sample extracts were analyzed for herbicides. Soil organic carbon tended to increase with tillage reduction and presence of cover crop and was positively correlated with herbicide sorption, especially in the surface. Across locations, herbicide half-lives ranged from 7 to 15 d in the soil surface. Tillage had mixed effects on herbicide persistence in surface soil, with higher herbicide concentrations in CT at early samplings, but differences were insignificant later on. The most consistent effects were observed in RT/NT with cover crops, where cover crop residues intercepted applied herbicide, impeding subsequent movement into soil. Herbicide dissipation in cover crop residues was often more rapid than in soil, with half-lives from 3 to 11 d. Herbicide retention in cover crop residues and rapid dissipation were attributed to strong herbicide affinity to cover crop residues (e.g., fluometuron Kd= 7.1 [in rye]; Kd= 1.65 [in Mississippi Dundee soil CT, NC]) and herbicide co-metabolism as cover crop residues decomposed. A fluometuron metabolite, desmethyl-fluometuron, was observed in most soil and cover crop samples after 1 wk. Only minimal herbicide or metabolite moved into the subsurface, and little treatment effect could be ascribed to herbicide or metabolite movement below 2 cm.
Corn competition alters the germinability of velvetleaf (Abutilon theophrasti) seeds
Authors: Nurse Robert E. , DiTommaso Antonio
Published: July 2006

Velvetleaf is a troublesome annual weed in many cropping systems of the United States and Canada. Differences in the growing environment of parent plants can influence the number, structure, germinability, and viability of seeds produced. Thus, the effects across a range of competitive environments and corn planting dates on velvetleaf seed production, germination, and seed coat weight were examined under field conditions. Seed production of velvetleaf increased with increasing biomass. Total velvetleaf reproductive output was reduced in competition with corn compared with monoculture stands. Corn planting date had no effect on the dormancy status of seeds, but increased competition from corn resulted in up to a 30% decrease in the proportion of seeds that were dormant. Seed and seed coat weights also decreased for plants of velvetleaf grown in competition with corn compared with those grown in monoculture. These findings suggest that velvetleaf plants growing in relatively noncompetitive environments, such as along field edges or in field areas with poor crop stands, are likely not only to produce a greater number of seeds but also a greater proportion of seeds that are dormant. This alteration in the dormancy status of velvetleaf seeds in the absence or presence of a crop provides unique opportunities for effective long-term management of the soil seedbank in this species, especially for velvetleaf individuals bordering fields or growing in fallow areas that might require more stringent control because of increased seed dormancy.
Scale dependent relationships between native plant diversity and the invasion of croftonweed (Eupatorium adenophorum) in southwest China
Authors: Lu Zhijun , Ma Keping
Published: July 2006

Croftonweed is an invasive plant in southwest China. We examined the relationships between its invasion patterns and native plant diversity at different spatio-temporal scales. At the 25 m2scale, invasion success was negatively correlated with native plant diversity, indicating that resource availability might be the dominant factor regulating community invasibility. At the 400-m2scale, both negative and positive relationships were detected, possibly identifying a spatial scale threshold where extrinsic environmental factors became more important to community invasibility. At the vegetation province scale, variations in physical environment outweighed the importance of intrinsic biotic factors and positive relationships between diversity and invader success were found. Native plant diversity also inhibited croftonweed over the course of community succession and at the early stages of invasion at local spatial scales. However, the changing relationship might be an artifact of sampling at different spatial scales.
A model for predicting invasive weed and grass dynamics. I. Model development
Authors: Rinella Matthew J. , Sheley Roger L.
Published: July 2006

Invasive weed managers are presented with a complicated and ever-enlarging set of management alternatives. Identifying the optimal weed management strategy for a given set of conditions requires predicting how candidate strategies will affect plant community composition. Although field experiments have advanced our ability to predict postmanagement composition, extrapolation problems limit the prediction accuracy achieved by interpreting treatment means as predictions. Examples of extrapolation problems include nonlinear relationships between competing plants, site-to-site variation in plant population growth rates, and the carrying capacities of desired species and weeds. Our objective was to develop a model that improves predictions of weed management outcomes by overcoming a subset of these problems. To develop the model, we used data from two field experiments in which four Kentucky bluegrass, six western wheatgrass, and six invasive plant (i.e., leafy spurge) densities were combined in field plots. Graphs of our model's predictions vs. observed field experiment data indicate that the model predicted the data accurately. Our model may improve predictions of plant community response to invasive weed management actions.
Coffee senna (Cassia occidentalis) germination and emergence is affected by environmental factors and seeding depth
Authors: Norsworthy Jason K. , Oliveira Marcos J.
Published: July 2006

Laboratory and greenhouse experiments were conducted to determine the effect of light, temperature, moisture stress, solution pH, and burial depth on coffee senna germination and emergence. Seeds germinated equally with or without light, and pretreatment with red or far-red light did not affect germination. Optimum temperature for germination was 25 C, and a high germination percentage (> 70%) occurred from 12.5 to 30 C. The low temperature threshold for germination was between 10 and 12.5 C, whereas the upper threshold was near 45 C. Coffee senna germination in response to moisture stress and solution pH differed at 15 and 30 C. At −0.4 MPa, no germination occurred at 15 C, whereas 15% germination occurred at 30 C. Optimum germination was at pH 6, but further increases in pH had a more negative effect on germination at 15 C than at 30 C. Coffee senna germination ranged from 9 to 12% at pH 3, but was 0% at pH 10, which indicates that coffee senna germination was more tolerant of acidic than basic solutions. Depth-mediated emergence inhibition was sigmoidal, with greatest emergence on the soil surface. Emergence from 2- to 10-cm depths reached 95% of the total emergence 1 to 3 d earlier in a sandy loam than in a sand soil. Mean emergence depth was 1.7 cm in the sand and 2.4 cm in the sandy loam soil. Knowledge gained from this research will be instrumental in developing a better understanding of the requirements for coffee senna germination and emergence, allowing further development and improvement of integrated weed management strategies specific to this troublesome weed.
Cloning, characterization, and expression of growth regulatorCYCLIN D3-2in leafy spurge (Euphorbia esula)
Authors: Horvath David P. , Anderson James V. , Jia Ying , Chao Wun S.
Published: July 2006

We have isolated both a genomic and near full length cDNA clone for a D-class cyclin gene from the perennial weed leafy spurge. Sequence analysis indicates that this gene has the highest similarity toCYCLIN D3-2of Arabidopsis. This gene is preferentially expressed in growing shoot apices and is up-regulated in adventitious buds on resumption of growth following loss of correlative inhibition (apical dominance).CYCLIN D3-2is also induced in nongrowing adventitious buds of plants treated with gibberellic acid or after removal of leaves—treatments known to up-regulate expression of G1 to S phase transition–specific genes such asHISTONE H3in adventitious buds.CYCLIN D3-2was not induced on removal of the apical and axillary buds. Expression ofCYCLIN D3-2is down-regulated in adventitious crown buds during initiation of ecodormancy in early winter. Sequence comparisons ofCYCLIN D3-2with its putative orthologue from Arabidopsis identified several conserved motifs in the promoter region and a conserved region capable of forming a stable hairpin loop in the 5′ untranslated region. Conservation of these noncoding sequences across species strongly suggests they have a regulatory function.
Resistance in Canadian biotypes of wild mustard (Sinapis arvensis) to acetolactate synthase inhibiting herbicides
Authors: Warwick Suzanne I. , Sauder Connie , Beckie Hugh J.
Published: July 2006

Multiple cases of ALS inhibitor-resistant weed biotypes are reported for many species, including wild mustard. The physiological extent and molecular basis of resistance to ALS inhibitors was compared in four biotypes of wild mustard from western Canada: a sulfonylurea (SU)-resistant (R) biotype from Manitoba detected in 1992; an SU (ethametsulfuron)-R biotype from Alberta detected in 1993 (metabolism-based resistance); an SU-R biotype from Manitoba detected in 2002; and a SU- and imidazolinone (IMI)-R biotype from Saskatchewan detected in 2002. Herbicide dose-response experiments confirmed that the two Manitoba biotypes were resistant to the SU herbicides ethametsulfuron and tribenuron : thifensulfuron mixture, whereas the Saskatchewan biotype was resistant to both SU herbicides and to imazethapyr, an IMI herbicide. Sequence analysis of theALSgene detected target site mutations in three of the four R biotypes, with amino acid substitutions Pro197(CCT) to Ser (TCT) [Domain A of the gene] in the two SU-R Manitoba biotypes and Trp574(TGG) to Leu (TTG) [Domain B] in the Saskatchewan biotype. The Alberta SU-R biotype had the sameALSnucleotide and amino acid sequence as the susceptible population at these two positions. Two heterozygous individuals [Trp574(Tt/gG)] were detected in the Saskatchewan biotype, and genetic segregation for nucleotide bases and resistance phenotype was consistent with single gene control. Nucleotide variation in neutral regions of theALSgene varied with biotype, with no variation in the two Manitoba biotypes, two variants in the Saskatchewan biotype, and 16 neutral nucleotide polymorphisms (0.9%) in the Alberta biotype. The occurrence of at least three different ALS inhibitor-R biotypes in this important weed species is likely to impact negatively on the use of ALS inhibitors, such as the IMIs, and serves as a warning for strict implementation of herbicide rotations to prevent or delay the evolution and spread of such populations.
Wet heat as a mechanism for dormancy release and germination of seeds with physical dormancy
Authors: van Klinken Rieks D. , Flack Lloyd
Published: July 2006

Mexican palo-verde is a serious woody weed in tropical parts of the world. Like many such leguminous species, it has relatively large seeds with hard-seeded (physical) dormancy. It therefore has the potential for long-lived seed banks that are difficult to manage. The physiology of hard-seeded dormancy is still relatively poorly understood but has important implications for weed management. We propose that wet heat is a potentially important dormancy release mechanism for summer rainfall tropical regions. We described the relationships between wet heat and dormancy release (in water; three seed sources) and germination (near saturation; single seed source) by testing seeds at constant temperatures between 10 and 60 C. The logistic transformation of the temperature–dormancy relationship was best described by a quadratic equation below a threshold of ∼ 33.6 C and a linear equation above that threshold. The relationship was the same for all seed sources other than a phase shift of up to 6.6 C, which is likely to be of biological significance. Germination occurred between 15 and 40 C and was limited by cold stress at ≤ 20 C and heat stress > 35 C. The sensitivity of dormancy to naturally encountered temperature ranges suggests that wet heat is an important dormancy release mechanism and one that can be exploited when developing management strategies for invasive populations.
Longevity ofStrigaseeds reconsidered: results of a field study on purple witchweed (Striga hermonthica) in Bénin
Authors: Gbèhounou Gualbert , Pieterse Arnold H. , Verkleij Jos A. C.
Published: July 2006

Germination and longevity of purple witchweed seeds stored in nylon gauze bags in the soil in situ were tested in northern Bénin over a 2-yr period, covering the rainy seasons in 1994 and 1995. The seeds were collected at Ina Station in November 1993 from corn and sorghum fields. It appeared that germination percentages of the seeds, which were stimulated by GR24 to germinate, as well as their viability according to a tetrazolium test, decreased steadily in wet soil. During the 1994 rainy season, germination percentage of seeds, which reached maximum values of 30 to 74%, decreased to values of 11 to 17%. During the 1995 rainy season, the number of germinating seeds decreased further, and at the end of this season the germination percentage approached zero. Seed viability also decreased in line with the decrease in germination. In addition to the study on longevity under field conditions, seeds also were exposed to various water regimens in pots. In the pot experiment, purple witchweed seed viability and germination declined in moist soil treatments. The dying-off process observed contradicts the common opinion on longevity ofStrigaseeds in their natural environment. “Wet dormancy” was not observed in the course of the rainy season.
The Status of Weed Science at Universities and Experiment Stations in the Northeastern United States
Authors: Derr Jeffrey F.
Published: July 2006

Weed science is an important component of pest management. Weeds cause approximately 12% loss in United States crop production, reduce crop quality, poison livestock, and adversely affect human health, recreation, and transportation. Herbicides comprise approximately 65% of pesticide expenditures, whereas insecticides and fungicides each comprise less than 20%. The total effect of weeds, including crop losses and costs of control, in the United States was estimated in 1994 to be $20 billion annually. A survey was prepared and mailed to weed scientists at universities and experiment stations in the northeastern United States to determine the number of faculty positions and course offerings devoted to weed science. There are approximately five times as many entomologists and more than three times as many plant pathologists as weed scientists at universities in the northeast. There are more than six times as many graduate students currently in entomology and more than four times as many in plant pathology compared with weed science. Few undergraduate courses in weed science are taught, and most universities have no graduate classes in weed science. There are almost seven times as many undergraduate entomology courses and more than twice as many plant pathology courses as weed science classes in this region. There are more than 17 times as many graduate entomology courses and more than 15 times as many plant pathology courses compared with weed science graduate classes. There are no departments devoted solely to weed science in the northeast, whereas entomology and plant pathology departments are both common. Most universities have little to no faculty assigned to aquatic, forestry, noncrop weed control, weed ecology, or laboratory trials, and numbers assigned to agronomic and horticultural crop weed management are limited. Additional university resources are needed if weed science research, teaching, and extension efforts are to meet the priority needs in weed management.
Response of Rice Cultivars to V-10029
Authors: Zhang Wei , Webster Eric P. , Leon Christopher T.
Published: July 2006

A study was conducted in 2002 and 2003 to evaluate response of seven rice cultivars to V-10029 applied at 20 and 40 g ai/ha to two- to three- or four- to five-leaf rice. Differential response of the rice cultivars to V-10029 was observed. Medium-grain ‘Earl’ was less tolerant to V-10029, as reflected by increased injury, shorter plants, and fewer plants at 7 d after late postemergence treatment and shorter plants and lower grain yield at harvest, when compared with nontreated Earl. Growth of medium-grain ‘Bengal’ was initially inhibited by V-10029; however, plant height at harvest and rice grain yield of Bengal were not affected. All long-grain cultivars exhibited tolerance to V-10029, both initially and at harvest. The results indicate that rice cultivars vary in tolerance to V-10029.
Herbicide Seed Treatments for Control of Purple Witchweed (Striga hermonthica) in Sorghum and Millet
Authors: Dembélé Bouréma , Dembélé Daouda , Westwood James H.
Published: July 2006

A promising approach for the control of parasitic weeds is herbicide seed priming, which consists of soaking crop seeds in a herbicide solution such that the herbicide is later present in the crop seedling to inhibit growth of attaching parasites. This technique is effective where selectivity exists between crop and parasite; for example, varieties of imidazolinone-resistant maize. However, seed priming has not been reported for sorghum or pearl millet, two crops that are greatly affected by purple witchweed. Research was initiated to evaluate herbicides for potential use as seed priming agents in these crops. Auxin-mimic and acetolactate synthase-inhibitor class herbicides were evaluated; specifically, clopyralid, 2,4-DB, dicamba, picloram, and prosulfuron. For sorghum, immersion of seed in 0.5% (w/v) ae 2,4-DB for 5 min 1 d before planting reduced purple witchweed densities to levels 20 to 50% of nontreated controls. However, this concentration was at the threshold of crop toxicity and reduced sorghum yields in some experiments. None of the herbicides tested consistently reduced purple witchweed on pearl millet. This research illustrates both the potential and limitations of adapting seed priming technology for sorghum and pearl millet.
Managing Volunteer Potato (Solanum tuberosum) in Field Corn with Mesotrione and Arthropod Herbivory
Authors: Boydston Rick A. , Williams Martin M.
Published: July 2006

Volunteer potato is becoming increasingly detrimental in potato production regions. We assessed methods to manage the weed in field corn with herbicides and arthropod herbivory. In greenhouse trials, new tuber production was reduced at least 95% in ‘Ranger Russet’, ‘Russet Burbank’, ‘Russet Norkotah’, and ‘Shepody’ potato varieties by mesotrione applied at 0.11 kg/ha. In field studies conducted near Paterson, WA, a single application of mesotrione at 0.07 or 0.11 kg/ha applied at the time of tuber initiation (mid-postemergence [MPOST]) controlled potato top growth 96 to 98% in 2002 and 2003. Mesotrione applied at earlier stages of potato growth, preemergence or early postemergence, controlled potatoes less than mesotrione applied MPOST. All herbicide treatments prevented yield loss in field corn compared with nontreated checks. Mesotrione reduced new potato tubers and tuber weight more than any other herbicide. Herbivory of volunteer potato by Colorado potato beetle reduced tuber number 21% and tuber density 23% in the absence of herbicides and appeared to further suppress the weed in combination with herbicides. Whereas treatments containing mesotrione were most effective against volunteer potato, arthropod herbivory supplemented weed suppression and may be an important component in reduced or low-input weed management systems.
Tropical Spiderwort (Commelina benghalensis): A Tropical Invader Threatens Agroecosystems of the Southern United States
Authors: Webster Theodore M. , Burton Michael G. , Culpepper A. Stanley , York Alan C. , Prostko Eric P.
Published: July 2006

Tropical spiderwort (more appropriately called Benghal dayflower) poses a serious threat to crop production in the southern United States. Although tropical spiderwort has been present in the United States for more than seven decades, only recently has it become a pest in agricultural fields. Identified as an isolated weed problem in 1999, tropical spiderwort became the most troublesome weed in Georgia cotton by 2003. Contributing to the significance of tropical spiderwort as a troublesome weed is the lack of control afforded by most commonly used herbicides, especially glyphosate. Vegetative growth and flower production of tropical spiderwort were optimized between 30 and 35 C, but growth was sustained over a range of 20 to 40 C. These temperatures are common throughout much of the United States during summer months. At the very least, it appears that tropical spiderwort may be able to co-occur with cotton throughout the southeastern United States. The environmental limits of tropical spiderwort have not yet been determined. However, the rapid spread through Georgia and naturalization in North Carolina, coupled with its tolerance to current management strategies and aggressive growth habit, make tropical spiderwort a significant threat to agroecosystems in the southern United States.