Dandelion Control Research Articles

Chemometrics integrated with in silico pharmacology to reveal antioxidative and anti-inflammatory markers of dandelion for its quality control

BackgroundDandelion is an herb with high nutritional and medicinal values, which has been listed in Chinese Pharmacopeia, European Pharmacopoeia and British Pharmacopoeia, gaining increasing acceptance around the world. However, the current quality control of dandelion is lagging behind. Only in Chinese Pharmacopeia, cichoric acid is used as a marker compound for its quality evaluation, whereas, it can not comprehensively reflect the bioactivity of dandelion.MethodsThis study developed a strategy by integrating chemometrics with in silico pharmacology to reveal the bioactive markers of dandelion for its quality control. Firstly, the major chemicals in dandelion were characterized using HPLC-DAD-MS/MS, and the corresponding antioxidant and anti-inflammatory activities were evaluated in vitro. Subsequently, the active components were screened by relating the chemicals and bioactivity of dandelion via grey relational assay and partial least squares regression analysis. The potential active components were then subjected to a validation for their activities. Moreover, in silico pharmacology was utilized to evaluate the contribution of active components to efficacy.ResultsA total of 22 phenolic compounds were characterized. Among them, cichoric acid, caffeic acid and luteolin were identified as quality markers owing to their good correlations with the bioactivities of dandelion. These three markers were quantified in frequently-used dandelion species, viz. Taraxacum mongolicum Hand.-Mazz. (TAM) and T. officinale F. H. Wigg. (TAO). TAM, with acceptably higher content of cichoric acid and caffeic acid, showed better antioxidant activity than TAO. While TAO included higher content of luteolin, presenting slightly more effective in anti-inflammation.ConclusionAn useful strategy for the quality marker discovery was successfully designed. And the results provided more knowledge for the quality evaluation of dandelion.

Material Basis Elucidation and Quantification of Dandelion through Spectrum–Effect Relationship Study between UHPLC Fingerprint and Antioxidant Activity via Multivariate Statistical Analysis

The excessive expression of reactive oxygen species is closely connected to many diseases. Considerable studies have demonstrated dandelion as well as its ingredients exhibited antioxidant activity. However, specific material basis reflecting the antioxidant activity has not been comprehensively investigated. In this study, a spectrum–effect relationship study on dandelion between fingerprinting and antioxidant activity was analyzed in detail, while a UHPLC quantification method developed and completely validated for simultaneous determination of active ingredients in dandelion. With the establishment of dandelion fingerprints of different regions, 24 common peaks were characterized. The classic FRAP method and ABTS methods were then used to detect their antioxidant activity. Partial least squares regression analysis, bivariate correlation analysis and grey correlation method were used to accomplish the spectrum–effect relationship. Eventually, the ingredients with antioxidant activity which could be considered as candidate quality markers of dandelion were discovered through spectrum–effect relationship analysis. The six compounds including caftaric acid, chlorogenic acid, caffeic acid, chicoric acid, isochlorogenic acid A, and isochlorogenic acid C were quantitatively determined. The developed UHPLC assay method was accurate, precise, and reliable. The study has elucidated the antioxidant material basis of dandelion and provided a scientific basis for the quality control of dandelion.

Mixing the correct nitrogen source and rate with 2,4-D increases efficacy in hard and soft water

Hard water antagonism of 2,4-D dimethylamine (DMA) is avoided with the inclusion of ammonium sulfate (AMS) as a water conditioning agent in mixtures. In addition to functioning as an adjuvant, AMS is also a nitrogen (N) fertilizer. Two experiments evaluated the efficacy of 2,4-D DMA when mixed with alternative N sources and rates. The first experiment sought to determine the influence of alternative N sources and N rates on 2,4-D DMA efficacy in comparison to AMS. The second experiment more closely evaluated the influence of AMS rate on 2,4-D DMA efficacy. Nitrogen sources included AMS, ammonium nitrate (AMN), potassium nitrate (KNO3), urea–ammonium–nitrate (UAN), and urea. Each N source was tank-mixed with 2,4-D at both an adjuvant rate (20 g L−1 or 25 ml L−1) and a fertilizer rate (24.4 kg N ha−1) in both soft (0 mg CaCO3 L−1) and hard (600 mg CaCO3 L−1) water. Efficacy of the mixtures was assessed on dandelion (Taraxacum officinale F.H. Wigg.) in the greenhouse. Without consideration to water hardness level or N rate, 2,4-D DMA efficacy with the N sources was: AMN = UAN > AMS = Urea > KNO3. Ammonium sulfate reversed hard water antagonism of 2,4-D DMA at the adjuvant rate, but not at the fertilizer rate. When applied at the adjuvant rate in hard water, dandelion control rankings from 2,4-D mixes were generally: AMN = UAN = AMS > Urea > KNO3. It is not advised to mix KNO3 with 2,4-D applications based on reduced efficacy. The second experiment determined that 2,4-D efficacy decreased as AMS rate increased above the commonly used adjuvant rate (2% w/w, 20 g L−1), likely from salting out. Applicators desiring to use AMS as a foliar fertilizer should apply AMS separate from 2,4-D DMA to prevent potential antagonism.

Influence of hard water on 2,4-D formulations for the control of dandelion

AbstractThe herbicide 2,4-D is used in a variety of cropping systems, especially in grasses because it is a selective postemergence broadleaf herbicide. However, the most common formulation (2,4-D dimethylamine) is antagonized when mixed in hard water. The objective of this research was to determine which formulations of 2,4-D or premixes of various formulations of synthetic auxin herbicides are subject to hard water antagonism. Formulations surveyed for hard water antagonism in the first experiment included 2,4-D dimethylamine, 2,4-D diethanolamine, 2,4-D monomethylamine, 2,4-D isopropylamine salt, 2,4-D choline salt, 2,4-D isooctyl ester, and 2,4-D ethylhexyl ester. Synthetic auxin formulation types in the second experiment included water-soluble, emulsifiable concentrates and emulsion-in-water. All formulations were mixed with both soft and hard water (600 mg CaCO3 L−1) and applied to dandelions to determine whether antagonism occurred in hard water. Water-soluble (amine and choline) 2,4-D formulations were antagonized by hard water, but water-insoluble (ester) 2,4-D formulations were not antagonized. Similar results were found by formulation type with water-soluble synthetic auxin premixes antagonized but emulsifiable concentrates not antagonized. Furthermore, water-soluble salt formulations were not antagonized when formulated in premixes with other synthetic auxin herbicides as an emulsion-in-water. This research demonstrates that all 2,4-D water-soluble formulations and water-soluble premixes with phenoxycarboxylic acid herbicides are subject to hard water antagonism. Formulations of 2,4-D containing emulsifying agents protect against antagonism by the water-insoluble nature of ingredients in their formulation.

Weed control by 2,4-D dimethylamine depends on mixture water hardness and adjuvant inclusion but not spray solution storage time

AbstractHerbicides are an important tool in managing weeds in turf and agricultural production. One of the earliest selective herbicides, 2,4-D, is a weak acid herbicide used to control broadleaf weeds. Water-quality parameters, such as pH and hardness, influence the efficacy of weak acid herbicides. Greenhouse experiments were conducted to evaluate how varying water hardness level, spray solution storage time, and adjuvant inclusion affected broadleaf weed control by 2,4-D dimethylamine. The first experiment evaluated a range of water-hardness levels (from 0 to 600 mg calcium carbonate [CaCO3] L−1) on efficacy of 2,4-D dimethylamine applied at 1.60 kg ae ha−1 for dandelion and horseweed control. A second experiment evaluated dandelion control from spray solutions prepared 0, 1, 4, 24, and 72 h before application. Dandelion and horseweed control by 2,4-D dimethylamine was reduced when the CaCO3 level in water was at least 422 or at least 390 mg L−1, respectively. Hard-water antagonism was overcome by the addition of 20 g L−1 ammonium sulfate (AMS) into the mixture. When AMS was included in spray mixtures, no differences were observed at 600 mg CaCO3 L−1, compared with distilled water. Spray solution storage time did not influence dandelion control, regardless of water-hardness level or adjuvant inclusion. To prevent antagonism, applicators should use a water-conditioning agent such as AMS when applying 2,4-D dimethylamine in hard water.

Mowing Timing Does Not Affect the Efficacy of Broadleaf Herbicides Applied to Control Dandelion (Taraxacum officinale)

Core Ideas More information is needed to precisely define mowing restriction recommendations for systemic broadleaf herbicides. Sufficient leaf tissue remained after mowing to allow for herbicide absorption, translocation, and subsequent control of dandelion. Mowing 4 days before to 4 days after herbicide treatment did not impact herbicide efficacy.

Selective Broadleaf Weed Control in Turfgrass with the BioherbicidesPhoma macrostomaand Thaxtomin A

Both regulatory and consumer forces have increased the demand for biopesticides, particularly in amenity areas such as turfgrass. Unfortunately, few natural products are available for selective weed control in turfgrass. Two bioherbicides reported to control broadleaf weeds without injuring turfgrass arePhoma macrostomaand thaxtomin A. Field and container experiments were conducted to evaluate PRE and POST efficacy ofP. macrostomaand thaxtomin A on regionally important broadleaf weeds. In container experiments, PRE applications ofP. macrostomaprovided 65 to 100% control of dandelion, marsh yellowcress, and flexuous bittercress, equivalent to that of pendimethalin. Control of yellow woodsorrel, henbit, hairy galinsoga, common chickweed, or annual bluegrass was less than with pendimethalin. In contrast, POST applications did not control any species as well as an industry-standard synthetic auxin herbicide. PRE or POST applications of thaxtomin A controlled six of the eight species tested as well as the industry-standard PRE or POST herbicides. In field tests, overall PRE broadleaf weed control withP. macrostomaand thaxtomin A peaked 4 wk after treatment at 64 and 72%, respectively, and declined afterward, suggesting that these bioherbicides possess short residuals and therefore must be reapplied for season-long control. Overall POST broadleaf weed control usingP. macrostomaand thaxtomin A was only 41 and 25%, respectively. PRE followed by early-POST applications of thaxtomin A provided ≥ 86% henbit control. These results suggest that bothP. macrostomaand thaxtomin A are capable of controlling certain broadleaf weeds in turfgrass. However, both lack efficacy on some important weed species, particularly chickweed. Thaxtomin A efficacy on henbit was improved by increased dose and by PRE followed by early-POST applications.

Divalent Cations in Spray Water Influence 2,4-D Efficacy on Dandelion (Taraxacum officinale) and Broadleaf Plantain (Plantago major)

2,4-dichlorophenoxyacetic acid (2,4-D) is a common ingredient in POST broadleaf herbicides labeled for use in turf, pastures, rangeland, and grain crops. The herbicide 2,4-D is a weak acid, and when dissociated can bind to cations present in hard-water spray solutions and/or fertilizer solutions. Experiments were conducted with 2,4-D dimethylamine to evaluate the effect of cation solutions on herbicide efficacy on the perennial broadleaf weeds dandelion and broadleaf plantain. The objectives of this research were to (1) determine if 2,4-D efficacy is influenced by the divalent cations, calcium (Ca), magnesium (Mg), manganese (Mn), and zinc (Zn) in spray solution; and (2) determine if adding the adjuvant ammonium sulfate (AMS) to the spray solution can overcome antagonism. Broadleaf plantain and dandelion control was reduced and plant size and mass increased when 2,4-D was applied in a Ca solution in comparison to deionized water. However, 2,4-D antagonism was overcome when AMS was added as an adjuvant to the spray solution. Magnesium caused 2,4-D antagonism on both weed species in one run of the experiment similar to Ca solution and AMS was successful at overcoming antagonism when added to the tank mixture. Some 2,4-D antagonism from Mn was noticed even when AMS was in the tank mix, but Zn fertilizer solutions did not antagonize 2,4-D activity on either weed species. Although divalent cations can antagonize 2,4-D dimethylamine and reduce perennial broadleaf weed control, adding AMS can overcome this antagonism when Ca and Mg are the primary cations in spray solution. Applicators should avoid using Mn fertilizers when applying 2,4-D dimethylamine because AMS did not successfully overcome antagonism.

Springtime Dandelion (Taraxacum officinale) Control with Seven Postemergence Herbicides Applied at Three Anthesis Stages

Although spring is not considered the optimal time for herbicidal control of most cool-season broadleaf weeds in turfgrass, spring applications are often required. Most new postemergence broadleaf herbicides combine several active ingredients, possibly resulting in synergistic, antagonistic, or additive effects. Therefore, as new herbicides become available, information is needed about their performance when applied in the spring. The objective of our study was to determine the effect of spring application timing on dandelion control with seven commercially available postemergence herbicides. Products were applied at their lowest labeled rate for dandelion control at three spring application timings, which coincided with dandelion anthesis stages (pre-, peak-, or post-bloom). A grid was used to determine percent dandelion control at several rating dates. The 2010 site had a denser turfgrass stand with smaller dandelions and was irrigated more frequently compared with the 2011 site. In 2010, all herbicides gave 98% or greater control at 30 days after treatment (DAT) when applied post-bloom; when applied pre- or peak-bloom, control was 80% or greater for all herbicides except for two products applied peak-bloom. At pre- and peak-bloom, products combining a protoporphyrinogen oxidase (PPO) inhibitor with a 2,4-D ester formulation were superior to most other herbicides. When evaluated at the end of the growing season in 2010, all herbicides provided 89% or greater control at all three timings. In 2011, with a less dense turfgrass stand, larger dandelions, and less frequent irrigation, control was more variable and shorter-lived among herbicides. When applied pre-bloom, all products containing 2,4-D provided 87% or greater control 60 DAT. Post-bloom application generally gave similar control to the pre-bloom timing. Peak-bloom application resulted in the poorest overall control at 60 DAT, but products combining a PPO inhibitor with a 2,4-D ester formulation performed better than most other herbicides. By the end of the season, dandelion regrowth caused reduced overall control at all timings, but overall control was poorest when applied at peak-bloom. In summary, peak-bloom applications should be avoided, especially if dandelion pressure is high. Products combining PPO inhibitors with ester forms of 2,4-D were most effective across all spring application timings. Products containing amine forms of 2,4-D may provide effective control if applied pre- or post-bloom.

Volatility of Broadleaf Weed Herbicides When Applied to Turfgrass

Laboratory and field studies were conducted in 2010 and 2011 to evaluate the volatility of commonly used turfgrass broadleaf herbicides when applied to tall fescue (Lolium arundinaceum Schreb.). Herbicides were applied at the highest label rate for dandelion (Taraxacum officinale G.H. Weber ex Wiggers) control. Turfgrass flats treated with herbicides were placed in enclosures containing tomato plants. In laboratory experiments, tomatoes exposed to turfgrass treated with products containing amine formulations of synthetic auxin herbicides exhibited minimal injury, but exposure to products containing low-volatile ester formulations caused significant negative effects on tomato quality, epinasty, and callus formation. Generally, products containing low-volatile ester formulations of synthetic auxin herbicides exhibited less volatility, compared to 2,4-D butyl ester (volatile standard). A subsequent field study corroborated the laboratory results, although injury symptoms were less severe. Turfgrass managers should avoid herbicides containing low-volatile ester formulations when vulnerable non-target plants are nearby, and/or when environmental conditions such as high temperature favor volatility.

식물생장조절물질 처리가 서양민들레 종자 발아에 미치는 영향

서양민들레는 국화과 식물로서 한국 전역에서 자생하고 있다. 최근에는 서양민들레의 효능으로 인해 최근 약용식물로 재배되고 있다. 그러나 서양민들레는 골프장 잔디밭이나 과수원에서는 잡초로 고려되고 있다. 본 실험은 다른 농도의 식물생장조절물질[gibberellins (<TEX>$GA_3$</TEX>); kinetin; salicylic acid (SA); ethephon)] 처리가 서양민들레 종자발아율에 미치는 영향을 조사하기 위해 수행하였다. 실험결과, <TEX>$GA_3$</TEX> 및 kinetin 처리 모든 농도에서 무처리에 비하여 종자발아율이 약 24.2~41.9% 높았다. Ethephon 0.5 mM의 처리에서는 무처리에 비해 종자발아율이 7.5% 높았으나, 1.0 및 1.5 mM 처리에서는 약 11~22% 가량 낮은 경향이었다. 반면에 SA와 <TEX>$GA_3$</TEX>의 혼합처리 경우에는 했을 때 종자발아율은 SA 단독처리보다 더욱 낮았다. Dandelion (Taraxacum officinale) is a member of family Asteraceae that grows all over the Korea. Recently, dandelion was cultivated for medicinal crops because of its positive medicinal effects. However, dandelion is considered as a troublesome weed in grass lawns of golf course and orchards. This study was conducted to investigate the effect of plant growth regulators [gibberellins (<TEX>$GA_3$</TEX>); kinetin; salicylic acid (SA); ethephon)] with different concentration on seed germination control of dandelion. Seed germination rates were increased in all concentration of <TEX>$GA_3$</TEX> and kinetin treatment compared to control. In the 0.5 mM of ethephon application, seed germination rate was more increased than that of control while seed germination rate was reduced in 1.0 and 1.5 mM of ethephon treatments. Seed germination rate was significantly decreased with different SA dilutions compared to control. The germination rate was more reduced when SA was applied in combination with <TEX>$GA_3$</TEX> than only SA treatments.

Efficacy of Corn Gluten Meal for Common Dandelion and Smooth Crabgrass Control Compared to Nitrogen Fertilizers

Efficacy of Corn Gluten Meal for Common Dandelion and Smooth Crabgrass Control Compared to Nitrogen Fertilizers

Influence of Foliar Moisture on Postemergent Granule Herbicide Control of White Clover and Dandelion in Cool-Season Turf

Field studies were conducted in 2007 and 2008 to determine the influence of foliar moisture on the performance of three postemergent granular herbicides against white clover, Trifolium repens L., and dandelion, Taraxacum officinale (Weber). The herbicides utilized were LockUp 3-Way (2,4-D/penoxsulam/dicamba), Scotts Turf Builder with Plus 2 Weed Control (2,4-D/MCPP-p) and Lebanon ProScape Fertilizer with Trimec Herbicide (2,4-D/dicamba/MCPP-p). Herbicides were applied to individual plots in the morning when dew was present and then later the same day when foliar moisture had dissipated. Weed control was assessed at intervals of approximately 2, 4 and 8 weeks after treatment. The presence of foliar moisture generally improved the performance of all herbicides evaluated. Given that commercial applications generally target a complex of weeds the results indicate that optimum performance of granular postemergent herbicides will occur when applications are made to moist foliage.

Annual Meeting, Winnipeg, Manitoba, 2009

Annual Meeting, Winnipeg, Manitoba, 2009

Mulched Maple and Oak Leaves Associated with a Reduction in Common Dandelion Populations in Established Kentucky Bluegrass

Previous research has shown that maple (Acer spp.) leaf litter resulted in fewer common dandelions (Taraxacum officinale) when mulched into established turfgrass. However, the leaves used in that research may have contained herbicide residues and were separated by genus, not species. Our research compared the effects of pesticide-free mulched maple and oak (Quercus spp.) leaves on dandelion populations in an established kentucky bluegrass (Poa pratensis) stand maintained as a residential lawn on sandy loam soil. The objectives of this study were to quantify the effectiveness of maple or oak leaf mulches as an organic common dandelion control method and to identify which maple species and rates (particle size and rate per unit area) provided the most effective control. The experimental design was a randomized complete block with treatments arranged as a 5 × 2 × 2 + 1 factorial, with tree leaf species, leaf particle size, leaf application rate, and control as main factors. Leaf species were red maple (Acer rubrum), silver maple (A. saccharinum), sugar maple (A. saccharum), high sugar content sugar maple, and red oak (Quercus rubra). Particle sizes were coarse (0.4–1.0 inch2) and fine (≤0.2 inch2), and application rates were low (0.5 kg·m−2) and high (1.5 kg·m−2). Mulch applications were made in Fall 2003 and 2004 and data were collected beginning in Spring 2004 on kentucky bluegrass spring green-up, and common dandelion plant counts. The high application rate, regardless of tree genus or species, resulted in the highest green-up ratings. Common dandelion plant counts after one (2003) and two (2003 and 2004) mulch applications at the high rate showed that up to 80% and 53% reduction was achieved, respectively. Results indicate that mulching leaves regardless of genus (oak or maple) or maple species into established turfgrass as a leaf litter disposal method will increase spring green-up and contribute to a reduction in common dandelion population.

Mulched Maple and Oak Leaves Associated with a Reduction in Common Dandelion Populations in Established Kentucky Bluegrass

Previous research has shown that maple (Acer spp.) leaf litter resulted in fewer common dandelions (Taraxacum officinale) when mulched into established turfgrass. However, the leaves used in that research may have contained herbicide residues and were separated by genus, not species. Our research compared the effects of pesticide-free mulched maple and oak (Quercus spp.) leaves on dandelion populations in an established kentucky bluegrass (Poa pratensis) stand maintained as a residential lawn on sandy loam soil. The objectives of this study were to quantify the effectiveness of maple or oak leaf mulches as an organic common dandelion control method and to identify which maple species and rates (particle size and rate per unit area) provided the most effective control. The experimental design was a randomized complete block with treatments arranged as a 5 × 2 × 2 + 1 factorial, with tree leaf species, leaf particle size, leaf application rate, and control as main factors. Leaf species were red maple (Acer rubrum), silver maple (A. saccharinum), sugar maple (A. saccharum), high sugar content sugar maple, and red oak (Quercus rubra). Particle sizes were coarse (0.4–1.0 inch2) and fine (≤0.2 inch2), and application rates were low (0.5 kg·m−2) and high (1.5 kg·m−2). Mulch applications were made in Fall 2003 and 2004 and data were collected beginning in Spring 2004 on kentucky bluegrass spring green-up, and common dandelion plant counts. The high application rate, regardless of tree genus or species, resulted in the highest green-up ratings. Common dandelion plant counts after one (2003) and two (2003 and 2004) mulch applications at the high rate showed that up to 80% and 53% reduction was achieved, respectively. Results indicate that mulching leaves regardless of genus (oak or maple) or maple species into established turfgrass as a leaf litter disposal method will increase spring green-up and contribute to a reduction in common dandelion population.

Population Dynamics of Broadleaf Weeds in Turfgrass as Influenced by Chemical and Biological Control Methods

A 3-yr field study was conducted to determine the effect of a biological control agent,Sclerotinia minorJagger, and a common herbicide, Killex, on the population dynamics of dandelion and other broadleaf species and on the dandelion seed bank. Treatments were applied as one spring, one early autumn, or a spring plus an early autumn treatment per year. The response of the dandelion population to a spring herbicide treatment was similar to two applications per year (spring and early autumn). Significantly less dandelion control occurred after the first early autumn application of the herbicide. Two weeks after application, spring or early autumn treatments withS. minorwere equally effective in suppressing dandelions. In the second year of the two applications per year ofS. minortreatment, weed control was equivalent to the herbicide. By the third year of the one spring application ofS. minor, weed control was equivalent to the herbicide. Generally over the study period, the early autumn application ofS. minorwas less effective than the spring or the spring and early autumn applications. TheS. minortreatments significantly reduced the dandelion seed bank, and this effect was not significantly different from the Killex herbicide treatment. The rate, frequency, and seasonal timing of application had no effect on the dandelion seed-bank size, but terminating the application would gradually replenish the seed bank. Populations of white clover, broadleaf plantain, birdsfoot trefoil, and common ragweed were similarly suppressed by either theS. minoror the herbicide treatments. Yellow woodsorrel significantly increased after 1 yr of herbicide treatment compared with theS. minorand untreated control treatments, indicating a possible weed species shift. Turf quality was improved because of the herbicide andS. minortreatments, but grass injury and smooth crabgrass invasion were recorded in 17% of herbicide-treated plots.

Immediate Effects of Time and Method of Alfalfa Termination on Soil Mineral Nitrogen, Moisture, Weed Control, and Seed Yield, Quality, and Nitrogen Uptake

ABSTRACT Three field experiments were conducted on Gray Luvisol (Typic Cryoboralf) soils in northeastern Saskatchewan to compare the effects of alfalfa (Medicago sativa Leyss) stand termination with tillage and herbicides at different times on mineral nitrogen (N) (ammonium-N and nitrate-N) and moisture content of soil in spring (experiments 1 and 2), soil moisture, volunteer alfalfa and dandelion control, plant density, seed yield, protein concentration and N uptake for wheat (Triticum aestivum L.), barley (Hordeum vulgare L), canola (Brassica rapa L.), and pea (Pisum sativum L.) crops (experiment 3). Termination treatments included combinations of times (in mid-June after cut 1, in mid-August after cut 2 and in mid-May during spring) and methods [tillage alone, herbicides alone (glyphosate + 2,4-D amine and also clopyralid + 2,4-D ester in experiment 3) and these herbicides + tillage]. Tillage alone significantly increased spring soil nitrate-N levels over herbicides alone or herbicides + tillage. Termination after cut 1 had the highest levels of soil nitrate-N. There was little effect of time and method of termination on soil ammonium-N and moisture content in spring. Herbicides + tillage generally provided better control of both volunteer alfalfa and dandelion in the four crops than tillage or herbicides alone. In general, alfalfa termination with herbicides alone significantly reduced plant density, seed yield, and N uptake of all crops and protein concentration of cereals only due to effects on levels of soil nitrate-N, dandelion control, and crop injury by clopyralid or 2,4-D residues in soil. Plant density, seed yield, N uptake and protein concentration of crops tended to decline with delay in termination time. The results of this study support the use of some tillage in alfalfa stand termination in helping to control volunteer alfalfa and dandelion and optimize annual crop yields and quality.

Control Strategies for Common Dandelion (Taraxacum officinale) in No-Tillage Cropping Systems

Common dandelion has developed into a troublesome agronomic weed for no-tillage corn and soybean producers in Michigan and throughout the north central region of the United States. Field experiments were conducted on established populations of common dandelion in 2001 to 2002 and 2002 to 2003 to evaluate the effect of preplant and sequential herbicide applications on established populations of common dandelion. Preplant treatments of glyphosate or 2,4-D ester were applied early fall, late fall, early spring, and late spring. For both glyphosate and 2,4-D ester, the fall applications were more effective than the spring applications. Glyphosate at 840 gae/ha was more effective than 2,4-D ester at 1,120 gae/ha at each application timing. A single application of glyphosate or 2,4-D ester applied either in the fall or spring did not provide season-long control of common dandelion. Sequential treatments of glyphosate following preplant applications of either glyphosate or 2,4-D ester provided season-long control of common dandelion.

Common Dandelion (Taraxacum officinale) Control with Postemergence Herbicides in No-Tillage Glufosinate-Resistant Corn

Common dandelion has developed into a troublesome agronomic weed for no-tillage corn producers. A postemergence herbicide application is often required to reduce common dandelion competition. Field experiments were conducted in 2002 and 2003 to evaluate 22 postemergence herbicide treatments for efficacy on established populations of common dandelion in no-tillage corn. All herbicides were applied to five- to six-collar corn at registered rates with typical adjuvants. At 28 d after treatment (DAT) the most effective treatments included glufosinate and mesotrione providing at least 76% control of common dandelion. All other herbicide treatments provided less than 40% common dandelion control 28 DAT. Common dandelion control was evaluated 56 DAT when regrowth of treated plants was observed for some herbicide treatments. AT 56 DAT, dicamba + diflufenzopyr was the most effective treatment, providing 83% control of common dandelion. In 2002, all herbicide treatments, with the exception of flumiclorac, resulted in corn yields greater than the nontreated.