Degradation of 1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl) urea (fluometuron) in a sandy loam soil was investigated in time-course and 14CO2 evolution studies. Degradation occurred only in nonautoclaved samples and was more rapid in glucose-amended soil, indicating that it is a function of microbial metabolism. Time-course studies showed that the pathway of degradation of fluometuron in soil is similar to that previously reported for other substituted ureas, involving a two-step demethylation, probably followed by hydrolysis of the urea linkage to form the aniline derivative. Further evidence for degradation was a small but significant recovery of 14CO2 from soil treated with fluometuron labeled in the trifluoromethyl group.

The Nebraska till-plant system of planting corn (Zea mays L.) moves weed seed away from the corn row. A reduction of weed seed in the row reduces the number of weeds emerging with the corn. In contrast, the conventional disking and plowing system of seedbed preparation does not remove weed seed from the row.

Interference studies utilizing manipulated and natural infestations of giant foxtail (Setaria faberi Herrm. ♯ SETFA) in soybeans [Glycine max (L.) Merr. ‘Williams’] were conducted at Urbana, IL, in 1982 and 1983. Giant foxtail clumps, each consisting of 3 to 6 plants per dm2, were used to determine the effect of clump density on giant foxtail dry weight and soybean seed yield. In both years, regression equations predicted a soybean seed yield loss of 0.8% for each giant foxtail clump per 9 m of row. The highest density of 30 clumps per 9 m of row reduced soybean yield 26%. In a second study, fluazifop {(±)-2-[4-[(5-(trifluoromethyl)-2-pyridinyl)oxy]phenoxy]propanoic acid} at 0.28 kg ai/ha or fluazifop + alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl)acetanilide] at 0.28 + 2.24 kg/ha applied 10 or 15 days after emergence gave maximum giant foxtail control with little or no reduction in soybean seed yield. Interference from uncontrolled giant foxtail began to reduce soybean dry-matter accumulation 15 days after emergence under favorable growing conditions in 1982. Under less favorable conditions in 1983, similar effects were not observed until 25 days after emergence.

Field studies conducted at six locations in Georgia and one location in Virginia evaluated imazethapyr and imazethapyr mixtures for weed control, crop tolerance, and peanut yield. Imazethapyr applied early postemergence controlled bristly starbur, coffee senna, common cocklebur, Ipomoea species, jimsonweed, prickly sida, and smallflower morningglory at least 91% and controlled yellow and purple nutsedge 88 and 98%, respectively. Paraquat plus bentazon applied early postemergence did not control the aforementioned weeds as well as imazethapyr or imazethapyr mixtures. Paraquat applied with imazethapyr reduced bristly starbur control 15% compared to imazethapyr alone but did not influence control of the other species. Imazethapyr control of bristly starbur was not improved by the addition of bentazon. Sicklepod control was less than 24% with imazethapyr and was at least 58% with imazethapyr plus paraquat Imazethapyr plus paraquat controlled sicklepod better than paraquat plus bentazon at three of the four locations evaluated. Imazethapyr did not control Florida beggarweed, while imazethapyr plus paraquat controlled at least 53%. Peanut injury was minimal 30 d after application for all treatments.

Experiments were conducted to determine the productivity, inter-, and intraspecific competitive ability of giant foxtail accessions resistant (PCW1) and susceptible (AC1) to acetyl-coenzyme A carboxylase (ACCase) inhibitors. Under noncompetitive conditions in the field, shoot dry biomass, plant height, and leaf area over time were similar between the PCW1 and AC1 accessions. The instantaneous relative growth rate and instantaneous net assimilation rate did not differ between the accessions; however, the instantaneous leaf area ratio was slightly greater for the AC1 accession than the PCW1 accession. The seed yield was similar between the PCW1 and AC1 accessions. Addition series experiments were conducted in the field to determine the intraspecific competitive ability of the PCW1 and AC1 accessions. Regression surface analysis of reciprocal mean shoot dry biomass and seed yield indicated that the relative competitive ability of the PCW1 and AC1 accessions was similar. Replacement series experiments were conducted in the greenhouse with or without corn to determine the interspecific competitive ability of the accessions. The relative growth rate, shoot dry biomass, and seed yield of the PCW1 and AC1 accessions were greater without than with corn competition. The relative competitive ability of the PCW1 and AC1 accessions was similar with or without corn competition based on shoot dry biomass or seed yield. These results indicated that the intra- and interspecific competitive ability of the PCW1 and AC1 giant foxtail accessions are similar and suggest that resistance to ACCase inhibitors has not reduced the relative fitness of the PCW1 accession.

In greenhouse studies, the American strain of Striga gesnerioides (Willd.) Vatke, indigo witchweed, was potted with a wide range of potential hosts, including some known to be parasitized by this species elsewhere, and with agricultural and ornamental crops of importance in the southern United States. The host range of the indigo witchweed was very limited and no major crop species were seriously affected. Based on these host studies, it appears that indigo witchweed poses little danger to American agriculture. Other strains of the parasite were likewise shown to be host specific.

Adsorption isotherms were obtained for buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}, VEL 3510 {1-β,β-dimethoxy-1-methyl-3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]urea}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4 (1H)-pyridinone} on soil organic matter (H- and Ca-saturated), Ca-montmorillonite, and Cape Fear sandy loam soil. Prometryn [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine] was included as a reference. The order of adsorption on all adsorbents was fluridone ≥ prometryn > > tebuthiuron ≥ VEL 3510 > buthidazole. Fluridone adsorption on the various adsorbents was: H-organic matter > Ca-montmorillonite > Ca-organic matter > > Cape Fear sandy loam. Tebuthiuron, VEL 3510, and buthidazole adsorption on the various adsorbents was in the order: H-organic matter > Ca-organic matter = Ca-montmorillonite > Cape Fear sandy loam. Adsorption of all herbicides increased with decreasing pH, suggesting that the adsorption mechanism was molecular under neutral pH conditions and ionic under acidic conditions. All of the herbicides were adsorbed in high amounts as protonated species on IR-120-H cation exchange resin and in low amounts as molecular species on IR-400-Cl anion exchange resin. Buthidazole and VEL 3510 were adsorbed in high amounts as anionic species by the IR-400-Cl exchange resin at high pH levels.

Buried seeds of witchgrass (Panicum capillare L., # PANCA) exposed to natural seasonal temperature changes in Lexington, KY, for 0 to 35 months exhibited annual dormancy/nondormancy cycles. Seeds were dormant at maturity in early October. During burial in late autumn and winter, fresh seeds and those that had been buried for 1 and 2 years became nondormant. Nondormant seeds germinated from 76 to 100% in light at daily thermoperiods of 15/6, 20/10, 25/15, 30/15, and 35/20 C, while in darkness they germinated from 1 to 24%. In late spring, seeds lost the ability to germinate in darkness, and by late summer 63 to 100% of them had lost the ability to germinate in light. As seeds became nondormant, they germinated (in light) at high (35/20, 30/15 C) and then at lower (25/15, 20/10, and 15/6 C) temperatures. As seeds reentered dormancy, they lost the ability to germinate (in light) at 15/6 C and at higher thermoperiods 2 to 3 months later.

The effect of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] on the germination and growth of 14 plant species was investigated. A 10-3 M concentration of the herbicide did not reduce germination as much as 10% for corn (Zea mays L. ‘Pioneer 3369A’), English pea (Pisum sativum L. ‘Thomas Laxton’), sicklepod (Cassia obtusifolia L.), or wheat (Triticum aestivum L. ‘Coker 68–15′) but reduced germination of oat (Avena sativa L. ‘Coker 227′) to 0, lettuce (Lactuca sativa L. ‘Grand Rapids’) to 11%, and peanut (Arachis hypogaea L. ‘Florunner’) to 14%. A 10-6 M concentration did not affect the germination of any species tested. A 10-5 M concentration did not significantly decrease length or fresh weight of corn, morningglory, or wheat roots but had at least some adverse effect on all other species tested. At this concentration root length was less than 2/3 of the control for English pea, cucumber (Cucumis sativus L. ‘Ashley’), radish (Raphanus sativus L. ‘Scarlet Globe’), sicklepod, and soybean [Glycine max (L.) Merr. ‘Ransom’]. Metolachlor was supplied to germinating seeds of barley (Hordeum vulgare L. ‘Barsoy’), English pea, and corn either only in the shoot, seed, or root zone, or to all parts. One kg/ha applied in the shoot zone of barley and corn significantly reduced seedling height and dry weight but had no effect when applied in either the seed or root zone. Application in all zones was approximately twice as detrimental as when applied in only the shoot zone. Application of 4 kg/ha in only the shoot, seed, or root zones of English pea did not decrease seedling height or dry weight but application in all zones decreased these values about 98%. A 10-5 M concentration of metolachlor decreased leucine uptake by cucumber root tips but not its incorporation into protein. A 10-4 M concentration strongly reduced leucine uptake and slightly decreased leucine incorporation into protein.

Ragweed Parthenium (Parthenium hysterophorus L. # PTNHY) was found to exhibit autotoxicity. The active principle(s) were isolated from two parts of the plant using polar system. Principle(s) from the inflorescence were more effective than from the leaves. Leachates derived from the plant decreased percent cell survival and chlorophyll content. Leachates from leaves were more toxic to ragweed parthenium when applied to the foliage than when applied through the roots. The polar allelochemicals were highly effective in preventing rooting and sprouting of stem cutting and in reducing the regeneration potential of mature ragweed parthenium plants.

Cogongrass is a troublesome, invasive weedy species with reported allelopathic properties. The phytotoxicity of different constituents isolated from roots and aerial parts of this species was evaluated on garden lettuce and creeping bentgrass. No significant phytotoxic activity was detected in the methylene chloride, methanol, or water extracts when tested at 1.0 mg ml−1. However, the total essential oil extract of cogongrass aerial parts was active. Bioactivity-guided fractionation of this extract using silica gel column chromatography led to the identification of megastigmatrienone, 4-(2-butenylidene)-3,5,5-trimethyl-2-cyclohexen-1-one (also called tabanone), as a mixture of four stereoisomers responsible for most of the activity. Tabanone inhibited growth of frond area of lesser duckweed, root growth of garden onion, and fresh weight gain of garden lettuce with 50% inhibition values of 0.094, 3.6, and 6.5 mM, respectively. The target site of tabanone is not known, but its mode of action results in rapid loss of membrane integrity and subsequent reduction in the rate of photosynthetic electron flow.

The depths of leaching of S-ethyl dipropylthiocarbamate (EPTC), S-propyl butylethylthiocarbamate (pebulate), S-propyl dipropylthiocarbamate (vernolate), S-ethyl hexahydro-lH-azepine-l-carbothioate (molinate), and S-ethyl cyclohexylethylthiocarbamate (hereinafter referred to as R-2063) were compared in five different types of soils contained in glass columns. The depths of leaching in mineral soils were directly correlated with the water solubilities of the herbicides. The order of leaching from greatest to the least was molinate, EPTC, vernolate, pebulate, and R-2063. With all compounds tested, the depth of leaching decreased as the clay content of the soil increased. Leaching depth also decreased as organic matter increased. In peat soil containing 35% organic matter, no movement out of the treated zone could be detected with any of the thiocarbamate herbicides tested when leached with 8 in of water.

Horse purslane, a C4 species, is a branched, prostrate, and annual weed of upland field crops throughout the tropics. Experiments were conducted to determine the influence of various environmental factors on seed germination and seedling emergence of two populations of horse purslane. Seeds were collected from rice fields of the International Rice Research Institute (the IR population) and from sorghum fields of the University of the Philippines (the UP population); the two sites were 5 km apart in Los Baños, Philippines. Germination response of both populations was greater at 30/20 C and35/25 C day/night temperatures than they were at 25/15 C alternating day/night temperatures. Germination of both populations was greater in the light/dark regime than in darkness. In dark, depending on the temperature, seed germination of the UP population ranged from 37 to 62%, whereas seed germination of the IR population was < 20%. Exposure to 5 min at 117 and 119 C for the IR and UP populations, respectively, reduced germination to 50% of maximum germination. Osmotic potential of −0.26 MPa inhibited germination to 50% of the maximum for the UP population, whereas the corresponding value for the IR population was −0.37 MPa. Seeds placed on or near the soil surface had maximum emergence, and emergence declined with increase in seed burial depth. Seedling emergence of the UP and IR populations was 74% and 13%, respectively, for seeds placed on the soil surface. For both populations, no seedlings emerged from a soil burial depth of 6 cm or more. Germination and emergence responses to light and seed burial depth differed between the two populations of horse purslane. Residues on the soil surface of up to 6 Mg ha−1 did not influence seedling emergence of either populations. Knowledge gained in this study could contribute to developing components of integrated weed management strategies for horse purslane.

The critical period of weed control (CPWC) for ‘Pardina’ and ‘Brewer’ lentil was determined in field experiments near Pullman, WA, in 2008 and 2009. Trial treatments were kept either weed free for periods of 0, 14, 25, 35, 45, 60, 75, or ∼90 d after emergence (DAE), or weeds were allowed to grow before removal for periods of 0, 14, 25, 35, 45, 60, 75, or ∼90 DAE. Averaged across varieties, lentil with season-long weed interference had 29.5 and 32% seed yield reduction compared to weed-free lentils in 2008 and 2009, respectively. When measured at crop maturity, a 1% loss in lentil seed yield resulted from each 5.68 g m−2 of dry weed biomass. Based on a 5% yield loss threshold, the CPWC for lentil was estimated to be from 270 to 999 growing degree days (GDD), 22 to 57 DAE, or crop growth stage (CGS) 7 to the early pod stage during 2008. In 2009, the CPWC was 624 to 650 GDD, with no occurrence of a CPWC when estimated using DAE and CGS. Spiny sowthistle emerged and competed with the lentil crop later in the growing season than mayweed chamomile, indicating that mayweed chamomile may be an earlier and stronger competitor than spiny sowthistle.

A goosegrass biotype with suspected resistance to acetyl-CoA carboxylase (ACCase) inhibitors was identified in Georgia. The objectives of this research were to evaluate the resistance level of this biotype to ACCase inhibitors, efficacy of various herbicide mechanisms of action for control, and the physiological and molecular basis of resistance. In greenhouse experiments, the rate of diclofop-methyl that reduced dry shoot biomass 50% (SR50) from the nontreated for the resistant (R) and susceptible (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 was cross resistant to clethodim, fenoxaprop, and fluazifop. The R and S biotypes were equally susceptible to foramsulfuron, glyphosate, monosodium methylarsenate (MSMA), and topramezone. In laboratory experiments, the two biotypes had similar foliar absorption of 14C-diclofop-methyl. Both biotypes metabolized 14C-diclofop-methyl to diclofop acid and a polar conjugate, but the R biotype averaged ∼2 times greater metabolism than the S biotype. Gene sequencing revealed an Asp-2078-Gly substitution in the ACCase of the R biotype that has previously conferred resistance to ACCase inhibitors. A second mutation was identified in the R biotype that yielded a Thr-1805-Ser substitution that has been previously reported, but is not associated with ACCase resistance in other species. Thus, the Asp-2078-Gly substitution is the basis for resistance to ACCase inhibitors for the R biotype. This is the first report of ACCase-inhibitor resistance in goosegrass from the United States and from a turfgrass system.

Two species of invasive goldenrods, Solidago canadensis and Solidago gigantea, are spread over all territories of Lithuania. Solidago × niederederi, a putative hybrid between S. canadensis and native Solidago virgaurea, was found in 27 populations mixed with the parental species. This research represents the characterization of S. × niederederi in comparison to the other mentioned Solidago species, with the use of one-way analysis of variance (ANOVA), principal-components analysis (PCA), and discriminant analysis of a large data set. Twenty quantitative, four qualitative, and five ratio morphological and anatomical characteristics, pollen viability, and somatic chromosome numbers of the four Solidago species were studied with the aim to ascertain inter- and intraspecific variation and reliable features identifying S. × niederederi, and to test the hypothesized hybrid origin. The PCA of morphological and anatomical characteristics showed the clear intermediate position of S. × niederederi compared to S. canadensis and S. virgaurea. The results showed that the most informative characteristics for the distinction of hybrids from parental species are floral traits such as the lengths of the disc, ray florets, and involucre. The intermediate stomatal characteristics and sharply decreased pollen viability discovered herein could potentially be used as an additional discriminating character in Solidago hybrid identification and support the hybrid origin of S. × niederederi.

Biotypes of eastern black nightshade were found in Illinois and Indiana that were not controlled by postemergence applications of imazethapyr. Greenhouse studies were conducted to determine whole-plant responses to the imidazolinone herbicides imazethapyr and imazamox and to the sulfonylurea herbicide primisulfuron-methyl. The Illinois and Indiana resistant biotypes were highly resistant to imazamox and imazethapyr but were not cross-resistant to primisulfuron-methyl. DNA sequencing of acetolactate synthase (ALS) genes showed that the molecular basis for resistance in both resistant biotypes was a single base-pair mutation within Domain C that changed an alanine to a threonine in their encoded enzymes. In vitro enzyme assays showed that the Illinois resistant biotype's ALS enzyme was 789- and 881-fold less sensitive than that of the susceptible biotype to imazamox and imazethapyr, respectively. The Indiana resistant biotype's ALS enzyme was 110- and 158-fold less sensitive than that of the susceptible biotype to imazamox and imazethapyr, respectively. These results are consistent with the amino acid substitution found in the ALS enzyme of both resistant biotypes of eastern black nightshade.

Feather fingergrass is a major weed in agricultural systems in northern Australia and has now spread to southern Australia. To better understand the biology of this emerging weed species, its growth, development, and seed biology were examined. Under field conditions in South Australia, seedlings that emerged after summer rainfall events required 1,200 growing degree days from emergence to mature seed production and produced 700 g m−2 shoot biomass. Plants produced up to 1,000 seeds panicle−1 and more than 40,000 seeds plant−1, with seed weight ranging from 0.36 to 0.46 mg. Harvested seeds were dormant for a period of about 2 mo and required 5 mo of after-ripening to reach 50% germination. Freshly harvested seed could be released from dormancy by pretreatment with 564 mM sodium hypochlorite for 30 min. Light significantly increased germination. Seed could germinate over a wide temperature range (10 to 40 C), with maximum germination at 15 to 25 C. At 20 to 25 C, 50% germination was reached within 2.7 to 3.3 d, and the predicted base temperature to germinate was 2.1 to 3.0 C. The osmotic potential and NaCl concentration required to inhibit germination by 50% were −0.16 to −0.20 MPa and 90 to 124 mM, respectively. Seedling emergence was highest (76%) for seeds present on soil surface and was significantly reduced by burial at 1 (57%), 2 (49%), and 5 cm (9%). Under field conditions, seeds buried in the soil persisted longer than those left on the soil surface, and low spring–summer rainfall increased seed persistence. This study provides important information on growth, development, and seed biology of feather fingergrass that will contribute to the development of a more effective management program for this weed species in Australia.

Poverty brome (Bromus sterilis L.) [sterile or barren brome, syn. Anisantha sterilis (L.) Nevski] is a problematic UK arable weed. There are currently no confirmed cases of glyphosate resistance in any weed species in the United Kingdom or in B. sterilis worldwide. However, there are reports of poor control by glyphosate in this species. Here, we report experiments to confirm the suspected on-farm resistance of B. sterilis populations to glyphosate. Glyphosate screening and dose–response experiments established that glyphosate sensitivity of three UK B. sterilis populations exhibiting poor field control is outside the normal range of sensitivity of 30 sensitive populations and adjacent unexposed populations. Control of sensitive populations ranged from 49% to 82% and for suspected resistant populations from 21% to 30%. Dose–response ED50 values of sensitive populations ranged between 241 and 313 g ai ha−1; corresponding values of suspected resistant populations ranged between 420 and 810 g ha−1, and resistance indices ranged from 1.55 to 4.5. Suspected resistant populations were incompletely controlled at the recommended field rate of glyphosate (540 g ha−1), while adjacent unexposed populations were completely controlled. We conclude that some UK populations of B. sterilis have reduced glyphosate sensitivity and are in the process of evolving resistance. This is the first reported case of reduced glyphosate sensitivity in any UK weed species and in B. sterilis worldwide. This, coupled with increasing glyphosate use, highlights the need for increased vigilance and monitoring for glyphosate resistance in the United Kingdom.

Levels of inter- and intrapopulation genetic variation were determined in five North American populations of leafy spurge using chloroplast DNA (cpDNA) RFLPs and RAPD markers. Thirteen plastome types were identified among 123 individuals collected from five geographically separated populations. Number of plastomes within a population ranged from one to seven, with four of the populations having a predominate type plus one or more rarer types. Some plastome types were shared by populations, but plastome distribution among populations was nonrandom. RAPD markers indicated greatest relatedness among individuals within a population. Relatedness among populations as established through RAPDs was greater for geographically closer populations; this relationship was not observed for cpDNA markers. Differences in the range of movement for pollen and seed may account for differences between results of the cpDNA and RAPD analyses. The high degree of genetic variability among North American leafy spurge suggests possible multiple introductions or a high degree of variability within leafy spurge populations in its native range.