The storage root of alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.] growing in terrestrial habitats is an important metamorphic organ for its propagation, overwintering, and spread. However, the regulatory mechanism adventitious root expansion to form storage roots is still unclear. To reveal the changes accompanying the root-swelling process, we quantified sugar, soluble protein, and phytohormone content in adventitious and storage roots. Results demonstrated that sucrose, fructose, and soluble protein increased in storage roots, whereas abscisic acid (ABA), indoleacetic acid (IAA), brassinosteroid (BR), gibberellin, jasmonic acid, and cytokinin (trans-zeatin [tZ] and isopentenyladenine [iP] and the corresponding ribosides tZR and iPR). tZ-type (tZR and tZ) content decreased, suggesting the involvement of sugars and hormones in the formation of storage roots. To further reveal the molecular basis of A. philoxeroides’s ability to form storage roots and provide candidate genes for molecular function analyses, we assembled a de novo transcriptome of A. philoxeroides based on four sets of RNA-sequencing data. According to functional annotation and expression profiling, 42 unigenes involved in sucrose synthesis and hydrolysis were identified, in addition to 70, 58, and 78 unigenes in ABA, BR, and IAA signal transduction, respectively. The quantitative reverse transcriptase polymerase chain reaction analysis revealed 21 unigenes involved in sugar metabolism and hormone signal transduction were differentially expressed during the formation of storage roots. These results revealed metabolic changes during the formation of storage roots and provide candidate genes involved in sugar and phytohormone metabolism in A. philoxeroides.

Meadowfoam seed meal (MSM), a by-product after oil extraction, has potential uses for crop growth enhancement or weed control. The herbicidal effect of MSM is the result of a secondary metabolite, glucosinolate glucolimnanthin (GLN). Field evaluations were conducted using concentrations of 3, 5, and 7% by weight and two forms (nonactivated and activated) of MSM applied as soil amendments. No injury was observed on lettuce transplanted 7 d after MSM incorporation in 2011. Activated MSM at 7% reduced weed emergence up to 71%. Lettuce leaf N content was at least 8.5-fold greater in MSM treatments compared to the untreated control. Greater soil nitrate levels correlated with greater weed biomass in MSM-amended plots. Isothiocyanate, a potent herbicidal compound, was detected in soil incorporated with 7% activated MSM. In 2012, 2.86 g m−2 of activated MSM, applied as a split or single dose, was evaluated for weed control efficacy and crop injury response. The split MSM application provided weed control similar to that from the single MSM application. The split and single MSM applications inhibited spiny sowthistle emergence more than 95% compared to the untreated control. A single application of activated MSM as a PRE soil amendment suppressed weeds and increased lettuce yield.

Molecular techniques are useful tools for solving taxonomic confusion among species. Polymerase chain reaction (PCR) and polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) methods were applied for the identification of barnyardgrass, early watergrass, and late watergrass. Total DNA was extracted from 266 accessions, which were collected from different rice growing areas of Turkey. The two primer sets (trn-a and trn-b1, and trn-c and trn-d) specific to a target region of the intergenic spacer between trnT (UGU) and trnL (UAA) and the entire intron region of trnL (UAA), respectively, were used in PCR amplifications. Of the 266 accessions of Echinochloa spp., only eight accessions gave a similar fragment size, which was slightly shorter than 495 bp. The PCR product obtained with the primers trn-a and trn-b1 gave two fragments when EcoRI restriction enzyme was used in barnyardgrass and early watergrass. However, not all accessions of late watergrass were digested with this enzyme. In contrast to EcoRI, the PCR product obtained using the trn-c and trn-d primer set was digested into two fragments by using AluI restriction enzyme in all accessions of late watergrass; whereas, it was not digested in barnyardgrass and early watergrass. This molecular differentiation among barnyardgrass, early watergrass, and late watergrass supports the hypothesis that late watergrass is not a synonym of early watergrass in Turkish accessions.

Understanding the effects of crop management practices on weed survival and seed production is imperative in improving long-term weed management strategies, especially for herbicide-resistant weed populations. Kochia [Bassia scoparia (L.) A.J. Scott] is an economically important weed in western North American cropping systems for many reasons, including prolific seed production and evolved resistance to numerous herbicide sites of action. Field studies were conducted in 2014 in a total of four field sites in Wyoming, Montana, and Nebraska to quantify the impact of different crop canopies and herbicide applications on B. scoparia density and seed production. Crops used in this study were spring wheat (Triticum aestivum L.), dry bean (Phaseolus vulgaris L.), sugar beet (Beta vulgaris L.), and corn (Zea mays L.). Herbicide treatments included either acetolactate synthase (ALS) inhibitors effective on non-resistant B. scoparia or a non–ALS inhibiting herbicide effective for both ALS-resistant and ALS-susceptible B. scoparia. Bassia scoparia density midseason was affected more by herbicide choice than by crop canopy, whereas B. scoparia seed production per plant was affected more by crop canopy compared with herbicide treatment. Our results suggest that crop canopy and herbicide treatments were both influential on B. scoparia seed production per unit area, which is likely a key indicator of long-term management success for this annual weed species. The lowest germinable seed production per unit area was observed in spring wheat treated with non–ALS inhibiting herbicides, and the greatest germinable seed production was observed in sugar beet treated with ALS-inhibiting herbicides. The combined effects of crop canopy and herbicide treatment can minimize B. scoparia establishment and seed production.

In a recent essay, Harker and coauthors stated that considering herbicide resistance as a wicked problem “without clear causes or solutions” ignores what weed scientists know about the biology and management of herbicide-resistant weeds. In this response, we argue that this misrepresents what is meant by “wicked” and that the wicked problem concept is valuable in understanding the multifaceted nature of herbicide resistance as a human-caused phenomenon.

In North Carolina, the shoots of naturally-established, field grown, foliated specimens of turkey oak (Quercus laevis Walt.) and red maple (Acer rubrum L.) were treated in August with aqueous dilutions of three herbicidal products at three rates each. Simulated rainfall was applied at ½ or 1 inch at 5, 15, 60, or 120 min after herbicidal application. Responses measured 10 and 13 months after herbicidal application were percent control of original shoots, percent control of new shoots, shoot height, and number of live stems/plant. Neither the ester nor amine derivatives of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were reduced as to their action on woody plants by the simulated rainfall applied. The action on woody plants of 4-amino-3,5,6-trichloropicolinic acid (picloram) plus 2,4-dichlorophenoxyacetic acid (2,4-D) was markedly reduced by the application of all of the simulated rain treatments at any of the intervals at which they were applied following herbicidal treatment.

Field experiments over 3 yr at Lethbridge, Alberta, determined the effect of various downy brome densities and times of its emergence on winter rye biomass and seed yield. Downy brome reduced yields most when it emerged within 3 wk of rye, but densities of more than 100 downy brome m-2 were required to reduce yields by 20 to 30%. The greatest reductions in rye biomass (28%) and seed (33%) yields over the 3 yr occurred when 400 downy brome m-2 emerged with the crop. Downy brome, at densities up to 400 plants m-2, emerging 6 wk after rye or in early spring, reduced rye biomass and seed yield less than 10% in all years. Winter rye effectively shaded downy brome (40 to 90%) for much of the growing season.

One of the important steps in the maturing of a field of science is the establishment of a journal devoted to that field. A centralized means of publication is almost a necessity if a given branch of knowledge is to progress. “Weeds” is an attempt to fulfill that requirement for the science and art of weed control. If need is a measure of probable success, the success of “Weeds” is assured. Weed control literature has been published in every kind of journal — agronomic, horticultural, engineering, chemical, botanical, — and farm papers of all types, to make only a beginning.

Imbibition of pretreated velvetleaf (Abutilon theophrasti Medic.) seed was most rapid when the chalazal region was wetted, but submergence of the chalaza in water delayed seed germination. Respiratory measurements indicated that the seed coat did not inhibit gas exchange under our experimental conditions. Effects of 2,4-dinitrophenol on germination indicated that radicle emergence and radicle growth were distinct processes, and that radicle emergence was more sensitive to low concentrations of the uncoupler.

Aerial applications of pelleted tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N, N′-dimethylurea} at 1 kg/ha to rangeland reduced canopy cover of the subshrub false broomweed (Ericameria austrotexana M.C. Johnst.) by 69 to 78%. Complete control was obtained with 2 kg/ha of tebuthiuron. Picloram (4-amino-3,5,6-trichloropicolinic acid) pellets applied at 2 kg/ha controlled false broomweed in two of four experiments; effectiveness of soil-applied picloram appeared to depend upon sufficient rainfall to move the herbicide into the soil soon after treatment. After the first growing season following application, density of herbaceous species tended to be higher in plots receiving either herbicide than in untreated plots. Picloram suppressed curlymesquite [Hilaria berlangeri (Steud.) Nash], but had little effect on other components of the herbaceous vegetation. Abundance of curlymesquite increased substantially following applications of tebuthiuron, at the expense of annual and short-lived perennial grasses and herbaceous broadleaf species.

Two applications of benefin (N-butyl-N-ethyl-α,α,α,-trifluoro-2,6-dinitro-p-toluidine), profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], prosulfalin N-[[4-(dipropylamino)-3,5-dinitrophenyl]sulfonyl]-S,S-dimethylsulfilimine, and napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] provided full-season large crabgrass [Digitaria sanguinalis (L.) Scop.] control in turfgrass. Benefin was applied at 3.3 kg/ha in March and 2.2 kg/ha in May while other herbicides were applied at 2.2 kg/ha in March and May. Satisfactory goosegrass [Eleusine indica (L.) Gaertn.] control was obtained with a single March treatment with prosulfalin, but two applications of napropamide in March and May were required for similar control. None of the herbicide treatments severely injured common bermudagrass [Cynodon dactylon (L.) Pers.] or Kentucky bluegrass [Poa pratensis (L.) ‘Common’] in these studies. Prosulfalin at 6.6 kg/ha applied as single treatment or 3.3 kg/ha in each of two applications resulted in moderate injury to Kentucky bluegrass in 1 of 2 yr.

At least two weedings within the first 5 weeks after sowing are necessary to minimize yield reduction caused by weeds in cowpea [Vigna unguiculata (L.) Walp.]. During a 3-yr study, a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 2.0 to 3.0 kg/ha, DCPA (dimethyl tetrachloroterephthalate) at 10.0 kg/ha, or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] at 2.0 or 2.5 kg/ha controlled most annual grasses effectively. Itchgrass (Rottboellia exaltata L.) was controlled with pendimethalin at 2.5 kg/ha, but metolachlor had no effect on this weed. These herbicides caused no crop injury and cowpea grain yield was as good as in the handweeded and weed-free plots. Alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl) acetanilide] applied preemergence at 2.0 kg/ha was effective against annual weeds, but was phytotoxic to cowpea.

Three grass selective herbicides, sethoxydim, fluazifop, and haloxyfop, applied to wild oat plants at the five-leaf stage inhibited growth and induced chlorosis in leaves. Young and actively growing tissues were affected first. Stem elongation in wild oat was inhibited within 2 days of treatment with sethoxydim and within 5 days of treatment with fluazifop or haloxyfop. At these same observation times, internodes that were elongating rapidly at the time of treatment were constricted at the base. These symptoms were followed by necrosis of the internode tissue. Histological examination of the affected internodes indicated that the herbicides inhibited cell division in very young internodes and inhibited both cell division and cell elongation in slightly older internodes. Initial injury occurred in the epidermal, cortical, and procambium cells of the peripheral regions of the stems located at the base of the affected internodes. Necrosis then progressed to the center of the stem tissue and all cells in the internodes were killed within 14 days of treatment. All three herbicides caused similar morphological and histological effects on developing wild oat stems.

Greenhouse and laboratory experiments were conducted to evaluate the tolerance of four commercial sugarbeet varieties to s-metolachlor and dimethenamid-P, determine the principle site of absorption of these herbicides, and determine the physiological basis for differential tolerance among varieties to these herbicides. ‘Beta 5833R’ was the most tolerant sugarbeet variety, and ‘Hilleshog 7172RZ’ was the most susceptible sugarbeet variety to injury from s-metolachlor and dimethenamid-P. The primary site of s-metolachlor and dimethenamid-P absorption was through the sugarbeet roots; however, some absorption occurred through the sugarbeet hypocotyl. Sugarbeet injury was greater from dimethenamid-P than s-metolachlor when sugarbeet was grown in soil. However, when sugarbeet was grown hydroponically, injury from the herbicides was similar, indicating that the relative availability of these herbicides in the soil greatly influenced sugarbeet injury. Reduced translocation and slower metabolism of 14C-dimethenamid-P in both the roots and shoots of the sugarbeet plants most likely contributed to the greater susceptibility of sugarbeet to dimethenamid-P compared with s-metolachlor. Metabolism of 14C-herbicides in sugarbeet shoots was 0.7 to 2.1 h slower in the more susceptible sugarbeet varieties compared with the more tolerant variety, Beta 5833R. This was the most significant factor contributing to differences in sugarbeet variety tolerance to both s-metolachlor and dimethenamid-P.

Spreading dogbane is an important weed of wild blueberry fields that decreases yields and hinders harvest operations. A range of experiments was conducted to evaluate the impact of abiotic factors on dogbane seed germination. Freshly harvested seeds were largely nondormant with viability ranging between 67 and 84%. Prolonged exposure to light neither promoted nor inhibited germination. Germination rates and total seed germination varied with temperature and osmotic potential. Significantly fewer seeds germinated at 5 C compared with 10, 15, and 20 C. There was a significant quadratic relationship between dogbane germination and osmotic potential, with significant numbers of seeds germinating at levels as low as −0.5 MPa. Emergence rates declined exponentially with depth in the soil and as many as 9% of seeds germinated but were unable to reach the soil surface. Results indicate that substantial seed germination in blueberry fields is possible and primary dispersal without wind occurs over a very short distance.

A study was undertaken to determine whether the relative leaf stages of common annual weeds and crops could serve as a reliable indicator of the time of weed emergence. Ten annual broadleaved and grass weeds were sown at successive intervals in field corn and soybean at Harrow, ON, Canada, in 1997, 1998, and 1999. All weeds emerging at a particular crop leaf stage were assigned to a cohort. Leaf numbers of the crop and different weed cohorts were recorded at 2- to 3-d intervals up to the eight-leaf stage of corn and the fourth trifoliate of soybean. For each weed species, categorical data analysis revealed a high degree of association between the leaf stage of a crop and the leaf number expected for an individual weed of a given cohort. For example, by the third trifoliate of soybean, most of the weeds emerging with the crop (VE cohort) had 8 to 10 leaves, whereas weeds in the V1, V2, and V3 cohorts averaged about seven, four, and two leaves, respectively. Year to year variation in the correspondence between crop and weed leaf numbers generally was small once variation due to time of weed emergence was removed, with one exception. Dry surface soil conditions during emergence of the VE cohort in corn in 1999 resulted in delayed leaf appearance of many weeds with respect to the crop. The relationship between weed and crop leaf stages can provide information for management decisions in two ways: (1) it indicates the relative time of weed emergence in assessing the need for control, and (2) it indicates the crop stage at which scouting for particular weed leaf stages should occur.

To assess the risk of gene movement between winter wheat and jointed goatgrass, information about the reproductive development of jointed goatgrass, winter wheat, and related hybrid plants is required. Seedlings from five jointed goatgrass populations, winter wheat, spring wheat, and jointed goatgrass by wheat reciprocal hybrid plants were exposed to 4, 7, or 10 C temperatures for 0, 2, 4, 5, 6, 6.5, 7, or 8 wk. Vernalized seedlings were transferred to a greenhouse set to 30/18 C day/night temperatures and 16-h photoperiod. Growth stages on all plants were recorded twice a week. All spring wheat and spring wheat related hybrid plants reproduced (as measured by the first reproductive node) in the absence of vernalization. Plants of jointed goatgrass population A-R, winter wheat, and winter wheat related hybrids were unlikely to reproduce in the absence of vernalization. Plants of jointed goatgrass populations B-W, G-S, E-S, and F-W reproduced in the absence of vernalization, and the likelihood that these plants would reproduce was different from all other plants. Plants that entered their reproductive phases together were not in synchronous development at anthesis. Plants in these studies differentially passed through the reproductive phases between the first reproductive node and anthesis. Our results demonstrate that variation in vernalization response exists among several jointed goatgrass populations, and reveal that the reproductive behavior of vernalized jointed goatgrass plants at anthesis is delayed compared to vernalized winter wheat and related hybrid plants. Hybrid plants produced between spring wheat and jointed goatgrass were vernalization insensitive. We hypothesize that hybridization between wheat and jointed goatgrass occurs as a result of cross-pollination between the younger reproductive tillers of jointed goatgrass and older reproductive tillers of wheat. The use of an early maturing wheat cultivar may exploit the difference in reproductive development and reduce the risk of hybrid production.

Soil samples with and without a past history of dimethyl-2,3,5,6-tetrachloroterephthalate (DCPA) treatment were obtained from New York. A third sample was obtained from a field in Colorado where DCPA had been ineffective as a herbicide. The populations of bacteria and actinomycetes in these soils were determined and the actinomycetes were more prevalent in the samples with previous DCPA treatment than in untreated samples. Subsequent treatment resulted in an increase in actinomycete population and little change in bacterial population. In pure culture and in soils, the addition of DCPA had no adverse effect upon microbial growth, and several microorganisms appeared to utilize the herbicide as a carbon source. Two degradation products were methyl-2,3,5,6-tetrachloroterephthalate and 2,3,5,6-tetrachloroterethalic acid.

Nematodes are the most damaging pathogens of cotton and one of the most important pathogens of peanut. Weeds can support nematode reproduction and reduce the effectiveness of crop rotation as a management tool. This study documents the relative host status of tropical spiderwort for (1) the reniform nematode and the southern and peanut root-knot nematodes and (2) the fungal pathogen southern stem rot. A reproductive factor (RF) was calculated for each nematode (final number divided by initial number). Galling was estimated (0–10 scale) for the root-knot species. The southern root-knot nematode reproduced well on tropical spiderwort, with a gall rating of 3.1 and an RF of 15.5. The peanut root-knot nematode also reproduced well on tropical spiderwort, with a gall rating of 2.1 and an RF of 7.2. Trials with the reniform nematode were analyzed independently. In the first trial with the reniform nematode, the RF was 2.4 on tropical spiderwort and 1.4 on cotton. In the second trial, the RF was 3.6 on tropical spiderwort and 13.5 on cotton. The severity of symptoms caused by southern stem rot was estimated on a scale of 0 to 10. In the first trial, peanut had a disease severity rating of 4.0 and tropical spiderwort had a rating of 1.4, and the fungus could be seen growing on 40% of the tropical spiderwort plants. In the second trial, peanut had a disease severity rating of 10.0 and tropical spiderwort had a rating of 5.0, but the fungus could be seen growing on all of the tropical spiderwort plants. It appears that tropical spiderwort is a sufficiently good host for some of the primary nematode and fungal pathogens of major crops in the southeastern United States that its presence at typical plant population densities will greatly reduce the pathogen-suppressive effects of crop rotation.

Research was conducted to formulate a seedling johnsongrass emergence model as influenced by temperature and burial depth using the poikilotherm rate equation. A series of constant-temperature growth chamber experiments with johnsongrass seed buried at various depths in fritted clay was conducted to develop a temperature/burial emergence database. The poikilotherm rate equation was fit to the emergence data from burial depths of 0 to 2.5 cm at constant temperatures between 20 and 44 C. These data were then combined to formulate a single poikilotherm rate equation to model the emergence of seedling johnsongrass from 0 and 2.5 cm deep and 20 to 44 C. This combined model was validated against two independent emergence data sets with good results.