A framework is presented to consider the value and utility of molecular-based research in weed science. Four themes are used to illustrate why adopting molecular approaches might be helpful. First, the rationale for academic institutions adopting molecular approaches is outlined, including strengths, weaknesses, opportunities, and threats (SWOT) analysis. Second, research strategy and synergies developed into other functions, such as education, consultancy, and business, is considered. Third, project management as a vehicle for integrating technical and personnel skills is examined. Finally, specific examples of outputs such as the application of functional genomics for herbicide discovery are described. The adoption of molecular-based methods can have far-reaching benefits in agriculture and biotechnology. Communicating these benefits within the scientific community and beyond, particularly to end users, is of fundamental importance.

Winged sea lavender [Limonium lobatum (L.f. Chaz)] is emerging as a significant weed of field crops in southern Australia. Several environmental factors affecting germination and seedling recruitment were examined to provide a better understanding of the behavior of its seedbank. At maturity, weed seeds were dormant for a period of around 2 mo, but dormancy was easily broken with scarification or by pretreatment with 564 mM NaOCL for 30 min, which confirms the role of the seed coat in regulating seed germination. Exposure to light significantly increased germination. Seeds were able to germinate over a broad range of temperatures (5 to 30 C), with maximum germination (~92%) at temperatures between 10 and 30 C. At 20 to 25 C, 50% germination was reached within 1.3 to 2 d, and the predicted base temperature for germination of the two populations ranged from 1.4 to 3.9 C. The NaCl concentration required to inhibit germination by 50% was 230 mM, with some seeds capable of germination at salinity levels as high as 480 mM. These results indicated greater tolerance to salinity in L. lobatum than many other Australian agricultural weed species previously investigated. Seedling emergence was the highest (51% to 57%) for seeds present on the soil surface and was significantly reduced by burial at 1 cm (≤11%) and 2 cm (≤2%), with no emergence at 5 cm. Under field conditions, seedling recruitment varied considerably among the three experimental sites. The level of seedling recruitment was negatively associated with rainfall received at the site, organic carbon (OC) level, and microbial biomass of the soil. Rapid decay of weed seeds in high-OC soils appears to be an important determinant of seedling recruitment in this species and could explain greater occurrence of L. lobatum on soils with low OC and low microbial activity in low-rainfall areas of southern Australia. Furthermore, many such soils in southern Australia are affected by salinity, which would enable L. lobatum to be more competitive with crops and other weeds present at a site.

Yellow starthistle is an invasive plant of canyon grasslands in north-central Idaho. The distribution of yellow starthistle is associated with general landscape characteristics that include land use and specific terrain-related features such as elevation, slope, and aspect. Slope and aspect can be considered as indicators of plant community composition and distribution. Hence, these variables may be incorporated into prediction models to estimate the likelihood of yellow starthistle occurrence because plant communities differ in susceptibility to invasion. An empirically derived nonlinear model based on landscape characteristics has previously been developed to predict the likelihood of yellow starthistle occurrence in north-central Idaho. Although the model was used to predict the invasion potential of yellow starthistle into new areas, it could also be used as auxiliary data for classifying this weed species in remotely sensed imagery. To accomplish this, the predicted values from the model are regarded as prior information on the presence of yellow starthistle. A Bayesian image classification algorithm using this prior information is then applied to a corresponding set of remotely sensed data. This results in a map indicating the posterior probabilities of yellow starthistle occurrence given the landscape characteristics. This technique is demonstrated and is shown to reduce omissional error rates by 50% when the landscape characteristics are incorporated into the classification process.

Survival of hydrilla (Hydrilla verticillata Royle) plants and propagules after removal from water and desiccation under controlled conditions were studied. Both apical and sub-apical sections of hydrilla plants were physiologically alive after drying for 16 h at 30 C and 40% relative humidity. Tubers survived drying conditions longer than turions. There was 16.7% sprouting in tubers that had been dried for 64 h, while percent sprouting of turions decreased sharply as the drying period increased from 0 to 8 h.

Distribution patterns of foliar applied herbicides can be studied by x-ray element mapping provided the herbicide contains an atom with an atomic number of 11 (sodium) or greater. The suitability of an herbicide for element mapping increases as the number of similar detectable atoms per molecule increases. Herbicides containing one detectable atom per molecule provide usable element maps at concentrations of 1.12 kg/ha and higher. Inaccurate element maps can result from: (1) Formulation components containing detectable atoms the same as those of the active ingredient. (2) Herbicide volatility during analysis due to reduced pressures and heating. (3) Specimen topography preventing x-ray detection at some locations on the plant surface. (4) Herbicide concentrations that are below the minimum detectable limit. If adequate precautions are followed in the use of x-ray element mapping, a wide range of uses exist in weed science.

Bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifway’] injured by MSMA (monosodium methanearsonate) plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] or 2,4-D [(2,4-dichlorophenoxy)acetic acid] plus mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} plus dicamba (3,6-dichloro-o-anisic acid) recovered more rapidly when nitrogen (N) was applied in sequence with the herbicides than when no N was applied. Bermudagrass recovery was faster with less injury within 2 weeks after herbicide treatment when N was applied at the first MSMA plus metribuzin treatment or when N was applied at 2 weeks after the first 2,4-D plus mecoprop plus dicamba treatment. Turf quality at 4 weeks or later was consistently as good or better in plots where N was applied at 2 weeks after the first application of either herbicide combination than when N was applied earlier.

MSMA (Monosodium methanearsonate) applied postemergence at 4.5, 6.7, or 9.0 kg/ha controlled wild oat (Avena fatua L.) in new plantings of Kentucky bluegrass (Poa pratensis L. ‘Pennstar’) and in perennial ryegrass (Lolium perenne L. ‘Reveille,’ ‘Pennfine’). MSMA at 4.5 kg/ha was almost as effective as the higher rates in controlling wild oat. MSMA at 2.2 kg/ha was less effective in some experiments. Visual injury to the perennial grasses was negligible. Satisfactory grass stands developed at all MSMA rates. Perennial ryegrass seed yields were higher than the untreated check in most experiments when MSMA was applied at 4.5, 6.7, or 9.0 kg/ha before the grass reached the boot stage. When MSMA was applied after the ryegrass reached the boot stage, some of the treatments reduced ‘Reveille’ perennial ryegrass seed production.

The uptake, translocation, and fate of 14C-labeled 3,6-dichloro-o-anisic acid (14C-dicamba) were studied in wheat (Triticum aestivum L., 'Selkirk’) and wild buckwheat (Polygonum convolvulus L.) as resistant and susceptible species, respectively. Selectivity could not be explained by interspecific differences in uptake of 14C-dicamba by leaf sections submerged in exogenous solutions. 14C-dicamba accumulated in meristems of wild buckwheat but not in the youngest tillers of wheat. Moreover, wheat main culms conjugated or metabolized 14C-dicamba more quickly than did wild buckwheat meristems. Therefore, selectivity of dicamba apparently was related to interspecific differences in translocation and metabolism.

Benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid) formulated as the dimethylamine salt was evaluated for common cocklebur (Xanthium pensylvanicum Wallr.) and prickly sida (Sida spinosa L.) control in soybeans [Glycine max (L.) Merr.] between 1977 and 1979. Benazolin was applied alone or in admixtures with acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide], dinoseb (2-sec-butyl-4,6-dinitrophenol) plus naptalam (N-1-naphthylphthalamic acid), and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] over-the-top of soybeans {V3 to V12 [V(N); vegetative stage with “N” nodes on the main stem beginning with the unifoliolate node]}. Benazolin effectively controlled common cocklebur at rates of 0.2 and 0.4 kg/ha. Soybean tolerance was acceptable even with a repeat application of 0.4 kg/ha. Early-season (July) control was less than late season (August) because it took 2 to 3 weeks for benazolin to kill common cocklebur. Prickly sida control was poor with benazolin even at 0.6 kg/ha. Soybean tolerance and seed yields were higher when soybeans were treated with admixtures of benazolin plus bentazon than with benazolin alone. Antagonism was observed with this admixture for prickly sida and late-season common cocklebur control. Antagonism was eliminated with ratios of benazolin to bentazon of 1 to 3 applied in a single application or a 1 to 1.5 ratio repeated.

Tissue and cell culture offer weed scientists many opportunities to research herbicide effects on plants. This review will discuss examples in which plant cells grown in vitro have been used to study herbicide action. Plant cell and tissue culture have many advantages over the use of whole plants; however, several disadvantages that exist are discussed. Cell cultures can be established for most plant species and provide a relatively homogeneous system for studying herbicide action. Responses of plant cells to herbicides are usually correlated with responses at the whole plant level, and cells have the advantage of posing fewer physical barriers to herbicide uptake and translocation. Cell culture techniques discussed include: screening candidate herbicide compounds; investigating herbicide efficacy, mechanism of action, metabolism, and uptake; and ascertaining mechanisms of herbicide resistance, selecting for resistance, and regenerating crops.

Absorption of the isooctyl ester of (2,4,5-trichlorophenoxy)-acetic acid varied more than 20% in four woody species when incident light intensity was increased from 40 to 4,000 ft-c. Variations in translocation of the herbicide of 45 to 50% in post oak (Quercus stellata Wangenh.) and water oak (Quercus nigra L.) accompanied changes in illumination. Light intensity did not affect translocation in longleaf pine (Pinus palustris Mill.) or American holly (Ilex opaca Ait.)

Weed species respond to the cumulative effect of multiple practices employed within weed management systems. However, this response is rarely studied at the system level, and the relationships between weed communities and management systems in crops are not well understood. We used multivariate analyses to assess relationships among tomato management systems and weed species identified through on-farm sampling of 59 fields. Giant foxtail, common lambsquarters, prickly sida, and carpetweed were common in all systems. Eastern black nightshade was common in the conventional processing and mixed fresh-market systems but largely absent from the organic system. Barnyardgrass and goosegrass were common in the organic fresh-market system but not in the other systems. Canonical correspondence analysis identified distinct associations between specific species and the management systems. Common purslane was strongly associated with the rain-fed, mixed fresh-market system, and barnyardgrass, goosegrass, yellow nutsedge, and green foxtail were associated with the irrigated, organic fresh-market system. Indicator species analysis identified five species that were significant indicators of the organic, fresh-market system and one species that was a significant indicator of the rain-fed, mixed fresh-market system. Weed populations persist or increase when a set of species-specific environmental conditions are met. The association of weed species in this study with particular systems supports the hypothesis that weed communities are strongly affected by management systems.

In greenhouse studies, postemergence applications of 0.1 or 0.3 kg ai/ha mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} as a tank mixture with 0.3, 0.4, or 0.6 kg ai/ha acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, or as a pretreatment 3, 5, or 7 days prior to acifluorfen treatment, often increased injury to ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. ♯3 IPOHE], velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), compared to the injury from either herbicide alone. All sequential treatments with 0.1 kg ai/ha mefluidide and 0.3 kg ai/ha acifluorfen increased injury and decreased dry weight of ivyleaf morningglory and velvetleaf when compared with 0.6 kg/ha acifluorfen alone.

The genetic variation of quackgrass as a species and the array of environments in which it is found indicate that selection in these different environments could lead to differentiation among quackgrass populations. Yet, a highly diverse environment might not promote the genetic divergence of quackgrass if it poses contradictory selection pressures. To assess the extent of divergence among quackgrass populations, this study compared the morphology of populations of quackgrass for 1 yr in Rosemount, MN, in a “common garden” study. The quackgrass was initially collected from three different farming systems in southeast Minnesota: corn–soybean (CS), oats–hay–corn (OHC), and permanent pasture (PP). The systems represent pasture or arable land and differ in cropping rotations and levels of disturbance. Although no differences among farming systems were detected in multivariate or univariate comparisons, a significant farming system effect was detected between CS and PP systems when the most diversified system, OHC, was excluded from the analysis. Consistent with this result, a principal components analysis suggested that plants from two of the three farming systems exemplified contrasting modes of perennial plant growth. Relative to each other, the CS plants showed more features of the “guerrilla” growth mode (longer intra-ramet distances, sparse, large patches), whereas PP plants showed more “phalanx” mode features (short intra-ramet distances, dense, smaller patches). Plants from the most diversified system, OHC, did not fit into either growth form, and for this farming system, the variation among populations was the highest. The results suggest that the CS and PP systems selected for distinct growth forms, whereas the diversified OHC system did not. This is consistent with the hypothesis that diversification of a farming system and weed management decreases the risk of evolution of a weed population highly adapted to control measures used in that farming system.

Metham (sodium methyldithiocarbamate), applied alone or in combination with dichlobenil (2,6-dichlorobenzonitrile) in foam, was effective in killing roots of eucalyptus (Eucalyptus camaldulensis Dehnhardt) or willow (Salix hindsiana Benth.). An air-aqueous (19 to 1) foam of these herbicides was at least 20 times as effective as the aqueous mixture alone. Killing of the root with metham was rapid and extended above the lower treated portion, with the extent of necrosis resulting from translocation of the herbicide varying with concentration of metham that was used. The amount of the root killed with dichlobenil was limited to the treated area regardless of concentration. Four weeks were required to control the larger roots. Root killing with metham proceeded via both the aqueous and vapor phases. Results from labeling trees with 14C-assimilates indicated that neither translocation nor accumulation were greatly affected by metham or dichlobenil except in the tissues actually killed. However, transport and accumulation into untreated roots were reduced for a few weeks by dichlobenil. Similar results were obtained with cotton (Gossypium hirsutum L. ‘Acala’) treated with dichlobenil.

Cacodylic acid (hydroxydimethylarsine oxide) and MSMA (monosodium methanearsonate) gave slightly-visible inhibition of bacterial growth in pure culture at 1000 mg/L arsenic and moderate inhibition at 10,000 mg/L arsenic. There were no effects at 100 mg/L arsenic. Carbon dioxide evolution from three kinds of forest floor declined with increasing concentrations of MSMA and cacodylic acid. Increasing concentrations of MSMA caused an increase in carbon dioxide evolution from soil but cacodylic acid had no effect. Concentrations less than 10 mg/kg arsenic forest floor including L, F, and H horizons, or soil had no pronounced effect on organic matter decomposition.

Pricklypear (Opuntia spp.) is a major constraint to rangeland livestock production in several resource areas of Texas. The phenological and physiological stages of pricklypear have heretofore been ignored in relation to timing of herbicide applications. The phenology, percent total nonstructural carbohydrates (TNC), and water content in Lindheimer pricklypear (Opuntia lindheimeri Engelm. # OPULI) were monitored biweekly for 2 yr in the southern Rolling Plains of Texas. TNC in cladophylls, crowns, and roots declined sharply from bud break (late March to late April) through the period of rapid development of new cladophylls and fruits, with minimum levels occurring during mid-July to early August. This depletion period coincides with the period when control has traditionally been attempted with broadcast applications of translocated herbicides with erratic results. Replenishment of TNC in cladophylls and basal crowns occurred during August through March or mid-April; major increases in root TNC occurred from early autumn through midwinter. Application of herbicide in late summer, autumn, or winter when TNC is being replenished in organs bearing meristematic tissue may be more effective for pricklypear control if the herbicide is translocated with photosynthates.

Intact wheat plants and wheat calli responded similarly to varying concentrations of imazapyr. Fifty percent growth inhibition of wheat callus occurred with 0.05 μM imazapyr after 70 d. As imazapyr concentration increased from 0 to 10 μM, the free isoleucine, leucine, and valine decreased from 160 to 35, 260 to 49, and 310 to 59 pmol mg−1, respectively. Resistant calli, which had relative growth rates exceeding a calculated upper prediction interval, were obtained by in vitro selection at 2 and 5 μM imazapyr. Resistant calli growing on 2 μM imazapyr had free isoleucine, leucine, and valine concentrations intermediate to the control and susceptible callus.

The double pot technique was used to study the effects of uptake site of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl—phenyl]-4(1H)-pyridinone} on early shoot and root development of soybean [Glycine max (L.) Merr. ‘Williams’] and cotton (Gossypium hirsutum L. ‘Acala SJ-1′). Soybean is susceptible and cotton is resistant to fluridone. Root uptake in soybean resulted in increased shoot length in the epicotyl and shoot apex, reduced shoot fresh weight, chlorosis of primary and trifoliolate leaves, as well as reduced root length, branching, and fresh weight. Shoot uptake resulted in reduced shoot length above the hypocotyl, reduced shoot weight, severe chlorosis of primary leaves, and inhibition of trifoliolate leaf formation. The reduction in the root length, branching, and weight was less by shoot uptake than by root uptake. In cotton, root uptake resulted in reduced shoot length in the epicotyl and shoot apex, slight reduction in shoot weight, no effect on chlorosis of cotyledon leaves, moderate to slight chlorosis of the true leaves, and no effect on root length, branching, or fresh weight. Shoot uptake resulted in reduced length of all shoot components and shoot weight, chlorosis of cotyledon leaves and the true leaves, and reduced root length, branching, and weight. Compared to soybean, cotton required much higher fluridone concentrations to show the above effects. It was generally concluded that in soybean, uptake by both the root and the shoot contributed significantly to the injury, whereas in cotton, shoot uptake was relatively more important.

Laboratory studies were conducted to determine the ability of the extenders dietholate and SC-0058 to prevent enhanced biodegradation of EPTC and butylate applied to Wisconsin soils with different histories of carbamothioate herbicide use. Enhanced EPTC and butylate biodegradation occurred in soils previously treated with those herbicides. Enhanced biodegradation of dietholate occurred on soils previously treated with that extender plus either EPTC or butylate. Enhanced dietholate biodegradation was observed when applied alone or in combination with butylate or EPTC. Application with dietholate prevented enhanced biodegradation of butylate but not EPTC even though enhanced biodegradation of dietholate was occurring. Enhanced biodegradation of SC-0058 did not occur. SC-0058 prevented enhanced EPTC and butylate biodegradation even in soils previously treated for three consecutive years with the respective herbicide plus SC-0058. Application of either 1.1 or 2.2 kg/ha SC-0058 plus 6.7 kg/ha EPTC provided equal or better wild proso millet control and sweet corn yields than applications of EPTC alone or EPTC plus dietholate.