Broomrapes (Orobanche and Phelipanche species, Orobanchaceae) are obligate root parasites of dicotyledonous plants. This taxonomic group includes seven weedy parasites of agricultural crops that damage vegetables, sunflower (Helianthus annuus L.), and legumes. Processing-tomato (Solanum lycopersicum L.) fields in Israel have been recently found infested with a new broomrape, first identified as nodding broomrape (Orobanche cernua Loefl.) based on its host. However, its morphology resembled the closely related sunflower broomrape (Orobanche cumana Wallr.), an obligate parasite of sunflower. The new race (CUCE) parasitized sunflower, tomato, and tobacco (Nicotiana tabacum L.) in vitro, in a polyethylene bag system and in pots. Its seeds germinated in response to strigolactones (orobanchol, 5-deoxystrigol, 2′-epiorobanchol, and GR24) and dehydrocostus lactone (DCL), whereas O. cumana seeds responded only to DCL and GR24, and O. cernua only to strigolactones. Based on morphological similarities with O. cumana, shared molecular markers with O. cumana, ability to parasitize sunflower and respond to sunflower-germination stimulants, it was concluded that CUCE is a new race of O. cumana, with a host range expanding to Solanaceae crops. While being an important noxious weed of sunflower, this new O. cumana race is currently spreading and posing a threat to processing tomato in Israel. This finding is an alarming indication that broomrapes can shift host range and that similar new races of O. cumana could potentially appear in other countries.

If there was no heavy rainfall or surface irrigation before corn emergence, as ethyl-N,N-di-n-propylthiolcarbamate (EPTC) at 3 lb/A was incorporated deeper into the soil, more corn plants were injured, the height of plants was reduced, and a loss in weight or yield occurred, although the germination of the corn seed was not affected. Implements used to incorporate EPTC did not produce significantly different amounts of corn injury where used at the same depth.

Metabolic incorporation of adenine-2-14C by Saccharomyces cerevisiae was examined for alterations produced by 3-amino-1,2,4-triazole (amitrole) and histidine. The radioactivity recovered from cells after a 4-hour incubation was found predominantly in ethanol-insoluble components (nucleic acids and proteins) of untreated cultures. Amitrole inhibited incorporation of 14C into insoluble components. Carbon-labeled imidazoleglycerol phosphate, a precursor of histidine, and labeled imidazoleglycerol accumulated in the ethanol-soluble fraction of amitrole treated cells. Imidazoleglycerol accumulated in the external medium. Histidine prevented 14C incorporation into the hot trichloroacetic acid-insoluble residue (protein), prevented amitrole-induced imidazoleglycerol and imidazoleglycerol phosphate accumulation, and circumvented amitrole inhibition of 14C incorporation into the hot trichloroacetic acid-soluble (nucleic acids) fraction.

Common lambsquarters was treated with metamitron (M) and glyphosate (G) to investigate chlorophyll content as a single, biological parameter for indicating sub-lethal-treated weeds. In three different greenhouse experiments the herbicides were applied at dose rates of 1/8, 1/4 and 1/2 times the M-recommended dose rate (= 0.7 kg ai ha−1), and 1/16, 1/8, and 1/4 times the G-recommended dose rate (= 1.44 kg ai ha−1), respectively. Three weeks after herbicide application the chlorophyll content in leaves of plants treated with 1/2 M was lower than the control. At the same time the chlorophyll content in leaves of plants treated with 1/8 and 1/4 M was higher than the control. The chlorophyll content in the leaves of plants treated with 1/16 and 1/8 G was also higher than the control, but the chlorophyll content in the leaves of plants treated with 1/4 G was equal to the control. A dose of 1/2 M killed 30% of available plants within 29 d, but most of the plants were still alive after 29 d when 1/4 M, 1/8 M, 1/4 G, 1/8 G and 1/16 G had been used. The fresh weight of the biomass reflected the fitness of the plants observed with time and was related to chlorophyll content. The dry weight of the biomass, however, was probably related to the typical action of metamitron and glyphosate. Measurements with a remote sensing technique supported the measurement of chlorophyll with a spectrophotometer confirming a significant discrepancy with time between a herbicide's affect on chlorophyll content and on plant growth. Because differences in chlorophyll content may have caused differences in the progress of plant degradation in sub-lethal- and lethal-treated plants, it is concluded that the chlorophyll content can be used as a single, biological parameter for indicating sub-lethal dose rates of metamitron and glyphosate.

Intraspecific and interspecific interference effects on growth, gas exchange, and water potential of wild oat and spring barley were measured under greenhouse conditions using a 1:1.06 barley to wild oat replacement series. Intraspecific barley interference affected barley growth more than interspecific wild oat interference. Interspecific wild oat interference with barley reduced wild oat growth more than intraspecific interference. Wild oat plant height surpassed barley plant height near barley anthesis. Growth and gas exchange of barley and wild oat responded the same to short-term water stress.

Application time did not greatly influence control of velvetleaf (Abutilon theophrasti Medik. # ABUTH) or common lambsquarters (Chenopodium album L. # CHEAL) in no-till corn (Zea mays L. ‘Pioneer 3747’) with fluorochloridone {3-chloro-4-(chloromethyl)-1-[3-(trifluoromethyl) phenyl]-2-pyrrolidinone}. Giant foxtail (Setaria faberi Herrm. # SETFA) control was reduced as much as 25% by 90 days after planting when fluorochloridone was applied early preplant rather than preemergence. Fluorochloridone at 0.8 kg/ha applied preplant or preemergence gave 83% or greater control of common lambsquarters and giant foxtail for the entire growing season. However, velvetleaf control with the same treatments was 61% or less. Fluorochloridone caused minimal corn injury. Greenhouse bioassay indicated that fluorochloridone may carry over and injure soybean [Glycine max (L.) Merr.] the year after application. Imbibition of fluorochloridone by seed of corn and giant foxtail did not reduce germination at concentrations up to 10-3 M. Giant foxtail seedling fresh weight was reduced 80% following imbibition of 10-5 M fluorochloridone. Corn seedling fresh weight was not reduced by imbibition of up to 10-4 M fluorochloridone.

Emergence patterns of foxtail in spring wheat following soybean were evaluated for three seeding dates and three tillage regimes. Cumulative foxtail emergence, as a percentage of total plants emerged in the growing season, was generally not influenced by tillage regime throughout most of the emergence period, but when differences occurred, emergence was lower with no-till than with moldboard plow. Foxtail seedling densities were greater in no-till and chisel plow than in moldboard plow. Weed biomass and wheat yields were not affected by tillage regime. Delaying wheat seeding reduced foxtail percent emergence and emerged seedling density. Differences in emergence patterns of foxtail were attributable to thermal accumulation after seeding. Wheat yield was not influenced by seeding date in 2 of 3 yr.

Integration of two or more methods in a weed control strategy may produce a positive interaction. In this study, sequential applications of sublethal rates of 2,4-D and the plant pathogen Sclerotinia minor were assessed for integrated control of common dandelion. S. minor was prepared as a granular treatment of fungal-colonized barley grits. Treatments of 2,4-D (25 or 50% of the recommended field rate) and S. minor treatments (20, 40, or 60 g m–2 rate) were applied alone or sequentially with a 3 wk interval. Fourteen days after inoculation (DAI), sequential applications of either rate of 2,4-D with 40 or 60 g m–2 of S. minor caused greater damage than either treatment alone (P = 0.05). By 21 and 28 DAI, control from 60 g m–2 of S. minor alone was equivalent to any of the sequential treatments (P = 0.05). At all assessment times, the combination of either rate of 2,4-D and 20 or 40 g m–2 of S. minor caused damage equivalent to or greater than that caused by 60 g m–2 of S. minor alone (P = 0.05). According to Colby's test for interactions, 19 of 24 assessments of the sequential treatments were synergistic. Therefore, sequential treatments of sublethal rates of 2,4-D and S. minor can interact positively to increase damage. This synergistic interaction may reduce the rate of either component required for adequate levels of control, possibly decreasing the cost or volume of use of herbicides in traditional weed control strategies.

Field studies were conducted in 1995 and 1996 to determine the rate response of velvetleaf seedling survival, seed production, and shoot biomass to postemergence herbicides in corn and soybean. Dicamba and imazethapyr were applied to corn and soybean, respectively, at 1, ½, ¼, ⅛, 1/16, 1/32, and 0× labeled rates. Velvetleaf mature plant density was linearly related to seedling density, thus indicating that seedling survival was not density dependent, even after seedling densities exceeded 150 plants m−2. Seedling survival as influenced by herbicide was described by a dose–response curve in corn and soybean. In corn, seedling survival ranged from 0 to 48% across herbicide treatments and years. Seedling survival was greater at the ½× or lower herbicide rates than at the 1× rate. In soybean, maximum seedling survival was 61 and 14% in 1995 and 1996, respectively, and minimum seedling survival was less than 2% in each year. Seedling survival was less in 1996 than in 1995 because velvetleaf was infected with wilt in 1996. In soybean, seedling survival was 20 times greater when treated with herbicides at the ½× rate than when treated at the 1× rate in 1995, but seedling survival was similar when herbicides were applied at 1, ½, ¼, and ⅛× rates in 1996. Velvetleaf fecundity (seeds per plant) was dependent on mature plant density in 1995 but was density independent in 1996. Fecundity as influenced by herbicide was described by dose–response curves in corn each year and in soybean in 1995. In 1995, velvetleaf treated with herbicides at ½× and ¼× rates produced 20 to 30 times more seed per square meter than when treated with herbicides at the 1× rate. Differences in seed per square meter were exaggerated by high densities of velvetleaf. Seed per square meter did not differ between velvetleaf treated with herbicides at 1× or ½× rates in corn or soybean in 1996. Wilt infection of velvetleaf in 1996 was the likely cause of differences in herbicide performance between years. Herbicides at reduced rates were not effective at limiting seedling survival and seed production compared to 1× rates in the absence of wilt. As a result, long-term management of velvetleaf with herbicides at reduced rates likely will be difficult, especially in areas with high densities, unless integrated with other management practices.

The longevity of brown and black forms of seed of halogeton (Halogeton glomeratus (M. Bieb.) C. A. Mey.), buried at four depths, was determined for a 10-year period in Nevada, Idaho, Utah, and Washington. The black form of seed had almost 100% field germination at all depths by the end of the first year and had completely germinated or was nonviable by the end of the second. Brown seed on the soil surface began field germination the first year at all locations and had germinated or become nonviable at the end of 6 years. Burial at 1, 3, and 6 inches delayed the peak of viability and tended to increase longevity of brown seed. Germination was less than 0.5% at the end of 10 years, and viability was near zero under both field and laboratory conditions. Seed germinated and lost viability most rapidly in Washington, the location where most favorable winter conditions for germination occurred.

Aspects of the life history and population dynamics of the Platte thistle (Cirsium canescens Nutt.), a rangeland weed, were studied in the Nebraska Sandhills from 1977 through 1979. This thistle is a monocarpic perennial, reproducing only by seed production, which typically occurs in small, scattered groups of plants. Seedling mortality at four sites was 75% during the first year, mostly because of dry moisture conditions. In plots with good vegetative cover, thistle rosette plants had a lower mortality rate, but growth rate was slower than that of rosette plants in plots with sparse vegetative cover. Seed heads developed during May and June and gained more than one-half of their dry weight shortly before maturing. Plants averaged 72, 197, and 303 seeds at three sites. Within sites, plants produced seeds in proportion to the number of seed heads per plant. Although naturally occurring biological-control agents have little effect on the vegetative growth phase of the life cycle, they greatly reduce the production of seeds.

Techniques were developed for evaluating herbicides on submersed, floating, and emersed aquatic weeds. Among 75 herbicides evaluated on three species of submersed weeds only 1:1′-ethylene-2:2′-dipyridylium (diquat); 1:1′-dimethyl-4:4′-dipyridylium (paraquat); di-N,N-dimethylcocoamine salt of 3,6-endoxohexahydrophthalic acid (endothal); and acrylaldehyde (acrolein) gave 85 percent or better control at 1 ppmw in still-water tests. Only acrolein and the di-N,N-dimethylcocoamine salt of endothal were effective on submersed weeds at 1 ppmw in the limited-exposure test. The evaluation of 17 herbicides on three species of floating aquatic weeds indicated that diquat was effective when applied at rates of 1 or 2 lb/A. The tertiary fatty acid amines of 2,4-dichlorophenoxyacetic acid (2,4-D) were more effective on floating weeds than an ester of 2,4-D. Many of the 78 herbicides evaluated on alligator-weed (Alternanthera philoxeroides (Mart.) Griseb.) killed the tops, but only two retarded the sprouting of underwater nodes longer than 6 weeks. Applications of 20 lb/A of 2-(2,4,5-trichlorophenoxy)-propionic acid (silvex) in two formulations retarded sprouting of underwater nodes for 8 weeks.

Glyphosate-resistant (GR) crops have been rapidly adopted in the United States and the evolution of GR weeds throughout the world has also been on the rise. With experience, weed scientists and crop advisers develop “intuition” on the basis of field history and current in-field conditions for predicting whether escaped weed biotypes may be herbicide resistant. However, there are no previous reports on the association of in-field crop management factors with the prediction of herbicide resistance. By using in-field survey data, we tested the accuracy of predicting glyphosate resistance in late-season horseweed escapes. We hypothesized that glyphosate resistance in late-season horseweed populations found in soybean fields could be predicted using in-field knowledge of crop residues and the appearance and distribution of weeds in the field. Field survey data were collected to determine the distribution and frequency of GR horseweed populations in Indiana soybean fields during September and October of 2003, 2004, and 2005. After the in-field survey, soil properties for sampled field locations were also collected from the U.S. Department of Agriculture Natural Resources Conservation Service Web Soil Survey. GR horseweed predictions used in-field presence of crop residues and the appearance, abundance, and distribution of weeds in the field. The significance of independent data factors were determined by chi-square statistics. The interactions and relative significance of multiple factors were modeled using classification and regression tree analysis. Our results indicated that the most important factor for predicting GR populations was the identification of an altered plant phenotype after injury from POST glyphosate. This was followed by crop rotation, field distribution, and the presence of other escaped weed species in the field in a model with a classification rate of 0.68.

Canada thistle was named Carduus arvensis by Tabernaemontanus in 1687, Cirsium arvense by Tournefort in 1700, Serratula arvensis by Linné in 1753, Cirsium arvense by Scopoli in 1772, Carduus arvensis by Robson in 1777 and Cnicus arvensis by Hoffman in 1804. The name Cirsium arvense Tourn. was adopted, but more recently Canada thistle has been referred to as Cirsium arvense (L.) Scop. The cardinal number of chromosomes for the Cirsium genus is 17.

The efficiency of cotton production has been materially increased since 1949 through the use of several pre- and post-emergence herbicides. In the high-rainfall areas, combinations of a pre-emergence herbicide such as isopropyl N–(3–chlorophenyl)carbamate (CIPC) or 3–(3,4–dichlorophenyl)–1,1–dimethylurea (diuron) with one of several post-emergence oils have given more dependable control than the use of single herbicides. In the irrigated areas, early-season weeds have been less of a problem and more attention has been given to herbicides for the control of late-appearing grasses and vines. The substituted ureas, 3–(p–chlorophenyl)–1,1–dimethylurea (monuron) and diuron, have been the most successful herbicides for this use.

One of the major prerequisites to a study of the vegetative buds on the rhizomes of quackgrass is the development of a method in which the rhizomes may be grown where bud growth can be observed easily. Since buds on the rhizomes of quackgrass are subterranean and since immediate observations of growth responses are virtually impossible, it was concluded that a method should be devised which would provide in vitro conditions favorable for growth. Changes in bud activity or dormancy could then be followed throughout the growing season. The method should also be such that observations of and treatments to the rhizomes could be made without disturbing them. Several methods have been used previously, but they do not lend themselves readily to observation or treatment.

Greenhouse and growth chamber studies were conducted to determine conditions for infection of the fungal pathogen Colletotrichum truncatum (Schw.) Andrus and Moore on Florida beggarweed (Desmodium tortuosum (Sw.) DC. # DEDTO and to determine the host specificity of this fungus. Optimum conditions for disease development were 14 to 16 h incubation in 100% relative humidity (RH) at 24 to 29 C. Control of Florida beggarweed with 105 to 107C. truncatum spores/ml was greatest in the cotyledon stage and decreased with plant age. Ten of 18 Desmodium species tested were susceptible to the Florida beggarweed isolate of C. truncatum but 13 other plant species and varieties were resistant and 61 were immune.

These studies were an attempt to evaluate some of the factors affecting the detoxification of 2,2–dichloropropionic acid in soils. Residual toxicity is a factor that must be evaluated before effective use can be made of any herbicide. Stability is preferred for purposes of soil sterilization; rapid disappearance of the herbicide may be essential in preplanting treatments; and in foliar applications, rapid disappearance of the material that reaches the soil may be important. Detoxification is usually considered to be the result of one or more of the several processes, decomposition, leaching, adsorption, and volatilization.

The response of wheat (Triticum aestivum L.) and wild oat (Avena fatua L.) to barban (4-chloro-2-butynyl-m-chlorocarbanilate) was studied as influenced by plant morphology and air temperature after application. Growth of wheat and wild oat seedlings was reduced by barban at 0.3 μg and 0.6 μg applied to the first node, respectively. Barban application to the base and midpoint of the first leaf blade required a lower dose to reduce wild oat growth than wheat growth. Increased tillering occurred from barban injury to the main culm in wheat. Wheat and wild oat susceptibility to barban increased as the post-treatment temperature decreased from 32 to 10 C. Barban selectivity for wild oats in wheat was greater at 27 and 21 C than at 16 and 10 C.

This paper focuses primarily on the means by which biochemical information can be used to identify enzymes which, upon inhibition, produce lethal phenotypes and the enzyme inhibitor design strategies that have the highest probability of not only inhibiting the enzyme but also translating that inhibition into herbicidal efficacy. The identification of an exquisitely lethal target site is the key initial component to this approach and has often been one of the most difficult steps because the attributes of a lethal site have, at best, been ill-defined. An examination of the characteristics of known targets provides some insight as to the definition of a lethal target. Recently, antisense RNA suppression of enzyme translation has been used to determine the extent of inhibition required for toxicity and offers potential as a strategy for identifying lethal target sites. After identification of a lethal target, detailed knowledge of the enzyme's chemical and kinetic mechanism as well as the protein's structure may be used to design potent inhibitors. Various types of inhibitors may be designed for a given enzyme. The advantages and disadvantages of a given type with respect to in vivo efficacy as well as the probability of herbicide resistance development will be discussed.