Clopyralid, picloram, triclopyr, metsulfuron, and tebuthiuron were applied to control kudzu on four loblolly pine forest regeneration sites during July 1997. Spot treatments were applied to recovering kudzu in June 1998 and June 1999. Soil leachate was monitored for these five herbicides from July 1997 to December 2000. All herbicides were detected in shallow (51–58 cm deep) and deep lysimeters (84–109 cm deep). Clopyralid was not persistent and limited leaching occurred, with residue levels of 0.4 to 2.8 μg L−1 in 12 of 102 deep lysimeter samples. Picloram was mobile and persisted at 0.6 to 2.5 μg L−1 in shallow and deep lysimeters for at least 10 mo after the initial application. Triclopyr residues were not persistent in shallow lysimeters and remained < 6 μg L−1 during the study. Metsulfuron persisted at < 0.1 μg L−1 for 182 to 353 d in shallow lysimeters and at < 0.07 μg L−1 for 182 to 300 d in the deep lysimeters in various plots. Tebuthiuron peaks in the deep lysimeters ranged from 69 to 734 μg L−1 34 to 77 d after the first spot treatment. In the soil that was essentially a fill area, tebuthiuron residues remained > 400 μg L−1 (402–1,660 μg L−1) in the shallow lysimeter samples and > 180 μg L−1 (181–734 μg L−1) in the deep lysimeters throughout a 354-d period that followed the first spot application. When used as part of a forest regeneration program, the relative potentials of the herbicides to move into shallow groundwater were: tebuthiuron > picloram > metsulfuron > clopyralid > triclopyr.

In a study of the selective action of 3-(3,4-dichlorophenyl)-l-methoxy-l-methylurea (linuron), parsnip (Pastinaca saliva L., var. Harris Model) possessed a high degree of tolerance as compared to tomato (Lycopersicum esculentum Mill., var. Kokomo). Linuron was readily taken up by the roots of tomato and distributed throughout the plant, but it remained mostly in the roots of parsnip. Linuron in the leaves of parsnip was metabolized, to a great extent, while very little of the metabolite (s) was found in tomato. The herbicide caused rapid and complete inhibition of photosynthesis in tomato, and the plants never recovered. Photosynthesis in parsnip was inhibited but only temporarily. Therefore, it appears that the selectivity of linuron on these two species may be explained by the two mechanisms of differential accumulation in the foliage and metabolism of the herbicide.

Infrared spectroscopy was used to study the hydrolysis of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] upon interaction with homoionic soil colloids. Montmorillonite, an allophanic soil clay, and a montmorillonitic Coker soil clay were saturated with H+, Al3+, Cu2+, and Ca2+ and treated with atrazine and hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Hydrolysis of atrazine was evaluated by the presence of a strong hydroxyatrazine carbonyl absorption band at 1745 cm-1. The H+- and Al3+-saturated montmorillonite and montmorillonitic Coker soil clay promoted atrazine hydrolysis while Ca2+- or Cu2+-saturated montmorillonite did not. A small degree of atrazine hydrolysis was detected in the Cu2+-Coker soil clay. Dehydration of Ca2+- or Cu2+-Coker soil clay after equilibration with atrazine increased the hydrolysis of atrazine. The allophanic soil clay did not catalyze the hydrolysis of atrazine when the exchange complex was saturated with H+, Al3+, Ca2+, or Cu2+. Moreover, Al3+-allophane was not sufficiently acidic to protonate hydroxyatrazine. Thus, a major difference exists between soil allophanic colloids, montmorillonitic soil clays, and montmorillonite as catalysts in the protonation and hydrolysis of atrazine.

Research was conducted to determine the potential for allelopathy to occur in pastures infested with bitter sneezeweed. Aqueous extracts of bitter sneezeweed leaves reduced alfalfa and Italian ryegrass seedling growth as much as 50% at concentrations of 0.5% (w/v). Leaf extracts were more phytotoxic than either stem or root extracts and seedling growth was reduced more than seed germination. Bitter sneezeweed tissue mixed in potting soil at concentrations as low as 0.3% w/w reduced alfalfa seedling numbers by 43%, plant height by 26%, and foliage dry matter production by 54% compared to plants cultured in soil without bitter sneezeweed leaf tissue. The potential concentration of bitter sneezeweed leaf material in soil in the pasture ecosystem was determined to be 0.5% w/v in the liquid phase and 0.2% w/w in the solid phase. Alfalfa seedling growth was reduced by 70% when germinating seed were placed under a bell jar with a potted mature bitter sneezeweed plant compared to control seedlings. A potential exists for bitter sneezeweed interference with developing alfalfa and Italian ryegrass seedlings following fall interseeding into pastures infested with bitter sneezeweed.

Above-ground seedling development was characterized for five annual grass weeds: downy brome, bulbous bluegrass, jointed goatgrass, Italian ryegrass, wild oat; and three cereals: winter wheat, winter barley, and winter triticale in field experiments over two years. The rate of leaf production on the main stem of each species was linearly related to cumulative growing degree days (GDD) since planting. Leaf production rates were faster for bulbous bluegrass, downy brome, Italian ryegrass, wild oat, and barley than for wheat, triticale, and jointed goatgrass. The main stem development stage when individual tillers appeared was similar in all species except under poor seedbed conditions in 1991, in which case lower-node tillers were delayed in the cereals and jointed goatgrass, but not in most of the weed species. Bulbous bluegrass, downy brome, and barley had the same percentage of plants produce the first four primary tillers on the main stem in both years; the other species showed more year-to-year variation. Seedling heights at full emergence were generally greater for large-seeded species. Small-seeded species compared to large-seeded species tended to have greater relative increases in plant height over time. Knowledge of comparative development rates between these weeds and cereals could provide information for development of growth models for each of the species and could also improve understanding of the competitive relationships between grass weeds and cereal grains.

Kochia growing on an industrial site where chlorsulfuron was applied repeatedly over several seasons was confirmed to be resistant to chlorsulfuron and several other acetolactate synthase (ALS) -inhibiting herbicides. In growth room experiments, resistant (R) plants were 2 to >180 times more resistant to five sulfonylurea herbicides and one imidazolinone herbicide (imazethapyr) than susceptible (S) plants, as measured by the ratio of dosages required to inhibit shoot dry matter accumulation by 50% (GR50 R/S). Similarly, in vitro assays of ALS activity indicated that from 3 to 30 times more herbicide was required to inhibit the enzyme from R plants than from S plants. Results of ALS enzyme assays indicated that R kochia was approximately equally resistant to metsulfuron, triasulfuron, and thifensulfuron, and 2.5 times more resistant to tribenuron than thifensulfuron. However, the response of R kochia growing in a spring wheat crop in the field was not consistent with results of the ALS enzyme assays. In field experiments, thifensulfuron at 32 g ai ha−1 had little effect on R kochia. In contrast, metsulfuron, triasulfuron, and tribenuron at 8 g ha−1 did not reduce R kochia seedling densities, but caused severe stunting such that 2 mo after treatment the shoot biomass of plants in untreated plots was four times greater than in sprayed plots. Herbicides with alternative modes of action including fluroxypyr, bromoxynil/MCPA ester, dichlorprop/2,4-D ester, and 2,4-D ester provided good control of R kochia in the field. Quinclorac did not reduce kochia densities, but surviving plants were stunted. To delay or avoid development of ALS inhibitor-resistant kochia populations, these alternative herbicides applied alone or in tank mixtures could be incorporated into a herbicide rotation.

The appearance of triazine resistance in a number of weed species has provided some opportunities for plant breeders to develop triazine-resistant crop varieties through classical breeding techniques. The sources of genes utilized by plant breeders for desirable characteristics are usually limited by the normal reproductive barriers that distinguish species. The occurrence of a triazine-resistant biotype of birdsrape mustard (Brassica campestris L. # BRSRA) has allowed for the development of commercially useful triazine-resistant varieties of canola (low erucic acid, low glucosinolate oilseed rape, B. napus L.). The cytoplasm of triazine-resistant birdsrape mustard was transferred interspecifically to oilseed rape, by a technique commonly known as back-crossing, in conjunction with selection for chromosome number. ‘OAC Triton′, the first triazine-resistant canola variety, appears to be finding commercial acceptance in Canada, in spite of some limitations in agronomic performance. Although it should be possible to transfer this triazine-resistant cytoplasm to other economic Brassica species including the cole crops and mustards, conventional plant breeding techniques cannot separate the gene conferring triazine resistance from other genes in the resistant weed biotype's cytoplasm. This problem may limit the utility of triazine-resistant cytoplasms from weed biotypes in classical crop breeding.

This study describes the distribution patterns of Johnsongrass populations present in 38 commercial corn fields located in three major corn growing regions of Spain. A total of 232 ha were visually assessed from the cabin of a combine during harvesting using a three-category ranking (high density, low density, no presence) and recording the georeferenced data in a tablet personal computer. On average, 10.3 and 3.9% of the surveyed area were infested with high and low density of Johnsongrass, respectively. Most of the infested area was concentrated in a few large patches with irregular shape. Small patches (less than 1,000 m2) represented only 27% of the infested area. Management factors could explain much of the spatial distribution of this weed in the studied fields. Tillage direction was the main factor explaining patch shape: the length width−1 ratio of the patches was greater than two in the tillage direction. In sprinkler irrigated fields, higher levels of infestation were generally observed close to the sprinkler lines. Areas close to the edges of the field had a higher risk of infestation than the areas in the middle of the fields: a negative relationship between distance from the edge and weed abundance was established. Because a few patches, located in some predictable parts of the field, such as field edges, represent most of the seriously infested area, site-specific treatments of these areas could reduce herbicide inputs, until more reliable, spatially precise and practical detection, mapping, and spraying systems are developed.

The literature relating to the impact of other pests on weeds of agroecosystems is minimal. A great deal of literature discusses the effect of organisms used for biological control of weeds; however, pest organisms used as biological control agents are not the subject of this paper. The objective of this review is to present what is known about the impact of insect, pathogen, and nematode pests on weeds; to outline some of the gaps in our knowledge; to present concepts from the ecological literature that might provide insight; and to discuss implications for integrated pest management. The limited data that are available suggest that weeds require fewer resources to survive in the presence of the pest complex than the crop and that weeds would potentially have a greater ability to survive, compete, and reproduce in a competitive environment compared to the planted crop. We suggest that three categories of weed response to polyphagous crop pests may occur in agricultural fields: susceptible weed species or biotypes that host the pest with severe effects on growth and fecundity and therefore are of limited concern in terms of competition for resources; tolerant weed species that host the pest without severe effects on growth and fecundity, resulting in effective competition with the crop and larger pest populations; and resistant weed species that do not host the pest but compete effectively with the crop. We propose the hypothesis that the weed community in many agricultural fields is dominated by plant species that are tolerant or resistant to the endemic pest complex, particularly the soil pest complex, because of constant selection pressure from these pests.

The uptake of 14C-labeled butoxyethanol ester of (2,4-dichlorophenoxy)acetic acid (BEE of 2,4-D) from water by three species of fed and fasted fish was studied. Fish were exposed to either 0.3 or 1.0 mg/L of herbicide for up to 168 hr. Combined residues of the 2,4-D ester and its metabolic products were determined radiometrically in eight tissues and organs. Extracts of these organs were examined by thin layer chromatography and autoradiography. Maximum residue concentrations were observed in most organs of fed fish within 1 to 2 hr of exposure, and within 1 to 8 hr of exposure for fasted fish. After maximum residue concentrations were reached, the herbicide and/or its metabolites were eliminated rapidly.

An effective technique was developed for partitioning the environment of intact submersed aquatic plants. The technique facilitates absorption and translocation studies by permitting application of radioactive herbicides to selected portions of the plants. Root and shoot treatments of Potamogeton pectinatus L. for 24 to 96 hours with C14-labeled 2,3,6-trichlorophenylacetic acid (fenac) showed no leakage across the partitioned system. Little or no basipetal translocation of the herbicide was observed. Limited acropetal translocation occurred and this was reduced by removal of tubers prior to herbicide application. Accumulation of activity in nodal regions of the stem was noted.

Selective control of Egyptian broomrape is extremely difficult because the close association between host crop and parasite limits the use of most mechanical and herbicidal approaches. However, this host–parasite interaction can also form the basis of the simplest control strategy: parasite-resistant crops. Although much work has been conducted to identify and characterize mechanisms of parasite resistance, varieties with stable resistance are still unavailable for most affected crops. The development of resistant crops can be accelerated by genetic engineering to the extent that important aspects of the host–parasite interaction are understood. In this study, we characterize a variety of gene promoter elements with respect to parasite induction and expression pattern. Studies were conducted using transgenic plants expressing fusions of the β-glucuronidase reporter gene with promoter elements from several genes. Promoters from genes known to have increased expression in response to pathogen attack or wounding showed localized, induced expression after parasitism. These included phenylalanine ammonia lyase, chalcone synthase, sesquiterpene cyclase, and HMG1 (3-hydroxy-3-methylglutaryl CoA reductase). In contrast, the systemic acquired resistance–associated gene PR-1a was not induced by parasitism. Non–defense-related genes varied in response, with squalene synthase being repressed, whereas farnesyltransferase was highly expressed in the region of parasite attachment. These results demonstrate a range of expression, both in intensity and tissue specificity, in response to parasitism.

Pseudomonas syringae pv. phaseolicola formulated with an organosilicone surfactant was tested as a potential bioherbicide for kudzu. Greenhouse studies were performed to determine the effect of kudzu plant age and leaf age on disease severity and growth of the bacterium in planta. Eight-week-old plants were more diseased 4 wk after spraying and had a higher potential for regrowth 7 wk after spraying than 12-wk-old plants. Young leaves developed water-soaked lesions earlier than older leaves and supported higher populations of bacteria. Data from field experiments at two separate locations indicated that single applications in late spring were as effective as multiple applications in early spring and were enhanced by repeat application. Three months after the beginning of the experiment, extensive regrowth occurred for all bioherbicide treatments and no differences were noted between treatments and the nontreated control.

Field experiments were conducted during 1980, 1981, and 1982 to evaluate the effect of tillage and sicklepod density on sicklepod (Cassia obtusifolia L. # CASOB) interference with soybeans [Glycine max (L.) Merr.] and soil water use. In the absence of sicklepod, soybean yields were similar in nontilled plots covered with a straw mulch and in conventionally tilled plots with no mulch in all years. In the presence of sicklepod, higher soybean yields were obtained with the non-tilled-mulched plots than with the tilled plots at corresponding sicklepod densities and sicklepod fresh weights. Early soil water loss was greater in the tilled plots with increasing sicklepod density causing lower soil water content in both tillage treatments. Soil water depletion was greater in the no-till treatments during the soybean pod-filling stage.

Seeds of green foxtail [Setaria viridis (L.) P. Beauv. # SETVI] and giant foxtail (S. faberi Herrm. # SETFA) were collected from mature plants in the field and recovered from three soil depths under two types of tillage. Fungi colonizing the caryopses were isolated to determine the effect of tillage and soil depth on fungal colonization and the field flora. Alternaria alternata (Fr.) Keissler and Epicoccum purpurascens Ehrenb. ex Schlecht. were the two fungi most frequently isolated from the hand-harvested seeds. Percentages of fungal colonization were directly related to size of the caryopses. The most frequently isolated fungus species recovered from seeds from soil were A. alternata, Cladosporium cladosporioides (Fresen.) de Vries, E. purpurascens, and two unidentified fungi with sterile mycelium. One sterile fungus had white rough mycelium, and the other had dark mycelium. These two sterile fungi had a detrimental effect on foxtail seed germination in the laboratory. Caryopsis colonization seems to be related to the placement of the crop residues in the soil. In reduced-tillage plots, more caryopses were colonized in the top soil layer (0 to 7.5 cm) than in the 7.5- to 15-cm layer. In plowed soils, greater colonization occurred at the lower depth.

The influence of various additives on the absorption and translocation of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} butyl ester in oats (Avena sativa L. var. ‘Lyon’) was determined. Fluazifop absorption and translocation by oats 48 h after application were less when applied with safflower (Carthamus tinctorius L.), sunflower (Helianthus annuus L.), soybean [Glycine max (L.) Merr.], linseed (Linum usitatissimum L.), and palm (Eleais quineeneis Jacq.) oil than with petroleum oil. However, fluazifop absorption and translocation continued to increase for the 96-h duration of the experiment when applied with soybean oil but only for 24 h when applied with petroleum oil. The 14C-fluazifop-label recovery was higher when applied with oils than when applied alone, which may have been due to reduced fluazifop volatility when it was emulsified with the oils. Absorption and translocation of fluazifop applied with glycerol or various emulsifiers were equal to or less than fluazifop absorption and translocation when applied with petroleum oils but were greater than fluazifop absorption and translocation when applied with seed oils 48 h after application. Fluazifop absorption and translocation were similar whether soybean or petroleum oil additives were applied with or without emulsifiers. Totally refined seed oils only slightly increased fluazifop absorption and translocation compared to fluazifop with once-refined or degummed seed oils.

The effect of chlorotoluron on different slender foxtail populations that survived normal agricultural rates of this herbicide (2.5 to 3.5 kg ai ha–1) was investigated under controlled laboratory conditions. Among five populations tested, two had tolerance for the herbicide. The ED50 values for these biotypes ranged from 0.33 to 2.43 kg ha–1. Assays with radiolabeled 14C-chlorotoluron indicated similar absorption and translocation of the herbicide between susceptible and resistant biotypes. Chlorophyll fluorescence and Hill reaction analysis seem to support the view that the mechanism of resistance of one biotype to the herbicide is due to degradation/detoxification rather than to modification of the target site, although compartmentation processes cannot be ruled out. This resistant biotype had high tolerance to other photosynthetic inhibiting phenylureas, including linuron, chlorbromuron, diuron, monolinuron, and neburon.

Efficacy of an indigenous fungus, Exserohilum monoceras, for the control of 3 Echinochloa species was evaluated and compared under both regulated greenhouse and screenhouse (field plots netted with 2 layers of metal mesh screening to exclude vertebrate pests) conditions. Under greenhouse conditions, an inoculum dose of 2.5 × 107 conidia m−2 killed all seedlings of both barnyardgrass and E. glabrescens, whereas an inoculum dose of 5.0 × 107 conidia m−2 was required to obtain 100% mortality of junglerice seedlings. The 1.5-leaf stage of all 3 Echinochloa species was the most susceptible. Increasing inoculum density increased weed control efficacy on younger or older Echinochloa seedlings. The highest level of control was observed for E. glabrescens, less for barnyardgrass, and least for junglerice. Under screenhouse conditions, Exserohilum monoceras caused more than 90% mortality of Echinochloa species when the inoculum was formulated as an oil emulsion or when applied as a dry powder.

Weed control in tomato production systems is difficult because few are registered. The use of rye for weed control and its influence on transplant tomato yields was investigated during 1986 and 1987 at two locations in IN to determine if cover crops can provide an alternative weed management technique. ‘Wheeler’ rye was sown in the fall of 1985 and 1986, and mowed or desiccated with glyphosate at various times before planting ‘IND 812'tomatoes. At the time of glyphosate application, rye residues reduced the growth of overwintering weeds by 93% or more compared to bare ground (no cover crop) areas. The time of desiccating rye prior to planting tomatoes affected the extent of weed suppression by rye residues. In 1986, rye treated 4 wk before planting (WBP) tomatoes provided up to 89% suppression of weed growth at 2 wk after planting (WAP) tomatoes, but no measurable weed suppression 5 WAP tomatoes. Rye treated 2 WBP tomatoes provided up to 97% weed suppression up to 5 WAP tomatoes. In 1987, weed suppression varied between locations and differed from 1986. At Lafayette, rye treated 2 and 1 WBP tomatoes provided greater than 81% suppression of weed growth up to 8 WAP tomatoes. Rye mowed and the residues placed into a plot at a known density also reduced weed growth (60%) 8 WAP tomatoes. At Vincennes, however, rye treated 2 and 1 WBP in 1987 did not reduce weed growth later than 4 WAP tomatoes compared to the unweeded, bare ground treatment. The mowed rye residues at Vincennes suppressed weed growth (96%) up to 8 WAP tomatoes. Tomato yield was correlated to weed suppression. In 1986, tomato yield in the rye treated 2 WBP tomatoes was comparable to yield in the bare ground, weeded controls. However, tomato yield in rye plots treated 4 WBP tomatoes was similar to yield in the bare ground, unweeded control. In 1987, tomato yields in all rye plots (mowed, treated 2 and 1 WBP tomatoes) were similar to tomato yields in the bare ground, weeded control at Lafayette. At Vincennes, only the mowed rye treatment yielded comparably to the bare ground, weeded control. In general, rye plots that were weeded yielded similar to or up to 28% more than a bare ground, weeded control. Tomato yields were not reduced by rye residues. Tomato yields in rye residues that provided effective suppression of weed growth (greater than 80%) for a minimum of 4 to 5 WAP tomatoes were comparable to bare ground, weeded controls.

Glasshouse studies were undertaken to determine the effect of imposed moisture stress on the phytotoxicity of haloxyfop; the absorption, translocation, and metabolism of 14C-haloxyfop; and 14C-photoassimilate partitioning in johnsongrass and large crabgrass. Following foliar applications of haloxyfop at 30 and 25 g ai ha–1 to large crabgrass and johnsongrass, respectively, control 15 days after treatment was 92% for nonstressed plants and less than 12% for water-stressed plants. Foliar absorption of 14C-haloxyfop was reduced by moisture stress 1, 3, 5, and 24 h after treatment (HAT) in large crabgrass and 1, 3, 5, 48, and 72 HAT in johnsongrass. Regardless of stress treatment, absorption in both species reached a maximum by 24 HAT. Translocation of the radiolabel from the treated leaf to plant parts above and below the node of the treated leaf was inhibited by moisture stress in large crabgrass and johnsongrass at all harvest intervals beginning 5 and 24 HAT, respectively. Metabolism of 14C-haloxyfop was not altered by moisture stress. Fixation of 14CO2 and subsequent distribution of the 14C-photoassimilates were reduced by moisture stress. Decreases in photoassimilate translocation were similar to reductions in 14C-haloxyfop translocation. Moisture stress reduced the phytotoxicity of haloxyfop in the two grasses, and the reduced activity of haloxyfop appeared to be partially related to changes in herbicide absorption and translocation.