The relative tolerance of one-year-old peach and apricot seedlings to 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 2-methoxy-4,6-bis = (isopropylamino)-s-triazine prometryne was established by soil surface and soil incorporated applications. In all cases, the relative tolerance to both herbicides was greater for peach than apricot. Reciprocal grafts of peach and apricot budded seedlings indicated that the rootstock did not alter the tolerance. The greater tolerance of peach over that of apricot was attributed to physiological detoxification occurring in the scion.

The ultraviolet absorption spectra of aqueous dispersions of 2-chloroallyl diethyldithiocarbamate (CDEC) were altered by relatively short periods of exposure to far ultraviolet radiation. Evidence of molecular decomposition also was obtained from solvent partitioning characteristics, gas chromatography, and bioassays. Ultraviolet irradiation of soil surfaces treated with the herbicide decreased its persistence, but no evidence of decomposition was obtained.

Direction and rate of translocation of sucrose* from urea* 2,4-D* (2,4-dichlorophenoxyacetic acid) and amitrole* (3-amino-l,2,4-triazole) were toward regions of active growth. In oak seedlings translocation was slower than in cotton seedlings. In oak seedlings growing leaves and shoots constitute active sinks toward which tracers move. Sucrose* from urea* translocates freely; 2,4-D* moves less freely because of accumulation enroute; amitrole* is intermediate between these. High humidity induces rapid and extensive uptake of tracers by oak seedlings; the increase over normal transport is mainly in the xylem.

The dicamba-resistant cropping system was developed to be used as a tool to control multiple-resistant weed species, particularly Palmer amaranth (Amaranthus palmeri S. Watson). However, dicamba applications have resulted in off-target movement of the herbicide to susceptible neighboring vegetation, with frequent damage to non–dicamba resistant soybean [Glycine max (L.) Merr.]. Pod malformation and subsequent auxin-like injury to progeny is common when parent soybean plants are exposed to the herbicide post-flowering. Yet no publication to date has conveyed the presence of dicamba in seed. The objective of this study was to determine whether dicamba exists and at what quantities inside soybean seed following a low-dose exposure in the pod-filling stage using radiolabeled herbicide as a tracer. Non–dicamba resistant soybean plants were grown in the greenhouse until the pod-filling growth stage and then treated with 2.8 g ae ha−1 of dicamba (1/200 of the recommended rate of 560 g ae ha−1). Immediately afterward, [14C]dicamba (approximately 6.4 kBq per plant) was applied to the adaxial surface of one trifoliate leaf located in the midportion of each plant. The greatest amount of [14C]dicamba recovered was in seeds and in pods, and these plant parts accumulated 44% and 38% of the total absorbed, respectively. Chromatography results showed that the totality of the [14C]dicamba present in the soybean seeds was in the phytotoxic form, except for a single sample, in which one metabolite was detected (possibly 5-hydroxy dicamba). Precautions should be taken to avoid dicamba exposure to sensitive soybean fields, especially those dedicated to seed production, as this may result in low seed quality and symptomology on progeny plants.

The evaluation of herbicidal weed control is often difficult, time-consuming, and non-precise. Neither weed counts, weights, ratings, effects on labor requirements, nor other common methods are wholly satisfactory for general use, although most of these methods are of value for one or more specific purposes.

The alkanolamine salts of 2,4–dinitro–o–secondary butyl phenol (DNBP) have been used frequently as a pre-emergence herbicide in cotton without causing injury. However, under some conditions the chemical has severely reduced the stand. This paper presents data that show the effects of rainfall, lime, soil type, and temperature on the phytotoxicity of dinitro to cotton seedlings.

The use of insects in the biological control of weeds necessitates that these insects have very restricted host ranges. Specialized insects boring in stems or living in seed pods have adaptations which obligate them to their host plant. However, the leaf-feeding beetle, Chrysolina quadrigemina Suffrian, imported for the control of St. Johnswort (Klamath weed) (Hypericum perforatum L.) through its feeding habits, tropistic responses and synchronization of its life history to the growth phases of the plant has shown that it is restricted to its preferred host plant.

Glasshouse and field experiments were conducted on fine sandy loam, sandy clay loam, and clay to study under high temperatures 2-chloroallyl diethyldithiocarbamate (CDEC) and ethyl N,N-dipropylthiolcarbamate (EPTC) incorporated with the surface ½, 1, 2, and 3 in of soil and unincorporated. Herbicides, sprayed on the soil surface, were incorporated either manually in the glasshouse or with a powered, rotary tiller in the field. The principal weed species were Palmer amaranth (Amaranthus palmeri S. Wats.), redroot pigweed (Amaranthus retroflexus L.), junglerice (Echinochloa colonum (L.) Link), and barnyardgrass (Echinochloa crusgalli (L.) Beauv.). Performances of herbicides were determined by counting the plants 2 weeks after treatment.

The herbicidal performance of CDEC was greater when the applications were incorporated with the surface ½ or 1 in whereas the performance of EPTC increased with increasing depths of incorporation up to 3 in. Soil temperature, soil moisture losses, and the distribution of herbicide in soil apparently contributed to differential herbicide performance.

The overall objective of research at ICRISAT (International Crops Research Institute for the Semi-Arid Tropics) is to develop effective, economically feasible, improved weed-management systems for major crops and cropping systems of the Semi-Arid Tropics (SAT). Initially, emphasis has been on surveys, ecological studies, weed management in crops, and herbicide screening. The aim was to identify possible cultural, mechanical, biological, and chemical inputs, and to determine their relative feasibility for small farmers. Systems research has involved manipulation of cropping systems to obtain better weed management and identification of the most effective techniques. Herbicide-related studies are designed to increase productivity rather than reduce the cost of hand weeding. Research on individual crops has been aimed at determining the extent of crop-weed competition in major crops. In collaboration with economists, operations research in farmers' fields was initiated to observe the success of farmers' weed-control methods. The primary program emphasis will be the evaluation of weed-management principles that may have wide applicability throughout the SAT. This paper outlines the approaches to weed-management research at ICRISAT and gives a conceptual framework of future research needs.

Soil-incorporated treatments of dichlobenil (2,6-dichlorobenzonitrile) at 4.5 or 9 kg/ha completely controlled field horsetail (Equisetum arvense L.) for 2 yr and at 9 kg/ha, control was 90 to 99% in the third year. Mulching with sawdust after surface application of dichlobenil gave similar results. In an area treated at 9 kg/ha and isolated from emerged field horsetail, there was no reappearance of field horsetail until 5.5 yr after treatment. Japanese holly (Ilex crenata Thunb.) and azalea (Rhododendron X ‘Rosebud’) planted a year after treatment made as much growth in treated as in adjacent untreated soil. Douglas fir seedlings [Pseudotsuga menziesii (Mirb.) Franco] made as much growth in treated as in untreated soil only when planted 2 yr after treatment. Strawberry (Fragaria X ‘Northwest’) plants made approximately 80% as much top growth in treated as in untreated soil when planted 2 yr after herbicide application.

African lovegrass [Eragrostis curvula (Schrad.) Nees] is an invasive weed that is threatening biodiversity around the world and will continue to do so unless its efficient management is achieved. Consequently, laboratory and field-based experiments were performed to analyze several measures of germination to determine the effect of drought stress, radiant heat stress, and burial depth and duration (longevity) on E. curvula seeds. This study investigated seeds from four spatially varied populations across Australia: Maffra and Shepparton, VIC; Tenterfield, NSW; and Midvale, WA. Results showed that increasing drought stress reduced and slowed germination for all populations. Maffra (24% vs. 83%) and Shepparton (41% vs. 74%) were reduced at the osmotic potential of ≤−0.4 MPa, while Tenterfield (35% vs. 98.6%) and Midvale (32% vs. 91%) were reduced at ≤−0.6 MPa, compared with the mean of all other osmotic potentials. Radiant heat at 100 C significantly reduced and slowed germination compared with 40 C for Tenterfield (62% vs. 100%), Shepparton (15% vs. 89%), and Midvale (41% vs. 100%), while Maffra (75% vs. 86%) had consistent germination. For the effect of burial depth and duration (longevity), there was no significant difference across the 14-mo period; however, the 0-cm burial depth had a significantly lower final germination percentage compared with depths of 3, 5, and 10 cm (24% vs. 55%). Although each trial was conducted independently, the results can be used to help identify efficient control measures to reduce infesting populations. Recommended measures include using soil moisture monitoring to detect which conditions will promote germination, as germination is encouraged when the osmotic potential is >−0.6 MPa; exposing seeds to radiant heat (>100 C) using methods such as prescribed burning; and limiting soil disturbance over time to reduce seed establishment.

Field studies were conducted over a 7-yr period at Lacombe, Alberta, to study the relationship between the duration of Tartary buckwheat interference [Fagopyrum tatarium (L.) Gaertn. # FAGTA] and yield of barley (Hordeum vulgare L.), oats (Avena sativa L.), wheat (Triticum aestivum L.), flax (Linum usitatissimum L.), and rapeseed (Brassica campestris L.). The data were pooled over years and analyzed by multiple regression. The equations were as follows: ŷ = 15.46 + 0.39X1 + 0.00x2 −0.11x3 (barley), ŷ = −15.44 + 0.49x1 + 0.02x2 + 0.08x3 (oats), ŷ = −2.04 + 0.39X1 + 0.05x2-0.03x3 (wheat), ŷ = −4.38 + 1.14x1 −0.04x2 + 0.01x3 (flax), and ŷ = −13.85 + 0.40x1 – 0.01x2 + 0.04x3 (rapeseed); where ŷ was the estimated percent yield loss of the crop, x1 was the duration (days) of the Tartary buckwheat in the crop, x2 was the number of Tartary buckwheat plants/m2, and x3 was the number of crop plants/m2. The time that Tartary buckwheat remains in the crop contributed most to the yield loss observed in all crops. Yield loss between 0.4 and 1.1% per day was attributed to this variable alone. For a given x1, x2, and x3 value the order of percent yield loss was flax>oats>wheat> barley>rapeseed.

In field studies, surfactant and phytobland oil were compared as additives to herbicides and herbicide combinations for postemergence weed control in cotton (Gossypium hirsutum L. ‘Stoneville 7A’). Addition of phytobland oil to MSMA (monosodium methanearsonate) and MSMA + fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], dinoseb (2-sec-butyl-4,6-dinitrophenol), or norea [3-(hexadydro-4,7-methanoindan-5-yl)-1,1-dimethyl-urea] had no significant effect on weed control when applied as directed treatments to weeds in cotton 7 to 15 cm tall. In cotton 15 to 23 cm tall, addition of phytobland oil to MSMA + linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and MSMA + linuron + prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] increased weed control when compared to the same treatments with surfactant. MSMA + linuron + phytobland oil decreased cotton yields. Addition of phytobland oil to DSMA (disodium methanearsonate) and DSMA combinations had no effect on weed control when compared to the same treatments with surfactant. There were no differences in several paraffinic phytobland oils or surfactant when used as additives to MSMA + fluometuron for weed control in cotton 7 to 15 cm tall.

Native Polyacrylamide gel electrophoresis (PAGE) and enzyme activity staining were used to identify possible progenitor species of velvetleaf (Abutilon theophrasti Medic. # ABUTH). Multiple forms of superoxide dismutase activity were observed in each of the plants surveyed. Three enzyme forms were common to all the species and bio types while one form was different in the velvetleaf biotypes compared to the other species. Multiple forms of peroxidase activity were also detected. The three velvetleaf biotypes possessed identical enzyme forms with minimal similarity to peroxidase forms found in the other species. Multiple forms of esterase activity separated as two nonoverlapping groups. A slowly migrating group was observed in all the velvetleaf biotypes and a more rapidly migrating group characterized the remaining Abutilon species. The results of this study indicated that the progenitors of velvetleaf were not among the species surveyed and suggested that the progenitors may no longer be extant.

Acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} applied alone and in mixtures with propanil [N-(3,4-dichlorophenyl)propanamide] reduced rough grain yield of rice (Oryza sativa L. ‘Lebonnet’ or ‘Bond’) by 7% when applied at the late-booting or heading growth stages, averaged over several rates of application. Earlier applications did not reduce rice yield. The highest rate (0.6 kg ai/ha) of acifluorfen alone and in mixtures with propanil at 3.4 kg ai/ha reduced grain yields more than lower rates (0.1 or 0.3 kg ai/ha). Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} alone and in mixtures with propanil reduced rough grain yields of rice by 18% when applied at the late-booting growth stage, averaged over several rates of applications, but did not affect yields when applied at the early-tillering, jointing, or early-booting growth stages. Whole-grain milling yield and germination of rice seed were not affected by acifluorfen or triclopyr alone or in mixtures with propanil, regardless of rate or growth stage of application.

Growth of green foxtail (Setaria viridis (L.) Beauv.) was effectively controlled in the greenhouse by applying the sodium salt of trichloroacetic acid (TCA) as a postemergence treatment, when a rate of 0.84 kg/ha was used; when application preceded the two-leaf stage; and when 2.54 mm of water were available daily for moving TCA into the soil. There were significant interactions of TCA rate with light intensity, temperature, and source of seeds on the response of green foxtail. Seedhead production was curtailed at rates of 0.56 kg/ha or above when plants were grown under high light intensities (19,250 to 22,000 lux) and at moderate temperatures (20 to 22 C). Rates of 1.68 kg/ha or more were required to stop heading of foxtail grown at high temperature (27 C).

Bermudagrass is a difficult perennial weed to manage in Louisiana sugarcane. Research was conducted to compare interrow tillage practice, postharvest residue management, and herbicide placement on bermudagrass proliferation and sugarcane yield. Tillage frequencies included conventional (four tillage operations per season), reduced (two tillage operations), and no-till. Residue management practices included removal by burning, sweeping from row top into the wheel furrow, and not removed. Spring herbicide placement treatments included broadcast, banded, or no herbicide application. With conventional tillage, broadcast and banded herbicide applications resulted in similar bermudagrass cover in the first and second ratoon crops, but bermudagrass cover was greater when using banded applications (22%) compared with broadcast application (15%) in the third-ratoon crop. Bermudagrass cover was greatest with no-till. When herbicides were banded, bermudagrass cover was greater in reduced tillage than conventional tillage in all three ratoon crops. Postharvest residue management did not affect bermudagrass ground cover. In plant cane, sugarcane yields were lowest when herbicide was not applied. In ratoon crops, sugarcane and sugar yield were reduced when herbicide was not applied regardless of tillage practice. Cane and sugar yield were generally equal when comparing reduced and conventional tillage. Total sugarcane yield (4 crop yr) for the no-till program was reduced 11, 15, and 25%, respectively, when herbicides were broadcast, banded, and when herbicide was not applied, compared with conventional tillage. Failure to remove residue reduced sugarcane yield by 5, 7, and 10% in first, second, and third ratoons, respectively, compared with burning. Eliminating unnecessary tillage practices can increase profitability of sugarcane through reduced costs, but it will be imperative that herbicide programs be included to provide adequate bermudagrass control and that postharvest residue is removed to promote maximum sugarpostane yield.

Hydrilla is one of the most serious aquatic weed problems in the United States, and fluridone is the only U.S. Environment Protection Agency (USEPA)–approved herbicide that provides relatively long-term systemic control. Recently, hydrilla biotypes with varying levels of fluridone resistance have been documented in Florida. Fluridone-susceptible (S) and several fluridone-resistant (R1 to R5) hydrilla biotypes varying in resistance levels were maintained in 950-L tanks under ambient sunlight and day-length conditions. To correlate varying levels of fluridone resistance to ploidy in hydrilla, flow cytometric analysis was performed. Differential ploidy levels (diploid, 2n = 2x = 16; triploid, 2n = 3x = 24; and tetraploid, 2n = 4x = 32) were reported among different hydrilla biotypes, plants within each biotype, and within shoot tissues of the same plant. Triploid plants were predominant in all biotypes. Diploid plants were observed in all hydrilla biotypes except the susceptible hydrilla (S). Plants with tetraploidy were rare within biotypes. The diploid, triploid, and tetraploid plants had nuclear DNA contents of 2.43 to 2.73 pg, 3.44 to 3.71 pg, and 4.64 to 4.90 pg, respectively, and no differences were observed among plants with same ploidy for nuclear DNA content in different hydrilla biotypes. Endoreduplication patterns were observed in diploid plants of R1 and R3 biotypes. However, no plant with higher ploidy levels (triploid or tetraploid) in any hydrilla biotypes showed endoreduplication.

Anecdotal reports suggest waterhemp is becoming more difficult to control with glyphosate. Waterhemp accessions collected primarily in Illinois before 1996, in 1998 to 1999, and in 2003, were evaluated for differential responses to glyphosate treatment. The pre-1996 group consisted of 10 accessions, whereas the 1998 to 1999 and 2003 groups consisted of 45 accessions each. Plants 10 to 12 cm in height from each waterhemp accession were treated with 0 or 220 g ae ha−1 glyphosate. Although shoot dry biomass 14 d after treatment, expressed as a percentage of the untreated, varied within and among accessions, the mean responses of the three groups were similar. However, when glyphosate responses were divided into 10 arbitrary classes (0 to 10, 11 to 20, …, and 81 to 90; > 91% of untreated), the number of plants within each class differed among groups. Most notably, the proportion of plants in the range of 0 to 30% of the untreated control decreased with time when progressing from the pre-1996 to the 2003 accessions. The relative frequency of waterhemp plants that were ≥ 100% of the untreated plants (i.e., uninjured by glyphosate) in the pre-1996, 1998 to 1999, and 2003 groups were 5, 6, and 5%, respectively. In a separate trial, waterhemp populations that exhibited the least sensitivity to glyphosate at 220 g ha−1 were controlled by 870 g ha−1 glyphosate. These results suggest that waterhemp, as a whole, within Illinois has not become less sensitive to glyphosate over the past few years. However, the proportion of plants that are most sensitive to glyphosate may be decreasing within populations.

The synthetic auxin herbicides, aminocyclopyrachlor and clopyralid, control dicotyledonous weeds in turf. Clippings of turfgrass treated with synthetic auxin herbicides have injured off-target plants exposed to herbicide-laden clippings. Labels of aminocyclopyrachlor and clopyralid recommend that clippings of treated turfgrass remain on the turf following a mowing event. Alternative uses for synthetic auxin-treated turfgrass clippings are needed because large quantities of clippings on the turf surface interfere with the functionality and aesthetics of golf courses, athletic fields, and residential turf. A white clover bioassay was conducted to determine the persistence and bioavailability of aminocyclopyrachlor and clopyralid in turfgrass clippings. Aminocyclopyrachlor and clopyralid were each applied at 79 g ae ha−1 to mature tall fescue at 56, 28, 14, 7, 3.5, and 1.75 d before clipping collection (DBCC). Clippings were collected, and the treated clippings were recycled onto adjacent white clover plots to determine herbicidal persistence and potential for additional weed control. Clippings of tall fescue treated with aminocyclopyrachlor produced a nonlinear regression pattern of response on white clover. Calculated values for 50% response (GR50) for visual control, for normalized difference vegetative index (NDVI), and for reduction in harvested biomass were 20.5, 17.3, and 18.7 DBCC, respectively, 8 wk after clippings were applied. Clippings of tall fescue treated with clopyralid did not demonstrate a significant pattern for white clover control, presumably because clopyralid was applied at a less-than-label rate. The persistence and bioavailability of synthetic auxin herbicides in clippings harvested from previously treated turfgrass creates the opportunity to recycle clippings for additional weed control.