The full spectrum of herbicide resistance in a weed can vary according to the mechanistic basis and cannot be implied from the selective pressure. Common ragweed (Ambrosia artemisiifolia L.) is an important weed species of horticultural crops that has developed resistance to linuron based on either target site– or non–target site resistance mechanisms. The objective of the study is to characterize the cross-resistance to metribuzin of linuron-selected biotypes of A. artemisiifolia with target site– and non–target site resistance and determine its genetic basis. Crosses were made between two types of linuron-resistant biotype and a linuron-susceptible biotype, and the progeny were further backcrossed with susceptible plants to the third backcross (BC3) generation to determine their responses to both herbicides compared with parental lines. The target site–based linuron-resistant biotype was cross-resistant to metribuzin, and resistance to both herbicides was maintained at the same level in the BC3 line. In contrast, the linuron-selected biotype with a non–target site resistance mechanism was not cross-resistant to metribuzin. In addition, the BC3 lines deriving from the non–target site resistant parents had very low-level resistance. While the target site–resistance trait is maintained through multiple crosses, non–target site based resistance would be lost over time when selection is absent or insufficient to retain all genes involved in resistance as a complex trait. This would imply A. artemisiifolia biotypes with different mechanisms would need to be managed differently over time.

Field experiments were conducted at the Montana State University Southern Agricultural Research Center, Huntley, MT, in 2011 through 2013 to determine the effect of nitrogen (N) rate, seeding rate, and weed removal timing on weed interference in barley. A delay in weed removal timing from the 3- to 4-leaf (LF) stage to the 8- to 10-LF stage of barley resulted in up to 3.5-fold increase in total weed biomass and 10% reduction in barley biomass, and this was unaffected by a N rate that ranged from 56 (low) to 168 (high) kg ha−1. The effect of N rate on barley biomass was more pronounced when weed removal was delayed from the 3- to 4-LF stage to the 8- to 10-LF stage of barley and in nontreated plots. Increasing the barley seeding rate from 38 to 152 kg ha−1 increased the barley plant density by 50%, biomass by 13%, and grain yield by 29%, averaged over N rates and weed removal timing. On the basis of 5 and 10% levels of acceptable yield loss, the addition of ≥112 kg N ha−1 delayed the critical timing of weed removal by at least 1.3 wk in barley, compared with the 56 kg N ha−1 rate. A medium or high N rate prevented reduction in barley grain quality (plumpness and test weight) observed when the seeding rate was increased from 38 to 76 or 152 kg ha−1 at the low N rate. In a separate greenhouse study, the effect of N rate on the effectiveness of various herbicides for controlling wild oat, green foxtail, kochia, or Russian thistle was investigated. Results highlighted that wild oat or green foxtail grown under 56 kg N ha−1 (low N) soil required 1.4 to 2.6 times higher doses of clodinafop, fenoxaprop, flucarbazone, glyphosate, glufosinate, pinoxaden, or tralkoxydim for 50% reduction in shoot dry weights (GR50) compared with plants grown under 168 kg N ha−1 (high N). Similarly, a reduced efficacy of thifensulfuron methyl + tribenuron methyl, metsulfuron methyl, or bromoxynil+pyrasulfotole was observed (evident from the GR50 values) for kochia or Russian thistle grown under low- vs. high-N soil. Information gained from this research will aid in developing cost-effective, integrated weed management (IWM) strategies in cereals and in educating growers on the importance of fertilizer N management as a component of IWM programs.

Research was conducted using a functional malachite green colorimetric assay to evaluate acetyl-coenzyme A carboxylase (ACCase) activity previously identified as resistant to sethoxydim and select aryloxyphenoxypropionate (FOPs) herbicides, fenoxaprop, and fluazifop. Two resistant southern crabgrass [Digitaria ciliaris (Retz.) Koeler] biotypes, R1 and R2, containing an Ile-1781-Leu amino acid substitution and previously identified as resistant to sethoxydim, pinoxaden, and fluazifop but not clethodim was utilized as the resistant chloroplastic ACCase source compared with known susceptible (S) ACCase. Dose-response studies with sethoxydim, clethodim, fluazifop-p-butyl, and pinoxaden (0.6 to 40 µM) were conducted to compare the ACCase–herbicide interactions of R1, R2, and S using the malachite green functional assay. Assay results indicated that R biotypes required more ACCase-targeting herbicides to inhibit ACCase activity compared with S. IC50 values of all four herbicides for R biotypes were consistently an order of magnitude greater than those of S. No sequencing differences in the carboxyltransferase domain was observed for R1 and R2; however, R2 IC50 values were greater across all herbicides. These results indicate the malachite green functional assay is effective in evaluating ACCase activity of R and S biotypes in the presence of ACCase-targeting herbicides, which can be used as a replacement for the 14C-based radiometric functional assays.

Agricultural spray drone (ASD) use in managed turfgrass has been given limited attention in the scientific literature. Further, deposition patterns of ASD spray have been obscured in previous research by ambient wind, crop canopy interference, and limited sampling resolution. Using a continuous sampling method involving blue colorant and water sprayed over white Kraft paper that was assessed via digital image analysis of stain objects and referenced spectrophotometric analysis of extractant, deposition metrics were estimated across a 29.3-m transect perpendicular to an ASD or ground-sprayer spray swath. The ASD applies very fine droplets that are highly concentrated with herbicide, similar to ultra–low volume treatments, that improved smooth crabgrass [Digitaria ischaemum (Schreb.) Schreb. ex Muhl.] control compared with a ground sprayer when the ASD was operated 2 m above the turf. Unfortunately, these very fine droplets also drift, leading to four times greater droplet density at distance of almost 12 m away from the targeted spray swath following an operational height of 10 m compared with 2 m. As ASD operational height increases, drift and effective swath width at 30% coefficient of variation uniformity increases, while effective application rate, total deposition, and D. ischaemum control by quinclorac herbicide decreased. Total deposition decreased 6% for each meter increase in ASD operational height, likely due to evaporation. The potential losses due to evaporation are a serious consideration for ASD use that has received little attention in the scientific literature. Our data suggest that ASD operational height should be as low as possible, but modification of spray systems may be needed to improve homogeneity of spray pattern.

Common lambsquarters (Chenopodium album L.) is one of the most troublesome weeds in soybean [Glycine max (L.) Merr.] and corn (Zea mays L.) fields in northeast China. In 2017, a C. album population that survived imazethapyr at the recommended field rate was collected from a soybean field in Heilongjiang Province in China. Experiments were conducted to determine the basis of resistance to imazethapyr and investigate the herbicide-resistance pattern in C. album. Dose–response tests showed that the resistant population (R) displayed high resistance to imazethapyr (20-fold) compared with the susceptible population (S). An in vitro acetolactate synthase (ALS) activity assay indicated that the ALS of the R population was resistant to imazethapyr compared with the ALS of the S population. Sequence analysis of the ALS gene revealed that the GCA was replaced by ACA at amino acid position 122, which resulted in an alanine to threonine substitution (Ala-122-Thr) in the R population. The R population displayed cross-resistance to thifensulfuron-methyl and flumetsulam but susceptibility to bispyribac-sodium, flucarbazone, glyphosate, mesotrione, and fomesafen. These results confirmed that the basis of imazethapyr resistance in C. album was conferred by the Ala-122-Thr substitution in the ALS enzyme. This is the first report of the target-site basis of ALS-inhibiting herbicide resistance in C. album.

Vipergrass [Dinebra retroflexa (Vahl) Panzer] is an annual weed of the Poaceae family distributed in several parts of Australia, Asia, and Europe. Very limited information is available on its germination response to different environmental conditions. Knowledge of its seed ecology and biology could help in formulating better weed management decisions. Experiments were conducted to study the effect of alternating temperatures, light conditions, salt stress, water stress, seed burial depths, and wheat residue amounts on the germination or emergence of D. retroflexa. Also, different pre- and postemergence herbicides were evaluated to control D. retroflexa. The highest germination (98%) was recorded at 30/20 C followed by 35/25 C (95%). Light was required for the germination of D. retroflexa. Germination decreased with an increase in sodium chloride (NaCl) concentrations. Even at 80 mM NaCl, 81% of seeds germinated, indicating D. retroflexa’s high salt tolerance. Seed germination gradually decreased with an increase in water stress, and no germination was recorded at −0.8 MPa osmotic potential. The emergence of D. retroflexa decreased with an increase in seed burial depths. The highest germination (83%) was recorded for surface-sown seeds, and emergence was reduced to 0 at a burial depth of 2 cm. Seedling emergence decreased from 82% to 2% when the crop residue load was increased from 0 to 800 kg ha−1. Applications of preemergence herbicides (at field rates), such as diuron, isoxaflutole, pendimethalin, pyroxasulfone, S-metolachlor, terbuthylazine, and triallate, and postemergence herbicides, such as clethodim, haloxyfop-methyl, glufosinate, glyphosate, imazamox plus imazapyr (a commercial mixture), and paraquat, resulted in complete control (100%) of D. retroflexa. Knowledge gained from this study will help us to understand the potential spread of D. retroflexa to other areas and to formulate integrated weed management strategies for its effective control.

Each year increasing numbers of garden chrysanthemums (Chrysanthemum morifolium Ram.) are grown in the field by commercial nurseries. The cost of labor for weeding and the scarcity of efficient seasonal labor presents a serious problem. This study was undertaken to determine if weeds in chrysanthemum plantings could be safely controlled chemically.

Field studies have been conducted at the Irrigation Experiment Station, Prosser, Washington, to determine the effects of 2,4–dichlorophenoxyacetic acid (2,4–D) in irrigation water on certain crop plants. The possibilities of contaminating irrigation water through the use of 2,4–D for weed control, particularly on ditchbanks, prompted these investigations. The response of Red Mexican beans and sugar beets to 2,4–D in irrgation water has been reported (1, 2). This publication deals with Concord grapes, a woody-type of crop plant.

Polychlorobenzoic acids (PBA), 2,3,6-trichlorobenzoic acid (2,3,6-TBA), and 2,3,6-trichlorophenylacetic acid (fenac) sprays were applied safely for the eradication of perennial weeds at not over 20 pounds per square inch in winds less than 11 miles per hour in and near cotton. Use of these herbicides near soybeans was hazardous because very small quantities of them caused leaf deformities and some loss in seed yield.

Increasing the forage yield of rangeland by controlling big sagebrush (Artemisia tridentata Nutt.) with fire, chemicals, or mechanical means has become a common procedure. The main problem confronting researchers has been the remarkable ability of sagebrush to re-establish itself after a control program. Fire and mechanical means of control have proved to be effective in killing established sagebrush. However, a heavy stand of young sagebrush often becomes re-established within a few years (3). Since the use of chemicals for sagebrush control has developed within the last decade, very little is known concerning the re-establishment of the plant in chemically controlled areas.

The cranberry (Vaccinium macrocarpum) is a low growing, perennial, woody plant of the boglands of the northern United States. Because cranberries are grown commercially on wet, low lying soils, the fields are often infested with a wide range of weeds common to such areas. Among the most common weeds of Wisconsin cranberry bogs are (1) sedge family: Carex oligosperma, Dulichium arundinaceum, and Eriophorum uirginicum; (2) rush family: Juncus effusus and J. canadensis; (3) horsetail family: Equisetum arvense and E. fluviatile; (4) fern family: Onoclea sensibilis and Osmunda regalis; (5) water plantain family: Sagittaria latifolia; (6) grass family: Leersia oryzoides, Glyceria canadensis and Calamagrostis canadensis; (7) composite family: Ambrosia artemisiifolia, Bidens connata, and Solidago graminifolia; (8) primrose family: Lysimachia terrestris and L. thyrsiflora; (9) buckwheat family: Polygonum sagittatum and P. amphibium; (10) rose family: Potentilla palustris and Rubus hispidus; (11) mint family: Lycopus uniflorus and Scutellaria epilobiifolia; (12) St. Johnswort family: Hypericum uirginicum; (13) gentian family: Menyanthes trifoliata; (14) willow family: Salix nigra and Populus tremuloides. Many other weed species occur in cranberry bogs, but they do not present a serious cultural problem.

Vinasse, a liquid fermentation residual of bio-ethanol production that also contains solid particles in suspension, is commonly used as a soil amendment. Previous studies reported vinasse reduced seed germination and seedling establishment, suggesting herbicidal activity. Laboratory experiments were conducted to determine whether vinasse herbicidal activity is present in the liquid or solid phase, and whether it affects plants during seed early germination (i.e., imbibition), late germination (i.e., embryo growth and radicle protrusion), or seedling growth. Most of the herbicidal activity was associated with the liquid phase, and for most species, seed viability was predominantly affected after the imbibition phase. Susceptibility to vinasse was species dependent. Lettuce (Lactuca sativa L.) germination was <8% when seeds were imbibed and germinated in vinasse solutions or imbibed in water and germinated in vinasse. Conversely, imbibing lettuce seeds in vinasse solutions and germinating them in water did not change their germination in comparison with seeds imbibed and germinated in water (>80% germination). Wheat (Triticum aestivum L.) and sicklepod [Senna obtusifolia (L.) H. S. Irwin & Barneby] germination decreased 10% and 35% when seeds were imbibed and germinated in vinasse, respectively, while Palmer amaranth (Amaranthus palmeri S. Watson) and southern crabgrass [Digitaria ciliaris (Retz.) Koeler] germination decreased >90%. All evaluated species reduced radicle growth as vinasse concentration increased. Filtered liquid vinasse with reduced concentration of salt and ionic compounds inhibited radicle growth similarly to unfiltered vinasse, indicating that the herbicidal activity was not due to osmotic effects and was likely present in the organic liquid phase. Amaranthus palmeri, S. obtusifolia, and D. ciliaris increased the proportion of dormant seed more than 2-fold when they were imbibed or imbibed and germinated in vinasse solutions. Vinasse might be useful for weed management to reduce germinable weed seedbanks by increasing seedling mortality and seed dormancy either by properly timing of its application as a soil amendment or by purifying herbicidal compounds and using them directly for weed control.

A new method for taking soil samples was devised. Vacuum is used to move the soil in an air stream from the sampling site into a sealed bag. Much of the hard, time-consuming work can be eliminated with this new method of sampling. No differences were noted in bioassay plants grown in samples of soil taken in the conventional manner, as compared to plants grown in samples taken with the vacuum device.

Many speakers preface their remarks to a group such as this with the statement, “I am most happy to be here, and have the opportunity to discuss with you…”. I have deliberately avoided that opening remark in most talks, but in this case that bit of rhetoric is appropriate. I am indeed most happy to once again address that professional society with which I have been most closely and most happily associated.

Cultures of Streptomyces tendae grown on Actinomyces medium containing clomazone contained less geosmin 48 h after inoculation than untreated controls, suggesting a possible inhibition of reactions prior to sesquiterpenoid biosynthesis. However, exposure to clomazone increased geosmin accumulation in S. tendae cultures grown on Hickey-Tresner medium and in cultures of the fungus Penicillium expansum. Additionally, clomazone increased accumulation of a sesquiterpenoid tentatively identified as a eudesmol in S. tendae, indicating possible point(s) of inhibition subsequent to sesquiterpenoid biosynthesis. Geosmin biosynthesis was induced by transferring cultures of S. tendae inoculated on Actinomyces medium to Hickey-Tresner medium 24 h after inoculation. When harvested at 48 h, geosmin biosynthesis-induced-cultures exposed to clomazone contained more geosmin than untreated controls, indicating that response of a single taxon to clomazone can be rapidly altered by changing medium composition.

Napropamide [2-(a-naphthoxy) N,N-diethylpropionamide] applied to cranberry (Vaccinium macrocarpon Ait.) as a granular or wettable powder formulation at 20 kg/ha in March 1978 controlled aster (Aster subspicatus Nees) and birdsfoot trefoil (Lotus corniculatus L.) without any phytotoxicity to ‘McFarlin’ cranberry vines. Earlier application in February was ineffective, and late application in April injured the vines. Napropamide 10% granular applied at 14 kg/ha in March 1979 controlled aster 90% and birdsfoot trefoil 70%, and the 50% wettable powder formulation controlled aster 90% and birdsfoot trefoil 80%. Applications of granular napropamide at 12 kg/ha in March of 1979 or 1980 controlled both weeds 70%.

Foliar abscission induced by mist blower applications of endothall [7-oxabicyclo(2,2,1)heptane-2,3-dicarboxylic acid] combined with ethephon [(2-chloroethyl)phosphonic acid] occurred within 14 days on six field-grown deciduous species. Refoliation was essentially complete after one dormant season except on pin oak (Quercus palustris Muenchh.), which exhibited shoot damage from May and June treatments. Abscission did not occur on coniferous species. Effective doses ranged from 150 to 2,400 μg/ml endothall with 4,800 μg/ml ethephon. In greenhouse experiments on white ash (Fraxinus americana L.), the most effective levels of surfactant with endothall/ethephon ranged from 0.5 to 1.3%, and a spray volume as low as one-quarter runoff gave adequate coverage.

Six substituted dinitrobenzamine herbicides, including butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine], dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), were evaluated as directed broadcast sprays applied and soil incorporated at time of last cultivation (layby) of cotton (Gossypium hirsutum L. ‘Acala SJ-2’). At the rates used, all herbicides provided more than 90% control of annual grasses. During 1976 and 1977, control of redroot pigweed (Amaranthus retroflexus L.) and smooth pigweed (Amaranthus hybridus L.) ranged from 90 to 100% and none of the herbicides differed significantly in their effect. However in 1975, butralin at 1.1 kg/ha did not improve pigweed control when compared to the untreated control. None of the herbicides consistently controlled black nightshade (Solanum nigrum L.) and except pendimethalin, none caused detectable cotton injury. In 2 of 3 yr, pendimethalin caused enlarged growth of the cotton stem in the cotyledonary node area contacted by the herbicide spray. Stem breakage following wind occurred in about 5% of the cotton plants; however, the injury was not manifested by reduced yield. None of the herbicides influenced cotton yield. Residues from soil samples collected 4 months after herbicide application reduced growth of Japanese millet [Echinochloa crus-galli (L.) Beauv. var. frumentacea (Link) Wright]3 and grain sorghum [Sorghum bicolor (L.) Moench] 24 to 49%.