Rates of 0, 1.7, and 3.4 kg/ha of 3-amino-2,5-dichlorobenzoic acid (chloramben) were incorporated to 0, 3.8, and 7.6-cm depths in 0.7 by 0.7-m microplots under low, moderate, and high rainfall conditions. Soybean [Glycine max (L.) Merr., var. Amsoy] injury increased with increasing depth of incorporation of 3.4 kg/ha chloramben. Chloramben incorporation under low rainfall conditions significantly improved control of giant foxtail (Setaria faberii Herrm.), smooth pigweed (Amaranthus hybridus L.), and velvetleaf (Abutilon theophrasti Medic.) compared to surface treatments. Jimsonweed (Datura stramonium L.) was not controlled well by chloramben regardless of rate or incorporation depth. In larger field plots over a 3-year period, 3.4 kg/ha chloramben incorporated with a disc produced slight but insignificant soybean injury. Giant foxtail, smooth pigweed, common ragweed (Ambrosia artemisiifolia L.), and velvetleaf control with incorporated chloramben was equal to or better than the control obtained with surface-applied chloramben. Regardless of method of application, control of common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed, and annual morningglory (Ipomoea spp.) was poor.

A portable, multiple-tanked spray apparatus has proved convenient and effective for field tests, particularly in steep and remote areas where more elaborate sprayers cannot operate. No hand pumping is necessary and the quickly interchangeable multiple tanks permit mixing and preloading of spray materials in the laboratory. The resultant saving of time in the field often means the difference between completion of a spraying experiment in 1 day rather than 2 or 3, a factor that increases in importance with the remoteness of the research area.

The genetic variation at 12 isozyme loci was investigated in the three species (Xanthium italicum, X. strumarium, and X. orientale) forming a X. strumarium complex in Italy. Very little variation was found within species at the loci studied in contrast to the considerable interspecies genetic differentiation at several loci. The gene differentiation between species was ranged from 61 to 91%. The observed genetic structure of the X. strumarium complex was consistent with that found for predominantly autogamous species. The values of maximum outcrossing rates estimated in original sampling sites and in a field test ranged from 8 to 17%, confirming previous observations that Xanthium species are predominantly self-pollinated. Gene duplications were evident in the three Xanthium species because of their likely polyploid origin. The percentage of duplicate loci exhibiting “fixed heterozygosity” was 25, 25, and 16% in X. italicum, X. strumarium, and X. orientale, respectively. Data presented supported that both mating system and ploidy level were fundamental features in adaptation process of investigated Xanthium species. Some evidence suggested that polyploidization occurred before speciation of X. italicum, X. strumarium, and X. orientale. As a consequence, a common ancestral progenitor could be postulated for the three species. During geographical adaptation, the three species fixed alternative alleles in some loci, and the process was favored by the predominantly autogamous mating system. On the contrary, fixed heterozygosity in duplicated loci allowed maintenance of a sufficient level of gene diversity in the three Xanthium species to ensure wide adaptability in different microhabitats (i.e., abandoned land, roadsides, and field crops) and to avoid the negative effect of inbreeding depression.

Preemergence applications of DCPA (dimethyl 2,3,5,6-tetrachloroterephthalate) controlled germinating seedlings of largeseed dodder (Cuscuta indecora Choisy) in alfalfa, and the control continued throughout the season. Applications of DCPA were necessary prior to germination of dodder seed. Under California conditions, applications of DCPA made during early winter (December) provided early season control but not satisfactory control throughout the season as was accomplished with the March treatments. Autoradiographic studies showed only limited movement of tracer in alfalfa plants.

The herbicide 4-amino-3,5,6-trichloropicolinic acid (picloram) was applied to several bermudagrasses (Cynodon spp.). Most of the grasses were susceptible to picloram; however, some were resistant and recovered within 16 months from the initial treatment. There were no detectable metabolites of 14C picloram in bermudagrass (C. dactylon (L.) Pers. ‘U-3’) or common Kentucky bluegrass (Poa pratensis L.). Also, there were no abnormal changes in cells of swollen nodes of picloram-treated bermudagrass that could explain the selective herbicidal injury of picloram on bermudagrass.

In Louisiana approximately 300,000 acres of sugarcane are grown each year for the manufacture of sugar. Another 125,000 acres are necessary for the rotation program, making approximately 425,000 acres devoted to the production of cane. Of these, 100,000 acres were estimated in 1950 to be so badly infested with Johnson grass (Fig. 1) that a control program was necessary to obtain economic yields of cane. In addition to this acreage, headlands, ditchbanks, and roadsides of many additional plantations were infested with Johnson grass and constituted a potential threat to the cane fields.

An enzymatic (amylase) pretreatment was developed that allows quantitative recovery of the parent compound from soil samples receiving the pesticide in starch-encapsulated formulation. The pretreatment involves adding amylase, dissolved in a phosphate buffer solution, to soil samples and incubating the resulting slurry at 50 C for 1 h. Efficiency of this pretreatment was tested on two soils, a silty clay and a loamy sand, receiving atrazine and alachlor in the starch-encapsulated formulation. The inexpensive method adds approximately 1 h to the extraction procedure and a twofold increase in percentage recovery of starch-encapsulated atrazine. The enzyme pretreatment is not necessary for quantitative recovery of pesticides that have rapid rates of release such as alachlor. The method will be useful for studying starch encapsulation pesticide behavior in the soil environment.

Sericea lespedeza (Lespedeza cuneata (Dumont) G. Don, var. Serala) was planted in three field experiments at three seeding rates with four rates of S-propyl dipropylthiocarbamate (vernolate). Grass and broadleaf weed populations were reduced, but sericea was unaffected by vernolate incorporated preplant. Use of a herbicide permitted a reduction in seeding rate with no decrease in sericea stand or forage yield. This treatment permitted harvesting a cutting of hay the establishment year with only a minor effect on production the next year. The beneficial effect of vernolate on sericea yield continued the second year, mainly because sericea plants were better established and more vigorous. Sericea seeding rate did not affect weed competition or forage yield. A seeding rate of 11 kg/ha with 3.4 kg/ha vernolate was the most practical treatment.

Studies in New Mexico showed basal and stump applications of ester and oil-soluble amine formulations of 2-(2,4,5-trichlorophenoxy)propionic acid (silvex) to be effective for control of saltcedar (Tamarix pentandra Pall.). Trees with trunks 2 inches or larger in diameter were harder to kill than smaller trees and retreatment was often needed. Spraying the lower 2 feet was no more effective than spraying the lower foot. Cutting the larger trees and spraying the stump increased effectiveness.

Annual sowthistle (Sonchus oleraceus L.) is a broadleaf weed that is increasing in prevalence in the northern cropping regions of Australia. Being a member of Asteraceae family, this weed possesses many biological attributes needed to thrive in varying environments and under differing weed management pressures. Interference of this weed in a wheat (Triticum aestivum L.) crop was examined through field studies in 2016 and 2017. Different densities of S. oleraceus were evaluated for their potential to cause yield loss in wheat: 0.0 (weed-free), low (9 to 15 plants m−2), medium (29 to 38 plants m−2), and high (62 to 63 plants m−2). Based on the exponential decay model, 43 and 52 plants m−2 caused a yield reduction of 50% in 2016 and 2017, respectively. Yield components such as panicles per square meter and grains per panicle were affected by weed density. At the high weed infestation level, S. oleraceus produced a maximum of 182,940 and 192,657 seeds m−2 in 2016 and 2017, respectively. Sonchus oleraceus exhibited poor seed retention at harvest, as more than 95% of seeds were blown away by wind. Adverse effects on crop, high seed production, and wind-blown dispersal may lead to an increased prevalence of this weed in the absence of an integrated weed management strategy utilizing both herbicides and nonchemical options.

Glyphosate-resistant (GR) horseweed [Conyza canadensis (L.) Cronquist; syn.: Erigeron canadensis L.] interference can substantially reduce corn (Zea mays L.) yield. The complementary activity of 4-hydroxyphenylpyruvate dioxygenase (HPPD) and photosystem II (PSII) inhibitors has been investigated for the control of several weed species, and in many cases has been synergistic; however, there is little information on the interaction of HPPD- and PSII-inhibiting herbicides for postemergence control of GR C. canadensis in corn. Four field trials were studied over 2 yr (2019, 2020) in Ontario, Canada, in commercial corn fields with natural infestations of GR C. canadensis to evaluate the level of GR C. canadensis control with three HPPD-inhibiting herbicides (mesotrione, tolpyralate, and topramezone) and three PSII-inhibiting herbicides (atrazine, bromoxynil, and bentazon) applied individually and in tank-mix combinations, and to document the interaction of the three HPPD inhibitors tank mixed with the three PSII inhibitors. Mesotrione, tolpyralate, and topramezone controlled GR C. canadensis 83%, 84%, and 72%, respectively, at 8 wk after application (WAA). Bromoxynil and bentazon controlled GR C. canadensis 71% and 79%, respectively, while atrazine provided only 31% control at 8 WAA. The joint application of atrazine, bromoxynil, or bentazon with mesotrione increased GR C. canadensis control from 83% to 100% at 8 WAA. Tolpyralate tank mixed with atrazine, bromoxynil, or bentazon controlled GR C. canadensis 96%, 98%, and 98%, respectively, which was comparable to the mesotrione tank mixes at 8 WAA. Topramezone plus atrazine, bromoxynil, or bentazon controlled GR C. canadensis 91%, 93%, and 95%, respectively, at 8 WAA. Interactions between HPPD and PSII inhibitors were synergistic for all combinations of mesotrione or tolpyralate with atrazine, bromoxynil, or bentazon. The interaction between topramezone and PSII inhibitors was additive. All nine tank mixes controlled GR C. canadensis >90%. This study concludes that bromoxynil or bentazon, instead of atrazine, can be co-applied with mesotrione, tolpyralate, or topramezone without compromising GR C. canadensis control in corn.

Field studies were established in 1974 and 1975 at various locations in San Diego County, CA, to evaluate several herbicides for the control of chamise (Adenostoma fasciculatum H.&A.) and redshank chamise (Adenostoma sparsifolium Torr.). Herbicide effects on vegetation were reevaluated in 1982. Plots originally treated with 2.2 or 4.5 kg ae/ha of glyphosate [N-(phosphonomethyl)glycine] had virtually no chamise regrowth 8 yr after treatment. The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], combinations of 2,4-D with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or dichlorprop [2-(2,4-dichlorophenoxy) propionic acid], fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and picloram (4-amino-3,5,6-trichloropicolinic acid) had no long-term effects on chamise. Soil collected in 1982 from glyphosate-treated plots contained similar numbers of chamise seeds but fewer seeds of other species compared to untreated plots. Canopy cover of redshank chamise was similar in treated and untreated plots after 8 yr. These results document the effectiveness of glyphosate in killing the underground root-crown of chamise, which prevented sprouting, but not redshank chamise.

Field studies were conducted over 3 yr in central Spain to investigate the tolerance of common vetch and oat to some preemergence herbicides and their effects on weed control, forage yields, and botanical composition of the forage mixture. Pendimethalin was the only herbicide that injured common vetch. Pronamide and pronamide plus diuron injured oat by affecting plant emergence. Prevalent weed species were fumitory, henbit, and wild buckwheat. All herbicides provided more than 90% control of fumitory and most herbicides except pronamide provided more than 90% control of henbit relative to the untreated check. Wild buckwheat stands were reduced by isoxaben (68%), linuron (40%), prometryn (69%), pronamide (86%), and pronamide plus diuron (61%). More than 90% control of prostrate knotweed was achieved with isoxaben, pronamide, and terbutryn. Pronamide and pronamide plus diuron reduced forage yields and increased vetch in the forage. The untreated vetch and oat monocrop treatments showed the competitive advantage of oat over vetch and weedy species.

The etymology of herbicide has been traced to a U. S. trademark originally registered by William J. Reade of the Reade Manufacturing Company.

Greenhouse and laboratory experiments were conducted to evaluate the influence of two organosilicone surfactants and spray nozzle types on the spray deposition, absorption, translocation, and efficacy of the monoethanolamine salt of clopyralid on honey mesquite. Sylgard 309 or Silwet L-77 added to the spray solution at 0.1, 025 and 0.5% by vol did not increase spray deposition, absorption, translocation, or phytotoxicity of clopyralid applied at 140 g ae ha-1 on honey mesquite compared to no surfactant An air-assist spray nozzle at 9.4 L ha-1 by vol resulted in greater initial clopyralid deposit on honey mesquite than hydraulic nozzles at 9.4 or 187 L ha-1 by vol, but air-assist application did not increase phytotoxicity compared to hydraulic nozzles.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 3.4 and 6.7 kg/ha controlled weeds present in sweet potatoes (Ipomoea batatas L. ‘Jewel’, ‘Centennial’, ‘Caromex’) at two locations in North Carolina. Yield was not reduced from slight early season injury observed with the herbicide treatments. Most sweet potato root samples contained less than the detectable limit of 0.05 ppmw of alachlor. At one location, samples of the cultivars Jewel and Centennial that received 6.7 kg/ha contained 0.06 and 0.05 ppmw, respectively. Averaged over locations, residue levels in soil samples from plots treated at 6.7 kg/ha decreased from 1.55 ppmw initially to less than 0.05 ppmw by 16 weeks after application.

Maturation rate, pod production, and density of common milkweed (Asclepias syriaca L.) were determined at sites in east-central Missouri. Emergence of milkweeds in May was followed by blooming of flowers in late June, production of full-size follicles (average of 5.1 per plant) by late July, and release of seed in mid-September. Density was 1 to 3 plants per m2 and spacing of plants in 1.4 m2 samples was equidistant. Significant. positive correlations were found between mean height of milkweeds and pH, magnesium and calcium concentrations in the soil, and between density and pH of the soil.

Greenhouse hydroponic and field experiments were conducted to determine the effect of nitrogen (N) fertilizer on eastern black nightshade growth and N content. After 4 wk in hydroponics, the greatest shoot dry mass occurred in the 5 or 10 mM nitrate treatments. An exponential model was strongly correlated with eastern black nightshade root and shoot growth in the 5 or 10 mM nitrate treatments. Eastern black nightshade reached the exponential stage of growth approximately 21 d after transfer to the nitrate treatments. Root dry mass was only 10% of shoot biomass. There was a substantial increase in height and growth rate when plants were fertilized with 168 kg N ha−1. Eastern black nightshade was at its maximum growth 12 wk after planting, and fresh mass increased with N up to 336 kg N ha−1, the greatest N concentration in the study. The greatest N content was in the upper leaves and the least in the lower stem. These results indicate that eastern black nightshade growth is favored by high rates of N.

Sorption and desorption of cyanazine with three Mississippi Delta soils (two silt loams and one silty clay) were studied under laboratory conditions. Cyanazine sorption calculated using the Freundlich equation was greatest for the Sharkey silty clay soil. Partition coefficients (K d values) for cyanazine sorption ranged from 1.67 to 1.82, 1.92 to 2.15, and 3.65 to 3.96 ml g−1 for the Bosket silt loam, Dubbs silt loam, and Sharkey silty clay soils, respectively. Differences in sorption and K d values were attributed to clay content. At a given initial cyanazine concentration, cyanazine was desorbed more readily from the silt loam soils than from the Sharkey clay after the first 4-h desorption cycle. Desorption from the Sharkey clay continued for a longer period than that from the silt loam soils, with up to 6% cyanazine desorption from the Sharkey clay after a 16-h desorption cycle compared with 0% for the silt loam soils. Cyanazine losses increased with decreasing clay content, Dubbs = Bosket > Sharkey. This implies a potential relationship between cyanazine desorption and surface runoff losses of cyanazine.