Whole plant and tissue culture experiments were conducted to determine the difference in phytotoxicity of 2,4-D and its metabolite, 2,4-DCP, to red clover. At the whole plant level, the mean concentration of 2,4-DCP (10 mM) required to cause 50% growth inhibition (I50) of shoot dry weight was 24 times greater than for 2,4-D (0.42 mM). Using callus tissue, the I50 value for 2,4-DCP (0.28 mM) was 22 times greater than for 2,4-D (0.013 mM) based on dry weights. The callus tissue was 36 and 32 times more sensitive to 2,4-DCP and 2,4-D than shoot tissue based on dry weights, respectively. These data indicate that 2,4-DCP was less phytotoxic than 2,4-D to red clover both in vitro and in vivo.

Young orange [Citrus sinensis (L.) Osbeck ‘Pineapple sweet orange’] trees are more sensitive to bromacil (5-bromo-3-sec-butyl-6-methyluracil) than young mandarin (Citrus reticulata Blanco ‘Cleopatra mandarin’) trees. Pineapple sweet orange roots absorbed twice as much 14C from bromacil, and accumulated three times as much in the leaves, as did Cleopatra mandarin. The amount of conjugated metabolites formed was the same in the roots of the two cultivars, but twice as much formed in the leaves of Cleopatra mandarin as in the leaves of Pineapple sweet orange. The principle metabolite was 5-bromo-3-sec-butyl-6-hydroxymethyluracil; a minor metabolite was tentatively identified as 5-bromo-3-(3-hydroxyl-1-methylpropyl)-6-methyluracil. No 5-bromouracil was detected. Citrus cultivars differ in their ability to accumulate and metabolize bromacil into conjugated nonphytotoxic compounds.

The influence of repeated clipping of the shoots on the translocation of 14C-assimilates and 2,2-dichloropropionic acid 2-14C (dalapon) into the rhizome system of established johnsongrass (Sorghum halepense (L.) Pers.) was studied when regrowth was in the preboot, boot, and flowering stages. Radioautography and radio-assay procedures were used to follow the distribution of label within the plants. Plants defoliated three times prior to treatment showed no increase in basipetal translocation over plants defoliated once. As plants matured to the flowering stage, assimilate translocation into rhizomes increased. This increase was closely related to the degree of secondary rhizome growth occurring at time of label application. During preboot, assimilate movement was restricted to rhizome apices with very little retention in intervening tissue. Labeled dalapon followed a similar translocation pattern to that of assimilates. The role of assimilate translocation and storage as correlated with life cycle changes in carbohydrate nutrition of established johnsongrass is discussed.

A survey of the phytophagous insect fauna of Russian thistle (Salsola kali L., var. tenuifolia Tausch) showed that this weed serves as an alternate feeding and/or breeding host to a number of economically important insects in southern California.

BAS 9052 {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexene-1-one} and difenopenten {4-[4-[4-(trifluoromethyl)phenoxy]phenoxy]-2-pentenoic acid} concentrations less than 1% (w/w) did not normally inhibit apparent photosynthesis (AP) of corn (Zea mays L. ‘Mo 17 × B73′) leaves for at least 24 h. However, leaf growth was completely inhibited by BAS 9052 within 24 h. Leaf AP was initially more inhibited in soybean (Glycine max L. ‘Corsoy’) than in corn by each herbicide, but within 48 h soybean AP was usually recovering and plants grew normally. Because inhibition of corn leaf growth preceded that of AP, leaf photosynthesis could not be a primary mode of action for BAS 9052.

Studies were conducted to determine acifluorfen and lactofen absorption, translocation, and metabolism in protox-inhibiting herbicide-susceptible and -resistant common waterhemp. Acifluorfen and lactofen absorption was similar in both biotypes. Herbicide absorption was 12% in both susceptible and resistant common waterhemp 6 h after treatment (HAT). Absorption increased to 32 and 42% in susceptible and resistant plants, respectively, at 72 HAT. Translocation was similar in both biotypes for both herbicides. Herbicide translocation out of the treated leaf ranged between 5 and 15%. In a separate study, resistant common waterhemp plants were treated with acifluorfen or lactofen, alone or with tridiphane. Acifluorfen or lactofen injury to resistant common waterhemp was not altered with the addition of tridiphane. Treatments of 14C-acifluorfen or -lactofen on susceptible and resistant common waterhemp resulted in similar lactofen metabolism in both biotypes, but acifluorfen was not metabolized in either biotype within 24 HAT. This data indicate that differences in herbicide absorption, translocation, or metabolism are not the mechanism of common waterhemp resistance to protox-inhibiting herbicides.

Injury to weeds from sublethal doses of POST herbicides may reduce the effect of weed interference on crop yield. Information on how herbicide dose influences weed mortality, growth, and seed production is needed to assess the potential benefit of applying reduced herbicide doses. Field experiments were conducted at Mead, NE, in 2001 and 2002 to quantify velvetleaf mortality, growth, and corn–velvetleaf interference in response to varying doses of three POST herbicides. Untreated velvetleaf at six densities (0, 1, 3, 6, 12, and 20 plants m−1 corn row) was grown in mixture with corn to establish a baseline corn–velvetleaf interference relationship. Treated velvetleaf at a density of 20 plants m−1 row received one of five doses of dicamba, halosulfuron, or flumiclorac. Untreated velvetleaf height, biomass, and seed capsule production were greater in 2002 than 2001 and declined with increasing velvetleaf density in both years. Corn yield was not affected by untreated velvetleaf in 2001, but yield loss increased with increasing velvetleaf density in 2002. Mortality of herbicide-treated velvetleaf was 56% greater in 2001 than 2002 and increased with increasing herbicide dose. Maximum height of treated velvetleaf was similar for all treatments in 2001 but declined with increasing herbicide dose in 2002. Biomass and seed production of treated velvetleaf varied among herbicides in 2002 and decreased with increasing dose. Corn yield was not influenced by velvetleaf in 2001, but yield loss in response to herbicide-treated velvetleaf declined with increasing herbicide dose in 2002. Results show that the assumption that weeds surviving herbicide application are as competitive as untreated weeds is incorrect. Reduction in growth and resource consumption by herbicide-damaged weeds reduced the negative effects of weeds on corn.

A mixed stand of green rabbitbrush (Chrysothamnus viscidiflorus (Hook.) Nutt. var. puberulus Jepson) and big sagebrush (Artemisia tridentata Nutt.) was sprayed at different dates for 3 years with potassium salt of 4-amino-3,5,6-trichloropicolinic acid (picloram) at ¼, ½, and 1 1b/A, propylene glycol butyl ether esters of 2,4-dichlorophenoxyacetic acid (2,4-D) at 1, 2, and 3 1b/A, and a mixture of triisopropanolamine salts of picloram plus 2,4-D at ¼ plus 1 and ½ plus 2 1b/A. Picloram at ½ and 1 1b/A controlled rabbitbrush but not sagebrush. Poor rabbitbrush control and fair to good sagebrush control resulted from 2,4-D. The mixture of picloram and 2,4-D controlled rabbitbrush well but only partially controlled sagebrush. Forage release from brush control was negligible the first 2 years after spraying. During the third and subsequent years, production of crested wheatgrass (Agropyron desertorum (Fisch.) Schult.) was greatly increased.

Chlorimuron antagonized the activity of quizalofop on broadleaf signalgrass when applied in greenhouse studies as a postemergence tank mix. In vitro leaf disc assays utilizing 14C-acetate or 14C-pyruvate as substrates were conducted to ascertain the effect of clorimuron and quizalofop on fatty acid biosynthesis and to determine if antagonism between the two herbicides occurs at the biochemical sites of action. Incorporation of 14C-acetate in control treatments was linear with time to 120 min. Acetate incorporation in the presence of quizalofop (1.1 μM) was also linear but was inhibited 30 min after initialization of the reaction. The concentration of quizalofop that inhibited 14C-acetate incorporation 50% (I50) was 0.54 μM. Chlorimuron, up to 155 μM, had no effect on 14C-acetate incorporation. A mixture of quizalofop (1.1 μM) and chlorimuron (4.8 μM) inhibited 14C-acetate incorporation similar to that of quizalofop alone at 1.1 μM. Quizalofop I50 for incorporation of 14C-pyruvate was 1.1 μM, and clorimuron at 4.8 μM decreased incorporation 15%. Excess unlabeled pyruvate (5 μM) had no effect on either 14C-acetate or 14C-pyruvate incorporation in the presence of both herbicides. It is believed that antagonism of quizalofop by clorimuron is not due to an excess pool of pyruvate resulting from inhibition of acetolactate synthase by chlorimuron.

A multiple access key, or polyclave, and a traditional dichotomous key were constructed for the identification of 40 species of weed seedlings. The polyclave contained 3.4 times more information than the dichotomous key; however, there was no difference in the frequency of accurate identifications or in the time required to make accurate identifications using either system. The relative values of traditional keys and polyclaves for weed seedling identifications are discussed.

The loss of 2-chloroallyl diethyldithiocarbamate (CDEC) from the dry surface of four soils was followed over a 24-hr period by spectrophotometric procedures. As the temperature was in creased from 31 C to 44 C and to 54 C, average losses from all soils increased from 33 to 47 to 54%, respectively. There was relatively little difference in rates of loss from the different soils. Loss at 44 C at low (20%) and moderate (65%) relative humidity generally was similar in magnitude. Losses from a wet soil surface at 44 C were much more rapid than from a dry soil.

The compound 3-amino-1, 2,4-triazole (ATA) is water soluble, heterocyclic and will react with most acids and bases to form salts. Several workers have reported that ATA is a promising herbicide for the control of a number of weed species. ATA was first noted to have defoliating and regrowth-inhibiting properties on cotton in tests conducted by workers of the Texas Agricultural Experiment Station in 1952. The compound was found to increase the effectiveness of many commercial defoliants while adding the property of regrowth inhibition. During 1954 and 1955, a number of tests were conducted with various salts and derivatives of ATA in the hope that they would be more effective at lower rates as cotton defoliants and regrowth inhibitors. The present paper compares the performance of ATA with eight of its salts or derivatives which were found to be the most successful in defoliating cotton and controlling regrowth after preliminary screening in the greenhouse.

The bentgrasses comprise an adaptable group of grasses that include introduced species, cultivated turfgrasses, and native plants in North America. Their distribution in cultural landscapes has not been documented, and this gap in knowledge has limited the development of predictive ecological risk assessments for creeping bentgrass engineered for herbicide resistance. In this study, bentgrass distribution and abundance were surveyed in 289 plots in an 8.5 km2 site surrounding a golf course in the northeastern United States. Four introduced species and two native bentgrasses were identified in seminatural and managed plant communities. Across the study site, 77% of the plots containing creeping bentgrass also had invasive plants. Bentgrasses co-occurred with critical habitat for threatened or endangered animals. Multivariate logistic regression analysis showed that bentgrasses were positively correlated with herbaceous plant cover and mowing, but negatively correlated with tree canopy cover, shrub cover, poorly drained soils, and leaf litter. The most influential ecological factors were tree canopy cover and soil moisture. Geospatial information about these two ecological factors was combined with mathematical models to generate two habitat suitability maps. The favorable environments map (FEM) showed that highly suitable bentgrass habitat covered 36% of the study site and included common features such as home lawns and railroad right-of-ways. Our results suggest that release of herbicide-resistant creeping bentgrass in this cultural landscape could potentially result in pollen-mediated gene flow, interspecific hybridization, environmental hazards, and herbicide selection pressure in some areas. Habitat suitability maps could be critical tools for predictive ecological risk assessments, monitoring projects, and management of herbicide-resistant bentgrasses.

The hypothesis that leaf injury from applications of fenuron (3-phenyl-1,1-dimethylurea) is a direct result of a lack of photosynthate did not explain the results of experiments with seedlings of shrub live oak (Quercus turbinella Greene) supplied with an acorn food reserve supplemented with glucose solution, and with seedlings whose acorns were excised or left attached to the seedlings. An alternate hypothesis is offered: acute leaf injury from phenylurea treatment is due to one or more components of the electron transport chain, between the chlorophyll b pigment system and the reduction of triphosphopyridine nucleotide, which are left in a toxic oxidized state as a result of the phenylurea block in the oxygen-liberating system. Evidence also favors the above interpretation rather than the idea that toxicity results from the accumulation of a toxic oxidized product on the oxygen-liberating pathway. Although leaf injury appears to be due to toxic components of the inhibited photosynthetic apparatus, the ultimate cause of death of the entire plant is starvation.

Besides its effect on photosynthesis, fenuron at high concentrations also causes inhibition of root growth.

Growth chamber and greenhouse studies were conducted to evaluate effects of long-term low-light intensity on wild oat control with imazamethabenz and fenoxaprop. Seventy percent shading imposed during the entire experimental period resulted in enhanced activities for both herbicides applied at early and later growth stages. Such shading also reduced wild oat regrowth following application of imazamethabenz and fenoxaprop. When applied to plants exposed to 70 to 90% prespraying shading, both herbicides had phytotoxicity similar to, or better, than plants grown under continuous shading. Postspraying shading has less effect on herbicidal activity than prespraying shading or prolonged shading, especially with imazamethabenz. Full-light treatment more adversely affected fenoxaprop activity than imazamethabenz activity.

The adsorption of picloram (4-amino-3,5,6-trichloropicolinic acid) was determined on an Aiken silt loam, on three cation exchange resins and on a single anion exchange resin. Adsorption data were evaluated using parameters in the Freundlich equation and their dependance upon cationic composition of the exchange complex, the ionic composition of the equilibrium solution, and the equilibrium solution pH. For the Aiken soil saturated with metallic cations the order of decreasing picloram adsorptive capacity was Fe+3 = Cu+2 > Al+3 > Zn+2 > Ca+2 > native soil. Increases in adsorption compared to the native Aiken soil could be explained on the basis of decreases in the equilibrium solution pH except for Fe+3, Zn+2, and especially the Cu+2 treatments. The adsorptive capacity of the Aiken soil was altered by the addition of several salts simulating addition of fertilizer salts. The Cu+2 and Zn+2 salts were the only treatments showing increased adsorption which could not be explained readily by pH changes. KH2PO4 and NH2CONH2 (urea) reduced picloram adsorption. Dowex 50-1 × 4, a strongly acidic cation exchange resin, showed increased picloram adsorptive capacity in the order Cu+2 > Al+3 > Ca+2 > Zn+2 = H+. Cellex CM, a weakly acidic cellulose exchanger had increased adsorptive capacities in the order of Cu+2 > Ca+2 > Al+3 > Na+ > Fe+3 > Zn+2. Picloram adsorption by an anion exchange resin at pH 6.1 was nearly 100%. These results suggest that complex formation of picloram with polyvalent cations on the exchange complex is likely especially for Cu+2 and to a lesser extent Fe+3 and Zn+2. In soils such complex reactions would most probably involve organic matter, polyvalent cations, and picloram. The formation of chelate ring species is proposed.

All of us expect good food in adequate quantities. The question is how to reach this aim in the near future with an increasing world population (Table 1). A comparison of past figures with those forecast for the coming years tells us that in the near future the rate of population growth will greatly outpace the available arable land. Dietary energy requirements will increase. Consumption of grain crops will increase although on a smaller scale than in the past. The need for protein products will also continue to soar.

Watering with 1 surface cm or more following spray treatment with dicamba (2-methoxy-3,6-dichlorobenzoic acid) and picloram (4-amino-3,5,6-trichloropicolinic acid) markedly increased inhibition of shoot growth from rhizome sections of quackgrass (Agropyron repens (L.) Beauv.) and bromegrass (Bromus inermis Leyss). Shoots were most sensitive to the herbicides at early stages of development. Bromegrass and quackgrass were about equally susceptible to the two herbicides. Uptake through roots or rhizomes was more effective than foliar uptake. Kentucky bluegrass in established sod was not injured by dosages of the two herbicides that killed or controlled quackgrass. Young stands of Kentucky bluegrass were more sensitive.

To evaluate the effect of different soil moisture levels on the phytotoxicity of soil applications of arsenic trioxide (As2O3), water and alcohol extractable soil arsenic (As) data were related to the growth and development of 4-month-old Monterey pine (Pinus radiata D. Don.) in greenhouse soil cultures. Also, various rates of As2O3 and water were applied to the surface of soil columns to determine the effective penetration of soluble As. Under normal moisture regime, 8000 lb/A of As2O3 were required for high phytotoxicity on a Chenango silt loam, with excessive moisture resulting in an increase in this phytotoxic effect. With water and alcohol extraction procedures, an adequate range of values was obtained in relation to the total As2O3 rates and plant responses. Lethal concentrations of As in the soil columns were limited to the surface 3 in depth in the silt loam.

Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] at 2.2 to 4.4 kg/ha controlled goosegrass [Eleusine indica (L.) Gaertn.] without injuring bermudagrass [Cynodon dactylon (L.) Pers.], but severely injured overseeded common ryegrass (Lolium multiflorum Lam. common) and perennial ryegrass (Lolium perenne L. ‘Medalist VI′) for a 5 – to 6-week period after treatment in the spring and thus reduced turf quality. The transition was poor because ryegrass was killed faster than bermudagrass could initiate new spring growth. The combination of bensulide [O, O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] and oxadiazon applied as a single treatment at 6.7 + 1.7 kg/ha controlled goosegrass as effectively as did oxadiazon applied alone at 2.2 kg/ha or higher rates and did not injure the turf, so the transition from cool-season grass to bermudagrass was uniform. Aeration of an overseeded bermudagrass turf after applications of oxadiazon did not significantly decrease goosegrass control.