ED50 values (the dosage required to reduce the posttreatment gain in dry weight by 50%) for diclofop applied to green and yellow foxtail [Setaria viridis (L.) Beauv. ♯3 SETVI and S. lutescens (Weigel.) Hubb. ♯ SETLU] at the two- and four-leaf stages were calculated from linear regression equations derived by plotting the logarithm of the applied dosage against the relative growth reduction expressed as a probit value. At the two-leaf stage, green foxtail was more susceptible to the chemical than yellow foxtail but at the four-leaf stage there was no significant difference in response of the two species. At least part of the difference in sensitivity of the two species at the two-leaf stage could be accounted for by differences in spray retention, with green foxtail retaining 1.8 times (expressed as μL/cm2) or 3.5 times (expressed as μL/g dry weight) as much spray as yellow foxtail, despite the fact that yellow foxtail had a greater projected leaf area. At the four-leaf stage, the amount of spray retained by both species calculated on a per gram dry-weight basis was significantly less than at the two-leaf stage, accounting in part for the higher ED50 values obtained at the later growth stage. However, there appeared to be no direct relationship between the amount of spray retained and the comparative growth response of the two weeds at the later stage of application.

Under greenhouse conditions, approximately 50% visible control of bermudagrass [Cynodon dactylon (L.) Pers. ♯3 CYNDA], quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE], and wirestem muhly (Muhlenbergia frondosa L. ♯ MUHFR) was obtained using 0.56 kg/ha glyphosate [N-(phosphonomethyl)glycine], CGA-82725 {2-propynyl-2-[4-([3,5-dichloro-2-pyridinyl] oxy) oxy)phenoxy propanoate}, 0.28 kg/ha fluazifop-butyl {(±)-butyl 2-[4-[(5-(trifluoromethyl)-2-pyridinyl)oxy] phenoxy] propanoate}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, and 0.11 kg/ha haloxyfop-methyl [methyl 2-(4-((3-chloro-5-(trifluoromethyl)-2-pyridinyl)oxy)phenoxy)propanoate]. Except for quackgrass, sethoxydim and fluazifop-butyl reduced shoot regrowth in plants clipped 3 to 6 h after treatment Sethoxydim required a 24-h duration on quackgrass foliage to reduce growth. Fresh weights of haloxyfop-methyl- and CGA-82725-treated plants required a 12- to 24-h clipping for reduced regrowth in all species. For all herbicides and species tested, little or no regrowth occurred when plants were clipped 48 h after treatment. A 1-h interval between split applications of sethoxydim and a 24-h interval between split applications of fluazifop-butyl and haloxyfop-methyl reduced fresh weights of bermudagrass regrowth when compared to an equivalent single rate. Regrowth of treated quackgrass indicated a 24-h interval was required for reductions with split applications of sethoxydim, fluazifop-butyl, and haloxyfop-methyl. Wirestem muhly regrowth was reduced after a 1-h interval between applications. In all species, superior control was obtained using two half-rate applications compared to one full-rate application.

Experiments were conducted in growth chambers to evaluate the effect of soil temperature and soil moisture on the distribution of 14C-photoassimilates and 14C-glyphosate [N-(phosphonomethyl) glycine] in quackgrass [Agropyron repens (L.) Beauv. ♯3 AGRRE]. When 14C-glyphosate was applied to leaves, the radioactivity was less in the rhizome buds of plants exposed to 7-C soil temperature than in plants exposed to 12- and 18-C soil temperatures after 2 days. In plants with leaves exposed to 14CO2, the radioactivity from 14C-photoassimilates was greatest in rhizomes and rhizome buds of plants at the 12-C soil temperature. As soil moisture levels were decreased, uptake of C-glyphosate into leaves declined, and transport to the daughter shoots, rhizomes, and rhizome buds was reduced. The concentration of 14C-photoassimilates in the rhizome system of water-stressed quackgrass plants was similar to that in nonstressed plants. This study shows that the patterns of glyphosate distribution differ from those of photoassimilate distribution in quackgrass plants exposed to water stress.

The influence of metribuzin [4-ammo-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] on net photosynthesis of goosegrass [Eleusine indica (L.) Gaertn. ♯3 ELEIN] and six cultivars of bermudagrass [Cynodon dactylon (L.) Pers. ♯ CYNDA cvs. ‘Common’, ‘Tufcote’, ‘Vamont’, and ‘Midiron’, Cynodon transvaalensis Davy., and Cynodon dactylon X Cynodon transvaalensis ‘Tifway’] was evaluated. Metribuzin rapidly inhibited carbon dioxide (CO2) uptake within 1 h after application in both goosegeass and bermudagrasses. Very often, net photosynthesis was completely inhibited. Net photosynthesis in goosegrass was inhibited by lower rates of metribuzin than those required for similar reduction in bermudagrasses. Common, Tufcote, Tifway, and C. transvaalensis bermudagrasses were less sensitive to metribuzin than Midiron and Vamont based upon the degree of inhibition of net photosynthesis, the rate of its recovery, and the level of foliar injury. Recovery from inhibition of net photosynthesis was observed in both species 24 h after treatment with low metribuzin rates. High rates caused several days lag period before net photosynthesis resumed. After 10 days, 95% of the goosegrass foliage was injured (either chlorosis or necrosis) from 2 kg ai/ha metribuzin treatment. The threshold concentration for inducing leaf injury in bermudagrasses was 1 kg ai/ha. Inhibition of photosynthesis was initially rapid in both grasses; however, recovery was evident earlier and there was less foliar injury in bermudagrasses than in goosegrass. Selective control of goosegrass in bermudagrass may therefore be partially dependent upon rapid metabolism and/or inactivation of metribuzin in the bermudagrass.

Velvetleaf (Abutilon theophrasti Medic. ♯4 ABUTH) seeds were exposed to variable moisture and temperatures from 15 to 100 C. As temperature increased, the percent of permeable seeds increased. Soaking 1 h at 70 C reduced hard seeds from 99 to 15 percent. Increased available water increased the effect of temperature on reduction of hard seeds. Thus, immersion in hot water was more effective than dry or humid heat. High temperature acted within a few minutes to reduce hardseededness. Viability of hard seeds was reduced at temperatures above 70 C. Germination of permeable seeds was optimal at 24 to 30 C and declined above 35 C. Germination of permeable seeds decreased after pretreatments above 40 C. Temperature and duration of heat exposure were inversely related to germination inhibition. Recently harvested seeds (3-yr-old) remained hard under alternating 4 to 34 C but became permeable after drying at 34 C. Old seeds (15-yr) did not become permeable after drying.

Desert saltgrass [Distichlis stricta (Torr.) Rydb. ♯3 DISST] tolerated extremely high concentrations of boron in nutrient solution and was far more tolerant of this micro-nutrient than was reed canarygrass (Phalaris arundinacea L. ♯ TYPAR). Boron concentrations in nutrient solution necessary to reduce growth of desert saltgrass shoots and roots by approximately 50% after 28 days of exposure were 500 and 600 ppm, respectively. In contrast, shoot and root growth of reed canarygrass was decreased approximately 50% by boron concentrations of 82 and 29 ppm, respectively. After 28 days, reed canarygrass shoots contained approximately four times as much boron as desert saltgrass shoots. Reed canarygrass has a higher transpiration rate than desert saltgrass, but this difference did not appear to cause the differential boron concentrations in the shoot tissues of the two species.

The effect of exposing tame oat (Avena sativa L. ‘Hudson’) to trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and triallate [S-(2,3,3-trichloroallyl) diisopropylthiocarbamate] during seed imbibition was investigated in a growth cabinet at 21 C in the absence of light. Caryopses were imbibed in 0.0, 1.5, and 3.0 ppmv aqueous dilutions of trifluralin and triallate for up to 10 h, after which germination was continued in distilled water. Germination was not affected following imbibition in either herbicide. Both herbicides produced distinct visual symptoms of herbicide injury during subsequent seedling growth. Coleoptile length of 5-day-old seedlings was reduced following imbibition in a 1.5-ppmv dilution of either herbicide. Triallate at 1.5 ppmv resulted in a reduction in shoot dry weight. Both herbicides were largely excluded from embryos of imbibing caryopses. Seedlings were unaffected when cultured from embryos excised from caryopses imbibed in trifluralin and triallate dilutions. Seedling phytotoxic effects resulted from residual activity of trifluralin and triallate retained by the pericarp and testa of imbibed caryopses. Presence of the hull during imbibition decreased the phytotoxic effect of both herbicides on shoot growth. These findings suggest that germinating seedlings of Avena spp. may be affected by trifluralin and triallate at an earlier stage than previously realized.

Mature achenes from tansy ragwort (Senecio jacobaea L. ♯3 SENJA) capitula borne on lower branches had greater average dry weights and higher percentage germination than those closer to the apex, but these higher averages were obtained because more achenes in these samples were filled. Physiological maturity was attained in ray achenes 21 days past flowering (DPF), 24 DPF in peripheral disk achenes, and 27 DPF in central disk achenes. Maximum germination occurred at 18 DPF in ray and peripheral disk achenes and at 21 DPF in central disk achenes. Neither achene type was shown to have innate dormancy. Disk and ray achenes germinated most rapidly at alternating temperatures of 30/20 C.

Toxicities of the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine], SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate), and SC-0545 (trimethylsulfoxonium carboxymethylaminomethylphosphonate) were similar to hard red winter wheat (Triticum aestivum L. ‘Centurk 78′) at equal dosages, carrier volumes, carrier water qualities, and sulfuric acid concentrations in the greenhouse and field at Lincoln, NE. Toxicity of HOE-00661 [ammonium (3-amino-3-carboxypropyl)-methylphosphinate] was less than the other herbicides at equal dosages. Rate of development of injury to wheat was similar at 0.4 kg/ha for glyphosate, SC-0224, and SC-0545, but greater for HOE-00661 up to 4 days after application and less thereafter. Reductions in carrier volume from 190 to 96 L/ha resulted in improved phytotoxicities for glyphosate, SC-0224, and SC-0545 at 0.1 kg/ha and HOE-00661 at 0.4 kg/ha. Addition of 0.25% (v/v) concentrated sulfuric acid to 190 L/ha of well water carrier resulted in improved phytotoxicities for glyphosate, SC-0224, and SC-0545 at 0.1 kg/ha and HOE-00661 at 0.4 kg/ha. Carrier water with reduced levels of polyvalent cations resulted in increased phytotoxicities of glyphosate, SC-0224, and SC-0545 at 0.1 kg/ha in 190 L/ha. Phytotoxicity of HOE-00661 was not affected by carrier water quality. Glyphosate, SC-0224, and SC-0545 at equal rates and HOE-00661 at a 4 X rate showed similar toxicity to wheat.

Pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] degradation in three soils did not follow first-order kinetics but could be described by a quadratic model. Degradation increased as soil temperature increased in the order 10, 20, 35, and 30C. The rate was the same as 75 and 100% field capacity but slower at 50%. At the same temperature and soil moisture the influence of soil type was small. Based on chemical analysis of soil from field and laboratory studies, the half-life was approximately 47 days. Based on biological analyses of soil, the half-life was 78 to 111 days.

The penetration, translocation, and metabolism of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} in ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. ♯3 IPOHE], velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), and soybean [Glycine max (L.) Merr.] were studied. An application to plants of 0.3 kg ai/ha mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} 0, 3, 5, or 7 days prior to treatment with 14C-acifluorfen often altered one or more of the physiological processes under study. Pretreatment of ivyleaf morningglory with mefluidide 3, 5, or 7 days prior to application of 14C-acifluorfen increased penetration of 14C and decreased metabolism of acifluorfen, while translocation was unaffected. All mefluidide treatments increased penetration of 14C-acifluorfen into velvetleaf, while the 3-, 5-, and 7-day pretreatments decreased acifluorfen metabolism. Penetration of acifluorfen into common cocklebur was unaffected by pretreatment with mefluidide. However, the 7-day mefluidide pretreatment of common cocklebur increased translocation of 14C into the upper leaves and decreased acifluorfen metabolism. Penetration and translocation of the radiolabel from 14C-acifluorfen in soybean was unaffected by pretreatment with mefluidide. Metabolism of acifluorfen by soybean was decreased by the 0-day mefluidide treatment but was unaffected by the 3-, 5-, or 7-day mefluidide pretreatment.

Rough-rice yield of drill-seeded paddy rice (Oryza sativa L. ‘Lebonnet’ and ‘Starbonnet’) at stands of 215 to 270 plants/m2 at Stuttgart, Arkansas were reduced 18% by season-long competition of spreading dayflower (Commelina diffusa Burm. f. ♯3 COMDI) at a density of 22 plants/m2. Competition durations of 20, 40, 60, or 80 days did not reduce rice yields. None of the durations of competition affected head-rice yields (percent whole milled kernels) or germination of rice seed.

Solutions containing 24 or 120 g ae/L of amine or salt formulations of glyphosate [N-(phosphonomethyl) glycine], triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and picloram (4-amino-3,5,6-trichloropicolinic acid) were applied to small shrubs with a carpeted roller. Glyphosate reduced the live canopy cover of false broomweed (Ericameria austrotexana M.C. Johnston) by 83 to 87% at one site but only by 37 to 58% at another location. The lower concentration of picloram reduced false broomweed cover by at least 92%, and the higher concentration completely controlled the weed at both study sites. Effectiveness of triclopyr was usually intermediate between glyphosate and picloram. Removing a scraper designed to abrade stems prior to herbicide deposition reduced the effectiveness of picloram but not other herbicides. The herbicides reduced canopy cover of common goldenweed [Isocoma coronopifolia (Gray) Greene ♯3 IOCCO] by 92 to 100%. Common goldenweed was also controlled by 2,4-D [(2,4-dichlorophenoxy)acetic acid] amine applied with the carpeted roller. In glasshouse experiments, 1.2 to 60 g ae/L of 2,4-D amine reduced live canopy dry weight of common goldenweed by 73 to 88% at 5 months after application with a carpeted roller.

Similar uptake and translocation patterns were observed in sweet pepper (Capsicum annuum L. ‘Keystone Resistant Giant’) and hot pepper (Capsicum chinense L. ‘Bohemian Chili’) following foliar applications of 14C-bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. In both species, most of the 14C absorbed remained in the treated leaves, with minimal acropetal and basipetal translocation from the application site. A significantly faster rate of herbicide metabolism occurred in hot pepper at 1 and 4 days after application compared to sweet pepper. Two unidentified metabolites of bentazon were isolated from methanol extracts of the two species.

Glyphosate [N-(phosphonomethyl)glycine] had several effects on carbon translocation in sugarbeet (Beta vulgaris L. ‘Klein E multigerm’): a) import of carbon by sink leaves was inhibited, b) net starch accumulation in source leaves was stopped, and c) carbon export from source leaves in the dark was stopped following 10 h of treatment in the light. During periods when no carbon was exported, glyphosate also was not transported from treated leaves. The limitation of glyphosate transport, resulting from disruption of carbon metabolism, appears important in the study and use of the herbicide.

The development of 157 tanoak [Lithocarpus densiflorus (Hook. and Am.) Rehd.] and 130 Pacific madrone (Arbutus menziesii Pursh) sprout-clumps 1 to 6 yr after cutting or burning was studied on a range of sites in southwest Oregon. The width and area of sprout-clumps originating from trees ≥ 2-cm stem diameter at 1.4-m height of both species was related to the size of the parent stem and time since cutting (tanoak, r2 = 0.77 and 0.75; Pacific madrone, r2 = 0.84 and 0.83). The sprouting capacity of tanoak develops slowly, and 5 to 6 yr after cutting, sprout-clumps produced by small tanoak 40 to 50 yr old averaged only 37 cm in diameter. Prediction equations, along with stem-diameter distributions of these species in forest stands, can be used to estimate hardwood foliar cover up to 6 yr after cutting.

In a Crowley silt loam, between 30 kPa, continuous flood, and alternate flood laboratory treatments at 25 C, dissipation of incorporated oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] varied little, with an average of 59% remaining after 20 weeks. In the greenhouse, subsurface application of oxadiazon reduced its phytotoxicity but increased its persistence up to four times more than with surface-applied oxadiazon. In the field, 50% of the surface-applied oxadiazon dissipated from the soil within 6 to 11 days when the soil was flush irrigated and then flooded, compared to 15 to 17 days when the soil was irrigated but not flooded in two rice (Oryza sativa L.) management systems. Oxadiazon dissipation in the field was greater during the first 2 or 3 weeks after application than in the laboratory study. This is explained at least partially by the lack of herbicide incorporation in the field.

Dispersal studies of musk thistle (Carduus nutans L = C. thoermeri Weinmann) seeds by wind were performed to determine the percentage of seeds removed from the vicinity of the plant where the seeds originated. For the different wind velocities tested (up to 5.6 m/s) less than 1% of the seeds were blown further than 100 m. Most seeds were deposited within 50 m of the point of release. A Gaussian model of seed dispersal based on experimentally determined parameters and published data adequately described these results.

In crop/weed interactions a method is needed to reduce the complex data derived from interference research to a simple form which can be utilized immediately. A response surface technique was utilized in analyses involving densities, duration of interference, interference abilities of different species, and weed growth rates. At high weed densities interfering for long durations, multispecies interference is not additive but at low densities additiveness is approached. Soybean [Glycine max (L.) Merr.] yield loss from multispecies weed interference was calculated by subtracting the percent yield loss from the most competitive weed and then repeating the same procedure for remaining weeds. Interference data for weed species in which fewer data were available were determined by linear interpolation for densities of more comprehensively researched, closely related species. Polynominal regression curves were utilized to predict weed age and future weed size from weed height. These analyses can produce information to assist soybean producers in recognizing economically detrimental threshold levels of weed infestations which require the initiation of control measures.

Field tests in 1980 and 1981 indicated that smooth pigweed (Amaranthus hybridus L.) competition affected cotton (Gossypium hirsutum L. ‘GSA 71′) water relations by reducing plant water status early in the season and by shading late in the season. Early in the growing season, cotton leaf water potential and turgor pressure reductions as great as 0.53 and 0.21 MPa, respectively, were measured at a smooth pigweed density of 2.5 plants m-2. Late in the 1981 growing season, smooth pigweed reduced the photon flux density reaching the cotton canopy by 90% at midday. The shaded conditions resulted in increased cotton water potential under low soil water conditions, but the inability to reduce solute potential lowered the turgor pressure of cotton, irrespective of soil water level. Comparisons of smooth pigweed and cotton water relations indicated that smooth pigweed had the capacity to maintain higher water potential and turgor pressure than cotton. The more favorable water status of smooth pigweed resulted in part from increased water extraction at lower depths in the soil profile and higher diffusive resistance, thereby reducing transpirational water loss.