The efficacy of Alternaria helianthi on imazaquin-susceptible and -resistant biotypes of common cocklebur was evaluated with and without imazaquin. A. helianthi caused severe damage to both biotypes when applied at 80,000 conidia ml−1 at the five- to six-leaf stage. Symptoms included necrotic lesions, stunting, and mortality. Mortality from imazaquin at 140 g ai ha−1 was 0 and 100% and mortality from A. helianthi at 80,000 conidia ml−1 was 33 to 75% and 67 to 100% for resistant and susceptible biotypes, respectively, and surviving plants showed reduction in height, dry weight, and number of new leaves. The combination of imazaquin at 18 g ai ha−1 and A. helianthi at 40,000 conidia ml−1 was not synergistic or antagonistic in killing common cocklebur.

Yield loss was related to weed species composition and density in permanent plots, recorded several weeks after sowing of spring cereals in southern Sweden. A range of agronomic situations was included by experimentally varying fertilizer application and sowing density in 33 field trials in different locations during 3 yr. Direct gradient analysis, using yield loss as the sole predictor, arranged weed community composition in the spring along a gradient of small to large yield losses. Yield loss could be explained, to some extent, by the species composition in the spring. Species associated with situations with large losses were hempnettle and wild radish, whereas several benign species were identified based on their association with lack of yield loss. The results suggest that possible predictive tools using spring species composition would be improved if they also considered soil type and seed rate. Some agronomically important weed species were not identified as associated with yield loss when assessed in terms of their abundance in the spring, which may limit the possibilities of basing management decisions on weed plant density in the spring.

Greenhouse and field experiments were conducted to investigate degradation rates and efficacy of EPTC (S-ethyl dipropyl carbamothioate), butylate [S-ethyl bis(2-methylpropyl)carbamothioate], vernolate (S-propyl dipropylcarbamothioate), and cycloate (S-ethyl cyclohexylethylcarbamothioate) in soils with and without prior history of thiocarbamate use. Herbicide persistence was measured by an oat (Avena sativa L.) bioassay, and giant foxtail (Setaria faberi Herrm. # SETFA) control was visually estimated in field studies. Both greenhouse and field studies indicated that enhanced thiocarbamate degradation occurred when the same herbicide (EPTC, butylate, or vernolate) was applied over successive years. Addition of dietholate (O,O-diethyl O-phenyl phosphorothioate) or fonofos (O-ethyl-S-phenylethylphosphonodithioate) increased thiocarbamate persistence and giant foxtail control in soils with prior thiocarbamate exposure. Use of dietholate or fonofos two or three consecutive years with EPTC or butylate again resulted in enhanced degradation. EPTC persistence and giant foxtail control were not affected by prior treatments or tank mixes with carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate). Rotation away from successive applications of the same thiocarbamate herbicide (EPTC, butylate, or vernolate) improved herbicide efficacy.

Runoff water was sampled over a 2-year period from an 8-ha site that had been treated and retreated with 4-amino-3,5,6-trichloropicolinic acid (picloram) at the rate of 1.12 kg/ha in the spring of 1969 and 1970. Runoff water was sampled adjacent to the plots and in two creek systems up to 2.0 km from the plots. Samples taken adjacent to the plots declined to less than 10 ppb by 10 to 12 weeks after application. Eight days after application, water sampled 1.2 km from the plots contained less than 1 ppb of picloram. Less than 1.0 ppb levels were occasionally detected 1.6 km from the plots 8 months after treatment.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triaazine] diffused at a rate of 15.2 × 10−8 sq cm/sec at 25 C which was faster than the diffusion rate of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) in the same soils. Diffusion rates were highly correlated with total surface area of the soil. Increasing soil moisture content, soil pH, and soil temperature resulted in greater diffusion rates. A relative indication of herbicide mobility may be obtained from some of the physical and chemical properties of the soils and herbicides involved; however, rate of diffusion appears to be governed by a combination of soil and herbicide properties.

Spurred anoda [Anoda cristata (L.) Schlect.] seed germination averaged 0.5 to 3.0% for seeds buried in the field for up to 20 months under natural conditions. These same seeds averaged over 76% germination after scarification with concentrated sulfuric acid, indicating hard seed coat involvement in seed dormancy. Germination was unaffected by light variables but increased as temperature increased. Germination of scarified seed increased from 50% to 85% as temperature was increased from 18 C to 30 C. Spurred anoda developed more slowly than did cotton (Gossypium hirsutum L. ‘Coker 310′) for the first 45 days. After that spurred anoda grew more rapidly until by 60 days after emergence, the weed was larger than cotton as measured by shoot height and total leaf surface area. This difference in development between cotton and spurred anoda indicates postemergence directed sprays of herbicides might be useful as a control tool.

Nalta jute and redweed are widespread and significant broadleaf weed species of the tropics. Experiments were conducted to determine the effects of various environmental factors on seed germination and seedling emergence of these species. Light was not required for germination in either species. Germination was stimulated by seed scarification, suggesting that inhibition of germination in these species is mainly due to the hard seed coat. Scarified seeds of both species germinated over a wide range of alternating temperatures (25/15, 30/20, and 35/25 C). Both species were moderately tolerant of salt and osmotic stress, but nalta jute tolerated more stresses than redweed. Seedling emergence of nalta jute and redweed was greater than 87 and 93%, respectively, at soil depths of 0 to 2 cm but decreased as depth increased, with no emergence at 8 cm. Seedling emergence of both species was reduced by the addition of rice straw, though a high amount (4 to 6 t ha−1) of straw was required to suppress emergence significantly. The information gained from this study could facilitate the development of effective weed control programs.

The objective of this research was to develop a model to predict common cocklebur seedling emergence in spring tillage and no-spring-tillage systems in the presence and absence of a soybean canopy. A Weibull function was used to accumulate heat units (i.e., growing degree days) at a 2.5 cm soil depth on days when mean soil temperature, soil water potential, and soil thermal fluctuation were above established thresholds. The base temperature, soil water potential, and soil thermal fluctuation thresholds used for model development were 17 C, −100 kPa, and 7.5 C, respectively. A single function adequately described common cocklebur seedling emergence in the presence and absence of drill-seeded soybean from data combined over an artificial (2004) and natural seedbank (2005) (R2 = 0.986). Model parameterization differed between the artificial and natural seedbank in the absence of spring tillage, but emergence was adequately described, regardless of soybean presence. Separate parameter estimates for the artificial and natural seedbanks were needed to adequately describe emergence in the system without spring tillage (R2 = 0.975 to 0.984). The ability of the model to account for reduced emergence when soil moisture is limited or when daily thermal fluctuation requirements are not met could assist practitioners with assessments associated with field scouting for weeds as well as other management decisions.

The triethylamine salt of triclopyr [(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid and the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid) were applied as soil, foliar, and soil-plus-foliar treatments to greenhouse-grown huisache [Acacia farnesiana (L.) Willd.]. At 1.12 kg/ha, picloram was more effective (97 to 100% defoliation) than triclopyr (51 to 83%) in defoliating huisache. Triclopyr was more effective at 2.24 kg/ha than at 1.12 kg/ha in defoliating huisache, except when applied to the soil. Soil or soil-plus-foliar treatments of triclopyr at 2.24 kg/ha were not significantly different from those of picloram at 1.12 kg/ha 15 weeks after treatment. Triclopyr and picloram content was determined in and on leaves, stems, and roots at 0, 3, 10, and 30 days after treatment. More picloram than triclopyr was found in the leaves 30 days after treatment with foliar sprays at equal rates. Soil, foliar, and soil-plus-foliar treatments resulted in greater accumulation of picloram than triclopyr in stem tissue. Herbicide concentrations in roots were usually low. Reasons for the greater herbicidal activity of picloram than of triclopyr in huisache are not clear; however, the greater accumulation of picloram than of triclopyr in leaf and stem tissue may partially explain the difference in herbicide activity.

The herbicides glyphosate [N-(phosphonomethyl)glycine], hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], and pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynl)benzamide] were evaluated for effectiveness in quackgrass (Agropyron repens L. Beauv.) control when applied in the fall, a time that is desirable in a short-growing-season area such as Atlantic Canada. Glyphosate at 1.12 kg/ha applied to quackgrass in grain stubble gave good control. Glyphosate at 1.12 kg/ha in late October gave better control than the same rate applied in late September. At low rates of 0.56 and 1.12 kg/ha, glyphosate gave better quackgrass control when fall-applied than when spring-applied. No differences were noted between seasons at the 2.24-kg/ha rate of glyphosate. Pre-treatment with nitrogen at 35 kg/ha 30 or 15 days before application, or on the day of application, did not improve quackgrass control with glyphosate. Pronamide gave fair to good control. Hexazinone at 2.24, 4.48, or 6.72 kg/ha gave poor control when fall-applied, but excellent control when spring-applied.

Common purslane (Portulaca oleracea L.) seeds, produced by the same plants, had different degrees of dormancy. The dormancy variations were caused neither by low seed viability nor by location on the plant where seeds were produced. Seed water content and seed age at time of collection contributed to, but were not solely responsible for, the dormancy variations. Immature, brown seeds of high water content were less dormant than the more mature, black seeds of low water content. The immature seeds germinated better in the dark than did the more mature seeds. A puncture in the seed, over the radicle, broke purslane dormancy. Dormancy was not caused by blockage of water imbibition by seeds. Purslane dormancy developed during later stages of seed maturation on the mother plant.

The herbicide, 2,6-dichlorobenzonitrile (dichlobenil), applied to the soil surface at 2 lb/A controlled dodder (Cuscuta spp.) and other weeds for 4 to 6 weeks in the field, and did not injure established alfalfa (Medicago sativa L.) significantly. Soil incorporation increased the herbicidal effect of dichlobenil on alfalfa and dodder, but alfalfa injury was increased more than dodder control. Dichlobenil was effective when applied just before sprinkler irrigation, or on moist soil after irrigating. In the greenhouse, dichlobenil vapors moved from a wettable powder formulation mixed with moist soil or from granules on the surface of moist soil, and killed dodder in adjacent untreated soil.

Rates of dissipation, control of troublesome aquatic weeds, and toxicity to fish by the disodium and dipotassium salts of 7-oxabicyclo(2,2,1)-heptane-2,3-dicarboxylic acid (endothall) in farm reservoirs and in growth pools were studied from 1964 to 1967. In 4 out of 14 reservoir applications, initial concentrations of 0.3 to 1.4 ppm dissipated to near the limit of detection in 8 to 20 days. In the other 10, the dissipation ranged from 23 to an increase of 160% in 12 days. The average dissipation was 71%. In growth pools, initial concentrations of 0.5 to 4.0 ppm of endothal dissipated to 0.26 to 2.5 ppm in 12 days.

Addition of ammonium nitrate greatly increased the absorption of solutions of the isooctyl ester of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) by sweetgum (Liquidambar styraciflua L.), post oak (Quercus stellata Wangenh.), red maple (Acer rubrum L.), and loblolly pine (Pinus taeda L.) leaves. Phosphoric acid alone and mixed with ammonium nitrate caused less increase. Ammonium nitrate speeded translocation of the herbicide in post oak but not in the other species.

Field experiments determined the potential interaction of insecticides and propanil [N-(3,4-dichlorophenyl) propanamide] in drill-seeded rice (Oryza sativa L. ‘Bond’). The carbamate insecticides carbaryl (1-naphthylmethylcarbamate) and methomyl {S-methyl N-[(methylcarbamoyl) oxy] thioacetimidate} interacted more severely with propanil than the organophosphate methyl parathion [O,O-dimethyl O-(p-nitrophenyl) phosphorothioate] in emulsifiable or encapsulated formulations. Carbaryl and methomyl injured rice vegetatively when applied from 7 days before to 4 days after propanil. Carbaryl was the only insecticide that interacted with propanil to reduce rice grain yield. Insecticides interacted adversely with propanil on rice grain yield when they were applied 2 days before propanil treatment. Insecticide interactions with propanil from most to least phytotoxic to rice plants for all times of application were: carbaryl > methomyl > emulsifiable methyl parathion > encapsulated methyl parathion.

Fourteen tomato genotypes, eastern black nightshade, and 35 Lycopersicon accessions were screened for tolerance to acifluorfen. Tolerant and susceptible genotypes occurred in most species. Fifteen genotypes were chosen for further study depending on their fresh weight after acifluorfen treatment Over all 15 genotypes, there was no correlation between trichome density and acifluorfen tolerance; however, in L. esculentum, cultivars with the most trichomes were the most tolerant There was an inverse relationship between stomata density and tolerance. Amount and composition of epicuticular wax and cuticle thickness did not correlate to acifluorfen tolerance.

Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} was evaluated on three Wyoming soil types for control of big sagebrush (Artemisia tridentata Nutt.), silver sagebrush (Artemisia cana Pursh.), and phytotoxic effects on associated vegetation. Big sagebrush was controlled with tebuthiuron at application rates of 0.6 to 1.1 kg ai/ha, whereas silver sagebrush was not completely controlled. Prairie junegrass [Koeleria pyramidata (Cam.) Beauv.], western wheatgrass (Agropyron smithii Rydb. ♯3 AGRSM), needleandthread (Stipa comata Trin. ♯ STDCO), and green needlegrass (Stipa viritdula Trin. ♯ STOVI) were not significantly reduced with tebuthiuron up to 1.1 kg ai/ha. Blue grama (Bouteloua gracilis H.B.K. ♯ BOBGR), downy brome (Bromus tectorum L. ♯ BROTE), plains pricklypear (Opuntia polyacantha Haw. ♯ OPUPO), and broom snakeweed [Gutierrezia sarothrae (Pursh.) Britt. and Rugsby, ♯ GUESA] were tolerant to tebuthiuron at rates up to 1.1 kg ai/ha.

A simple, inexpensive soil perfusion unit for use in studying the microbial decomposition of pesticides is described. This unit has the advantage of being equally adaptable to positive or negative pressure systems.

The percentage of quackgrass (Agropyron repens (L.) Beauv.) rhizome buds producing shoots was greater with one-inch than with six-inch or longer rhizomes. The longer the rhizome cutting, the stronger the shoot and the greater the recovery from deep planting. Recovery of rhizomes covered with four or more inches of soil was poor. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) at 1½ and 3 lb per acre did not affect the number of shoots produced. It was more effective when applied ½ inch above rhizomes than one inch or three inches above them.

The persistence of soil-surface applied ethyl N,N-di-n-propylthiolcarbamate [EPTC] was studied at air velocities of ⅓ to 4 mph in special air-flow equipment. Persistence was inversely related to velocity though the effect was quantitatively changed by soil composition and the materials used in formulating the EPTC spray.