Caryopses (seeds) of fall panicum (Panicum dichotomiflorum Michx.) have a dormancy that is not easily overcome. Although accelerated after-ripening for 4 weeks was partially successful in overcoming dormancy, a dark imbibition at 35 C for about a week was more effective and also interacted strongly with an accelerated after-ripening. In either case, activation of phytochrome by red irradiation was required to induce germination. Similarly, alternating temperatures allowed germination of red-treated seeds but constant temperatures did not. More seeds germinated in sealed flasks than in dishes. The enhancement of germination in sealed flasks appeared to be related to increased CO2 levels. The data suggested a multiple dormancy in fall panicum seeds. One dormancy, the most intense, was relieved by high-temperature imbibition. The residual dormancy was relieved by active phytochrome and alternating temperatures.

Repeated applications of amine methylarsonate over a two year period resulted in significant reductions in nutsedge tuber numbers at 1.3, 2.6 and 3.8 ounces per 1000 sq. ft. Single annual applications of amine methylarsonate at the same rates were ineffective. Amine methylarsonate and disodium monomethylarsonate treatments gave moderate reductions in nutsedge tuber numbers in thin Bermudagrass turf after one season.

Dormant weed seeds are difficult to kill and, with the exception of soil sterilization methods, current weed control techniques are not effective against dormant weed seeds. This study was conducted to investigate the effects of temperature, light, soil moisture, burial depth, ethephon, and potassium nitrate (KNO3), and their interactions on the germination of false chamomile seeds under controlled conditions. False chamomile was photoblastic and thermophilic and germinated rapidly within the first 4 days of incubation under all conditions. Regression analysis indicated that ethephon and KNO3 had quadratic effects on false chamomile germination. Ethephon enhanced germination more than KNO3. There was a linear reduction in germination with increased storage time, and it is projected that zero germination should occur after 9 yr of storage at room temperature. Soil moisture had a positive linear effect and a positive interaction with ethephon on false chamomile germination. Very little germination occurred when seeds were buried 5 cm deep even with high soil moisture.

The effect of humidity on the rate and direction of translocation of stem-injected (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in bean (Phaseolus vulgaris L., var. Stringless Green-pod) seedlings was determined. A total of 0.75 μg of 14C-labeled 2,4,5-T was injected into the stem with a 1-μl syringe pipette. Translocation was determined by assaying the nutrient solution and plant parts for 14C. High relative humidities enhanced downward translocation to roots and nutrient solutions. About 41% of the applied 2,4,5-T was found in the nutrient solution after 2 days' treatment at about 95% relative humidity while only 23% was found when treatment was conducted at 20% relative humidity. Low humidity during treatment caused much more 2,4,5-T to be translocated upward to the primary leaves and young shoots of the seedlings and this effect was more pronounced in plants which were grown in low humidity prior to treatment. The results confirm the conclusions of others and show that the increased basipetal phloem transport of herbicides in plants under high humidity is not due to an effect on penetration of herbicides in leaf tissue.

Seed germination responses to temperature and osmotic stress were determined for smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb.] and seven species of Ipomoea. Cypressvine (I. quamoclit L.), willowleaf (I. wrightii Gray) and smallflower morningglory germinated and seedlings developed more slowly than the other morningglories at 16 C. Maximum germination of ivyleaf [I. hederacea (L.), Jacq. var. hederacea], entireleaf [I. hederacea (L.) Jacq. var. integriuscula Gray], pitted (I. lacunosa L.), tall [I. purpurea (L.) Roth], cotton (I. trichocarpa Ell.), and smallflower morningglories occurred in 24 h at 20 C. Cypressvine and willowleaf morningglories reached maximum germination in 24 h at 24 C. Optimal root-hypocotyl development occurred at 24 C for pitted, tall, and willowleaf morningglories, while all other species required a temperature of 28 C for maximal root-hypocotyl development in 4 days. Increasing osmotic pressure decreased or delayed germination of all morningglory species. Species tolerance to osmotic stress during germination could be ranked, most to least tolerant, as follows: ivyleaf=entireleaf>pitted=cotton>tall = willowleaf>cypressvine=smallflower. Maximum germination was delayed approximately 24 h for each 2 bar increment increase in osmotic pressure.

The yield potential and the effect on yield loss of canola of different densities of volunteer barley were investigated at three locations in western Canada. Field studies were conducted from 1982 to 1986. Rectangular hyperbolic models based on data pooled over years, locations, and canola cultivars, and incorporating different densities of volunteer barley and canola accurately portrayed field responses in most instances. Results indicated that volunteer barley severely reduced canola yield. However, financial losses due to reduced canola yield were partly offset by the volunteer barley crop.

The influence of six Arkansas soils on the leaching characteristics of derivatives of 3-amino-2,5-dichlorobenzoic acid (amiben) and 3-nitro-2,5-dichlorobenzoic acid (hereinafter referred to as dinoben) in slotted soil columns was determined using large crabgrass [Digitaria sanguinalis (L.) Scop.] bioassay. The ammonium and aluminum salts of amiben and the sodium salt of dinoben were easily leached and leaching was not noticeably affected by soil type. The ammonium salt of amiben was not adsorbed, while the methyl ester of amiben was adsorbed by these soils. Adsorption was related to the clay and organic matter content of the soil. Methyl and butoxyethyl ester derivatives of amiben and dinoben resisted leaching in these soils and the amide of amiben was intermediate in leaching. The adsorption and leaching behavior of the ester derivatives of these compounds were complicated by their rapid hydrolysis in these soils. The hydrolyzed product behaved identically to the salt derivatives of the compounds in leaching, adsorption, and chromatographic properties. Hydrolysis of the methyl ester was inhibited by soil sterilization, dry soil, and temperatures below 20 C. In non-sterile, warm, moist soil, the half-life of the methyl ester of amiben was 28 hr. Four species of Bacillus were capable of hydrolyzing the methyl ester of amiben in pure culture studies.

Experiments conducted in North Carolina and Virginia compared weed control, peanut yield, and net returns with systems using imazethapyr applied at various times and the regional standard treatment of paraquat applied at the ground-cracking stage of peanut (GC) followed by acifluorfen plus bentazon applied POST. Imazethapyr was applied PPI, PRE, GC, or POST at 70 g ae ha−1. Imazethapyr also was applied sequentially PPI plus GC, PPI plus POST, and PRE plus POST at 35 + 35 and 70 + 70 g ha−1. Late-season control of common ragweed and a mixture of entireleaf, ivyleaf, and pitted morningglories by the standard treatment ranged from 85 to 100%. Spurred anoda was controlled 80%, and common lambsquarters and prickly sida were controlled completely. Control of common lambsquarters, prickly sida, and morningglory by imazethapyr applied one or more times was similar to control by the standard. Control by imazethapyr exceeded that by the standard only for spurred anoda. The most effective time for applying imazethapyr varied by species and locations. Imazethapyr was equally effective on common lambsquarters and spurred anoda when applied PPI, PRE, or GC. Prickly sida and morningglory were controlled best when imazethapyr was applied PPI or PRE and GC, respectively. Common ragweed was controlled poorly with single applications of imazethapyr. Applying imazethapyr sequentially improved consistency of control across the range of species. In most cases, imazethapyr applied sequentially at 35 + 35 g ha−1 controlled all weeds as well as or better than when applied once at 70 g ha−1. Overall, imazethapyr at the registered rate of 70 g ha−1 was most effective when applied PPI at 35 g ha−1 followed by 35 g ha−1 at GC. Except for common ragweed, weed control with this treatment was similar to that by the standard. Peanut yield and net returns with this treatment were similar to those with the standard at three of four locations.

Absorption, translocation, and metabolism studies using 14C-quinclorac were conducted with quinclorac-sensitive Digitaria sanguinalis and quinclorac-tolerant Eleusine indica at the one- to two-tiller growth stage cultured under hydroponic conditions. After an 80-h exposure time, both species had absorbed nearly equal amounts of 14C-quinclorac (27 and 22% for D. sanguinalis and E. indica, respectively). Over the exposure period, the absorption curve for D. sanguinalis was curvilinear, with the maximum absorption occurring approximately 48 h after exposure. The response curve for E. indica was linear across the exposure period. Results from the translocation studies showed that 95% of the absorbed 14C-quinclorac remained in the treated leaf for D. sanguinalis after 80 h. However, only 58% of the absorbed 14C remained in the treated leaf of E. indica. Most of the 14C translocated out of the leaves moved to the tiller, the crown, and new leaf tissue. There was no appreciable exudation of 14C-quinclorac by either species during the absorption period. Results of the metabolism studies showed that neither the susceptible species (D. sanguinalis) nor the tolerant species (E. indica) metabolized the parent quinclorac herbicide. Spray retention studies showed that E. indica (tolerant) retained more applied quinclorac than D. sanguinalis (sensitive). Overall results suggested that a large difference in tolerance of the two species to quinclorac involves mechanisms other than absorption, metabolism, or spray retention.

Seedlings of 22 plant species were evaluated in aqueous suspensions of N-(2-mercaptoethyl)benzenesulfonamide S-(O,O-diisopropyl phosphorodithioate) (bensulide), dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA), and 1-(2-methylcyclohexyl)-3-phenylurea (siduron) to determine their value as indicator plants for bioassays. The species showing the greatest sensitivity by reductions in root or shoot lengths were evaluated in soil mixtures to determine the level of sensitivity under soil conditions. These indicator plants, in most cases, proved reliable in detecting the presence and movement of bensulide, DCPA, and siduron in soils from field-treated plots. There appeared to be no accumulation in soil treated with four annual applications of bensulide, DCPA, or siduron.

Genetic variability for loci governing enzyme/morphological variants and for herbicide response was determined in 10 populations of the slender wild oat (Avena barbata Pott. ex Link ♯ AVEBA), six populations of wild oat (Avena fatua L. ♯ AVEFA), and three populations of godetia (Clarkia williamsonii Lewis & Lewis). The enzyme loci were identified by starch gel electrophoresis and included peroxidase, 6-phosphogluconate dehydrogenase, esterase, and leucine aminopeptidase for the slender wild oat; peroxidase, esterase, leucine aminopeptidase, and malate dehydrogenase for the wild oat; and esterase, phosphoglucoisomerase, leucine aminopeptidase, acid phosphatase, and glutamate oxaloacetate transaminase for godetia. Morphological loci included lemma and leaf sheath hairiness for the oats. For both the enzymatic and morphological loci, levels of genetic variation for each population were quantified by a polymorphic index. The herbicide barban (4-chloro-2-butynyl 3-chlorophenylcarbamate) was used on the wild oats; bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) was used on godetia. Genetic variation for herbicide response was based on genetic variances calculated from phytotoxicity scores. Populations were ranked from highest to lowest for the polymorphic indices and the genetic variances. Concordance between the rankings was tested by rank correlation. Statistically significant relationships were found between the enzyme/morphological characters and herbicide response in the slender wild oat and the wild oat. For some species, the level of genetic variation for response to herbicides appears to be associated with genetic variation for enzymatic and morphological loci.

Interference for 40 d after emergence (DAE) of corn, cotton, peanut, and snap bean by four glyphosate-resistant (GR) and four glyphosate-susceptible (GS) Palmer amaranth populations from Georgia and North Carolina was compared in the greenhouse. Greater interference from Palmer amaranth, measured as crop height and fresh weight reduction, was noted in cotton and peanut compared with corn or snap bean. Crop height 15 to 40 DAE was reduced similarly by GR and GS populations. Crop fresh weight, however, was reduced 25 and 19% in the presence of GS and GR populations, respectively. Measured as percent reduction in fresh weight, GR and GS populations of Palmer amaranth were controlled similarly by glufosinate, lactofen, paraquat, and trifloxysulfuron applied POST. Atrazine and dicamba controlled GR populations more effectively than GS populations.

A method is described for the large-scale production of a granular formulation of Alternaria macrospora Zimm. The granular preparation consisted of spores, mycelia, and vermiculite. This formulation of A. macrospora, applied preemergence or postemergence, controlled spurred anoda (Anoda cristata Schlecht.) plants in greenhouse and field tests. The pathogen did not significantly affect emergence or dry weight production of cotton (Gossypium hirsutum L. ‘Stoneville 213’) seedlings. The fungicides PCNB (pentachloronitrobenzene) and ETMT [5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole] did not significantly affect spurred anoda control with A. macrospora. The method for production and formulation of A. macrospora was modified to produce spores and granular formulations of other Fungi Imperfecti: Drechslera sp. and Fusarium spp. (Moniliales), Colletotrichum spp. (Melanconiales), and Phyllosticta sp. (Sphaeropsidales).

At intervals of 3 to 56 days, propanil (3′,4′-dichloropropionanilide) at 4.5 kg/ha was applied after treatments of carbofuran (2,3-dihydro-2,2- dimethyl-7-benzofuranylmethyl carbamate) at 0.7 kg/ha. Their interaction injured rice (Oryza sativa L., ‘Starbonnet’) vegetatively, but did not reduce grain yields, milling quality, or seed viability. Leaf chlorosis and necrosis developed within 7 days after propanil treatment and lasted for 2 to 4 weeks. As the time interval between carbofuran and propanil treatments increased, leaf injury decreased. Older rice recovered more quickly than younger rice. Interaction of carbofuran and propanil did not cause chlorosis or necrosis of rice leaves when the insecticide was applied 5 days after the herbicide. Propanil alone, applied once at 4.5 kg/ha, or applied sequentially at 4.5 kg/ha each time, caused only slight chlorosis of rice leaves.

A field experiment was conducted to determine the influence of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] and/or chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl)benzenesulfonamide} on germination, coleoptile growth, and mineral accumulation of seed from treated parent plants. The herbicides were applied postemergence in the spring to ‘Vona’ and ‘Centurk’ winter wheat (Triticum aestivum L.). The rate of metribuzin was 360 g ai/ha, with chlorsulfuron applied at 18, 35, or 70 g/ha. Metribuzin reduced grain yields of both varieties approximately 40%, whereas chlorsulfuron at the higher rates reduced grain yields of only Vona. Seed germination was not affected by either herbicide, but metribuzin, when applied alone, reduced coleoptile growth of Vona seed. The addition of chlorsulfuron to metribuzin eliminated this growth reduction. The mineral concentration of the seed of both varieties indicated that metribuzin and chlorsulfuron did not affect mineral translocation to the seed by the parent plant.

Sixty percent of the roots of sugarbeets (Beta vulgaris L.) at harvest were aberrant in the zone of the hypocotyledonary neck when 0.84 kg/ha of α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was sprayed primarily on the hypocotyledonary tissues of seedlings in the 10 to 12-leaf stage, compared to 7% when soil surrounded most of the hypocotyledonary tissues at the time of application. Trifluralin did not reduce the yield of roots or kilograms of sucrose per hectare in either treatment. Sucrose content and purity were lower, and total nitrogen was more than twice as high in sections of neck and root tissues where the aberrations were the most severe as compared to normal sections of neck and root tissues from the untreated plots. In the greenhouse, trifluralin inhibited the growth of primary and lateral roots in sugarbeet seedlings.

Ten herbicides were each applied at two rates to Panache loam for 5 or 6 yr as soil-incorporated broadcast sprays directed to the base of cotton (Gossypium hirsutum L. ‘Acala SJ-1’) at last cultivation. Chemical determinations 6 months after annual treatment showed that trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], benefin (N-butyl-N-ethyl-a,a,a-trifluoro-2,6-dinitro-p-toluidine), DCPA (dimethyl tetrachloroterephthalate), and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] residues were essentially confined to the tilled zone of soil; whereas, bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercapteothyl)benzenesulfonamide], fluometuron [1,1-dimethyl-3-(a,a,a,-trifluoro-m-tolyl)urea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] residues were found below the tilled zone. At time of retreatment, annual residue determinations from the upper 15 cm of soil showed that nitralin and prometryn had dissipated completely and residues of the other herbicides and were notably reduced as compared to levels at cotton harvest. One year after final treatment herbicide residues below the tilled zone were essentially nondetectable, except for diuron, linuron, and fluometuron. There was no evidence of herbicide accumulation in soil with repeated applications.

Regression models of the effect of weed density on crop yield can form the basis of weed management programs by helping growers decide whether weed control is economically justified. However, few studies have examined whether one regression model can be used across a wide range of tillage systems and crop rotations. We used a nonlinear analysis of covariance to examine experiments conducted in 1990 and 1991 on the interaction of weed interference with conventional, fall chisel, and no-till systems, and rotations of corn, soybean, and wheat on a clay loam soil. Corn and soybean suffered heavy losses due to interference by green foxtail (a mixed population of robust purple and robust white varieties). Both tillage system and crop rotation altered the relationship between weed density and yield for corn in 1990 and 1991, but tillage was not a factor for soybean in 1991. Companion experiments on a sandy loam soil found no relationship between weed density and dryland corn yield in the drought year 1990, but weed density greatly decreased yield in irrigated corn. In 1991, the same model fit both dryland and irrigated corn grown in sandy loam soil. Foxtail density did not affect average weight per foxtail plant in any of our experiments, which indicates a lack of intraspecific competition. Competitiveness of corn better explained variation in dry weight per foxtail than did weather. Economic thresholds for foxtail interference are not constant but vary with weather, cropping system, and soil type.

Field studies were conducted at two locations in Missouri in 1990 and 1991 to evaluate control of velvetleaf, ivyleaf morningglory, and cocklebur in soybean with label rates (1×) or reduced rates (0.5×) of four PPI herbicides followed with or without cultivation and POST application of one fourth (0.25×) the label rate of imazethapyr. Weed control and soybean yield with the 0.5× rate of preplant clomazone, imazaquin, metribuzin, and metribuzin + chlorimuron followed by either cultivation or imazethapyr POST was equivalent to a 1× rate of the PPI herbicides followed by either cultivation or imazethapyr. Weed control and soybean yield with the 0.5× rates of the PPI herbicides without cultivation or POST imazethapyr were lower than with 1× rates of PPI herbicides.

The impact of four weed management systems on weed seed reserves in soil, yearly weed problem, and production of barley, corn, pinto bean, and sugarbeet was assessed where these crops were grown in rotation for 4 consecutive years in four cropping sequences. Weeds were controlled in each crop with only conventional tillage or conventional tillage plus minimum, moderate (system 1), and intensive (system 2) levels of herbicides. Seed of annual weeds from 11 genera were identified, with barnyardgrass and redroot pigweed comprising 66 and 19%, respectively, of the initial 90 million weed seed/ha present in the upper 25 cm of the soil profile. After the fourth cropping year, overall decline in total number of weed seed in soil was 53% when averaged over four cropping sequences and four weed management systems. Over the 4-yr period, about 10 times more weeds escaped control in system 1 than in system 2; and within a crop, the fewest number of weeds escaped control annually in barley. System 2 had the highest herbicide use in each cropping sequence, the fewest weeds at harvest, and the smallest adjusted gross return over the 4-yr period in three of four cropping sequences.