Corn (Zea mays L.) in soybeans [Glycine max (L.) Merr.] currently can be controlled with either glyphosate [N-(phosphonomethyl)glycine] applied to corn that is taller than soybeans, or diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} sprayed over-the-top of both corn and soybeans. We found a wide range in tolerance to over-the-top spray applications of glyphosate among 240 F2 hybrids of corn. Glyphosate was then applied with a rope-wick to one tolerant and one susceptible F2 corn hybrid growing in soybeans. In only two instances out of six (three stages of growth times 2 yr), the susceptible corn was controlled better than the tolerant corn; but, in these two instances, the better control was not reflected in greater soybean yields. In another experiment, one F2 corn hybrid identified (in a previous study) as tolerant of diclofop and one identified as susceptible were sprayed in soybeans with over-the-top diclofop treatments. In 11 instances out of 12 (two stages of growth times three rates times 2 yr), the susceptible corn was controlled better than the tolerant corn, and in nine of these instances, the better control was reflected in greater soybean yields. Corn parentage could be important in determining the degree of control obtained with either herbicide, but this is more likely with diclofop than with glyphosate.

We compared diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, as an early over-the-top spray treatment, and glyphosate [N-(phosphonomethyl)glycine], applied twice in repeated applications with a rope-wick applicator, for control of simulated volunteer corn (Zea mays L.) planted in clumps at various intervals in rows of soybeans [Glycine max (L.) Merr.]. Uncontrolled corn at the lowest density (clumps 2.4m apart in the row) reduced soybean yields an average of 31%. Both herbicides were highly effective in controlling corn, but when corn densities were high, diclofop treatments often resulted in greater soybean yields than did glyphosate treatments — presumably because corn interfered with the soybeans for a longer time before glyphosate was applied.

Three musk thistle (Carduus thoermeri Weinm.) sites that were infested with a weevil (Rhinocyllus conicus Froel.) and a fourth non-infested site were evaluated for numbers of insects and seeds per seed head. At four successive weekly intervals, seed heads were sampled just after flowering. Initial sampling was in 1978 and was repeated in 1979. Weevil incidence in heads blooming during the first week was 6.7/head in 1978 and 28.0 in 1979. At infested sites, production of fully developed seeds averaged 28% less than at the non-infested site in 1978 and 78% less in 1979. Heads that were in bloom during the fourth sampling week had an infestation rate less than one weevil/head in both years. Fully developed seeds germinated well (96 to 99%) and were not affected by date of bloom. Because many heads bloomed during the third and fourth weeks, a large number of viable seeds were still produced at infested sites.

Pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl] -N,N′-dimethylurea} was applied aerially on duplicate plots at 2.2 and 4.4 kg/ha in spring, summer, fall, and winter of 1978 and 1979. Treatments were made near Bryan in the Claypan Resource Area of Texas on an area supporting a stand of mixed brush consisting mostly of oak (Quercus) species. Soils were sampled at eight locations in each plot at depths of 0 to 15 and 15 to 30 cm in March 1980. Bioassays using ‘Tamcot’ cotton (Gossypium hirsutum L.) and ‘Caddo’ wheat (Triticum aestivum L.) were done in the greenhouse to detect levels of tebuthiuron residues in the soil. A standard curve was developed to compare known concentrations of tebuthiuron to the unknown content from treated plots. Tebuthiuron persisted in all treated soils and ranged from 0.08 to 0.49 μg/g. Concentrations were usually greater in soil treated in 1979 than in 1978 and in soil treated with 4.4 kg/ha of tebuthiuron than 2.2 kg/ha. No consistent differences in tebuthiuron residues existed either between soil depths or among seasons of application using the bioassay.

A single foliar application of glyphosate [N-(phosphonomethyl)glycine] at 2.2 kg/ha controlled fragrant waterlily (Nymphaea odorata Ait.). Seeds that germinated during the year of glyphosate treatment or the following spring reestablished the fragrant waterlilies. A second application of glyphosate, once the seedlings had reached the surface of the water, resulted in long-term control.

Absorption, translocation, and metabolism of the methyl ester of 14C-flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] (hereafter referred to as flamprop-methyl) and 14C-barban (4-chloro-2-butynyl-m-chloro carbanilate) in wild oat (Avena fatua L.) were investigated to determine the basis of the synergistic interaction between the two herbicides. The mutual effects of the two herbicides were studied when they were applied together to wild oat at the two- and four-leaf stage. The addition of the commercial formulation of barban, barban formulation additives, technical barban, or the nonionic surfactant polyoxyethylene-6-tridecylether resulted in varying degrees of increase in the absorption of 14C-flamprop-methyl. Translocation of 14C-flamprop-methyl following leaf application in wild oat was mainly acropetal. The addition of commercial barban to 14C-flamprop-methyl did not influence the pattern of 14C translocation. Metabolism of flamprop-methyl by wild oat at either leaf stage was not influenced by barban. Absorption of 14C-barban was increased by the addition of the commercial formulation of flamprop-methyl and by polyoxyethylene-6-tridecylether. The addition of flamprop-methyl did not influence the pattern of translocation and metabolism of 14C-barban in wild oat at either leaf stage. It is concluded that increased absorption of flamprop-methyl and barban by wild oat at the two- and four-leaf stages is the most important factor in the synergistic interaction between these herbicides. Translocation and metabolism of the herbicides do not seem to be important factors in the synergism observed.

A field study was conducted for 3 yr to evaluate residual levels of fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) for their effects on injury and yields of rice (Oryza sativa L.). All three herbicides consistently injured rice and reduced yield at application rates above 0.1 kg/ha. These herbicides were similar in their effects on rice, but trifluralin was slightly more phytotoxic than fluchloralin or profluralin. Bioassay showed fluchloralin and trifluralin to be more inhibitory than profluralin of root and shoot elongation. The order of toxicity of the vapors of these herbicides arising from treated soil was found to be trifluralin > profluralin > fluchloralin. Grain sorghum (Sorghum bicolor L. Moench) was slightly more sensitive to these herbicides than was rice when seedlings were grown in treated soil and over 10 times more susceptible than rice to injury from their vapors. Both plant species were less affected by the herbicides in silty clay than in silt loam soil.

Laboratory and field experiments were conducted to describe the root system of honeyvine milkweed [Cynanchum laeve (Michx.) Pers.], and to study factors affecting the growth of plants from root fragments of shallow, ascending roots. The root system of a typical plant was composed of lateral roots radiating from a sparsely-branched, vertical taproot. Laterals tended to concentrate in a boundary area between a loamy surface soil and a zone of clay accumulation, this boundary area being below the zone of cultivation. Vertical taproots were found to a depth of 2 m, with sections collected at this and shallower depths demonstrating the ability to produce aerial shoots. In laboratory studies, root sections were killed either by freezing for 2 h or by drying at either 20 or 30 C for 24 h. The optimum temperature for shoot development from root sections was between 20 and 30 C. Shoot emergence and growth from buried root sections were generally unaffected by either depth of planting or root length. As many as 45 daughter shoots were produced from a single plant originating from seed, and 27 daughter shoots were developed from a root section 131 days after planting. The maximum distance daughter shoots were observed from original plants 131 days after planting was 111 cm.

The presence of a straw mulch on the soil surface did not significantly affect the persistence of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] in the soil. The half-life of metribuzin was 5.3 days in 1979 and 12.5 days in 1980 in the field when the time the herbicide was exposed on the soil and straw surface prior to rainfall or irrigation was 10 and 0 days, respectively. The half-life of metribuzin was 17.1 days in the greenhouse where soil temperature was lower and leaching, volatilization, and photodegradation losses were less than in the field. Increasing the amount of straw on the soil surface greatly decreased the initial soil reception of metribuzin as well as the amount of metribuzin that was subsequently washed off the straw by water. Less than 45% of the applied metribuzin reached the soil surface when 2250 kg/ha of straw was present and 0.3 cm or more of water was applied.

The persistence and effectiveness in pumpkin [Cucurbita moschata (Puch.) Poir.] weed control of several starch xanthide (SX) and commercial formulations of the ammonium (NH3) salt and methyl (CH3) ester of chloramben (3-amino-2,5-dichlorobenzoic acid) were studied in the laboratory and field. The soluble concentrate (SC) of chloramben NH3 salt and the emulsifiable concentrate (EC) of chloramben CH3 ester controlled weeds throughout the growing season on a silt loam soil. SC chloramben NH3 salt was not effective, and EC chloramben CH3 ester was inconsistent in weed control on sandy soil. Manipulation of the SX formulation produced products with slow, uniform release rates. The release rates (crosslinking reagent in parenthesis) rank as follows, from fastest to slowest: SX(Ca2+) CH3 ester = SX(H2O2) acid > SX(H2O2) CH3 ester > SX(Fe3+) acid > SX(Fe3+) CH3 ester. In trials on silt loam and sand, SX formulations did not control weeds better than EC chloramben CH3 ester.

Laboratory and field studies were conducted to compare the degradation rate of EPTC (S-ethyl dipropylthiocarbamate) in soils with a previous history of EPTC application vs. soils with no prior EPTC application. Laboratory experiments showed a rapid breakdown of 14C-carbonyl EPTC to 14CO2 in Kennebec silt loam (sil) and Tripp very fine sandy loam (vfsl) with prior exposure to EPTC. A single prior application of EPTC to Tripp vfsl was sufficient to increase the rate of 14CO2 evolution. The rate of EPTC degradation in Tripp vfsl with a history of EPTC exposure was dependent on soil moisture from below 3% and independent of moisture above 3%. Patterns of degradation at 5, 15, and 25 C in the Kennebec sil with and without prior history were described by exponential decay. EPTC was degraded more rapidly at 15 and 25 C in the Kennebec sil with a prior EPTC history. Under field conditions the breakdown of EPTC in a Kennebec sil with and without prior exposure to EPTC was similar to laboratory results.

A computer-based data collection system is described. It captures all the qualitative and quantitative data necessary to print an abstract from a weed-control experiment. The output is in the form of a research report that contains many abstracts. Users of the system are weed workers in western Canada who wish to contribute to the annual edition of the Research Report of the Expert Committee on Weeds (Western Canada). Each year, users fill out a set of forms and send them to a central location where the data are entered into a computer. In 1976, 60% of the research report was successfully computer-printed. The computer system captured a higher percentage of weed-control information than was present in the old system with narrative reports. A survey of weed workers indicated that the type of information entered in the report was satisfactory.

Flowering dates, seed production, and disease and insect susceptibility of seven Ipomoea spp. and smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb.] were determined under field conditions in 1973 and 1974. Seed produced per plant were as follows: ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], 6000; entireleaf morningglory [I. hederacea (L.) Jacq. var. integriuscula Gray], 5000; pitted morningglory [I. lacunosa L.], 10000; wild tall morningglory [I. purpurea (L.) Roth.], 26000; commercial tall morningglory [I. purpurea (L.) Roth ‘Crimson Rambler′], 15 000; cypressvine morningglory (I. quamoclit L.), 9000; cotton morningglory [I. trichocarpa Ell. var. torreyana (Gray) Shinners], 9000; palmleaf morningglory (I. wrightii Gray), 7000; and smallflower morningglory, 11000. Seed weights were about 29, 26, 22, 21, 19, 13, 19, 37, and 5 mg/seed, respectively. Pitted morningglory appeared to have a qualitative short day-length requirement for flower initiation and the other species appeared less day-length sensitive. Ivyleaf morningglory and entireleaf morningglory were highly susceptible to orange rust [Coleosporium ipomoeae (Schw.) Burrill] and white rust [Albugo ipomoea panduratae (Schw.) Swingle], but the other Ipomoea species were only slightly susceptible and smallflower morningglory was resistant. Cotton bollworms (Heliothis zea Boddie) and cabbage loopers (Trichoplusia ni Hubner) fed preferentially on ivyleaf morningglory and entireleaf morningglory.

The absorption, translocation, and metabolism of 14C-ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] in sugarbeet (Beta vulgaris L.), common ragweed (Ambrosia artemisiifolia L.), redroot pigweed (Amaranthus retroflexus L.), and common lambsquarters (Chenopodium album L.) were studied as possible bases for selectivity of preemergence-applied ethofumesate. The sensitive redroot pigweed and common lambsquarters plants translocated more 14C-ethofumesate from nutrient culture to the leaf tissue than did the tolerant sugarbeet and common ragweed. The radioactivity was more highly concentrated in sugarbeet and common ragweed roots. The rapid metabolism of ethofumesate by sugarbeet and common ragweed, particularly that which accumulated in the leaf tissue, appeared related to tolerance.

Differences in susceptibility of sugarbeet (Beta vulgaris L.) to preemergence application of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate], pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], and TCA (trichloroacetic acid) were evaluated in several combination treatments. Exposure of plants to ethofumesate severely decreased epicuticular wax deposition on leaf surfaces. Separation of epicuticular wax into major components by gas-liquid chromatography indicated that ethofumesate decreased deposition of alkanes and sec-ketones, but increased the percentage of long-chain waxy esters. TCA also decreased deposition of alkane and ketone components, but not of waxy esters. Waxes were unaffected by pyrazon. Greater foliar absorption of 14C-ethofumesate, 14C-desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)], and 14C-ethofumesate + 14C-desmedipham was observed in plants that received preemergence treatments of ethofumesate plus TCA compared to pyrazon or a control.

Dormant, dehulled red rice (Oryza sativa L. ‘Louisiana strawhulled′) germinated 80 to 90% at 30 C upon exposure to 10-3 M kinetin (6-furfurylaminopurine), benzyladenine (6-benzylaminopurine), or isopentenyladenine [6-(3-methylbut-2-enylamino)purine] at pH 3.5. Zeatin [6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine] was also active, eliciting 45% germination at 10-3 M. Adenine was inactive at concentrations as high as 10-2 M. There was little influence of light and no effect of initial pH of the medium upon cytokinin-stimulated germination. At 20 C the response to cytokinins was reduced, but germination of non-dormant seeds was not prevented. At 30 C, the germination of dehulled red rice with 10-3 M kinetin occurred rapidly, with almost 70% germination after 2 days. When dehulled seeds were incubated in water and then transferred to kinetin, percent germination decreased as the duration of water incubation increased. The loss of cytokinin response did not parallel the timecourse of imbibition. Cytokinins did not break dormancy of intact seeds. The hull appeared to limit kinetin uptake and inhibited germination even when kinetin was forced into intact seeds by vacuum infiltration. Dry-after-ripening of intact seeds at 30 C did not increase the kinetin-sensitivity of intact red rice.

Caffeic acid, chlorogenic acid, coumarin, p-coumaric acid, ferulic acid, fumaric acid, gallic acid, hydrocinnamic acid, p-hydroxybenzoic acid, juglone, and pyrocatechol were examined for effects on germination of nine crop and weed species: cotton (Gossypium hirsutum L.), cantaloupe (Cucumis melo L.), corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], hemp sesbania [Sesbania exaltata (Raf.) Cary], sicklepod (Cassia obtusifolia L.), velvetleaf (Abutilon theophrasti Medic), prickly sida (Sida spinosa L.), and redroot pigweed (Amaranthus retroflexus L.). Germination tests with 10-3 and 10-5 M solutions were conducted under controlled conditions in petri dishes at 25 C in the dark. At 10-3 M, coumarin, hydrocinnamic acid, juglone and pyrocatechol inhibited germination, but p-hydroxybenzaldehyde and p-hydroxybenzoic acid were not effective and others had intermediate effects. There was little effect by any compound at 10-5 M. Chlorogenic acid, p-hydroxybenzaldehyde, and pyrocatechol, each combined with coumarin, inhibited germination. The combination of coumarin plus p-hydroxybenzaldehyde had an additive effect on hemp sesbania and prickly sida, inhibiting germination to a greater extent than either compound alone. The lack of inhibitory action at the higher concentration of some of these chemicals suggests they may not exhibit a high allelopathic potential.

The comparative susceptibility of weedy okra [Abelmoschus esculentus (L.) Moench.] and three commercial okra cultivars (′Dwarf Green Long Pod′, ‘Clemson Spineless', and ‘White Velvet′) to six preemergence herbicides was evaluated in the greenhouse. Okra can be controlled in cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.] fields with appropriate preemergence herbicide use. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] completely controlled okra at 0.2 to 0.8 kg/ha. Fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] at 0.9 to 1.8 kg/ha and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} at 1.2 to 2.4 kg/ha controlled okra, but at the 0.6 kg/ha rate cyanazine did not control wild okra and fluometuron at 0.45 kg/ha did not completely control any cultivar. Norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone] bleached the cotyledons and young leaves of okra, but gave 50% or less control even at 2.4 kg/ha. Both the weedy and commercial okras were completely resistant to trifluralin (α,α,α-trifluoro-2,6-dinitro -N,N-dipropyl-p-toluidine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] but higher rates of these herbicides affected okra growth.

Field experiments were conducted at four locations to evaluate the efficacy of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], simazine [2-chloro-4,6-bis(ethylamino)-s-triazine], buthidazole {3[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} and 2,4-DB [4-(2,4-dichlorophenoxy) butryic acid] treatments for common dandelion (Taraxacum officinale Weber) control in established alfalfa (Medicago sativa L.). Most herbicides temporarily reduced common dandelion populations at all locations, but by the end of the first year only buthidazole reduced them on fine-textured soils, but buthidazole, metribuzin and fall-applied simazine reduced populations on coarse-textured soils. Only buthidazole controlled common dandelion in the year following application at all locations. Control of common dandelion did not consistently increase total forage yield or quality or increase alfalfa yield and stands compared to the untreated check. Buthidazole reduced alfalfa and total forage yield on coarse-textured soils.