Clear and black polyethylene mulches were placed over raised seed beds in four studies during a 3-yr period. At intervals during treatment times of up to 12 weeks, soil samples were taken and the recovered seed were tested for germination. The number of seed killed and depths to which they were killed varied with species. The study included natural seed populations of annual bluegrass (Poa annua L. ♯3 POAAN), barnyardgrass (Echinochloa crus-galli (L.) Beauv. ♯ ECHCG), annual species of Cyperus, dayflower (Commelina communis L. ♯ COMCO), and goosegrass (Eleusine indica L. Gaertn. ♯ ELEIN). After 40 days exposure under clear mulch, seed of dayflower were killed to a depth of 11 cm. Under the same conditions, seed of annual Cyperus sedges and barnyardgrass were killed only in the upper 3 to 4 cm. After 3 weeks under clear plastic, germinable seed of goosegrass were recovered only at depths greater than 5 cm. Seed in plots under clear polyethylene mulch were killed more quickly than those in plots covered with black polyethylene mulch.

Phytotoxicity of fluazifop-butyl {butyl 2-[4-[(5-trifluoromethyl)-2-pyridinyl)oxy] phenoxy] propanoate}, haloxyfop-methyl {methyl 2-[4-[(3-chloro-5-(trifluoromethyl)-2-pyridinyl)oxy)phenoxy] propanoate}, and sethoxydim {2-[1-ethoxyimino)-butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} increased as carrier volume was decreased from 570 to 24 L/ha. Addition of crop oil concentrate to the spray solution increased phytotoxicity, especially at carrier volumes of 190 L/ha and above. Sorghum plants were treated with the same amount of active ingredient in a single 1-, 2-, 4-, 8-, 16-, or 24-μl droplet. Smaller, more concentrated droplets were more phytotoxic than larger, more dilute droplets, with or without crop oil concentrate. Application site of single herbicide droplets also influenced phytotoxicity. In general, application of concentrated droplets to metabolically active leaf tissue resulted in maximum phytotoxicity.

Research was conducted from 1978 through 1980 at Headland, AL, to evaluate the use of herbicides, mechanical cultivation, and hand-hoeing as components of a total weed control system for peanuts (Arachis hypogaea L.). Herbicides or two cultivations alone failed to provide acceptable weed control, peanut yields, or net returns for the 3-yr period. However, adding two cultivations to the herbicide treatments produced acceptable weed control, peanut yields, and net returns for the 3-yr period. Average peanut yield for herbicide(s) plus two cultivations was 3200 kg/ha with an average net return of $260/ha. Two cultivations plus two hoeings without herbicide(s) produced good results with an average 3-yr yield of 3380 kg/ha and a net return of $280/ha. Herbicide(s) plus two cultivation treatments that had net returns equal to two cultivations plus two hoeing treatments were: dinoseb (2-sec-butyl-4,6-dinitrophenol) at 5.0 kg ai/ha applied at ground-cracking ($300/ha); dinoseb + alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 1.7 + 3.4 kg ai/ha applied at ground-cracking ($310/ha); and alachlor at 4.5 kg/ha applied preemergence ($320/ha). Treatments containing herbicide(s) plus two cultivations plus two hoeings did not substantially improve weed control, peanut yields, or net returns over herbicide(s) plus two cultivations.

The presence of a dinitroaniline-resistant biotype of goosegrass [Eleusine indica (L.) Gaertner. ♯3 ELEIN] was confirmed in the northeastern area of South Carolina. It was also found in seven adjoining counties. It showed resistance to seven dinitroaniline herbicides but not to herbicides from six other chemical groups. One biotype was not affected by trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 3.4 kg ai/ha where a dinitroaniline-susceptible biotype was controlled at 0.3 kg/ha. Under similar conditions, another biotype showed resistance to trifluralin at 0.6 kg/ha but was controlled at 1.1 kg/ha, indicating that at least two unique biotypes may exist.

The absorption and translocation of sethoxydim {2[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} as influenced by bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] were studied in goosegrass [Eleusine indica (L.) Gaertn. ♯3 ELEIN]. The presence of bentazon in the treatment emulsion decreased foliar absorption of 14C applied as 14C-sethoxydim by about half. Significantly less 14C was found in the treated leaf, shoot tissue above the treated leaf, shoot tissue below the treated leaf, and roots of plants treated with a mixture of 14C-sethoxydim and bentazon than with 14C-sethoxydim alone. After 6 h, 3.5% of applied 14C was recovered from plant parts other than the treated leaf in the absence of bentazon, compared to 1.1% of that applied in combination with bentazon. The difference in foliar absorption between the two treatments may account for the antagonistic interaction between these herbicides observed in the field.

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.

Dormant and nondormant kochia [Kochia scoparia (L.) Schrad. ♯3 KCHSC] seed populations were buried at six soil depths in Colorado. Portions of both populations remained viable for 36 months. Persistence increased with burial depth in both populations. Seed loss from the initially dormant population was limited to germination in situ, but seed loss from the initially nondormant population included significant viability loss at burial depths of 10 cm or less. Persistence of both populations was regulated by dormancy retention. Shallow tillage practices are predicted to decrease seed persistence in soil and increase successful seedling emergence. Deep tillage practices are predicted to reduce seedling emergence but increase soil seed populations.

Sicklepod (Cassia obtusifolia L. ♯3 CASOB) seed were obtained from 10 locations in nine southern states, and plants were grown in a nursery for 3 yr. In field experiments, plant height, seed per pod, number of seed per plant, and number of pods per plant varied among seed sources and years. The vegetative growth phase, as measured from emergence to the initiation of the first floral buds, was approximately 30 days shorter for plants grown from the Tennessee source than for those grown from seed collected in Alachua, FL, in all 3 yr. Hand-harvested seed from plants grown from the 10 seed sources that were planted in 1982 were planted beside the original source sicklepod seed in 1983, and both flowered at approximately the same time, indicating self-fertilization. Percent germination of hand-harvested sicklepod seed from the 10 sources ranged from 2 to 11% for 1981 and 3 to 23% for 1982.

Benzyl isothiocyanate (BITC) was extracted from mature papaya (Carica papaya L.) seeds and applied to imbibed velvetleaf (Abutilon theophrasti Medic. ♯3 ABUTH) seeds. Complete inhibition of germination occurred at a concentration of 6 × 10-4 M BITC, and only 28% (compared to controls) of the seeds germinated after 4 days exposure to the 4 × 10-4 M treatment. Corn (Zea mays L. ‘DeKalb XL-66′) was unaffected even at higher concentrations; however, 72% of imbibed soybeans [Glycine max (L.) Merr. ‘Tiger’] germinated in 6 × 10-4 M BITC. When this natural inhibitor was applied to etiolated velvetleaf seedlings at 4 × 10-4 M, 100% died in 2 days.

Field research was conducted during the summers of 1981 and 1982 in order to determine relative infection and population increase of lesion nematodes (Pratylenchus spp.) on seven weed species that commonly occur in field-bean (Phaseolus vulgaris L.) fields in western Nebraska. Weeds were grown at three densities with and without fieldbeans. A representative sample of the root systems from plants in each plot was removed in August and the nematodes were extracted and counted. No difference in nematode infection rate was found among weed population levels. Nematodes per gram of dry root were not different in weeds grown with or without fieldbeans. Weeds grown with fieldbeans had smaller root systems, and consequently total nematodes per root system were less than in weeds grown in the absence of fieldbeans. There was a significant difference among most weed species when nematodes per gram of dry root were estimated. Hairy nightshade (Solanum sarachoides Sendt. ♯3 SOLSA) and barnyardgrass [Echinochloa crus-galli (L.) ♯ ECHCG] supported the highest numbers of nematodes per g oven-dry roots, redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) and common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE) had least numbers of nematodes/g oven-dry roots, and infestation levels on other weed species were variable but generally intermediate.

False broomweed (Ericameria austrotexana M.C. Johnst.) had lower near-infrared (0.75- to 0.90-μm waveband) reflectance than did six other associated rangeland species and mixed herbaceous vegetation. False broomweed's low near-infrared reflectance was attributed to its erectophile (erect-leaf) canopy structure. Other species had planophile (horizontal-leaf) or intermediate-leaf orientation. False broomweed's low near-infrared reflectance caused its image to be dark reddish-brown on color-infrared (0.50- to 0.90-μm waveband) film, compared with red or magenta images of other rangeland species. Microdensitometric measurements made on the film showed that false broomweed had significantly higher optical counts than those of associated species and mixtures of species.

The growth of wild oat (Avena fatua L. ♯3 AVEFA) under different moisture regimes was investigated under field conditions and in a growth chamber. In the field, growth of wild oat under low moisture conditions (0.6 cm water per week – Regime 1) was significantly reduced compared to growth under high moisture conditions (2.5 cm water per week – Regime 2). Maximum reductions of 49, 33, and 38% were recorded in the leaf area, dry weight, and number of viable tillers, respectively. The growth of wild oat in soil watered daily to a soil moisture content (SMC) of 10% (water potential −6.5 bars) in the growth chamber was less than for plants in soil watered daily to 20% SMC (-0.3 bars). Maximum reductions of 55, 57, and 38% were recorded in the leaf area, dry weight, and number of viable tillers, respectively. Wild oat growth was more adversely affected by reducing the SMC from 20 to 10% after, rather than before, the four-leaf stage. By the last sampling date, stomatal diffusion resistance of the most severely water-stressed plants was 25 s·cm-1 compared to between 5 and 10 s·cm-1 for the plants receiving more water.

Jointed goatgrass (Aegilops cylindrica Host. ♯3 AEGCY) has a quantitative requirement for vernalization in order to flower. In greenhouse and field studies, increasing periods of vernalization progressively reduced the number of days needed for plants to mature following transfer from the cold treatment to favorable growing conditions. Plants that had been vernalized at 3 ± 2 C for 8 weeks as imbibed seed took 120 days to flower following transfer to the greenhouse. Unvernalized controls flowered 197 to 222 days after planting in the greenhouse. Lengthening periods of vernalization from 2 to 8 weeks increased the number of seedheads per plant and dry weight per seedhead. Vernalized plants partitioned more dry matter into seedheads than unvernalized controls. The ratio of seedhead dry weight to vegetative shoot dry weight increased with duration of vernalization, even though vernalization did not alter total shoot dry-matter production. In field studies, plants that were established in the fall flowered sooner and more synchronously after resumption of growth in the spring than those that were planted in the spring and flowered in the summer. Plants seeded after May failed to flower in the same summer.

When grown without soybean [Glycine max (L.) Merr.] interference, eastern black nightshade (Solanum ptycanthum Dun.) planted in May produced as many as 7000 berries and 800000 seeds per plant. Eastern black nightshade planted in mid-July produced as many as 100 berries, but those planted in mid-August failed to produce berries. Eastern black nightshade produced less than 85 berries per plant when planted with soybeans in May, 0 to 3 berries per plant when planted into soybeans in June, and no berries when planted into soybeans in July. However, when soybeans were defoliated in July to simulate hail injury, eastern black nightshade that had been planted with soybeans in May produced up to 1600 berries per plant, and those planted into the defoliated soybeans in July produced up to 58 berries per plant. We suggest, therefore, that in vigorously growing soybeans, control of eastern black nightshade emerging in the row would only be required through June to prevent berry production. If, however, the soybean canopy were disturbed by hail or other factors, eastern black nightshade seedlings emerging in late July or early August might produce berries by soybean harvest.

Witchweed, [Striga asiatica (L.) Kuntze5 STRLU], an important parasitic weed throughout much of the old world, occurs as a recent (30 yr) introduction in a limited region in North and South Carolina. Reproduction in this population has been shown to occur primarily through self-pollination of flowers. Genetic diversity in two populations from this region was assessed, utilizing starch gel electrophoresis and staining of enzymes. An average of 64 individuals was observed to be monomorphic at an estimated minimum of 32 genetic loci coding 18 enzyme systems. This lack of polymorphism is attributable to the probable founding of the population by one or a few individuals coupled with the predominantly autogamous breeding system.

An indigenous soil-borne fungus was isolated from infected seeds and seedlings of Texas gourd [Cucurbita texana (A.) Gray] and evaluated as a mycoherbicide. The pathogen was identified as Fusarium solani App. & Wr. f. sp. cucurbitae Snyd. & Hans. Only Cucurbita species were susceptible in host range tests. Ample quantities of microconidia for greenhouse and field plot inoculum were produced in shake culture on Richards' solution. Granular inoculum for field plot tests was produced in 5% (w/w) cornmeal/sand medium. In controlled-environment experiments, inoculated Texas gourd seedlings were killed over a range of air temperatures from 16 to 40 C. Optimum air temperature for disease development was 26 to 30 C. Complete kill of 4- and 8-cm-tall seedlings was achieved after 3 weeks when sprayed until runoff with a microconidial suspension containing 2.0 × 106 spores/ml. Texas gourd seedlings were effectively controlled in field plots (99% maximum) with liquid or granular inoculum. Soil samples from infested plots indicated that the fungus persists up to 12 months in a fine sandy loam, but after 12 months inoculum levels were insufficient to cause disease on seedlings grown under optimum conditions for disease development.

Sicklepod (Cassia obtusifolia L. ♯6 CASOB), hemp sesbania [Sesbania exaltata (Raf.) Cory ♯ SEBEX], and showy crotalaria (Crotalaria spectabilis Roth. ♯ CVTSP) were grown in controlled-environment greenhouses with day/night temperatures of 23/17, 26/20, 29/23, and 32/26 C. Plant height, leaf area, and total dry weight at 53 days after planting increased significantly with temperatures between 23/17 and 29/23 C in sicklepod and showy crotalaria, and between 23/17 and 32/26 C in hemp sesbania. In all species, leaves were produced more rapidly as temperature increased. Axillary branch leaf production was greatest at 29/23 C in sicklepod, and at 29/23 and 26/20 C in showy crotalaria; hemp sesbania showed little axillary branch development. Total dry-matter production in all species was closely correlated with leaf area duration, but not with net assimilation rate. Differences in total main stem leaf area in all species were primarily due to differences in leaf number rather than to differences in leaf size at maturity.

Photosynthetic growth of 9 of the 11 known species of the family Rhodospirillaceae was strongly inhibited by atrazine. Growth of a wild-type strain of the bacterium Rhodopseudomonas sphaeroides van Niel was almost completely inhibited by 100 μM concentrations of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. These herbicides gave 50% inhibition of growth at concentrations of 35 and 25 μM, respectively. Through continuous culture of the wild-type R. sphaeroides in the presence of 100 μM atrazine, strains of the organism were selected in which photosynthetic growth was highly resistant to both atrazine and diuron. Members of the genus Rhodopseudomonas isolated from two natural ecosystems showed various levels of resistance to 100 μM atrazine, but Rhodopseudomonas showing a high level of resistance were more common among the isolates from a pond-mud sample which had been exposed to runoff from atrazine-treated cropland than from a sample of a lake mud never exposed to triazines.

Insensitivity to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and certain other herbicides was found in plants of horseweed (Conyza canadensis (L.) Crong. ♯4 ERICA) collected from vineyards where atrazine had been applied extensively. There were no differences in the uptake, translocation, or accumulation of radiolabeled atrazine between plants of the susceptible and resistant biotypes. However, atrazine at 1 × 10-4 M caused no inhibition of photosynthetic electron transport in resistant leaves. Photosynthetic characteristics of leaves of susceptible and resistant plants showed different sensitivities to atrazine, but similar sensitivities to diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] and ioxynil (4-hydroxy-3,5-diiodobenzonitrile). Isolated chloroplast membranes from resistant plants exhibited a resistance factor of 1000 to atrazine but only 10 to 30 to methylthio-s-triazines. DNOC (4,6-dinitro-o-cresol) was found to be more effective in susceptible chloroplasts than in resistant ones. A marked reduction in the galactolipid content, especially digalactosyl diglyceride, was found in resistant leaves. It is suggested that these alterations in lipid content and composition may contribute to atrazine resistance in horseweed.

The applicability of fluorescence measurements for the detection of herbicide effects in whole leaves was analyzed. Based on the results known for isolated chloroplasts, normalized variable fluorescence of the initial rise was shown to be an appropriate tool for monitoring effects of photosystem II (PS II) herbicides. Equipment is described for monitoring the degree of inhibition by fluorescence induction measurements and microcomputer data analysis. The method is used to study the effect of pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], BAY DRW 1139 [4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one], and phenmedipham {3-[(methoxycarbonyl)amino] phenyl (3-methyl-phenyl)carbamate} after foliar application to different species. A rapid decrease of normalized variable fluorescence indicates penetration into leaf cells of all species tested. During a 5- to 7-day experiment, the apparent variable fluorescence decreased continuously in herbicide-susceptible plants, while it recovered in resistant plants due to an internal detoxification mechanism. The described method provides a rapid, simple, and nondestructive tool for analyzing the kinetics of penetration and detoxification of PS II herbicides in whole leaves.