The absorption of norflurazon [4-chloro-5-(methylamino)-2-(3-(trifluromethyl)phenyl)-3(2H)-pyridazinone] by 1-cm segments cut from the apical 5-cm roots of velvetleaf (Abutilon theophrasti Medik. # ABUTH) was studied. Norflurazon absorption was rapid in the first 10 min but there was very little increase thereafter up to 120 min. Norflurazon also penetrated the entire tissue volume within 30 min after the root segments were placed in absorption solution. Norflurazon did not accumulate to concentrations above the external solution over 120 min, and 90% of the absorbed herbicide diffused freely out of the tissue within 10 min. The metabolic inhibitor KCN did not affect norflurazon uptake, whereas pretreatment of root tissue with DNP increased absorption. Anoxia increased absorption by 60 and 120% above aerated treatment at 10 min and 2 h, respectively. These experiments suggest that norflurazon, which is considered to move primarily in the apoplast, moved into both the apoplast and symplast of velvetleaf root cells by simple diffusion.

The glandular trichomes on velvetleaf (Abutilon theophrasti Medic. # ABUTH) stems and petioles exude liquid globules which are phytotoxic in petri plate bioassays. Because the exudate is easily removed with water, it was hypothesized that it may be washed from velvetleaf stems and petioles into the surrounding soil environment where it may exert allelopathic influences. Field and greenhouse studies attempted to separate the influence of exudates from other mechanisms of interference by removing exudates from some velvetleaf plants and not from others. Velvetleaf trichome exudates did not increase interference by velvetleaf in either field or greenhouse studies. A velvetleaf accession from Rosemount, MN, produced 1.4 times more exudate/stem dry weight than another accession from Stoneville, MS. However, the MS exudate was about 1.4 times more toxic in petri plate assays when compared to the MN exudate. Although greenhouse-grown plants had approximately 3.3 times more exudate/stem dry weight than field-grown plants, the field exudate was 1.6 times more toxic. The activity of velvetleaf exudates was also assayed in autoclaved and nonautoclaved soil. Although active in autoclaved soil, extract activity was lost at all but the highest dosage when the soil was not autoclaved. Microorganisms appear to rapidly detoxify the velvetleaf toxin(s) and may reduce or eliminate its impact in the field.

Full-season interference effects of hemp sesbania [Sesbania exaltata (Raf.) Cory. # SEBEX] on cotton (Gossypium hirsutum L. 'Stoneville 213′) were investigated on a fine sandy loam soil for 3 yr at Stoneville, MS. Experimentally induced hemp sesbania populations of ≥ 3223 plants/ha significantly reduced cotton yields. Interference of hemp sesbania at 3223, 6456, 16 114, and 32 228 plants/ha, equivalent to 1, 2, 5, and 10 plants/3.3 m, reduced seed cotton yields by 19, 25, 45, and 53%, respectively. Cotton boll weights were reduced by 9% when hemp sesbania infestations were ≥ 16 114 plants/ha. Cotton plant density, seedling vigor, and initial cotton white blooms/ha at ≤75 days after planting (DAP) did not differ with varying densities of hemp sesbania. Cotton white blooms/ha were reduced by 32 228 hemp sesbania plants/ha by 77 DAP and by all weed densities by 98 DAP. Hemp sesbania height was equal to or greater than cotton height by 55 to 65 DAP. Light penetration at 1 m above the top of the cotton canopy was 36% less than in weed-free plots when hemp sesbania densities were ≤6446 plants/ha. Likewise, light penetration was reduced at the cotton canopy top and at midcanopy but was not less at the soil surface unless hemp sesbania densities were ≤ 32 223 plants/ha.

Seeds of green foxtail [Setaria viridis (L.) P. Beauv. # SETVI] and giant foxtail (S. faberi Herrm. # SETFA) were collected from mature plants in the field and recovered from three soil depths under two types of tillage. Fungi colonizing the caryopses were isolated to determine the effect of tillage and soil depth on fungal colonization and the field flora. Alternaria alternata (Fr.) Keissler and Epicoccum purpurascens Ehrenb. ex Schlecht. were the two fungi most frequently isolated from the hand-harvested seeds. Percentages of fungal colonization were directly related to size of the caryopses. The most frequently isolated fungus species recovered from seeds from soil were A. alternata, Cladosporium cladosporioides (Fresen.) de Vries, E. purpurascens, and two unidentified fungi with sterile mycelium. One sterile fungus had white rough mycelium, and the other had dark mycelium. These two sterile fungi had a detrimental effect on foxtail seed germination in the laboratory. Caryopsis colonization seems to be related to the placement of the crop residues in the soil. In reduced-tillage plots, more caryopses were colonized in the top soil layer (0 to 7.5 cm) than in the 7.5- to 15-cm layer. In plowed soils, greater colonization occurred at the lower depth.

In controlled-environment chambers, the scentless plant bug Niesthrea louisianica Sailer damaged reproductive structures of velvetleaf (Abutilon theophrasti Medik. # ABUTH) and reduced viable seed production by 98 to 99%, in comparison with insect-free control plants. The insect completed its life cycle on velvetleaf in two temperature regimes simulating warm growing-season conditions in Mississippi (29/23 C day/night) and Minnesota (24/18 C). Feeding by N. louisianica delayed flowering, capsule development, and capsule and seed maturation in biotypes of velvetleaf from Mississippi and Minnesota, in both temperature regimes. Numbers and weights of capsules and seed were lower in the infested plants. Augmentation of natural populations of N. louisianica to increase population density early in the growing season might be effective in reducing velvetleaf seed production.

The influence of two weed management systems was determined on weed seed and seedling populations and on yields of cantaloupe (Cucumis melo L. var. reticulatus Naudin ‘Perlita′), bell pepper (Capsicum annuum L. var. grossum ‘Grande Rio 66′), cotton (Gossypium hirsutum L. ‘CP 3374′), onion (Allium cepa L. ‘1015Y′), and cabbage (Brassica oleracea, var. capitata L. 'Sanibel′) sequentially grown in two 3-yr cycles. Palmer amaranth (Amaranthus palmeri S. Wats. # AMAPA) did not exist initially, but hurricane-introduced seed populations increased to 1.1 billion/ha as seed populations of common purslane (Portulaca oleracea L. # POROL) decreased from 786 million/ha to 124 million/ha in the 6-yr period, without weeding or herbicide. Use of herbicides and handweeding reduced Palmer amaranth seed populations 98%, but 18 million/ha still remained after 6 yr. The use of herbicides and Palmer amaranth interference decreased the seed populations of common purslane by 84%, but handweeding was inefficient. Yields of all but the first crop of cantalouple were almost totally eliminated by season-long interference of Palmer amaranth. Savings with the utilization of herbicides rather than handweeding ranged from $62/ha for cotton to $4703/ha for bell pepper.

Polyacrylamide electrophoresis and spectroscopic methods were used to characterize biotypes A and B itchgrass [Rottboellia exaltata L.f. # ROOEX] and their F2 progeny. Electrophoretic analyses of F2 progeny showed that differences between these two biotypes are multiallelic. Spectrophotometric data indicated differences between the photosynthetic apparatus of the two biotypes. These differences may reflect different abilities to adapt to varying light conditions and infer that these biotypes promote survival of the species by increasing the number of environmental nitches that R. exaltata can occupy.

Several crop and weed species were field grown to maturity and their residues incorporated with soil to determine the effects of the plant residues on the growth of subsequent plantings in a spring-fall planting sequence in 1980 to 83. Growth of Palmer amaranth (Amaranthus palmeri S. Wats. # AMAPA) was studied in 1984 and 1985, and the effects of soil-incorporated Palmer amaranth on the growth of cabbage (Brassica oleracea var. Capitata L.) and carrot (Daucus carota L. var. sativa) seedlings were studied in 1985. Under warm, moist, saline soil conditions and intense sunlight following the spring plantings of the 1980 to 83 study, soil-incorporated residues of Palmer amaranth inhibited the growth of carrot 49% and onion (Allium cepa L.) 68%. Johnsongrass (Sorghum halepense L. Pers. # SORHA) residues inhibited the growth of onion 67%, and in one of two years inhibited the growth of cabbage 26% and common sunflower (Helianthus annuus L. #HELAN) 10%. In 1984 and 1985, Palmer amaranth grown at population densities of 300 plants/m2 attained heights of nearly 2 m and biomass of 2 to 3 kg/m2 within 10 weeks after planting. Phytotoxicity with these biomasses persisted 11 weeks in cabbage and carrot plantings. In 1985, phytotoxicity was dissipated 16 weeks after soil incorporation of the weed.

This paper describes the communities of weeds in cereal and oilseed crops in Saskatchewan, using data collected in a 4-yr survey that sampled more than 400 fields. The survey data for the 40 most common weeds were analyzed in an attempt to distinguish natural groups of weed species and to compare the weed communities associated with the different crops and with different soils. The crops were barley (Hordeum vulgare L.), flax (Linum usitatissimum L.), oats (Avena sativa L.), rape (Brassica campestris L., Brassica napus L.), and wheat (Triticum aestivum L.). Phytosociological association and cluster analysis indicated that the associations of the weed species were more or less independent of the crop, although some differences existed and were determined more by soil or the associated climate. The 40 most common species were divided into three groups related to the soil and climatic subregions of the province.

Studies were conducted to investigate the reproductive biology and herbicide response of horsenettle (Solanum carolinense L. # SOLCA) and robust horsenettle (Solanum dimidiatum Raf. # SOLDM) that are common in peanut (Arachis hypogaea L.) production. Of these two species, horsenettle had a higher rate of seed germination, greater ability for seedling establishment in a competitive situation (pasture), greater ability to regenerate from smaller root fragments, and greater ability to regenerate from progressively greater depths in soil. Horsenettle was relatively more sensitive to glyphosate [N-(phosphonomethyl)glycine] (1.1 and 2.2 ai kg/ha), propylene glycol butyl ether esters of 2,4-D [(2,4-dichlorophenoxy)acetic acid] (0.8 and 1.7 ae kg/ha), and the ethanolamine salt of 2,4-D (1.7 ae kg/ha) than robust horsenettle. Conversely, robust horsenettle was more sensitive to dicamba [3,6-dichloro-2-methoxybenzoic acid)] (0.3 and 0.6 ae kg/ha). In a field study, dicamba applied annually in July or August for 2 yr at a rate of at least 1.1 kg/ha controlled 92% or more.

Acid-scarified hogpotato (Hoffmanseggia densiflora Benth. ex. Gray # HOFDE) seed incubated in distilled water germinated at least 94% when incubated at constant 15, 20, 30 C, and at alternate 20/30 C (20 C for 16 h and 30 C for 8 h) temperatures. Highest germination in buffered solutions occurred at pH 5.0 and 6.0 with reduced germination at lower and higher pH levels. Sodium chloride concentrations of 50 mM and greater reduced the germination rate. Percent germination after 9 days was reduced at NaCl concentrations of 100 mM and greater. Radicle lengths measured after 3 days were significantly reduced with increasing NaCl concentration. Twenty-day-old hogpotato seedlings having three true leaves were able to resprout after topgrowth removal. Regrowth occurred on 15% of the seedlings approximately 15 days after top removal.

Field experiments were conducted at Lincoln, NE, in 1983 and 1984 to determine the effectiveness of subsurface jet injection of herbicides on a simulated shattercane [Sorghum bicolor (L.) Moench # SORVU] infestation in corn (Zea mays L.). Alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] and EPTC (S-ethyl dipropyl carbamothioate) plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide), incorporated with a disc or applied from the subsurface and surface with a jet injector attached to a sweep plow, generally produced higher corn yields and shattercane control than herbicides applied with the sweep to the subsurface only. EPTC plus dichlormid controlled shattercane better than alachlor. Cultivation improved shattercane control by at least 10% in conjunction with most jet injection and disc-incorporated alachlor treatments. Cultivation increased corn yields by about 10 to 20% when averaged over all herbicides and application patterns. A subsurface plus surface herbicide injection system supplemented with cultivation would be a possible method of incorporating herbicides in reduced tillage to selectively control shattercane in corn.

Experiments were conducted in 1982, 1983, and 1984 to determine whether herbicides can effectively control weeds in annual statice (Limonium sinuatum Mill.) without reducing the marketability of the crop. A greenhouse evaluation of chlorpropham (1-methylethyl 3-chlorophenylcarbamate), napropamide [N,N-diethyl-2-(1-naphthalenyloxy)propanamide], EPTC (S-ethyl dipropyl carbamothioate), oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyi)-1,3,4-oxadiazol-2-(3H)-one}, and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] indicated that preemergence applications of the latter three herbicides resulted in the most effective weed control and least statice injury. Oxadiazon was the most effective for broadleaf and grass ed control in field-grown statice. Yield and quality were greatest in oxadiazon-treated plots and exceeded those of the handweeded controls. Annual statice was most sensitive to trifluralin.

Velvetleaf (Abutilon theophrasti Medik. # ABUTH) is difficult to control with existing weed control strategies. Some measure of control can be obtained with a fungus, Colletotrichum coccodes (Wallr.) Hughes, used as a bioherbicide, but when the bioherbicide application was combined with the plant growth regulator thidiazuron (N-phenyl-N′-1,2,3-thidiazol-5-yl-urea), weed control was substantially improved. Thidiazuron alone interfered with normal development of velvetleaf, causing stunting and initiation of axillary bud growth. Tank mix applications of C. coccodes and thidiazuron acted synergistically to increase velvetleaf mortality. When C. coccodes was applied 10 days after thidiazuron as a split application, weed control was less than for tank mix applications. However, two applications of C. coccodes plus thidiazuron were more effective than equivalent single tank mix applications. Under laboratory conditions, high concentrations of thidiazuron (2× field application rates) inhibited growth of C. coccodes, but at field application rates thidiazuron did not reduce disease development. Combinations of thidiazuron and C. coccodes may provide effective control of velvetleaf in the field.

The effect of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5 -triazin-2-yl)amino] carbonyl] benzenesulfonamide} on the phytotoxicity of postemergence applications of the methyl ester of diclofop ((±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} to Italian ryegrass [Lolium multiflorum (Lam.) # LOLMU] was investigated in field and greenhouse experiments. The addition of chlorsulfuron (14.8 g ai/ha field, 12.4 g/ha greenhouse) to 0.90 kg/ha diclofop reduced Italian ryegrass control 27% in the field and increased Italian ryegrass fresh weights in the greenhouse more than twofold over diclofop alone. The antagonism was more evident when combinations were used to treat Italian ryegrass in the three-leaf stage than the two- or four-leaf stage. Sequential applications yielded results similar to tank mix combinations. Chlorsulfuron and diclofop were approximately 400 and 50%, respectively, more active on Italian ryegrass when applied preemergence than when applied postemergence. Combinations of chlorsulfuron and diclofop applied preemergence to Italian ryegrass resulted in additive responses.

One and two postemergence (POE) applications of the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy] propanoic acid} or sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} following preemergence (PRE) application of fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea} were compared to a preplant-incorporated (PPI) application of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] plus fluometuron PRE or pendimethalin plus fluometuron PRE for annual grass control in cotton (Gossypium hirsutum L.) and net economic return to land, overhead, and management. One POE application of either fluazifop or sethoxydim following fluometuron PRE resulted in greater control of a high population of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. # BRAPP] and greater yield and net return than a PPI application of trifluralin or pendimethalin plus fluometuron PRE. A second application of fluazifop or sethoxydim increased late-season control but did not increase yield or net return. In a high population of large crabgrass (Digitaria sanguinalis L. # DIGSA), fluometuron PRE plus two POE applications of fluazifop or sethoxydim resulted in grass control, lint yield, and net return similar to trifluralin or pendimethalin PPI plus fluometuron PRE. No differences in grass control, crop response, or net return were noted between PPI application of trifluralin or pendimethalin. Control of broadleaf signalgrass and large crabgrass with pendimethalin plus fluometuron PRE was less than with pendimethalin PPI plus fluometuron PRE. In fields with a low population of large crabgrass, fall panicum (Panicum dichotomiflorum Michx. # PANDI), and goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], fluometuron PRE provided excellent season-long control. No benefits were obtained from addition of a grass herbicide. No treatments affected cotton maturity or fiber quality.

Field and growth chamber experiments were conducted from 1983 to 1985 to determine the relationships between loss in plant productivity and plant residue-crop-weed density in no-till wheat (Triticum aestivum L.) and to document chemical management and cultivar options for such a cropping system. Untilled stubble left on the soil at rates of 0.5 and 3 t/ha reduced wheat density and grain yield in continuous winter wheat. Stem densities of cheat (Bromus secalinus L. # BROSE) and downy brome (B. tectorum L. # BROTE) in mulched treatments averaged about 682, 679, and 38 stems/m2 in 1983, 1984, and 1985, respectively. In the nonmulched treatment, weed density and standing dry matter ranged from 5 to 30 stems/m2 and 2 to 6 g/m2, respectively. Removal of residues eliminated key habitat characteristics required for the establishment of Bromus spp. Preemergence and early postemergence applications of BAY SMY 1500 [4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one] at 2 kg/ha controlled both species of Bromus in no-till wheat. The herbicide treatment slightly delayed maturity of 10 wheat cultivars, but control of cheat and downy brome allowed nine cultivars to attain their yield potential, improving grain yield over that of untreated plots. ‘Vona’ wheat did not tolerate the herbicide and was susceptible after emergence. BAY SMY 1500 widens the spectrum of weed management and wheat cultivar options for an annual conservation production system of winter wheat.

Experiments were conducted for 3 yr to evaluate the effects of the ethyl ester of fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy] phenoxy] propanoic acid} on rice (Oryza sativa L. 'Starbonnet′) applied at 112 and 168 g ai/ha or as two applications of 112 g ai/ha applied 10 to 14 days apart. Fenoxaprop did not adversely affect grain yield, panicle weight, seed weight, or seed germination when applied before the booting stage of both sprinkler-irrigated and flooded rice. Rice height was sometimes reduced by treatment at earlier growth stages, but yields were not affected. With the exception of applications at early jointing (internode elongation = 6 mm) in 1983, milling yield was not adversely affected by fenoxaprop applications made prior to booting of both sprinkler-irrigated and flood-culture rice. Applications during heading adversely affected most yield parameters.

A series of experiments were conducted from 1983 through 1986 to determine the efficacy of encapsulated starch formulations of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] in conventional and no-till soybean [Glycine max (L.) Merr.] production. The encapsulated starch formulations remaining on the soil surface were significantly more effective than the emulsifiable concentrate when applied in February, March, or April. Encapsulated trifluralin products prepared by both the starch xanthate and starch borate processes were as effective as the emulsifiable concentrate even when used in conventional-tillage systems for weed control and for maintaining soybean yields. Our data indicate that an effective and economical herbicide such as trifluralin need not be lost in no-till soybean production if new controlled-release formulation technology is used by the agricultural industry.

Weed control in reduced-tillage corn (Zea mays L. ‘Pioneer 3732′) with butylate [S-ethyl bis(2-methylpropyl) carbamothioate] and EPTC (S-ethyl dipropyl carbarnothioate) was not reduced when these herbicides were applied jointly with dry or liquid fertilizer. In most cases, application with fertilizer resulted in weed control similar to that observed when the herbicide was applied in water at 285 L/ha. Butylate applied as a granular formulation also gave weed control similar to the spray at 285 L/ha. Application in 95 L/ha of water consistently resulted in reduced weed control. Corn injury was not greatly influenced by application method, and differences in corn yield appeared to be due to differences in weed control. Growth chamber bioassays indicated that both butylate and EPTC dissipated more rapidly when applied in 95 L/ha of water than the other application methods, which may explain differences in weed control observed in the field.