Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide]-binding in excised root segments of corn (Zea mays L. ‘NC + 59′) was confined to cell wall fractions (residue and 500 g pellet) remaining after homogenization and to components of the 100 000 g supernatant. Binding increased in both the cell wall and soluble fractions with continued exposure to napropamide. Microautoradiographs revealed that the napropamide bound in the cell walls was located in epidermal, cortical, and stelar tissue. Various proteins were capable of binding napropamide in vitro; however, protease treatment did not liberate the radioactivity bound in the cell wall fragments. Carbohydrate release from the cell wall material with cellulase was not correlated with the solubilization of bound radioactivity and wall carbohydrate monomers did not appear to bind to napropamide in vitro. A portion of the radioactivity found in the soluble components (at 100 000 g) was associated with a molecule of MW > 600. The continued influx of napropamide was due to binding to cell wall components and molecules within the cell.

Absorption of 2,4-D [(2,4-dichlorophenoxy) acetic acid], dicamba [3,6-dichloro-o-anisic acid], and the isopropylamine salt of glyphosate [N-(phosphonomethyl) glycine] by excised honeyvine milkweed [Cynanchum laeve (Michx.) Pers.] leaves was determined. Experimental variables included leaf position (terminal vs. basal), a surfactant, 4-isopropenyl-1-methylcyclohexane plus unspecified emulsifiers (SA-77), and leaf collection dates. Absorption of the three herbicides by terminal and basal leaves was increased by the addition of the surfactant. However, the surfactant increased absorption into basal leaves more than into terminal leaves. The surfactant reduced surface tension and increased drying time of water droplets on adaxial leaf surfaces by 50%. The pH of the herbicide solutions was reduced from about 5.8 to about 3.9 by SA-77. Absorption of all three herbicides was greater into terminal than into basal leaves when the surfactant was not present, but the difference disappeared when the surfactant was added. Generally, no differences were observed in the absorption of 2,4-D and dicamba. Glyphosate absorption was greater in terminal leaves collected after a period of adequate moisture than after a period of dry soil conditions.

Field and greenhouse research was conducted during 1980 and 1981 to evaluate the effects of carrier volume, surfactant concentration, and treatment date on glyphosate [N - (phosphonomethyl)glycine] toxicity to annual-grass weeds and volunteer small grains. Glyphosate phytotoxicity increased as carrier volume was decreased from 190 to 24 L/ha. The presence of a surfactant in the spray solution did not influence grass control when glyphosate was applied in a carrier volume of 24 L/ha. When glyphosate was applied in 48 or 95 L/ha, the presence of surfactant resulted in better grass control than glyphosate without surfactant. When applied in 190 L/ha, glyphosate with 0.5% (v/v) surfactant gave better grass control than glyphosate alone or commercially formulated glyphosate. When glyphosate was applied to plants under water stress, little control was achieved regardless of plant growth stage. Glyphosate application to grass after head initiation also resulted in reduced control. Maximum weed control with glyphosate was attained when applications were made to seedlings growing actively because of adequate soil moisture and favorable temperatures.

The influence of buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}, diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] on fluorescence emission and post-luminescence decay in chlorella (Chlorella vulgaris Beyer) was studied. All three herbicides blocked photosynthetic electron transport and thus enhanced fluorescence. Buthidazole was the most active, a 79% increase in fluorescence being observed when algal cultures were exposed to 1 × 10-6 M herbicide for 5 min, and a 206% increase with an exposure time of 60 min. Postluminescence in chlorella exposed to 1 × 10-6 M buthidazole for 5, 10, 20, and 60 min was inhibited 15, 34, 58, and 69%, respectively. Diuron and atrazine inhibition of postluminescence was much less than that of buthidazole. The ratio of relative fluorescence to relative postluminescence can be sued to give a numerical value (C) for the phytotoxicity of this type of herbicide to a given plant species.

Solarization by means of transparent polyethylene sheets for 1 week in mid-summer significantly (P = 0.05) reduced numbers of viable prickly sida (Sida spinosa L.), common cocklebur (Xanthium pensylvanicum Wallr.), velvetleaf (Abutilon theophrasti Medic.) and spurred anoda [Anoda cristata (L.) Schlect.] seeds remaining after burial in soil. Solarization treatments for 1 to 4 weeks significantly reduced the total weed emergence of prickly sida, pigweeds (Amaranthus species), spurred anoda, morningglories (Ipomoea species), horse purslane (Trianthema portulacastrum L.), and various grass species from natural seed populations for the growing season by 64 to 98%. Purple nutsedge (Cyperus rotundus L.) emergence was increased by solarization in some instances. It was not determined if the increased emergence was from tubers or seeds. Maximum temperatures at the 1.3-cm soil depth under the polyethylene sheets reached 65 to 69C for 3 to 4 h of the mid-afternoon on clear days as compared with 43 to 50C at 1.3 cm in the soils that were not covered. Surface soil-moisture levels were also elevated under the polyethylene covers. Although solarization did not eliminate dormant weed seeds from the germination zone, the treatment killed nondormant seeds and greatly reduced the number of weed seedlings that otherwise would have emerged.

Spotted spurge (Euphorbia maculata L.) and prostrate spurge (E. supina Raf.), both in subgenus Chamesyce, were examined by light and electron microscopy using a caffeine - fixation technique to sequester the phenolic pools intercellularly. Both species have typical dicotyledon-type Kranz anatomy. Sequestered phenolic pools were located in vacuoles in epidermal and mesophyll cells. Only in spotted spurge, however, were additional phenolic pools formed in bundle - sheath cells. This study was undertaken because allelopathy has been demonstrated in prostrate spurge and because phenolic compounds have been implicated in allelopathy. These results would indicate that spotted spurge should also be allelopathic.

The effects of herbicide concentration, adjuvants, and temperature on the phytotoxicity of CGA-82725 {2-propynyl 2-[4-[3,5-dichloro-2-pyridinyl)oxy] phenoxy] propionate}, RO 13-8895 {acetone-O-[D-2-[p-(α,α,α-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime}, and BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one} to large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were evaluated. The addition of adjuvants increased the toxicity of BAS 9052 OH at herbicide rates below 0.14 kg ai/ha, whereas the adjuvants had little effect on the activity of CGA-82725 or RO 13-8895. There were no differences among the adjuvants in enhancing grass control with any of the herbicides. Control of large crabgrass with CGA-82725 or BAS 9052 OH was not affected by temperature at the time of spraying; RO 13-8895 was slightly more toxic at 16 C than at 32 C. Soybean [Glycine max (L.) Merr.] had good tolerance to the three herbicides at rates 3 to 10 times those recommended; no differences in tolerance were observed among seven soybean cultivars. Stage of growth and the addition of an emulsifiable oil adjuvant did not affect soybean tolerance to BAS 9052 OH.

Tank mixtures of herbicides for control of emerged winter weeds and preemergence control of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were evaluated on bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’ # CYNDA] fairways over a 2-yr period. Glyphosate [N-(phosphonomethyl)glycine] applied at 0.28 kg ai/ha in tank mixtures with DCPA (dimethyl tetrachloroterephthate) at 11 kg ai/ha controlled a higher percentage of parsley-piert (Alchemilla microcarpa Boiss. Reut. # APHMI) than either herbicide alone. When applied for spur weed (Soliva spp.) control, DCPA was antagonistic in the tank mixture with simazine [2-chloro-4,6-bis(ethylamino)-s-txiazine]. During one yr of the 2-yr study period, control of large crabgrass was less in plots treated with combination of DCPA and glyphosate than in plots treated with DCPA alone. Less large crabgrass control was obtained in plots treated with bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] at 11 kg ai/ha in combinations with either paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) or 2,4-D [(2,4-dichlorophenoxy)acetic acid] plus mecoprop {2-[(4-chloro-o-tolyl)oxy]propionic acid} plus dicamba (3,6-dichloro-o-anisic acid) than when treated only with bensulide.

Research was conducted at Rosemount, Minnesota in 1979 and 1980 to evaluate the effect of soil moisture on quackgrass [Agropyron repens (L.) Beauv. # AGRRE] interference in soybeans [Glycine max (L.) Merr.]. Four treatments were studied: 1) nonirrigated soybeans, 2) irrigated soybeans, 3) nonirrigated soybeans, quackgrass-infested, and 4) irrigated soybeans, quackgrass-infested. Percent N, P, and K of soybeans was not affected by quackgrass interference. Irrigation did not increase the yield of quackgrass-free soybeans. The yield of quackgrass-infested soybeans was increased by irrigation when soil moisture was limited, but yields were always less than quackgrass-free soybeans. Quackgrass was nearly the same height or taller than the soybeans at all stages of soybean development and offered substantial competition for light throughout the growing season. This research indicates that an adequate supply of soil moisture can reduce quackgrass interference in soybeans, but cannot eliminate it, since quackgrass apparently continues to compete with soybeans for light.

The control of greasewood [Sarcobatus vermiculatus (Hook.) Torr.] and salt rabbitbrush [Chrysothamnus nauseosus ssp. consimilis (Greene) Hall and Clem.] was investigated with application of 2,4-D [(2,4-dichlorophenoxy)acetic acid] and a mixture of 2,4-D and picloram (4-amino-3,5,6-trichloropicolinic acid). The herbicides were applied at 2-week intervals from May 1 to August 1. Greasewood had accelerated shoot growth and was most susceptible to application of 2,4-D during June. Accelerated shoot growth and maximum susceptibility to 2,4-D of salt rabbitbrush began in June and extended into July. Mortality of greasewood and salt rabbitbrush from 2,4-D at 2.2 kg/ha applied at optimum dates averaged 72 and 87%, respectively. The picloram/2,4-D mixture was more effective for greasewood control than 2,4-D alone in 1 yr at very early and late application dates on a xeric site and only at the last date of application on a mesic site. Reapplication of 2,4-D at 2.2 and 3.3 kg/ha in June to partially controlled stands gave excellent control of both greasewood and rabbitbrush.

Field experiments were conducted for 2 yr to determine the influence of picloram (4-amino-3,5,6-trichloropicolinic acid) and a commercial mixture of picloram plus 2,4-D [(2,4-dichlorophenoxy)acetic acid] (1:16, w/w) on control of wild oats (Avena fatua L. # AVEFA) with four postemergence herbicides. The phytotoxicity to wild oats of barban (4-chloro-2-butynyl m-chlorocarbanilate) or difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) in 1981 and diclofop {2-[4-(2,4-dichlorophenoxy)-phenoxy] propanoic acid} or flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] in 1981 and 1982 was reduced when these herbicides were applied in a mixture with picloram plus 2,4-D. Consequently, the use of these mixtures for broad-spectrum weed control in one spray operation is not recommended. Picloram applied at a rate equivalent to the amount present in the picloram plus 2,4-D mixture did not influence the control of wild oats obtained with any herbicide, indicating that the antagonism was due to the 2,4-D component of the picloram plus 2,4-D mixture.

Combinations of herbicides applied preplant incorporated and preemergence plus at layby were evaluated in corn (Zea mays L.) at three Nebraska locations in 1977 through 1980 for their effectiveness in providing season-long weed control. Pendimethalin [N-(1 -ethylpropyl) - 3,4-dimethyl - 2,6 - dinitrobenzenamine], pendimethalin + atrazine [2- chloro - 4 - (ethylamino) -6 - isopropylamino) -s- triazine ], metolachlor [2 - chloro - N - (2 - ethyl - 6 - methylphenyl) - N - (2 - methoxy -1 - methylethyl) acetamide], alachlor [2 - chloro -2′,6’ - diethyl - N- (methoxymethyl)acetanilide], cyanazine {2 -[[4 - chloro- 6 - (ethylamino) - s - triazin-2 - yl] amino] -2 -methylpropionitrile}, and cyanazine + atrazine were shown to be selective to corn and effective in controlling late - germinating weeds. Irrigated - corn yield was not increased by layby herbicide applications on the weed species and weed densities present in these experiments.

Twenty days after rice (Oryza sativa L. ‘IR28’) emergence, water was withheld from the stress treatment for 20 days while the control was kept well-watered by furrow irrigation. In the control plots, rice leaf water potential at 0800 hours was –5.5 bars and leaf length 30 cm on the 12th day of stress. In the stress treatment, leaf water potential decreased to –8 bars and leaf length to 20 cm, when no weeds competed with rice. With maximum weed competition, rice leaf water potential decreased to –18 bars and leaf length to 15.5 cm. on the 20th day of stress, dawn (0600 h) leaf water potential of rice in the stress treatment was reduced from –8 bars when no weeds competed with rice to –19 bars when competition was maximum. The weed species had higher water potential values than the rice in both control and water-stress treatments.

In greenhouse studies, the potential interactive effects of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] treatments combined with the air pollutant ozone (O3) or the antioxidants, piperonyl butoxide {α-[2-butoxyethyl) ethoxy]-4,5-dimethylenedioxy-2-propyltoluene} and n-propyl gallate, on the growth of sorghum [Sorghum bicolor (L.) Moench ‘Funk G522DR’] seedlings that were protected or unprotected with the antidote, CGA-43089 [α-(cyanomethoximino)-benzacetonitrile], were examined. Metolachlor was applied preplant incorporated at rates of 2.2, 3.9, and 5.6 kg/ha, and it was evaluated against fumigation with O3 at 0.2 and 0.3 ppmv or against 4.9, 6.7, and 9.0 kg/ha of each antioxidant applied preplant incorporated. In combination treatments, shoot dry weight at 30 days after planting was reduced more than expected by metolachlor in the presence of the protectant CGA-43089 and ozone or some rates of the two antioxidants, suggesting synergism. In the absence of the protectant, CGA-43089, growth responses of sorghum to combination treatments of metolachlor with ozone or propyl gallate suggested an additive effect, although some treatments of metolachlor combined with piperonyl butoxide interacted synergistically.

Freshly harvested smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb. # IAQTA] seed germinated best after 25 to 60 s of scarification in an electric scarifier equipped with 100 to 120 grit emery cloth. Optimum temperature for germination was 25C. At 10 and 45C no germination occurred for up to 7 days. Eight and 12 days after planting in silt loam soil there was 85 and 98% emergence of smallflower morningglory from depths of 0.5 to 1 cm, whereas no emergence was observed from depths of 6 cm or greater 12 days after seeding.

Experiments were conducted to determine the influence of water depth, fall flooding, and burial depth on the development of common waterplantain (Alisma triviale Pursh. # ALSPA) in wild rice (Zizania palustris L.). The optimum water depths for common waterplantain from corms were 20 cm when grown outside in submerged pots at St. Paul and 2 and 15 cm when grown in a sloping field at Grand Rapids. Growth of common waterplantain from seeds was maximum at the lowest water depths (2 to 7 cm) at both locations. Wild rice dry weight and seed yield in the same experiments were maximum at the 20- and 30-cm water depths at St. Paul and the 15- and 28-cm depths at Grand Rapids. The increased wild rice seed yield and dry weight at these depths was related to increased tiller production. Wild rice yield was similar at all water depths at Grand Rapids when grown with common waterplantain from corms at a density of 11 plants/m2. Water depths that decreased the effect of common waterplantain interference with wild rice, reduced wild rice yield. Establishment of common waterplantain from corms was maximum at the 5- and 15-cm depths and was severely reduced at the 0- and 30-cm soil depths in soils not flooded in the fall but flooded in the spring. Fall flooding killed all corms regardless of burial depth. Corm mortality under fall-flooded conditions may be due to the effects of ice-encasement.

Herbicides were applied annually in March or March plus August to bermudagrass [Cynodon dactylon (L.) Pers. Tifdwarf’] putting greens for 6 yr. Bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] delayed early spring growth of bermudagrass less than the other herbicides, but did not adversely affect turf quality during the growing season. Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] treatments applied twice each year severely retarded turf growth and reduced the quality and stand of bermudagrass. Napropamide [2-(α-naphthoxy)-N, N-diethylpropionamide] and prosulfalin {N-[[4-dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine} treatments reduced root growth of bermudagrass.

Effects of temperature and interference were examined in a replacement series experiment with cotton (Gossypium hirsutum L. 'Stoneville 213′), spurred anoda Anoda cristata (L.) Schlecht. # ANVCR), and velvetleaf (Abutilon theophrasti Medic. # ABUTH). Plants were grown in controlled-environment greenhouses at day/night temperatures of 32/23 or 26/17 C, and harvested 14 or 39 days after planting. Height, dry weight, and leaf area at both harvests, and dry matter production and leaf area duration for the harvest interval were significantly greater in all species at 32/23 C than at 26/17 C. Interference reduced the dry weight per plant and leaf area at day 39, and dry matter production for the harvest interval. Cotton was somewhat superior to both weeds as a competitor at 32/23 C, while spurred anoda was somewhat superior to cotton and velvetleaf at 26/17 C.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 3.4 and 6.7 kg/ha controlled weeds present in sweet potatoes (Ipomoea batatas L. ‘Jewel’, ‘Centennial’, ‘Caromex’) at two locations in North Carolina. Yield was not reduced from slight early season injury observed with the herbicide treatments. Most sweet potato root samples contained less than the detectable limit of 0.05 ppmw of alachlor. At one location, samples of the cultivars Jewel and Centennial that received 6.7 kg/ha contained 0.06 and 0.05 ppmw, respectively. Averaged over locations, residue levels in soil samples from plots treated at 6.7 kg/ha decreased from 1.55 ppmw initially to less than 0.05 ppmw by 16 weeks after application.