Seed production was studied near Lincoln, Nebraska for musk or nodding thistle (common names used for large-flowered species of Carduus – C. macrocephalus Desf., C. nutans L., C. thoermeri Weinm.). Four levels of seed maturity were studied from separate groups of plants with the heads harvested at the full-bloom stage, 2 days after full bloom, 4 days after full bloom, and at full maturity. The first heads to bloom (terminal) averaged about 1000 seeds/head and the last to bloom (lateral branches near the base of the plant), ca. 125. Plants produced only 26 good quality seeds/plant when the heads were all clipped at the full-bloom stage, but the plants with heads allowed to go to maturity produced 3580 of the good quality seeds/plant. Plants with heads clipped at 2 and 4 days after full bloom produced 72 and 774 good quality seeds, respectively.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 6.7 kg/ha, twice the recommended rate, stunted early-season growth of ‘Jubilee,’ ‘Commander,’ and 'Stylepak’ sweetcorn (Zea mays L.) 9 to 15%, reduced plant populations of Commander and Stylepak 12 to 15%, reduced the kernel yield of Jubilee and Stylepak 14 to 16%, and delayed ripening of Jubilee and Stylepak by 2 or 3 days. Alachlor at 3.4 kg/ha slowed early-season growth of Jubilee and Stylepak, but reduced yield and delayed ripening of only Jubilee. EPTC (S-ethyl dipropylthiocarbamate) + R-25788 (N,N-diallyl-2,2-dichloracetamide) and vernolate (S-propyl dipropylthiocarbamate) + R-25788 at 4.5 + 0.4 or 9.0 + 0.8 kg/ha did not reduce the growth, yield, or quality of the three sweetcorn cultivars. Planting date did not influence the response of sweetcorn to the herbicides. In these experiments, none of these herbicides injured sweetcorn severely, as has sometimes occurred in commercial fields.

Greenhouse benches and pots were specially designed to facilitate herbicide research on plants. Four 0.8-cm risers were added to the bottom of polyethylene pots to improve drainage after subirrigation or surface watering. A rule die was made to punch out paper discs needed to cover the holes in the bottom of the pots to prevent soil loss during watering or drainage. Flat, level greenhouse tables with a 3-cm hinged side around the edges, were covered with 2-mm polyethylene sheeting to facilitate water retention when the side was in the up position during subirrigation and subsequent drainage of water when the side was down. Much time was saved and the soil was watered more uniformly by this system. Economics dictated discarding pots after herbicide experiments rather than incurring the expense of washing them and risking contamination of subsequent experiments.

Waterhyacinth [Eichhornia crassipes (Mart.) Solms] grown in screen-enclosed, outdoor aquaria were treated with factorial combinations of 0, 0.75, 1.5, or 3 kg/ha of the experimental growth retardant EL-509 [α-(4-chlorophenyl)-α-(1-methylethyl)-5-pyrimidine-methanol] and zero, one, two, or three pairs of waterhyacinth weevils (Neochetina eichhorniae Warner)/plant, with three replicates of each weevil-number by retardant level combination. When plant growth was evaluated over a time course, significant effects of weevils and retardant were observed. After 127 days, however, waterhyacinth was reduced as weevil numbers increased, but the growth retardant was ineffective without weevils. Weevils appeared to be more effective when used in combination with the retardant, and the combined effects were additive.

BAS 9052 {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} effectively controlled annual grasses in soybean [Glycine max (L.) Merr.] alone or in combination with bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] in greenhouse and field experiments. The activity of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} on annual grasses was reduced if combined with bentazon in a tank mixture. The wettable powder formulation of bentazon, as well as a day temperature of 30 C, slightly reduced the antagonistic interaction from that of the emulsifiable concentrate formulation of bentazon or a day temperature of 15 C. In greenhouse studies ‘Corsoy’ soybean plants were injured by the diclofop-bentazon combination. In field studies, however, the injury was not sufficient to reduce grain yields.

Greenhouse studies were conducted using bentgrass (Agrostis tenuis Sibth. ‘Highland′) as a bioassay species to measure herbicidal activity of 3.4 kg/ha of the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] when applied directly to the soil surface prior to bentgrass emergence. Activity of glyphosate also was examined by applying glyphosate to a moist soil surface and placing alfalfa (Medicago sativa L. ‘Vernal′) and red clover (Trifolium pratense L. ‘Kenstar′) seeds on the sprayed surface 3, 6, 9, and 24 h later. In two high-organic soils, glyphosate reduced bentgrass growth in each of four experiments, even when applied up to 5 days before bentgrass emergence. Significant glyphosate activity was measured in one of the experiments in another organic soil and in three of the experiments in a Chehalis sandy loam soil. Germination and growth of alfalfa and red clover were reduced when seeds were distributed on a sprayed soil surface up to 24 h after glyphosate application. These results show that glyphosate, at least under certain conditions, can cause significant crop injury when used prior to planting or emergence of some species.

The selectivity of five foliage-applied herbicides, 2,4-D [(2,4-dichlorophenoxy)acetic acid], dichlorprop [2-(2,4-dichlorophenoxy)propionic acid], glyphosate [N-(phosphonomethyl)glycine], fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, applied at three phenological stages of development to five Sierran shrub species, deerbrush [Ceanothus integerrimus var. californicus (Kell.) G. T. Benson.], greenleaf manzanita (Arctostaphylos patula Greene), bearmat (Chamaebatia foliolosa Benth.), snowbrush ceanothus (Ceanothus velutinus Dougl.), and whiteleaf manzanita (Arctostaphylos viscida Parry), was compared. Treatments in the summer and fall were less effective than spring applications. Periods of herbicide susceptibility generally corresponded to times when moisture stress was low and photosynthesis was high.

Three herbicides, amine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid], glyphosate [N-(phosphonomethyl)glycine], and dicamba (3,6-dichloro-o-anisic acid) were applied for field bindweed (Convolvulus arvensis L.) control in grain/summerfallow or grain/legume rotations. After the first year all herbicide retreatments were made using 2,4-D amine. The 2,4-D treatment at 3.4 kg/ha gave 65% field bindweed control. Field bindweed control averaged 17% higher when the 2,4-D was applied in August rather than July. The 3.4-kg/ha rate gave 45% better field bindweed control than the 1.1 kg/ha rate. Dicamba at 6.7 kg/ha gave 90% field bindweed control and glyphosate at 4.5 kg/ha gave 86% control. Dicamba persisted in the soil for 1 to 3 yr after application and caused winter wheat (Triticum aestivum L.) and lentil (Lens culinaris Medik.) yield loss. Crop yields were highest more than 90% of the time from plots treated with 2,4-D or glyphosate.

A field study was conducted to develop systems using cultural and chemical methods for control of bermudagrass (Cynodon dactylon L.) in cotton (Gossypium hirsutum L.). Several control options were promising. On areas prepared either with a moldboard plow or a disk, the sodium and magnesium salts of dalapon (2,2-dichloropropionic acid) at 4.7 kg/ha directed to 25-cm-high cotton and repeated at the 40-cm height or the ethyl ester of difenopenten {4-[4-[4-(trifluoromethyl)phenoxy] phenoxy]-2-pentenoic acid} directed to 15-cm-high cotton and repeated at the 30-cm height, with either standard or close cultivation as needed, provided good bermudagrass control. On areas prepared with a moldboard plow, the isopropyl amine salt of glyphosate [N-(phosphonomethyl)glycine] at 4.4 kg/ha over-the-top as a fall application with cultivation as needed was promising.

Soybean [Glycine max (L.) Merr.] cultivars ‘UFV1’ and ‘UFV2’ grown at Viçosa and Florestal, Brazil, and ‘Bonus' and ‘Wells' at Urbana, Illinois, were sprayed at growth stages R5.5 to R6 (full-pod) or R7 (50% defoliation) with the desiccant/herbicides glyphosate [N-(phosphonomethyl)glycine], paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), or sodium chlorate:sodium borate (50:50, w/v). Desiccation of plants by paraquat significantly reduced seed weight and germination at all locations and increased the incidence of Alternaria and Phomopsis spp. at Urbana. Analysis of the combined data from the Brazilian locations showed a significant decrease in seed germination for all treatments except paraquat sprayed on the UFV2 at R7 and sodium chlorate: sodium borate sprayed on UFV1 at R7. Herbicide application at R7 did not result in consistent increases in seedborne Fusarium or Phomopsis spp. at any Brazilian location. Rainfall and temperature at seed maturation were more important variables in pod-to-seed infection by these fungi than increased rates of tissue senescence caused by the desiccants.

Responses of Rhizoctonia solani Kuhn to napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide], were evaluated by measuring whole-cell respiration, mitochondrial respiration, ATP synthesis, and membrane leakage. Whole-cell respiration, measured with an O2 electrode, was stimulated in the presence of napropamide at 1.1, 2.2, and 4.4 × 10−5 M. Mitochondrial respiration was stimulated at 1.1 × 10−11 M, but higher concentrations were inhibitory. The addition of 10−5 M napropamide to isolated mitochondria of R. solani resulted in reduced ATP synthesis, measured by the firefly luciferase assay, and in increased membrane permeability as measured by increases in electrical conductivity of filtrates from R. solani grown in culture medium containing napropamide. These results indicate that, under laboratory conditions, napropamide reduced ATP synthesis, caused membrane leakage, and stimulated respiration in R. solani.

The allelopathic potential of wheat [Triticum aestivum (L.) ‘Doublecrop′] straw residue was evaluated on weed-seed germination and seedling growth. The inhibition of weed-seed germination and seedling growth was extract-, species-, and temperature-dependent. The extracts prepared by agitating and soaking caused greater inhibition than those obtained by leaching. The descending order of species susceptibility was ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.], velvetleaf (Abutilon theophrasti Medic.), pitted morningglory (Ipomoea lacunosa L.), hemp sesbania [Sesbania exaltata (Raf.) Cory], sicklepod (Cassia obtusifolia L.), and Japanese barnyard millet [Echinochloa crus-galli var. frumetaceae (Roxb.) Link]. Incubation at 35 C caused the greatest inhibition of germination and growth.

In greenhouse studies, soil organic matter reduced the herbicidal activity of ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine). Fifty percent inhibition (I5.0) values for barnyardgrass [Echinochloa crus-galli (L.) Beauv.] stand, injury, and shoot fresh weight increased as the soil organic-matter level increased. No difference in ethalfluralin tolerance was found among 16 cucumber (Cucumis sativus L.) cultivars. When grouped according to market type, fresh market cultivars tended to be injured more than pickling cultivars by excess ethalfluralin. Both shoots and roots of cucumber absorbed the herbicide, but exposure of roots to ethalfluralin was more toxic than exposure of shoots. Field studies indicated that with certain edaphic and environmental conditions, cucumbers can be injured by preemergence applications of ethalfluralin. Injury was greatest in a low organic-matter soil following a heavy rain. Ethalfluralin at 1.3 kg/ha gave adequate weed control in 1 and 3% organic-matter soils, but not in a 9% organic-matter soil.

Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] is a preemergence herbicide used for the control of most annual grasses and many annual broadleaf weeds. Its influence on the uptake and translocation of N, P, K, Ca, Mg, Cu, Fe, and Zn by four plant species was observed. Napropamide influenced, in some cases dramatically, the uptake and movement of the essential elements, but its influence was not consistent from one type of plant to another.

The effects of common cocklebur (Xanthium pensylvanicum Wallr.) on soybean [Glycine max (L.) Merr. ‘Wells′] development and seed yield were investigated at Urbana, Illinois, from 1974 through 1977. Increased densities of common cocklebur reduced soybean seed yield, total dry weight, and number of pods per plant. Under full-season competition, one common cocklebur/3 m of row reduced soybean seed yield by 3 to 12%. Soybean seed yield, total dry weight, and number of pods per plant increased as the length of time from soybean emergence to common cocklebur emergence increased. Common cocklebur emerging 4 weeks after soybean emergence reduced soybean seed yield by 7%. As duration of competition with common cocklebur increased, soybean seed yield, total dry weight, and number of pods per plant decreased. The reduction in soybean seed yield was less than 10% when common cocklebur was removed 6 weeks after soybean emergence. Effects of common cocklebur competition with soybeans in Illinois were similar to those observed in the southern United States.

Intraspecific interference of populations of sunflower (Helianthus annuus L.) and velvetleaf (Abutilon theophrasti Medic), as well as interspecific populations of these two broadleaf weeds, in sugarbeets (Beta vulgaris L. ‘Mono Hy D2′) was determined in 2-yr field experiments. Sunflower was more competitive in sugarbeets than was velvetleaf. At densities of 6, 12, 18, and 24 sunflower plants/30 m of row, root yields were reduced 40, 52, 67, and 73%, respectively. At the same densities of velvetleaf, root yields were reduced only 14, 17, 25, and 30%, respectively. Interspecific interference of these two broadleaf weeds at the same densities reduced root yields 19, 36, 43, and 56%, respectively. The minimum number of weeds required/30 m of row to reduce sugarbeet root yields was predicted to be 1 for sunflower, 9 to 12 for velvetleaf, and 2 to 7 for an equal population of sunflower and velvetleaf.

In field tests, common cocklebur (Xanthium pensylvanicum Wallr.) was controlled at the one- and two-leaf stages with 0.3 kg/ha acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}. Four-leaf common cocklebur required 1.1 kg/ha for comparable control. Acifluorfen at 0.6 and 0.8 kg/ha controlled 96 and 90% of entireleaf morningglory [Ipomoea hederacea (L.) Jacq. var. integriuscula] atone- and two-leaf stages, respectively, but control was reduced as plants aged. Dark applications (2100 h) were more effective than those at sun-up (0600 h) or midday (1200 h) in control of hemp sesbania [Sesbania exaltata (Raf.) Cory], pitted morningglory (Ipomoea lacunosa L.), and smooth pigweed (Amaranthus hybridus L.). Hour of application had no significant influence on control of common cocklebur or prickly sida (Sida spinosa L.). An increase in surfactant (80% alkyl aryl polyoxyethylene glycols) concentration enhanced acifluorfen control of entireleaf morningglory and Texas gourd [Cucurbita texana (A.) Gray] at the 0.3-kg/ha rate applied 2 weeks after emergence. Soybean [Glycine max (L.) Merr.] injury was increased with the 1.1-kg/ha rate when surfactant concentration was increased from 0.5 to 0.75%. Increasing the spray volume increased pitted morningglory control but decreased hemp sesbania control. In the growth chamber, better control of pitted morningglory and common cocklebur was obtained at high (35 C day, 26 C night) than at low temperatures (27 C day, 18 C night) when plants were treated 1 week after emergence.

The relationship between pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone] in soil solution and dosage was examined in two soils under slurry equilibrium conditions and at field water capacity. In a sandy soil, the partition coefficient, calculated from a regression analysis of soil water content on dosage applied, was similar under slurry conditions and at field water capacity, but in a loamy sand, high in organic matter, the partition coefficient was somewhat higher at field water capacity than the estimated 4.71 measured in a great excess of water. In the sandy soil, neither the partition coefficients under slurry conditions nor at field water capacity were significantly different from Freundlich's k. Under slurry conditions in the loamy sand this difference was barely significant, whereas at field water capacity the estimated partition coefficient was significantly higher than Freundlich's k. Soil water sampling at field water capacity a fortnight after the start of the experiment showed a considerable increase in partition coefficient compared with the first sampling after 2 days, and the relationship in a sandy soil showed a slight non-linear trend, but that of the loamy sand still appeared to be linear. A desorption experiment indicated that the recovery of soil-adsorbed pyrazon was almost complete.

A field study was conducted with 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) at 1× and 2× rates in soybeans [Glycine max (L.) Merr.] for 2 consecutive yr to evaluate their persistence in soil and to determine their residual effect on rice (Oryza sativa L.). In another field study that was conducted to evaluate the effect of winter flooding on the persistence of 4× rates of the same herbicides, gas chromatographic analysis and bioassay procedures both revealed increased dissipation of these herbicides because of winter flooding. Flooding rice for 2 or 4 months during winter reduced the adverse effect from herbicidal residues. Laboratory studies evaluated the persistence and volatility of these herbicides at 4 and 25 C in two soils at three moisture contents (air-dried, field capacity, and flooded). The persistence of the three herbicides was similar in the field and in the laboratory and usually followed the order fluchloralin > profluralin = trifluralin. Volatility was most rapid with moisture at field capacity, but overall dissipation was most rapid in flooded soil. Significant dissipation and volatility losses of all three herbicides occurred at 4 C in flooded soil and in soil at field capacity. These studies indicated that winter flooding is effective in reducing the concentration of dinitroaniline herbicides in soil.

In tobacco (Nicotiana tabacum L. 'Speight G-28′) exposed to benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) vapors from treated soil, the leaves formed after treatment were shortened, narrowed, distorted in shape, and had an abnormal vein pattern. The leaves that had developed before treatment did not have these symptoms. More leaves developed on treated than on untreated plants. The height of treated plants was reduced and many axillary buds became active prematurely. The injured leaves, in general, had fewer epidermal cells, stomata, and trichomes per unit surface area; a smaller volume of intercellular space; and were thicker than those of untreated plants. Many of the meristematic cells in the leaf primordia and shoot apex of treated plants contained large and distorted nuclei and were oriented in improper planes. The plate meristems established by activity of the marginal meristems gave rise to a mass of undifferentiating parenchyma cells in the mesophyll of the young leaves. There was little formation of the palisade or spongy mesophyll layers, but enlargement of the undifferentiating cells caused a radial expansion of the lamina.