Both gibberellic acid and the substituted phthalimide AC-94377 [1-(3-chlorophthalimido)cyclohexanecarboximide] actively promoted germination of dormant seeds in five species out of nine. The species that responded to both compounds included wild oat (Avena fatua L.), wild mustard [Brassica kaber (DC.) L.C. Wheeler], curly dock (Rumex crispus L.), field pennycress (Thlapsi arvense L.) and tansy phacelia (Phacelia tanacetifolia L. Benth.). on a weight-per-weight basis, the ability of AC-94377 to stimulate germination was equal to, or greater than, GA3. The other two substituted phthalimides tested, AC-92803 [2-(3-chlorophthalimido)-2-methyl-2-isobutyl-acetamide] and AC-99524 [1-tetrahydrophthalimido-cyclohexane-carboximide], had either slight or no stimulatory activity.

For 3 yr, fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} at 0.1, 0.2, and 0.3 kg/ha, was applied with or without 0.6 kg/ha of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) before the preplanting irrigation for cotton (Gossypium hirsutum L.). Without trifluralin, fluridone at 0.1 kg/ha controlled less than 60% of annual grasses or redroot pigweed (Amaranthus retroflexus L.), but the 0.3-kg/ha rate controlled 90%. With trifluralin, fluridone at all rates controlled 98% of these weeds. Fluridone alone controlled 85% or more of black nightshade (Solanum nigrum L.). Fluridone did not alter cotton stand or yield. Fluridone residues 8 months after treatment reduced growth of several crops and weeds by 75% or more.

Salicylic acid, p-hydroxybenzoic acid, caffeine, hydroquinone, and umbelliferone were evaluated in the greenhouse for their effects on shoot dry-weight accumulation of several crop and weed species. With the exception of caffeine, all the chemicals reduced shoot growth in oats (Avena sativa L. ‘Goodfield’). Chemicals applied preplant incorporated, preemergence, or postemergence were effective, depending upon the rate of chemical. When applied preplant incorporated at rates as high as 56.0 kg/ha, most of the chemicals reduced growth of corn (Zea mays L. ‘B73 × Mo17′), soybean [Glycine max (L.) Merr. ‘Corsoy’], velvetleaf (Abutilon theophrasti Medic.), redroot pigweed (Amaranthus retroflexus L.), and wild proso millet (Panicum miliaceum L.). Exceptions were caffeine on corn and soybean and hydroquinone on soybean. At 11.2 kg/ha the chemicals inhibited the weed species more than the crop species. Postemergence applications of caffeine and hydroquinone inhibited growth of the weed species more than the crop species. Hydroquinone at 1.1 kg/ha inhibited redroot pigweed, but rates as high as 11.2 kg/ha did not inhibit soybean. These experiments show that growth of agronomically important crops and weeds can be inhibited differentially by allelopathic chemicals.

Winter chilling in the field removed the primary dormancy in common ragweed (Ambrosia artemisiifolia L.) seeds and allowed them to germinate in both light and darkness. A secondary dormancy was induced in the spring and seeds again failed to germinate in light or darkness. Kinetin (K) + ethephon (E) + gibberellin A4 + A7 (GA4+7) applied to the soil in December prevented secondary dormancy. The following May only 20% of the seeds at the 15-cm depth remained viable. The rest had germinated or decayed. In contrast, 89% of the untreated seeds remained viable. Application of K + E + GA4+7 on April 22 and May 2 also broke the secondary dormancy. Gibberellin A3 (GA3) was less effective than GA4+7 in preventing or breaking secondary dormancy.

The effect of duration of spurred anoda [Anoda cristata (L.) Schlecht.] competition on maturity and yield of three cotton (Gossypium hirsutum L.) cultivars was studied during 1975 through 1977. The seed cotton yields averaged over 3 yr for ‘DES 21326-04′, 'Stoneville 213′, and ‘Deltapine 16’ were 1850, 1570, and 1520 kg/ha, respectively. DES 21326-04 produced 50% of its yield 3 to 8 days earlier than Deltapine 16 or Stoneville 213 with no spurred anoda competition and 6 to 10 days earlier with spurred anoda competition. Spurred anoda competition from planting until July 10, August 10, and September 10 resulted in average yield decreases of 12, 37, and 38%, respectively. Yield reductions varied with cultivar. Deltapine 16 was more competitive than the other two cultivars. Early-season spurred anoda competition reduced the yield of the earliest-maturing cultivar DES 21326-04 more than that of Deltapine 16 or Stoneville 213.

Translocation of 14C-glyphosate [N-(phosphonomethyl) glycine] in tall morningglory [Ipomoea purpurea (L.) Roth., ‘Heavenly Blue’] was compared with movement of 14C-photosynthate. The flow of photosynthate was manipulated by creating assimilate sinks in mature leaves and cotyledons using combinations of stem girdling, leaf shading, and localized cytokinin application. Comparisons of 14C distribution patterns indicated minor differences between glyphosate and assimilate sink partitioning when 14C-glyphosate or 14CO2 were applied to a single leaf. Labeled glyphosate moved upward through stem girdles in greater proportions than 14C from photosynthate, suggesting a greater capacity for glyphosate to transfer from symplast to apoplast. When 14C-glyphosate was applied to the stem, 14C still moved symplastically to natural and artificial sinks, but apoplastic movement into all transpiring tissues above the site of application greatly increased. Results support the classification of glyphosate as an ambimobile rather than a phloem-mobile herbicide.

Losses of picloram (4-amino-3,5,6-trichloropicolinic acid) in water exposed to sunlight ranged from 50 to 80% after 1 days' exposure (14 h sunlight) and 95% or more after 4 days exposure (56 h of sunlight) at four locations in Southern Arizona. Samples exposed at the highest elevation (2800 m) consistently lost picloram more quickly than samples at the lower elevations. Dry, recrystallized picloram losses were 11, 47, and 67% after 1, 2, and 4 days of sunlight exposure, respectively. At the same times, picloram losses in water were 65, 89, and 99%, respectively. These results indicate that photodecomposition is an important factor for the use and residue longevity of picloram on high-altitude rangelands of the western United States.

Growth dynamics, water relations, and photosynthesis of soybean [Glycine max (L.) Merr. ‘Ransom’], common cocklebur (Xanthium pensylvanicum Wallr.), jimsonweed (Datura stramonium L.), prickly sida (Sida spinosa L.), sicklepod (Cassia obtusifolia L.), smooth pigweed (Amaranthus hybridus L.), spurred anoda [Anoda cristata (L.) Schlect.], and velvetleaf (Abutilon theophrasti Medic.) were compared in a controlled-environment greenhouse programmed for 32C day and 23C night temperatures. Net photosynthetic rates, net assimilation rates, and water-use efficiency on a whole-plant or single-leaf basis were greatest in the C4-plant, smooth pigweed. Total dry-matter production at 29 days after planting was greatest in common cocklebur and least in jimsonweed. Interspecific differences in dry-matter production were highly positively correlated with leaf area duration and negatively correlated with net assimilation rate. Threshold leaf water-potential levels causing stomatal closure varied among species. The stomata of jimsonweed were the most sensitive to water stress and those of prickly sida were the least sensitive.

Tall ironweed (Vernonia altissima Nutt.) is a perennial with underground, axillary vegetative buds from which new shoots are produced. In a 2-yr study, tall ironweed plants averaged 6115 seeds/plant. Germination of buried seeds increased with increased time of burial. Foliar herbicide applications were evaluated for control of tall ironweed plants in the pre- to early-bud stages of growth. The triethylamine salt or ethylene glycol butyl ether ester of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was the most effective, providing 93 to 90% control of top growth and regrowth of tall ironweed. The butoxyethanol and propylene glycol butyl ether esters of 2,4-D [(2,4-dichlorophenoxy) acetic acid] alone and in combination with the amine salt of triclopyr also provided excellent control.

Herbicide effects on chromate leakage from liposomes prepared from crude soybean [Glycine max (L.) Merr.] phosphatidylcholine were determined over a concentration range of 2.5 × 10-5 to 5.0 × 10-3 M. Dye levels in the dialysate were measured spectrophotometrically (370 nm) after 1 h. Barban (4-chloro-2-butynyl-m-chlorocarbanilate) at 2.5 to 5.0 × 10-4 M and PCP (pentachlorophenol) at 0.5 to 1.0 × 10-3 M induced significant leakage. MCPB {4-[(4-chloro-o-tolyl)oxy] butyric acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and ioxynil (4-hydroxy-3,5-diiodobenzonitrile), all at 2.5 × 10-3 M, also caused dye leakage, but metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] induced dye leakage only at 3.0 to 5.0 × 10-3M. Nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] were least effective over the concentration range tested.

Sodium alginate was used to prepare pelletized formulations for each of five fungi. Aqueous mixtures of 1.0% (w/v) sodium alginate and homogenized mycelia of Alternaria cassiae Jurair & Khan, Alternaria macrospora Zimm., Fusarium lateritium Nees ex Fr., Colletotrichum malvarum (A. Braun & Casp.) Southworth, or a Phyllosticta sp. were pelletized by dropwise additions of each mycelial-alginate mixture into 0.25 M CaCl2. Abundant conidia were produced on the pellets 24 to 48 h after the pellets were spread into trays and exposed 10 min/12 h to 275-W sunlamps. These conidia germinated readily (90 to 100%) and readily infected the respective host plants. Each liter of mycelium plus growth medium from submerged liquid cultures produced 4 L of the mycelial-alginate mixture. Each liter of the mycelial-alginate mixture produced approximately 18 g of air-dried formulation. When 10% (w/v) clay was incorporated into the pellets, each liter of the mycelial-alginate mixture produced approximately 118 g of air-dried formulation. The pelletized fungi sporulated readily following storage at 4 or 25 C for 6 to 8 months. This method of pelletization is potentially useful for the formulation of inoculum of fungi used as mycoherbicides, for the mass production of pycnidium-forming fungi, and for the production of inoculum for host-plant resistance studies.

The bleaching effects of norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone] and of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] were compared using the intact microalga Scenedesmus acutus and the fungus Phycomyces blakesleeanus. Under the influence of oxyfluorfen, but not of norflurazon, pigments and membranes were degraded. This activity is typical for oxyfluorfen. Norflurazon prevented carotene synthesis, but did not cause degradation of carotenoids, chlorophylls, or 35S-sulfolipid, a marker of photosynthetic membranes. Furthermore, light-induced ethane evolution by Scenedesmus is substantial with oxyfluorfen, but not with norflurazon present. Oxyfluorfen apparently causes radical-initiated peroxidation of polyunsaturated fatty acids.

Using nutrient culture techniques, it was determined that a 14-day exposure to metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] concentrations in the range of 10-6 M reduced lengths and weights of seedling sweet corn (Zea mays saccharata L. ‘NK-199′) shoots and roots by 30 to 50%. With the exception of root weight, intensity of inhibition was proportional to day length. Reductions in accumulation of Ca, Mg, K, and P accompanied decreases in sweet corn growth. A 4-day exposure of sweet corn to 2.8 and 5.6 × 10-6 M metolachlor had no significant effect on growth and nutrient accumulation when treatments were followed by a 9-day incubation in metolachlor-free nutrient solution.

Residue levels of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} in soil were determined indirectly by measuring the chlorophyll content of wheat (Triticum aestivum L.) grown on a Norfolk sandy loam (Typic paleudult; fine loam, siliceous, thermic) 14, 22, 39, and 66 days after a preemergence application of the herbicide. The half-life for 0.22 and 0.45 kg/ha of fluridone was estimated to be 18 days. Phytotoxicity increased with increasing pH in newly-treated soils and in soil sampled 14 days after treatment. Higher chlorophyll levels in wheat grown in soil sampled 39 days after fluridone application indicated a decrease in biologically-active herbicide. Soil removed from the field following later cultivation produced small reductions in chlorophyll at pH 4.0 and 5.2, but at pH 7.0 significant fluridone activity was still present in the soil after 66 days. Cultivation may have increased the surface concentration of the herbicide.

The dimethylamine salt of 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] combined with toxaphene (chlorinated camphene) or acifluorfen [5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoic acid] and toxaphene combined with acifluorfen at several rates each were applied in the greenhouse and field to sicklepod (Cassia obtusifolia L.) to determine interactions. Toxaphene plus 2,4-DB treatments produced synergistic or additive responses in the greenhouse and in the field. Antagonistic or additive responses were observed with acifluorfen plus 2,4-DB treatments in the greenhouse, but not in the field. Acifluorfen plus toxaphene produced only additive responses in the greenhouse with synergistic interactions observed under field conditions.

Controlled burning during winter reduced densities of common goldenweed [Isocoma coronopifolia (Gray) Greene] by 33 to 44% and suppressed canopy cover and height of surviving common goldenweeds for 2 yr. Applied to an unburned infestation, 2,4-D [(2,4-dichlorophenoxy) acetic acid] or dicamba (3,6-dichloro-o-anisic acid) granules only partially controlled common goldenweed at rates of 2 kg/ha or less. Tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or picloram (4-amino-3,5,6-trichloropicolinic acid) pellets provided excellent control of common goldenweed if applied at 2 kg/ha during March and at 1 kg/ha if applied after burning in February. The burning pretreatment appeared to synergistically enhance effectiveness of herbicides applied at relatively low rates. Increases in standing crop of buffelgrass (Cenchrus ciliaris L.) following burning were usually small and temporary, but effective herbicide treatments and burn-herbicide combinations increased buffelgrass standing crop by as much as three-fold.

The kinetics of chlorophyll (Chl) fluorescence was used as a tool for detecting herbicide inhibition in studies using intact soybean [Glycine max (L.) Merr.] leaves. The terminal level of fluorescence (FT), obtained 150 s after the onset of illumination of the abaxial leaf surface, was found to be independent of the dark preadaptation interval and to vary little between leaflets and leaves within and among untreated plants. Increases in FT were detected in plants following the foliar application of herbicides which inhibit photosynthetic electron transport. Fluorescence measurements indicated significant electron transport inhibition in leaves following treatment with 40-mM solutions of either atrazine [2-chloro-4-(ethylamino)-6-(isopropyiamino)-s-triazine] or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] after 0.5 and 1 h, respectively. Results of this study indicate that Chl fluorescence can be used to measure injury qualitatively by photosynthetic electron transport-inhibiting herbicides in intact plants long before visual symptoms of injury occur. Possible uses of this sensitive, rapid, and non-destructive technique for studying herbicide penetration as affected by adjuvants and environmental factors are discussed.

Adsorption of five phenylurea herbicides, metobromuron [3-(p-bromophenyl)-1-methoxy-1-methylurea], monolinuron [3-(p-chlorophenyl)-1-methoxyl-1-methylurea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea], and CGA-15646 [3-(3-chloro-4-methylphenyl)-1,1-dimethylurea] by eight selected soils of Czechoslovakia were studied. Constants from Freundlich and Langmuir equations were calculated and correlated with the major soil properties. Freundlich K values ranged from 1.84 to 128, and the Freundlich equation was better fitted to the adsorption isotherms than was the Langmuir equation. Soil organic-matter content was the most important factor influencing the range of adsorption.

CGA-43089 [α-(cyanomethoximino)-benzacetonitrile] seed treatment was evaluated at three Nebraska locations during 1979 and 1980 for grain sorghum [Sorghum bicolor (L.) Moench] protection from injury by metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], four other chloroacetanilide herbicides, and three metolachlor + s-triazine combinations. Acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide] caused the most frequent and severest injury to unprotected and protected sorghum. Soilincorporated metolachlor produced more consistent injury than preemergence application to unprotected sorghum, but placement did not affect CGA-43089 protection. Sorghum-stand reduction was the type of injury most frequently encountered, but crop yield was least affected. CGA-43089 always protected the grain sorghum from yield reduction with these herbicides.

Seedling emergence of broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. & Rusby], threadleaf snakeweed [G. microcephala (DC.) Gray], common goldenweed [Isocoma coronopifolia (Gray) Greene], and false broomweed (Ericameria austrotexana M.C. Johnston) was studied in the glasshouse. Germination of these species is known to be light-stimulated. Seed of all four subshrubs germinated readily if placed on the surface or partially pressed into the soil. Emergence was reduced by covering seed with soil to a depth of less than 1 mm. Few seedlings emerged from a depth of 1 cm, and none emerged from a depth of 2 cm. Rate of emergence also decreased with increasing depth of placement. Soil texture had little effect on emergence. Rapid germination on the soil surface is consistent with other aspects of the regenerative strategy of common goldenweed and false broomweed, which do not depend upon a buried seed bank for regeneration. Seed burial probably provides a form of enforced dormancy in the small, long-lived seeds of the two snakeweed species.