Cell cultures of soybean (Glycine max (L.) Merrill ‘Acme’) were exposed to media containing 4-amino-3,5,6-trichloropicolinic acid (picloram) for 15 days. Picloram also was supplied once in droplets (water) to cotyledons of 10 to 13-day-old seedlings of cotton (Gossypium hirsutum L. ‘Champion’). The amounts of picloram necessary to reach and exceed the 50% tolerance limit (TL50) of the cell cultures (inhibition) and of the primary leaf buds (toxicity) were established, and internal picloram concentrations then were determined. Internal concentrations at the TL50 were 0.17 nM/g fresh weight and 14.7 nM/g fresh weight for cell cultures and leaf buds, respectively. These values are approximately 10−7 and 10−5 molar. In leaf buds, concentrations increased rapidly for 36 hr after treatment and declined slowly thereafter. Primary leaf buds accumulated up to several times the lethal internal concentration of picloram when the dosage to the cotyledons was increased by one order of magnitude.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] and 2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine (ametryne) were tested for growth regulatorlike effects. In the presence of 10 μg/ml of kinetin, atrazine had no effect on the growth of callus tissue of soybean (Glycine max Merr. ‘Lee’), but ametryne at 10−14M concentration stimulated callus growth and the production of roots. High concentrations of both atrazine and ametryne inhibited the growth of excised roots of tomato (Lycopersicon esculentum Miller ‘Atkinson’). Ametryne, and to a lesser extent atrazine, increased percent germination of seed of lettuce (Lactuca sativa L. ‘Grand Rapids’) and tobacco (Nicotiana tobaccum L. ‘Sansum’) exposed to only 4 min of red light. Both atrazine and ametryne stimulated adventitious root formation by excised hypocotyls of mung beans (Phaseolus aureus Roxb.) in the absence of 10 ppm of exogenous indoleacetic acid (IAA) but not in its presence. A high concentration of atrazine (10−6M) in the presence of IAA decreased root initiation in comparison with the IAA-treated controls.

Microbial degradation of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine (hydroxyatrazine) was investigated in three Oregon soils. Hydrolysis of atrazine was determined by the presence of 14C-hydroxyatrazine in methanol extracts. Respired 14CO2 from the 14C-ethyl side chain of atrazine represented less than 10% of the added 14C in the soils after 28 days. Degradation was dependent on soil type, atrazine concentration, and moisture content. The isopropyl and ring constituents of atrazine were subject to minimal attack. The hydroxyatrazine ring was attacked more readily than the atrazine ring. Hydroxyatrazine accounted for approximately 10% of the extracted 14C from 14C-atrazine-treated Parkdale-A, Parkdale-C, and Coker soils and 40% from the Woodburn soil. Hydrolysis was the dominant pathway of detoxification in the Woodburn soil, whereas detoxification of atrazine in Parkdale-A, Parkdale-C, and Coker soils was a combination of chemical hydrolysis and slow microbial degradation by N-dealkylation of the ethyl side chain constituent.

Investigations with exogenous test solutions showed that abscisic acid (ABA) inhibited germination of nondormant seeds and that gibberellins (GA) promoted the germination of yellow foxtail (Setaria lutescens (Weigel) Hubb.) The effect of the promoters was much more readily demonstrated with excised caryopses than with intact seeds. Cytokinins reversed ABA inhibition of germination; GA did not, but the two promoters in combination were more effective than the cytokinin alone. The reversal occurred only at one end of the embryonic axis, the shoot end. An endogenous inhibitor was extracted from dormant and nondormant yellow foxtail seeds and compared with ABA by chromatography, electrophoresis, and bioassays. The extracted inhibitor was very similar to ABA in six paper-chromatography solvent systems, three paper electrophoresis runs at different pH values, and three bioassays. Paper electrophoresis was an effective means of separating the two plant hormones, ABA and gibberellic acid (GA3).

In laboratory experiments, plant extracts of small everlasting (Antennaria microphylla Rydb.), field pussytoes (A. neglecta Greene), and leafy spurge (Euphorbia esula L.) were toxic to germinating seeds. Extracts of small everlasting inhibited vegetative development of leafy spurge, and soil taken from the immediate vicinity of roots inhibited germination and radicle elongation of germinating seeds of some species. Small everlasting competes vigorously with leafy spurge, and this competition cannot be attributed to morphology and growth habit. It suppressed vegetative growth of leafy spurge from rhizome sections in which the two species were competing in pots. In field experiments, this shallow-rooted, lowgrowing plant exhibited a marked inhibition on the growth of the vigorous, deep-rooted perennial, leafy spurge, as did the soil in which small everlasting had been growing. Antibiotic competition appears to be significant with the Antennaria spp., and the paucity of forbs in patches of leafy spurge, even when bare ground is visible between shoots, suggests that this species also exerts antibiotic effects on other plants. Allelopathy is probably a significant influence in interspacial relationships of species in most plant communities. A fuller knowledge of these relationships and their causes could lead to the utilization of this phenomenon in weed control.

Studies were conducted to determine the stage of growth at which curly dock (Rumex crispus L.) and broadleaf dock (Rumex obtusifolius L.) can propagate vegetatively from a rootstock. Curly dock plants were grown from seed in the greenhouse and phytotron under long-day conditions. Curly dock seedlings were capable of regrowth from a rootstock 47 days from seeding in the greenhouse. Some of the phytotrongrown plants attained this capacity 31 to 38 days after seeding; while all demonstrated this ability at 41 days. Broadleaf dock produced flower stalks within 38 days in phytotron studies but was not capable of regeneration during this same period of time. Broadleaf dock was capable of regrowth from a rootstock approximately 51 days after seeding in the phytotron.

A system for controlling yellow nutsedge (Cyperus esculentus L.) in soybeans [Glycine max (L.) Merr.] which involved preplanting tillage, late planting, herbicides, and cultivation was evaluated in 1969 and 1970. In Illinois on a Drummer silty clay loam, S-ethyl dipropylthiocarbamate (EPTC) and S-ethyl diisobutylthiocarbamate (butylate), incorporated in the soil before planting, gave good and fair control of yellow nutsedge, respectively, but both injured soybeans initially. S-propyl dipropylthiocarbamate (vernolate), also incorporated before planting, controlled yellow nutsedge as well as EPTC did, and resulted in less injury to soybeans. Soybean yields were not reduced by any of the thiocarbamate treatments. Incorporation of 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor) or 2-chloro-N-isopropylacetanilide (propachlor), just before planting, controlled at least 90% of the yellow nutsedge in both years, whereas preemergence applications were only moderately successful and dependent on rainfall. In field microplots, alachlor and vernolate provided only fair control of yellow nutsedge when applied to the soil surface, but they both controlled 95% of the yellow nutsedge when incorporated 7.6 cm. In greenhouse studies on selective control of yellow nutsedge in soybeans, alachlor exhibited a wider margin of safety to soybeans than did vernolate.

Tobacco (Nicotiana tabacum L. ‘Samsun N. N.’) leaves were treated with (2,4-dichlorophenoxy)acetic acid (2,4-D) at a concentration of 500 mg/L by the syringe infiltration technique and then sampled at regular intervals. Electron microscopic examination of the treated tissue revealed that the response of the mesophyll cells to 2,4-D was related to the age of the leaf at the time of treatment. Expanding leaves from the upper portion of the plant exhibited a high degree of tolerance to 2,4-D. Mature, fully-expanded leaves from the lower part of the plant were highly sensitive to the herbicide, with the mesophyll cells undergoing rapid structural breakdown. This breakdown involved a rupturing and disintegration of the tonoplast, plasmalemma, and membranes of chloroplasts and mitochondria.

Purple nutsedge (Cyperus rotundus L.) plants were analyzed for free reducing sugars, free glucose, free plus acid hydrolyzable fructose, phosphorus, and iron. The only sugars detected were sucrose, glucose, and fructose. Sucrose was the most concentrated sugar in the shoots with the greatest concentration in the younger leaves. Sucrose was also the most concentrated sugar in mature rhizomes. Glucose and fructose were the most concentrated sugars in the actively growing rhizomes and tubers. Phosphorus was concentrated in the actively growing leaves and rhizomes, while iron was most concentrated in older tissues including rachises with seedheads, mature shoots, tubers, and rhizomes.

Canada thistle (Cirsium arvense (L) Scop.) includes many regional races that are heritable, distinct ecotypes. When cultured at Bozeman, Montana a group of these ecotypes varied in phenological, morphological, and anatomical characteristics. These ecotypes also responded differently to (2,4-dichlorophenoxy)acetic acid (2,4-D) and 3-amino-s-triazole (amitrole). Stomatal frequency and area on leaves also differed among ecotypes studied. Although stomatal frequency and stomatal area differed among the ecotypes studied, there was no correlation with herbicide response. Apparently, stomata were not a significant portal of entry of 2,4-D into the upper surface of Canada thistle leaves.

The following herbicides were evaluated for relative phytotoxicity to cotton (Gossypium hirsutum L. ‘Acala SJ-1′), purple nutsedge (Cyperus rotundus L.), and yellow nutsedge (Cyperus esculentus L.) under greenhouse conditions: 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl)acetanilide (CP-53619); 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (VCS-438); 4-chloro-5-(dimethylamino)-2-α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone (San-6706); 2-(α naphthoxy)-N,N-diethyl-propionamide (R-7465); and S-isopropyl 5-ethyl-2-methyl-piperidine-1-carbiothioate (R-12001). Herbicides were incorporated 6.35 cm deep, at rates of 1.12, 2.24, and 4.48 kg/ha, into a fine sandy loam prior to planting. All treatments except the low rate of alachlor and VCS-438 controlled yellow nutsedge for 8 weeks. R-7465 and R-12001 at 1.12 kg/ha and San-6706 at 2.24 kg/ha controlled purple nutsedge for 8 weeks. Alachlor and CP-53619 were somewhat less effective against purple nutsedge than yellow nutsedge, but their intermediate rates suppressed purple nutsedge for 4 weeks. Even the high rate of VCS-438 was ineffective against purple nutsedge. Cotton, in terms of fresh shoot weight, exhibited considerable tolerance to 1.12 and 2.24 kg/ha of VCS-438 and CP-53619 and 1.12 kg/ha of R-7465. Applications of 2.24 kg/ha of CP-53619 and 1.12 kg/ha of R-7465, however, suppressed the development of lateral roots of cotton. Other rates of these herbicides and all rates of alachlor, R-12001, and San-6706 moderately to severely injured cotton in most of the experiments.

A 2-year field study was conducted to determine the effects of fertilization on elodea (Elodea canadensis Michx.), eurasian watermilfoil (Myriophyllum spicatum L.), and heartleaf pondweed (Potamogeton pulcher Tuckerm.). Plants, water, and sediment were sampled and inorganic mineral contents determined. Water concentrations of NO3, NH4, P, and K increased sharply following fertilization and generally reached maximum values within 7 days after treatment. Concentrations of these nutrients decreased rapidly after reaching maximum values. In the first year, plant growth was not increased due to fertilization while in the second year only heartleaf pondweed produced significantly greater yields. Elodea and eurasian watermilfoil grew better in the control environment, presumably due to less competition from algae, whose growth was increased by the addition of fertilizer. At the end of the study the top 1.3 cm of bottom sediment had increased in cation exchange capacity (C. E. C.), organic matter, total N, and available P for all treatments while the underlying sediment remained relatively unchanged. Available P was greater in the surface of the fertilized sediment than in the surface of the control sediment.

Seedling emergence and growth of downy brome (Bromus tectorum L.), medusahead (Taeniatherum asperum (Sim.) Nevski), and tumble mustard (Sisymbrium altissimum L.) were favored by seed burial, pitting of the soil surface, and soil movement. These conditions maintained temperatures and soil and atmospheric moisture in the range required for establishment.