Absorption and metabolism of 14C-3-amino-2,5-dichlorobenzoic acid (amiben) by six plant species were investigated for correlation with species sensitivity. Plant sensitivity was determined from amiben concentrations required to give 50% reduction of radicle extension of germinating seedlings and shoot dry weight of 10-day-old plants (I50). The I50 values showed that soybean (Glycine max (L.) Merr., squash (Cucurbita pepo L.), and ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) were tolerant, cucumber (Cucumis sativus L.) was intermediate and giant foxtail (Setaria faberii Herrm.) and velvetleaf (Abutilon theophrasti Medic.) were susceptible. Neither the amount of amiben absorbed, the transport to shoots, the concentration of radioactivity soluble in methanol, nor the distribution of radioactivity among amiben, N-(3-carboxy-2,5-dichlorophenyl)-glucosylamine (hereinafter referred to as N-glucosyl amiben), and an unidentified amiben conjugate (amiben-X) was associated with species sensitivity in 11-day-old plants. In seedling tissues, neither the concentration of methanol-soluble nor methanol-insoluble radioactivity correlated with sensitivity. Highly significant correlations between the log percentage composition of amiben, amiben-X, and N-glucosyl amiben in the methanol-soluble fraction of seedlings and log I50 for radical elongation were obtained; the correlations were negative for amiben and amiben-X but positive for N-glucosyl amiben.

I AM most happy to signal the opening of the eighth meeting of the Weed Science Society of America, the first under our new name. Let me welcome you to New Orleans and to several days of stimulating meetings and discussions with your colleagues from Canada, Latin America, and the United States.

Herbicides applied April 30, May 10, or October 14 gave best control of musk thistle (Carduus nutans L.). The most effective herbicide at all dates and rates was 4-amino-3,5,6-trichloropicolinic acid (picloram). Two lb/A of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) also was effective at all spring dates. Two lb/A of 2,4-dichlorophenoxyacetic acid (2,4-D) resulted in excellent control of musk thistle when applied May 10 or October 14.

More musk thistle seedlings became established in nongrazed, cool season grass pastures than in nongrazed, mixed warm season grass pastures. Greater germination was attributed to the reserve moisture and accumulation of litter which served as an excellent germination medium. However, only one musk thistle plant remained in the nongrazed pastures 1 year after seeding. The remainder of the seedlings and young rosettes found in the protected areas in 1965 had succumbed to the heavy competition by 1966.

Differential germination of corn chamomile (Anthemis arvensis L.) achenes was associated with achene size. Germination increased with reduction in achene size. Lower germination of large achenes was caused by a physical restriction of embryo expansion rather than by chemical inhibition or the preventive entrance of water or oxygen through the pericarp. This physical restriction was caused by lignified portions of the pericarp surrounding the seed.

In field trials, 2 gpa of oil enhanced the herbicidal activity of 3-amino-1,2,4-triazole (amitrole) and a mixture of amitrole + ammonium thiocyanate (hereinafter referred to as amitrole-T) on quackgrass (Agropyron repens (L.) Beauv.). None of the oils consistently increased the toxicity of other foliarly-applied herbicides. A paraffinic mineral oil enhanced the activity of amitrole on quackgrass to a greater degree than NH4SCN. The inclusion of a paraffinic mineral oil enhanced both the amount and the rate of 14C-amitrole and amitrole-T translocated from the treated leaf to the shoots and roots, this being more pronounced with amitrole (twelvefold) than with amitrole-T (twofold).

A poisonous pasture weed, western whorled milkweed [Asclepias subverticillata (Gray) Vail] is capable of spreading in a few years from scattered clumps, highly variable in number of stems, to an almost solid, uniform stand. The most effective herbicide evaluated for its control was 4-amino-3,5,6-trichloropicolinic acid (picloram). Use of 2-methoxy-3,6-dichlorobenzoic acid (dicamba) gave only fair control. The herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4–5-trichlorophenoxyacetic acid (2,4,5-T), 2-(2,4,5-trichlorophenoxy)propionic acid (silvex), and 3-amino-l, 2,4-triazole (amitrole) were ineffective. The addition of amitrole did not enhance the effectiveness of dicamba or picloram for control of this species.

Simulated rainfall at 0.1, 0.5, and 2.0 in applied to six crops in the field previously treated with 1.5 lb/A of the dimethylamine salt of 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) resulted in an average herbicidal loss from the forage of 21, 60, and 93%, respectively. One inch of rain removed an average of 80% of 2,4-DB applied at 0.5, 1.5, and 2.0 lb/A to birdsfoot trefoil (Lotus corniculatus L.). Loss of the herbicide was attributed to the dissolving of herbicide in water and subsequent runoff from leaf surfaces, and an acceleration of herbicidal decomposition in the plant. Light interception decreased the rate of 2,4-DB breakdown in alfalfa (Medicago sativa L.) but was not considered to be of practical importance.

Susceptible and resistant ecotypes of Canada thistle (Cirsium arvense L.) were grafted in various combinations of stock and scion to determine if the activity of 3-amino-l,2,4-triazole (amitole) was altered by passage through the plant tissue. It appeared that the differential susceptibilities of ecotypes of Canada thistle were not caused by a change in the activity of amitrole.

Seedlings of wheat (Triticum aestivum L.), corn (Zea mays L.), and sorghum (Sorghum vulgare Pers.) were exposed to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) in solution culture. Following prolonged treatment, the tolerant species, corn and sorghum, accumulated leaf concentrations of unaltered atrazine which were comparable to those found in the sensitive species at the point of acute toxicity. In the sensitive species, wheat, there did not seem to be a critical leaf concentration of atrazine which was necessary to bring about acute toxicity. The leaf concentration in wheat could be raised by increasing the concentration of atrazine in the nutrient solution or by lowering the temperature at which the plants were grown. The loss of chlorophyll in sensitive species was closely related to and preceded acute toxicity symptoms.

Leaching of seven s-triazines in Lakeland fine sandy soil under greenhouse and field conditions was demonstrated by use of oats (Avena sativa L., var Seminole) and cucumber (Cucumis sativis L., var. Palomar) for bioassay. Depth of leaching was determined by abnormalities of these species grown in soil samples from the surface of treated soil to a depth of 22 in in the field and to 36 in in columns. Symptoms of injury by the different materials were similar and included primarily leaf chlorosis of both species and bending and breaking of cucumber stems within 7 to 10 days after planting; plants that failed to survive usually died 12 to 14 days after planting. Leaching of 2-methoxy-4-ethylamino-6-isopropylamino-s-triazine (atratone) was greatest, followed in decreasing order by 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine), 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 2-chloro-4-diethylamino-6-isopropylamino-s-triazine (ipazine), 2-ethylamino-4-isopropylamino-6-methylmercapto-s-triazine (ametryne), and 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne). Oats did not significantly reduce the soil concentration of ametryne and prometryne during a growing period of 56 days.

The metabolism of S-propyl-1-14C dipropylthiocarbamate (vernolate) was studied in soybean (Glycine max (L.) Merr., var. Lee) seedlings. The degradation of vernlate-14C to 14CO2 was dependent on the age of seedlings. Pretreatment with non-labeled vernolate resulted in a reduction of catabolic oxidation of vernolate-14C to 14CO2, a reduction of cellular incorporation, and a corresponding increase in ethanol soluble metabolites. Paper chromatographic separation of ethanol extracts revealed the presence of two major metabolites and two minor metabolites. The relative abundance of these metabolites was dependent on the age of seedlings and the time of exposure. Results of the time course study suggested the conversion of metabolite 3 to metabolite 4.

Applications of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 1/2 and 1 lb/A and ethyl N,N-dipropylthiocarbamate (EPTC) at 1 1\2 and 3 lb/A were incorporated preplant with five different tillage implements to determine the influence of incorporation on weed control effectiveness in safflower (Carthamus tinctorius L.). Weed yields were lowest in plots incorporated with the tandem disc and rotary incorporator. Oats (Avena sativa L.) were overseeded 1 year later on the entire safflower plot area. Stand loss occurred on plots receiving the high rate of both herbicides and incorporated with the disc or rotary incorporator.

Uptake and translocation of 6,7-dihydrodipyrido[1,2-a:2′, 1′-c]pyrazidiinium salt (diquat) in elodea (Elodea canadensis Michx) was investigated by autoradiography and counting of plants treated with diquat-14C. Uptake initially was very rapid followed by a slower accumulation of diquat. Part of this uptake was reversible in water and rapidly reached a saturation value while the slower uptake was nonreversible. This reversibility of uptake appears to indicate an initial passive adsorption probably followed by accumulation. Slight basipetal and acropetal movement of diquat was demonstrated with accumulation in the nodes and axillary buds. Movement was unaffected by light versus dark treatments. Diquat injured treated and adjacent untreated shoots of elodea to almost the same extent. This transfer occurred whether or not the treated and untreated shoots were in contact.

Considerable differences in rate of root elongation were observed. Species studied in order of decreasing rate root elongation were cocklebur (Xanthium pensylvanicum Wallr.), palmer amaranth (Amaranthus palmeri S. Wats.), barnyardgrass (Echinochloa crusgalli (L.) Beauv.), buffalobur (Solanum rostratum Dunal), kochia (Kochia scoparia (L.) Schrad.), crabgrass (Digitaria sanguinalis (L.) Scop.), sorghum (Sorghum vulgare L., var. RS 610), Russian thistle (Salsola kali L., var. tenuifolia Tausch), and tumblegrass (Schedonnardus paniculatus (Nutt.) Trel.). In 15 days, cocklebur and tumblegrass roots grew 33 and 11 in, respectively. With all species, the rate of root elongation always exceeded the rate of height increase. There was poor correlation between rate of root elongation and weed height, top weight, and root weight.

The herbicide l-(2-methylcyclohexyl)-3-phenylurea (siduron) suppressed the growth of soil bacteria, Azotobacter sp. and Chlorella vulgaris whereas siduron had no effect on actinomycetes, filamentous fungi, soil ciliates and other algae. Siduron had no effect upon the growth of Thiobacillus thioparus, Euglena gracilis, and Streptomyces griseus. The degradation product, 2-methylcyclohexylamine (hereinafter referred to as 2-MCHA) suppressed the growth of Aztobacter chroococcum and soil ciliates. Aniline, another degradation product of siduron, depressed the growth of Aspergillus versicolor and A. fischeri; however, A. ochraceus, A. candidus, A. clavatus, A. nidulans, A. flavus, Botrytis cinerea, and Rhizopus nigricans were not affected. None of these fungi was influenced in growth by 2-MCHA. Streptomyces griseus grew significantly less in the presence of aniline. The growth of Chlamydomonas pyrenoidosa, C. radiata, Anabaena catenula, and Rhizobium leguminosarum were not influenced by 10 ppm aniline or 10 ppm 2-MCHA.

Herbicides were applied postplant to field grown peanuts (Arachis hypogaea L.) and cotton (Gossypium hirsatum L.) in association with various cultivation devices. Rotary cultivations were compatible with single or multiple chemical treatments applied to soil. For eight preemergence herbicides commonly used on a nonincorporated basis, use of the multiple-application multiple-rotarycultivation technique, in comparison to the common method of use, increased the early-season weed control rating from 3.4 to 4.5 (scale 1.0 = no control, 5.0 = perfect), reduced weeds from 209 to 37 plants/50 sq ft, increased length of control from 36 to 50 days, and reduced the manual hoe time requirement from 24 to 10 hr/A. Incorporation of single or multiple chemical treatments decreased crop safety for some herbicides especially where cotton was the crop. The power driven rotary cultivator was superior to the standard sweep-equipped cultivator and the weeder for use in conjunction with multiple chemical applications. Herbicidal applications incorporated with the rotary cultivator at 0, 7, and 14; 7, 14, and 21; or 0, 14, and 28 days after planting provided equal weed control.

Foliar sprays of 4-amino-3,4,5-trichloropicolinic acid (picloram) controlled winged elm (Ulmus alata Michx.) more effectively than 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). Picloram and 2,4,5-T in a mixture effectively controlled the elm. Sprays of 2,4,5-T with ammonium thiocyanate (NH4SCN) added, and a (1:1) combination of NH4SCN and 3-amino-1,2,4-triazole (amitrole) additive, controlled the elm. Foliar sprays of 2,4,5-T without additives have been relatively ineffective. Soil moisture shortage, followed by watering immediately after treatment of winged elm with 2,4,5-T-C14, increased the translocation of 2,4,5-T as compared to plants maintained in moist or dry soils.

Picloram controlled winged elm when applied with an injector or as a soil treatment. The 2,4,5-T diluted in diesel oil, applied as an injector treatment, effectively controlled winged elm.

Conflicting reports on the dissipation of ie isopropyl N-phenylcarbamate (IPC) and isopropyl N-(3-chlorophenyl) carbamate (CIPC) prompted the present investigation on the dissipation and biological activity of these two herbicides. The dissipation patterns of IPC and CIPC were similar. Under the field and laboratory conditions described, more than 90% of both herbicides was gone in 4 weeks. CIPC was biologically more active than IPC on all plants tested, and both herbicides were nearly 10 times more toxic to buckwheat (Fagopyrum esculentum Moench.) in quartz sand as in a silt loam soil. Although both herbicides were present in equal amounts throughout their dissipation, CIPC appears to persist longer in field applications, as it is more toxic to most plants than IPC.

The translocation of disodium methanearsonate (DSMA) and amine methanearsonate (hereinafter referred to as AMA) in purple nutsedge (Cyperus rotundus L.) was studied following foliar applications. Tracer techniques with DSMA-14C and chemical analyses for elemental arsenic (hereinafter referred to as As) suggested apoplastic and symplastic movement of both arsenicals. Chromatographic studies of extracts from DSMA-14C-treated plants indicated that the compound was not readily broken down. The carbon-arsenic bond appeared to remain largely intact, although some 14C activity was found in respiratory CO2 several days after treatment. A comparison between the Rf value of the radioactive plant extract to that of standard DSMA-14C suggested that a plant extract-DSMA complex may have been formed. Over 85% of the material applied to the plant remained in the treated shoots. DSMA moved in both acropetal and basipetal directions, and such movement within a single leaf was not influenced by relative leaf age. The arsenicals were not redistributed in the shoot or in the tuber system, but As was accumulated in terminal tubers following repeated applications.

Unicellular green algae were used as test organisms in experiments designed to provide an insight into the mode of action of 3-(m-trifluoromethylphenyl)-1,1-dimethylurea (fluometuron). Fluometuron suppressed the autotrophic growth of Chorella pyrenoidosa Chick (hereafter referred to as C. pyrenoidosa) and Euglena gracilis Klebs-strain ‘Z’ (hereafter referred to as Euglena) and the extent of inhibition was a function of herbicidal concentration. Euglena was less sensitive than C. pyrenoidosa. Treated cells contained less protein and chlorophyll than untreated cells, but the inhibitory effect of the herbicide on the algal growth was overcome when the organisms were grown heterotrophically. Fluometuron did not adversely influence respiration or the light-independent reactions that lead to the formation of chlorophyll or chloroplast precursors. It did interfere with the light-dependent or the greening process of chlorophyll synthesis and with photosynthetic oxygen evolution. Fluometuron appears to be selectively toxic to one or more light-mediated biochemical reactions required for the formation and function of photosynthetic pigments and organelles.