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.

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.

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.

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.

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.

A tractor-mounted mist blower was as effective as a high-volume ground sprayer or an airplane sprayer for applying herbicides to control hardwoods in two tests in central Louisiana. Two lb/A of butoxyethanol ester of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were slightly better than one, and May treatments were more effective than August treatments.

An assay technique utilizing Chlorella vulgaris Beijerinck gave highly significant responses to low concentrations of aqueous 3-(p-chlorophenyl)-l,l dimethylurea (monuron), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), and 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) following 6 days of incubation. Water extracts of diuron from soil assayed with this organism were highly correlated with diuron added to the soil. Similar correlations for oats (Avena sativa L.) grown on the soil and for diuron in the water extracts as dichloroaniline serve to substantiate the relative effectiveness of the method. Assay of soil samples from field residue plots taken 150 days after herbicidal application showed that active residues of diuron and prometryne were detectable by the organism. Although the chemical method was faster, it has the disadvantage of measuring any dichloroaniline residues rather than only the active residues. The method developed insures a considerable saving in time over herbicide assays involving higher plants and gives reasonably good quantitative data on low concentrations of toxic monuron, diuron, and prometryne.

In greenhouse experiments, soil-incorporated combinations of 0,0-diethyl S-[2-(ethylthio)-methyl]-phosphorodithioate (phorate) or 0,0-diethyl S-[2-(ethylthio)-ethyl]-phosphorodithioate (disulfoton) with a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) resulted in increased cotton (Gossypium hirsutum L.) seedling growth as compared to trifluralin used alone. This result apparently was due to the greater numbers of secondary roots in the zone of incorporation. Phorate was more effective than disulfoton in overcoming the inhibitory effect of trifluralin on secondary root development. A comparison of granular and emulsifiable phorate showed no advantage for either formulation. The combination of phorate and trifluralin in a 1-inch soil core, into which seeds of cotton were planted and surrounded by trifluralin-treated soil, also increased secondary root development as compared to using trifluralin alone.

Sublethal concentrations of isopropyl N-(3-chlorophenyl)- carbamate (CIPC) labeled with 14C in the ring or side chain were applied to all leaves present or to the roots of redroot pigweed (Amaranthus retroflexus L.), pale smartweed (Polygonum lapathiofolium L.), and parsnip (Pastinaca sativa L.). These species were selected because of their different susceptibilities to CIPC. The herbicide did not move out of the treated leaves in pigweed and smartweed and only slightly in parsnip in 21 days. In root treatment (3 days), the herbicide moved to all plant parts and the extent of movement was essentially the same in all species. Water soluble metabolites, which differed in Rf values were extracted from all three species. The metabolites apparently were not the result of cleavage of the CIPC molecule, but were more likely conjugates of CIPC with natural plant component(s). Very little 14CO2 was released by any of the species in 3 days. These data indicate that differences in movement and metabolism are not sufficient to account for the different susceptibilities of these three plant species.

The prolificacy of honeyvine milkweed [Ampelamus albidus (Nutt.) Britt.] was investigated. Mature seeds stored at 0, 10, and 24 C and germinated at 32 C demonstrated high viability from harvest to 1 year old. Immature seeds were slightly less viable but followed the same trends in germination. Studies with rhizomes excavated at four different times throughout the year showed that segments 1 inch long with at least one live bud were capable of generating regrowth. These reproductive characteristics with the inherent tenacity of honeyvine milkweed indicate a potentially serious weed problem in many agricultural regions of the United States.

Quackgrass (Agropyron repens (L.) Beauv.) was controlled with applications 1 to 8 months prior to plowing and planting of from 1 to 4 lb/A 2,3,5-trichloro-4-pyridinol (pyriclor). Corn (Zea mays L., hybrid W530) planted on pyriclor-treated plots grew normally and yielded as well as on plots given the standard preplow treatment of 2 lb/A of 2-chloro-4-ethylamino-6-isopropylamino-5-triazine (atrazine). Oats (Avena sativa L., var. Portage) was injured by soil residues of pyriclor from 2-lb/A applications made 20 months previously. Alfalfa (Medicago sativa L., var. Vernal) was somewhat more tolerant of pyriclor than was oats.

Foliar applications of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) at 0.05 to 1.0 lb/A caused characteristic injury symptoms on cucumber (Cucumis sativus L.) plants. Analytical methods were evaluated and found suitable in detecting atrazine in cucumber leaves sprayed at a low rate of 0.005 lb/A. For analytical detection, tissue samples should be taken as soon as necrotic symptoms appear, 4 to 7 days after suspected drift, and frozen immediately.

Smooth bromegrass (Bromus inermis Leyss.) treated in the fall tended to be more damaged than that treated in the spring, regardless of herbicide. Nitrogen fertilizer reduced the loss in yield resulting from herbicides but was least effective with 1 lb/A of 4-amino-3,4,6-trichloropicolinic acid (picloram). Laboratory studies showed that roots of smooth bromegrass were the primary site of picloram uptake. Root uptake explained the severe damage in curred from applications of picloram made in the fall. The order of increasing phytotoxicity of herbicides to smooth bromegrass studied in these experiments was 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4-dichlorophenoxyacetic acid (2,4-D)<2-methoxy-3,6-dichlorobenzoic acid (dicamba) < picloram.

The loss of 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 4-amino-3,5,6-trichloropicolinic acid (picloram) in runoff water was determined with a gas chromatograph and bioassays. When determined 24 hr after application, losses of dicamba and picloram were greater from sod plots than from fallow plots while 2,4,5-T losses were about equal. Four months after application, losses of all herbicides averaged less than 1% of that lost 24 hr after application. The amount of picloram lost in a simulated rainfall of 0.5 inch varied with rate, but the percentage lost was the same. The slope of the plot and movement over untreated soil influenced the percentage of picloram lost. The maximum loss obtained for any herbicide was 5.5% and the average approximately 3%.

Dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA) on the soil surface inhibited rooting at bermudagrass (Cynodon dactylon L., var 328) stolon nodes. Histological studies of these root tips showed that cell division had ceased while cell enlargement continued for some time. Cells became excessively large and irregularly shaped. In corn (Zea may L., var. Pioneer 310), radicle cell size was about the same in both instances; however, treated tissue contained six times as many dinucleate cells as untreated radicle tissue. Numerous nuclei were at metaphase stage of mitosis in treated tissue. In untreated onion (Allium cepa L., var. Yellow Globe Danvers) root tips, many nuclei were found at anaphase and telophase stage of mitosis while very few cells were dividing in treated tissue.

Growth chamber and field studies were conducted to investigate the possibility of an interaction between the herbicides 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin), a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), 3- (m-tri-fluromethylphenyl)-1,1-dimethylurea (fluometuron), and 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne), and the seedling disease organism Rhizoctonia solani Kuehn in cotton (Gossypium hirsutum L.). When high levels of trifluralin or prometryne were used in the growth chamber, an interaction with the pathogen that was injurious to the cotton occurred. Prometryne and fluometuron produced an antagonistic effect on R. solani.

Under field conditions, R. solani usually caused cotton injury. Interactions injurious to the cotton occurred between trifluralin and a low level of R. solani and between nitralin and a high level R. solani infestation. No interactions occurred with fluometuron or prometryne. In all instances, the effect occurred only when the herbicides were being used at high rates.

Spray and granular forms of isopropyl N-(3-chlorophenyl)-carbamate (CIPC, ethyl N,N-dipropylthiocarbamate (EPTC), a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and 2,4-bis(isopropylamino) -6-methylmercapto-s-triazine (prometryne) were incorporated preemergence to barnyardgrass Echinochloa crusgalli (1.) Beauv.) and broadleaf weeds with a rotary tiller, wheel hoe, rotary spike, or row wheel into pre-irrigated or dry soil at three locations. The locations varied in type of soil, climatic conditions, and the species of broadleaf weeds. Rotary tiller incorporation generally resulted in best weed control with both spray and granular forms under all conditions. Herbicides usually performed best in pre-irrigated soil. Sprays and granules were equal in performance at coastal and intermediate locations; granules were more effective in the desert location. Herbicidal effectiveness was influenced by method of incorporation, form of treatment, soil moisture, environmental location, and weed type.

Field studies were conducted over a 2-year period at Urbana, Illinois, to evaluate soybean (Glycine max (L.) Merr., var. Harosoy 63 and Wayne) and weed yields as influenced by row spacing, variety, weed control methods, and 2,3,5-triiodobenzoic acid (hereinafter referred to as TIBA). Soybean yield increased and weed yield decreased as row spacing was decreased. Compared to the yield from 40-inch rows, soybean yield increase was 10, 18, and 20% for 30, 20, and 10-inch rows, respectively. Both cultivation and applications of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) controlled annual grass weeds at all row spacings. Cultivation controlled broadleaf weeds at all row spacings. Some broadleaf weeds, unaffected by trifluralin, made sufficient growth to impair soybean yields in wide rows but not in narrow rows.

From 1962 to 1967, we evaluated herbicides for control of natural infestations of reed canarygrass (Phalaris arundinacea L.) on canal banks of the Huntley, Montana irrigation project. Two,2-dichloropropionic acid (dalapon) and 3-amino-1,2,4-triazole ammonium thiocyanate (hereinafter referred to as amitrole-T) controlled reed canarygrass. These herbicides were compared with a number of others. Spring foliage treatments with a combination of amitrole-T at 2 1b/A and dalapon or trichloroacetic acid (TCA) at 5 or 10 1b/A were more effective than amitrole-T at 4 1b/A. Amitrole-T was more tolerant to fine grasses such as Kentucky bluegrass (Poa pratensis L.) or redtop (Agrostis alba L.) than dalapon and in some situations it was more desirable than dalapon. Dalapon and TCA were more effective as late fall or early winter treatments to control reed canarygrass during the following growing season. Rates of 20 or 40 1b/A controlled the grass for one season even at the water's edge where it is usually more persistent. At 5 to 10 1b/A, 2,3,5-trichloro-4-pyridinol (pyriclor) controlled reed canarygrass, and it also was effective at 2 1b/A with 2 1b/A of amitrole-T.

A technique was developed for evaluating the stability of a herbicide suspended in nitrogen solutions of varying molarity. Dispersion stability is expressed as the difference in specific gravity (D value) between a salt solution + herbicide and the salt solution alone using a Westphal balance. The lower the D value, the less herbicide in suspension. Even very low molar solutions significantly lowered the D value. Further, the lower the percent active ingredient in the herbicide the more effectively the surfactants, and possibly other components of the formulated product, offset the adverse effect of salt on dispersion stability.