Thirty herbicides were tested for possible effects upon the incorporation of radioactivity from malonic acid-2-14C into lipid by excised hypocotyls of hemp sesbania (Sesbania exaltata (Raf.) Cory). Concentrations of 1 to 20 mg/L were used. Inhibition was caused by 3-nitro-2,5-dichlorobenzoic acid (dinoben), 2-chloro-N,N-diallylacetamide (CDAA), 2-chloroallyl diethyldithiocarbamate (CDEC), 7-oxabicyclo(2.2.1)heptane-2,3-dicarboxylic acid (endothall), 2,6-dichlorobenzonitrile (dichlobenil), 3,5-diiodo-4-hydroxybenzonitrile (ioxynil), and pentachlorophenol (PCP). At 1 mg/L, stimulation was caused by 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 3-amino-2,5-dichlorobenzoic acid (amiben).

Inhibition of cotton (Gossypium hirsutum L.) and soybean (Glycine max (L.) Merr.) lateral roots by alpha, alpha, alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) was directly related to depth and method of incorporation. Root inhibition of the crop plants was reduced when trifluralin was incorporated shallowly after planting with either a power tiller or a ground-driven tiller, to a depth no greater than 0.5 in above seed placement. A bioassay of the soil showed that disking trifluralin-treated plots before bedding caused the greatest retention of the material 3 weeks later, and that retention was less when the herbicide was applied and shallowly incorporated after planting. Further studies on the relationship of soil persistence of trifluralin to depth of incorporation 6 months after application, showed no herbicide present in plots not incorporated while only minimal residues were found where incorporation was no deeper than 1 in. Residues in plots incorporated below the 2-in depth were moderate at 0.5 to 1 lb/A rates and high at the 2 lb/A rate and above.

An experiment was conducted comparing wheat (Triticum aestivum L., var. Pembina) and wild buckwheat (Polygonum convolvulus L.) grown alone in pots, in full competition, and in root competition at three levels each of soil fertility and soil moisture, and harvested at three dates.

Wheat was a better competitor than wild buckwheat when considering dry matter production. With each succeeding harvest, the dry matter production and the total nitrogen and phosphorus uptake increased more for plants grown alone than in competition. Competition caused a reduction in the nitrogen and phosphorus content of wheat and wild buckwheat at the first harvest, while reductions in dry matter did not occur until the second harvest. Wheat increased in dry matter and nitrogen more than wild buckwheat with each higher level of soil moisture when grown alone but not when in competition. When grown alone or in competition, wheat increased linearly in dry matter production with increases in fertility while wild buckwheat produced maximum dry matter with medium fertility. The total nitrogen increased in wheat and wild buckwheat with each higher level of fertility, while total phosphorus increased only in wheat.

Wild buckwheat used less water than wheat to produce a gram of dry matter and per milligram of phosphorus uptake when grown alone, while the plants in competition were intermediate in water usage to plants grown alone. Wild buckwheat and wheat used similar amounts of water per unit of nitrogen uptake when grown alone and increased their water usage when grown in competition. Water efficiency for nitrogen and phosphorus uptake and dry matter production usually decreased with plant maturity and higher soil moisture, and increased with higher soil fertility.

In 1965–66, we observed root development of two plant types of rush skeletonweed (Chondrilla juncea L.). Rosette bud formation on both plant types occurred on the upper 5-cm zone of the taproot after seed dispersal in the fall until flower-stem initiation the following spring. Incubation at various temperatures of lateral root sections from field grown plants showed a cyclic sprouting pattern with the highest percentage during late fall and early spring, and no sprouting during June. Bud production was most frequent at the proximal end of the sections. The earlier-flowering plant type contained an average of 6.7 and 6.0 major roots after 6 and 18 months of growth whereas the late-flowering type contained 10.7 and 16.0 major roots for the same periods of growth. The early-flowering plant roots were larger in diameter than those of the late-flowering plants. Both root types increased in diameter as distance from the point of attachment increased excluding root apex. Unattached secondary plants resulting from vegetative propagation were found of both plant types.

In a greenhouse experiment, dosages of 2-methoxy-3,6-dichlorobenzoic acid [dicamba] and 2-methoxy-3,5,6-trichlorobenzoic acid [tricamba] required initially to reduce fresh weights of snap beans (Phaseolus vulgaris L.) 50% (hereinafter referred to as ED50 values) increased as clay and organic matter increased in five soils. In all soils, 2,3,6-trichlorobenzoic acid [2,3,6-TBA] was about equally toxic, but ED50 values for 2,3,6-trichlorophenylacetic acid [fenac] and 2-methoxy-3,6-dichlorophenylacetic acid [hereinafter referred to as methoxy fenac] decreased as clay and organic matter increased. Under experimental conditions of alternately moist and dry soil, phytotoxicity of dicamba, tricamba, and methoxy fenac decreased with time, but that of 2,3,6-TBA and fenac remained approximately the same for about 22 months. When soils were maintained moist throughout the incubation period, 3-amino-2,5-dichlorobenzoic acid [amiben] was least persistent, dicamba intermediate, and 2,3,6-TBA and fenac most; under these conditions, phytotoxic effects of 2,3,6-TBA and fenac decreased with time. In soil-enrichment studies, fenac, methoxy fenac, dicamba, and 2,3,6-TBA, in comparison with 2,4-dichlorophenoxyacetic acid [2,4-D], appeared very resistant to microbial degradation.

No effect was shown of 3-amino-l,2,4-triazole (amitrole) upon the incorporation of alanine or histidine into soluble protein in bean (Phaseolus vulgaris L.) hypocotyls grown in darkness. The metabolic derivative of amitrole, β-(3-amino-1,2,4-triazolyl-l-)α-ala-nine (hereinafter referred to as 3-ATAL), also had no effect upon histidine incorporation. Serine incorporation was increased 56% in the presence of amitrole, but this may result from a reduction of endogenous serine pools. No evidence indicates a general disruption of protein synthesis. Activity from amitrole-5-14C was readily incorporated into bean protein, but hydrolysis revealed no 3-ATAL. Most of the activity was recovered as amitrole. Amitrole in the presence of riboflavin and light attacked bovine serum albumin, probably by free radical formation. Hydrolysis of bovine serum albumin revealed mainly amitrole. Apparently, the entry of amitrole into bean protein is by free radical formation.

Initial and residual phytotoxicity of 3-(m-trifluoromethylphenyl)-1, 1-dimethylurea (fluometuron) in seven soils was studied under greenhouse condition, using oats (Avena sativa L., var. Brave) as the bioassay species. The phytotoxicity of fluometuron in four of the soils, with an organic matter range of 1.0 to 5.0%, was not different at any one of the five cropping periods. Inactivation of fluometuron was more rapid in Eden silty clay loam with 3.3% organic matter than in Maury silty clay loam/silt loam with 7.2% organic matter. Phytotoxicity was significantly correlated with organic matter and soluble phosphorus during the first two cropping periods, and with cation exchange capacity, exchangeable calcium, total exchangeable bases, and soluble phosphorus during the last three croppings.

Safer methods of herbicide application are needed for irregular planting areas. The herbicide 2,6-dichlorobenzonitrile (dichlobenil) was incorporated into various organic mulches so that a specified depth of mulch delivered the desired concentration of herbicide. The incorporation technique provided equal or better weed control than either the dichlobenil or mulch used alone. In addition, prolonged effect of the dichlobenil was realized into the second year when it was incorporated into the mulch. Increasing the mulch depth to 4 inches increased the weed control. A nutrient supplemented mulch in conjunction with the dichlobenil increased the growth of many woody ornamental plants as much as 300 to 400%.

Corn (Zea mays L.) plots receiving broadcast spray applications of triazine herbicides without cultivation yielded as much as plots receiving the standard two cultivations for weed control. One cultivation resulted in an average 6% increase in corn grain yield on herbicide treated plots. This yield increase probably was due to improved weed control. Weed growth reduced grain yields an average of 1.23 bu/A for each 100 lb/A of dry weeds. In some experiments, increases in corn yield due to improved weed control by cultivation on plots treated with herbicides were less than increases expected based on weed growth reductions. This disparity may have been due to injury to the corn by cultivation.

The herbicides, S-ethyl hexahydro-1 H-azepine-l-carbothioate (molinate) applied preemergence and 3′,4′-dichloropropionanilide (propanil) applied as a contact spray at several dates, were evaluated for control of barnyardgrass (Echinochloa crusgalli (L) Beauv.) in water-seeded rice (Oryza sativa L., var. Caloro) flooded continuously to a shallow (3 inch) depth. Propanil applied when barnyardgrass had 6 to 9 inches of leaves exposed gave higher yields than earlier or later applications. Molinate gave the best barnyardgrass control when it was applied as a granule, incorporated, and applied onto dry soil. Molinate controlled the three major phenotypes of barnyardgrass. Germinating barnyardgrass seed were severely inhibited in growth by molinate concentrations greater than 0.3 ppm while germinating rice seed were not inhibited until the concentrations were greater than 5 ppm. Low concentrations of molinate stimulated shoot growth of both rice and barnyardgrass.

The translocation of 2-methoxy-3,6-dichlorobenzoic acid (dicamba-7-14C) in purple nutsedge (Cyperus rotundus L.) at different stages of development and under various light regimes was studied using autoradiography and liquid scintillation counting techniques. The fate of the herbicide was investigated by means of thin-layer chromatography. Dicamba was slowly but appreciably translocated in purple nutsedge following application to the leaves or roots. Foliarly applied dicamba movement proceeded both acropetally and basipetally, and the herbicide became widely distributed throughout the aerial parts of the plant and accumulated in the regions of meristematic activity. Dicamba was barely detectable in the underground organs, although it was excreted into the culture medium and passed through the rhizomes and tubers into daughter plants. Root-applied dicamba distribution was general throughout the plant except within the tubers and the tips of the leaves. Dicamba was barely detectable within the tubers, although it was present in quantity at or near the surface. Dicamba accumulation was evident at the tips of the leaves. Translocation was enhanced under low light conditions. Distribution of dicamba was profoundly affected by the stage of development of the plant. Greater translocation and broader distribution of the herbicide occurred in the vegetative stage of development. After flowering, movement out of the treated leaf decreased. Studies indicated that the herbicide was not degraded by the plant during the 10 days following treatment.

The phytotoxicities of soil-incorporated 2,6-dichlorobenzonitrile [dichlobenil] and 2,6-dichlorothiobenzamide [hereinafter referred to as SD-7961] were compared in five soils in the greenhouse. Dichlobenil and SD-7961 were about equally toxic to snap beans (Phaseolus vulgarus L., var. Black Valentine) in each of the five soils. The herbicides were more toxic in Christiana loam than in the other four soils. Phytotoxic residues of both herbicides disappeared most rapidly from Hagerstown silty clay loam and Christiana loam and least rapidly from Sharkey clay. Gas chromatographic analyses of soil extracts confirmed that dichlobenil was most persistent in the clay. Small amounts (0.14 ppmw or less) of 2,6-dichlorobenzoic acid [hereinafter referred to as 2,6-DBA] were detected in soil from greenhouse pot cultures about 9 months after incorporation of dichlobenil. In a field experiment at Beltsville, Maryland, residues of dichlobenil persisted from one season to the next but did not build up in soil sprayed annually for 3 years with 4 or 8 lb/A. Some movement from the surface 6 in into the 6 to 12-in zone occurred on plots sprayed 2 years in succession with 8 lb/A or once with 40 lb/A. Rapid loss of dichlobenil occurred during summer months. When the concentration of dichlobenil on the 40-lb/A plots dropped to about 10%, subsequent loss occurred at a very slow rate.

The effects of temperature and the annual growth cycle on the formation of root suckers were determined by propagating root cuttings of black locust (Robinia pseudoacacia L.). The percentage of cuttings which formed suckers in an air temperature of 60 F was significantly lower than that of cuttings at 70 to 80 F. In the annual growth cycle experiment, cuttings removed in June formed significantly fewer suckers than those removed during January, March, August, or November.

Barnyardgrass [Echinochloa crusgalli (L.) Beauv.], duck-salad [Heteranthera limosa (Sw.) Willd.], hemp sesbania [Sesbania exaltata (Raf.) Cory], and northern jointvetch [Aeschynomene virginica (L.) B.S.P.] significantly reduced rice [Oryza sativa L.] yields. Damage to rice increased as populations of barnyardgrass, hemp sesbania, and northern jointvetch increased. Barnyardgrass and duck-salad lowered yields during early season, but hemp sesbania and northern jointvetch decreased yields in late season.

Weed control during the fallow year and yields of subsequent winter wheat (Triticum aestivum L.) were lower on unsprayed plots than on plots treated with 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) at 2 lb/A or 3-amino-l,2,4-triazole (amitrole) at 1/2 lb/A plus 3-(p-chlorophenyl)-l,l-dimethylurea (monuron) at 1 lb/A. The moldboard plow gave the most effective weed control in the winter wheat-fallow rotation followed by the oneway and the sweep plow. Sweep plow tillage left the greatest amount of plant residues on the soil surface to prevent wind and water erosion, but it did not consistently destroy shallow-rooted downy brome (Bromus tectorum L.) plants. Average downy brome stands in winter wheat on fallow plots tilled with the sweep plow, oneway, and moldboard plow were 331, 114, and 16 plants per 54 sq ft, respectively. Winter wheat yields averaged for the sweep plow, oneway, and moldboard plow treatments were 17, 18, and 20 bu/A, respectively. The most feasible method of controlling weeds in a winter wheat-fallow rotation, found in this study, was oneway tillage in combination with the lower herbicide rates.

The gross morphological effects of the herbicide 4-methyl-sulphonyl-2,6-dinitro-N,N-dipropylaniline [nitralin] on roots of corn (Zea mays L., var. U. S. 13) suggested abnormal cytological behavior. Roots of corn plants treated preemergence with nitralin developed digitate to globose swelling in the region of active cell division of the root tip. Cytological examination of the affected area showed that the effects of the herbicide were prevention of cell wall formation, enlargement of cells, and extensive replication of nuclei, and suggests that a primary effect of nitralin is on cell division and that this may be a primary mechanism of action as a herbicide.

A 3-year ecological study of physical, chemical, and biological factors affecting the growth of submersed aquatic weeds was conducted in four irrigation and drainage canals in south Florida. Growth of aquatic vegetation was influenced by light intensity which decreased in a geometric ratio to water depth. The light penetration into the water was influenced by dissolved coloring matter and turbidity. A high concentration of nitrogen was found in three of the canals. Nitrogen entered the canals as sewage effluent discharged into the water and as fertilizer runoff from surrounding farmland. Density of aquatic vegetation harvested at intervals of 6 months from clipped plots varied from zero in a newly dug canal to 22,000 lb green weight/A in an old established canal. During the 3-year study, there was a complete shift of the vegetation from southern naiad (Najas guadalupensis (Spreng.) Magnus) to Florida elodea (Hydrilla verticillata Casp.) in two of the canals, but there was no change in plant species in two canals. No other chemical and physical factors evaluated in the study limited submersed aquatic weed growth in these canals.

Degradation of 3-amino-l,2,4-triazole-5-C14 (amitrole-5-C14) in autoclaved, potassium azide, ethylene oxide, and dry-heat sterilized soil was compared with that observed in nonsterile soils by measuring evolved C14O2. Amitrole degradation occurred in azide and ethylene oxide-sterilized and nonsterile soils but not in autoclaved soils. Only slight degradation occurred in autoclaved soil re-inoculated with mixed cultures of soil microorganisms isolated from soil in which amitrole had been rapidly degraded. Addition of EDTA-Na to nonsterile and ethylene oxide sterilized soils reduced amitrole degradation. Addition of organic amendments to amitrole treated soil stimulated microbial activity but reduced amitrole degradation. Addition of specific metallic salts to certain soils increased the rate of amitrole degradation. Amitrole degradation occurred rapidly in several free radical generating chemical systems. These results and additional observations indicate that amitrole degradation, at least in three soils examined, was largely a chemical process, and that microbial involvement was only indirect.

Research Biologist to do field research on agricultural chemicals. Maintain liason with research scientists in southern U.S.A. Travel time 20%. Living area Little Rock, Arkansas. Salary open. Ph.D. in one of biological sciences and 2 to 5 years experience. Age 25 to 35. Ability to establish research programs and assume direction of research establishment with cooperating institutions. New position. Contact K. L. Hill, Air Products 8c Chemicals, Inc., P. O. Box 538, Allentown, Pa. 18105.