The temperature at which seeds of witchweed (Striga asiatica (L.) Kuntze), an obligate parasite, were stored markedly influenced the length of time that the seeds remained dormant. Dormancy was broken completely by storing seeds collected in August, 1960, at 88 F for 6 weeks, at 75 for 24 weeks, at 40 for 32 weeks and at 0 F for 40 weeks. Seed viability was lost rapidly when the storage of seeds was continued at 88 or 100 F plus 100% relative humidity after seed dormancy had been broken. All of the seeds stored under those conditions were non-viable within 20 weeks after storage began. The viability of seeds stored at 75, 40 or 0 F had not decreased after 26 months for 1960 seeds. Seeds collected in 1961 and stored at those three temperatures or at 88 F plus 20% relative humidity for 14 months did not decrease in per cent viability. A hypothesis on the physiology of the dormancy, viability, and germination of witchweed seeds is presented.

The response of purple nutsedge (Cyperus rotundus L.) clones grown from single tubers to 3-amino-1,2,4-triazole (amitrole), butoxyethanol ester of 2,4-dichlorophenoxyacetic acid (2,4-D), and ethyl N,N-di-n-propylthiolcarbamate (EPTC), and the response of established nutsedge to amitrole were studied under field conditions of the Georgia Piedmont Plateau. Clones were essentially eradicated by two applications of amitrole initiated up to 4 weeks after shoot emergence and by EPTC incorporated at 1 or 2 weeks after emergence. Excellent control resulted from 9 applications of 2,4-D initiated 1 or 2 weeks after shoot emergence. Timely applications of amitrole to an established stand controlled but did not eradicate nutsedege. This decreased response in an established stand seemed due, in part, to irregular emergence of plants in the established stand.

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) applied in nutrient solution to corn, cotton, and soybeans reduced transpiration both in intact plants and excised shoots. This effect occurred only in the light. Microscopic examination revealed that atrazine caused closure of the stomates. Atrazine treated plants had higher moisture levels than the checks 12–24 hours after treatment, but later percentages were lower than the checks.

Disodium endothal (3,6 endoxohexahydrophthalic acid) was applied to a number of emergent and submerged aquatic species and was found to be particularly effective in controlling pondweeds, Potamogeton spp. On P. foliosus, P. crispus, and P. pectinatus, liquid and granular preparations appeared to be equally effective. Endothal was not very effective on some species, such as waterwillow, Justicia americana, and creeping waterprimrose, Jussiaea repens L. var. glabrescens, although defoliation did occur.

The herbicides n-propyl ethyl-n-butylthiolcarbamate (PEBC), PEBC + 2,3-dichloroallyl diisopropylthiol-carbamate (DATC), PEBC + ethyl N,N-di-n-propylthiolcarbamate (EPTC), and PEBC + 2,3,3-trichloroallyl diisopropyldithiolcarbamate (CP-22819) among others produced effective control of lambsquarters (Chenopodium album), pigweed (Amaranthus retroflexus), Setaria spp. and other weed species without undue injury to sugar beet seedlings. PEBC + DATC also gave control of wild oat (Avena fatua), and increased the control of lambsquarters; however, this latter effect was inversely related to the control of other broad-leaved weeds. Control equal to PEBC was produced by PEBC + EPTC with 2.5 lb. less total active ingredient per acre. The herbicide 3,6-endoxohexahydrophthalic acid (endothal) gave inferior control of weeds. None of the herbicides tested effectively controlled kochia (Kochia scoparia).

2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), ethyl N,N-di-n-propylthiolcarbamate (EPTC), and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) were shown to aid in the establishment of rose clover (Trifolium hirtum All.) and harding-grass (Phalaris tuberosa L. var. stenoptera (Hack.) Hitch.) by reducing competition from resident annual plants, primarily medusahead (Elymus caput-medusae L.). The success of preemergence herbicides was shown to depend on fall precipitation in amounts great enough to permit seed germination and plant growth before winter temperatures become limiting. The degree of weed control necessary to aid in seedling establishment was low, sometimes lower than could be measured by estimates of ground cover.

Inclusion of any one of several ethoxylated nonionic surfactants in aqueous spray mixtures of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) greatly increased its toxicity to crabgrass (Digitaria sanguinalis (L.) Scop.). Phytotoxicity of sprays made up from commercially formulated diuron was greater than when technical diuron was used. The toxicity of diuron was also increased by the addition of any of several low-molecular-weight alcohols to the spray mixture.

The turbidity of diuron suspensions was greatly decreased by addition of any of several nonionic, anionic, or cationic surfactants which contained a fatty acid or fatty acid derivative as the hydrophobic portion of the molecule. Phytotoxicity of diuron applied with ethoxylated nonylphenol surfactants was associated with ethylene oxide (hydrophil) content. Surfactants containing nonylphenol, alkylthiol, or tridecylphenol as hydrophobes appeared essentially equal in their abilities to increase diuron toxicity, but dodecylphenol surfactants were slightly less effective.

Peach trees treated with the herbicide mixture of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) and 3-amino-1,2,4-triazole plus ammonium thiocyanate (amitrole-T) had higher leaf nitrogen and more growth than trees where the weeds were controlled by hand hoeing or a black plastic mulch. Apple trees had higher leaf nitrogen and more growth when treated with simazine and amitrole-T than with no weed control. In both peaches and apples more growth and higher leaf nitrogen resulted from the herbicide treatments than from supplemental nitrogen treatments, indicating that the herbicide influenced the nitrogen metabolism of these trees.

3-Amino-1,2,4-triazole (amitrole) sprayed on annual grassland infested with medusahead (Elymus caput-medusae L.) at 1/2 to 4 lb/A when medusahead was in the boot or soft dough stage reduced viable caryopses from 60 to 100 percent, and seed production the following year from 75 to almost 100 percent. 1,2-Dihydropyridazine-3-6-dione (maleic hydrazide) and 2,2-dichloropropionic acid (dalapon) reduced viability of medusahead seeds, but were less effective than amitrole. Viable caryopses of soft chess (Bromus mollis L.) were reduced and the year following treatment soft chess was decreased in the stands by early application (boot stage of medusahead) but not by late application of herbicides, when the soft chess heads were dry.

Preplanting, soil-incorporated treatments of fenac (2,3,6-trichlorophenylacetic acid sodium salt) at 1, 2, 4, and 8 lb/A, 2,3,6-TBA (2,3,6-trichlorobenzoic acid dimethylamine salt) at 8, 12, and 16 lb/A, and 2,4-D 2,4-dichlorophenoxyacetic acid amine salt) at 12 lb/A applied in 1960 to six soil types infested with witchweed (Striga asiatica (L.) Kuntze) resulted in some control of witchweed as measured by visual observations and corn yield. Two or three additional postemergence applications of 2,4-D at 1 lb/A were required to prevent witchweed seed production for the growing season. Witchweed parasitism on corn was greatly reduced by a preplanting treatment of fenac at 2 lb/A plus 2,4-D as a postemergence treatment.

All rates of 2,3,6-TBA and fenac at 8 lb/A caused moderate to severe corn injury with the most severe injury occurring on soils with relatively high clay content in the subsoil. Soil residual studies and field observations indicated fenac and 2,3,6-TBA may be present in Coastal Plain soils for more than 18 months.

Greenhouse evaluation of 30 s-triazine compounds indicated that several of them were suitable for pre-emergence weed control in Lee soybeans. The s-triazines least toxic to soybeans generally contained either methoxy or methylmercapto substituents but most of these were highly toxic to crabgrass (Digitaria sanguinalis (L.) Scop.). Soybeans were more tolerant to ethylamino substituted s-triazines than to isopropylamino derivatives. Chloro derivatives were generally toxic to soybeans. Proplyamino, allylamino, methoxypropylamino, ethoxy, trichloromethyl, and amido substitutions had much less effect on soybean selectivity than those previously mentioned.

Field evaluation of several s-triazines, preemergence, confirmed the tolerance of soybeans to 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne), 2-ethylamino-4-isopropylamino-6-methylmercapto-s-triazine (ametryne), and 2-isopropylamino-4-methylamino-6-methylmercapto-s-triazine (norametryne) at rates that provided adequate weed control.

The effect of fully-saturated bicyclic and partially-saturated tricyclic dimethylureas and dimethylthioureas on the photolytic activity (Hill reaction) of chloroplasts isolated from turnip greens (Brassica spp.) was studied. Photochemical activity was measured potentiometrically with ferricyanide as the electron acceptor. Chemicals tested were 3-[5-(3a,4,5,6,7,7a-hexahydro-4,7-methanoindenyl)]-1,1-dimethylurea; 3-(chloro-2-norbornyl)-1,1-dimethylurea; 1,1-dimethyl-3-(2-norbornyl)urea; and the 3 corresponding thioureas. Concentrations of the 3 polycyclic ureas required to inhibit the Hill reaction by 50 percent (I50) were respectively 4.0 × 10-6 M, 1.2 × 10-5 M, and 6.6 × 10-5 M. The thioureas were not very inhibitory to the Hill reaction; consequently, their I50 values were not determined. The fully or partially-saturated polycyclic dimethylureas were weaker inhibitors of the Hill reaction than the phenyldimethylureas. The decreased inhibitory activity of the polycyclic ureas was attributed to increased lipophilic properties, unfavorable spatial configurations, and lack of resonance interaction between the ring system and the imino nitrogen.

Long-term compensation points in waterstargrass (Heteranthera dubia (Jacq.) Mac M), coontail (Ceratophyllum demersum L.), and duckweed (Lemna minor L.) were near 2–3% full sunlight during a 28-day period. Fresh weight of H. dubia increased as temperature increased from 15 to 30 C and as light intensity increased from 110 to 1000 foot-candles. Fresh weight of C. demersum increased as temperature increased above 20 C and as light intensity increased from 120 to 550 foot-candles. The L. minor strain used in this experiment was not temperature-dependent and increased in fresh weight and frond number at 25 and 30 C as light intensity increased from 77 to 550 foot-candles.

Orchardgrass (Dactylic glomerata L.) and Kentucky bluegrass (Poa pratensis L.) were used as test species to study the phytotoxicity of mixtures of 2,2-dichloropropionic acid (dalapon) and dimethylarsinic acid (cacodylic acid). A technique involving ED50 values, a shortened graphic procedure, and probit transformations was developed. Mixtures in which cacodylic acid was in excess indicated synergistic effects on bluegrass and additive effects on orchardgrass. Dalapon in excess in the mixtures appeared to have had an antagonistic effect on cacodylic acid. Orchardgrass was more tolerant to cacodylic acid than bluegrass.

The butoxyethanol and propylene glycol butyl esters of 2,4-dichlorophenoxyacetic acid (2,4-D) were applied to and recovered from the leaf surfaces of garden bean and corn plants. Both the acid and the ester of 2,4-D were recovered, indicating that hydrolysis of the esters had occurred. The acid and esters of 2,4-D were also found in both leaves and stems of the bean plants, indicating that further hydrolysis had occurred within the plants. Bean plant homogenates incubated with 2,4-D esters yielded 2,4-D acid. The root exudate from corn plants treated with 2,4-D butoxyethanol ester showed the presence of both acid and ester.

The effect of ethyl N,N-di-n-propylthiolcarbamate (EPTC) on photosynthesis was determined by C14O2 fixation by red kidney bean, Phaseolus vulgaris L., leaves following root application of this herbicide in a time-course study at various concentrations of the herbicide. EPTC inhibited C14O2 fixation at relatively high concentrations and long exposures of the herbicide, but did not alter the relative distribution of C14 in the various labeled compounds. The effect of EPTC on the respiration of excised embryos of corn and mung bean (Phaseolus aureus Roxb.) following 24 or 48 hr exposures to the herbicide. When the data were expressed on a fresh-weight basis, it indicated that EPTC stimulated respiration, but the same data expressed on an embryo basis did not show this stimulation. EPTC inhibited the growth and the concurrent increase in fresh weight of these embryos. The effect of EPTC on oxidative phosphorylation was determined with cucumber mitochondria. EPTC markedly inhibited both phosphorus uptake and oxygen consumption. Phosphorus esterification was more sentitive than oxygen utilization: this gave a reduced P/O ratio or an uncoupling effect. However, since the concentration of EPTC required to produce these effects was quite high, the physiological significance of the results is questionable.

The apparent solubility in water of 2-ethylamino-4-isopropylamino-6-methylmercapto-s-triazine [ametryne], 3-(3,4-dichlorophenyl)-1,1-dimethyl urea [diuron], and 2-chloro-4-ethylamino-6-isopropylamino-s-triazine [atrazine] was increased when a surfactant was added to the water. At 0.5% surfactant concentrations, considerable variation in solubility was found, both as regards the herbicide and surfactant used, as measured by ultraviolet absorption spectrophotometry. The two triazines were more soluble in cationic surfactants, followed by anionic and nonionic; diuron was more soluble in cationic followed by nonionic and anionic types.

Minimum lethal levels of surfactant in water for 2 week old cucumber plants varied from about 0.1% for the cationic to 0.2% for most nonionic and 1.0% or more for anionics of the alkyl aryl sulfonate type.

Herbicide performance was markedly altered by soil incorporation, depth of incorporation, crop seed placement, soil type, and rainfall. Of the 25 herbicides studied, 2-chloro-N,N-diallylacetamide (CDAA) and isopropyl-N-(3-chlorophenyl)carbamate (CIPC) and mixtures of them showed most promise. Herbicide-placement studies showed that the selectivity of these herbicides in cotton largely depends on herbicide placement in relation to the crop seed and on rainfall. Without rainfall, CDAA incorporated in moist soil above the cotton seed provided excellent weed control with minimal injury to cotton. CDAA was readily leached from the zone of germinating weed seed by rain or irrigation on coarse-textured soils. Without rainfall, CIPC was slightly inferior to CDAA in weed control but more stable in performance over a wider range of environmental conditions. Mixtures of CDAA and CIPC were somewhat superior to either alone. Commercial usage of these herbicides in moist soil depends on the development of suitable equipment for application.

In tests conducted from 1951 to 1961 in the Peace River section of Alberta, 3-(p-chlorophenyl)-1,1-dimethylurea (monuron) was applied to vigorous quackgrass (Agropyron repens (L.) Beauv.) sods on different soils. These tests showed: 1) tillage either before or after application of monuron strongly reduced its effect; 2) when used without tillage it did not matter whether monuron was applied in the early summer or early autumn, but when used with tillage it was best applied in the early summer; 3) 40 lb/A applied without tillage eradicated quackgrass under all conditions except when it was established in an unusually deep and loamy soil; 4) killing quackgrass by monuron usually took 2 years; and 5) lethal rates of monuron prevented quackgrass re-establishment for from 1 to 7 years and satisfactory growth of cereal crops for 10 years or more.

During the vegetative phase of barnyardgrass (Echinochloa crusgalli (L.) Beauv.) development, the leaves, axillary buds (tillers) and permanent root system were initiated and developed. First adventitious roots appeared on the 6th day after germination. Internode elongation, which was coincident with a change from a vegetative phase to a reproductive phase of the plant, was observed in the field about 30 days after germination. At this time the main stem had 4–5 maturing leaves. Typically, barnyardgrass formed 8 leaves on the main axis from primordia which were initiated during the first two weeks after germination. The first tiller primordium appeared in the axil of either the 1st or 2nd leaf on the day of emergence from the soil. In the field, tillering was observed from the twelfth day. Heading began on the 40th day and the first mature seeds were formed about 64 days after germination.