A hypothesis that low temperature acts directly on physiological development of coast fiddleneck (Amsinckia intermedia Fisch. and Mey.) by restricting thiamin content, and limiting growth, was investigated. Restoration of normal growth by application of thiamin, made the plant more susceptible to 2,4-dichlorophenoxyacetic acid (2,4-D) at low temperatures.

Field dodder (Cuscuta campestris Yunck.) emerged as well in total darkness as in light, but seedlings did not twine about the host. Under the shade of alfalfa, dodder emerged normally, but attachment was reduced more than 90% and delayed 7 to 10 days. Attached dodder shaded by alfalfa did not develop its characteristic golden color, grew very slowly, and was delayed in maturity 3 to 4 weeks.

Herbicides 3-(p-chlorophenyl)-1,1-dimethylurea (monuron); 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine); 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine); 2-methoxy-4,6-bis(isopropylamino-s-triazine (prometone); 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine); and 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne) were studied in four soils. The behavior of monuron, propazine, atrazine, and simazine was similar in each soil, while prometryne and prometone exhibited greater interactions with the soils. Phytotoxicity and movement of the herbicides in soil were inversely related to extent of adsorption.

The hypothesis that leaf injury from applications of fenuron (3-phenyl-1,1-dimethylurea) is a direct result of a lack of photosynthate did not explain the results of experiments with seedlings of shrub live oak (Quercus turbinella Greene) supplied with an acorn food reserve supplemented with glucose solution, and with seedlings whose acorns were excised or left attached to the seedlings. An alternate hypothesis is offered: acute leaf injury from phenylurea treatment is due to one or more components of the electron transport chain, between the chlorophyll b pigment system and the reduction of triphosphopyridine nucleotide, which are left in a toxic oxidized state as a result of the phenylurea block in the oxygen-liberating system. Evidence also favors the above interpretation rather than the idea that toxicity results from the accumulation of a toxic oxidized product on the oxygen-liberating pathway. Although leaf injury appears to be due to toxic components of the inhibited photosynthetic apparatus, the ultimate cause of death of the entire plant is starvation.

Besides its effect on photosynthesis, fenuron at high concentrations also causes inhibition of root growth.

Results were based on plant response with light levels in energy units, in accord with use of the spectrum by plants. Dry weight yields of control plants, and reductions of yields by 2,4-dichlorophenoxyacetic acid (2,4-D) below those of control plants were greatest in red light, followed by pink, yellow, white, green, and blue light, in that order. Sucrose mixed with 2,4-D or applied alone to plants altered the combined light-herbicide effect but little. Differences in concentration of 2,4-D affected respiration more than photosynthesis, as measured by CO2 exchange under different light qualities. In spectral effects, pink light caused greatest reduction of photosynthesis by 2,4-D at 500 ppm, while greatest promotion of respiration occurred under red light with 2,4-D at 1000 ppm.

The initial and residual toxicities, after 13, 22, and 31 weeks, of dimethyl 2,3,5,6-tetrachloroterephthalate (DCPA), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), 3-(hexahydro-4,7-methanoindan-5-yl)-1,1-dimethylurea (norea), 2,4-bis(isopropylamino)-6-methylmercapto-s-triazine (prometryne), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) were determined in the greenhouse in four soil types by an oats bioassay. DCPA caused the least oat injury initially, and also after 13 weeks. None of the herbicides persisted in amounts toxic to oats for as long as 22 weeks when applied at concentrations approximately equivalent to field rates necessary for weed control. The residual toxicities of these same herbicides, after 22 weeks or longer, were also determined in Bosket silt loam collected from two depths in two preplanting subsurface and two preemergence surface field experiments by using oats, cotton and / or soybeans as bioassay indicators. Results from field applications at rates recommended for weed control in cotton confirmed that neither DCPA, diuron, norea, nor trifluralin persisted in amounts toxic to oats, soybeans, or cotton; however, prometryne residues were moderately toxic to oats and soybeans. Prometyrne residues from a 4 lb/A non-incorporated subsurface treatment were nearly twice as toxic to oats 25 weeks after application, as were residues from the same amount applied as a surface preemergence treatment.

Ethyl N,N-dipropylthiolcarbamate [EPTC] inhibited the deposition of external foliage wax of cabbage (Brassica oleracea L. var. capitata, L.). Wax inhibition was correlated directly with the rate of application of EPTC. Differential inhibition of wax deposition showed that foliage waxes were important in inhibiting the penetration and absorption of the alkanolamine salts of 4,6-dinitro-o-sec-butylphenol [DNBP]. Several other thiolcarbamates also altered the susceptibility of treated plants to subsequently applied herbicides. When EPTC was applied as a spray, only leaves then in the bud were affected. Leaf primordia developed later were not affected. Granular applications of EPTC extended the period during which the formation of foliage wax was inhibited. The reduction of foliage wax resulted in increased spray retention and decreased contact angle of spray droplets. EPTC increased the transpiration rate proportionally to its rate of application.

Soil samples were taken from 32 commercial cotton fields of the mid-south which had been treated with one or more practical applications of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron)2 every year for the past 4 to 8 years. These samples showed no phytotoxic residues in laboratory and greenhouse studies conducted approximately one year after the last application. Cotton seed samples from eight of these fields were analyzed, and none contained a detectable residue of diuron or any of its breakdown products. Diuron degradation in soil under field conditions was demonstrated by isolation and identification of the intermediate breakdown products: 3-(3,4-dichlorophenyl)-1-methylurea, 1-(3,4-dichlorophenyl)urea, and 3,4-dichloroaniline.

Cotton plants were treated with 2,4-D-2-C-14 (2,4-dichlorophenoxyacetic acid) applied with pentachlorophenol and arsenic acid. Seed kernels and regrowth leaves were extracted and various components of the extracts were applied to leaf surfaces and injected into the stems of cotton seedlings. Results indicated that 2,4-D itself and/or a metabolite of 2,4-D, were responsible for the persistence of the 2,4-D stimulus in cotton.

When 2-(2,4,5-trichlorophenoxy)propionic acid-1-C14 (silvex) was applied to Opuntia polyacantha Haw. (prickly pear), pad absorption, root absorption, and translocation were low. The rate of translocation, as measured by acid fuchsin movement, was one cm per hour, about one tenth that found in soybean. Increasing the temperature from 21 to 32 C only slightly increased root absorption and upward translocation of silvex. Pre-treatment of a prickly pear pad, either with a 4% 2,2-dichloropropionic acid solution or mechanical removal of the cuticle, increased the absorption and translocation of subsequently applied silvex. The decarboxylation of silvex was 2 to 3 times greater in soybean than in prickly pear plants. Sixteen days after silvex was applied to prickly pear, four C14-metabolites were found in addition to unaltered silvex.

The phytotoxicity from preemergence applications of the herbicides 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), isopropyl N-(3-chlorophenyl) carbamate (CIPC), 2-chloroallyl diethyldithiocarbamate (CDEC) and 2-chloro-N,N-diallylacetamide (CDAA) was measured at 17 field locations in the coastal plain of North Carolina over three years. Site selections were made with specific regard for soil organic matter, which varied from 0.7 to 48.8 percent. Phytotoxicity responses determined at four to five weeks after treatment were the amounts of herbicide required to cause a 50 percent reduction in (1) soybean dry shoot weight, (2) cotton dry shoot weight and (3) number of weedy annual grasses. Fourteen factors were measured at each location to characterize soil, climatic and biotic factors, and correlated with plant responses obtained. For simazine, diuron and CIPC the factors measured accounted for 60 percent of the plant response variation. The highest simple correlation was usually between soil organic matter and plant response. Phytotoxicity of the aromatic herbicides was inversely correlated with soil organic matter level. CDAA and CDEC usually gave reliable and repeatable performance at constant rates on soils containing between 3 and 40 percent soil organic matter. Below 3 percent soil organic matter, extreme variation in CDAA and CDEC toxicity was encountered.

Imopea purpurea (L.) Roth and /. hederacea (L.) Jacq. significantly and equally reduced soybean yields and plant height, and increased lodging and the difficulty of harvesting. Damage to soybeans increased as the population of morningglories increased. Control of morningglories was needed for 6 to 8 weeks from the date of soybean planting. Morningglories germinated throughout the season and emerged from a depth of 6 inches below the soil surface.

A substantial movement of sugar from alfalfa (Medicago sativa L.) to dodder (Cuscuta sp.) was noted in all experiments, while autoradiograms indicated little or no movement from the parasite to the host. Even when metabolic activities in the host were limited, dodder continued to withdraw sugars from the host.

Carrot (Daucus carota L. var. Imperator) seeds were planted in soil treated with amiben-C14 at 3 and 6 lb/A. Plants were harvested after 69, 103, and 191 days, autoradiographed or analyzed for the radioactivity in the 80 percent ethanol soluble fraction and in the insoluble fraction. The highest concentration of radioactivity was on or near the surface of the roots, but some radioactivity was present throughout the leaves and roots. The concentration of radioactivity decreased with time both in the soluble fraction and insoluble fraction of the root; in contrast it decreased in the insoluble fraction and increased in the soluble fraction of the leaves.

Disks of carrot root were placed in an aerated solution of amiben-C14. After 6 days, only 18.7 percent of the amiben remained unaltered. About 4 percent of the radioactivity was released as C14O2; 64.3 percent was present in an unknown compound which may contain a sugar moiety; the remaining 11.8 percent was distributed among four additional unknown compounds.

Opuntia laevis or O. polyacantha (prickly pear) plants exhibited little water loss, exceptional viability, low nutrient requirements for growth, slight photosynthetic activity, slow translocation, and low transpiration rate as compared with corn or soybean plants. The limited number of stomata, thick wax cuticle, and high water binding ability of cell mucilage in prickly pear are largely responsible for the aforementioned physiological characteristics. These studies show that prickly pear pads, which are modified stems, are not efficient organs for metabolic activities. Water extracts of prickly pear tissue applied to corn seeds were found to induce pronounced growth stimulation of corn seedlings.

Internal dormancy (the state of internally arrested growth) in western ironweed (Vernonia baldwini Torr.) buds consisted of a recurring annual cycle of high and low activity with transition periods. Trends in sprouting activity were similar regardless of whether activity was measured by sprouting of buds following removal of stems in the field, or by sprouting of rhizome section buds in moist sand. Bud activity measurement was quantitatively different by the two methods, however, and the apparent period when internal dormancy developed also differed. A number of interdependent factors modified activity. At various points in the cycle, the stem apex inhibited bud growth; the stem alone inhibited bud growth; a transient block due to immaturity occurred in some buds; and two temperature-related blocks occurred. Bud age and location on the rhizome had little effect on activity. During the period of internal dormancy, sprouting of buds apparently stimulated activity of adjacent buds. Temperature greatly affected expression of internal dormancy; prolonged moist cold treatment eliminated it.

We developed a technique for obtaining buds which were alike except for the state of dormancy, and measured aerobic respiration and enzyme activities in internally dormant, and active but non-growing, buds of western ironweed (Vernonia baldwini Torr.). In both types of buds respiratory quotient was centered at about 1.2, and slightly higher in the active buds. Respiration rate paralleled specific malic dehydrogenase activity; both were lower in dormant than in active buds. Specific peroxidase and polyphenol oxidase activities did not differ markedly in dormant and in active buds. Respiration rate and all enzyme specific activities increased markedly when active buds were permitted to grow.

In the greenhouse, picloram (4-amino-3,5,6-trichloropicolinic acid) prevented germination of side-oats grama [Bouteloua curtipendula (Michx.) Torr.,] big bluestem (Andropogon gerardi Vitman), switchgrass (Panicum virgatum L.) and blue grama [Bouteloua gracillis (HBK) Lag.] when applied preemergence. When applied at 1.5 lb/A or more at the two-leaf stage in the greenhouse and field, picloram significantly reduced plant numbers of all species. Of the four species big bluestem appeared to be the most tolerant to picloram in the seedling stages. Germination was reduced when 2,4-D (2,4-dichlorophenoxyacetic acid) was applied preemergence to side-oats grama and the plant numbers of this species and switchgrass were reduced when treated at the two-leaf stage.

The application of picloram to established native range did not reduce forage production or desirable plant frequency. All treatments reduced forb production. Picloram gave very good control of western yarrow (Achillea lanulosa nutt.), white heath aster (Aster ericoides L. nutt.), and western ironweed (Vernonia baldwini Torr.). White sage (Artemisia ludoviciana nutt.) was resistant to 4 lb/A of picloram.

The relationship of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] decomposition to microbial activity in two soils was determined. Microbial responses to temperature, added energy material, and time were measured by evolution of CO2 from herbicide-treated soil samples. Evaluation of herbicide decomposition was made by bioassay and radioassay. Herbicide inactivation was directly related to metabolism of soil organic carbon. Larger amounts of herbicide were inactivated per unit of soil carbon metabolized in Norfolk loamy sand than in Decatur clay loam. This was associated with less soil specific surface and consequently greater concentration of herbicide on soil particle surfaces in Norfolk compared to Decatur soil. Addition of microbial energy sources accelerated decomposition of atrazine and diuron in both soils. Herbicide decomposition was closely associated with repeated additions of energy material, indicating an incidental or nonpreferential involvement in microbial metabolism. Decomposition of atrazine doubled with each 10-degree rise in temperature from 10 to 30 C, paralleling the response of soil organic matter decomposition. Diuron decomposition approximately tripled with each 10-degree rise in temperature.

Where sugar beets followed the year after one year's use of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine), the carryover, measured by beet response was correlated with the time, the method, and the rate of atrazine used, and the time of plow-down. Where beets were the second crop after an atrazine application, carryover was correlated with the rate of application only. Carryover was greatest following two consecutive years' use of atrazine. Sugar beets were more sensitive to atrazine than were soybeans, navy beans, or oats.