Laboratory experiments were conducted to determine the fate of 14C-EPTC in a soil that had a history of vernolate application and exhibited accelerated degradation of carbamothioate herbicides compared to nonhistory soil. A very rapid mineralization of the herbicide to 14CO2 was evident in history soil, compared to nonhistory soil. The two soils did not differ in the amounts of the EPTC lost through volatilization or in the nonextractable radioactive fractions. Except for small quantities of EPTC-sulfoxide and sulfone, no other metabolites were detected. Degradation of 14C-EPTC, as determined by evolution of 14CO2 in history soil, was drastically inhibited following soil sterilization by means of autoclaving or gamma irradiation. Soil disinfestation by solarization, methyl bromide, or metham had a pronounced inhibitory effect during the first 6 days, but was less effective than sterilization. Treatment of a history soil with the fungicide 2-methoxyethylmercury chloride and dietholate strongly inhibited EPTC degradation, while thiram and fentin acetate had only short lasting effects. Cycloheximide, an antifungal antibiotic, had little effect on the degradation of EPTC while chloramphenicol, an antibacterial antibiotic, inhibited the herbicide degradation. These results indicate that accelerated degradation of EPTC is linked to the activity of soil microorganisms, e.g. bacteria, and can be controlled by sterilization and chemical treatments.

Regression analysis of clomazone adsorption on 19 soils and sediments yielded a positive correlation and linear relationship between distribution adsorption constants (Kd) and soil organic carbon content. The agreement of the experimental mean Koc with Koc values predicted from the octanol-water partition coefficient and water solubility of clomazone indicated hydrophobic bonding was one mechanism responsible for adsorption. Kaolinite and montmorillonite had a strong affinity for clomazone, and adsorption increased with the charge of the cation on the clay exchange sites. Adsorption was not correlated with the clay content of soils and sediments, indicating that organic coatings on clay in soils may block adsorption sites on clay surfaces. The adsorption of clomazone on some soils and sediments with high clay contents was greater than predicted based on organic carbon content alone, however, indicating clay contributed to adsorption on these samples.

The effect of chlorsulfuron on growth, infective ability, and symbiotic performance of legume bacteria was investigated. Bacterial growth in pure culture was unaffected by the addition of 0.55 and 5.5 μM chlorsulfuron. Early root hair infections of alfalfa by bacteria were inhibited by chlorsulfuron at 0.28 pM but not at 0.0028 pM in the root media. Inhibition of infection resulted from herbicidal effects on the root hair development. When inoculated red clover and alfalfa plants were grown in aseptic cultures in the presence of 0, 5.5, or 55 μM of chlorsulfuron, only 55 μM of herbicide inhibited the development and nodulation of plants. Early emergence and growth of alfalfa plants in soil supplemented with 2 × 10-6, 2 × 10-3, 2, 4, and 8 g/ha of chlorsulfuron were unaffected. However, 5 to 8 days after emergence plants grown in soil supplemented with 4 or 8 g/ha of chlorsulfuron were severely damaged, with no nodules developed. Nodulation occurred in plants grown in soil containing 2 × 10-3, 3 × 10-6, and 2 g/ha chlorsulfuron, but the nitrogenase activity of the nodules of these plants was less than for control plants. Plants grown in soil containing 2 g/ha of chlorsulfuron developed normally only after an initial growth inhibition of 5 to 6 weeks. The inhibition of nodulation and nitrogenase activity of nodules grown in the presence of chlorsulfuron is probably due to adverse effects of the herbicide on plant growth and development rather than on the rhizobia.

Genetic variation within a nonweed (coastal) population of poorjoe was measured in an experimental population subjected to soybean and intraspecific competition for space and light. A sib analysis was used to estimate phenotypic and genetic variance/covariance components of aboveground biomass production and five independent measurements of growth defined by a path-coefficient model. A multivariate analysis of response to selection was applied to predict evolutionary change in the growth measurements in response to selection for performance under soybean and intraspecific space/light competition; sufficient genetic variation was present in the experimental population to allow a rapid response to this selection. Selection under competitive conditions was predicted to cause the nonweed population to emerge earlier, grow faster early in development, change in growth form, and grow faster under a soybean canopy. Most of these changes would increase the resemblance of the selected population to a weed population of poorjoe. However, the growth rate of the selected population under a soybean canopy was predicted to become greater than that actually observed in the present-day weed population. Multivariate analysis of response to selection may be generally useful in predicting evolutionary response of plant pest populations to control practices.

Wax filaments > 100 μm long on the epidermis of johnsongrass leaves and culms occurred only around the edge of costal cork-silica cell pairs and intercostal silica cells. Silica cells alternating with cork cells occurred in rows over veins. Solitary or occasionally paired cork-silica cells occurred between veins. The high silicon content of silica cells was verified with X-ray mapping of silicon. X-ray analysis also indicated that wax filaments contained silicon. Scanning electron micrographs (SEM) of dislodged intercostal silica cells showed that wax filaments emerged from an integument that surrounded the silica cell. It is theorized that at high ambient temperatures the silica gel in silica cells provides the localized cooling necessary to solidify liquid wax constituents as they are extruded onto the surface of the plant.

A population level, two-compartment, temperaturedependent model that predicts date of seedling johnsongrass flowering was formulated. The model consisted of a fourparameter poikilotherm rate equation to describe development rate as a function of temperature and a temperature-independent Weibull function to distribute flowering times for the population. Experiments were conducted to determine the effect of temperature, nitrogen availability, and water availability on development of seedling johnsongrass. Development was most sensitive to temperature while the effect of nitrogen concentration and water availability was minimum and inconsistent. The model was tested against three independent field data sets and provided accurate prediction of flowering dates for each data set.

Spraying with tank mix combinations of the fungus Colletotrichum coccodes and the plant growth regulator thidiazuron increased mortality, decreased biomass and height of velvetleaf, and increased soybean yield in field experiments. The velvetleaf isolate of C. coccodes was compatible with thidiazuron, and tank mix combinations consistently improved control over either component alone. In the moist 1986 season the fungus and the growth regulator interacted synergistically to increase velvetleaf mortality. In the drier 1987 season no significant interaction was detected between the two components.

The effects of the plant growth regulator thidiazuron and the plant pathogen Colletotrichum coccodes on ethylene synthesis by velvetleaf and prickly sida were investigated. Untreated velvetleaf seedlings produced 1.5 and 2.3 pmol ethylene/mg fresh weight 24 and 48 h after treatment. Treatment with thidiazuron at 200 g ai/ha or C. coccodes at 1 × 109 spores/m2 increased ethylene production by 4.9 and 3.5 pmol/mg, respectively, in 24 h; and by 10.6 and 15.8 pmol/mg, respectively, in 48 h. Combination treatments caused synergistic increases in ethylene production by velvetleaf seedlings of 17.7 and 49.6 pmol/mg in 24 and 48 h, respectively. Thidiazuron at 10 μM, combined with an extract of C. coccodes mycelia, increased ethylene synthesis by more than 4-fold in vacuum-infiltrated excised velvetleaf petioles within 48 h. Thidiazuron at 50 g/ha, combined with an extract of C. coccodes mycelium, increased ethylene synthesis 16-fold in prickly sida seedlings in 24 h. Aminocyclopropane carboxylic acid (ACC), a precursor of ethylene, stimulated ethylene production by velvetleaf petioles more than 8-fold when supplied at 0.75 mM; thidiazuron and the pathogen effects were not discernible in its presence. Aminoethoxyvinyl-glycine (AVG), an inhibitor of ACC synthase, inhibited overall ethylene production by velvetleaf seedlings more than 40% when supplied at 0.58 to 0.67 mM, without obscuring the stimulatory effects of thidiazuron and the pathogen. These results indicate that the growth regulator and the plant pathogen or an extract of the pathogen act in concert to increase ethylene synthesis in velvetleaf. Stimulation probably occurs before the synthesis of ACC in the ethylene biosynthetic pathway.