Over a 3-year period, pigweed (Amaranthus sp.) was successfully controlled in grain sorghum (Sorghum bicolor (L.) Moench) with preemergence aerial application of 2-chloro-4, 6-bis(isopropylamino)-s-triazine (propazine) and postemergence application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) in 4.7 to 47 L/ha of various carriers. Equally good pigweed control was obtained with ground application of the herbicides with as little as 37 L/ha carrier. Liquid formulations of the two herbicides gave results comparable to an 80% wettable powder formulation.

Greenhouse and field studies were conducted with 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron). Tolerant soybean (Glycine max (L.) Merr.) and susceptible tall morningglory (Ipomoea purpurea (L.) Roth.) and ivyleaf morningglory (I. hederacea (L.) Jacq.) were studied with both root and foliar chloroxuron applications. Soybean tolerance to chloroxuron was reduced when treatments occurred in the unifoliate stage; greatest soybean tolerance was noted when soybeans were treated in either the cotyledonary or third trifoliage stage. Tall and ivyleaf morningglory were susceptible to chloroxuron until about 21 days of age (five true leaves), after which resistance increased. Root applications of chloroxuron were more phytotoxic than foliar applications for soybeans and both species of morningglory. In a 3-year study in the field, the following sequential herbicide treatments of either α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin), 4-(methylsulfonyl-2,6-dinitro-N,N-dipropylaniline (nitralin), S-propyl dipropylthiocarbamte (vernolate), or 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) applied preemergence plus chloroxuron postemergence resulted in higher soybean yields than any single herbicide treatment. Weed control was better with the sequential combinations. All sequential combinations with chloroxuron caused soybean injury. Greatest soybean injury occurred when chloroxuron was applied in the first and second trifoliate stage than in the third trifoliate stage. Vernolate alone caused some injury in certain years.

Seedlings of switchgrass (Panicum virgatum L. ‘Blackwell’), sideoats grama (Bouteloua curtipendula [Michx.] Torr. ‘Premier’), and native vine mesquite (Panicum obtusum H. B. K.) tolerated 0.28 kg/ha of 3,6-dichloro-o-anisic acid (dicamba) applied preemergence. After emergence, sideoats grama tolerated 0.56 kg/ha dicamba. Preemergence or postemergence applications of 1.12 and 2.24 kg/ha severely retarded shoot production of all three species. Soil residues in the surface 2.5 cm reduced root production of grass seedlings, whereas placement of dicamba 7.6 or 15.2 cm deep was not detrimental. All grass species germinated and grew for 21 days in soil containing up to 63 ppb of dicamba without reduction in shoot production. Overall order of susceptibility to dicamba was ranked as vine mesquite > switchgrass > sideoats grama.

Over a 2-year period no treatment differences were noted in 4-amino-3,5,6-trichloropicolinic acid (picloram) concentrations recovered from grass and yaupon (Ilex vomitoria Ait.) tissues treated with 1.12 kg/ha of picloram in mixture with dimethyl sulfoxide (DMSO) and surfactant (X-77).4 Less than 1 μg of picloram per gram of fresh weight of grass or yaupon was present in aerial tissue 6 months after treatment, in yaupon stem tissues 1 month after treatment, and in yaupon root tissue 5 days after treatment. Tissues sampled 1 year after treatment were devoid of picloram residue; tissues sampled 1 year after retreatment had levels ranging from 0.04 to 0.26 μg/g. The April application of 1.12 kg/ha of picloram plus 5.0% X-77 plus 10.0 or 25.0% of DMSO produced more effective canopy reduction of yaupon 1 year after treatment than did other herbicide treatments or dates of treatment. Increased canopy reduction by retreatment the second year suggests that X-77 rather than DMSO was the effective component in the spray mixtures.

Vapor of a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-loluidine (trifluralin) emitted from soils was collected in xylene and assayed by gas chromatography. Increasing the trifluralin application rate in soil surface treatments from 0.56 to 4.48 kg/ha resulted in substantial increases in vaporization from soils during the 2 hr immediately after treatment. Increasing the spray volume from 2.34 to 300 kl/ha with water reduced the rate of trifluralin vapor emission by approximately half. When trifluralin was applied as a spray (2.34 kl/ha) and then incorporated into soils of varying moisture contents, 4 to 10 times more trifluralin volatilized in 12 hr than when it was percolated into air-dry soils with sufficient water to yield equivalent soil moisture contents. The techniques employed were not sufficiently sensitive to detect trifluralin vapor loss occurring more than 12 hr after treatment. The amount of trifluralin lost during the first 12 hr was less than 5% of that applied to the soil, even under the most favorable conditions for volatilization.

Seeds of six weed species were buried in the field at depths of 2.5, 7.6, and 15.2 cm. Seed germination after various light and temperature treatments was determined before burial and after recoveries in darkness at 3-month intervals over 12 and 20-month periods. In one experiment the five species studied were ungerminable before burial. After 6 months burial, most species responded to light but became ungerminable again after this time. These results suggest cycles of dormancy where seeds pass from total dormancy at maturation to a phytochrome-controlled dormancy after burial and then return to total dormancy. During the phytochrome-controlled dormancy period, some species were highly light sensitive. In another experiment the response of yellow rocket (Barbarea vulgaris R. Br.) seeds to thirteen light and temperature treatments was determined before and after burial. Without light treatment, germination of the recovered seeds at various temperatures was low. Germination was usually high after brief exposures to red light, particularly in seeds recovered from 15.2 cm. Very large increases in germination were induced by light exposures of 3 × 10−9 Einsteins cm−2 incident in the 600 to 680-nm region (1 sec). The evidence suggests changes in total phytochrome (Ptot) are responsible for a seasonal change in light sensitivity and a previously undescribed type of dormancy.

Nineteen different genera of weeds encompassing twelve plant families were surveyed for hydrolytic enzymes which were able to metabolize the amide bonds in several groups of herbicides. Propanil (3′,4′-dichloropropionanilide), 1,1-dimethyl-3-phenylurea (fenuron), and isopropyl carbanilate (propham) were employed as enzyme substrates, representing the amide, urea, and carbamate classes. Propanil was hydrolyzed at widely diverse rates by approximately 70% of the plants tested. Only one plant showed a hydrolysis of propham and fenuron. The study demonstrates a widespread distribution of hydrolytic enzymes capable of degrading the herbicide, propanil. An apparent lack of hydrolytic enzymes able to metabolize propham and fenuron was also noted.

Delayed planting or “stale seedbed” for weed control in close-drilled (20-cm rows) soybeans [Glycine max (L.) Merr. ‘Amsoy’] was evaluated for 3 years. The system combined final seedbed preparation 3 to 6 weeks before planting with herbicide application at planting time. The best control of six weed species and highest soybean yields were obtained by a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) application at the time of seedbed preparation followed by 3-(3,4-dichlorophenyl)-1-methylurea (linuron) application at planting and by linuron application at planting without the early trifluralin application. Applications of 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) at planting, either with or without trifluralin treatments, resulted in less weed control and lower soybean yields than comparable treatments with linuron. However, even the best treatments failed to provide the weed control necessary to prevent substantial soybean yield reduction in heavy infestations of weeds that emerge in large numbers after planting, and that resist the phytotoxic action of the herbicides.

Fenac [(2,3,6-trichlorophenyl)acetic acid] and 4-amino-3,5,6-trichloropicolinic acid (picloram) at 28 and 2.2 kg/ha, respectively, controlled woollyleaf bursage (Franseria tomentosa Gray) for 3 years in noncropped areas. Effective control of woollyleaf bursage was obtained when treated at the bud stage or earlier with an ester formulation of (2,4-di= chlorophenoxy)acetic acid (2,4-D) at 2.2 kg/ha or 3-amino-s-triazole (amitrole) at 4.5 kg/ha in an oil-water emulsion carrier or 3,6-dichloro-o-anisic acid (dicamba) at 2.2 kg/ha in a water carrier with 0.5% surfactant. Picloram, at 0.44 kg/ha or more, controlled woollyleaf bursage at any time of application.

The foliar uptake of 4-amino-3,5,6-trichloropicolinic acid (picloram) and its phytotoxicity in mixtures with several phenoxy herbicides were studied using bean (Phaseolus vulgaris L. ‘Red Kidney’). The greatest accumulation of picloram occurred in the growing point, stem, and axillary buds. Transport from the treated leaf occurred within 6 hr and continued for at least 7 days. The effectiveness of herbicide combinations containing picloram was related to the particular plant part measured. A synergistic reduction in fresh and dry red kidney bean weight was obtained with (2,4-dichlorophenoxy) acetic acid (2,4-D) or 2-[(4-chloro-o-tolyl)oxy]propionic acid (mecoprop) when applied in combination with picloram, whereas 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) and picloram gave an antagonistic response. An investigation of the antagonistic reaction of 2,4-DB with picloram indicated that picloram prevented the movement of 2,4-DB, while 2,4-DB increased both the distribution and the amount of picloram translocated from the point of application.

A higher population of common purslane (Portulaca oleracea L.) developed on a smooth seedbed than a rough seedbed. Purslane germinated best when the seed were placed on the soil surface, and the percentage germination decreased progressively as depth of seed placement increased. Growth of common purslane was greater at elevated nutrient levels and was dependent on adequate phosphorus in the nutrient media. High soil temperature requirements for optimum germination make common purslane a middle to late-growing season weed in the central United States. Often preemergence herbicides which are effective on common purslane have become ineffective by the time the common purslane population has developed, and postemergence herbicides which do not injure the individual crop species must be relied on for common purslane control.

Soil residue levels were studied to a depth of 2.4 m for a period of 2 years after application of 1.12 kg/ha of 4-amino-3,5,6-trichloropicolinic acid (picloram). Thirty days after application 93 ppb were recovered in the top 15 cm of soil. Residues were less than 5 ppb at depths of 46 to 122 cm. Six months after application, residues were between 5 and 10 ppb down to 183 cm and less than 5 ppb between 198 and 244 cm. Residues to depths of 244 cm were less than 5 ppb 1 year after treatment. Residue levels to similar depths were studied in two soil types for a period of 1 year after application of conventional and polymerized picloram sprays and granules (3.4 kg/ha of picloram). Conventional sprays resulted in significantly higher soil residues for the sampling period than polymerized sprays. Residues from polymer granules were likewise significantly greater than from polymer sprays. Conventional and polymer formulations were identical with respect to movement through the soil.

Removal of nitrogen and phosphorus by waterhyacinth [Eichhornia crassipes (Mart.) Solms] in static and flowing water was investigated. Milligrams of phosphorus absorbed per plant per day in static water averaged 1.1, 2.1, 3.1, and 1.6 in 10, 25, and 50% Hoagland's solution and in sewage effluent, respectively, while in flowing water the values were 1.7, 2.5, and 3.3 for 10, 25, and 50% Hoagland's solution. Milligrams of nitrogen absorbed per plant per day from these same solutions averaged 5.3, 11.4, 19.8, and 6.6 from static water and 9.9, 18.4, and 20.8 from flowing water. Transpiration per plant per day averaged approximately 175 mi in static water and 225 ml in flowing water. One hectare of waterhyacinth plants under optimum conditions could absorb the average daily nitrogen and phosphorus waste production of over 800 people.

Absorption, translocation, metabolism, and action of 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid (endothall) in annual bluegrass (Poa annua L.), Kentucky bluegrass (Poa pratensis L. ‘Merion’), and creeping bentgrass (Agrostis stolonifera L. ‘Penncross’) were studied. Selective action on annual bluegrass from root applications of endothall was attributed to differences in absorption and action of the herbicide. Morphological differences among species, spray retention, and endothall action contributed to selectivity following foliar applications.

The leaching of α,α,α-trifluoro-2,6-dinitro-N,N,-dipropyl-p-toluidine (trifluralin) and 3,5-dinitro-N4,N4-dipropylsulfanilamide (oryzalin) with and without surfactants was studied in soil columns. In dry soil without surfactants leaching of trifluralin was less than that of oryzalin and did not amount to more than a few centimeters despite the use of light soil and large amounts of herbicide. In wet soil trifluralin leached more than twice as deep as in dry soil with the same amount of water. The addition of surfactants at a concentration of 2% of the spray volume increased both depth of water penetration and herbicide movement into the soil. The most pronounced effect of surfactants was the increase in movement of trifluralin in dry soil, but they also increased trifluralin movement in wet soil. There was no direct relationship between the ability of the surfactants to improve water penetration and their effects on leaching of the two herbicides. It was therefore concluded that increased leaching was due to an effect of surfactants on the sorption-desorption balance rather than on improved penetration of water. The improved movement of trifluralin into the soil as a result of surfactant action was also evident from another experiment in which surfactants increased the herbicidal activity of trifluralin sprayed preemergence on the soil surface.

The germination responses of seeds from 11 weed species to various chemical and physical treatments were studied. Germination of nine species was promoted by gibberellic acid and inhibited by abscisic acid, suggesting that germination of some weed seeds may be controlled by appropriate levels of these substances. Most of the weeds that germinated better after a hot-water soak treatment responded to sonication and infrared treatment, indicating that temperature was a factor in the germination response obtained with these methods, although physical disruption of the seed coat also was involved.

Microscopic examination of central and soft offset bulbs of wild garlic (Allium vineale L.) at senescence of the parent plants in May and June revealed embryonic plants with numerous root primordia and four or five shoot primordia. Hardshell bulbs and aerial bulblets contained only one or two root primordia and three leaf primordia. The embryonic plants of central, soft offset, and hardshell bulbs elongated slowly during the after-ripening period. Rapid cell division, cell elongation, and initiation of new leaves took place after termination of the after-ripening period in all but the dormant hardshell bulbs. In November, new hardshell bulbs could be seen at the base of plants developed from central and soft offset bulbs.

Endothall (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid) was evaluated for controlling annual bluegrass (Poa annua L.) infestations in Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis stolonifera L.) turfs. Growth of annual bluegrass was selectively suppressed by three applications of 0.6 kg/ha of endothall, two or three applications of 1.1 and 2.2 kg/ha, and one application of 4.5 kg/ha made to the single plant sand cultures. Field treatments were variable and seasonably dependent. Endothall selectively killed annual bluegrass when applied to roots in sand culture at a concentration of 2.7 × 10−4 molar. A granular formulation of endothall provided selective control of annual bluegrass in field and greenhouse studies. High watering frequency prior to application, low organic matter content of the underlying soil, and predominance of the annual biotype of annual bluegrass enhanced the selective action at the lowest rates of endothall application.

Wild cane (Sorghum bicolor (L.) Moench) absorbed equal amounts of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine). The plants metabolized 70% of the atrazine and 30% of the simazine absorbed and translocated to the shoot during 24 hr. The major metabolites formed were hydroxyderivatives and very hydrophilic metabolites which were chromatographically identical to peptide conjugates of atrazine, e.g., S-(4-ethylamino-6-isopropylamino-s-triazinyl-2)-glutathione and S-γ-L-glutamyl-(4-ethylamino-6-isopropylamino-s-triazinyl-2)-L-cysteine. Wild cane formed peptide conjugates of atrazine more rapidly than of simazine, but hydroxylation of these s-triazines occurred at approximately the same rate.

Runoff water was sampled over a 2-year period from an 8-ha site that had been treated and retreated with 4-amino-3,5,6-trichloropicolinic acid (picloram) at the rate of 1.12 kg/ha in the spring of 1969 and 1970. Runoff water was sampled adjacent to the plots and in two creek systems up to 2.0 km from the plots. Samples taken adjacent to the plots declined to less than 10 ppb by 10 to 12 weeks after application. Eight days after application, water sampled 1.2 km from the plots contained less than 1 ppb of picloram. Less than 1.0 ppb levels were occasionally detected 1.6 km from the plots 8 months after treatment.