The absorption and translocation of 14C-labeled α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione methazole from nutrient solutions of various temperatures by (Arachis hypogaea L. ‘Starr’) seedlings were determined. The accumulation of trifluralin in roots at 24 hr after exposure to trifluralin was greatest at 21 C and decreased at higher temperatures up to 38 C. The amounts of trifluralin translocated and accumulated in hypocotyls, tops, and cotyledons were small but generally increased with temperature. The initial rate of absorption of trifluralin was greater in excised lateral root tips than in tap root tips, but there was a greater accumulation in excised tap roots at 24 hr. The initial rates of absorption were higher for excised lateral roots at high temperatures. Total absorption of trifluralin at equilibrium was not proportional to the initial rates of absorption but was highest at low (21 C) and high (38 C) temperatures for excised lateral roots. The absorption of methazole by roots and translocation to other plant parts increased linearly with temperature, and it tended to accumulate in the mature leaf tissue.

Preplanting treatment of filter paper or soil containing α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) with any of a wide variety of plant lipids prevented the phytotoxic action of the herbicide in laboratory situations. The protective action of externally applied lipids was attributed to preventing sorption of trifluralin by seedlings. However, protection by internal lipids also appeared likely. A significant correlation (1% level) was demonstrated between seedling sensitivity to trifluralin and the lipid content of dry seeds of 11 weed and crop species. Artificially induced increases in the internal lipid content of wheat (Triticum aestivum L. ‘Mediterranean’) seed resulted in greater tolerance of seedlings to trifluralin. Therefore, it is hypothesized that selective phytotoxicity of trifluralin to young seedlings is determined in part by the amount of endogenous lipids available to trap trifluralin and keep it from its site of phytotoxic action. Tolerance above that predicted from seed lipid content was observed in a twelfth species of the study.

The competitiveness of 10 soybean [Glycine max (L.) Merr.] cultivars to weeds, their tolerance to twice normal rates of commonly used soybean herbicides, and the soil residual properties of these herbicides were studied during 4 years at Lincoln, Nebraska. Three soybean cultivars showing the least percentage yield loss from weeds were ‘Harosoy 63′, ‘Amsoy’, and ‘Corsoy’; whereas cultivars showing the greatest yield loss were ‘Hawkeye 63′, ‘Shelby’, and ‘Lindarin 63′. The two herbicide treatments causing the greatest average soybean yield loss were 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) at 4.5 kg/ha and α,α,α-trifluro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) at 2.2 kg/ha. Cultivar selection was important in reducing soybean yield loss from herbicides as linuron at 4.5 kg/ha reduced yields 5% for ‘Harosoy 63’ to as much as 31% for ‘Ford’. ‘Neal’ oat (Avena saliva L.) yields showed 4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline (nitralin) to be the most persistent herbicide in soil in this study followed by trifluralin. Plowing the soil eliminated the phytotoxicity of nitralin and trifluralin to subsequently planted oats.

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.

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.

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.

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.

The competitiveness of 10 sorghum [Sorghum bicolor (L.) Moench] hybrids to weeds and their tolerances to commonly used sorghum herbicides were studied across Nebraska. The three best weed competitors in this study were sorghum hybrids ‘RS 671′, ‘RS 690′, and ‘AKS 663′; whereas the three poorest weed competitors were ‘AKS 614′, ‘NB 505′, and ‘RS 633′. Sorghum hybrids showing a significant yield reduction from a 2× rate of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) were ‘SD 441′, ‘SD 451′, and ‘NB 505′. ‘SD 441 also suffered a significant yield reduction from a normal rate of 2-chloro-N-isopropylacetanilide (propachlor) applied preemergence plus a 4× rate of (2,4-dichlorophenoxy)acetic acid (2,4-D) applied postemergence. With the above exceptions, sorghum hybrids generally showed considerable tolerance to 2× rates of herbicides commonly used on sorghum.

Samples of the spray pattern delivered by a tractormounted field sprayer were intercepted with 10 petri dishes divided between two heights in each of eight plots sprayed with 1.12 kg/ha of 4-amino-3,5,6-trichloropicolinic acid (picloram). The sprayer produced predictable residues on the intercept plates; no differences occurred between residues collected at ground level and 46 cm above the ground; and no differences occurred between replicate plots. Fractionation and analysis of specific plant parts, whose position relative to direction of spray and surrounding brush had been noted, revealed that the spray system delivered uniform coverage almost regardless of brush orientation.

The relative drift of droplet and vapor of butyl ester and dimethylamine formulations of (2,4-dichlorophenoxy)acetic acid (2,4-D) was determined under conventional crop spraying procedures in the field. Labelled herbicides were mixed with spray solution or emulsion, and the ground deposit and the air-borne droplet and vapor clouds drifting from the target area were collected. The mass of the dimethylamine formulation drifting as droplets was 3 to 4% of the material sprayed. No significant amounts of this material were collected as vapor or particulate drift. For the butyl ester, in addition to the droplet drift, 25 to 30% of the material was collected as vapor drift in the half hour after spraying. Thus the drift potential from the butyl ester was about 8 to 10 times greater than that from the dimethylamine formulation under the conditions of these tests.

Purple nutsedge (Cyperus rotundus L.) control with (2,4-dichlorophenoxy)acetic acid (2,4-D) and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) was increased in greenhouse and growth chamber studies by application of these herbicides in an undiluted isoparaffinic oil carrier rather than water. Two applications of 2,4-D at 2.2 kg/ha in the oil carrier inhibited tuber and shoot production and reduced the number of viable tubers present, but two applications of linuron at 0.6 or 2.2 kg/ha in the oil inhibited only shoot production from repotted tubers. Studies with labeled 2,4-D showed an increase in both rate and quantity of penetration of this herbicide into purple nutsedge when applied in oil rather than water. Labeled linuron was applied to purple nutsedge and to beans (Phaseolus vulgaris L. ‘Improved Tendergreen’) and also showed an increase in penetration with the oil rather than water. Translocation out of treated leaves was not increased for either 2,4-D or linuron by application in the oil carrier.

Preemergence herbicidal activities of 27 3-phenoxypyridazine derivatives were evaluated in pots under upland and submerged conditions. Each of the compounds containing an alkyl or halogen at the ortho position of the benzene ring showed marked herbicidal effects. The activity of some disubstituted compounds carrying one of the substituents at the ortho position was the next. Among the compounds tested, 3-(2-methylphenoxy)-, 3-(2,3-dimethylphenoxy)-, 3-(2,4-dimethylphenoxy)-, and 3-(2,6-dimethylphenoxy)-pyridazines exhibited an excellent margin of selectivity for tomato (Lycopersicum esculentum Mill.), cotton (Gossypium hirsutum L.), soybean (Glycine max (L.) Merr.), and Azuki bean (Phaseolus angularis Wight). For transplanted rice (Oryza sativa L. ‘Norin No. 29′) under submerged conditions, 3-(2-isopropylphenoxy)-and 3-(2-n-butylphenoxy)-pyridazines showed a remarkable margin of selectivity, though the herbicidal activity of both compounds was slightly inferior to that of 3-(2-methylphenoxy)-pyridazine.

Seed fields of white clover (Trifolium repens L. ‘New Zealand’ and ‘Louisiana S-1′) were treated with the dimethylamine salt and the isooctyl ester of 4-(2,4-dichlorophenoxy)-butyric acid (2,4-DB). Rates of application were 0.56, 1.12, and 1.68 kg/ha. Applications were made at the vegetative, bud, and flowering stages of growth. All treatments applied at the vegetative and bud stages of growth significantly reduced white clover seed production. Reductions in clover seed production usually became more severe as the rate of 2,4-DB increased.

Polymerized and conventional (2,4-dichlorophenoxy)-acetic acid (2,4-D), (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T), 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloro-picolinic acid (picloram) were applied alone and in certain combinations to several brush species. Generally there were no significant differences in effectiveness between conventional and polymerized herbicides on honey mesquite (Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockrell), huisache (Acacia farnesiana L. Willd.), Macartney rose (Rosa bracteata Wendl.), live oak (Quercus virginiana Mill.), whitebrush (Aloysia lycioides Cham.), and winged elm (Ulmus alata Michx.). Conventional granular picloram was more effective on yaupon (Ilex vomitoria Ait.) than polymerized formulations.

Three herbicides, 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine), and 3-tert-butyl-5-chloro-6-methyluracil (terbacil), applied annually at 0.45, 0.90, and 1.80 kg/ha for 2 or 3 years to establish forage alfalfa (Medicago sativa L. ‘Ranger’), effectively controlled downy brome (Bromus tectorum L.), tumble mustard (Sisymbrium altissimum L.), and prickly lettuce (Lactuca serriola L.). However, downy brome control decreased to less than half and broadleaf control ceased 18 months after the final herbicide application. Atrazine injured alfalfa most. Usually, annual applications of 0.45 kg/ha did not reduce yield. Greenhouse and field bioassay data indicated that the herbicides leached below the 0 to 32.5 cm soil zone and persisted. Residues were absorbed by roots of crops planted 2 to 3 years after the last application. Injury was similar whether the last application was made 18 or 30 months previously. The order of crop tolerance was sweet corn (Zea mays L. ‘Rugosa’) > potatoes (Solarium tuberosum L. ‘Norgold’) > winter wheat (Triticum aestivum L. ‘Nugaines’) > bush beans (Phaseolus vulgaris L. ‘Humilis’) ≅ sugar beets (Beta vulgaris L. ‘U. & I. hybrid No. 8′).

Volunteer castorbean (Ricinus communis L.) was most effectively controlled by preemergence application of 2-chloro-4,6-bis(isopropylamino)-s-triazine (propazine) at 1.1 to 2.2 kg/ha in grain sorghum (Sorghum bicolor (Moench) L.) and by 1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea (fluometuron) at 1.7 to 2.2 kg/ha in cotton (Gossypium hirsutum L.). Preplant applications of propazine were not as effective as preemergence treatments. Efficacy of soil-applied herbicides was greatest when 1 to 2 cm of rain occurred within 7 to 10 days after application. Effective postemergence treatments on castorbean seedlings with two to eight true leaves were 2-chloro-4(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) at 1.1 to 1.7 kg/ha, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) at 0.9 kg/ha, or 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) at 0.9 kg/ha.

Picloram (4-amino-3,5,6-trichloropicolinic acid) did not influence germination but differentially regulated postgermination growth of range grass seedlings. Radicle elongation of buffalograss (Buchloe dactyloides [Nutt] Elgelm.), sideoats grama (Bouteloua curtipendula [Michx.] Torr.)3, and switchgrass (Panicum virgatum L.) in petri dishes was reduced by 125 ppb picloram, whereas shoot elongation was not retarded by 1,000 ppb. Buffalograss, sideoats grama, and switchgrass seedlings, germinated in soil containing 500 ppb picloram, were usually not reduced in topgrowth production. However, topgrowth production of Arizona cottontop (Digitaria californica [Benth.] Henr.) and vine mesquite (Panicum obtusum H. B. K.) was reduced by 125 to 250 ppb of picloram in soil. Relative tolerance to picloram was ranked buffalograss, sideoats grama>switchgrass>vine mesquite, Arizona cottontop.

Microbial degradation of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) and 2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine (hydroxyatrazine) was investigated in three Oregon soils. Hydrolysis of atrazine was determined by the presence of 14C-hydroxyatrazine in methanol extracts. Respired 14CO2 from the 14C-ethyl side chain of atrazine represented less than 10% of the added 14C in the soils after 28 days. Degradation was dependent on soil type, atrazine concentration, and moisture content. The isopropyl and ring constituents of atrazine were subject to minimal attack. The hydroxyatrazine ring was attacked more readily than the atrazine ring. Hydroxyatrazine accounted for approximately 10% of the extracted 14C from 14C-atrazine-treated Parkdale-A, Parkdale-C, and Coker soils and 40% from the Woodburn soil. Hydrolysis was the dominant pathway of detoxification in the Woodburn soil, whereas detoxification of atrazine in Parkdale-A, Parkdale-C, and Coker soils was a combination of chemical hydrolysis and slow microbial degradation by N-dealkylation of the ethyl side chain constituent.

Purple nutsedge (Cyperus rotundus L.) plants were analyzed for free reducing sugars, free glucose, free plus acid hydrolyzable fructose, phosphorus, and iron. The only sugars detected were sucrose, glucose, and fructose. Sucrose was the most concentrated sugar in the shoots with the greatest concentration in the younger leaves. Sucrose was also the most concentrated sugar in mature rhizomes. Glucose and fructose were the most concentrated sugars in the actively growing rhizomes and tubers. Phosphorus was concentrated in the actively growing leaves and rhizomes, while iron was most concentrated in older tissues including rachises with seedheads, mature shoots, tubers, and rhizomes.

Seedling emergence and growth of downy brome (Bromus tectorum L.), medusahead (Taeniatherum asperum (Sim.) Nevski), and tumble mustard (Sisymbrium altissimum L.) were favored by seed burial, pitting of the soil surface, and soil movement. These conditions maintained temperatures and soil and atmospheric moisture in the range required for establishment.