The effect of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] and gibberellic acid (GA3) on increase in length of corn (Zea mays L.) epicotyl segments and the interactions between alachlor (0, 5 × 10-6, 5 × 10-4, 4.4 × 10-4, and 5 × 10 M) and GA3 (0, 1 × 10-6, 2.8 × 10-4, and 1 × 10-4 M) were investigated. Alachlor significantly inhibited growth of these segments while GA3 usually increased growth. GA3 in combination with alachlor caused a significant increase in growth compared to alachlor alone resulting in growth comparable to that occurring in untreated tissues. The magnitude of GA3 induced growth in the presence of alachlor depended upon the concentrations of the herbicide and GA3 employed. Alachlor was, however, able to inhibit the GA3 induced growth. The maximum degree of growth inhibition resulted from exposure of the segments to alachlor with or without GA3 from the start of incubation. This inhibition decreased as the exposure to alachlor was delayed. Alachlor started inhibiting growth in the presence of GA3 after the first 9 hr of incubation and after the first 21 hr of incubation in the absence of GA3.

Phytotoxicity of herbicides in water was measured before and after exposure to gamma radiation from a 60Co irradiator. Chromatographic methods and bioassays were used to measure alterations that occurred during 60Co exposure. Phytotoxicity of picloram (4-amino-3,5,6-trichloropicolinic acid and trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) solutions was reduced even with the lowest dose of 60Co, 1.7-megarad (Mrad). Alterations in phytotoxicity of atrazine (2-chloro-4-ethylamino-6-esopropylamino-s-triazine) and dicamba (3,6-dichloro-o-anisic acid) solution occurred only at 5 Mrad, which was the highest dose used. The phytotoxicity of atrazine solutons increased with the 5-Mrad irradiation. Thin layer chromatography (TLC) data showed that all herbicides were altered by 60Co irradiation. Several products resulted when trifluralin was irradiated.

Benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) applied as a preplant incorporated treatment followed by application at the ground-cracking stage (GC) of a mixture of alachlor [(2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] plus naptalam (N-1-naphthylphthalamic acid) and dinoseb (2-sec-butyl-4,6-dinitro-phenol) significantly increased the yield of peanuts (Arachis hypogaea L. ‘Florunner’). Delaying treatment with the GC mixture for 10 days did not significantly depress peanut yields when averaged over all soils, although exceptions occurred within soil series. Substantial and consistent yield reductions occurred when the herbicide sequences terminated with five repeated applications of dinoseb, especially on the Ruston soil. Late planted peanuts often were more susceptible to intensive herbicide treatments than the early plantings. Beginning intensive sequential treatments with vernolate (S-propyl dipropylthiocarbamate) reduced yields more than when benefin initiated the sequence. Average yields of Florunner peanuts were increased significantly by the insecticide disulfoton (O,O-diethyl S[2-(ethylthio)ethyl]phosphorodithioate) on the Greenville and Ruston soil series, but not on the Dothan soil. The disulfotan x herbicide interaction was not significant. Herbicides interacted more frequently with planting date, treatment time, soil series, and year than did disulfoton.

Inhibition and subsequent recovery of net CO2 exchange (NCE) by single leaves of 53 grass species of the subfamilies Festucoideae, Panicoideae, and Eragrostoideae was monitored following limited root uptake of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Rates of NCE recovery were correlated with rates of 14C-atrazine metabolism in leaf sections of festucoid and panicoid grasses but not eragrostoid grasses. Rates of NCE recovery among the nine festucoid and 12 eragrostoid species tested did not exceed 0.2 and 1.1 mg CO2 per dm2 per hr/hr, respectively, whereas for the 31 panicoid species, it ranged from 0.2 to 2.4 mg CO2 per dm2 per hr/hr. Selected species exhibiting NCE recovery rates exceeding 1.2 mg CO2 per dm2 per hr/hr were tolerant to 1.0 kg/ha preemergence and 1.25 kg/ha postemergence atrazine applications. These panicoid species included a number of common weed species belonging to the genera Digitaria, Panicum, and Setaria, as well as species belonging to Bracharia, Pennisetum, Sorghum, and Zea. Unchanged 14C-atrazine accounted for 11.3 to 92.7% of the total 14C-radioactivity extracted from 14C-atrazine infiltrated leaf sections following an 8-hr incubation period. N-dealkylation, hydroxylation, and peptide conjugation occurred in all species, although rates of these metabolic pathways varied widely among species. Recovery of NCE was correlated with formation on the glutathione-atrazine conjugate, and conjugation was the major detoxification pathway in species exhibiting tolerance to atrazine.

A spray chamber was constructed to spray herbicides or growth regulators on small potted plants. Syphon-type pneumatic atomizing nozzles were used to eliminate the need to pressurize the spray solution. Two stationary overhead nozzles deliver the solution to plants rotating on a turntable. The chamber permits convenient and accurate regulation of volume and rate of chemical application for laboratory and greenhouse investigations.

Three thousand accessions of the U.S. Dep. Agric. World Collection of Avena sp. germ plasm were screened for their ability to exude scopoletin (6-methoxy-7-hydroxy coumarin), a naturally occurring compound shown to have root growth inhibiting properties. Twenty-five accessions exuded more blue-fluorescing materials than a standard oat cultivar (Avena sativa L. ‘Garry’). Analysis of the exuded materials revealed that four accessions exuded up to three times as much scopoletin as ‘Garry’. When PI 266281 was grown with wild mustard [Brassica kaber (D.C.) L.C. Wheeler var. pinnatifida (Stokes) L.C. Wheeler] for 16 days in sand culture, the growth of the wild mustard was significantly less than that obtained when the weed was grown with ‘Garry’. Wild mustard plants grown in close association with PI 266281 exhibited severe chlorosis, stunting, and twisting which appeared indicative of chemical or allelopathic effects rather than simple competition. Analysis of the culture solution indicated that levels of scopoletin were too low to cause the observed effects and it is postulated that the final toxic effects were possibly due to the exudation of scopoletin and other allelopathic compounds.

Phytochrome was assayed in vivo in the rhizomes of 12 to 14-week old johnsongrass [Sorghum halapense (L.) Pers.] plants. The phytochrome levels decreased basipetally from the apex through the eighth node. The decrease was logarithmic on a dry weight basis, but less rapid on a per segment basis. On a dry weight basis, higher phytochrome measurements were obtained with samples from the interior of the rhizome than from the external regions. The far-red absorbing form of phytochrome (Pfr) was shown to be very labile at 25 C in johnsongrass rhizomes. These results provide a basis for examining photomorphogenic responses of rhizomes to light and for correlating these responses to phytochrome photophysiology.

Dormant (fresh) and nondormant (afterripened) prickly sida (Sida spinosa L.) seeds were extracted and bioassayed for both inhibitory and promotory growth regulators. Both dormant and nondormant prickly sida seeds contained water-soluble inhibitors, but these inhibitor levels in nondormant seeds did not change after 8 hr of incubation. A basic inhibitor was present in dormant seeds, but not in nondormant seeds. Exogenous growth regulators stimulated germination of dormant seeds only when a portion of the seed coat was removed. Promoter levels in nonincubated, dormant and nondormant seeds were similar, but there were increases in promoter levels in nondormant seeds after 8 hr of incubation. However, it was not determined whether the promoter increases were a cause or a result of germination.

Foliar application of 2.8 μg/plant of glyphosate [N-(phosphonomethyl)glycine] to greenhouse grown sorghum [Sorghum bicolor (L.) Moench ‘Tophand’] seedlings resulted in increased fresh weight. As glyphosate levels were increased to 11.2 μg/plant, diameter of the basal growth zone increased while fresh weight decreased. In growth chamber studies with sorghum and wheat [Triticum aestivum (L.) ‘Era’] seedlings, glyphosate caused the greatest reduction in fresh weight at the optimum growth temperatures for both species. Glyphosate inhibited normal production of basal buds in wheat at the optimum growth temperature and stimulated bud production at temperatures above the optimum. Under normal growth conditions, basal buds in sorghum do not develop; however, application of glyphosate stimulated basal bud development under normal and above-normal temperature conditions. Histochemical analysis of malate dehydrogenase activity in apical meristem tissue of treated sorghum seedlings indicated that growth of the apex was normal and viable.

The movement of biologically active levels of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide] was followed by monitoring photosynthetic activity of plant parts after application of the herbicide. Bentazon was applied to roots, stems, petioles, portions of the canopy, and portions of individual leaves of 4- to 24-day-old common cocklebur (Xanthium pensylvanicum Wallr.) at rates comparable to field application rates. Application of bentazon anywhere on the plant either slowed or stopped photosynthesis in leaves acropetal to the point of application. Contact of bentazon with stems, petioles or roots contributed to the phytotoxicity of the herbicide.

These studies were conducted in the laboratory on two soils at two temperatures to define the rate of degradation and the associated rate law for trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), and 2,6-dinitro-N-(3-pentyl)-α,α,α-trifluoro-p-toluidine (hereafter referred to as Unnamed). Rate of degradation was directly correlated with temperature and moisture content. First order kinetics adequately described the rate of degradation at 15 C, but the simple first order assumption was not sufficient to describe degradation at 30 C. The implication of our interpretation is that at 30 C two rate processes may operate in the soil degradation of these three dinitroaniline herbicides. The data show an initial rapid first order rate of degradation with a subsequent change to a slower first order process. First half lives ranged from 0.4 to 1.8 months at 30 C and were consistently lower in a loam than in a sandy loam soil.

Ethofumesate (2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate) applied preemergence or early postemergence at 0.8 to 4.5 kg/ha eliminated annual bluegrass (Poa annua L.) in Italian ryegrass (Lolium multiflorum Lam.) seed fields. Rattail fescue (Festuca myuros L.) was more difficult to control. The 0.8 kg/ha rate controlled only 55% of the rattail fescue. Rates of 1.1 to 1.7 kg/ha controlled 72 to 95% and rates of 2.2 to 4.5 kg/ha eliminated rattail fescue. All ethofumesate treatments except one, 2.2 kg/ha applied postemergence in Experiment 7, reduced weed competition enough so that ryegrass seed yields were increased. At 4.5 kg/ha, a rate double that required to eliminate rattail fescue, seed yields were as high or higher than at 2.2 kg/ha rate, indicating that ethofumesate has at least a twofold safety margin on Italian ryegrass. The germination of ryegrass seed harvested from plots treated with ethofumesate at 0, 2.2, and 4.5 kg/ha was not affected by the treatments.

Eight substituted dinitroaniline herbicides were studied for relative effectiveness in controlling weeds and for tolerance of peas (Pisum sativum L.). Greenhouse trials comparing 10-5 M herbicide solutions added to washed silica sand indicated that trifluralin (α,α,α-trifluroro-2,6-dinitro-N,N,-dipropyl-p-toluidine) and dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine) were the most phytotoxic to peas. Field trials conducted over a 3-yr period using 0.84 and 1.68 kg/ha application rates demonstrated that all eight of the herbicides successfully controlled the weeds present. Use of trifluralin resulted in the lowest shelled pea yields at both rates of application. Significant reductions in yield occurred from the 1.68 kg/ha rate of trifluralin in 1973 and 1975 when compared with the untreated checks. While major differences did not occur between the other chemicals, the greatest average pea yields resulted from the use of oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), dinitramine, and fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)analine].

Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] significantly reduced the incidence of stem rot caused by the soil-borne pathogen Sclerotium rolfsii L. in field-grown peanuts (Arachis hypogaea L. ‘Florunner’). Dinoseb (2-sec-butyl-4,6-dinitrophenol) (1.7 kg/ha) used alone also reduced stem rot, but when combined with oxadiazon control was not significantly improved, although yields were significantly increased. Dinoseb was toxic to S. rolfsii in laboratory tests, suggesting that disease reductions and yield increases are attributable to this observation. Oxadiazon was non-toxic to the pathogen, indicating that disease control must be indirect, perhaps relating to the reduced plant spreading observed in treated plots. The reduction in ground contact is thought to reduce the probability of contacting pathogen inoculum. The potential value of oxadiazon in an integrated pest management system appears to be good because of simultaneous weed and disease control as well as frequent yield increases. This potential may be improved by use of dinoseb in the same program. Disease control is apparently an expression of the direct toxicity of dinoseb and the indirect effects of oxadiazon.

Field experiments were conducted to study the feasibility of using several dinitroaniline herbicides for the selective control of johnsongrass [Sorghum halepense (L.) Pers.] from seed and rhizomes in soybeans [Glycine max (L.) Merr. ‘Bragg’]. The herbicides were incorporated into the soil with two disk cultivations immediately after application. These were trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 0.6 to 2.2 kg/ha, nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] at 0.6 to 2.2 kg/ha, dinitramine (N4,N4-diethyl-α,α,α,-trifluoro-3,5-dinitrotoluene-2,4-diamine) at 0.4 to 1.5 kg/ha, fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline] at 0.6 to 2.2 kg/ha, profluralin [N-(cyclopropyl-methyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] at 0.8 to 3.4 kg/ha, butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] at 1.7 to 6.7 kg/ha, AC-92390 (N-sec-butyl-2,6-dinitro-3,4-xylidine) at 0.8 to 3.4 kg/ha, and AN-56477 [N,N-di(2-chloroethyl)-4-methyl-2,6-dinitroaniline] at 2.2 to 4.5 kg/ha. On Bosket sandy loam soil, the best average johnsongrass control over a 2-yr period was obtained following profluralin at 1.7 kg/ha and butralin at 3.4 kg/ha. These treatments also resulted in highest average soybean yields. On Sharkey clay soil, profluralin at 3.4 kg/ha and butralin at 6.7 kg/ha resulted in maximum johnsongrass control and soybean yields. Immediate incorporation of profluralin and butralin into both soils for 2 successive years effectively controlled johnsongrass from rhizomes without soybean injury and with greatly increased soybean yields. Trifluralin, nitralin, and fluchloralin also provided acceptable johnsongrass control within individual experiments, and greatly increased soybean yields.

Tubers from purple nutsedge (Cyperus rotundus L.) plants grown in the greenhouse for 2 to 10 weeks did not germinate after foliar applications of 4 kg/ha glyphosate (N-(phosphonomethyl)glycine). Some tubers from 12- and 24-week-old purple nutsedge plants survived glyphosate application. Translocation of 14C-glyphosate from treated purple nutsedge leaves to other plant parts increased from 5% of the amount applied at 1 day to 19% at 4 days after application. Specific activity of 14C in tubers was greater than in leaves of plants 2- to 6-week-old. With increasing plant age, specific activity decreased in both tubers and leaves. As purple nutsedge grew older, total 14C translocated increased in tubers, and decreased slightly in leaves. Thin layer chromatography showed no evidence of glyphosate metabolism in purple nutsedge.

Surfactants were evaluated in the greenhouse for their ability to enhance glyphosate [N-(phosphonomethyl) glycine] toxicity to common milkweed (Asclepias syriaca L.) and hemp dogbane (Apocynum cannabinum L.). Ethoxylated amines were among the most effective groups of surfactants. Nonionic ether and ester ethoxylates combined with a dimethyl amine or a quaternary ammonium salt were more effective than any of these surfactants alone. Effectiveness of ethoxylated amine surfactants was altered by pH changes. Cat-ionic surfactants tended to be more effective than nonionic surfactants. With exceptions, surfactants were more effective with increased ethoxylation. Amine surfactant effectiveness increased with increasing concentrations up to 0.3% (w/v). Surfactant effectiveness on a molar basis was more closely related to the ethylene oxide content of the surfactant than was effectiveness on a percentage basis. Contact angle was not related to surfactant effectiveness at high or low surfactant concentrations. Ethoxylated stearyl ether and amine surfactants gave optimum effectiveness at hydrophile-lipophile balance (HLB) values of 15 to 16 and 19 to 20, respectively. Surfactants with a low HLB were usually less effective. Effectiveness of surfactant combinations was quite variable and difficult to predict. Therefore, the indiscriminate addition of surfactants to glyphosate spray mixtures which already contain a surfactant should be avoided.

During 1971 and 1972, 4,400 adults of Rhinocyllus conicus Froelich were introduced into southern California from Italy for the biological control of milk thistle [Silybum marianum (L.) Gaertner]. These flowerhead-infesting weevils were colonized at nine, and successfully established at five, widely separated locations. Field data on the incidence and increase of R. conicus at colonization sites are presented. Biotic mortality factors reported for R. conicus in southern California include predation of eggs by ladybird beetles (Hippodamia sp.) and of adults by snakeflies [Raphidia (Agulla) adnixa Hagen] and spiders, destruction of weevils in flower-heads consumed by cattle and rodents, and larval and pupal parasitism by pyomotid mites.