A 50:50 mixture of phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) and desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)] was applied at 1.1, 2.2, and 4.4 kg/ha to weed-free sugarbeets (Beta vulgaris L. ‘Mono-HyD2’) at three growth stages in the morning and afternoon to evaluate factors associated with phytotoxicity. Sugarbeet stand loss from herbicide application had a much greater effect on yield than temporary vigor loss. Increasing herbicide rate always increased stand loss. Spraying in the afternoon was much less injurious than spraying in the morning when maximum temperature during the day exceeded 22 C. Excessive stand loss occurred, even with the 1.1 kg/ha rate and 4 to 6 leaf sugarbeets, when sprayed on the morning of a day with maximum temperature of 30 C or greater. Yield loss was determined by percent stand loss and by sugarbeet stand density prior to herbicide application. Significant sucrose yield loss occurred with all rates when applied in the morning to a marginal sugarbeet stand.

Seeds of barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common purslane (Portulaca oleracea L.), fimbristylis [Fimbristylis miliacea (L.) Vahl.], goosegrass [Eleusine indica (L.) Gaertn.], monochoria [Monochoria vaginalis (L.) Presl.], pale smartweed (Polygonum lapathifolium L.), rice flatsedge (Cyperus iria L.), slender amaranth (Amaranthus viridis L.), smallflower umbrella plant (Cyperus difformis L.), and sour paspalum (Paspalum conjugatum Bergius), were placed in nylon mesh bags and buried at 0 (surface), 2.5, 7.5, 15, and 25 cm depths in the soil in November 1974 for 10, 20, 30, 60, 90, 120, 180, 240, 300, and 365 days. They were then recovered from soil to test their germination in petri dishes. Seeds on the soil surface had lower percent germination than those that were buried. Statistical data showed that the total percent germination was not significantly different for the seeds buried at 2.5 cm and deeper in soil when examined at the same burial intervals. During the experiment, the total percent germination of seeds was classified into three groups: (a) percent germination remained constant and relatively high, as for smallflower umbrella plant, common purslane, goosegrass, and slender amaranth; (b) percent germination remained at a plateau for 240 days and then gradually declined at 300 and 365 days, as for sour paspalum; and (c) percent germination was low at the beginning and the end of the experimental period but high in the middle, as for barnyardgrass, monochoria, pale smartweed, rice flatsedge, and fimbristylis. During the experiment, common purslane, barnyardgrass, and monochoria reached a germination peak within the first 5 days. Seeds of the 7 other species germinated within 3 to 5 days or 6 to 10 days, depending on the combination of innate dormancy, temperature, and light intensity.

The influence of artificial shading (0, 30, 47, 70, 80, and 94% shade) on growth of yellow nutsedge (Cyperus esculentus L.) and the time required for developing canopies of several crops to intercept a given amount of light were investigated in field studies to estimate the potential of crops to compete with yellow nutsedge for light. Average number of shoots and tubers and total dry matter production of yellow nutsedge increased in direct proportion to increased amounts of light (correlation coefficient (r ≥.98). Compared to no shade, flower production was substantially reduced by 30 and 47% shade and was essentially absent under more dense treatments. Photosynthetically active radiation (PAR) measured at weekly intervals indicated that light interception occurred first within the drill row of crops, then on shoulders of planting beds, and finally in furrows. The most rapidly developing canopies studied [corn (Zea mays L.), potatoes (Solanum tuberosum L.), and safflower (Carthamus tinctorius L.)] intercepted 90% or greater PAR, including illumination in furrows, within 8 to 9 weeks after planting. About 12, 12, and 16 weeks were required for 80% interception for cowpeas [Vigna unguiculata (L.) Walp.], milo [Sorghum bicolor (L.) Moench.], and cotton (Gossypium hirsutum L.), respectively. Fall-planted barley (Hordeum vulgare L.) intercepted about 90% PAR by March 12. Alfalfa (Medicago sativa L.) intercepted about 90% PAR within 2 to 3 weeks after individual cuttings. Although onions (Allium cepa L.) planted in December intercepted 95% of the PAR in each of the two drill rows per bed about 26 weeks after planting, only 20 to 30% interception occurred in furrows and row middles.

Seven substituted dinitrobenzamine herbicides were evaluated at two rates as preplant soil-incorporated treatments for 2 yr. Herbicides were applied broadcast and incorporated 7 cm deep into a sandy loam with a power-driven rototiller before the preplanting irrigation and 3 weeks before crop planting. Cotton (Gossypium hirsutum L. ‘Acala SJ-1’) stands were reduced by the higher rate of nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], dinitramine (N4,N4-diethyl-a,a,a-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], and AN 56477 [N,N-di-(2-chloroethyl)-2,6-dinitro-4-methylaniline]. Cotton yields were reduced by the higher rate of nitralin, dinitramine, and AN 56477. The poorest weed control was obtained with the lower rate of nitralin, AN 56477, and butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine]. A bioassay with Japanese millet [Echinochloa crus-galli (L.) Beauv. var. frumentacea (Roxb.) Wight] and grain sorghum [Sorghum bicolor (L.) Moench] was used to evaluate herbicides remaining in soil sampled 1, 120, and 240 days after application. Residual herbicide phytotoxicity at 240 days indicated dinitramine < trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) = butralin < profluralin [N-(cyclopropylmethyl)-a,a,a-trifluoro-2,6-dinitro-N-propyl-p-toluidine] = AN 56477 < nitralin < fluchloralin. In greenhouse experiments, cotton taproot elongation was retarded by both rates of nitralin, dinitramine, and AN 56477 and by the higher rate of fluchloralin. All herbicides inhibited lateral roots of cotton in the herbicide-treated zone of soil, but butralin and profluralin caused the least inhibition.

Ten herbicides were each applied at two rates to Panache loam for 5 or 6 yr as soil-incorporated broadcast sprays directed to the base of cotton (Gossypium hirsutum L. ‘Acala SJ-1’) at last cultivation. Chemical determinations 6 months after annual treatment showed that trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], benefin (N-butyl-N-ethyl-a,a,a-trifluoro-2,6-dinitro-p-toluidine), DCPA (dimethyl tetrachloroterephthalate), and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] residues were essentially confined to the tilled zone of soil; whereas, bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercapteothyl)benzenesulfonamide], fluometuron [1,1-dimethyl-3-(a,a,a,-trifluoro-m-tolyl)urea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] residues were found below the tilled zone. At time of retreatment, annual residue determinations from the upper 15 cm of soil showed that nitralin and prometryn had dissipated completely and residues of the other herbicides and were notably reduced as compared to levels at cotton harvest. One year after final treatment herbicide residues below the tilled zone were essentially nondetectable, except for diuron, linuron, and fluometuron. There was no evidence of herbicide accumulation in soil with repeated applications.

Procedures were developed for simultaneous control of big sagebrush (Artemisia tridentata Nutt.), green rabbitbrush [Chrysothamnus viscidiflorus Var. Viscidiflorus (Hook.) Nutt.] and downy brome (Bromus tectorum L.) with the herbicide karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1, 1-dimethylurea]. After a season of fallow, the herbicide-treated areas were seeded with perennial grasses. During the 4 yr of testing at several locations, karbutilate at 1.1 kg/ha controlled the shrubs and downy brome. A herbaceous fallow was maintained with 0.6 kg/ha of the herbicide, but 1.1 kg/ha was necessary for green rabbitbrush control. Perennial grass seedling establishment was highly variable among sites and years of testing. If germination of the seeded species occurred in the fall, stands were poor. When germination was delayed by the onset of cold weather until spring, excellent stands were obtained on plots treated 1 yr previous to seeding with 1.1 kg/ha of karbutilate. Residual herbicide activity was harmful at the time of fall seeding but herbicide residues declined by spring as shown by bioassay of soils.

The phytotoxicity of glyphosate [N-(phosphonomethyl) glycine] on seeds (protected or non-protected with soil) and seedlings of Italian ryegrass (Lolium multiflorum Lam.) and red clover (Trifolium pratense L.) was studied in the greenhouse. Percent germination of Italian ryegrass seeds covered with soil was significantly reduced with glyphosate applied at 4 kg/ha. The direct treatment over the seeds on the soil surface was more toxic, reducing the number of established seedlings at dosages of 3 and 4 kg/ha. In the two red clover seed treatments, germination was significantly reduced with 2 kg/ha of herbicide. Even though germination was reduced at intermediate rates of glyphosate, shoot growth and tillering were improved and yields of dry weight were equivalent to that of untreated plants. Postemergence applications of glyphosate were phytotoxic to both species with the effects becoming more pronounced at increasing dosages. However, at equal dosage, red clover was less susceptible than Italian ryegrass. The patterns of foliar absorption and translocation of 14C from 14C-glyphosate was similar in Italian ryegrass and red clover. 14C was translocated throughout the plants and exhibited apoplastic and symplastic movement.

Several soil-applied and two foliar herbicides were evaluated for weed control in established alfalfa (Medicago sativa L.) in two experiments for two consecutive years. Most of the soil-applied herbicides effectively controlled weeds in the first harvest year following application; however, there was little carry-over into succeeding years. Except for the low rate of secbumeton [N-ethyl-6-methoxy-N′ (1-methylpropyl)-1,3,5-triazine-2,4-diamine] in the first alfalfa cutting of 1973, no herbicide treatment significantly increased alfalfa yields over the control plot. In fact, some herbicides caused injury to alfalfa at high rates of application, as did reapplication a second year at the original rate of application.

The effect of fall frost on the activity of glyphosate [N-(phosphonomethyl)glycine] on alfalfa (Medicago sativa L. ‘Vernal’) and quackgrass [Agropyron repens (L.) Beauv.] was studied in a room of the Biotron, a controlled environment facility of the University of Wisconsin, and in the field in the fall. In a Biotron time-course study, the most effective day of treatment for quackgrass control was the day after the first frost. Quackgrass plants treated the morning after frost had significantly higher uptake and translocation of glyphosate (93%, 55%) than plants treated 4 days before frost (71%, 32%) and greater translocation than plants treated 5 days after frost (24%). In the field, glyphosate was most active on quackgrass when applied the morning after the first frost of the fall. Control of quackgrass treated with 0.4 kg/ha of glyphosate increased from 10% when treated 4 days before the first frost to a maximum of 91% when treated the day of the first frost. No significant effects of frost in decreasing glyphosate toxicity to alfalfa were found. These results minimize the possibility of using this herbicide to remove quackgrass from alfalfa.

Infrared spectroscopy was used to study the hydrolysis of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] upon interaction with homoionic soil colloids. Montmorillonite, an allophanic soil clay, and a montmorillonitic Coker soil clay were saturated with H+, Al3+, Cu2+, and Ca2+ and treated with atrazine and hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Hydrolysis of atrazine was evaluated by the presence of a strong hydroxyatrazine carbonyl absorption band at 1745 cm-1. The H+- and Al3+-saturated montmorillonite and montmorillonitic Coker soil clay promoted atrazine hydrolysis while Ca2+- or Cu2+-saturated montmorillonite did not. A small degree of atrazine hydrolysis was detected in the Cu2+-Coker soil clay. Dehydration of Ca2+- or Cu2+-Coker soil clay after equilibration with atrazine increased the hydrolysis of atrazine. The allophanic soil clay did not catalyze the hydrolysis of atrazine when the exchange complex was saturated with H+, Al3+, Ca2+, or Cu2+. Moreover, Al3+-allophane was not sufficiently acidic to protonate hydroxyatrazine. Thus, a major difference exists between soil allophanic colloids, montmorillonitic soil clays, and montmorillonite as catalysts in the protonation and hydrolysis of atrazine.

Germination studies on camphorweed [Heterotheca subaxillaris (Lam.) Britt. & Rusby] revealed that freshly harvested disk achenes germinated best at 17.5 C (88%) while ray achenes were dormant. Camphorweed seed from disk achenes also germinated at temperatures as low as 3 C. Seedlings grown under long-day conditions at 23 C day and 8 C night temperatures for 144 days elongated at the rate of 0.18 cm/day. Plants grown under short-day conditions at the same temperature regime elongated at the rate of 0.06 cm/day. Total leaf surface area, fresh weight, and dry weight of shoots of plants grown under long days were at least 1.5 times greater than plants grown under short day conditions. Camphorweed, regardless of size and age, survived a 2-h exposure at −5 C. All plants in the rosette stage survived at −15 C in the freezer and an overnight temperature of −11.7 C in the field, whereas larger plants were killed at these temperatures. Stage of growth was an important factor in the herbicidal control of camphorweed. Plants in the rosette stage were generally more susceptible to herbicides than older plants. Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 3.4 kg/ha, paraquat (1,1′-dimethyl-4,4′-bypyridinium ion) at 0.6 kg/ha, methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] at 5.0 kg/ha, and a formulated mix of diuron [3–3,4-dichlorophenyl)-1,1-dimethylurea] and terbacil (3-tert-butyl-5-chloro-6-methyluracil) at 4.5 kg/ha provided adequate control of camphorweed in the rosette stage. Asulam (methyl sulfanilylcarbamate) at 2.2 or 4.5 kg/ha applied alone did not control camphorweed in the rosette form but was more effective on older plants. Various combinations of these herbicides were generally effective at both stages of growth.

Methods of assessing and describing the joint action of materials as herbicides are reviewed, and the shortcomings of the terms synergism and antagonism are discussed. Some of the lack of agreement on their meaning and evaluation is attributed to failure to define or recognize appropriate models to represent absence of synergism (and antagonism). General analytical and graphical procedures are presented, and for two simple models, the additive-dose model (ADM) and the multiplicative-survival model (MSM), the dose-response curves and isobols are compared. Three examples from recent literature are reworked.

Seven dinitroaniline herbicides were tested in the field for 3 yr at rates up to twice that normally used for annual grass control. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] gave 95 and 94% control of johnsongrass [Sorghum halepense (L.) Pers.] from rhizomes, respectively, after the third year at the double rate. These two herbicides controlled johnsongrass from rhizomes better than nitralin [4-methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] and pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] at comparable rates. After 3 yr, seed cotton (Gossypium hirsutum L. ‘Stoneville 213’) yields were higher with double rates of trifluralin, profluralin, fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], and pendimethalin, than with nitralin, dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), and butralin. In greenhouse studies, reduction of cotton raproot length by the dinitroaniline herbicides incorporated at the normal rate of use followed the order: butralin ≤ pendimethalin ≤ fluchloralin ≤ trifluralin < profluralin < dinitramine. All herbicides except pendimethalin at 0.28 and 0.56 kg/ha reduced lateral root production of cotton. The dinitroaniline herbicides at normal rates of use reduced fresh weight of cotton seedlings from 12 to 34%. The mean vapor toxicity of the dinitroaniline herbicides to Japanese millet [Echinochloa crus-galli (Roxb.) Wight ‘frumentacea’] shoots averaged from no injury with oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) and nitralin to 66% injury with dinitramine and trifluralin.

The uptake and distribution of 14C-bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate] was different among corn (Zea mays L.), soybean (Glycine max (L.) Merr.) and velvetleaf (Abutilon theophrasti Medic.) following preemergence application to a greenhouse soil mix. Autoradiographs of seedlings harvested 14 days after treatment, showed the 14C to be in (or on) those areas of the crop plant in contact with the treated soil. Velvetleaf translocated 14C residue throughout the shoot. Absorption of 14C-compound(s) from treated nutrient solution accumulated in the roots of the three species but to a greater extent in soybean. There was no difference in the concentration of 14C in the shoots. However, in corn and soybean the 14C-compound(s) was confined to the primary and secondary leaf veins while velvetleaf showed a general distribution throughout the leaf tissue. Velvetleaf absorbed and translocated bifenox from shoot zones to a greater extent than the crop plants. Some acropetal movement was noted following leaf application to corn and velvetleaf but movement was only 3% of applied 14C from the treated leaf. No movement was detected in soybean.

Herbarium records indicate that Russian pigweed (Axyris amaranthoides L.) entered the flora of Manitoba in 1886, spreading from there, by its own devices and by secondary introductions, to other provinces of Canada and to the United States. It is best established (to the extent of being considered a weed) in North Dakota and the prairie provinces of Canada.

The effect of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)], propanil (3′,4′-dichloropropionanilide), and dibromothymoquinone (DBMIB) (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) on proton translocation and photophosphorylation in isolated spinach (Spinacia oleracea L.) chloroplast fragments was investigated. In the absence of added cofactors, O2, or artificial electron acceptors, cyclic electron transport occurred, which was coupled to energy conservation. Under aerobic conditions O2 acted as the terminal acceptor in non-cyclic electron transport. Proton translocation and photophosphorylation in the cyclic process were enhanced by diuron, desmedipham, and propanil, while in the non-cyclic process they were inhibited by all three herbicides. DBMIB inhibited proton translocation and photophosphorylation in both processes. Proton translocation and its enhancement increased with increasing light intensities. The finding that the plastoquinone (PQ) antagonist DBMIB disrupted cyclic as well as noncyclic electron flow, while diuron enhanced the cyclic and inhibited the noncyclic process, indicated that the acceptor site for endogenously-cycling electrons must lie between the active site of diuron inhibition and PQ, The close similarity in the behavior of diuron, desmedipham, and propanil suggests that their site of action is the same.

In order to germinate successfully, large crabgrass [Digitaria sanguinalis (L.) Scop.] seeds require a period of after-ripening. Some changes, either physical, biochemical or both, must occur in these seeds during this after-ripening process. This paper reports the differences in the activities of several enzymes between dormant (non-after-ripened) and nondormant (after-ripened) large crabgrass seeds at various periods of hydration. The total protein content of dormant seeds does not change during imbibition but increases greatly in nondormant seeds at 48 and 76 h of hydration. Initially, nondormant seeds exhibit high alpha-amylase activity and low peroxidase and acid phosphatase activities. Alpha-amylase activity remains unchanged relatively in both dormant and nondormant seeds up to 36 h of hydration, but increases greatly in nondormant seeds at 48 and 76 h of hydration. Peroxidase activity, which is initially low in nondormant seeds, increases substantially at 48 and 76 h of soaking. Acid phosphatase activity in dormant seeds does not change following hydration but is gradually elevated in nondormant seeds with duration of soaking. Lipase activity in dormant seeds remains fairly constant upon hydration. In nondormant seeds, however, the activity gradually decreases with duration of soaking, the decrease being 3 to 4 fold at 76 h of imbibition. Except for lipase, there is a positive correlation in the activities of alpha-amylase, peroxidase, and acid phosphatases with the increase of total protein content of nondormant seeds.

Greenhouse and field studies demonstrated that plants compete for soil-applied atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Oats (Avena sativa L. ‘Neal’) and soybeans [Glycine max (L.) Merr. ‘Clark 63’] were grown in greenhouse bioassay studies to study the effects of plant population on bioassay sensitivity. High plant populations were not as effective as low plant populations in detecting low levels of atrazine in soil. Conversely, by increasing plant populations or decreasing soil volumes quantitative measurement of higher atrazine concentrations can be determined. A 14C-labeled atrazine study showed that by increasing soybean populations from one to six per pot, atrazine uptake per plant was decreased 50%. When soybeans were planted at a rate of six plants per 100 cm2 in a field treated with atrazine at 1.1 kg/ha, soybean dry weight production was 97% of the untreated control; when planted at a rate of one plant per 100 cm2, dry weight was only 26% of the comparable untreated check. Thus, herbicide rates for optimum weed control may have to be increased with increasing weed populations or increased crop seeding rates or both.