Field experiments were conducted on a Moody silty clay loam (pH 6.5) and a Crofton silt loam (pH 7.9) to evaluate the influence of soil texture and pH on metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] toxicity to soybeans [Glycine max (L.) Merr. ‘Amsoy 71’] as influenced by trifluralin [α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine]. One Crofton silt loam site contained atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] residue. Soybean growth and yield was not significantly affected by metribuzin and trifluralin applications on the Moody silty clay loam. On the Crofton silt loam without atrazine residue, substantial early season soybean injury from metribuzin did not result in significantly reduced soybean yield. Atrazine residue from previous row banding on corn (Zea mays L.) on the Crofton silt loam reduced soybean tolerance to metribuzin but normal use rates of 0.4 kg/ha metribuzin did not significantly reduce soybean yield. Trifluralin reduced early season soybean injury from metribuzin but this effect was not reflected in soybean yield. Metribuzin injury to soybeans was greater in years when more rainfall and cooler temperatures occurred following herbicide application. Metribuzin applied either preplant incorporated with or as an overlay on trifluralin resulted in equal soybean injury and yield.

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.

Germination studies were conducted on seed of wild poinsettia (Euphorbia heterophylla L.) collected in 1974 and 1975. Significant differences in germination existed between the seedlots. An alternating temperature regime of 25/35 C was optimum for germination, and no effect of light was noted at this temperature regime. However, light increased germination at temperatures of 25, or 35 C, and decreased it at 10/35 C. Storage of wild poinsettia seeds at 36 C for 2 to 12 weeks caused a significant decrease in dormancy as compared to corresponding storage at 5 C. Seed moisture levels below 7.7% did not seem to affect viability at 5 or 25 C after a storage period of 3 to 9 months. Seed viability decreased rapidly when seed were stored for 3 months at 25 C with a moisture content of 10.8% or at 5 or 25 C with a moisture content of 18.6%. Seeds buried in the fall at a depth of 5 cm germinated extensively in the field 9 months later. Field germination decreased as depth of burial increased.

A simple technique is described for rapid determination of weed seed, rhizome, corm, or bulb populations in soil. Soil samples were placed in nylon mesh bags. The soil was washed from the bags by machine leaving only a small residue including the desired propagules. These were hand separated and the soil population of a given plant species calculated. The total manipulation time per sample was approximately 10 min.

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.

In a 3-yr field study, seven dinitroaniline herbicides controlled all weeds adequately, except for two species. None of them controlled shepherdspurse [Capsella bursa-pastoris (L.) Medic.], and only nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] controlled common ragweed (Ambrosia artemisiifolia L.). EPTC (S-ethyl dipropylthiocarbamate) was included as a standard of comparison and provided satisfactory control of all weed species. Three-year averages of alfalfa (Medicago sativa L.) injury ratings at herbicide rates estimated to be equivalent in biological activity to 0.8 kg/ha and 1.7 kg/ha trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) respectively were: butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine] 0% and 3%, benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) 2% and 9%, profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] 5% and 19%, AC92390 (N-sec-butyl-2,6-dinitro-3,4-xylidine) 6% and 17%, trifluralin 6% and 26%, fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline] 14% and 45%, and nitralin 18% and 49%. EPTC caused an average 4% injury at 3.4 kg/ha. At equivalent rates to 0.8 kg/ha trifluralin, most treatments caused an increase in first cutting alfalfa yields accompanied by a decrease in weed yields, except in 1974 when few treatments resulted in increased alfalfa yields. Alfalfa recovered from early season injury caused by higher rates of the herbicides, so that total alfalfa yields were usually not reduced compared to the control. Total herbage yields (alfalfa + weeds) were not increased by any treatment, and were sometimes decreased, especially by high rates of the herbicides.

Wheat (Triticum aestivum L. ‘Waldron’) tolerance to barban (4-chloro-2-butynyl m-chlorocarbanilate) applied at 0.42 to 3.36 kg/ha 4 to 24 days after crop emergence was determined in the field and greenhouse and barley (Hordeum vulgare L. ‘Nordic’) tolerance in the field only. Wheat and barley tolerance to barban increased as application was delayed from 4 to 16 days after emergence. Wheat yields were reduced by barban at 0.84 kg/ha applied 4 days after emergence or by 1.68 and 3.36 kg/ha applied 4, 8, and 12 days after crop emergence. However, barban applied 16, 20, and 24 days after crop emergence did not reduce wheat yield regardless of barban rate. Barley yields were reduced by 1.68 kg/ha barban applied 4, 8, 12, and 16 days after emergence or by 3.36 kg/ha applied at all dates; however, greatest yield reductions occurred with applications 4, 8, and 12 days after crop emergence.

The metabolism of three 14C-ring-labeled herbicides, atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], chloramben (3-amino-2,5-dichlorobenzoic acid), and dicamba (3,6-dichloro-o-anisic acid) was studied in the earthworm, Lumbricus terrestris L., taken from plots treated with these herbicides for the past 10 yr and from control plots treated with no herbicides. For the two benzoic acid herbicides, acetone extracts of sand and earthworms from untreated plots contained more unmetabolized herbicide than similar extracts of sand and earthworms from treated plots, indicating a net enhancement of metabolism in worms from treated plots. For atrazine, the amount of unchanged herbicide in the acetone extracts of earthworm and sand were nearly equivalent. Finally, the relative metabolic stability of the three herbicides in decreasing order in earthworms from both control and untreated plots was chloramben>atrazine>dicamba.

Representative herbicides of the substituted ureas, uracils, s-triazines, benzonitriles, and bipyridyls, which are potent inhibitors of photosynthetic electron transport, markedly accelerated photooxidations (chlorophyll bleaching and lipid peroxidation) normally occurring in isolated intact chloroplasts. Other herbicides, which are not potent inhibitors of photosynthesis, did not accelerate photooxidations. The photooxidations, whether in the presence or absence of herbicides, were completely prevented by exogenously supplied NADH or NADPH but not by sucrose or mannitol. Herbicide-induced injury to barley (Hordeum vulgare L.) seedlings treated with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) was diminished by allowing the seedlings to absorb NADPH. These results provide additional support to the hypothesis that depletion of the source of reducing potential (NADPH) is responsible for chloroplast photooxidations and plant death following treatment with photosynthesis-inhibiting herbicides.

Fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] and tetrafluron {N,N-dimethyl-N′-[3-(1,1,2,2-tetrafluoroethoxy) phenyl] urea} are two urea-type herbicides for weed control in cotton (Gossypium hirsutum L.). In some years, because of cotton stand failure, an alternate crop must be established. Soybeans [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench] are possible alternate crops if they can withstand the residues left from herbicides used for weed control in cotton. Soybeans and grain sorghum were planted 3, 6 and 9 weeks after fluometuron and tetrafluron applications to soil at Knoxville and Milan, Tennessee, in 1975 and 1976. Tetrafluron residues were more toxic to grain sorghum and soybeans than were fluometuron residues. Grain sorghum was less susceptible than soybeans to both herbicides. Grain sorghum was planted 3 weeks after fluometuron (1.7 kg/ha) and tetrafluron (1.7 kg/ha) applications without severe yield reduction. Soybeans were planted in non-treated soil between banded tetrafluron (1.7 kg/ha on a treated area basis), 3 weeks after herbicide application, without significant yield reduction; but when a seedbed was prepared, a 9-week waiting period was required. When soybeans were planted into soil receiving a broadcast application of tetrafluron (1.7 kg/ha), a 9-week waiting period was not sufficient to reduce the residues to a non-toxic level. Soybeans planted 6 and 9 weeks following a broadcast application of fluometuron may or may not sustain yield reduction depending on rainfall frequency and intensity and soil type.

In 1972, a 50-yr study of seed longevity was initiated at Stoneville, Mississippi. Weed seeds were collected from 20 locallygrown species and mixed with soil. Replicate samples were placed in polypropylene screen envelopes and buried at soil depths of 8, 23, and 38 cm. Seed germination and viability were determined by germination tests and 2,3,5-triphenyl-tetrazolium chloride (TTC) treatments with recovered seeds. In general, the depth of burial had little effect on seed longevity. Based on the averages of the means at the three depths, the percentages of seeds still viable after burial for 2.5 yr were: spurred anoda [Anoda cristata (L.) Schlecht.] 71%; purple moonflower (Ipomoea turbinata Lagasca y Segura) 71%; johnsongrass [Sorghum halepense (L.) Pers.] 62%; velvetleaf (Abutilon theophrasti Medic.) 58%; goosegrass [Eleusine indica (L.) Gaertn.] 33%; hemp sesbania [Sesbania exaltata (Raf.) Cory] 29%; Texas panicum (Panicum taxanum Buckl.) 24%; common cocklebur (Xanthium pensylvanicum Wallr.) 18%; common eveningprimrose (Oenothera biennis L.) 14%; large crabgrass [Digitaria sanguinalis (L.) Scop.] 12%; sicklepod (Cassia obtusifolia L.) 10%; common purslane (Portulaca oleracea L.) 10%; white morningglory (Ipomoea lacunosa L.) 8%; redroot pigweed (Amaranthus retroflexus L.) 7%; prostrate spurge (Euphorbia supina Raf.) 6%; prickly sida (Sida spinosa L.) 5%; redvine (Brunnichia cirrhosa Gaertn.) 3%; Florida beggarweed [Desmodium tortuosum (Sw.) DC.] 3%; barnyardgrass [Echinochloa crus-galli (L.) Beauv.] 1%; and chickweed [Stellaria media (L.) Cyrillo] 0%.

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.

Granule, and in some cases, tablet and ball formulations of bromacil (5-bromo-3-sec-butyl-6-methyluracil), dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1,1-dimethylurea], and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethyl urea} were applied to three areas within 30 km of College Station in the Claypan Resource area of Texas. Woody species growing in the area included blackjack oak (Quercus marilandica Muenchh.), post oak (Quercus stellata Wangenh.), yaupon (Ilex vomitoria Ait.), winged elm (Ulmus alata Michx.), white ash (Fraxinus americana L.), mockernut hickory (Carya tomentosa Nutt.), and tree huckleberry (Vaccinium arboreum Marsh.). Granules were applied either broadcast or in rows at several intervals. Tebuthiuron was the most effective herbicide on oaks, winged elm, and white ash. Tebuthiuron and picloram were equally and most effective on yaupon, mockernut hickory, and tree huckleberry. Tebuthiuron + picloram at 2.2 + 2.2 kg/ha was the most effective herbicide treatment on huckleberry. However, a mixture of tebuthiuron + picloram (1:1 w/w) was usually no more effective than the same rate of tebuthiuron in the mixture applied alone. Tablet and ball formulations of karbutilate and tablet formulations of tebuthiuron were generally equally as effective as granules. Applications of picloram and tebuthiuron granules in rows 1.8, 3.0, 4.6, or 6.1 m apart gave control equal to broadcast applications except for picloram on yaupon. On yaupon all row spacing treatments of picloram were less effective than the broadcast treatment, whereas with tebuthiuron the 6.1-m spacing was least effective. Picloram and tebuthiuron granules applied in rows, approximately at 1.8-m intervals with a tractor, were as effective as granules applied by hand in straight rows.

Seeds of 82 species of weed and crop plants were tested for germinability after dry storage or storage in fresh water for 3 to 60 months. Seeds of 24 species did not germinate after storage in water for 12 months or less; whereas some seeds of 27 species germinated after 60 months in water storage. When stored in water for longer than 12 months some seeds of only 22% of the annual monocots tested germinated; whereas about 75% of the perennial monocots, and annual and perennial dicots germinated. Species whose seeds consistently germinated better after water storage than after dry storage were western waterhemlock [Cicuta douglasii (DC.) Coult. & Rose], woolly sedge (Carex lanuginosa Michx.), pale smartweed (Polygonum lapathifolium L.), bouncingbet (Saponaria officinalis L.), and blue vervain (Verbena hastata L.).

Five thiocarbamate herbicides, butylate (S-ethyl diisobutylthiocarbamate), EPTC (S-ethyl dipropylthiocarbamate), molinate (S-ethyl-hexahydro-1H-azepine-1-carbothioate), pebulate (S-propyl butylethyl-thiocarbamate), and vernolate (S-propyl dipropylthiocarbamate) were used in the greenhouse at doses of 0.5 to 5 kg/ha incorporated 6 cm deep in a silt loam. Purple nutsedge (Cyperus rotundus L.) tubers were planted 5 cm deep. Three and 9 weeks after treatments were applied, nutsedge plants were harvested. EPTC also was used at doses of 0.25 to 10 kg/ha and plants were harvested every 2 days up to 20 days and every 3 weeks up to 24 weeks. The most effective reduction in the number of sprouts above ground was given by butylate, EPTC, and vernolate followed by pebulate and molinate. Persistence was directly related to level of initial activity. No effect was observed on the number of tubers which sprouted. However, all the thiocarbamates stimulated the number of sprouts produced per nondormant tuber. These sprouts were abnormal and did not reach the soil surface. Treated tubers produced approximately twice as many sprouts as controls. The number of rhizomes produced from the basal bulb was reduced with all the thiocarbamates used, even 24 weeks after treatment for the higher doses.

The effects of 8-, 12-, and 16-h photoperiods on the growth and reproductive biology of purple nutsedge (Cyperus rotundus L.) were investigated over a 3-month period. Plants under the 8-h photoperiod produced the least total, shoot, root, rhizome, and tuber dry weight. Flowering occurred only at the 12-h photoperiod; thus, purple nutsedge is intermediate in flowering response to daylength. Although the total dry weight varied with photoperiod, the relative amount of dry weight (as percent of total weight) partitioned to shoots, roots, rhizomes, and tubers was constant.

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.

2,4-D [(2,4-dichlorophenoxy)acetie acid] and dalapon (2,2-dichloropropionic acid) were applied to a natural stand of annual weeds at a time near flowering to determine effects on seed production and the dormancy and viability of seeds produced. At rates of 0.6 and 1.1 kg/ha, 2,4-D reduced, respectively the seed production of common lambsquarters (Chenopodium album L.) 99 and 99%, redroot pigweed (Amaranthus retroflexus L.) 77 and 84%, and jimsonweed (Datura stramonium L.) 64 and 100%, while giant foxtail (Setaria faberi Herrm) seed production was increased to 307 and 381% of the control, respectively. Dalapon at rates of 2.2 and 4.5 kg/ha reduced respectively seed production of giant foxtail 100 and 100%, and jimsonweed 100 and 91%. Before and after overwinter burial in the soil, common lambsquarters seeds from plants treated with 4.5 kg/ha dalapon were less dormant than control seeds. After overwintering, redroot pigweed seeds from dalapon-treated plants were less dormant than controls, and more seeds survived the winter burial. Common lambsquarters and redroot pigweed seeds from plants treated with 1.1 kg/ha 2,4-D were more dormant than control seeds before overwintering,’ while giant foxtail seeds from 2,4-D treated plants were less dormant than controls after overwintering. Viability of seeds produced by herbicide-treated plants, as determined by germination in KCN, was not greatly different from control seeds. Treatment with 2,4-D or dalapon resulted in the production of common lambsquarters seeds which produced seedlings about half as vigorous as controls. Jimsonweed seedlings grown from seeds from 2,4-D-treated plants showed phenoxy herbicide injury symptoms.

The phytotoxicity of barban (4-chloro-2-butynyl m-chlorocarbanilate) applied 14 days after emergence to wheat (Triticum aestivum L. ‘Waldron’) and wild oat (Avena fatua L.), at constant, fluctuating or alternating day-night temperatures was determined in controlled environmental chambers. Wheat and wild oat susceptibility to barban increased as post-treatment temperature decreased. Maximum barban selectivity for wild oat in wheat occurred with a constant 18 C or an alternating 18 C day and 10 C night post-treatment temperature. At least three days of 10 C immediately following barban application were necessary to cause wheat injury. However, two days at 29 C immediately after barban application in an otherwise 10 C post-treatment regime reduced wheat injury. Further, a night temperature lower than the day temperature after barban application increased wild oat control but did not correspondingly increase wheat injury compared to the constant temperature treatments.