Herbicides can increase agricultural productivity and rural welfare where agronomic considerations or labor shortages favor their utilization, but ecological, social, and economic conditions in developing countries often favor alternative weed control methods. Traditional hoeing by peasant farmers in a Northeast Brazil upland region was found to be both effective and economical in comparison with other methods. In another Northeast Brazil region, government herbicide subsidies and payroll taxes were projected to encourage excessive use of herbicides at the expense of displaced workers with few alternative employment opportunities.

A technique using CaCl2 solutions for separating seed of approximately equal size and/or shape by relative density was developed using nine hard-seeded weed species and four soybean [Glycine max (L.) Merr.] cultivars having an average density of 1 g/ml or above. Relative seed densities were determined by the water displacement method. From a seed mixture of nine weed species and soybeans, three groups were obtained: Group I, sicklepod (Cassia obtusifolia L.) and smallflower morningglory [Jacquemontia tamnifolia (L.) Griseb]; Group II, hemp sesbania [Sesbania exaltata (Raf.) Cory], tall morningglory [Ipomoea purpurea (L.) Roth], cypressvine morningglory (Ipomoea quamoclit L.), and ivyleaf morningglory [Ipomoea hederacea (L.) Jacq.]; and Group III, soybeans, balloonvine (Cardiospermum halicacabum L.), and velvetleaf (Abutilon theophrasti Medic). Ipomoea lacunosa L. was divided between Group II and Group III due to the range of seed density within the seedlot. The minimum relative CaCl2 solution densities required to separate these seed were 1.38, 1.30, and 1.25 g/ml for Group I, Group II, and Group III, respectively. Further separation into individual species within a group was accomplished by screening in some cases. Sicklepod was separated effectively with this technique from seed screenings obtained from a commercial seed processing plant. There was no effect on germination from soaking weed seed or soybean for 40 min in the CaCl2 solution.

Two of three herbicides were applied repetitively in each of the years to a dense infestation of Canada thistle [Cirsium arvense (L.) Scop.] in timothy (Phleum pratense L.) and red clover (Trifolium pratense L.) sward in Carroll County, Maryland during the period 1969 to 1971. Picloram (4-amino-3,5,6-tricloropicolinic acid), eliminated red clover from the sward after the first year, and controlled 95 to 100% of the Canada thistle in the third year of treatment. The addition of a non-phytotoxic oil to picloram did not improve its efficiency. Dicamba (3,6-dichloro-o-anisic acid) reduced 57 to 87% of the red clover and 72% of the Canada thistle in the first year at a dosage of 1.12 kg/ha, but effected only 42% control in the third year of treatment. Both an amine and ester formulations of 2,4-D [(2,4-dichlorophenoxy) acetic acid] effected variable Canada thistle control and reduced the red clover stand 10 to 15% following the first application. The timothy yield was not significantly reduced during the 3 years of repeated application of all herbicides, but some necrosis of leaves was noted with dicamba and the high rate of 2,4-D. Soybeans [Glycine max (L.) Merr. ‘Delmar’] planted 1 yr following the last picloram application had curled leaves initially, but outgrew the injury. Soybeans planted 2 yr following the last application of the herbicides showed no significant reduction in yield indicating herbicide residues had been reduced to tolerable levels.

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.

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.

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%.

The effectiveness of activated charcoal in protecting seedling cotton (Gossypium hirsutum L. ‘Stoneville 213’) from diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] at 1.78 and 3.55 kg/ha was investigated under field conditions over a 5-yr period. Charcoal did not provide adequate protection when applied through the seed hopper box or sprayed in the seed furrow over each hill. Charcoal at 83 and 167 kg/ha applied as a spot over each hill of cotton gave adequate protection. Shallow incorporation of the charcoal significantly reduced the degree of protection. The optimum combination, providing maximum weed control and minimum crop injury, was diuron at 3.55 kg/ha applied over non-incorporated charcoal at 83 kg/ha.

The influence of seed age, planting depth, and temperature on the germination and emergence of ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. var. hederacea], white morningglory (Ipomoea lacunosa L.), and entireleaf morningglory (Ipomoea hederacea var. integriuscula Gray) was studied by using pure seed of each taxa that were collected in 1972, 1973, and 1974. Germination of acid-scarified white and entireleaf morningglory seed ranged from 64 to 98% at continuous 20, 25, 30, 35, and 40 C and at an alternating 20/30 C cycle. The ivyleaf morningglory germination range was 50 to 98% at these temperatures, except at 40 C germination was <25%. Germination of nonscarified seed was generally 30 to 60% lower than scarified seed for the three taxa. Germination of seed collected in 1972 for all three taxa was less than 10% with 6 days of exposure to 45 C and 100% relative humidity, and germination of seed collected in 1973 and 1974 ceased with 12 days of exposure. Maximum emergence for all taxa occurred at planting depths of 1.3 and 2.5 cm. Seed age influenced seedling emergence of white morningglory and ivyleaf morningglory but not entireleaf morningglory. Total numbers of seed produced per plant for white, entireleaf, and ivyleaf morningglory were 15,200, 14,600, and 5,800, respectively.

Glyphosate [N-(phosphonomethyl)glycine] (30, 125, 250 mg/L) in petri dishes had no effect on germination of prickly sida (Sida spinosa L.), velvetleaf (Abutilon theophrasti Medic), barnyardgrass [Echinocloa crus-galli (L.) Beauv.] and johnsongrass [Sorghum halepense (L.) Pers.] seeds, but additional experimentation indicated that glyphosate stimulated germination of redroot pigweed (Amaranthus retroflexus L.) seeds. Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion) (30, 125, 250 mg/L) did not affect germination of the three broadleaf species, but inhibited johnsongrass and barnyardgrass germination. In the greenhouse, soil surface applications of glyphosate (1.1, 2.2, 9.0 kg/ha) did not significantly affect emergence of these five weed species when they were on or beneath the soil surface at time of treatment. Paraquat (same rates) did not affect broadleaf weed emergence but some rates inhibited grass weed emergence when the seeds were treated while on the soil surface. It is unlikely that normal field use rates of glyphosate will influence weed emergence; whereas paraquat may inhibit the emergence of some grass weeds if the herbicide contacts seeds on the soil surface.

The uptake, translocation, and metabolism of the herbicide fluridone 1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone was studied in cotton (Gossypium hirsutum L. ‘Stoneville 213’) (fluridone tolerant) and corn (Zea mays L. ‘Migro 5040’), soybean [Glycine max (L.) Merr. ‘Calland’], and rice (Oryza sativa L. ‘Nato’) (fluridone susceptible). Uptake studies with 14C fluridone demonstrated that all species absorbed radioactivity with rice having the highest concentration. Equivalent concentrations of radioactivity were observed in corn, cotton, and soybean. Absorbed fluridone was retained primarily in the roots and the basal region of the stem of cotton, while in the herbicide susceptible species fluridone was readily translocated into the shoots. No appreciable metabolism of fluridone was observed in the roots or shoots of cotton and soybean. Tolerance of cotton to fluridone was primarily attributed to the limited translocation of the compound.

Germination of fruit of common lambsquarters (Chenopodium album L.) from three out of four sources was enhanced by 9 to 41% by removal of the fruit coat, and by 21% by washing the fruit for 70 h. Brown-black seed germinated more rapidly than the black and brown seed after washing for 70 h. The washing treatment appeared to remove some unknown inhibitors. After washing, seed germination was found to be positively correlated with seed size.

The persistence of isopropalin (2,6-dinitro-N,N-dipropylcumidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline] and trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) applied at recommended (1X) and high (2X) rates was studies in the field on two soils. A sorghum [Sorghum bicolor (L.) Moench ‘RS 610’] root bioassay showed that the recommended rates of the herbicides caused 20% or less root inhibition at the end of the growing season in 1972. Both nitralin and trifluralin were more persistent in 1974 than in 1972 as shown by the root bioassay and growth of fall-sown rye (Secale cereale L.). The yield of sweet corn (Zea mays L. var. rugosa Bonaf. ‘Gold Cup’) was not significantly reduced when grown 1 yr after the initial application of the herbicides.

When seed coats of scarlet morningglory (Ipomoea coccinea L.) were pricked with a needle or scarified by H2SO4, seed germination was improved. The highest percent germination was obtained with seeds pricked with a needle or exposed to H2SO4 for 180 min prior to incubation in moist paper towels. Seed planted in a potting mixture of sandy clay loam, ground sphagnum moss, and sand had the highest germination after 75 min exposure to acid. Scarlet morningglory seed germination was highest (74%) between 15 and 30 C after 144 h incubation.

The impact of a weevil (Rhinocyllus conicus Froel.) (Coleoptera: Curculionidae) on Carduus thistles in Virginia was evaluated in terms of seed reduction and viability during 1973 and 1974. Musk thistle (Carduus nutans L.) seed production from terminal and first lateral heads was reduced by 10% in 1973 and 75% in 1974 due to larval feeding of R. conicus. The greater seed reduction in 1974 was caused by heavy infestation (45% in 1973, 70% in 1974); there was a five-fold increase in the number of weevil pupation chambers per head over the previous year. Total seed production per plant decreased by 35 to 36% in both years despite increased plant vigor due to better growing conditions in 1974. Larval feeding reduced viability of mature musk thistle seeds. Although individual heads of plumeless thistle (Carduus acanthoides L.) were frequently destroyed by larval feeding, seed production from early heads of this thistle decreased by only 5% in 1973 and 4% in 1974 due to low rates of infestation (9% in 1973, 5% in 1974). Total seed reduction per plant for each of the two years was less than 0.2%. Infested heads of plumeless thistle did not produce sufficient seeds for evaluation of the weevil's impact on seed viability.

Yellow nutsedge (Cyperus esculentus L.) tuber maturity was studied to determine its influence on accumulation of 14C from urea and NAA (naphthaleneacetic acid). Radioactive carbon from the above sources accumulated in tubers in decreasing amounts as tubers became more mature when the plants to which they were attached were treated. Tubers that were young at treatment accumulated the highest concentration of radioactivity and parent tubers (most mature) accumulated the least 14C. Tubers that were classified as mature, but not parents, accumulated insignificant amounts of radioactive carbon.

Several differences between the mode of action of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate] were observed on wild oats (Avena fatua L.) in growth chamber experiments. Trifluralin exhibited little or no postemergence effect when applied to the soil surface. Surface applications of triallate interfered with deposition of epicuticular wax on leaf surfaces, and caused necrotic lesions, leaf break, and the abortion of the first leaf through the coleoptile. Trifuralin, but not triallate, incorporated in the soil reduced extension of the wild oat coleoptile. Soil-incorporated treatments involving trifluralin induced more extensive swelling of the mesocotyl, coleoptile node, and and coleoptile than triallate applied similarly. Triallate appeared to exert its major effect on cell elongation of the wild oat foliar material enclosed in the coleoptile. Trifluralin caused its greatest phytotoxic effect on the meristematic tissue at the region of the coleoptile node.

Some genetic and physiological aspects of seed germination of wild and weedy sunflowers were investigated in order to analyze their population differentiation in seed characteristics. Seed germination of six populations classified on the basis of morphology as Helianthus exilis Gray, H. exilis-bolanderi hybrids, and H. bolanderi Gray was studied under red light at 20 C. The average germination of the three groups respectively were 56, 63, and 42%. Germinability of individual plant progenies derived from populations of H. bolanderi and H. exilis was studied under red and far-red light combined with the pretreatments at two temperatures (10 and 20 C). Average germination per progeny reached a maximum of 59% with red light and 10 C in H. bolanderi. Far-red light promoted germination of H. bolanderi but was ineffective with H. exilis. The homogeneity of populations within each taxon and the fact that germinability differences among the H. bolanderi progenies were consistent over replications, suggest a genetic component of variation. However, progenies obtained by crossing selected individuals that germinated under certain light and temperature treatments, were not significantly correlated in germinability with that of their parents. Inheritance of germination characteristics appears to be complex and highly dependent on the environmental conditions.

Bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-(4) 3H-one 2,2-dioxide], cyperquat (1-methyl-4-phenylpyridinium), and perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide} were evaluated for their potential use as postemergence herbicides for selective yellow nutsedge (Cyperus esculentus L.) control in Kentucky bluegrass (Poa pratensis L.) in field studies. High rates of these herbicides as single or split applications were effective and only slightly reduced verdure of Kentucky bluegrass, indicating excellent selectivity. In greenhouse studies perfluidone exhibited growth retardant properties. Shoot dry weight production was inhibited and root dry weight of treated plants was markedly reduced. These two factors are undesirable features for commercial sod production.

Preemergence application of chloramben (3-amino-2,5-dichlorobenzoic acid) at 5.0 and 6.7 kg/ha, chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea] at 2.2 kg/ha, and linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] + nitralin [4-(methyl-sulfonyl)-2,6-dinitro-N,N-dipropylaniline] at 1.1 + 1.1 kg/ha controlled 95% or more of the barnyardgrass [Echinochloa crus-galli (L.) Beauv.], common lambsquarters (Chenopodium album L.), red-root pigweed (Amaranthus retroflexus L.), Powell amaranth (A. powellii S. Wats.), and hairy nightshade (Solanum sarachoides Sendt.), but reduced stands and injured direct-seeded asparagus (Asparagus officinalis L. ‘UC-66’). Linuron at 1.1 kg/ha controlled only 84% of the barnyardgrass and metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] at 0.6 kg/ha controlled about 50% of the hairy nightshade. Activated carbon applied at 56 and 112 kg/ha in a 3-cm band over the seeded row protected the asparagus from chloramben at 5.0 kg/ha, chlorbromuron at 2.2 kg/ha, and linuron + nitralin at 1.1 + 1.1 kg/ha. Weed control generally was reduced about 10% in the carbon band, but control was still 85 to 90%. Metribuzin reduced asparagus stands and vigor severely, even when 112 kg/ha of activated carbon was applied.

Seed lots of Macartney rose (Rosa bracteata Wendl.), yaupon (Ilex vomitoria Ait.) huisache [Acacia farnesiana (L.) Willd.], and honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] were exposed for various periods to radiofrequency (RF) dielectric heating by electromagnetic fields of 10 and 39 megahertz (MHz) at various field intensities in attempts to increase their germination. Both continuous-wave and pulse-modulated exposures were used at 39 MHz. Seed samples were preconditioned at temperatures from 24 to −43 C before exposure. Sixty-Hz a-c and d-c electrical treatments were included in some experiments. Although significant increases in germination were obtained by RF treatment of huisache and honey mesquite seed in some experiments, results with different huisache seed lots were inconsistent. The germination of Macartney rose seed was not increased, and no germination was observed in yaupon, regardless of the treatment employed.