The relative effectiveness of eight acetanilide herbicides for controlling annual weeds in processing peas (Pisum sativum L.) was evaluated in field studies and the susceptibility of peas to injury from these herbicides was studied in both the field and greenhouse. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] was the most phytotoxic to peas grown in washed silica sand in the greenhouse when the herbicides were applied at concentrations of 2 and 8 mg/L. Field trials conducted over a 2-yr period and simulated rainfall experiments in the greenhouse demonstrated that the phytotoxicity to peas by acetanilide herbicides applied preemergence at 2.2 and 4.5 kg/ha was greatly influenced by subsequent rainfall. When 2.5 cm of simulated rainfall were applied immediately after herbicide application, pea injury increased. Injury to peas was avoided in the field by delaying alachlor application at 2.2 kg/ha until peas began to emerge. This treatment also gave excellent control of annual grass weeds. Greenhouse studies demonstrated that injury to peas by all eight acetanilide herbicides at 2.2 and 4.5 kg/ha could be avoided by delaying application until pea emergence. Alachlor, propachlor (2-chloro-N-isopropylacetanilide), and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] gave slightly superior weed control than butachlor [N-(butoxymethyl)diethylacetanilide] and H 22234 [N-chloroacetyl-N-(2,6-diethylphenyl)-glycine ethyl ester].

A survey of the fungal and bacterial flora of waterhyacinth, [Eichornia crassipes (Mart.) Solms] infested with two arthropods, Neochetina eichhorniae Warner (weevil) and Orthogalumna terebrantis Wallwork (mite) was undertaken to determine the role of microorganisms in the decline of this host in Florida waters. Generally arthropod-infested plants were more diseased, had smaller laminae, lower numbers of live petioles and higher numbers of dead petioles per plant than noninfested plants. Several parasitic fungi, including some known pathogens of waterhyacinth, and soft-rot bacteria were isolated from arthropod-infested and noninfested plants. Higher numbers of microorganisms were present on arthropod-infested than on noninfested plants. The fungi and bacteria occurred randomly on arthropod-damaged waterhyacinth. No vector relationship was discovered between the arthropods and any fungus or bacterium. However, Acremonium zonatum (Saw.) Gams a virulent pathogen of waterhyacinth, and other necrotic leaf-spot diseases (‘disease B’) were predominant on arthropod-damaged plants. Disease B was independent of the arthropods, while A. zonatum incidence on waterhyacinth in sample sites was related especially to damage by adult mites. The origin of the observed association between A. zonatum symptoms and mite damage on laminae is unclear, even though field observations suggest a direct relationship between them. The weevil was also capable of aiding A. zonatum infections by creating points of entry for this pathogen into the host. In laboratory tests, waterhyacinths could be killed by the combined effects of the weevil and A. zonatum, although death did not ensue in the field under existing levels of this disease. The combined effects of arthropods and diseases led to reduction in the photosynthetic area of waterhyacinth and under severe stress, to root- and crown-rots. It is recommended that the process of biological control of waterhyacinth in Florida should include an integrated approach, using insects and pathogens.

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 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.

Greenhouse studies were conducted to investigate the basis for effective field control of yellow nutsedge (Cyperus esculentus L. var. esculentus) when atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-trizine] was applied late postemergence. Yellow nutsedge responded similarly to atrazine applied preemergence, early postemergence, or late postemergence. Yellow nutsedge growing with or without the presence of the mother tuber responded similarly to atrazine applied early postemergence. Atrazine application to the soil resulted in much greater yellow nutsedge injury than foliar application. The addition of oil enhanced atrazine activity when foliarly applied, but not when soil applied. Simulated rainfall immediately after postemergence applications enhanced yellow nutsedge control more than when simulated rainfall was delayed. The primary roots of yellow nutsedge appeared to be more important than other underground absorbing areas for atrazine uptake in young plants. Plants from tubers originating from lower soil depths produced secondary roots deeper, and these plants were less affected by atrazine applied preemergence than plants originating from tubers closer to the soil surface. A considerable reduction in atrazine activity was obtained when tubers were planted into soil 1 month after atrazine application.

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.

Herbicides used in corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and soybeans [Glycine max (L.) Merr.] were applied in the spring and their persistence into late summer was determined during 1974 to 1976. Composite soil samples from the top 5 cm of field plots were taken each August and bioassayed in the greenhouse. Bioassay species used were winter wheat [Triticum aestivum L.) and soybeans for herbicides used in corn and sorghum, and winter wheat and white mustard (Brassica hirta Moench) for herbicides used in soybeans. Soil persistence of triazine herbicides caused more injury to winter wheat, soybeans, and white mustard than any other class of herbicides tested. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] showed the most soil persistence of the five triazines evaluated. At normal field application rates, herbicides other than the triazines showed little injury to the bioassay plants. Soil persistence of herbicides was further reduced when combinations of reduced rates of each herbicide were utilized. Herbicides used for spring applications in corn showed more soil persistence in August than did the herbicides for sorghum, while herbicides for soybeans generally were least persistent. Postemergence herbicide applications resulted in more injury in bioassay species than preplant incorporated or preemergence applications. Persistence of some herbicides will restrict certain options to the grower such as changing crops in case of crop failure, fall planting of winter wheat, double cropping, or certain crop rotations.

Treatments that enhanced the germination of dormant seed of dwarf spikerush [Eleocharis coloradoensis (Britt.) Gilly] the most were chilling seed at 2 C for 3 months and then scarifying with sodium hypochlorite, scarifying seed and then chilling wet seed at 7 C for 3 months, or chilling wet seed at 2 C for 24 months. Percentage of germination for these treatments were 58, 56, and 65%, respectively. Scarifying seed with sodium hypochlorite after they had been chilled wet for 12 to 24 months at 2 C reduced germination. Other treatments that significantly enhanced germination were chilling seed wet for 4 months at 2 C, scarifying dry-stored seed with a 5.25% solution of sodium hypochlorite for 10 h, and soaking seed in concentrated hydrochloric acid for 24 min. These latter treatments resulted in germination percentages of 35, 33, and 35, respectively. Eighty percent of the viable seed usually germinated within 10 days, and when germination was poor, seed lacked embryos or were empty. Dormancy appeared to be due to an impermeable seed coat and not to a germination inhibitor.

Glyphosate [N-(phosphonomethyl)glycine] consistently controls many winter annual weeds in dormant bermudagrass [Cynodon dactylon (L.) Pers.] but injures actively growing turf. Experiments were conducted to determine the effects of dates of glyphosate treatments on control of winter annuals in different stages of maturity and on the tolerance of bermudagrass when applied to the turf at different stages of greenness from dormant turf in the winter to actively growing turf in the spring. Glyphosate was applied at rates of 0, 0.3, 0.6, 1.1, and 2.2 kg/ha to different plots of winter annuals and bermudagrass at 3-week intervals from February 13 to May 3. Glyphosate at 0.3 kg/ha controlled at least 90% of annual bluegrass (Poa annua L.), spur weed (Soliva sessilis P. & K.), and corn speedwell (Veronica arvensis L.) within a 6-week period regardless of the date of treatment. All glyphosate treatments injured bermudagrass when applied to semi-dormant or actively growing turf. Bermudagrass treated with glyphosate at 0.3 kg/ha was injured the least and the turf had essentially recovered by 6 weeks after treatment. However, the injury from higher rates (0.6 to 2.2 kg/ha) was too severe to be acceptable in turf areas. Glyphosate did not severely injure bermudagrass when applied to dormant turf.

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.

Biotypes of several annual broadleaved weeds tolerant to 2-chloro-s-triazines have been recorded, including common lambsquarters (Chenopodium album L.). The mechanism of resistance in common lambsquarter was based on the differential inhibition of the Hill reaction in chloroplasts by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]. Chlorophyll fluorescence and electron transport assays were used with isolated chloroplasts of atrazine-tolerant and susceptible biotypes, to determine the effect of atrazine and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on photosystem II (PS II) activity, differential atrazine penetration of the chloroplast envelope, and relative tolerance to chloro, methoxy, and methylthio triazines. Atrazine and diuron inhibited electron transport on the reducing side of PS II in susceptible biotype chloroplasts. In tolerant biotype chloroplasts only diuron inhibited electron transport whereas atrazine had only slight effects. There were no differences in the chloroplast membrane permeability to atrazine in the two biotypes. Chloroplasts of the atrazine-tolerant biotype of common lambsquarters were also tolerant to the other classes of triazines tested.

Chlorophyll content of wheat (Triticum aestivum L. ‘Mericopa’) and corn (Zea mays L. ‘Merit’) treated with the herbicide fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)-phenyl]-4(1H)-pyridinone} and grown under high light intensity (10.8 klux), was markedly reduced. Corn and wheat germinated from seeds treated with 10 uM fluridone and grown for 6 days were almost completely bleached. Under low light intensity (108 lux) the influence of fluridone on chlorophyll production was greatly reduced. Under very low light intensity (21.5 lux) this influence was almost completely lost. The effect of light on the activity of fluridone suggests that the inhibition of carotenoid production may represent the mode of action of this herbicide. This study shows that the carotenoid content of wheat or corn drops dramatically when these plants are treated with fluridone.

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.

Tobacco (Nicotiana tabacum L. ‘X-73’) callus tissue cultures were used in a bioassay system for determining the effect of the following substituted 2,6-dinitroaniline herbicides on growth: trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine); oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide); benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine); AC 92390 (N-sec-butyl-2,6-dinitro-3,4-xylidine); penoxalin [N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine]; GS-38946 (N-ethyl-N-tetrahydrofurfuryl-4-trifluoromethyl-2,6-dinitroaniline); chlornidine [N,N-di(2-chloroethyl)-4-methyl-2,6-dinitroaniline]; nitralin [4-(methylsulfonyl)2,6-dinitro-N,N-dipropylaniline]; dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine); isopropalin (2,6-dinitro-N,N-dipropylcumidine), and profluralin [N(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine]. The molar concentration required to inhibit fresh weight gain by 50% (I50) was determined by using linear regression analysis on data from a range of five concentrations of each chemical. I50 values did not correlate with structural variations or available physical constants. Herbicides listed in order of increasing activity are AC 92390< GD-38946<profluralin = isopropalin<benefin = chlornidine = trifluralin = nitralin<oryzalin = penoxalin < dinitramine. Exogenously applied D-α-tocopherol acetate at 100 times the I50 concentrations decreased the inhibition of tissue growth by the herbicides.

A 6-h imbibition in sodium azide solution stimulated nearly 100% germination of dormant wild oat (Avena fatua L.) seeds in petri dishes. Sodium azide stimulated germination in soil in both field and growth chamber experiments. Disc-incorporated sodium azide in soil at 11.2 kg/ha caused a 4-fold increase in wild oat emergence as 50% of the wild oat seeds in a natural infestation germinated compared to 12% in control plots. Wild oat seed germinated from greater soil depths following sodium azide application. Sodium azide appears to need a deep, thorough soil incorporation and adequate soil moisture for maximum stimulation of germination.

Several herbicide antidotes were used with barban (4-chloro-2-butynyl m-chlorocarbanilate) in the field and greenhouse. The seed treatments of R-25788 (N,N-diallyl-2,2-dichloroacetanilide) and NA (1,8-naphthalic anhydride) at 0.12 or 0.5% by seed weight reduced wheat (Triticum aestivum L. ‘Waldron’) injury with barban in the field and greenhouse. R-25788 and R-28725 (2,2-dimethyl-3-dichloroacetyloxazolidine) applied at 0.14 kg/ha as a spray with barban or R-28725 applied as a seed treatment at 0.06 or 0.25% by seed weight were ineffective in reducing wheat injury. S-449 (4-chloro-2-hydroxyiminoacetanilide) at 0.06 or 0.25% by seed weight reduced wheat injury with barban in the greenhouse; however, in the field these treatments increased wheat injury and reduced wild oat (Avena fatua L.) control.

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.

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.

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.