The herbicidal action of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} on corn (Zea mays L. ‘Goldencrossbantam’) was investigated in preemergence and postemergence experiments and hydroponic culture. Soil-applied sethoxydim did not inhibit corn germination. Leaves failed to emerge through the coleoptile with a high herbicide rate (1.6 kg ai/ha), but chlorotic leaves emerged at a lower rate (0.8 kg ai/ha). Growth of corn seedlings treated with a foliar application of 0.2 kg ai/ha was inhibited within 1 day after treatment, but at a lower application rate (0.05 kg ai/ha) growth continued with chlorotic zones on newly expanding leaves. Over the concentration range 3 × 10-5 to 1 × 10-6 M, sethoxydim inhibited the growth of primary roots of corn in hydroponic culture within 24 h. Cytological investigation showed that sethoxydim inhibited cell division but did not interfere with mitosis.

Pretreatment of etiolated cucumber cotyledons with potassium (K), benzyladenine (BA), or δ-aminolevulinic acid (ALA) for 20 h in the dark, followed by exposure to light for 24 h, increased chlorophyll and carotenoid content. A similar treatment with fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} decreased the levels of these photosynthetic pigments. However, when the etiolated cotyledons were pretreated with either BA or ALA for 20 h in the dark, followed by fluridone during a 24-h light period, the inhibitory effects of fluridone on chlorophyll content were reversed and the values were higher than the controls. In these treatments, ALA did not counteract the inhibitory effects of fluridone on carotenoids, but BA reduced the effects. In the cucumber cotyledon greening system, K was found to be most effective in stimulating both chlorophyll and carotenoid accumulation. When K was administered to the cotyledons either together with, prior to, or after the fluridone treatment, the inhibitory effect of fluridone on chlorophyll accumulation was totally eliminated and the stimulatory effects due to K were still maintained. Although K increased carotenoid content, it did not reverse the inhibitory effect of fluridone on carotenoids. From these findings it is concluded that the inhibition of chlorophyll and carotenoid accumulation by fluridone may be mediated via unrelated mechanisms at fluridone concentrations that do not totally eliminate or drastically reduce carotenoid content.

The mode of action and selectivity of oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] were investigated in tolerant rice (Oryza sativa L.) and susceptible barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯3 ECHCG]. Oxadiazon produced only brown spots on the foliage of rice plants at higher rates (> 500 ppmv), while LC50 for barnyardgrass was 250 ppmv. Translocation of 14C-oxadiazon from the treated leaf was minimal in both species; after 7 days, about 2 and 3% of applied 14 C translocated in rice and barnyardgrass, respectively. In rice, 14C recovered in water and chloroform washings of the treated leaf was 25% in each and in barnyardgrass, 20 and 18%, respectively. After water and chloroform washings, 14C-oxadiazon present in the treated leaf of barnyardgrass and rice was 36 and 26%, respectively. In rice and barnyardgrass, unaltered 14C-oxadiazon represented 86 and 79% of applied 14C, respectively, 7 days after application. In barnyardgrass 7 days after foliar application, oxadiazon inhibited 14CO2 fixation and the export of fixed carbon. The effects were less marked in rice.

One to 5.6 μM DCPA (dimethyl tetrachloroterephthalate) inhibited oat (Avena sativa L. ‘Victory’) root growth within 12 to 18 h. Treated roots were severely stunted and swollen. An analysis of cell division in roots treated with DCPA revealed a disruption of normal mitosis after prophase. Metaphase, anaphase, and telophase division figures were absent 8 to 10 h after treatment with 5.6 μM DCPA. In contrast, a 24-h treatment with 5.6 μM DCPA was necessary to eliminate prophase division figures. The number of aberrant division figures increased concomitantly with the reduction in normal division figures. The predominant type of aberrant division figure was a condensed prophase. When the aberrant division cycle was completed and cells entered interphase, the dispersed chromosomes coalesced to form large, polymorphic nuclei and, occasionally, micronuclei. Approximately 60% of the outer four tiers of cells in roots treated with 5.6 μM DCPA developed abnormal cell walls. These data suggest that DCPA causes root growth inhibition by disrupting several processes involving organized microtubules.

Seedlings of winged elm (Ulmus data Michx.), bur oak (Quercus macrocarpa Michx.), black walnut (Juglans nigra L.), eastern redcedar (Juniperus virginiana L.), and loblolly pine (Pinus taeda L.) were treated in nutrient solution with ring-labeled 14C-tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} or 14C-hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione]. Four hours later, 14C was detected in all sections of winged elm treated with 14C-tebuthiuron and 14C-hexazinone. Root absorption of the tebuthiuron label by the other species occurred in the order: loblolly pine > bur oak > black walnut = eastern redcedar. The sequence of 14C-hexazinone absorption was: loblolly pine > black walnut ≥ bur oak = eastern redcedar. Foliar accumulation of the tebuthiuron label occurred in the order: bur oak > loblolly pine > eastern redcedar = black walnut, whereas the sequence with hexazinone was loblolly pine > bur oak > black walnut = eastern redcedar. The presence of the three metabolites of hexazinone in loblolly pine suggests that it may be resistant to hexazinone as a result of its ability to degrade hexazinone rather than its ability to limit uptake.

Glyphosate transport was studied using the 14C-labeled herbicide. Because glyphosate appears to undergo little metabolism in plants, detected 14C was assumed to indicate the presence of glyphosate. Leaf-girdling experiments demonstrated that 14C-glyphosate [N-(phosphonomethyl)glycine] transport in treated quackgrass [Agropyron repens (L.) Beauv. ♯3 AGRRE] leaves occurred in both leaf symplast and apoplast. Symplastic transport was toward the leaf tip and the leaf base. Apoplastic transport was toward the leaf tip only. Rhizome-girdling experiments showed that translocation of glyphosate from a treated shoot to another shoot on the same rhizome occurs primarily in the rhizome symplast. Girdling the base of quackgrass culms showed that acropetal transport of glyphosate from the rhizome into quackgrass shoots is in the apoplast and the symplast of the culms of quackgrass shoots. Excision of rhizome buds and rhizome apices indicated that the rhizome is a sink for glyphosate independent of rhizome buds or rhizome apices. The concentration of 14C-glyphosate in rhizome buds was less in plants with rhizome apices removed than in those with apices intact. The concentration of C-glyphosate in rhizome apices did not differ between plants with buds removed and those with buds intact. 14C-glyphosate applied to a girdled rhizome apex remained primarily in the apex. Some transport of glyphosate past the girdle occurred, indicating apoplastic transport of glyphosate in the rhizome. Apoplastic transport of 14C-glyphosate in the rhizome was greatest in water-stressed plants.

A study was conducted at two locations to evaluate the effects of cheat (Bromus secalinus L. ♯3 BROSE) competition on four seeding rates (4.5, 9.0, 13.5, and 22 kg/ha) of alfalfa (Medicago sativa L. ‘Riley’). Three stages of first harvest (early bud, early bloom, and late bloom) were imposed on fall-planted alfalfa, with and without cheat overseeding, to determine the effects of harvest stage on alfalfa yield and quality. Cheat infestations significantly decreased alfalfa production and forage quality. Increasing the seeding rate of alfalfa only partially offset these losses. Harvesting early helped minimize the effect of cheat competition. First-harvest protein yield of forage was significantly decreased by, cheat overseeding. Total protein yield at first harvest was not affected by cutting stage but did increase with the two higher seeding rates of alfalfa.

Allelopathic effects of lantana (Lantana camara L. ♯3 LANCA) residues (root, shoot), foliar leachates, and the soil (where lantana was grown) on milkweedvine (Morrenia odorata Lindl. ♯3 MONOD) seed germination and growth over a 30-day period were examined. Foliar leachates or the soil collected from the field where lantana had been growing had no effect on the final germination percentage or the seedling growth of milkweedvine. Incorporation of dried lantana shoot or root material into soil had no effect on the final percentage germination but caused significant reductions in milkweedvine growth over a 30-day test period. Roots were more inhibitory than shoots. Fifty percent of milkweedvine seedlings died within 15 days after germination at 1% (w/w) dried lantana root incorporation into the soil, and higher concentrations increased seedling death. Lantana roots incorporated into the soil produced foliar symptoms such as wilting and desiccation, whereas lantana shoots incorporated into the soil produced yellowing of the foliage of milkweedvine. Allelopathic activity of lantana residues was still strong even after decomposition of lantana residues for 4 weeks prior to the planting of milkweedvine seeds.

Six multiple-cropping systems composed of: a) turnip (Brassica campestris spp. rapifera), corn (Zea mays L.), and snapbean (Phaseolus vulgaris L.); b) turnip, peanut (Arachis hypogaea L.), and snapbean; c) turnip, corn, and turnip; d) turnip, peanut, and turnip; e) snapbean, soybean [Glycine max (L.) Merr.], and cabbage (Brassica oleracea L.); and f) turnip, cucumber (Cucumis sativus L.), cowpea [Vigna unguiculata (L.) Walp.], and turnip were subjected to nematicide and weed control programs of cultivation or herbicides. Herbicide programs were superior to cultivation in control of weeds. Weeds remaining in the row following cultivation competed severely with crops. Weed species remaining were altered depending on the method of control and crop. Yellow nutsedge (Cyperus esculentus L. ♯3 CYPES) increased rapidly in all herbicide programs but not in cultivated plots. Pigweeds (Amaranthus spp.) were controlled by herbicides but increased in cultivated plots. Corn, peanut, soybean, and spring snapbean yields were higher in herbicide treatments than in cultivated treatments. Cucumber was the only crop that had increased yields for both main effects, herbicide and nematicide. Turnip was consistently injured in herbicide treatments, which was believed to be caused by residues from previous crops interacting with pathogens and possible allelopathic effects of decaying organic matter.

Maximum germination of flodman thistle [Cirsium flodmanii (Rydb.) Arthur ♯3 CIRFL] occurred at alternating temperatures of 10 to 20 and 20 to 30 C. Seeds germinated (20%) in 1.7 M NaCl. Light was important in seed germination; however, its absence could be overcome by adding 8.6 × 10-5 M GA3 (gibberellic acid) to the germination medium. The greatest seedling emergence occurred when seeds were planted on the soil surface and was lower when seeds were buried at any depth in the soil. Osmotic potentials at −0.5 MPa and greater reduced germination, but 3% of the seeds germinated at −1.3 MPa. Flodman thistle seedlings tolerated average plant water potentials of −0.9 and −1.1 MPa, but they died when the water potential was decreased to −1.5 MPa. Flodman thistle seedlings 43 days old and with four true leaves resprouted after topgrowth removal. Regrowth was evident on 75% of the clipped plants 13 days after initial topgrowth removal. Flodman thistle rosettes spread more rapidly and rosette survival was enhanced more in a weed-free nursery than in a weedy pasture.

The growth of green foxtail (Setaria viridis L. Beauv. ♯3 SETVI) and yellow foxtail [S. lutescens (Weigel.) Hubb. ♯ SETLU] in full sunlight, under 55 and 73% shade and within a wheat (Triticum aestivum L. ‘Neepawa’) stand, was compared in field experiments conducted over 3 yr. Shade resulted in a proportionately greater reduction in tiller number of yellow foxtail than of green foxtail. Plants growing in full sunlight produced up to five times more tillers than those growing in the crop. Averaged over the 3 yr, the two shade treatments reduced dry-matter accumulation of both species by 40% or more. The dry weight of plants within the crop was only about one-eighth of that of plants grown in full sunlight. Under both shade treatments and in the crop, yellow foxtail was consistently taller than green foxtail. Nevertheless, no differences in dry weight occurred between species under either shade treatment or in the crop. The results indicate that neither of the two species is distinctly more shade tolerant than the other, nor better adapted to compete with wheat.

The germination of milkweedvine (Morrenia odorata Lindl. ♯3 MONOD) seed at 20 or 25 C was unaffected by a 12-h photoperiod. The 12-h photoperiod, however, decreased germination by 50% at 15 C. No germination occurred at 35 C regardless of photoperiod. By alternating 35 C for 12 h with 20 C for 12 h, the germination percentage was 57%. Seedling growth was maximum at alternating temperatures of 30/20 C. Optimum pH for germination and seedling growth was 7 and germination did not occur at pH levels below 6. Seed germination declined steadily at osmotic stress below −0.12 MPa; no germination occurred at −0.5 MPa. Seedling growth was not influenced by osmotic stress down to −0.18 MPa. Germination percentages of seeds kept under aerated water and nonaerated water were similar, but the seedling growth was greater in aerated water. Seedling emergence was maximum from depths of 0.5 to 2.5 cm, but no seedling emerged from 0 or 10 cm. Planting depth was negatively correlated (r = −0.7) with shoot growth but positively correlated (r = +0.98) to root growth.

Various environmental factors were tested under laboratory conditions to determine their effects on germination of seeds of prickly sida (Sida spinosa L. ♯3 SIDSP). Neither freezing and thawing nor moist chilling at 5 C promoted seed germination. However, increasing the incubation temperature and subjecting seeds to wet-dry cycles enhanced germination; high temperatures were more effective than alternate wetting and drying. Shifting seeds from a lower to a higher temperature regime increased germination. Seeds shifted from 15/6, 20/10, 25/15, or 30/15 C to higher regimes of 20/10, 25/15, 30/15, 35/20, or 40/25 C germinated to greater percentages than did seeds kept continuously at the lower thermoperiods. With an increase in length of time seeds were at a lower temperature, there was an increase in the percentage that germinated after they were moved to a higher regime.

A culture medium and environmental conditions were selected for ovule culture of velvetleaf (Abutilon theophrasti Medic. ♯4 ABUTH), which allowed development parallel to that occurring in vivo. Of the six nutrient media evaluated, the most suitable one contained an organic nitrogen source and was of high osmotic potential. A liquid medium with a pH of 5 to 7, and culture for 14 days at 25 C under green light (1.3 μmole·m-2·-1) encouraged good embryo and ovule development. No difference was recorded between polyethylene glycol 20000 and mannitol in the medium used for dehydration and subsequent imbibition of cultured mature ovules. To investigate the effects of maternal tissues, surgical alterations were performed on the testa and funiculus of immature velvetleaf ovules. The intact testa appears to be a barrier to nutrient absorption and reduces the fresh and dry weights and embryo length. Ovule and embryo development was significantly better if either the testa was nicked or the funiculus removed.

The culture of ovules excised from velvetleaf (Abutilon theophrasti Medic., ♯4 ABUTH) capsules 5 days after anthesis was used to measure the effects of abscisic acid (ABA) and sucrose on embryo development and prevention of precocious germination. ABA at 1 × 10-7 M combined with 6% sucrose in the medium for the first 14 days of culture increased embryo development but prevented precocious germination. Higher concentrations of ABA inhibited embryo development. Without ABA, precocious germination increased directly with the concentration of sucrose in the medium, and embryos died. In vivo, ABA reached its highest concentration in ovules 5 days after anthesis but was undetectable after 16 days. Parental control of embryo development may involve ABA and an increasing concentration of osmoticum as seeds dehydrate during maturation.

Glyphosate [N-(phosphonomethyl)glycine] phytotoxicity to greenhouse-grown wheat (Triticum aestivum L. ‘Centurk’) was greatly reduced by Ca2+ in the carrier solution. Addition of ethylenediaminetetraacetic acid (EDTA) restored glyphosate phytotoxicity in hard water and increased phytotoxicity in deionized water. The phytotoxicity of 0.1 kg ae/ha glyphosate plus 1.0% (w/v) EDTA was equal to that observed for 0.2 kg/ha of the herbicide alone in deionized water or 0.4 kg/ha in water containing 200 ppm Ca2+. EDTA was more compatible with glyphosate in combination with X-77 or MON-0011 nonionic surfactant than with cationic surfactant (contained in a commercial formulation). Phytotoxicity could be increased by adding EDTA and nonionic surfactant to the latter formulation. EDTA increased glyphosate phytotoxicity to wheat when applied in water that contained high levels of calcium and bicarbonate. Glyphosate activity was greater at pH 4 than at pH 6 or 10, but EDTA was equally effective at pH 4, 6, or 10 for all levels of calcium tested up to 800 ppm. NaHCO3 probably reduced phytotoxicity by increasing the pH of the glyphosate solution.

Field studies were conducted to document the response of itchgrass [Rottboellia exaltata (L.) L.f. ♯3 ROOEX] in soybean [Glycine max (L.) Merr. ‘Forrest’] to selected herbicides and postplanting cultivation. Early cultivation stimulated emergence of itchgrass seedlings; however, when plots were cultivated two or three times, itchgrass was effectively removed from the tilled area. Cultivation had no effect on the density, height, standing biomass, or seed production of itchgrass plants in the soybean row but did increase soybean yield. In response to a density reduction of 90%, the average weight, number of tillers and branches, and seed production of single itchgrass plants increased by a factor of 2.9, 3.1, 2.3 and 2.6, respectively, in trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-treated plots. Individual plants did not increase growth following density reduction by a postemergence application of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Itchgrass plants competing for the entire season in plots treated with trifluralin reduced soybean yield approximately 21 g per weed, while itchgrass recovering from diclofop treatment and competing the remainder of the season reduced yield approximately 5 g per weed.

Field studies were conducted in North Carolina in 1981 and 1982 to evaluate the efficacy of postemergence over-the-top and postemergence-directed herbicides for control of five morningglory species: entireleaf [Ipomoea hederacea (L.) Jacq. var. integriuscula Gray], tall [Ipomoea purpurea (L.) Roth. ♯3 PHBPU], ivyleaf [Ipomoea hederacea (L.) Jacq. var. hederacea ♯IPOHE], pitted [Ipomoea lacunosa (L.) ♯ IPOLA], and scarlet [Ipomoea coccinea (L.) ♯IPOCC]. The glabrous morningglories (scarlet and pitted) were more easily controlled than the pubescent morningglories (ivyleaf, tall, and entireleaf). Lower soybean injury, higher morningglory control, and greater soybean seed yields were obtained with over-the-top herbicide applications at 4 weeks after planting (WAP) than at 6 WAP. Pitted morningglory was tolerant to low rates of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. This herbicide applied over the top at the R1 stage of soybean growth produced low yields, probably as a result of morningglory interference and herbicide injury to the soybeans. Postemergence-directed applications of linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] and metribuzin [4-amino-6-tert-butyl-3-(methylthio-as-triazin-5(4H)-one] alone or in tank mixtures with 2,4-DB resulted in soybean injury that ranged from 12 to 36%. Highest soybean seed yields (equivalent to weed-free control) from postemergence-directed herbicides were obtained with applications of 2,4-DB, linuron, and a tank mixture of metribuzin and 2,4-DB.

Bermudagrass [Cynodon dactylon (L.) Pers. ‘Tifway’] injured by MSMA (monosodium methanearsonate) plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] or 2,4-D [(2,4-dichlorophenoxy)acetic acid] plus mecoprop {2-[(4-chloro-o-tolyl)oxy] propionic acid} plus dicamba (3,6-dichloro-o-anisic acid) recovered more rapidly when nitrogen (N) was applied in sequence with the herbicides than when no N was applied. Bermudagrass recovery was faster with less injury within 2 weeks after herbicide treatment when N was applied at the first MSMA plus metribuzin treatment or when N was applied at 2 weeks after the first 2,4-D plus mecoprop plus dicamba treatment. Turf quality at 4 weeks or later was consistently as good or better in plots where N was applied at 2 weeks after the first application of either herbicide combination than when N was applied earlier.

Fluazifop-butyl {(±) butyl 2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, haloxyfop-methyl {methyl-2-[4-[[3-chloro-5-(trifluoromethyl-2-pyridinyl] oxy] phenoxy] propanoic acid}, and sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl-3-hydroxy-2-cyclohexen-1-one}exhibited soil herbicidal activity to annual grass species in greenhouse and field experiments. Control of forage sorghum [Sorghum bicolor (L.) Moench. ‘Rox Orange’] with all three herbicides was greater when seeds were planted at or near the soil surface than when planted 2, 4, or 6 cm deep. Imbibition of the herbicides by forage sorghum and soybean [Glycine max (L.) Merr.] seeds did not reduce germination at concentrations of 10-3 M or lower, but forage sorghum seedling survival and vigor were reduced by herbicide concentrations as low as 10-7 M. Fluazifop-butyl, haloxyfop-methyl, and sethoxydim were more phytotoxic when applied to the root zone than the shoot zone. Haloxyfop-methyl exhibited the longest soil residual control in the field followed by fluazifop-butyl and sethoxydim. Haloxyfop-methyl and fluazifop-butyl controlled simulated shattercane [Sorghum bicolor (L.) Moench. ♯3 SORVU] in soybeans with preemergence and early postemergence applications, whereas control from similar applications of sethoxydim was limited and variable.