The herbicide dichlobenil (2,6-dichlorobenzonitrile) inhibited soil nitrification significantly at 100 ppm following 1 and 2 weeks incubation but did not inhibit nitrification at the rates recommended for weed control.

Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] is a potent synergist of atrazine for postemergence control of weeds such as giant foxtail (Setaria faberi Herrm. ♯ SETFA) and large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA]. We determined whether: a) tridiphane could syngergize the activity of other herbicides known to be detoxified via enzymatic conjugation to glutathione, and b) differential toxicities of the synergized herbicides could provide control of proso millet (Panicum miliaceum L. ♯ PANMI) in corn (Zea mays L. “PAG SXIII”). Four herbicides were used in this study: EPTC (S-ethyl dipropylthiocarbamate), atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], CDAA (N-N-diallyl-2-chloroacetamide), and alachlor [2-chloro-2’,6’-diethyl-N-(methoxymethyl) acetanilide]. Herbicides and herbicide-synergist combinations were applied postemergence. In corn, tridiphane synergized the activity of EPTC at 2 and 4 kg ai/ha, causing 22 to 25% growth reduction. Atrazine was ineffective and CDAA only slightly effective in combination with tridiphane in causing growth reduction. However, alachlor was markedly synergized by tridiphane at both 2 and 4 kg ai/ha, resulting in 36 to 54% growth reduction compared with plants treated with herbicides alone. Proso millet followed a similar trend to corn: EPTC and alachlor were effectively synergized by tridiphane, while atrazine and CDAA were ineffective. Importantly, however, the rates of herbicide used for proso millet control were much lower than those used for corn. Our data suggest that tridiphane used in combination with EPTC or alachlor could provide improved control of proso millet in corn.

Behavior of 14C-haloxyfop-methyl {methyl 2-[4-[(3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoate} was examined in intact plants of soybean [Glycine max (L.) Merr. ‘Mead’], shattercane [Sorghum bicolor (L.) Moench. ♯ SORVU], and yellow foxtail [Setaria glauca (L.) Beauv. ♯ SETLU] and in cell cultures of soybean and yellow foxtail. Foliar absorption of 14C-haloxyfo-methyl by intact plants was almost complete within 48 h. Significant translocation occurred within 48 h of treatment, with soybean and shattercane plants translocating more 14C than yellow foxtail. Metabolism of 14C-haloxyfop-methyl in intact plants was similar among species. Haloxyfop-methyl was rapidly hydrolyzed to haloxyfop in treated leaves and then translocated to metabolically active areas within the plants. Significant quantities of polar products were also isolated. Soybean cells in suspension culture contained higher levels of 14C than did yellow foxtail cells. Most of the 14C in soybean cells was haloxyfop-methyl, while yellow foxtail contained mostly haloxyfop.

Absorption and translocation of 14C-glyphosate [N-(phosphonomethyl)glycine] by moisture-stressed common milkweed (Asclepias syriaca L. ♯ ASCSY) was studied in greenhouse and growth chamber experiments. Water-stressed [13% (w/w) soil moisture] common milkweed plants treated with glyphosate at 1.1 kg ae/ha produced shoot regrowth equal to untreated plants, whereas shoot regrowth of nonstressed [25% (w/w) soil moisture] glyphosate-treated plants was only 6% of untreated plants. All shoot regrowth originated from buds on the proximal half of roots. Common milkweed plants, maintained at 25% soil moisture, absorbed 44% of the 14C-glyphosate applied and translocated 20% from the treated leaf, whereas plants at 13% soil moisture absorbed 29% and translocated 7%. Wiping the leaf with tissue paper wetted with distilled water or chloroform prior to 14C-glyphosate application increased absorption from 35 (unwiped leaves) to 62 and 77%, respectively, for plants at 25% soil moisture, and increased absorption from 14 to 42 and 46%, respectively, for plants at 13% soil moisture. Wiping failed to increase translocation out of the treated leaf for plants at either soil moisture regime. Latex samples taken from the abaxial leaf surface opposite 14C-glyphosate-treated leaves and from petioles of treated leaves did not contain 14C, indicating that glyphosate did not enter laticifers. Proximal root buds accumulated less 14C-radioactivity than distal root buds and had lower respiratory rates, suggesting that proximal root buds are more dormant than distal root buds and thus accumulate less glyphosate.

Under greenhouse conditions, vaporization of oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] formulations (2 EC, 25 WP, 1G) was studied on cabbage (Brassica oleracea L. var. capitata L. F. alba DC. ‘Market Prize’), tomato (Lycopersicon esculentum Mill. ‘Campbell 37’), cucumber (Cucumis sativus L. ‘Straight 8’), and lettuce (Lactuca sativa L. ‘Salad Bowl’). The emulsifiable concentrate and granular formulations caused vapor injury to plants exposed under glass bell jars. Vapor injury to all species increased when exposure times were increased from 8 to 72 h. Lettuce was the most susceptible test species. Exposure temperatures of 18 and 29 C did not alter the amount of vapor injury apparent on tomato foliage. Oxyfluorfen vapor injury did not reduce dry weight of any test species.

Pot experiments were conducted in the field at Stuttgart, AR, during 1982 and 1983 to evaluate growth and morphological differences between strawhull and blackhull red rice (Oryza sativa L. ♯ ORYSA) biotypes collected from Arkansas, Louisiana, and Texas. All red rice biotypes were compared with rice (Oryza sativa L.) cultivars ‘Lebonnet’ and ‘Nortai’. Growth and morphological differences were greatest between cultivars and red rice biotypes, less between blackhull and strawhull types, and least among collections within blackhull or strawhull. Cultivars emerged slower, were shorter, tillered less, produced less straw and fewer panicles/plant, had a lower leaf area index, and had less grain shattering than most of the red rice biotypes. Blackhull red rice biotypes tillered 27% more, produced 18% more straw, and had later maturity than strawhull. Blackhull red rice from Arkansas emerged earlier, tillered 6 to 38% more, and produced 8 to 38% more panicles per plant than other red rice biotypes, whereas blackhull red rice from Texas was 11 to 26% taller at maturity than other biotypes.

The world distributions of yellow starthistle (Centaurea solstitialis L. ♯ CENSO) and Russian knapweed (Centaurea repens L. ♯ CENRE) are mapped based on information from world regional floras. A survey of weed specialists and herbaria was made in the United States, and the extent of the infestations and economic importance of these weeds was determined for the 48 contiguous states. Yellow starthistle currently occurs in 209 counties in 23 states and has apparently increased in abundance since 1970. Russian knapweed was reported in 412 counties in 21 states and does not seem to be spreading. Both of these weedy plant species are of greater economic importance in the western United States than in the east.

Uncertainty exists among extension agents and growers in northern Illinois whether a particular sorghum (Sorghum sp.) strain should be identified as johnsongrass [Sorghum halepense (L.) Pers. ♯ SORHA] or sorghum-almum (Sorghum almum Parodi. ♯ SORAL). To reduce confusion over its identity, field studies were conducted at Urbana, IL, in 1982 and 1983 to determine if phenotypic differences existed between a johnsongrass strain from Tennessee and the northern Illinois sorghum strain. Three planting dates (May 20, June 3, June 17) were used to determine if time of establishment would affect growth habits and phenotypic expression. Averaged over planting dates, the Illinois sorghum was taller (200 cm vs. 161 cm), produced more seed per panicle (2215 vs. 741), and had a larger shoot to rhizome plus root ratio (2:1 vs. 1:1) and a wider leaf blade (4.6 cm vs. 2.9 cm) than johnsongrass. In contrast, the johnsongrass produced more rhizomes per plant (51 vs. 10) with almost eight times the cumulative rhizome length per plant (778 cm vs. 117 cm). These results were consistent across planting dates. Comparison of chromosome counts from pollen mother cells and root tips showed both johnsongrass and the Illinois sorghum had 2n = 40; thus observed differences between the sorghum strains could not be explained by differences in chromosome number. The northern Illinois sorghum strain more closely resembled sorghum-almum morphologically than the Tennessee johnsongrass.

Achene germination of common crupina (Crupina vulgaris Cass. ♯ CJNVU) was 86% or greater at day/night temperatures ranging from 15/4 to 29/25 C. Germination was greatly reduced at a day temperature of 36 C, regardless of the night temperature. The time required for maximum germination (9 to 19 days) increased with decreasing night temperature. Maximum leaf area, rosette diameter, and dry-matter accumulation during vegetative growth occurred at 22/18 to 29/25 C, 22/18 C, and 22/18 C, respectively. The plants attained 50% or more of maximum dry-matter accumulation at day/night temperatures ranging from as low as 22/4 and 15/11 C to as high as 36/25 C. Net assimilation rate was relatively insensitive to growth temperature. Rosettes of common crupina grown at 22/11 or 29/18 C exhibited almost complete photosynthetic and respiratory temperature acclimation. Increasing the photoperiod from 10 to 12, 14, or 16 h accelerated flowering. Maximum achene production occurred in the 16-h photoperiod, but viable achenes were produced in all photoperiods. Temperature during vegetative growth influenced subsequent responses to photoperiod. Plants grown for 83 days in a 14-h photoperiod at 15/4 or 22/11 C and transferred to 26/20 C flowered and produced seed in photoperiods of 8 or 16 h. Plants grown at 29/18 or 36/25 C subsequently flowered only in the 16-h photoperiod at 26/20 C. Common crupina has a wide tolerance of variations in temperature and photoperiod. Its range in the United States can be expected to continue to increase.

Seed dormancy does not play a role in the germination ecology of curly dock (Rumex crispus L. ♯ RUMCR). This study confirms reports that freshly matured seeds are nondormant, and it shows that buried seeds exposed to natural seasonal temperature changes remain nondormant. From October 1981 through June 1983, seeds exhumed at monthly intervals germinated 80 to 100% at all thermo-periods. These results do not support suggestions that seeds of curly dock buried in soil enter dormancy. However, the results do explain why seeds of this species in the Beal and Duvel buried-seed experiments germinated when exhumed at various times during the growing season.

The influence of depth (0 to 20 cm) and duration (1 to 31 months) of burial on the deterioration, germination, and viability of common crupina (Crupina vulgaris Cass. ♯ CJNVU) was investigated in the field. Germination and decay of achenes prior to removal from the field were greater at 0- to 10- (7%) and 0- to 15- (21%) cm burial depths than at the 20-cm burial depth for 1980 and 1981 seedlots, respectively. After 25 months of burial, 41 and 26% of the achenes had not deteriorated for the 1980 and 1981 seedlots, respectively. Germination was greatest for nondeteriorated achenes recovered from 3- and 20-cm (63%) and least for the 10-cm burial depth (44%). Common crupina achenes recovered from the field over 25 months of burial exhibited a pronounced periodicity of germination, which was related to induced winter dormancy. The viability of achenes decreased linearly from 90 to near 0% over 31 months of burial.

Clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) was superior to 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), and triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} for control of honey mesquite (Prosopis glandulosa Torr. ♯ PRCJG) in the field. However, equal ratio mixtures of clopyralid + picloram or triclopyr (0.28 + 0.28 or 0.56 + 0.56 kg ae/ha) were as effective for honey mesquite control as clopyralid at rates of 0.56 and 1.12 kg/ha. Equal mixtures of picloram + 2,4,5-T, picloram + triclopyr, picloram + dicamba, triclopyr + 2,4,5-T, or triclopyr + dicamba were less effective in controlling honey mesquite than clopyralid alone or clopyralid + picloram or triclopyr in 1:1 mixtures. In the greenhouse, mixtures of clopyralid + 2,4,5-T, picloram, or triclopyr were highly effective for the control of honey mesquite. Mixtures of 2,4,5-T + picloram, 2,4,5-T + triclopyr, or triclopyr + picloram were also effective when applied at 0.28 + 0.28 kg/ha.

Field studies were established in 1974 and 1975 at various locations in San Diego County, CA, to evaluate several herbicides for the control of chamise (Adenostoma fasciculatum H.&A.) and redshank chamise (Adenostoma sparsifolium Torr.). Herbicide effects on vegetation were reevaluated in 1982. Plots originally treated with 2.2 or 4.5 kg ae/ha of glyphosate [N-(phosphonomethyl)glycine] had virtually no chamise regrowth 8 yr after treatment. The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid], combinations of 2,4-D with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] or dichlorprop [2-(2,4-dichlorophenoxy) propionic acid], fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and picloram (4-amino-3,5,6-trichloropicolinic acid) had no long-term effects on chamise. Soil collected in 1982 from glyphosate-treated plots contained similar numbers of chamise seeds but fewer seeds of other species compared to untreated plots. Canopy cover of redshank chamise was similar in treated and untreated plots after 8 yr. These results document the effectiveness of glyphosate in killing the underground root-crown of chamise, which prevented sprouting, but not redshank chamise.

Growth and regeneration of field horsetail (Equisetum arvense L. ♯ EQUAR) were investigated under field and greenhouse conditions. Field horsetail produced shoots during the entire summer but its growth was detrimentally affected by the presence of corn (Zea mays L.). Field horsetail regrew as well whether it had been hoed once or 16 times during the growing season; and during the subsequent summer, there were no significant differences between horsetail growth in plots kept weed-free the previous growing season and in plots where field horsetail grew freely. In the greenhouse, rhizome segments 1 cm long placed 15 cm deep easily regenerated plants. Simulations were done using the growth and regenerative ability of field horsetail to estimate its potential spread in agricultural fields. The results of these simulations indicate that this weed can infest a hectare within 6 yr of its introduction into a new area.

Large crabgrass [Digitaria sanguinalis (L.) Scop. ♯ DIGSA] control was higher when either DCPA (dimethyl tetrachloroterephthalate) or napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] was applied to bermudagrass [Cynodon dactylon (L.) Pers. ‘Common’] growing in soil with a pH of 5 than in soil with a pH of 6.4 in 2 of 3 yr. Soil pH did not influence the response of large crabgrass to oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] or benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine). Herbicides alone did not produce high-quality turf unless fertilizer was applied annually at 300 kg N/ha or more. Bermudagrass quality was higher after three yearly applications of 300 kg N/ha or more of fertilizer when soil pH was 5 than when soil pH was 5.6 or 6.4.

Oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] applied to bermudagrasses [Cynodon dactylon (L.) Pers.] at 4.5 kg ai/ha/yr in September reduced turf quality more than when treatments were applied anytime from April through August. The quality of ‘Tifway’ was reduced more than ‘Tifgreen’, ‘Tifdwarf’, or ‘Ormond’, and Ormond was reduced less than the other cultivars 3 weeks following oxadiazon treatment. Turf cover at the end of the growing season was not reduced with annual oxadiazon application at 4.5 kg/ha, whereas the cover was less in all plots treated with 13.5 kg/ha after four and five annual treatments. When compared with respective untreated cultivars, the cover of Tifway was reduced more from 13.5 kg/ha rate of oxadiazon than the other cultivars. Bermudagrass growth was retarded in the spring following oxadiazon applied the previous year.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} and RO-13-8895 {acetone-O-[d-2-[p-[(α,α,α-trifluoro-p-tolyl)-oxy]phenoxy]propionyl]oxime} were evaluated for quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE] control in ‘Norcen’ birdsfoot trefoil [Lotus corniculatus (L.)], ‘Monarch’ cicer milkvetch [Astragalus cicer (L.) Hook.], and ‘Arlington’ red clover [Trifolium pratense (L.)]. None of the herbicide treatments applied to weed-free legumes 3, 15, and 30 cm tall reduced crop ground cover or seed yield. Postemergence treatments of sethoxydim and RO-13-8895 applied to quackgrass in the one- to four-leaf stage, at rates from 0.56 to 1.1 kg ai/ha, gave control of 57 to 91% in September of the seedling year. Legumes in all postemergence herbicide-treated plots produced more seed than legumes in untreated plots, regardless of time of application. Sequential applications of sethoxydim, RO-13-8895, or fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} at 0.14 plus 0.14 kg ai/ha gave more effective quackgrass control and greater legume ground cover than single applications at 0.28 kg ai/ha.

Herbicide treatments containing the butoxyethanol ester of 2,4-D [(2,4-dichlorophenoxy)acetic acid], the dimethylamine salt of dicamba (3,6-dichloro-o-anisic acid), the potassium salt of picloram (4-amino-3,5,6-trichloropicolinic acid), and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] were applied for 6 yr to a pasture in east-central South Dakota containing leafy spurge (Euphorbia esula L. ♯ EPHES). Several treatments resulted in leafy spurge control exceeding 90%. Mean herbage dry-weight yield in treated plots was 2340 kg/ha, a 67% increase over untreated plots. Forage yields did not significantly differ among treatments controlling 90% or more leafy spurge. Marginal net return over marginal cost from herbicide treatments ranged from $35 to –$63/ha. Treatments providing satisfactory leafy spurge control with minimum economic risk were annual spring applications of 2,4-D at 1.7 kg ae/ha or dicamba + 2,4-D at 0.6 + 1.1 kg ae/ha and the biannual application of 2,4-D at 0.8 kg ae/ha.

Eight accessions of weedy nightshades representing five species were evaluated for response to four herbicides applied preemergence in growth chamber studies and four herbicides applied postemergence in greenhouse studies. Species differed in susceptibility to all herbicides evaluated. The largest differences were found with postemergence applications of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide}; hairy nightshade (Solanum sarrachoides Sendt. ♯ SOLSA) was relatively susceptible, but eastern black nightshade (S. ptycanthum Dun.) was very tolerant. S. ptycanthum, however, was one of the more susceptible species. It was always more susceptible than black nightshade (S. nigrum L. ♯ SOLNI) to all other herbicides evaluated.

The effect of rainfall on the performance of a tank mixture of desmedipham [ethyl m-hydroxycarbanilate carbanilate(ester)] and phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) applied postemergence to redroot pigweed (Amaranthus retroflexus L. ♯ AMARE), wild mustard (Sinapsis arvensis L. ♯ SINAR) and sunflower (Helianthus annuus L.) was evaluated in field studies. The occurrence of 1 mm of rain immediately after herbicide application significantly decreased the control of redroot pigweed and wild mustard. A rainfall quantity of 1 mm also reduced injury symptoms on sunflower. Simulating a 12.7-mm rain less than 18 h after desmedipham and phenmedipham application effectively reduced toxicity to redroot pigweed and sunflower. Toxicity to these two species increased at a lesser rate than for wild mustard as the time interval prior to rain was increased. A rain-free period of 6 h was predicted for near-maximum control of wild mustard with these herbicides.