The role of calcium in mediating resistance to several auxinic herbicides (i.e., 2,4-dichlorophenoxyacetic acid, [4-chloro-2-methylphenoxy] acetic acid, (±)-2-(4-chloro-2-methylphenoxy) propanoic acid [mecoprop], 3,6-dichloro-2-methoxy-benzoic acid [dicamba], or 4-amino-3, 5,6-trichloro-2-pyridinecarboxylic acid [picloram]) was investigated by modulating calcium dynamics of a susceptible (S) and resistant (R) biotype of wild mustard. The inhibitory effects of the auxinic herbicides on root length of the S seedlings were significantly reduced upon pretreatment with calcium in the presence of the calcium ionophore A23187. Conversely, the addition of verapamil, a calcium channel blocker, to the R seedlings increased their sensitivity to the auxinic herbicides. Valinomycin, a potassium channel ionophore, did not ameliorate the effect of the auxinic herbicides on both biotypes of wild mustard, thus indicating that the observed effects were specific for calcium. These results demonstrate that calcium plays a crucial role in the resistance of wild mustard to auxinic herbicides at the level of intact seedlings, thereby supporting our previous results using intact protoplasts.

The escalating evolution of weed species resistant to acetolactase synthase (ALS)-inhibitor herbicides makes alternative weed control strategies necessary for field crops that are dependent on this herbicide group. A fully integrated strategy that combined increased crop seeding rates (2X or 4X recommended), mechanical weed control with a minimum-tillage rotary hoe, and reduced-rate non–ALS inhibitor herbicides was compared with herbicides, rotary hoe, and seeding rates alone as a method of controlling ALS inhibitor–tolerant Indian mustard as a model weed. The full-rate herbicide treatment had the lowest weed biomass (98% reduction) and the highest yield of all treatments in 3 of 4 site-years, regardless of seeding rate. The fully integrated treatment at the 4X seeding rate had weed suppression rates equal to the full herbicide treatment at the recommended seeding rate. The fully integrated and reduced-rate herbicide treatments at the 4X seeding rate reduced weed biomass by 89% and 83%, respectively, compared with the control at the recommended seeding rate. The rotary hoe treatment alone resulted in poor weed control (≤38%), even at the highest seeding rate. Fully integrated and reduced-rate herbicide treatments at 2X and 4X seeding rates had yields equal to those of the full herbicide treatment at the recommended seeding rate. Partially or fully integrated weed control strategies that combine increased crop seeding rates and reduced-rate non–ALS inhibitor herbicides, with or without the use of a rotary hoe, can control weeds resistant to ALS-inhibitor herbicides, while maintaining crop yields similar to those achieved with full-rate herbicides. However, combining increased seeding rate, reduced-rate herbicides, and mechanical rotary hoe treatment into a fully integrated strategy maximized weed control, while reducing reliance on and selection pressure against any single weed control tactic.

Seed deterioration, and therefore seed germination potential, are highly influenced by relative humidity and temperature. However, limited species-specific information is available about the effect of long-term soaking in water on seed germination potential. Knowing the potential fate of a creeping bentgrass seed that falls in an irrigation canal is important for the study of transgene flow in this species at the landscape level. The objectives of this study were to evaluate the effect of soaking time and water temperature on germination of creeping bentgrass seed and to assess how fast a panicle could be moved in an irrigation canal. Germination was determined for seeds from panicles of three cultivars of creeping bentgrass that were soaked in water for up to 17 wk at two water temperatures, 4 and 20 C. Creeping bentgrass seeds did not lose their ability to germinate after 17 wk in water at 20 C and, although reduced, germination was still 46% after 17 wk in water at 4 C. The reduction in germination in seeds from panicles kept in water at 4 C was due to the induction of secondary dormancy, which was overcome by dry seed storage at room temperature. We quantified that a panicle that falls in an irrigation canal has the potential to travel downstream at an average rate of 19 m min−1 and move seeds that could potentially establish seedlings elsewhere. Therefore, movement of creeping bentgrass seed by water has to be considered as a means of gene flow.

Herbicides 4-amino-3,5,6-trichloropicolinic acid (picloram) and 5-bromo-3-sec-butyl-6-methyluracil (bromacil) effectively controlled live oak (Quercus virginiana Mill.) when applied in the spring and fall in south Texas. A mixture of picloram plus (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) also was effective. Higher rates of bromacil were required than for picloram or picloram plus 2,4,5-T for effective control. Bromacil was more injurious to herbaceous vegetation. The phenoxy herbicides (2,4-dichlorophenoxy)acetic acid (2,4-D) and 2,4,5-T were ineffective.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 10−5 M applied to etiolated corn (Zea mays L. ‘Michigan 500′) seedlings 6 or 12 hr before the isolation of chromatin from the roots markedly reduced ribonucleic acid (RNA) synthesis supported by the chromatin. The addition of Escherichia coli RNA polymerase failed to overcome the inhibition. Trifluralin increased the melting temperature of the chromatin. The presence of trifluralin during the isolation and reaction procedure inhibited RNA synthesis indicating possible trifluralin binding to the chromatin with subsequent reduction of template availability for transcription. Trifluralin did not inhibit chromatin activity in soybean [Glycine max (L.) Merr. ‘Hark’] seedlings.

Applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.1 kg/ha at the start of each growing season severely damaged established alfalfa (Medicago sativa L. ‘Beaver’) and reduced seed yield 32% over a 4-yr period. Dandelion (Taraxacum officinale Weber) populations were reduced but perennial sowthistle (Sonchus arvensis L.) increased in frequency. Dichlobenil (2,6-dichlorobenzonitrile) applied at 2.1 kg/ha controlled both dandelion and perennial sowthistle. Alfalfa was damaged initially but rapid recovery resulted in an increase in seed yield in 2 yr out of 4. Terbacil (3-tert-butyl-5-chloro-6-methyluracil) applied at 1.1 kg/ha also controlled dandelion and perennial sowthistle. No alfalfa damage was evident and seed yields were increased 34% over a 3-yr period. Seed yield increased 30% where asulam (methyl sulfanilylcarbamate) was applied at 4.5 kg/ha, but there was no visible effect on the growth of either alfalfa or weeds. Simazine [2-chloro-4,6-bis (ethylamino)-s-triazine], propham (isopropyl carbanilate) + PCMC (p-chlorophenyl-N-methyl carbamate), pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide], and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], did not affect alfalfa seed production significantly, although simazine and diuron did reduce dandelion populations.

Soybean [Glycine max (L.) Merr.] seedlings grown in the greenhouse in a Wisner loam soil showed a greater reduction in plant growth from an application of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) if fertilized with 224 kg/ha of P2O5. This interaction was not observed in tolerant corn (Zea mays L.) seedlings in any of the four soils studied. The injury in sand culture of high levels of atrazine to soybean, corn, pea (Pisum sativum L.), and sorghum (Sorghum vulgare L.) seedlings increased when high levels of P (phosphorus) were present. The high level of P did not increase atrazine uptake, and in corn atrazine did not increase 32P uptake. Plants receiving the atrazine-phosphate combination exhibited a higher rate of respiration providing a possible basis for the observed interaction. The high rate of P application slightly reduced atrazine metabolism by corn and pea but not by soybean and sorghum.

We investigated the toxicity of MSMA (monosodium methanearsonate), fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], and propanil (3′,4′-dichloropropionanilide) to soybeans [Glycine max (L.) Merr. ‘Hill’]. Over-the-top treatments were applied to soybeans at four stages of growth using MSMA at 0.1, 0.2, and 0.4 kg/ha, propanil at 0.2, 0.4, and 0.9 kg/ha, and fluometuron at 0.05, 0.1, and 0.2 kg/ha. Each herbicide caused 10 to 30% soybean injury at the lowest rate, and 40 to 70% injury at the highest rate. Soybeans treated earliest in the growing season usually recovered from injury better than soybeans treated later in the season. Soybean yields were reduced 50 to 70% by MSMA at 0.4 kg/ha and 25 to 35% by propanil at 0.9 kg/ha. Yield losses increased with stage of soybean maturity at time of treatment. Fluometuron at 0.2 kg/ha significantly reduced yield only when applied to soybeans with 7 or 10 trifoliolates or in midbloom.

Greenhouse and field experiments were conducted to determine effects of light, water, and chlorsulfuron on growth of Canada thistle. In the greenhouse, shoot and root dry weight, leaf area, and number of inflorescences decreased as light and water levels decreased. In the field, shoot and root dry weight, leaf area, and number of Canada thistle inflorescences were positively correlated with light intensity from 1832 to 30 μmol m−2 s−1 photosynthetic photon flux density (PPFD). The greatest effect of light was on inflorescence production which was eliminated at 30 μmol m−2 s−1 (PPFD). The combined effect of water stress and chlorsulfuron decreased root and shoot growth but did not eliminate it.

The potential of mourning doves (Zenaida macroura L.) as dispersers of leafy spurge (Euphorbia esula L. # EPHES) seeds was investigated by examing digestive tract contents and feces. Very few intact seeds passed through the digestive systems of wild or captive adult mourning doves. An average of less than one intact leafy spurge seed/g was recovered from fecal material found in dove nests. These results suggest that adult mourning doves are primarily consumers of leafy spurge seeds and rarely act as dispersal agents. It appears that dispersal is only possible when seeds passing through the digestive tracts of nestlings are deposited in the nest and the nest later falls.

Goosegrass, wide spread throughout the tropics and subtropics, is one of the most noxious weeds known. Recently, biotypes of goosegrass have been found resistant to the dinitroaniline herbicides. An alteration in the structure/composition of a tubulin protein has been postulated as an explanation for the hyperstable microtubules and the resistant phenotype. Our study was initiated to investigate the structure of the alpha (α)-, beta (β)- and gamma (γ)-tubulin related gene sequences in resistant, intermediately resistant, and susceptible biotypes. Heterologous tubulin gene clones were used as probes of restriction endonuclease-digested genomic DNA from each biotype, to determine gene size and copy number and to screen for restriction fragment length polymorphisms. The tubulin genes are organized into gene families. There are three to five α-tubulin genes, four to seven β-tubulin genes, and four to eight γ-tubulin genes. There was no evidence of multiple copies or tandem repeats of any individual gene sequence. Although RFLPs were observed, no significant difference in the banding pattern between the resistant and the susceptible biotypes was found for either α-, β-, or γ-tubulin gene families. Therefore, it is unlikely that the difference between the herbicide-response phenotypes can be attributed to large deletions or insertions in a tubulin gene.

The penetration, translocation, and metabolism of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} in ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. ♯3 IPOHE], velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), and soybean [Glycine max (L.) Merr.] were studied. An application to plants of 0.3 kg ai/ha mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} 0, 3, 5, or 7 days prior to treatment with 14C-acifluorfen often altered one or more of the physiological processes under study. Pretreatment of ivyleaf morningglory with mefluidide 3, 5, or 7 days prior to application of 14C-acifluorfen increased penetration of 14C and decreased metabolism of acifluorfen, while translocation was unaffected. All mefluidide treatments increased penetration of 14C-acifluorfen into velvetleaf, while the 3-, 5-, and 7-day pretreatments decreased acifluorfen metabolism. Penetration of acifluorfen into common cocklebur was unaffected by pretreatment with mefluidide. However, the 7-day mefluidide pretreatment of common cocklebur increased translocation of 14C into the upper leaves and decreased acifluorfen metabolism. Penetration and translocation of the radiolabel from 14C-acifluorfen in soybean was unaffected by pretreatment with mefluidide. Metabolism of acifluorfen by soybean was decreased by the 0-day mefluidide treatment but was unaffected by the 3-, 5-, or 7-day mefluidide pretreatment.

Sicklepod (Cassia obtusifolia L. ♯ CASOB) was planted at six densities (0 to 39.4/m2) and six durations of competition (0 to 10 weeks after seeding) in lima beans (Phaseolus lunatus L. cv. ‘Jackson Wonder’). The yield of green lima beans was inversely proportional to the density of sicklepod. In general, weed densities at 2.7 to 10.8 sicklepod/m2 did not significantly reduce yields, but higher populations frequently did. The average yields generally decreased if the duration of competition exceeded six weeks.

The dissipation of sodium azide (NaN3) from soil was significantly affected by pH, soil moisture, and relative humidity (RH). Loss was more rapid from acid than from alkaline soils. Moist soil (20 to 60% field capacity) or air dry soil in a moist environment (100% RH) lost NaN3 more rapidly than air dry soil in a dry (0% RH) environment. However, dissipation was decreased when soil moisture exceeded 60% field capacity. Degree of leaching and phytotoxicity of NaN3 was not affected by soil pH. Bioassay studies indicated that 10 ppm NaN3 in the soil significantly reduced germination and growth in plant species tested. At concentrations of NaN3 below 10 ppm, plant germination was often delayed but normal growth occurred after NaN3 dissipation.

The technique of microautoradiography was used to study the localization of 14C-SAN 6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H-pyridazinone] in cotton (Gossypium hirsutum L. ‘Coker 203’), soybean [Glycine max (L.) Merr. ‘Lee’], and corn (Zea mays L. ‘W.F. 9’). SAN 6706 was removed from the treatment solutions by absorption and also by adsorption onto the surfaces of roots. Absorbed SAN 6706 appeared to move primarily in the apoplast and to be translocated acropetally and laterally in the transpiration stream. The herbicide accumulated in striking concentrations in the lysigenous glands and trichomes of the cotton plant. This accumulation is postulated to be a major factor in lowering the effective concentration of SAN 6706 in the leaves of cotton as compared to the leaves of the more susceptible soybean and corn plants, and thus may be a significant factor in the tolerance of cotton to SAN 6706.

Experiments were conducted at the Lacombe and Lethbridge Research Stations to determine tralkoxydim activity at two leaf stages of green foxtail and wild oat and to determine tralkoxydim activity in tank mixtures with bromoxynil and thifensulfuron. Green foxtail and wild oat control was usually better when tralkoxydim was applied at the 2- to 3-leaf stage. However, tralkoxydim applied at the 4- to 5-leaf stage of the weeds often led to less weed topgrowth at harvest because later flushes of green foxtail and wild oat often occurred after the early applications. Nevertheless, wheat and barley yields usually indicated the importance of early weed removal. In greenhouse and field tank mixture studies, thifensulfuron antagonized tralkoxydim activity on green foxtail more than wild oat. Bromoxynil was less antagonistic than thifensulfuron, but significant reductions in green foxtail and wild oat control were detected in tralkoxydim tank mixtures with bromoxynil. In field studies, control of false cleavers with thifensulfuron or bromoxynil was not reduced in tank mixtures with tralkoxydim.

Canada thistle [Cirsium arvense (L.) Scop.] and field bindweed (Convolvulus arvensis L.) were controlled in asparagus (Asparagus officinalis L. ‘Mary Washington’) fields by repeated applications of dicamba (3,6-dichloro-o-anisic acid) at 0.6 kg/ha or 2,4-D [(2,4-dichlorophenoxy)acetic acid] + dicamba at 1.1 + 0.3 or 1.1 + 0.6 kg/ha. Applications of 2,4-D + dicamba at 1.1 + 0.6 kg/ha in early May and again in mid-June controlled 97% of the Canada thistle in asparagus fields. A third application about August 1 was required to give similar control of field bindweed. Rates of dicamba exceeding 0.6 kg/ha injured the asparagus.

Field trials were conducted in 1986 and 1987 to determine the effects of moisture on cinmethylin activity. The herbicide was applied preemergence at rates of 0.0, 0.3, 0.6, and 0.9 kg ai ha−1 to both dry and moist sandy loam soil, followed by varying irrigation regimes. Plant species used in the study included soybean, snap bean, cotton, peanut, and cucumber. Peanut was the most tolerant to cinmethylin, followed by cotton, soybean, snap bean, and cucumber. When cinmethylin was applied to a moist soil, less crop injury resulted than when it was applied to a dry soil. If 7.6 cm of water was applied shortly after cinmethylin application to a dry soil, severe crop injury occurred. When 2.5 cm of irrigation was applied within 8 h or at 5 days after cinmethylin application to a dry soil, crop injury was reduced when compared to applying 7.6 cm irrigation.

Laboratory studies were conducted to evaluate flumetsulam adsorption and mobility in seven Mississippi soils of different organic matter content, pH, and texture. Adsorption isotherms were determined for all soils using a 1:1 (soil: water) technique. In six of seven soils, Freundlich n constants were close to unity, suggesting a partitioning-like adsorption mechanism for flumetsulam. Mobility was examined using packed soil columns. 14C-flumetsulam recoveries in leachate ranged from 1 to 70% and were influenced by both organic matter content and soil pH. However, the effects of organic matter content and soil pH were not independent. Consequently, clear relationships between flumetsulam mobility and either organic matter content or soil pH were not established across all soils. However, among soils of similar pH (7.5 ± 0.3), mobility decreased linearly (R 2 = 0.75) as organic matter content increased from 0.7 to 3.6%. Across soils with similar organic matter content (3.9 ± 0.3%), mobility increased linearly (R 2 = 0.98) as soil pH increased from 5.3 to 7.2. Net adsorption constants (K d ) provided a more accurate assessment of flumetsulam mobility across all soils than K oc .

Simulated rainfall at 0.1, 0.5, and 2.0 in applied to six crops in the field previously treated with 1.5 lb/A of the dimethylamine salt of 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) resulted in an average herbicidal loss from the forage of 21, 60, and 93%, respectively. One inch of rain removed an average of 80% of 2,4-DB applied at 0.5, 1.5, and 2.0 lb/A to birdsfoot trefoil (Lotus corniculatus L.). Loss of the herbicide was attributed to the dissolving of herbicide in water and subsequent runoff from leaf surfaces, and an acceleration of herbicidal decomposition in the plant. Light interception decreased the rate of 2,4-DB breakdown in alfalfa (Medicago sativa L.) but was not considered to be of practical importance.