The introduced species weeping alkaligrass, and the native species Nuttall's alkaligrass, two of the most salt-tolerant C3 grasses found in arid and semiarid environments of western North America, occur within the Grande Ronde valley of eastern Oregon. Both species occur as weeds within Kentucky bluegrass seed fields and subsequently as grass seed contaminants. Two separate germination experiments were conducted to understand better the seed germination biology of these two species compared to Kentucky bluegrass under negative water potentials or high temperature conditions. Results of these studies indicate that although all three species benefited from an ionic enhancement associated with NaCl, weeping alkaligrass was the most drought and salt tolerant of the three species. Dry seeds of weeping alkaligrass were also particularly tolerant to high temperatures with no differences in germination at temperatures below 50 C, indicating that seed viability under nonirrigated field conditions should be unaffected by high soil temperatures. Under soil temperature conditions as high as 40 C, moist Kentucky bluegrass seeds had the greatest germination rates, indicating that this species should benefit from irrigation more than the other two species.

Pretreatment of bean (Phaseolus vulgaris L.) petiole sections with one of several metabolic inhibitors greatly stimulated the movement of 3-amino-2,5-dichlorobenzoic acid (amiben) and (2,4-dichlorophenoxy)acetic acid (2,4-D). However, the movement of 3-amino-s-triazole (amitrole), 3-(3,4-dichlorophenyl)-1-methylurea (linuron), and isopropyl m-chlorocarbanilate (chlorpropham) was stimulated only slightly or not at all. The basipetal movement of indole-3-acetic acid (IAA) was inhibited by concentrations of 2-sec-butyl-4,6-dinitrophenol (dinoseb) which stimulated respiration (5 × 10−7 M to 5 × 10−8M). Acropetal movement was stimulated by dinoseb concentrations greater than 10−5M. Translocation of root-applied amiben and 2,4-D to the stems and leaves of whole plants of bean, squash (Curcurbita pepo L.), and cucumber (Cucumis sativus L.) was stimulated by dinoseb root applications only at concentrations which were highly injurious to the plants. Amiben, 2,4-D, and their metabolites were extracted from dinosebtreated and untreated tissues. The stem exudate from cucumber plants fed amiben and 2,4-D via the roots contained primarily the parent compounds, which indicates that the parent compounds are the primary components translocated through the xylem.

The impact of either nicosulfuron or primisulfuron on maize dwarf mosaic virus (MDMV-A) severity in corn and corn susceptibility to MDMV-A infection were evaluated in greenhouse and laboratory studies. Neither herbicide influenced severity of MDMV-A in corn or corn susceptibility to the virus. Field experiments at five sites examined MDMV-A severity in corn as influenced by POST johnsongrass control with either nicosulfuron or primisulfuron applied at the fifth or eighth visible collar stage, no johnsongrass control, or johnsongrass control throughout the season with hoeing. Area under the cumulative virus curve (AUCVC) was reduced when either herbicide was applied at the fifth-leaf stage compared to the eighth-leaf stage, at four sites. Also, AUCVC was reduced when johnsongrass was controlled with a POST herbicide applied at the fifth or eighth collar stage compared to no control, at two sites. Increases in AUCVC were due to a greater number of infected plants rather than more severe MDMV-A infections.

Imbibed seeds of rough cinquefoil (Potentilla norvegica L.) remain dormant in darkness at constant and alternating temperatures. Full promotion of germination resulted after 3 days' dark imbibition at 25 C followed by 24 hr of continuous unfiltered fluorescent light. Germination was controlled by phytochrome. The sensitivity of the seeds to short light exposures was increased by the introduction of a temperature shift to 40 C for 2 hr, at the conclusion of the normal dark imbibition period at 25 C. The temperature shift also reduced the time required in continuous light to give full promotion of germination. The response to light was synergistically increased when the seeds were imbibed in 0.2% KNO3, and given the temperature shift. Nearly full promotion was reached with ca. 5 min of red light, and 50% germination occurred with as little as 1 sec. The system was still under phytochrome control. These findings suggest a mechanism by which soil populations of weed seeds may become physiologically conditioned to respond to very brief exposures to light.

Houndstongue is a troublesome weed of pasture, rangeland, and open forest in British Columbia, Canada. Recently, a root-feeding weevil was released in Canada that successfully controls houndstongue patches, but it has been difficult to propagate this weevil in sufficient numbers for widespread release. The goal of the current study was to develop methods for growing houndstongue as a crop in a farm-field setting for weevil propagation. Field experiments were conducted to determine optimum seeding dates, depths, and rates for houndstongue. The effects of straw-residue cover and nitrogen-application rates were also examined. More than 90% of the seed used was viable, and about 50% of the planted seed emerged. The most consistent plant densities occurred when houndstongue was seeded in October and had a winter and early spring moist chilling period to break seed dormancy. For fall seeded houndstongue, plants emerged equally well from 2- and 5-cm depths. Houndstongue is moderately responsive to nitrogen fertilizer but usually did not benefit from additional straw cover on the soil before emergence. Houndstongue plants also survived in drought conditions. In conclusion, this weed can be consistently grown as a crop for the propagation of a root-feeding weevil for houndstongue control.

Annual bluegrass (Poa annua L.) growing in bermudagrass completes its life cycle in May and dies leaving open spaces in the turfgrass. This occurs at a time when summer annual weeds are germinating and these weeds fill the space formerly occupied by the annual bluegrass. As the summer annual weeds die in the fall, annual bluegrass germinates and fills the space formerly occupied by the summer annual weeds. To control annual bluegrass, it is important to control the summer annual grasses and manage the bermudagrass [Cynodon dactylon (L.) Pers.] to maintain a competitive groundcover especially during the peak germination period for the weeds. Herbicide programs over a three-year period were designed to control annual grasses with treatments in April for large crabgrass [Digitaria sanguinalis (L.) Scop.], in May or June for goosegrass [Eleusine indica (L.) Gaertn.] and in late August for annual bluegrass. Oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-ozadiazolin-5-one] applied in August gave complete control of annual bluegrass. Although oxadiazon has a long residual life in the soil, annual bluegrass was poorly controlled with treatments made in June. Fall (August or September) applications of benefin [N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine], prosulfalin N-[[4-(dipropylamino)-3,5-dinitrophenyl] sulfonyl]-S,S-dimethylsulfilimine and butralin [4-(1,1-dimethylethyl-N-(1-methylpropyl)-2,6-dinitrobenzenamine] provided adequate control of annual bluegrass with only a few exceptions during the three-year period. Bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] gave variable control of annual bluegrass; however, this was improved in programs with oxadiazon which provide goosegrass control during summer. In these studies, DCPA [dimethyl tetrachloroterephthalate], even with three applications a year, gave very little control of annual bluegrass. When oxadiazon was used in rotation with DCPA, adequate control was obtained.

To be effective, postemergence herbicides must be absorbed and translocated to sites of action in proper form and quantity. Any factor that interferes in this process may account for differential sensitivity. Adjuvant effects on foliar absorption of BAY MKH 6561 by jointed goatgrass and downy brome were evaluated under growth chamber conditions. Absorption of BAY MKH 6561 by jointed goatgrass and downy brome without adjuvants was 41 and 30% of applied, respectively, 48 h after treatment (HAT). Herbicide absorption with methylated seed oil (MSO) was significantly higher than with nonionic surfactant (NIS) 24 and 48 HAT. The addition of urea ammonium nitrate (UAN) to MSO and NIS significantly increased absorption over MSO and NIS alone 24 HAT, but absorption was similar to that obtained with MSO 48 HAT. Averaged across adjuvant combinations, jointed goatgrass and downy brome absorbed 90 and 89% of applied BAY MKH 6561, respectively, 48 HAT. BAY MKH 6561 translocation and metabolism in jointed goatgrass, downy brome, and winter wheat were also evaluated. More 14C-BAY MKH 6561 translocated to shoot and root tissue in downy brome than in jointed goatgrass and winter wheat. Root exudation accounted for 26% of root-translocated BAY MKH 6561 in jointed goatgrass, 31% in downy brome, and 43% in winter wheat. Winter wheat, jointed goatgrass, and downy brome metabolized 82, 65, and 50% of absorbed 14C-BAY MKH 6561 12 HAT, respectively, and 97% metabolism occurred in all species 48 HAT. Exponential decay equations predicted a 7-h BAY MKH 6561 half-life in winter wheat, 10-h half-life in jointed goatgrass, and 13-h half-life in downy brome. Jointed goatgrass absorbed amounts of 14C-BAY MKH 6561 that were similar to those absorbed by downy brome, but jointed goatgrass was intermediate in translocation and metabolism compared to winter wheat and downy brome. Therefore, differential translocation and metabolism may explain differential field susceptibility observed between winter wheat, jointed goatgrass, and downy brome.

Endothall (7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid) was evaluated for controlling annual bluegrass (Poa annua L.) infestations in Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis stolonifera L.) turfs. Growth of annual bluegrass was selectively suppressed by three applications of 0.6 kg/ha of endothall, two or three applications of 1.1 and 2.2 kg/ha, and one application of 4.5 kg/ha made to the single plant sand cultures. Field treatments were variable and seasonably dependent. Endothall selectively killed annual bluegrass when applied to roots in sand culture at a concentration of 2.7 × 10−4 molar. A granular formulation of endothall provided selective control of annual bluegrass in field and greenhouse studies. High watering frequency prior to application, low organic matter content of the underlying soil, and predominance of the annual biotype of annual bluegrass enhanced the selective action at the lowest rates of endothall application.

African rue is an exotic, herbaceous perennial established in several western states that tolerates harsh, water-stressed conditions. The influence of water-deficit stress on herbicide response and subsequent herbicide fate within the plant were compared. African rue seedlings were deprived of water for 0 to 7 d to establish a gradient of water-deficit levels before treatment with hexazinone, imazapyr, or metsulfuron. At herbicide application, water-deficit treatments reduced plant water potential values from −1.0 MPa to −4.7 MPa, causing concomitant reductions in photosynthesis. Thirty-five days after treatment, dry weight of imazapyr- and metsulfuron-treated plants was reduced in plants exposed to more than 4 d water-deficit stress before herbicide application. In contrast, hexazinone-treated plants had less dry weight than water-stressed, nonsprayed control plants regardless of water-deficit stress. Seventy-two hours after herbicide application, African rue leaves absorbed from 5 to 42% of herbicide applied; however, herbicide absorption did not correlate to efficacy. Less than 12% of absorbed herbicide translocated out of the treated leaf, regardless of herbicide. Radiolabel translocated from the treated leaf to acropetal or root tissue did not differ among herbicide treatments, regardless of water deficit before herbicide application. However, compared to other herbicides, translocation to basipetal shoot tissue was greatest in imazapyr-treated seedlings with the largest water deficit at herbicide application. Increased translocation occurred at higher levels of water stress than were necessary to increase herbicide efficacy, suggesting differential translocation was not involved in enhanced efficacy. In summary, African rue seedlings absorbed and mobilized three different herbicides at all levels of water-deficit stress. In addition, the efficacy of metsulfuron and imazapyr increased as water-deficit stress increased, but efficacy of hexazinone was not influenced by plant water status. This unusual relationship between water-deficit stress and herbicide performance may enable improved African rue management under stressful environments.

Field experiments were conducted in 1984 and 1985 at Stuttgart, AR, to investigate the interspecific and intraspecific interference of broadleaf signalgrass densities of 0, 10, 50, 100, and 150 plants/m2 with rice. In 1984, significant reductions in rice leaf area index (LAI) occurred 6 weeks after emergence with all broadleaf signalgrass densities. The first reduction in LAI occurred 8 weeks after emergence at the density of 150 plants/m2 in 1985. Densities of 50 plants/m2 or greater reduced rice dry weight 6 weeks after emergence in 1984, and the highest density of 150 plants/m2 reduced rice dry weight 12 weeks after emergence in 1985. Height of rice was reduced by densities of 100 and 150 plants/m2. Linear regression equations indicated that each broadleaf signalgrass plant/m2 reduced rough rice yield 18 kg/ha both years. Growth of broadleaf signalgrass was reduced by interspecific and intraspecific interference. The dry weight of broadleaf signalgrass increased at a decreasing rate at plant densities of 100 to 150/m2 when grown alone in 1984 and 1985, when a quadratic equation best described the response. Regression equations indicated interspecific interference from rice reduced broadleaf signalgrass dry weight an average of 48 and 81% in 1984 and 1985, respectively. The height of broadleaf signalgrass was greater when grown with rice than when grown alone.

Bermudagrass plugs were transplanted from the greenhouse to the field at monthly intervals from March through October at Shafter, CA. Emergence began from the March plantings when soil temperatures at a depth of 5 cm reached 17 C. Although the initial growth of March, April, and May plantings was very slow, these plantings eventually produced about 60% more dry matter (2100 g/m2) than June, July, and August plantings (1300 g/m2) when harvested in December. At 8 weeks after planting, June to August plantings accumulated 120% more dry matter (460 g/m2) than March to May plantings (210 g/m2). At 12 weeks, dry matter accumulation was greatly reduced by shorter photoperiods and cool temperatures for March and September plantings (160 g/m2) when compared to all intermediate plantings (700 g/m2). All plantings, except October, produced rhizomes (15 to 120/m2) and seeds (154 to 73400/m2) before killing frosts occurred in late November. Although rhizomes and seeds were not collected until the 12-week harvest for the March to May plantings, these plantings produced or tended to produce the greatest number of rhizomes (85/m2) and seeds (49300/m2) by December. Rhizomes and seeds from the June to September plantings were collected within 8 weeks, indicating that declining photoperiods hastened rhizome and seed production.

Several methods were used to overcome herbicide phytotoxicity to upland rice (Oryza sativa L., ‘IR8′). Seed pelleting with activated carbon and band application of activated carbon slurry over the rice seed were ineffective in reducing the toxicity of chloramben (3-amino-2,5-dichlorobenzoic acid) and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to upland rice. In contrast, a 2.5-cm layer of activated carbon and vermiculite mixture (1:1) placed over the rice seed was effective in overcoming the toxicity of these herbicides. Deep sowing (3.0 to 4.5 cm) of rice seed was adequate in protecting upland rice from herbicides which are toxic to direct seeded, flooded rice but are not toxic to transplanted rice. The degree of protection from deep sowing, however, was determined by site of uptake, herbicide adsorption by soil, leaching, and inherent toxicity of the herbicides to rice seedlings.

A root washer was constructed which rapidly separated Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] roots larger than 1.3-mm diam with 96% or greater efficiency from cohesive clay soil. The washer removed 93 ± 15% of 43 200 cm clay soil from Canada thistle roots in 2 h. Small residual soil clods and organic debris were removed by hand after washing. The washing action did not damage the root system. From 4 to 6 h were required to wash the large Canada thistle roots from an equivalent volume of clay soil by hand, without using the washer. Rhizomes, seeds, and tubers also may be separated from soil with the washer. The tank and frame of this washer are durable, and moving parts such as bearings can be replaced easily.

Dithiopyr provides PRE and early POST control of smooth crabgrass, but POST efficacy is often inconsistent on tillered plants. Experiments were conducted to evaluate the interaction of temperature and growth stage on dithiopyr efficacy, absorption, translocation, and metabolism in smooth crabgrass. In greenhouse experiments, I50 (predicted rate to induce 50% injury) measured < 0.14, 0.14, and 0.15 kg ha−1 at low temperatures (average 23 C) for multi-leaf, one-tiller, and multi-tiller smooth crabgrass, respectively, while I50 measured < 0.14, 0.88, and > 2.24 kg ha−1 at high temperatures (average 32 C), respectively. Multi-tiller (three to five tillers) smooth crabgrass absorbed more root applied 14C-dithiopyr than multi-leaf (three to four leaves) and one-tiller plants, but specific radioactivity (Bq mg−1) was two to three times greater in multi-leaf plants compared to tillered plants. Smooth crabgrass treated at 15/10 C (day/night) had ≈ two times greater specific radioactivity following root applied 14C-dithiopyr than at 30/25 C. Radioactivity distribution to shoots from root applications measured 43, 30, and 20% of the total absorbed for multi-leaf, one-tiller, and multi-tiller plants, respectively. Smooth crabgrass had two times more foliar absorption of 14C-dithiopyr at 15/10 than 30/25 C while 14C losses were greater at 30/25 than 15/10 C. Smooth crabgrass metabolism of 14C-dithiopyr was ≈ two times greater at 30/25 than 15/10 C, and multi-leaf plants averaged 10 to 20% more metabolism than tillered plants at 7 d after treatment. Results suggest differential absorption, translocation, and metabolism may contribute to dithiopyr efficacy on smooth crabgrass at various growth stages, but use under high temperatures (30/25 C) could increase losses from volatilization, reduce foliar absorption, and increase metabolism compared to cooler temperatures (15/10 C).

Adjuvant effects on disease severity caused by the bioherbicide P. papaveracea on opium poppy were evaluated. Tween 20, Tween 80, Triton X-100, Tactic, CelGard, and Keltrol inhibited appressorium formation but not conidial germination on detached leaves. The disease severity varied from 11 to 83% necrosis in field experiments involving eight adjuvants at various concentrations plus 1 × 106 conidia ml−1 or minus pathogen. The three best-performing adjuvants when combined with pathogen, Tactic (1%, v/v), Bond (1%, v/v), and Tween 20 (1%, v/v), were included along with Tween 20 (0.001%, v/v) in field experiments in 1998. Tween 20 (1%, v/v) plus pathogen (1 × 106 conidia ml−1) caused the most severe disease, averaging 68% necrosis within 2 wk of treatment. Overall, plots treated with adjuvant plus P. papaveracea had a 22% reduction in capsule weight per plot as compared to plots treated with the adjuvant alone. Tactic (1%, v/v), Silwet-L77 (0.1%, v/v), Tween 20 (1%, v/v), and Tween 20 (0.001%, v/v) were included in field experiments in 1999. The treatment with Tween 20 (1%, v/v) plus pathogen (2 × 106 conidia ml−1) caused severe disease, averaging 56% necrosis within 2 wk of treatment. In 1999 plots treated with adjuvant plus pathogen averaged a 27% reduction in capsule weight as compared with plots treated with the adjuvants alone. The inclusion of Tween 20 (1%, v/v) with P. papaveracea conidia greatly enhanced efficacy on opium poppy.

Integrated management techniques for several U.S. winter wheat production regions have been proposed for jointed goatgrass control. These strategies may be improved by a greater understanding of the genetic and environmental influences on seed production and germination. Plants from six jointed goatgrass collections were grown in common garden nurseries at two Oregon locations over two growing seasons. Unbroken spikes from each collection were used to evaluate seed dormancy and quantify seed production by inflorescence position. Germination tests were conducted over 14 d using spikelets of dormant and after-ripened samples in growth chambers set to 25/15 C day/night temperatures and a 12-h photoperiod. Spikelet position on the spike affected germination of the secondary seed in dormant samples of jointed goatgrass Collections D and G. In contrast, spikelet position did not affect secondary seed germination in dormant samples of Collection B. Spikelet position did not influence secondary seed germination in nondormant samples of all three collections. Spikelet position affected germination of the primary positioned seed in dormant samples of Collection B, and in nondormant samples of Collections B, E, and H. Unbroken spikes from jointed goatgrass Collections B and D were used to quantify seed production per spikelet position on the spike and per floret position within the spikelet. Seed production by floret position depended on spikelet position on the spike. This relationship varied for spikes of different lengths and for samples from the two collections. Efforts to model the life history of jointed goatgrass and predict germination should be adjusted to account for floret position within the spikelet, spikelet position within the spike, and source population. We suggest that future dormancy and germination research include sampling seed from several weed populations and efforts be made to standardize germination tests according to seed position on the inflorescence.

Anionic herbicide transport properties of lipids were measured using the Schulman model of liquid-liquid membrane and parenchymateous tissue from potato (Solarium tuberosum L. ‘Russet’) tubers. The more polar lipids, lecithin and monogalactosyl dilinolenate, increased (2,4-dichlorophenoxy)acetic acid (2,4-D) exchange from the hydrophilic phase (buffered H2O:2,4-D solution) to the lipophilic phase (n-pentanol) more rapidly than the less polar triglycerides: tristearate, trioleate, and trilinolenate. The rate of 2,4-D exchange decreased with increased acidity of the hydrophilic phase indicating that polar lipids increased exchange of anionic herbicides through the liquid-liquid interface in the dissociated form. Potato tuber slices treated with lecithin accumulated more 2,4-D than did tissue receiving no lecithin, indicating that lecithin treatments increased 2,4-D accumulation by parenchymateous tissue when compared with untreated tissue.

Existing long-term cotton experiments established in 1976 with minimum and intensive herbicide programs were subdivided in 1985 and 1986 to determine the longevity of fluometuron and trifluralin soil residues after discontinuing herbicide application. In monoculture cotton, seed cotton yield increased when herbicide use was discontinued in 1985 and 1986 after 9 and 10 yr of continuous use, respectively, on a Sharkey silty clay and a Dundee silt loam soil. Yield increases coincided with reductions of fluometuron and trifluralin soil residues. Fluometuron dissipated from the Dundee silt loam soil by 10 mo after the last application but was present in the Sharkey silty clay soil at 0.20 ppmw after 28 mo. Trifluralin did not totally dissipate from either soil, and low levels were present in the Dundee (0.05 ppmw) and Sharkey (0.13 ppmw) soils 30 mo after the last application. Visual injury to fall-seeded wheat and vetch decreased as herbicide residues dissipated. Fall tillage had no significant effect on the rate of fluometuron or trifluralin dissipation from either soil but reduced seed cotton yields.

Field trials were conducted to investigate the influence of P application method on the critical period of smooth pigweed and common purslane interference in lettuce. Studies were carried out in low-P histosols, where supplemental P fertilization is needed for lettuce production. Phosphorus was either broadcast or banded 5 cm beneath the lettuce rows at rates of 250 or 125 kg ha−1, respectively. Seedlings of either smooth pigweed or common purslane were transplanted at a density of 16 plants per 5.4 m2 (6-m row by 0.9 m wide). Weed interference duration was achieved by manual removal 2, 4, 6, or 8 wk after lettuce emergence and subsequently keeping the plot weed free until harvest. A weed-free control within each P regimen was also established. Marketable head number, head fresh yield, and head diameter were measured at harvest. Weed-free lettuce fresh yield was 20% higher with banded P than broadcast applications. In the weed–lettuce mixtures, the P regimen by weed removal interaction affected lettuce fresh yield and head diameter but not head number. Compared with broadcast P application, banded P extended the time needed to cause significant weed interference in lettuce by 10 d: from 24 to 34 d for smooth pigweed and from 37 to 47 d for common purslane.

In the greenhouse, naptalam at 1.1 to 4.5 kg ai ha−1 antagonized activity of paraquat at 0.04 to 0.14 kg ai ha−1 in 14 of 16 rate combinations when applied to sicklepod. Sicklepod shoot fresh weight reduction was less compared to that obtained with paraquat alone when paraquat at 0.04 kg ha−1 was mixed with bentazon at 0.42 to 0.84 kg ai ha−1 or monocarbamide dihydrogensulfate at 14 to 58 kg ai ha−1. Paraquat activity on Florida beggarweed was antagonized by mixtures of paraquat at 0.04 or 0.07 kg ha−1 with bentazon at 0.63 or 0.84 kg ha−1 or paraquat at 0.04 to 0.14 kg ha−1 with naptalam at 3.4 or 4.5 kg ha−1. Mixtures of lactofen at 0.06 to 0.22 kg ai ha−1 with monocarbamide dihydrogensulfate at 14 kg ha−1 or lactofen at 0.06 or 0.16 kg ha−1 with alachlor at 1.4 to 2.8 kg ai ha−1 synergistically increased tall morningglory shoot fresh weight reduction. In the field, excellent sicklepod shoot fresh weight reduction by paraquat applied alone masked most antagonistic effects of paraquat mixtures. Addition of alachlor to monocarbamide dihydrogensulfate at 29 kg ha−1 improved activity on sicklepod compared to monocarbamide dihydrogensulfate applied alone.