Experiments were conducted for 3 yr to evaluate the effects of the ethyl ester of fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy] phenoxy] propanoic acid} on rice (Oryza sativa L. 'Starbonnet′) applied at 112 and 168 g ai/ha or as two applications of 112 g ai/ha applied 10 to 14 days apart. Fenoxaprop did not adversely affect grain yield, panicle weight, seed weight, or seed germination when applied before the booting stage of both sprinkler-irrigated and flooded rice. Rice height was sometimes reduced by treatment at earlier growth stages, but yields were not affected. With the exception of applications at early jointing (internode elongation = 6 mm) in 1983, milling yield was not adversely affected by fenoxaprop applications made prior to booting of both sprinkler-irrigated and flood-culture rice. Applications during heading adversely affected most yield parameters.

Row orientation in vineyards can affect the quantity of light intercepted by the crop's canopy. Consequently, the light available to weeds growing under the canopy might also be affected, with potential implications for their physiology, growth, and productivity. This hypothesis was tested in 2003 and 2004 in a central California vineyard having rows oriented east–west (EW) and north–south (NS) in a randomized complete block design. In April of both years, potted black nightshade seedlings were placed under grapevines of both row orientations and grown for about 10 wk. Photosynthetically active radiation (PAR) at the weed canopy zone (WCZ) of NS rows was bimodal, with peaks occurring at about 09:30 A.M. and 4:30 P.M. At those times, PAR approached 500 μmol m−2 s−1 (between 30 and 40% of full sun). In contrast, maximum PAR in the WCZ of EW rows was generally less than 75 μmol m−2 s−1 throughout the day. The ratio of red to far-red light was also greater in NS than EW rows in the morning and afternoon. In both row orientations, PAR was suboptimal for nightshade because maximum net photosynthesis occurred at light levels ≥ 500 μmol m−2 s−1, but nightshade in the NS rows had higher net photosynthetic rates than those in EW rows when subjected to higher ambient PAR. Stem extension and phenology of nightshade was not affected by vine row orientation, but plants in EW rows had greater leaf areas, leaf area ratios, leaf weight ratios, and lower specific leaf weights than plants in NS rows. Berry mass, seeds per berry, and estimated seed production was 40, 7, and 20% lower, respectively, for plants in the EW than in the NS rows. Dry mass and total nonstructural carbohydrates (TNC) of nightshade roots were also 25 and 45% lower, respectively, in EW than in NS plants. Thus, grapevine row orientation may affect nightshade fecundity by reducing light in the WCZ.

Leafy spurge is a tenacious perennial weed of the Northern Plains. This plant maintains a perennial growth cycle by controlled production and growth of numerous underground adventitious buds. We are using molecular tools to identify signaling pathways that control underground adventitious bud growth and development in leafy spurge. Toward this end, we have used three techniques to identify genes that are differentially expressed concomitantly with the breaking of quiescence in underground buds of leafy spurge. These techniques include differential display of cDNAs, random cloning and sequencing of genes expressed in growing buds, and microarray technology. To date, we have identified more than 16 genes that are differentially expressed in underground buds of leafy spurge during dormancy break and growth initiation. A detailed expression analysis of these genes will allow them to be grouped by their responses to various signals known to play a role in control of underground bud growth. This information will be used to identify key cis-acting elements involved in the regulation of these genes. How such information on signal transduction processes may be used for developing new weed control strategies by the identification of novel target pathways and development of DNA-based herbicides is presented.

A 3-yr field study was conducted to compare an in-row cultivator versus a standard row-crop cultivator to decisions made with WEEDCAM, a weed/corn management computer decision aid, for controlling annual weeds within the row in irrigated corn. In the absence of herbicides, weeds were always controlled better with the in-row cultivator than with the standard row-crop cultivator. However, grain yield and gross margin were affected only in 1991 when weeds emerged simultaneously with corn, and rain delayed the first cultivation 10 d. The in-row cultivator plots not only averaged 34% more grain ha-1 than the standard row-crop cultivator plots, but gross margin was $143 ha-1 more. Weed densities each year were about 95% less in plots managed in accordance with the computer model WEEDCAM simulations than in the non-herbicide treated post-planting tillage plots. Grain yields and gross margins were not affected by weed seedbank density, pre-cultivation tillage, or type of cultivator when weed management decisions were based on WEEDCAM simulation ranking. In the absence of herbicides, weeds can be controlled successfully in corn with an in-row cultivator, but success will depend on such factors as weed seedbank density, cultivation timeliness, and relative time of weed and corn emergence.

The effect of 1,4-naphthoquinone, 1,4-benzoquinone, and several CI and NH2-substituted quinones has been studied on growth, chlorophyll concentration, and oxygen evolution in Chlorella pyrenoidosa Chick. (Emerson strain). Drastic decrease of the studied parameters usually was noted after 24 to 48 hr treatment at 3×10–5 M concentration. The effect of the quinones was compared with that of 6,7-dihydrodipyrido [l,2-a:2,l-c-]pyrazidinium salt (diquat) and 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron). Diuron inhibited oxygen evolution immediately after addition, but could be washed out and the effect was reversible. Diquat had no inhibitory effect on oxygen evolution and chlorophyll content but caused a slight decrease in cell number. Although some quinones have an almost immediate effect on the oxygen-evolving mechanism, it seems more likely that the overall effect of the quinones is on the total physiological activity of the algal cells. Oxygen evolution seems to affected earlier than chlorophyll destruction, and the observed long-term damage is irreversible. Most of the compounds studied could be classified as algicidal, with the exception of diuron, diquat, and 1,4-benzoquinone which may be considered to be algistatic.

An experiment was conducted comparing wheat (Triticum aestivum L., var. Pembina) and wild buckwheat (Polygonum convolvulus L.) grown alone in pots, in full competition, and in root competition at three levels each of soil fertility and soil moisture, and harvested at three dates.

Wheat was a better competitor than wild buckwheat when considering dry matter production. With each succeeding harvest, the dry matter production and the total nitrogen and phosphorus uptake increased more for plants grown alone than in competition. Competition caused a reduction in the nitrogen and phosphorus content of wheat and wild buckwheat at the first harvest, while reductions in dry matter did not occur until the second harvest. Wheat increased in dry matter and nitrogen more than wild buckwheat with each higher level of soil moisture when grown alone but not when in competition. When grown alone or in competition, wheat increased linearly in dry matter production with increases in fertility while wild buckwheat produced maximum dry matter with medium fertility. The total nitrogen increased in wheat and wild buckwheat with each higher level of fertility, while total phosphorus increased only in wheat.

Wild buckwheat used less water than wheat to produce a gram of dry matter and per milligram of phosphorus uptake when grown alone, while the plants in competition were intermediate in water usage to plants grown alone. Wild buckwheat and wheat used similar amounts of water per unit of nitrogen uptake when grown alone and increased their water usage when grown in competition. Water efficiency for nitrogen and phosphorus uptake and dry matter production usually decreased with plant maturity and higher soil moisture, and increased with higher soil fertility.

Smutgrass is an invasive warm-season perennial bunch-type grass native to tropical Asia. The two varieties of smutgrass prevalent in Florida are small smutgrass and giant smutgrass. Laboratory seed germination experiments were conducted on both smutgrass varieties to determine the effect of various environmental factors on germination and emergence. The average germination rate for both varieties was 88% at 30/20 C day/night temperatures. Seed germination for both varieties was greater under simulated temperature flux than at constant temperatures. Seed of both varieties germinated at four simulated Florida temperature fluxes (22/11, 27/15, 33/24, and 29/19 C day/night), although the germination of small smutgrass and giant smutgrass was reduced at 33/24 and 22/11 C, respectively. Germination of small and giant smutgrass under dark conditions was 27 and 53%, respectively. Both smutgrass varieties germinated over a wide range of pH values. Small and giant smutgrass germination was inhibited at water potentials below −0.2 MPa and when small smutgrass seed was placed below the soil surface. Emergence of giant smutgrass seed did not occur below 3 cm. Both smutgrass varieties germinated over a broad range of environmental conditions, indicating their capability of year-round germination; however, germination is only likely to occur under field conditions during the summer growing season when rainfall is prevalent. These results indicate that both species have the ability to germinate over a wide range of environmental conditions but that germination is inhibited by moisture stress and depth of burial. Considering that giant smutgrass prefers higher temperatures than small smutgrass, the advent of rainfall from June through September is conducive for germination. Practices that focus on the germination pattern of smutgrass could lead to better long-term management of smutgrass in Florida.

In recent years the relationships of 3–(p–chlorophenyl)–1,1–dimethylurea (monuron) phytotoxicity and various factors in the soil have received considerable attention (1, 3, 5, 6). Similar information for 2–chloro–4,6–bis–(ethylamino)–s–triazine (simazin) is lacking because of its later development as a herbicide. The experiments reported here were initiated to compare (a) the toxicity of monuron and simazin in solution culture and in soil, (b) the inactivation of the two compounds in soil and, (c) their downward movement through soil columns.

Herbicides incubated in Wymore silty clay loam soil at field capacity at 15, 25, and 35 C showed 3-amino-2,5 dichlorobenzoic acid (amiben) the most persistent, 2,3,6-trichlorobenzoic acid (2,3,6-TBA) intermediate, and 2-chloro-4-ethylamino-6-isopropylamino-5-triazine (atrazine) the least persistent to microbial and/or chemical breakdown. All herbicides persisted much longer at 15 C than at 35 C. The average annual temperature below the plow layer is about 12 C. This helps explain the persistence of leached herbicides under field conditions.

Wild oat, a troublesome weed in cereals, infests about 11 million hectares of cropland in the United States. Diversifying cereal production with alternative crops, such as yellow mustard and canola, can provide flexibility in cropping systems, decrease production risks, and allow for effective weed suppression. The objective of the study was to quantify the competitive ability of yellow mustard and canola relative to wild oat in addition series field experiments, which were conducted in 1999 and 2000 near Genesee, ID. Biomass and seed production of wild oat were reduced 67 and 80%, respectively, in mixtures with yellow mustard, which was three to four times greater than the reduction in corresponding mixtures with canola. In addition, yellow mustard reduced the biomass and seed production of wild oat equally regardless of wild oat density. In contrast, the competitive effect of canola on wild oat biomass decreased 5 to 10 times when wild oat density increased from 100 to 200 plants m−2. Yellow mustard at all densities and at both biomass harvests suppressed wild oat biomass and seed production similarly. But suppression of wild oat by canola increased as canola density increased, and canola plants were more competitive at the flowering stage than at the rosette stage. Wild oat had little or no effect on yellow mustard seed yield but reduced canola seed yield 37%, when averaged over canola densities. Additionally, the oil content of canola seed was reduced 0.4% for every 1% of wild oat seed in the harvested seed. Models developed in this study accurately predicted plant populations of yellow mustard and canola that provided optimal weed suppression and crop yield for different wild oat populations.

Previous research has shown that flumioxazin, a herbicide being developed as a postemergence-directed spray (PDS) in cotton, has the potential to injure cotton less than 30 cm tall if the herbicide contacts green stem tissue by rain splash or misapplication. In response to this concern, five-leaf cotton plants with chlorophyllous stems and older cotton, 16-leaf cotton plants, with bark on the lower stem were treated with a PDS containing flumioxazin plus crop oil concentrate (COC) or nonionic surfactant (NIS). Stems of treated plants and untreated plants at the respective growth stage were cross-sectioned and then magnified and photographed using bright-field microscopy techniques. More visible injury consisting of necrosis and desiccation was evident in younger cotton. Also, there was a decrease in treated-stem diameter and an increase in visible injury with COC compared with NIS in younger cotton. The effects of plant growth stage and harvest time on absorption, translocation, and metabolism of 14C-flumioxazin in cotton were also investigated. Total 14C absorbed at 72 h after treatment (HAT) was 77, 76, and 94% of applied at 4-, 8-, and 12-leaf growth stages, respectively. Cotton at the 12-leaf stage absorbed more 14C within 48 HAT than was absorbed by four- or eight-leaf cotton by 72 HAT. A majority (31 to 57%) of applied 14C remained in the treated stem for all growth stages and harvest times. Treated cotton stems at all growth stages and harvest times contained higher concentrations (Bq g−1) of 14C than any other tissues. Flumioxazin metabolites made up less than 5% of the radioactivity found in the treated stem. Because of the undetectable levels of metabolites in other tissues when flumioxazin was applied PDS, flumioxazin was foliar applied to determine whether flumioxazin transported to the leaves may have been metabolized. In foliar-treated cotton, flumioxazin metabolites in the treated leaf of four-leaf cotton totaled 4% of the recovered 14C 72 HAT. Flumioxazin metabolites in the treated leaf of 12-leaf cotton totaled 35% of the recovered 14C 48 HAT. These data suggest that differential absorption, translocation, and metabolism at various growth stages, as well as the development of a bark layer, are the bases for differential tolerances of cotton to flumioxazin applied PDS.

Greenhouse, field, and laboratory experiments were conducted in northern Greece during 1996, 1997, and 1998 to study possible metribuzin resistance in Amaranthus retroflexus (redroot pigweed) and Chenopodium album (common lambsquarters) biotypes found in potato fields. The greenhouse experiments indicated that the suspected resistant biotypes (R) of both species were not controlled by metribuzin applied either pre- or postemergence at rates of 245, 490, 980, and 1,960 g ai ha−1 (the higher rate is eight times greater than the rate recommended for weed control in Solanum tuberosum [potato]). However, susceptible biotypes (S) were completely controlled by 245 g ai ha−1. Also, both R- and S-biotypes of either species were effectively controlled by prometryn applied either pre- or postemergence at 1.5 kg ai ha−1. The field trials confirmed that metribuzin applied either pre- or postemergence at rates of 490, 980, and 1,960 g ai ha−1 gave fair or partial control of the R-biotype of C. album, whereas prometryn applied preemergence at 1.5 kg ai ha−1 gave excellent control of this weed. Chlorophyll fluorescence measurements performed in laboratory experiments indicated that photosynthetic electron transport in metribuzin-incubated leaves detached from plants of the R-biotypes was not affected, but it was inhibited in leaves detached from plants of the S-biotypes. Electron transport was inhibited by prometryn in leaves detached from both S- and R-biotypes of either species. These results show clearly that the biotypes of both species developed resistance to metribuzin, but they were not cross-resistant to prometryn.

Leaflets of 1690 species of Old World and South American Astragalus collected from herbaria at Kew, England; Edinburgh, Scotland; Munich, Germany; and Vienna, Austria were analyzed qualitatively for toxic aliphatic nitro compounds. The catabolites of nitro compounds found in species of Astragalus (nitro-bearing), 3-nitro-1-propanol and 3-nitropropionic acid, are especially toxic to cattle and sheep. A total of 190 of 1624 (12%) Old World species, 30 of 66 (45%) South American species, and a single species of one Astragalus subgenus were positive for nitro compounds. Most Old World species that contained aliphatic nitro compounds were collected in the Middle East and the Union of Soviet Socialist Republics. Nitro compounds were detected in specimens of eight species collected between 1822 and 1836. The nitro-bearing species were chemotaxonomically related and grouped within taxonomic sections. The presence of two or three nitro-bearing species within a section indicated that other species within the same section might also be nitro-bearing.

Soil enrichment studies were conducted with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) with and without exogenous carbon and nitrogen. From 72 bacterial isolates obtained, eight representative ones were tentatively identified as members of the genus Pseudomonas based on size, shape, Gram reaction, and reaction on fluorescent and motility agar. Two of these eight isolates exhibited a significant increase in numbers of viable cells when grown in a medium with trifluralin as the only exogenous carbon and nitrogen source. Chromatographic analysis of culture medium extracts revealed the presence of a degradation product which was not present in the herbicide control. The concentration of this unknown was greatest at the 50 mg/L level of trifluralin which also supported the greatest bacterial growth.

One approach to the control of rhizomatous perennial weeds is to alter plant growth form to predispose the difficult-to-reach tissue to herbicides. Yellow nutsedge (Cyperus esculentus L.) was the test plant used in this study. Gibberellic acid induced erect rhizome growth whereas triiodobenzoic or naphthylphthalamic acids induced tuft-type growth as a result of a promoted and accelerated transformation of rhizomes to shoots.

Canada thistle is a serious perennial weed found throughout the northern regions of the United States and Canada. The weevil, Ceutorhynchus litura (F.), was first released in Canada in 1965 as a potential biological control agent for Canada thistle; however, its impact as a control agent has been sporadic. The objective of this study was to characterize C. litura impacts on the carbohydrate profile in Canada thistle roots through the growing season and to evaluate the potential for this biological control agent in causing stress to Canada thistle. Field plots, infested with C. litura, were established and extensively sampled for C. litura infestations. By sampling C. litura–damaged and undamaged Canada thistle shoots–roots through the season, we were able to establish the profile of free sugars and fructans in the roots and compare these levels to the presence and extent of insect damage. Levels of all free sugars and fructans were consistently found to be depressed in roots from C. litura–damaged shoots early in the summer during and shortly after the larval feeding period. Ceutorhynchus litura feeding in Canada thistle shoots appears to disrupt the movement of photoassimilates from leaves to roots. Late-season levels of free sugars and fructans indicate that roots do recover from these depressed levels, and in several instances, significant overcompensation occurred in the damaged roots. Measurement of free sugars and fructans to identify sublethal impacts of control tactics may allow the strategic combining of complementary tactics to maximize the impact of stresses on Canada thistle.

Inbreeding coefficients were determined for nine southeastern Idaho kochia populations using chlorsulfuron resistance as a phenotypic marker. Inbreeding coefficients in six of the populations approximated 0, indicating that these field populations were random mating. One population had an inbreeding coefficient of 0.32, indicating partial selfing. No susceptible genotypes were identified in one population, which suggested recent selection and skewed the inbreeding coefficient. One population had an inbreeding coefficient of −0.19, suggesting either heterozygote advantage or some recent selection in the population. Our results suggest that kochia populations generally approximate random mating. Therefore, unlinked alleles will be independently assorted in field populations of kochia.

Field studies were conducted from 1993 through 1995 to determine potential reductions in herbicide use and associated cost savings by utilizing a weed-sensing sprayer, named Detectspray, to control weeds throughout the fallow season and to control perennial weeds after crop harvest. The Detectspray system gave comparable weed control to conventional broadcast spraying on 80% of the application dates and reduced glyphosate/dicamba use over the fallow season by 19 to 60%. This reduced herbicide use resulted in cost savings of $6 to $32 ha−1. A fallow treatment that combined two herbicide applications with the Detectsprayer plus one to two wide-blade tillage operations was less costly than conventional tillage at two of 11 sites and at all sites retained more surface crop residues to reduce the risk of erosion. Postharvest glyphosate use on quackgrass with the Detectsprayer was reduced 50 to 78% compared to broadcast applications and resulted in cost savings of $16 to $25 ha−1. Clopyralid use on Canada thistle with the Detectsprayer was reduced 71 to 80%, with cost savings of $44 to $50 ha−1. The Detectspray system is a useful tool to effectively manage weeds in conservation fallow and reduced tillage cropping systems.

The response of tomato (Lycopersicon esculentum Mill. ‘Chico III’), jimsonweed (Datura stramonium L.), and velvetleaf (Abutilon theophrasti Medic.) to postemergence applications of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] applied after cloudy weather was determined by shading the plants artificially before field application of the herbicide. One day of 76% actual shade reduced the tolerance of tomato, jimsonweed, and velvetleaf to metribuzin, and 3 days of shade further reduced plant tolerance to the herbicide. The GR50 values showed that tomato was about 30 times more tolerant than jimsonweed and about 40 times more tolerant than velvetleaf to metribuzin. After 3 days of shade, 2 or 3 days of sunshine were required to return tomato to its full tolerance to metribuzin. After 3 days of cloudy weather, metribuzin applied at about 55% of the normal dose should control jimsonweed and velvetleaf. Weather conditions before postemergence applications of metribuzin will determine the appropriate timing of application and the herbicide dose.

An experiment examining the effect of burcucumber emergence date and corn competition on burcucumber fecundity was conducted in 1997 and 1998 in central Pennsylvania. Burcucumber seedlings were transplanted in the field in approximately 10-d intervals starting in late May through mid-August with or without competition from corn. Burcucumber plants grown without competition from corn produced 716 g dry matter and 4,500 seeds plant−1 in 1997 and 607 g dry matter and 1,800 seeds plant−1 in 1998. Biomass was greatest for plants established in late May, whereas seed production was greatest for plants established in mid-June. Although seed numbers were reduced in comparison to the May and June establishment periods, plants established as late as August still produced seed. Burcucumber established in corn produced 96% less dry matter and seed than the plants in a noncompetitive environment in both years of the study. Although the growth and seed production of burcucumber grown in corn was drastically reduced, plants established in mid-July still produced seed.