David R. Gealy

United States Department of Agriculture | USDA · Agricultural Research Service (ARS)

In recent years, water conservation efforts in rice production have necessitated the use of reduced irrigation input systems such as alternate wetting and drying (AWD) as a substitute to conventional continuous flood‐irrigated systems (FLD), but little is known about the role of AWD in altering outcrossing potentials between cultivated rice and wee...

Barnyardgrass [ Echinochloa crus-galli (L.) P. Beauv.] is one of the most troublesome and competitive weed species in rice ( Oryza sativa L.) grown under conventional flood (FLD) irrigation and is expected to be similarly damaging under alternate-wetting-and-drying (AWD) irrigation. Several indica rice genotypes have been shown to suppress E. crus-...

Weed-suppressive rice cultivars have the potential to reduce heavy reliance on synthetic herbicides in rice production. However, the economics of using weed-suppressive rice cultivars in conventional rice systems have not been fully evaluated. This study uses simulation and stochastic efficiency with respect to a function to rank weed-suppressive a...

Weeds are ubiquitous and economically damaging in southern U.S. rice systems. Barnyardgrass has consistently been one of the most prevalent and troublesome of these. Although most rice cultivars do not suppress weeds dramatically, certain Indica cultivars and commercial hybrids are known to suppress barnyardgrass aggressively in conventional, drill...

Studies were conducted to determine the impact of introgression of crop alleles into weedy rice populations. Seeds of 89 weedy rice accessions collected from Arkansas fields in 11 counties, with a history of Clearfield™ rice production, were planted in 2011 and sprayed twice with imazethapyr (0.071 kg ai ha⁻¹). Survivors were genotyped using an all...

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most important insect pest of rice in the United States. Management of L. oryzophilus mainly depends upon the use of insecticides due to the lack of effective alternative management tactics. A 3-yr field study was conducted to determine if difference exists among rice genotypes and cu...

Background: Volunteer rice (Oryza sativa L.) grains may differ in physico-chemical traits from cultivated rice, which may reduce the quality of harvested rice grain. To evaluate the effect of volunteer rice on cultivated rice, fields were surveyed in Arkansas, USA in 2012. Results: Cropping history that included hybrid cultivars in the previous...

Resumo The weed interference varies on several factors, especially the composition of the weed community and the ability to compete with the culture. Thus, this study aimed at evaluating the competitive ability of rice and different populations of red rice (strawhull or blackhull). The experiments were conducted in greenhouse from January to Augus...

High CO2 and high temperature have an antagonistic interaction effect on rice yield potential and present a unique challenge to adapting rice to projected future climates. Understanding how the differences in response to these two abiotic variables are partitioned across rice germplasm accessions may be key to identifying potentially useful sources...

Climate change is caused by the release of greenhouse gases in the atmosphere. Climate change will impact many activities, but effects on agricultural production could be acute. Estimates of annual damages in agriculture due to temperature increase or extended periods of drought will be more costly than damages in other activities. Yield losses are...

Ongoing increases in the human population necessitate that rice will continue to be a critical aspect of food security for the twenty-first century. While production must increase in the coming decades to meet demand, such increases will be accompanied by diminished natural resources and rising production costs that will alter how rice is grown and...

Molecular markers are useful for the identifi­cation of critical genes controlling agricultural traits of interest in crop germplasm and for the use of these genes in crop improvement using marker-assisted selection (MAS). The improve­ment of blast disease resistance of rice (Oryza sativa L.) varieties is one of the major goals for rice breeders. T...

Productivity of rice (Oryza sativa (L.)) is increasingly being constrained by limitations in the quantity, quality, and cost of water and nutrients, and competition from weeds (Pandey and Velasco 2005; Suriyagoda et al. 2014). In this issue, Weerarathne et al. (2015) report exciting research results from factorial glasshouse replacement series expe...

Many different crop species were selected for a common suite of "domestication traits," which facilitates their use for studies of parallel evolution. Within domesticated rice (Oryza sativa), there has also been independent evolution of weedy strains from different cultivated varieties. This makes it possible to examine the genetic basis of paralle...

Understanding the genetic architecture of adaptation is of great importance in evolutionary biology. US weedy rice is well-adapted to the local conditions in US rice fields. Rice blast disease is one of the most destructive diseases of cultivated rice worldwide. However, information about resistance to blast in weedy rice is limited. Here, we evalu...

Robust disease resistance may require an expenditure of energy that may limit crop yield potential. In the present study, a subset of a United States Department of Agriculture rice core collection consisting of 151 accessions was selected using a major blast resistance (R) gene, Pi-ta, marker and was geno-typed with 156 simple sequence repeat (SSR)...

Weedy red rice is a major weed pest of rice in the southern United States. Outcrossing between red rice and commercial tropical japonica rice cultivars has resulted in new weed biotypes that further hinder the effectiveness of weed management. In recent years, indica rice has been used increasingly as a germplasm source for breeding and for reduced...

The use of herbicide-resistant (HR) Clearfield® rice (Oryza sativa L.) to control weedy rice has increased in the past 12 years to comprise about 60% of rice acreage in Arkansas, where most US rice is grown. To assess the impact of HR cultivated rice on herbicide resistance and population structure of weedy rice, weedy samples were collected from c...

Weed control in rice is challenging, particularly in light of increased resistance to herbicides in weed populations and diminishing availability of irrigation water. Certain indica rice cultivars can produce high yields and suppress weeds in conventional flood-irrigated, drill-seeded systems in the southern United States under reduced herbicide in...

Although several studies have examined intra-specific variability in growth and yield to projected atmospheric CO2 concentration, [CO2], few have considered concurrent increases in air temperature and [CO2], and none have compared the relative responses of cultivated and wild, weedy crop lines. In the current study we quantified the growth and seed...

Aims Weed control in rice is challenging, particularly in light of increased resistance to herbicides in weed populations including Echinochloa crus-galli (L.) Beauv. Indica rice cultivars can produce high yields and suppress barnyardgrass, but have not been commercially acceptable in the U.S. due to inferior agronomic traits and grain quality. Our...

Weed-suppressive rice cultivars hold promise for improved and more economical weed management in rice. Interactions between roots of rice and weeds are thought to be modulated by the weed-suppressive activity of some rice cultivars, but these phenomena are difficult to measure and not well understood. Thus, above-ground productivity, weed suppressi...

Agricultural production is under increasing pressure by global anthropogenic changes, including rising population, diversion of cereals to biofuels, increased protein demands and climatic extremes. Because of the immediate and dynamic nature of these changes, adaptation measures are urgently needed to ensure both the stability and continued increas...

Weedy red rice is a troublesome weed problem in rice fields of the southern United States. Typically, red rice plants are much taller than rice cultivars, and most biotypes are either awnless with straw-colored hulls (strawhull) or have long awns with black-colored hulls (blackhull). Outcrossing between rice and red rice occurs at low rates, result...

Research was conducted to evaluate the weed suppression potential of ‘Rondo’ (4484-1693; PI 657830), a sister line (4484-1665), and other indica rice lines against barnyardgrass in field plots in Stuttgart, AR, using minimal herbicide inputs in two separate 3-yr experiments. Under weed pressure, Rondo and the sister line (4484-1665) generally produ...

Although recent and projected increases in atmospheric carbon dioxide can alter plant phenological development, these changes have not been quantified in terms of floral outcrossing rates or gene transfer. Could differential phenological development in response to rising CO(2) between genetically modified crops and wild, weedy relatives increase th...

In a 4-yr field study, "weed suppressive" rice cultivars provided 30% greater control of barnyardgrass and sustained 44% less yield loss (relative to weed-free) compared to "nonsuppressive" tropical japónica rice cultivars. ¹³C analysis revealed that rice root mass predominated vertically and laterally within the soil profile of plots infested with...

In greenhouse and field experiments, an invert emulsion (MSG 8.25) was tested with dried, formulated spores of the bioherbicidal fungus Colletotrichum gloeosporioides f. sp. aeschynomene, a highly virulent pathogen of the leguminous weed Aeschynomene virginica (northern jointvetch), but considered “immune” against another more serious leguminous we...

DNA sequence polymorphism at the Pi-ta gene in US weedy rice. Sliding window analysis of 7275 DNA sequences of the Pi-ta gene analyzed using DNASP software. Sites with alignment gaps were not counted in the window length (and slide). Window length was 50 and step size was 10. Graphic presentation of Pi-ta was shown at the bottom. (TIF)

Photograph of rice seeds of a US cultivar and a red rice. Seeds with/without hull were shown. (TIF)

Description of the US weedy rice accessions used in present study. (DOC)

Expression of the Pi-ta gene in US weedy rice accessions and cultivar Katy containing Pi-ta. Lane 1 Accession, 1111-01, lane 2, 1300-02, lane 3, 8-96, lane 4, Katy, and 5: Katy genomic DNA as a negative control. (TIF)

Weedy rice found in a commercial rice field, Stuttgart AR. Most of rice plants shown in the photo are weedy rice. Over 70% of field area was contaminated by the weedy rice population. (JPG)

Rice accessions of seven AA genome Oryza species used in the present study. (DOC)

The Pi-ta gene in rice has been effectively used to control rice blast disease caused by Magnaporthe oryzae worldwide. Despite a number of studies that reported the Pi-ta gene in domesticated rice and wild species, little is known about how the Pi-ta gene has evolved in US weedy rice, a major weed of rice. To investigate the genome organization of...

Assessing belowground plant interference in rice has been difficult in the past because intertwined weed and crop roots cannot be readily separated. A ¹³ C discrimination method has been developed to assess distribution of intermixed roots of barnyardgrass and rice in field soils, but the suitability of this approach for other rice weeds is not kno...

Background/Question/Methods Over 158 million hectares of rice are grown in the world providing a staple food for more than half the world’s population. Although there are several species of Oryza, essentially all cultivated rice is derived from O. sativa which can be genomically differentiated into five sub-populations. There are some 150,000 ric...

Assessing belowground plant competition is complex because it is very difficult to separate weed and crop roots from each other by physical methods. Alternative techniques for separating crop and weed roots from each other are needed. This article introduces a stable isotope method that can quantify the amounts of roots of rice and barnyardgrass in...

Shivrain VK, Burgos NR, Agrama HA, Lawton-Rauh A, Lu B, Sales MA, Boyett V, Gealy DR & Moldenhauer KAK (2010). Genetic diversity of weedy red rice (Oryza sativa) in Arkansas, USA. Weed Research50, 289–302. Weedy red rice (Oryza sativa) is a problematic weed in cultivated rice. About 50% of US rice is produced in Arkansas and 60% of these fields hav...

Because wild lines of the same species often represent a weedy constraint to cultivated crops in the field, any differential response to atmospheric carbon dioxide concentration, [CO2], may alter weed–crop competition and seed yield. We evaluated the growth and reproduction of cultivated rice (Oryza sativa L.; Clearfield, CL161) and red or weedy ri...

Weedy red rice is a highly troublesome weed of rice in the United States and throughout the world. Effective management of this weed has remained challenging to U.S. farmers, partly because of the biological diversity among red rice populations, resistance to or avoidance of control measures, and genetic similarities with crop rice that allow cross...

Gene transfer from weeds to crops could produce weedy individuals that might impact upon the evolutionary dynamics of weedy populations, the persistence of escaped genes in agroecosystems and approaches to weed management and containment of transgenic crops. The present aim was to quantify the gene flowrate from weedy red rice to cultivated rice, a...

The effect of seeding depth on emergence of red rice (Oryza sativa) ecotypes from Arkansas (AR), Louisiana (LA), and Mississippi (MS) was determined under dry-seeded rice production in clay and silt loam soils in Arkansas. By 21 d after planting (DAP), all red rice ecotypes had emerged from planting depths of 1.3, 2.5, 5.0, and 7.5 cm in both clay...

Barnyardgrass (BYG) has been the most frequently reported troublesome weed in rice because it is an aggressive invader, is difficult to control, and reduces yields significantly. A replacement series study was conducted to determine how a naturally suppressive cultivar (T65*2/TN 1; ‘PI 312777’), a nonsuppressive cultivar (‘Lemont’), and an F3 cross...

Red rice is a major weed of rice in the southern U.S. and can intercross with rice. Knowledge of the plant phenotypes from such crosses would be valuable for identification and management of these plants. Male-sterile long-grain tropical japonicas ‘Kaybonnet-1789’ and ‘Cypress-1819’ were crossed with two awned and two awnless U.S. red rice types. F...

The commercialization of imazethapyr-resistant (Clearfield™, CL) rice in the southern United States has raised serious concerns about gene flow to red rice, producing imazethapyr-resistant red rice populations. Our objectives were to determine the impact of planting date, CL cultivars, and red rice biotypes on outcrossing rate; and to investigate t...

A replacement series study was conducted in a greenhouse in 1998 and 1999 to evaluate the interference interactions among two rice cultivars and two red rice ecotypes. Plants were established in proportions of 3:0, 2:1, 1:2, and 0:3 (rice-red rice) plants/pot. Relative yield of Kaybonnet based on the shoot dry weight was lower than that of KatyRR o...

Red rice in the US is an aggressive weed that reduces the yield of rice and contaminates its grain. It is the same species as rice, which provides an opportunity for intercrossing. This genetic similarity complicates the management of red rice in fields and rice mills, but also indicates a potential for its use in rice breeding or niche markets. Ph...

Cultivated rice yield losses due to red rice infestation vary by cultivar, red rice density, and duration of interference. The competition effects of red rice could be influenced further by emergence characteristics, red rice biotype, and planting time of cultivated rice. We aimed to characterize the emergence of red rice biotypes at different plan...

Red rice, which grows taller and produces more tillers than domestic rice and shatters most of its seeds early, is a major weed in many rice-growing areas of the world. Field experiments were conducted at Stuttgart, AR in 1997 and 1998 to evaluate the growth response of the Kaybonnet (KBNT) rice cultivar to various population densities of three red...

Red rice is a major weed in rice production in the southern United States. Red rice and rice intercross because they are the same species. Our objectives were to determine the genetic diversity represented by accessions of red rice and to identify DNA markers that might be useful in identifying hybrids between red and cultivated rice. Red rice acce...

Field studies were conducted to compare the barnyardgrass suppression by four U.S. (‘Starbonnet’, ‘Kaybonnet’, ‘Lemont’, and ‘Cypress’) and three highly competitive, high-yielding Asian cultivars (‘PI 312777′, ‘Guichao’, and ‘Teqing’). The economic consequence of applying less than the recommended propanil rates to these cultivars was also evaluate...

Field experiments were conducted at the Rice Research and Extension Center at Stuttgart, AR, in 1997 and 1998 to evaluate the growth response of Stuttgart strawhull (Stgstraw) red rice to sowing densities of 0, 50, 100, and 150 kg ha−1 of ‘Kaybonnet,’ ‘Guichao,’ and ‘PI 312777’ rice cultivars. PI 312777 produced a greater leaf area index and tiller...

The transfer of the imazethapyr-resistant gene from Clearfield (CL) rice to red rice is an ecological risk. Flowering synchronization and genetic compatibility between cultivated rice and red rice could influence gene transfer. We examined the (1) variability in maximum outcrossing rate between 12 red rice biotypes and 'CL161' rice during their pea...

Carolina foxtail (Alopecurus carolinianus) has not been reported to host Magnaporthe oryzae. A collection of Carolina foxtail obtained from several Arkansas locations over a 4-year period was inoculated with four races of the fungus under greenhouse conditions and, in all cases, inoculation resulted in the formation of irregular, yellow and brown l...

Weedy rice, red rice (Oryza sativa L.), is a serious problem in rice-producing areas of the southern U.S. and various regions worldwide. It competes for production inputs, increases weed control cost, reduces yield and grain quality, and could eliminate economic returns. Research was conducted to compare: (i) the relative efficiencies of rice and w...

Sixteen red rice accessions from the southern United States were studied for their physical, milling, pasting, and thermal properties, chemical composition, and starch fine structure relative to cultivated medium- and long-grain rice varieties. All red rice samples were medium-grain, but their physicochemical properties were different from those of...

Red rice has long been a troublesome, conspecific weed of cultivated rice. Rice varieties carrying certain herbicide-resistant traits acquired through genetic modification (herbicide-resistant varieties) now offer new options for red rice control. In concert with this innovation is the risk of gene flow, which can result in the transfer of that spe...

Recent research of the Agricultural Research Service of USDA on the use of natural products to manage pests is summarized. Studies of the use of both phytochemicals and diatomaceous earth to manage insect pests are discussed. Chemically characterized compounds, such as a saponin from pepper (Capsicum frutescens L), benzaldehyde, chitosan and 2-deox...

Outcrossing between rice and red rice has been a concern because of their morphological similarities and oftentimes synchronous flowering. In 2000, pairs of rice and red rice with near synchronous flowering were planted in isolated field plots. In 2002, at least 2300 seeds produced from two of the pairs were planted in a greenhouse, and DNA was ext...

Red rice is a troublesome weed in rice-growing areas of the southern U.S. Red rice in Arkansas may be diverse enough to warrant some adjustments in weed control programs. A study was conducted at the Rice Research and Extension Center (RREC), Stuttgart, Ark., in 2003 to determine the phenotypic diversity of red rice in Arkansas. One hundred thirty-...

The genetic and agronomic consequences of transferring glufosinate (Liberty™) herbicide resistance from transgenic rice (Oryza sativa L.) lines to the noxious weed red rice (Oryza sativa L.) were evaluated under field conditions. Replicated field trials in Louisiana (LA) and Arkansas (AR) were conducted in 1997 to evaluate ten vegetative and reprod...

Rice (Oryza sativa L.) research field plots are likely to have nearly complete weed control whereas normal farmer field‐grown rice often have considerably greater weed populations. Consequently, a disparity might exist between nitrogen (N) requirements for producing maximum yields, in weedy (such as in some farmer fields) versus weed‐free rice (suc...

Palmleaf morningglory (IPOWR) and pitted morningglory (IPOLA) were compared in field and greenhouse tests under simulated rice field conditions to quantify flood tolerance characteristics of the two species. IPOWR survived a 13-cm flood in the field if the flood was applied 12 days after planting (DAP) or later. In contrast, IPOLA did not survive f...

Inheritance of resistance to diclofop was studied in three wild oat biotypes (designated B, C, and H) from the Willamette Valley of Oregon. Cultivated oat (cultivar 'Monida') was crossed, including reciprocals, to three wild oat biotypes. Leaves of each F1 plant were spotted with diclofop as a nondestructive test for resistance or susceptibility. A...

Laboratory experiments were conducted to determine the mechanism of resistance to diclofop in two wild oat biotypes (designated 'B' and 'C' biotypes) from the Willamette Valley of Oregon. Resistance could not be attributed to differential absorption, translocation, or metabolism of diclofop. Resistance was not correlated with membrane plasmalemma r...

Phytotoxic effects of metabolites from a naturally occurring rhizobacterial isolate, Pseudomonas syringae strain 3366, were determined on downy brome and 'Hill 81' winter wheat, along with 10 other weed and crop species. Centrifuged supernatant and concentrated ethyl acetate extracts from aerobic shake cultures of strain 3366 suppressed germination...

Phytotoxins produced by the naturally-occurring rhizobacterium, Pseudomonas fluorescens strain D7 (strain D7), in shake cultures from several media sources adversely affected downy brome at several growth stages and affected seeds, whole plants, and isolated cells. These uncharacterized phytotoxins inhibited root and shoot growth of downy brome by...

Drift of sulfonylurea and phenoxy herbicides from spring cereal fields to nearby spring pea and lentil crops was simulated by spraying pea and lentil with 2,4-D or the 2:1 commercial mixture of thifensulfuron and tribenuron at rates of 0, 0.33, 1, 3.3, or 10% of the use rates (X) for spring cereal crops approximately 3 and 5 wk after planting pea a...

Mayweed chamomile is an increasing weed problem in cropping systems of the Pacific Northwest. Modern farming practices that utilize conservation tillage systems and heavy application of nitrogen fertilizers have been associated with increased soil surface water potential and decreased soil pH. Therefore, soil water potential, soil pH, and temperatu...

Effects of root-shoot interference, soil water regimes, and soil nitrogen were evaluated to determine aggressivity for pea relative to mayweed chamomile in the greenhouse using replacement series experiments. Interference between pea and mayweed chamomile occurred mainly below ground, and soil water was more important than soil nitrogen in controll...

The first occurrences of wild oat resistance to diclofop in the Willamette Valley of Oregon were reported in 1990. Among eight resistant biotypes, GR 50 values for diclofop were 3 to 64 times greater than the GR 50 for a susceptible wild oat biotype. GR 50 values for other aryloxyphenoxypropionate herbicides varied from 1 to over 100 times greater...

Downy brome is a grassy weed that infests millions of acres of winter wheat in the Western United States and costs farmers millions of dollars in lost yields. It can not be controlled consistently using chemicals or cultural practices. Isolates of naturally occurring rhizobacteria have shown potential as biological control agents for downy brome. C...

Greenhouse experiments were conducted to evaluate phytotoxicity, absorption, and translocation of thifensulfuron when applied to pea at different rates, droplet sizes, and as dry particles. Thifensulfuron rates that reduced shoot dry weight by 25% were 0.46, 0.59, 0.98, and 1.21 g ai ha ⁻¹ for droplet diameters of 110, 155, 300, and 450 μm, respect...

Effects of a crude preparation of a phytotoxin from Pseudomonas fluorescens strain D7 (D7) on various physiological processes were evaluated in roots of downy brome seedlings. Cell division, respiration, and synthesis of protein, RNA, and DNA were not inhibited or only slightly inhibited under treatment conditions that caused substantial inhibition...

Destructive growth analysis of field replacement series experiments with mayweed chamomile and dry field peas was used to determine the competitive relationship between the two species. Mayweed chamomile produced similar amounts of leaf area and dry weight per plant in a dry year and a wet year. On the other hand, dry field peas produced 20% more l...

Field applications of the rhizobacterium, Pseudomonas fluorescens strain D7 (D7), have selectively suppressed downy brome in winter wheat test plots. A phytotoxin produced by D7 inhibits downy brome root growth. An assay system was developed for future investigations of the mechanism of action of this and other phytotoxins that inhibit root growth....

Root absorption of subtoxic levels of metribuzin and its ethylthio analog (ethyl-metribuzin) by downy brome, jointed goatgrass, and winter wheat increased by a factor of three to five times as temperature increased from 10 to 20 C. Absorption of ethyl-metribuzin per gram dry weight was similar for all three species. Absorption and distribution of e...

The binding rate of metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one, and its ethylthio analog (ethyl-metribuzin), 4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one to thylakoid membranes of downy brome (Bromus tectorum L.), jointed goatgrass (Aegilops cylindrica Host), and winter wheat (Triticum ae...

The absorption of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] and its ethylthio analog (ethyl-metribuzin) [4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one] by protoplasts of downy brome (Bromus tectorum L.) and jointed goatgrass (Aegilips cylindrica Host) was assayed by a modified silicone o...

Inhibition of net photosynthesis of jointed goatgrass and downy brome protoplasts by metribuzin and its ethylthio analog (ethyl-metribuzin) was greater at 25 than at 10 C. As temperature increased from 10 to 25 C, the concentration of ethyl-metribuzin required to inhibit net photosynthesis 50% (I 50 ) decreased by a factor of 3.5 and 4.3, respectiv...

Photosynthetic productivity parameters were determined for mayweed chamomile, a troublesome annual weed of the cropping systems in the Pacific Northwest. At a photosynthetic photon flux density of 1800 μE m ⁻² s –1 , maximum net photosynthetic rate of greenhouse-grown plants was 35 mg CO 2 dm ⁻² h –1 and maximum transpiration rate was 6.7 μg H 2 O...

Greening etioplasts in leaf tips of seedlings treated with varying, sublethal concentrations of metribuzin or its ethylthio analog for 12, 24, or 72 hr were examined by transmission electron microscopy to determine differential effects of these closely related herbicides in wheat (Triticum aestivum L. “Daws”) and downy brome (Bromus tectorum L.). I...

The influence of N fertilization on turgor maintenance was determined in leaves from well-watered and droughted Rosa rugosa L. Plants were fertilized for 60 days with a complete fertilizer with N at levels of 0, 200 or 500 ppm and then subjected to several drought cycles for 22 days. Plants receivmg no N were stunted and chlorotic, but had the grea...

Microautoradiographic techniques were utilized to localize quizalofop (ethyl-2-[4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoate) and fluazifop [butyl-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoate) in downy brome (Bromus tectorum L. #1 BROTE) spikelets. Excised downy brome spikelets were fed 14C-quizalofop (ethyl ester) or 14C-f...