| Title |
Investigators | Department | Objectives | Approach Keywords | Progress Reports | Impact Statements | Publications | |
Project * COL00664 | |
| Title | The Biology, Ecology, and Molecular Genetics of Key Weeds of Colorado Row Crops and Non-Cropland |
| Investigator(s) | Westra, P; Nissen, SJ; Leach, JE; Norton, AP; Shaner, DL; Ward, SM |
| Department | Bioagricultural Sciences and Pest Mgmt. |
| Objectives | 1) To determine the basis for glyphosate resistance in Palmer amaranth and to evaluate the impact of this resistance trait on Palmer amaranth biology and on gene flow from Palmer amaranth to other pigweed species. 2) To determine the molecular and genetic basis of dicamba resistance in kochia as a pilot project to evaluate the potential for dicamba resistance to develop in weeds. 3) To determine the biology, genetic, and physiology bases for differential feral rye response to management strategies in winter wheat. 4) To map, manage, and monitor key water-loving invasive plant species along the front range of Colorado. |
| Approach | Basic biochemical and molecular laboratory studies will be conducted to determine the basis for glyphosate resistance in Palmer amaranth and dicamba resistance in kochia. Issues such as target site mutations, gene over-expression, metabolism, or plant sequestration will be evaluated as possible mechanisms of resistance. Genetic crosses and gene flow via pollen movement will be used to determine if the glyphosate resistance in dioceous Palmer amaranth can move to 10 other members of the pigweed genus. Genetic crosses with distinct kochia lines will be used to determine the dominance of the dicamba resistance gene. Genetic fingerprinting and evaluation of herbicide response in feral rye will be used to evaluate the variable response exhibited to different management strategies in feral rye. Where possible, new biochemical or molecular techniques will be used to study the target weeds in this project. Tamarisk mapping and management will be conducted in field studies within riparian drainages along the front range of Colorado. The basic and applied research results of this project will be shared with clients through extension meetings and professional meetings. Research results will be published in peer reviewed journals. |
| Keywords | herbicide resistance, weed ecology, tamarisk, kochia, palmer amaranth, feral rye , invasive plants, water use efficiency, molecular genetics |
| Progress Reports | |
| 1993 | Sixteen crop rotations including wheat, fallow, corn, millet, and sunflower are being used to evaluate 1, 2, 3, and 4 seasons of integrated jointed goatgrass management in a study initiated in the fall of 1991. Highest jointed goatgrass densities (38 plants per square meter) occurred in wheat planted in the fall of 1991. Plots where corn or sunflower grew in 1992 following wheat, produced an average of 23 jointed goatgrass plants per square meter. All plots where spring crops were planted in 1993 showed additional jointed goatgrass decline. Ancillary research showed that deep plowing helps control jointed goatgrass, but allows unacceptable soil erosion potential. Volunteer rye had a faster growth rate than jointed goatgrass or wheat. This may help explain why volunteer rye overtops wheat in the spring. The intermediate growth rate of jointed goatgrass allows it to be (very) competitive with semi-dwarf wheat varieties. This study will help elucidate mechanisms of competition among these weeds and winter wheat. Growth parameter values generated will be used to develop a bioeconomic model for jointed goatgrass management in winter wheat. ===. |
| 1994 | Two long term rotation studies are in progress, one with natural goatgrass populations in Platner, CO and the second with seeded populations of the three winter annual grasses in Platteville, CO. After four years of crop rotations in Platner there have been few statistical differences in jointed goatgrass emergence rates. However, the previous years crop affects goatgrass emergence by the microenvironment imposed by the crop. Previous crops of corn and sunflower resulted in greater goatgrass emergence than fallow or proso millet. The Platteville crop rotation study is now in the fourth cropping season. Rotations with two years of spring planted crops have significantly reduced winter annual grass populations when compared to the normal wheat/fallow rotation. Seed bank flux was greatest in volunteer rye. Growth analysis experiments conducted under noncompetitive conditions and within a wheat canopy have consistently shown Volunteer rye to have greater growth attributes than wheat, jointed goatgrass and downy brome. Jointed goatgrass possesses similiar growth characteristics of the semi dwarf wheat variety Tam 107. Data analysis using the Richards function will generate parameter values which will allow a more mechanistic assessment of differential competitiveness of the grasses involved. |
| 1995 | Several field studies were initiated to evaluate the influence of various cultural and ecological factors on wheat yield reduction caused by jointed goatgrass. When 10 short to tall wheat varieties were grown in the presence of 60 or more jointed goatgrass plants per square meter, yields were reduced an average of 66%. Yield reductions per cultivar ranged from a low of 52% to as much as 77%. Thus some wheat cultivars are better able than others to tolerate jointed goatgrass competition. In a separate competition study with 5 levels of jointed goatgrass, yield reduction ranged from 16% at 3.5 jointed goatgrass plants per square meter to 35% at 25 jointed goatgrass plants per square meter. When jointed goatgrass emerged with winter wheat, it caused more yield reduction than when it emerged 2-3 weeks later than the wheat. A growth analysis of 41 jointed goatgrass accessions grown in a common nursery showed that they varied considerably in vigor, tiller production, and plant height at harvest. This nursery study will attempt to quantify some of the genetic variation in jointed goatgrass across the western region of the United States. The results of these studies, all of which were repeated in the fall of 1995, will be used to develop integrated management strategies for jointed goatgrass in winter wheat. |
| 1996 | Jointed goatgrass competition studies in a tall and short wheat variety showed that both wheat varieties were somewhat more competitive because of 10-15% greater plant height, a higher absolute growth rate, and a higher net assimilation rate for wheat. In economic threshold studies jointed goatgrass at 0 to 80 plants per square meter caused up to 60% yield reduction. Delaying jointed goatgrass emergence until 3 or more weeks after wheat emergence reduced jointed goatgrass seed production more than 70%. Spring planted jointed goatgrass in wheat produced viable seed. Crop rotations longer than 3 years out of wheat are needed to significantly reduce jointed goatgrass levels. Jointed goatgrass or volunteer rye competition combined with Russian wheat aphid caused an additive reduction in wheat yield while downy brome interacted synergistically. Competition studies showed that volunteer rye is more competitive than jointed goatgrass against winter wheat, and that downy brome is the least competitive of the grasses included in these studies. |
| 1997 | From 1994 to 1997, 55 jointed goatgrass accessions have been planted annually at the Agricultural Research Development and Education Center (ARDEC) of Colorado State University, Fort Collins. Most of the accessions were sent to CSU by weed scientists from KS, OK, WY, NE, UT, WA, OR, ID. The accessions have been grown in single rows with three replications. At physiological maturity, growth characteristics such as height, reproductive tiller number, biomass, and relative maturity are recorded. For jointed goatgrass DNA fingerprinting procedures have been initiated on eight of the accessions representing a range of geographic locations. These accessions include numbers 2, 16, 42, 45, 47, 49, 51, and 54. The DNA has been extracted, quantified, restricted, and amplified. Thus far, three different random, 10 base pair primers have been used to amplify the DNA fragments with the intention of using approximately 20 different primers, depending on the number of polymorphisms detected. Two on-farm research projects (in CO and NE) are being used to develop jointed goatgrass best management practices (BMPs) based on successful grower experiences and integrated component research, and compare the economics and effectiveness of the BMPs with common grower production practices through on-farm strip tests using grower equipment. Soil cores were taken on a 50 foot grid in each 5-10 acre field in July 1997 and sent for analysis to the Univ. of WY to determine background jointed goatgrass soil seedbank densities. The spatial distribution and density of jointed goatgrass was evaluated in five Colorado dry-land winter wheat fields. Characterizing the spatial pattern of jointed goatgrass in wheat fields may improve weed management. Field areas infested with jointed goatgrass were documented in June 1997. Patch edges were documented with a backpack global positioning system (GPS). The number of patches encountered per field varied from 1 to 8 and varied considerably in size. The area of each field that was infested with jointed goatgrass ranged from 6 to 42 percent. Average patch density ranged from 5 to 133 jointed goatgrass heads per quadrat and varied in and among fields. Estimated percent yield loss also varied in and among fields. Yield loss estimates by patch varied from 8 to 57 percent among all five fields. Estimated potential total wheat yield loss from jointed goatgrass competition by field ranged from 1 to 9 percent. Parameter values from Colorado economic threshold competition studies and addition series competition studies with a tall and short winter wheat variety have been incorporated into a jointed goatgrass bioeconomic model that is being developed by Dr. Bruce Maxwell from Montana State University. Field trials were established in the fall of 1997 to evaluate the potential to control downy brome, Japanese brome, jointed goatgrass, and volunteer rye with imazamox. Such control would be possible with new winter wheat varieties that are tolerant to imazamox. These studies will evaluate the effect of weed size, fall versus spring treatments, imazamox rate, and surfactants on control of these winter annual grass weeds. |
| 1998 | Jointed goatgrass management through the integration of wheat seeding rate, wheat seeding date , fertilizer placement, and cultivar (3) selection is being evaluated in a long term 10 acre field study near Akron, CO. This integrated study was designed based on results of earlier single-component research on jointed goatgrass. Control of volunteer rye, downy brome, and jointed goatgrass through crop rotations, novel chemistry, and competitive cultivars has been evaluated. Fields infested with rye and jointed goatgrass require 3 or more years out of winter wheat production to significantly reduce weed levels. The genetic diversity of 50+ U.S. jointed goatgrass accessions is being evaluated in field nursery studies and through DNA genetic analysis in greenhouse and laboratory studies. Four farmers in CO, KS, and NE are collaborating on large-scale field studies with diverse crop rotations to develop non-chemical methods of jointed goatgrass management. GPS and GIS technology were used to map jointed goatgrass patches in three winter wheat production fields. |
| 1999 | A long-term integrated study of jointed goatgrass management in winter wheat shows that increasing the wheat seeding rate increases wheat yield while reducing the presence and yield lowering impact of jointed goatgrass. When adverse weather conditions limit the growth and density of winter wheat, jointed goatgrass can show a dramatic response by producing more seed heads which results in increased seed in the soil. Best Management Practice sites for goatgrass management have been established utilizing best wheat cultivars, planting date, crop rotations, and fertilizer management to limit yield losses from jointed goatgrass. Imazamox shows great promise for jointed goatgrass control in resistant winter wheat, a big breakthrough because of the genetic relatedness of jointed goatgrass and winter wheat. Collaborative research with the CSU wheat breeding program is developing goatgrass management strategies based on this new technology. AFLP analysis of diverse jointed goatgrass accessions reveals what appears to be relatively little genetic diversity in this weedy species. |
| 2000 | The genetic variation of jointed goatgrass accessions from North America and the Middle East was evaluated utilizing RFLP and AFLP techniques. Less than 5% polymorphisms were detected utilizing any technique, even at the global level, suggesting that jointed goatgrass exhibits relatively little genetic diversity. This may simplify biological or chemical control of an important weed of winter wheat. Cultural practices such as use of a tall growing wheat cultivar, higher seeding rates for wheat, placement of nitrogen fertilizer 10 cm deep in the soil, and delayed wheat seeding all helped to reduce but not eliminate jointed goatgrass from wheat. Kochia genetic diversity is being evaluated in genetics studies utilizing 25 populations that differ in dicamba sensitivity and which have been selfed for 5 generations. Kochia control with new technologies is being evaluated. |
| 2001 | The genetic diversity of jointed goatgrass from the United States and from the middle east (thought to be its center of origin) was evaluated utilizing RAPD and AFLP molecular techniques. Regardless of the method or number of primers used, the number of polymorphisms detected was very low (less than 5%) suggesting that there may be relatively little genetic diversity in jointed goatgrass. Field research has further shown that 10 representative accessions of jointed goatgrass from these collections all demonstrated similar responses to various application rates of imazamox herbicide. Clearfield winter wheat that is resistant to imazamox has been commercially developed and tested in this program. Crop safety is good and use of imazamox provides a powerful new tool for greater than 95% control of jointed goatgrass . One year of research has been conducted to evaluate the incorporation of Clearfield wheat into central great plains dryland cropping systems which include the planting of corn, sunflower, millet, and sorghum. Nine kochia accessions that vary in dicamba tolerance have been selfed for 6 generations and will be used to make crosses to determine the inheritance patterns of dicamba tolerance in kochia. Crosses will be made in the spring of 2002 which will allow for subsequent testing of the progeny. |
| 2002 | AFLP techniques were used to evaluate the genetic diversity of jointed goatgrass which turned out to be not genetically very diverse. This may imply that control of any jointed goatgrass populations in the western US should be good with imazamox, a new herbicide which can be used in Clearfield wheat for control of winter annual grasses. A six year study showed that cultural practices alone were ineffective for control of jointed goatgrass. Use of diverse cropping systems improves long-term management of jointed goatgrass. Utilizing arabidopsis mutants and tobacco mutants, we have evaluated the differential ethylene production in kochia lines that differ in their response to dicamba herbicide. Most dicamba resistant lines are still sensitive to fluroxypyr, a new herbicide with excellent activity on kochia. Advanced lines of homozygous kochia are being used to study the genetics of herbicide resistance in kochia. |
| 2003 | Research progress has been made on the genetic diversity and management of jointed goatgrass. Demonstration of low level genetic diversity implies that new chemical control tactics should be quite similar across a large area of infestation. Although it is thought that herbicide resistance genes could move from new wheat varieties via hybrid bridges that can form between winter wheat and jointed goatgrass, our research has shown that less than 1% of spikes on hybrid plants form viable seed. Our research with the newly released imazamox tolerant variety Above has shown that best feral rye control occurs with fall herbicide application, but that jointed goatgrass can be controlled with fall or spring applications. Above has been planted on 125,000 acres of Colorado wheat ground in its second year of commercial use by growers who will use this new technology to selectively control winter annual grass weeds such as jointed goatgrass, feral rye, and downy brome. We have made progress in understanding the complex genetics of dicamba resistant kochia which appears to express resistance through multiple genes that are altered in resistant plants. It has taken 8 years to develop the homogeneous kochia lines with which to now conduct advanced genetic studies. |
| 2004 | One PhD student (David Belles) completed a research thesis elucidating some of the aspects of dicamba resistance in kochia. Part of the resistance appears to be due to high insensitivity of resistant kochia to ethylene which is produced following herbicide application. Arabadopsis and tobacco mutants were used to study the ethylene response in kochia. This project represent an excellent model for a herbicide resitance trait that is due to the interaction of multiple genes, making it more difficult to understand the genetics of this trait. A new MS student (Todd Gaines) has started a new research project related to gene flow in winter wheat and jointed goatgrass. Specifically, we are evaluating the potential for the Clearfield herbicide resistance gene to move into jointed goatgrass, a weed of winter wheat that will hybridize with winter wheat. We have found that hybrids of wheat and jointed goatgrass typically produce less than 1% viable seed under Colorado conditions. We have begun new research to evaluate the interaction of stressful growing conditions with the Clearfield gene in understanding occasional imazamox injury that is observed under commercial field conditions. We continue to share the results of these research projects with wheat producers through meetings and publications. |
| 2005 | In 2005 Dr. Brad Hanson, a post-doc, was hired to study the interactions of stress and imazamox herbicide on the performance of Clearfield wheats. Cold temperatures appear to reduce imazamox metabilism, occasionally leading to moderate crop injury. Double gene Clearfield wheats exhibit elevated tolerance under stress conditions. Todd Gains, a MS student has used the Above Clearfield wheat to determine gene flow from Above to conventional wheats and jointed goatgrass in growers commercial fields at the landscape level. Gene flow dropped off very rapidly with distance, but could still be measured at low levels 120 feet from the pollen source. Some conventional wheats appear to be more susceptible to gene flow than others, perhaps based on flowering timing or floral architecture. Pollen flow from Above to natural stands of jointed goatgrass did occur, but at very low levels. The genetics of a dicamba-resistance trait in kochia appears to be polygenic, but on-going studies should help determine the inheritance pattern. The resistance trait in kochia is not well described by an altered ethylene response in dicamba resistant kochis. |
| 2006 | Adoption of Clearfield wheat varieties to help manage jointed goatgrass, downy brome, and feral rye in Colorado continues to exceed expectations. Of these three weeds, feral rye remains the most problematic in terms of consistent, reliable control. Research in 2006 focused on the genetic diversity of feral rye, and included studies on the importance of herbicide application timing (fall vs spring), and feral rye stage of growth on the level of control achieved. Advances are being made in the incorporation of a double copy of the Clearfield gene into winter wheat to provide for additional crop tolerance and a higher level of feral rye control. Research continued on the inheritance of dicamba resistance in kochia. The results of several genetic crosses studied between resistant and susceptible populations point to dicamba resistance resulting from a single gene in kochia. This means that dicamba resistance will continue to evolve if dicamba is used intensively. Resistance is partially dominant meaning it will spread in pollen as well as by seed. Research on the mechanisms for glyphosate resistance in Palmer amaranth showed that while high levels of shimimate accumulate in susceptible plants, resistant Palmer amaranth plants show no accumulation over a wide range of glyphosate concentrations. This result, coupled with field observations, points to a high and very alarming level of glyphosate resistance that has developed in a very serious and aggressive annual broadleaf weed. Gene sequencing research on resistant plants revealed a consistent new amino acid change in a new region of the gene when no mutation as previously been reported. This may be a novel and important new mechanism of glyphosate resistance in plants. Understanding the mechanism of glyphosate resistance in Palmer amaranth may help direct development of new management strategies for this important weed. Research on gene flow from Clearfield winter wheat showed that the Clearfield gene can move via wheat pollen to other wheat varieties and to jointed goatgrass, although this occurs at a low level. |
| Impact | |
| 1999 | The spread and economic losses due to jointed goatgrass in winter wheat is being reduced through education, improved dryland crop rotations, use of competitive wheat cultivars, and development of new wheat varieties with resistance to Imazamox which control jointed goatgrass . |
| 2000 | Wheat producers are being encouraged to utilize integrated management strategies to combat jointed goatgrass in winter wheat. Development of Clearfield wheat shows great promise for control of jointed goatgrass. A national jointed goatgrass web page is heavily used as a source of educational material on the biology and control of jointed goatgrass. |
| 2001 | Judicious incorporation of Clearfield wheat into dryland cropping systems will provide the best opportunity to date to reduce or eliminate jointed goatgrass from wheat fields over time. Farmer interest in this new technology is extremely high, suggesting that adoption of such technology will be rapid and high. A better understanding of the genetics of herbicide tolerance in kochia will help in the development of new tools and new strategies for kochia management in dryland and irrigated crops. |
| 2002 | We will help Colorado producers more effectively control jointed goatgrass, feral rye, downy brome, and kochia by providing timely new information on the biology and genetic diversity of these weeds, including any differential response of weed populations to new herbicides which are useful for their control. |
| 2003 | The commercial use of imazamox resistant Above winter wheat will continue to grow as growers better understand the biology and management of weeds such as jointed goatgrass with imazamox. A better understanding of dicamba resistant kochia genetics will allow for the development of new and better kochia management strategies. |
| 2004 | Ongoing development of weed management strategies in Above (Clearfield) winter wheat has resulted in the planting of this new wheat on more than 10% of all Colorado wheat acres. This is one of the most rapid adoptions of new technology in the Colorado wheat industry. A second Clearfield variety is ready for release in 2005 to control jointed goatgrass. Our understanding of dicamba resistance in kochia shows that this polygenic trait makes it more difficult to understand than single point source mutations that confer herbicide resistance. We can provide growers with alternate forms of kochia control. |
| 2005 | Above Clearfield winter wheat has been rapidly adopted by Colorado wheat producers because of the effective control of jointed goatgrass, downy brome, and feral rye with imazamox herbicide . Above also has excellent agronomic characteristics as does Bond, the second Clearfield winter wheat released by Colorado State University. Understanding the genetics of dicamba resistant kochia has helped explain why this issue has not exploded across Colorado the way other herbicide resistance problems did in kochia with atrazine and ALS herbicides. In light of a new dicamba resistance gene being stacked in Roundup Ready crops, this research project on dicamba-resistant kochia will help provide early understanding of how this resistance develops in weeds which will be subjected to increased dicamba selection pressure in the future. |
| 2006 | Above and Bond Clearfield winter wheat varieties have been rapidly adopted by Colorado wheat producers because of the effective control of jointed goatgrass, downy brome, and feral rye with imazamox herbicide. These two varieties were planted on more than 10% of all Colorado wheat acres in the fall of 2006. As new double-gene Clearfield wheats enter the market, we anticipate additional abilities to control feral rye in wheat. Although dicamba resistant kochia continues to persist in central great plains fields at a low level, we know that stacking dicamba resistance with glyphosate resistance will put added pressure on kochia populations to become problematic in row crops. Our research shows that this resistance trait is likely to spread via seed and kochia pollen. Molecular research on glyphosate resistant Palmer amaranth should help scientists design new, more effective control measures for this weed. The gene flow research with winter wheat and jointed goatgrass provides field-level assessment of potential risks of novel trait movement in winter wheat, a key crop for Colorado farmers. |
| Publications | |
| 1993 |
Stump, W.L. and P. Westra. 1993. Comparative Growth Analysis of Three Winter Annual Grasses. WSSA Abstracts. 33:46. Stump, W.L. and P. Westra. 1993. Population Dynamics of Three Winter Annual Grasses under Various Cropping Systems. Proc. WSWS 46:8. Westra, P. 1993. Jointed Goatgrass Research and Extension Activities in Colorado. In 1993 National Jointed Goatgrass Symposium Proceedings. pp. 37- 42. |
| 1994 |
Westra, P., W. Stump, and V. VanGessel. 1995. Comparative Growth Analysis of Winter Wheat (TRITICUM AESTIVUM), Jointed Goatgrass (AEGILOPS CYLINDRICA), Downy Brome (BROMUS TECTORUM) and Volunteer Rye (SECALE CEREAL). WSSA Abstracts. 35:168 |
| 1995 |
CALLAN, Mary. Ph.D. Dissertation. 1996. In Vitro Selection for Sethoxydim Tolerant Wheat Cultivars KEBEDE, Z., P. Westra, and K. G. Beck. 1994. Jointed goatgrass competition in a tall and a short winter wheat variety. WSWS Proceedings 47:68 KEBEDE, Zewdu. Ph.D. Dissertation. 1996. Jointed Goatgrass Competition and Growth in Winter Wheat STUMP, William. Ph.D. Dissertation. 1996. Integrated Management of Winter Annual Grasses in Winter Wheat Westra, P. 1993. Jointed goatgrass research and extension activities in Colorado. IN: Jointed Goatgrass: A Threat to U.S. Winter Wheat, P. Westra and R. Anderson, editors, 75 pp. Available at CSU Weed Lab, Fort Collins, CO 80523. -- |
| 1996 |
Berti, A., C. Dunan, M. Sattin, G. Zanin, and P. Westra. 1996. A new approach to determine when to control weeds. Weed Sci. 44:496-503 Callan, Mary. 1996. PhD Thesis. In vitro selection for and biochemical analysis of sethoxydim-tolerant winter wheat (Triticum aestivum L.) 161 p Dunan, C. M., L. J. Wiles, R. L. Anderson, and P. Westra. 1996. A new approach to modeling weed population dynamics in crop rotations. WSSA Abstracts 36:82 |
| 1997 |
Jasieniuk, M, B. D. Maxwell, R. L. Anderson, B. M. Jenks, D. J. Lyon, S. D. Miller, D. W. Morishita, A. G. Ogg, S. Seefeldt, P. W. Stahlman, and P. Westra. 1997, Site-to-site and year-to-year variation in the demographic parameters of jointed goatgrass (Aegilops cylindrica) in winter wheat. WSSA Abstracts 37:84 Jasieniuk, M., B.D. Maxwell, R.L. Anderson, B.M. Jenks, D.J. Lyon, S.D. Miller, D.W. Morishita , A.G. Ogg, S. Seefeldt, P.W. Stahlman, P. Westra, and G. Wicks. 1997. Sensitivity testing of models predicting winter wheat yield loss as a function of jointed goatgrass and winter wheat density. Proc. WSWS 50:79 Kebede, Zewdu. 1997. Jointed Goatgrass Aegilops cylindrica Interactions with Winter Wheat Triticum aestivum. Ph.D. Thesis. Colorado State University, Ft. Collins. 176 p. Miller, P.A., P. Westra, and S.J. Nissen. 1997 Foliar absorption of MON 37500 in two brome species. Proc. WSWS 50:85. Miller, P. A., P. Westra, and S. J. Nissen. 1997. Rotational crop response to MON 37500, metsulfuron, prosulfuron, triasulfuron and tribenuron plus thifensulfuron. Proc. WSWS 50:60 Pester, T. A., P. Westra, T. D'Amato, and K. A. Howatt. 1997. Jointed goatgrass competition in winter wheat. Proc. WSWS 50:82. Stump, William. 1997. The Ecology and Biology of Volunteer Rye Secale cereale, Jointed Goatgrass Aegilops cylindrica, and Downy Brome Bromus tectorum. Ph.D. Thesis. Colorado State University, Ft. Collins. 98 p. Westra, P., Z. Kebede, and G. Beck. 1997. Competition and growth analysis of jointed goatgrass growing with a tall and short winter wheat variety. Proc. WSWS 50:84 |
| 1998 |
Pester, T. A., P. Westra, T. D'Amato, K. Howatt, R. L. Anderson, P. W. Stahlman, G. Wicks, D. J. Lyon, and S. D. Miller. 1998. Analysis of volunteer rye economic thresholds in winter wheat . Proc. WSWS 51:110 |
| 1999 |
Jasieniuk, M., B. D. Maxwell, R. L. Amderson, J. O. Evans, D. J. Lyon, S. D. Miller, D. W. Morishita, A. G. Ogg, S. Seefeldt, P. W. Stahlman, P. Westra, and G. A. Wicks. 1999. Fit of two crop yield functions to data from winter wheat-jointed goatgrass (Aegilops cylindrica) interference experiments. Proceedings WSWS 52:36-37 Jasieniuk, M., B. D. Maxwell, R. L. Amderson, J. O. Evans, D. J. Lyon, S. D. Miller, D. W. Morishita, A. G. Ogg, S. Seefeldt, P. W. Stahlman, F. E. Northam, P. Westra, Z. Kebede, and G. A. Wicks. 1999. Site-to-site and year-to-year variation in Triticum aestivum-Aegilops cylindrica interference relationships. Weed Science 47:529-538 Pester, T. A., P. Westra, R. L. Anderson, P. W. Stahlman, G. A. Wicks, D. J. Lyon, and S. D. Miller. 1999. Integrated Management Systems for Jointed Goatgrass in the Central Great Plains. Proceedings WSWS 52:159-164 Philip Westra. 1999. Effects Of Individual Cultural Practices on Jointed Goatgrass Management. Proceedings WSWS 52:151-152 |
| 2000 |
Pester, T. A., P. Westra, R. L. Anderson, D. J. Lyon, S. D. Miller, P. W. Stahlman, F. E. Northam, and G. A. Wicks. 2000. Secale cereale interference and economic thresholds in winter Triticum aestivum. Weed Scienc 48:720-727. Pester, Todd. 2000. Winter annual grass weed management in winter wheat. Ph.D. Thesis, Colorado State University. 107 pp |
| 2001 |
Belles, D. S., P. Westra, S. J. Nissen, and V. Carrithers. 2001. Control of five kochia accessions at three growth stages with fluroxypyr and dicamba. Proceedings WSWS 54:17 Fandrich, L., S. K. McDonald, S. J. Nissen, and P. Westra. 2001. BAY MKH 6561 dose response, application timing, and moisture stress effects on weeds and winter wheat. Proceedings WSWS 54:15 Ogg, P. J., G. Foster, D. Lyon, S. D. Miller, and P. Westra. 2001. Imazamox efficacy on different grass species in clearfield winter wheat in the central great plains. Proceedings WSWS 54:73 |
| 2002 |
Miller, J.N., P. Westra, and S. Nissen. 2002. Monitoring and assessing the stability of weed population dynamics in crop rotations based on roundup ready technology. Proceedings WSWS 55:12. O'Meara, S. and P. Westra. 2002. Production of geo-referenced weed density maps in irrigated corn for precision weed control. Proceedings WSWS 55:27. Sterling, R. D., S.J. Nissen, P. Westra, G. Foster, and P. Ogg. 2002. Differential response of jointed goatgrass and feral rye to imazamox. Proceedings WSWS 55:9. Westra, P., J. Daniel, and S. Parrish. 2002. Field studies with glyphosate formulations for weed control in diverse cropping systems. 2002. Proceedings WSWS 55:69. Wyse-Pester, D.Y., L. J. Wiles, and P. Westra. 2002. Infestation and spatial dependence of weed seedling and mature weed populations in corn. Weed Science 50:54-63. |
| 2003 |
Belles, D. S., S. Nissen, and P. Westra. 2003. Ethylene production as an indicator of auxinic herbicide tolerance in Kochia scoparia. Proceedings WSWS 56:96 Haley, S. D., M.D. Lazar, J. S. Quick, J. J. Johnson, G. L. Peterson, J. A. Stromberger, S. R. Clayshulte, B. L. Clifford, T. A. Pester, S. J. Nissen, P. H. Westra, F. B. Peairs, and J. B. Rudolph. 2003. Above winter wheat. Can. J. Plant Sci. 83:107-108. Lazar, M. D., S. D. Haley, J. S. Quick, J. J. Johnson, G. L. Peterson, J. A. Stromberger, S. R . Clayshulte, B. L. Clifford, T. A. Pester, S. J. Nissen, P. H. Westra, F. B. Peairs, and J. B . Rudolph. 2003. AP502 CL winter wheat. Can. J. Plant Sci. 83:109-110. Pester, T. A., S. M. Ward, P Westra and S. J. Nissen. 2003. Genetic diversity of jointed goatgrass (Aegilops cylindrica) determined with RAPD and AFLP markers. Weed Sci. 51:287-293. |
| 2004 |
2004 Colorado Wheat Handbook. 2004. Weed Management Guide "Featuring Clearfield Wheat" Colorado Association of Wheat Producers. 155 pages. Belles, D., Nissen,S., Westra,P. and Ward,S. M. 2004. The genetics of dicamba resistant/tolerant kochia. Proceedings WSWS 57:82 Belles, David S. 2004. The genetics and physiology of a dicamba resistance trait in kochia (Kochia scoparia L. Schrad.) Colorado State University PhD Thesis. 144 pages Helm, A., Westra,P. and Henry,B. 2004. The biology and water use of key summer annual weeds in Colorado crops. Proceedings WSWS 57:33 Helm, A., Westra,P. and Sterling,R. 2004. Fitting imazamox (Clearfield*) winter wheat into diverse great plains cropping systems. Proceedings WSWS 57:75 Westra, P., Cramer,G. C. and Iverson,R. D. 2004. Carfentrazone-ethyl applied alone and in tank mixes for TVM control of kochia and other weeds. Proceedings WSWS 57:67 Westra, P., Nissen,S. and Shaner,D. 2004. Clearfield winter wheat facilitates control of winter annual grasses. WSSA Abstracts 43:2. Westra, P., Nissen,S., Byrne Jr.,P. R. and Shaner,D. 2004. Tracking gene flow from Above imazamox tolerant (Clearfield*) wheat to conventional wheats and goatgrass. Proceedings WSWS 57:86 |
| 2005 |
Belles, D., Westra, and B. Hanson. 2005. Managing imazamox resistant wheat in crop rotations for jointed goatgrass control. Proceedings WSWS 58:22. Belles, D.S. 2004. The genetics and physiology of a dicamba resistance trait in kochia (Kochia scoparia L. Schrad.) PhD Thesis. Colo. State Univ., Dept of BSPM, Fort Collins, CO. 144 pages. Gaines, T., Byrne, P., Westra, P., and Nissen, S.J. 2005. Estimation of landscape level gene flow in wheat and jointed goatgrass. Proceedings WSWS 58:15. Hanson, B. D., D. L. Shaner, P. Westra, S. J. Nissen, and D. S. Belles. 2005. Do environmental stresses affect Clearfield wheat response to imazamox? Proc. West. Soc. Weed Sci. 58:29. Sterling, Reginald. 2005. Examining the effectiveness of imazamox using laboratory and field studies in winter wheat (Triticum aestivum L.) and annual grasses. MS Thesis. Colo. State Univ ., Dept of BSPM, Fort Collins, CO. 90 pages. Westra, P., Hanson, B.D., Belles, D.S., and Gaines, T. 2005. Jointed goatgrass by winter wheat hybrid dynamics in Colorado wheat fields. Proceedings WSWS 58:22. |
| 2006 |
Gaines, T. 2006. Estimating landscape level gene flow in wheat and jointed goatgrass. MS Thesis. 116 pp. Dept. of Bioagricultural Scienes and Pest Management. Colorado State University. Hanson, B. D., D. L. Shaner, P. Westra, S. J. Nissen. 2006. Response of Selected Hard Red Wheat Lines to Imazamox as Affected by Number and Location of Resistance Genes, Parental Background, and Growth Habit. Crop Sci. 46: 1206-1211. |