| Title |
Investigators | Department | Objectives | Approach Keywords | Progress Reports | Impact Statements | Publications | |
Project * COL00623 | |
| Title | Integrated Weed Management Strategies in Crop and Non-Crop Systems |
| Investigator(s) | Nissen, SJ; |
| Department | Bioagricultural Sciences and Pest Mgmt. |
| Objectives | This Experiment Station project has three main objectives dealing with integrated weed management in crop and non-crop situations. Objective 1. Cooperate with other CSU researchers to evaluate herbicide resistant weed management strategies, potential gene flow issues, and issues associated with long-term use of glyphosate-tolerant crop technology. The sustainability of current weed management technologies hinges on the ability of public and private sector researchers to identify management strategies that are most and least likely to result in the selection herbicide resistant weed populations, weed species shifts and gene flow between crops and related weed species. Objective 2. Identify and evaluate new weed management technologies in support of major and minor commodity groups. Weed control represents a major expense in the efficient production of most commodities. The expense and government regulations associated with the use of manual labor are a major concern. Many producers feel that the viability of their industry depends on reducing overall costs, specifically substituting chemical and mechanical weed control for hand labor. Objective 3. Develop cooperative projects with local, county and regional groups to address large scale invasive plant removal and restoration efforts. The initial stages of this effort will focus on tamarisk removal from riparian areas. The situation in many Colorado watersheds is more often tamarisk mixed with stands of native cottonwood and willow. Local, county and state agencies are interested in developing management strategies that are more appropriate for smaller upland watersheds where significant native vegetation is still present. The logic of starting with small upland watersheds is two fold. First, these sites are more manageable and second, starting at the top of the watershed decreases the potential for reinvasion. |
| Approach | Objective 1. A large replicated field experiment has been established at the CSU research farm to evaluate the potential impacts of long term, continuous glyphosate use in irrigated crop production. This experiment was established in 1998 and will continue for an additional three to four years. Conventional herbicide programs are being compared to 1) conventional herbicides rotated with glyphosate applications, 2) low rate glyphosate applications and 3) continuous glyphosate in a corn, sugar beet, spring wheat rotation. This project is providing data on the potential for selecting herbicide resistant weeds, shifting weed species composition and changing the weed seed bank. Wheat-to-wheat and wheat-to-jointed goatgrass gene flow is being evaluated using "Above" winter wheat (herbicide resistant wheat developed at CSU) as a model system for small grain crops. The major comparisons will be to establish the distances and success of pollen flow from commercial Above fields to surrounding standard varieties as compared to gene flow measured in small research plots. The herbicide resistance trait makes a convenient marker to identify hybrids. Objective 2. Five new products or new herbicide uses have been introduced for dry bulb onions over the past five years. Much of this success has been due to field studies that identified and evaluated new use patterns. This information was then communicated to industry representatives or brought to the attention of national commodity groups through the IR-4 process. This process will be continued to evaluate new products or uses for other commodities. Objective 3. Integrated management strategies for tamarisk removal are being evaluated at three field sites near Canon City, Colorado. The field experiment includes three large-scale treatments that include aerial herbicide applications , mechanical removal and a control plot. Superimposed on these treatments, will be the biocontrol agent Diorhabda elongata to evaluate the contribution that a foliar feeding biocontrol agent will have on long-term tamarisk control. In addition to monitoring the success of tamarisk removal, we are also comparing active versus passive restoration. |
| Keywords | herbicide resistant weeds, glyphosate tolerant crops, gene flow, minor crops, tamarisk biocontrol, plant restoration |
| Progress Reports | |
| 1996 | In Colorado, dry bulb onions are produced on approximately 18,000 irrigated acres, with an average gross revenue of over $50 million per year. Onion growers would like to reduce their reliance on hand labor for post-emergence weed control. Several herbicides evaluated under weed free conditions appear to have acceptable crop tolerance for pre-emergence and post-emergence weed control. Pendimethalin applied pre-emergence and ethofumesate applied alone as a pre-emergence treatment and applied post-emergence in combination with bromoxynil appear to provide good to excellent weed control with no adverse effects on onion yield. Pendimethalin is currently labeled for post-emergence applications only in onions and ethofumesate is used primarily in sugar beets. Thiazopyr was also evaluated for pre-emergence weed control in onions and appears to have acceptable crop tolerance at rates of 0.25 and 0 .375 lb ai/ac. Data was generated to support a Special Local Need 24C Label for post-emergence use of metolachlor in onions. Metolachlor would be very useful for the yellow nutsedge management in onions. Field survey data indicates that yellow nutsedge is a significant problem in all the onion producing areas of Colorado. |
| 1997 | The voluntary removal of DCPA (Dacthal) from the market will significantly impact weed control options available for onion growers in Colorado. Dacthal was the only broad spectrum pre-emergence herbicide for use in onions and many other vegetable crops. Research efforts have been concentrated on identifying and supporting the registration of pest management products for pre-emergence weed control in onions. Field studies were conducted to evaluate a number of potential compounds for pre-emergence weed control. Ethofumesate has consistently provided good to excellent weed control with acceptable crop safety at rates up to 2 kg/ha. Weed control can be achieved with rates as low as 0.33 kg/ha. Under weed free conditions onion yields were not significantly different from ethofumesate treated plots compared to untreated control or DCPA treatments. Pesticide Clearance Requests were submitted for ethofumsate on dry bulb onions by most onion growing states in the west (this effort was organized by Colorado). Data generated from this project have been used to support the need for ethofumesate as a pre-emergence and post-emergence compound for dry bulb onions. Ethofumesate use in dry bulb onions became a funded IR-4 project for 1998. Yellow nutsedge management has become a major concern for onion growers in Colorado and has been a second focus for research efforts. All major onion growing areas in the state have significant yellow nutsedge problems and 100% yield losses can occur with heavy infestations. Intense competition results in very small bulbs that have no market value. Metolachlor has a tolerance established on dry bulb onions by IR-4. Research was conducted to provide data in support of a Special Local Need Registration 24C. Under normal growing conditions metolachlor treated plots produced yields similar to untreated controls; however, adverse weather conditions can result in some stand reduction and yield loss. Heavy rainfall combined with below normal temperatures result in for injury symptoms. The weed control benefits appear to be much greater than the risk of herbicide injury. |
| 1998 | Field evaluations of candidate herbicides to replace DCPA in onions indicate that ethosumasate and pendimethalin are potential replacement compounds; however, black and hairy nightshade still represent a significant problem in dry bulb onions. Weed control in transgenic sugarbeets suggests that glyphosate and glufosinate are generally superior to standard sugarbeet herbicides. Glyphosate provides better grass control than glufosinate, but effective weed management programs can be build around both compounds. The use of residual herbicides as PPI, PRE or lay-by treatments appears to reduce the number of glyphosate and glufosinate applications required. Eptc losses during chemigation are significant and primarily dependent on air temperature. Metolachlor and dimethenamid are not susceptible to losses during chemigation. |
| 1999 | The effects of weed competition on crop yield and quality impact net income for producers. Crops like potatoes and onions are marketed for quality as much as yield. Field experiments were conducted to evaluate management options that would limit the effects of weed competition on these crops. The loss of DCPA for pre-emergence weed control in onions has significantly limited the producer's ability to economical control the variety of weeds commonly found in most production areas. Pendimethalin has been used for several years for post emergence weed control, but limited information is available on the suitability of pendimethalin as a pre-emergence replacement for DCPA. Six field experiments were conducted to further evaluate the potential for pendimethalin to be used as a pre-emergence herbicide in dry bulb onions. The six locations varied in soil and irrigation type. At all locations, pre-emergence applications of pendimethalin provided weed control superior to DCPA, with yields equal to, are greater than a handweeded check plot. EPTC is a commonly used for weed management in potatoes and is often applied by chemigation in major production areas of Colorado. Chemigation is an efficient method of application; however, continuing research has provided insights into the potential environmental fate of EPTC during and after chemigation. Soil moisture conditions at the time of application have a significant impact on the secondary volatility of EPTC. When EPTC is applied to soil with even moderate soil moisture, significantly amounts of the herbicide can be lost due to secondary volatility. Depending on soil moisture levels, EPTC losses can range from 30 to 60% within one hour of application. Chemigation or broadcast applications of EPTC to a dry soil surface greatly reduces the risk of volatility. |
| 2000 | Weed control in onions continues to be a significant input cost for growers; and with limited options for weed management, hand weeding is still necessary. Research has focused on developing new weed control technologies to replace DCPA for pre-emergence weed control. Early season weed competition can significantly reduce onion yield and quality. Pendimethalin has shown promise as an inexpensive pre-emergence herbicide for onions. Data generated by this research project has established rates and timing of pendimethalin applications that provide good to excellent early season weed control with acceptable crop tolerance. Pendimethalin provides good to excellent kochia control but has limited nightshade activity. Post-emergence nightshade and kochia control has been difficult with current technology. Weed control evaluations and onion variety response to fluroxypyr continue in support of a fluroxypyr IR-4 project. Ethofumesate has been evaluated for several years and is currently moving through IR-4 to establish a tolerance for dry bulb onions. |
| 2001 | Soil applied herbicides represent the mainstay of potato weed management. Yield and quality losses from weed competition force potato growers to aggressively control weeds in order to produce profitable yields. Weeds can also harbor insects that vector potato diseases and reduce harvest efficiency. Research efforts have focused on identifying newer herbicides that will provide different modes of action for control of herbicide resistant weeds and potentially have a lower risk for movement to ground water. Sulfentrazone and flumioxazin are newer herbicides that inhibit an enzyme involved in the early stages of chlorophyll production . These herbicides control a number of weed species important in potato production. Various nightshade species are very susceptible to these herbicides at low rates. Field research suggests that when applied as pre-emergence treatments there is sufficient crop safety for use in potatoes and that most commonly grown varieties are tolerant. Broadleaf weed control has been excellent over a number of years, across environments, soil types and irrigation systems. Data from this research was used to move sulfentrazone and flumioxazin into the IR-4 process. Residue tolerances and subsequent Special Local Need registrations are anticipated in the next several years. This new mode of action will provide potato growers with a valuable tool for the management of herbicide resistant weeds. |
| 2002 | Evaluations of new herbicides for weed control in potatoes have identified two compounds that have selectivity for weed control in potatoes. Sulfentrazone and flumioxazin have activity on weed species important in potato production and provide a new management tool for herbicide resistant weed management. Based on research results from this project that evaluated potato variety and weed response over several years and in Colorado's two potato production regions, a Section 18 label for sulfentrazone was granted in 2002. Because EPA approval was so late only a limited number of acres were treated with sulfentrazone in 2002. Growers were pleased with the results and cost so we anticipate that more acres will be treated in 2003. |
| 2003 | The current recommendation for herbicide resistant weed management is to rotate crops and herbicide modes of action. Until recently potato, dry bean and onion growers did not have many new modes of action to help reduce triazine and ALS resistant weed populations. Based on research results from this project potato, dry bean and onion growers will have new products with modes of action that were not available two or three years ago. Sulfentrazone now has a Section 3 label that includes applications to potatoes and dry beans. Field research results from this project have been used to support these new registrations. This project has also supported the Colorado onion industry by providing data necessary to support a Section 18 label request for fluroxypyr to control volunteer potatoes in dry bulb onions. Volunteer potatoes are not only highly competitive with the onion crop, but can also serve a source of late blight inoculum. |
| 2004 | Herbicide resistant weed management continues to be a significant issue for potato, onion, sugar beet and dry bean producers. Selection pressure is high in crops like corn and wheat where there are many other options for alternative modes of action. Producers that rely on other crops for their incomes must deal with these resistant weeds using a limited number of herbicide modes of action. Until recently potato, dry bean and onion growers did not have new modes of action to help manage triazine and acetolactate synthase (ALS) resistant weed populations. Based on research results from this project potato, dry bean and onion growers will have new products with modes of action that were not available two or three years ago. Sulfentrazone now has a Section 3 label that includes applications to potatoes and dry beans for 2004 field season, while flumioxazon has a Section 3 label for potatoes and onions for the 2005 field season. Field research results from this project have been used to support these new registrations and provide information to develop directions for use. This project has also supported the Colorado onion industry by providing data necessary to support a Section 18 label for fluroxypyr to control volunteer potatoes in dry bulb onions. Volunteer potatoes are not only highly competitive with the onion crop, but can also serve a source of late blight inoculum. This project has also provided data to support a Section 18 label for fomesafen to control ALS resistant common waterhemp, which appears to be moving into eastern Colorado from western Kansas. |
| 2005 | Riparian wetlands in the arid and semiarid west have been seriously degraded by the invasion of tamarisk. In a relatively short period of time this shrubby tree has destroyed native wetlands in Arizona, Southern California, Colorado, New Mexico, Texas and has moved north into Montana. Tamarisk control and restoration of native communities are possible, but this process can be very expensive and can fail to achieve the desired management goal. Research to evaluate integrated control strategies and their impacts on restoration success has been initiated at three locations in Southern Colorado. We found the interception of aerial applied herbicide, imazapyr, was only about 60% resulting in significant amounts of herbicide reaching the soil. This can seriously impact the cost of control and the success of subsequent native community establishment. In addition, the mechanical removal of tamarisk without herbicide treatments resulted in significant tamarisk regrowth (which we did anticipate) and the proliferation of another invasive species, downy brome (Bromus tectorum). The ease with which one invasive plant species replaces another in these disturbed areas is a serious issue that will need to be address in any management plan. Analysis of soil samples for herbicide residue suggests that since the initial application in fall of 2004, the amount of herbicide present in the soil has decreased by almost an order of magnitude. Greenhouse bioassays studies indicate that a number of important native species will still be affected by herbicide residues of this concentration. Of the species tested, alkali sacaton (Sporobolus airoides) appears to be one of the most sensitive, while western wheatgrass (Pascopyrum smithii) is much more tolerant. |
| 2006 | Recreation and irrigation are important uses of Colorado's limited aquatic resources. These uses are threatened by the spread and rapid growth of both native and exotic submersed aquatic plants. The invasive, Eurasian watermilfoil (Myriophyllum specatum), currently infests 33 states including Colorado and negatively impacts recreation and the efficiency of water delivery systems ie., irrigation and drainage canals. In Colorado, Eurasian watermilfoil has spread from a single location in Boulder County to at least 10 other locations mainly along the Front Range. The native, sago pondweed (Potamogeton pectinatus L.) , is a problem weed of rivers, irrigation and drainage canals throughout temperate and subtropical parts of the world. Sago pondweed is a recurring problem in irrigation canals along the Front Range and the eastern plains of Colorado. Once water temperatures reach 60F sago pondweed growth increases rapidly forcing irrigation districts to dredge canals with backhoes in order to maintain water flow. Field and greenhouse research projects were established to evaluate the efficacy of imazamox for Eurasian watermilfoil and sago pondweed control. Imazamox is an imidazolinone herbicide registered for a number of terrestrial uses and currently under investigation as a potential new herbicide for aquatic weed management. Working under an Experimental Use Permit from EPA, we used imazamox to treat three small lakes heavily infested with Eurasian watermilfoil and monitored weed control and imazamox dissipation from mid May to August. The imazamox treatments significantly reduced Eurasian watermilfoil growth, keeping these lakes completely open for the summer. The imazamox concentration in these lakes decreased rapidly after application due to photodegradation. The half-life of imazamox in these aquatic ecosystems was approximate 4 days. Emerged sago pondweed was not susceptible to imazamox; however, imazamox did reduce sago pondweed biomass by 95% when shoots emerged through treated soil. This indicates that imazamox could be used to treat dry irrigation ditches in the fall or spring and provide sago pondweed control the following irrigation season. |
| Impact | |
| 1999 | Pendimethalin appears to have sufficient crop safety for pre-emergence applications to dry bulb onions and would provide an economical alternative to DCPA, with reduced risk of surface or ground water contamination. The environmental responsible use of EPTC requires that factors affecting herbicide performance be understood and communicated to producers. This research has identified a number of key factors that producers can control to improve the efficiency of EPTC use. |
| 2000 | Data generated by this research was used to establish a delayed pre-emergence use for pendimethalin in dry bulb onions. This provided onion growers with an inexpensive way to control important weeds like kochia, lambsquarters and pigweed during stand establishment. This is the most critical period for weed management in onions. |
| 2001 | This research will provide potato growers with more options in the battle to control herbicide resistant weeds. The number of herbicide resistant weeds has increased significantly since 1975 and only one new product for weed control in potatoes has been introduced in the last 15 years. |
| 2002 | The impact of this new pest management technology will be to significanly reduce the cost of broadleaf weed control for growers. Current weed control costs per acre are approximately $30. New technology identified by this project can reduce that cost to $16 per acre. The savings to the Colorado potato industry would be approximately $1.1 million per year. In addition, this new product provides a new herbicide mode of action that is not currently used in potato production, providing a new tool for management of herbicide resistant weeds. |
| 2003 | For potato growers the impact of this new product is not just a new mode of action for weed control but a saving of as much as $14 per acre in weed control costs. This could save the potato industry in Colorado $1.1 million per year. The impacts to the dry bean industry are also significant because this new product should improve late season nightshade control. For onion growers with significant volunteer potato problems conventional control methods resulted in yield losses of 20-40%. Incorporating fluroxypyr in a weed management program could reduce yield losses to as little as 8-10%. |
| 2004 | Sulfentrazone and flumioxazon will not only provide potato growers with a new mode of action for weed control and resistance management, but could potentially save as much as $14 per acre in weed control costs. This could save the potato industry in Colorado $1.1 million per year. The impacts to the dry bean industry are also significant because this new product should improve late season nightshade control and provide a strategy to help control ALS resistant common waterhemp with to separate modes of action. For onion growers with significant volunteer potato problems conventional control methods resulted in a yield loss of 20-40%. Incorporating fluroxypyr in a weed management program could reduce yield losses to as little as 8-10%. Fortunately, there are a limit number of acres where onions are planted after potatoes. |
| 2005 | Land owners and land managers across the west now realize the enormous negative impact that tamarisk is having on riparian ecosystems. The main impact of this research will be to empower land managers and landowners to initiate tamarisk removal and restoration programs that 1) are adapted to infestation densities, 2) preserve and protect as much native flora as possible, and 3) incorporate complementary strategies (biological control, herbicides, fire, shredding, planting native species, etc) to reduce the need for highly disruptive and expensive tactics like root plowing and root raking. This research seeks to develop a database that provides land managers and landowners with information about probable outcomes of integrated pest management (IPM) strategies applied to various infestation types (high, medium and low density tamarisk) with varying levels of remnant native vegetation. |
| 2006 | A safe and cost effective method to control Eurasian watermilfoil will increase the recreational use of affected lakes and ponds, while the ability to control sago pondweed in irrigation canals will increase the efficiency of water delivery for irrigation and augmentation. Imazamox appears to be effective at much lower use rates than products currently labeled for Eurasian watermilfoil control and controlling sago pondweed with pre-emergence fall or spring application could reduce or eliminate the need to use acrolein. Acrolein is a highly toxic compound that was used for chemical warfare in World War I. Very few people are qualified to apply acrolein in the west and acrolein applications are dangerous and costly. |
| Publications | |
| 1999 |
Coggan, D., Brunk, G., and Nissen, S.J. 1999. Effect of soil moisture on EPTC volatility. Proceedings Western Society of Weed Science p. 10 Kazarian, D., Miller, P., Nissen, S.J., and Westra P. 1999. Dry edible bean response to shoot and foliar applications of dimethenamid, BAS656 and metolachlor. Proceedings Western Society of Weed Science p. 23 |
| 2000 |
Coggon, D. and S. J. Nissen. 2000. EPTC incorporation methods: effects of varying time and quantities of water. Proceedings of Western Society of Weed Science 53:59. Kazarian, D., S. J. Nissen, and A. Thompson. 2000. Sulfentrazone and flumioxazin for broadleaf control in potatoes. Proceedings of Western Society of Weed Science 53:76 Nissen, S. J. and M. Bartolo. 2000. Pendimethalin and ethofumesate as DCPA replacements in dry bulb onions. Proceedings of Western Society of Weed Science 53:60 |
| 2002 |
Coggon, D. F., S. J. Nissen, S. D. Miller, and R. G. Wilson. 2002. Flumioxazin as a component of weed management in dry beans. Proceeding Western Society of Weed Science 55:10. Wilson, D. E., S. J. Nissen, and A. Thompson. 2002. Potato variety and weed response to sulfentrazone and flumioxazin. Weed Tech. 16: 567-574. |