Progress 01/01/01 to 12/31/05
Outputs
In the final year, ALS-resistant giant foxtail was confirmed in Lancaster County, PA. Results of a greenhouse assay showed that the foxtail population was resistant to two sulfonylurea herbicides and cross resistant to an imidazoline. A third population of ALS resistant redroot pigweed was identified through a similar assay. The pigweed proved resistant to four ALS herbicides from three herbicide families. The biotype was also resistant to atrazine. Glyphosate resistance in horseweed was confirmed in 2005 at two different Pennsylvania locations through greenhouse assays. Two farms in Lehigh County were selected for a survey. In the survey, all soybean fields on the farms were examined for horseweed and weed seeds were collected. In addition, surrounding farms were surveyed and seeds were collected when available. The intent is to confirm presence or absence of glyphosate resistance in these fields and resurvey these same areas in the future to help assess the rate of
spread. A number of experiments evaluated resistant weeds in corn and soybean. An experiment focused on shattercane at the Landisville farm. The results showed that none of the soil applied treatments provided greater than 85% control, but most postemergence products provided good control. The population was not ALS-resistant. A number of experiments evaluated control of triazine-resistant common lambsquarters and other weeds in the field. Reduced rate mesotrione and isoxaflutole were tested for control of common lambsquarters and velvetleaf in the field and greenhouse. Both the field and greenhouse studies showed that these two products are extremely effective for control of velvetleaf and common lambsquarters. In the field, isoxaflutole provided at least 85% control of lambsquarters and common ragweed at 0.5X the full rate. Mesotrione applied PRE at 0.125X provided greater than 90% control of common lambsquarters and velvetleaf, but did not control common ragweed even at the full
rate. Mesotrione POST provided excellent control of lambsquarters at 0.25X the full rate. In the greenhouse, either herbicide applied PRE provided greater than 90% control of lambsquarters at 0.5X. Five years after initiation of a weed shift experiment, five weed species continued to be dominant in both corn and soybean; yellow foxtail is in decline in all treatments, except the soybean ALS-based treatment and the untreated check. Yellow foxtail has increased in the ALS-based treatment in the C-S-C rotation. Yellow nutsedge increased at first, but then declined in all treatments in years two and three. Volunteer glyphosate-resistant corn is an increasing problem in all soybean treatments except the ALS-based program. In addition, some other weeds were also noted over the last four years, including wild buckwheat and black medic. Finally, lambsquarters declined especially in the untreated check, while common ragweed increased. This change was also observed in the single glyphosate
treatment in the S-C-S rotation and in the ALS-based treatment in the C-S-C rotation.
Impacts
Three species with ALS-resistance have been documented in Pennsylvania. Multiple resistance to the trains has been identified in pigweed. This is alarming and will impact the ability to manage this weed with current technology. Although ALS-resistant shattercane was not identified in our study, the results confirmed that very few non-ALS herbicides effectively control shattercane in corn. The use of glyphosate-resistant corn and glyphosate will be the primary program available to corn growers with this problem. Glyphosate-resistant horseweed was documented in Pennsylvania. We estimate that between 500 and 1000 acres are currently infested with the resistant biotype. Developing strategies for managing ALS and glyphosate resistance are critical. Triazine resistance continues to be the most prevalent type of herbicide resistance in Pennsylvania. Our work showed that there are a number of effective nontriazine herbicides for control of triazine resistant lambsquarters in
corn. The potential to use reduced rates of several herbicides exists. Growers could reduce the cost of managing these weeds by adopting a reduced rate program. Our weed shift experiment showed that under conventional tillage and full herbicide rates in a corn-soybean rotation, after five years of glyphosate or ALS-based herbicides, only minor weed shifts occur. The weed seedbank and selected management will determine the trajectory of future weed problems. The need to monitor weed species shifts is critical for the continued availability of effective herbicides.
Publications
- Dillehay, B., Curran, W., Hall, M., and Mortensen, D. 2005. Glyphosate-resistant alfalfa (Medicago sativa) research in Pennsylvania. Proc. NEWSS 59:3.
- Dutt, T., Curran, W., and Dillehay, B. 2005. Controlling glyphosate - resistant alfalfa. Proc. NEWSS 59:5.
- Dillehay, B., Curran, W. S., Hall, M. H., and Mortensen, D. A. 2005. Glyphosate - resistant alfalfa research in Pennsylvania: First year observations. Abstract. WSSA 45:16.
- Dauer, J. T., Mortensen, D. A., and Humston, R. 2005. The role of wind dispersal in spreading a glyphosate-resistant weed. Proc. 90th Annual ESA meeting, Montreal, Canada. p142.
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Progress 01/01/04 to 12/31/04
Outputs
In the fourth year of this project, a number of experiments evaluated resistant and potentially resistant weeds in corn and soybean. The potential for glyphosate tolerant common lambsquarters was examined in corn. Glyphosate tolerant common lambsquarters has been reported by some researchers in the Northeast. In this study, glyphosate alone and in combination with other active ingredients was tested for the control of lambsquarters greater than 12 inches tall under challenging conditions. The results showed, that although the speed of control varied with treatments, all glyphosate treatments alone and in combination controlled the weed and there was no indication of increased glyphosate tolerance. A second experiment focused on ALS-resistant shattercane, another increasingly common weed in Pennsylvania. A number of ALS and non-ALS herbicides were tested in the field for control of shattercane in corn. The results showed that none of the soil applied treatments
provided greater than 85% control, but most postemergence products provided good control of the shattercane revealing that the population was not ALS-resistant. Glyphosate was also an effective treatment. A final field experiment examined the control of volunteer glyphosate resistant corn in soybean. Several successful treatments including clethodim and quizalofop were tested and successful rates and adjuvants were identified.
Impacts
This work showed that glyphosate is still an effective herbicide for control of common lambsquarters in glyphosate resistant crops. Poor control with glyphosate may be application error related rather than related to tolerance or resistance. However, growers should closely monitor their fields for changes in herbicide susceptibility and make appropriate changes in management when necessary. Although ALS-resistant shattercane was not identified in our study, the results confirmed that very few non-ALS herbicides and no soil applied herbicides effectively control shattercane in corn. If the ALS herbicides become obsolete for control of this weed, the use of glyphosate-resistant corn and glyphosate will be the primary program available to corn growers plagued by this weed.
Publications
- Curran, W.S., Lingenfelter, D.D., and Muse, C.B. 2004. Herbicide Field Trials Final Report Vol. 14. The Dept. Crop and Soil Sciences, Penn State University, University Park. http://weeds.cas.psu.edu/research.html#report.
- Lingenfelter, D.D. and Curran, W. S. 2004. Battle of the Bleachers II: How Low Can You Go? Proc. NEWSS 58:9.
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Progress 01/01/03 to 12/31/03
Outputs
In the third year of this project, a number of experiments evaluated control of triazine-resistant common lambsquarters and other weeds in the field. Reduced rate mesotrione and isoxaflutole treatments were tested for control of common lambsquarters and velvetleaf in the field. A greenhouse experiment further examined these two herbicides for common lambsquarters control. Both the field and greenhouse experiments showed that these two herbicides are extremely effective for control of velvetleaf and common lambsquarters. In the field, isoxaflutole PRE provided at least 85% control of common lambsquarters and common ragweed at 0.5X the full rate. Mesotrione applied PRE at 0.125X provided greater than 90% control of common lambsquarters and velvetleaf, but did not control common ragweed even at the full rate. Mesotrione POST provided excellent control of common lambsquarters at 0.25X the full rate. In the greenhouse, either herbicide applied PRE provided greater than 90%
control of common lambsquarters at 0.5X. Preliminary results showed that mesotrione POST provided about 70% control at 0.063X the full rate. Regression analysis determined that the PRE rate necessary to provide 90% control of common lambsquarters (I-90) was 0.026 and 0.0625 lb ai/acre for isoxaflutole and mesotrione, respectively. The I-90 for mesotrione POST was 0.025 lb/acre.
Impacts
This work showed that there are a number of effective herbicides to control triazine-resistant common lambsquarters in corn. The potential to use reduced rates of isoxaflutole or mesotrione for control of common lambsquarters and velvetleaf in corn exists. Growers could reduce the cost of managing these weeds by adopting a reduced rate program. However, growers also should consider what other weeds such as common ragweed are present in the field and how they will be managed.
Publications
- Curran, W.S., Lingenfelter, D.D. and Muse, C.B. 2003. Herbicide Field Trials Final Report Vol. 13. The Dept. Crop and Soil Sciences, Penn State University, University Park. http://www.weeds.psu.edu/research.html#report
- Lingenfelter, D.D., Curran, W.S., VanGessel, M.J., and Majek, B.A. 2003. Comparison of a nicosulfuron-based and glyphosate-based program for post weed control in corn. Proc. NEWSS 57:10.
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Progress 01/01/02 to 12/31/02
Outputs
In the second year of this project, the fifth and final year of a weed shift experiment was conducted. This project examined the effect of glyphosate and ALS-type herbicide programs on weed species dynamics. Five years after initiation, five weed species continue to be dominant in both corn and soybean with few exceptions; yellow foxtail is in decline in all treatments, except the soybean ALS-based treatment and the untreated check. Yellow foxtail has increased in the ALS-based treatment in the C-S-C rotation. Yellow nutsedge increased in 1999, but then declined in all treatments. Volunteer glyphosate-resistant corn is an increasing problem in all soybean treatments except the ALS-based program, which includes quizalofop in soybean. Volunteer glyphosate-resistant soybean increased starting in 2000, but only in the two glyphosate-based treatments. In addition, some other weeds were also noted at low frequency over the last five years, including wild buckwheat and black
medic. A number of other experiments evaluated control of triazine-resistant common lambsquarters and other weeds in the field. Mesotrione, a new herbicide from Syngenta was very effective on common lambsquarters and velvetleaf, but less effective on common ragweed. In a greenhouse experiment, ALS-resistant shattercane was confirmed for the first time in Pennsylvania. The shattercane came from a field in South Central Pennsylvania and proved to be resistant to two different families of ALS inhibiting herbicides. Only glyphosate provided effective control of the shattercane in the greenhouse experiment. Another population from a different farm is currently being tested.
Impacts
In summary, after five years of glyphosate or ALS-based herbicides in corn-soybean or soybean-corn rotation, only minor weed shifts have occurred. The weed seedbank and annual weed management tactics will determine the trajectory of present and future weed problems. If problem weed species exist, monitoring and altering management tactics will be important to preclude the development of future weed problems. As an example, another ALS resistant weed was confirmed in PA, bringing the total to two species. ALS-resistant shattercane evolved in a continuous corn production system that relied on frequent use of ALS herbicides. The need to monitor weed species shifts and changes in herbicide susceptibility are critical for the continued availability of effective herbicides.
Publications
- Handwerk, K., Curran, W. S., and Lingenfelter, D. D. 2002. Influence of glyphosate and ALS-type herbicides on weed population dynamics in corn-soybean rotation. Proc. NEWSS 56:98.
- Curran, W. S., Handwerk, K. and Lingenfelter, D. D. 2002. Temporal weed dynamics as influenced by corn and soybean herbicides. Abstr. WSSA 42:6.
- Curran, W. S., Lingenfelter, D. D., Yocum, J. O. and Muse, C. B. 2002. Herbicide Field Trials Final Report. The Dept. of Crop and Soil Sciences, Penn State University, University Park, PA. Vol 12; 261 pgs.
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Progress 01/01/01 to 12/31/01
Outputs
In the first year of this project, the fourth year of a weed shift experiment was conducted. This project examined the effect of glyphosate and ALS-type herbicide programs on weed species dynamics. Four years after initiation, five weed species continue to be dominant in both corn and soybean with few exceptions; yellow foxtail is in decline in all treatments, except the soybean ALS-based treatment and the untreated check. Yellow foxtail has increased in the ALS-based treatment in the C-S-C rotation. Yellow nutsedge increased in 1999, but then declined in all treatments in 2000 and 2001. Volunteer glyphosate-resistant corn is an increasing problem in all soybean treatments except the ALS-based program, which includes quizalofop in soybean. Volunteer glyphosate-resistant soybean increased starting in 2000, but only in the two glyphosate-based treatments. In addition, some other weeds were also noted at low frequency over the last four years, including wild buckwheat
and black medic. Finally, common lambsquarters declined especially in the untreated check in 2001, while common ragweed increased. This change was also observed in the single glyphosate treatment in the S-C-S rotation and in the ALS-based treatment in the C-S-C rotation. Other experiments in 2001 examined common ragweed and triazine-resistant (TR) common lambsquarters control in corn. This year's field experiment with ragweed suggests that environmental factors rather than herbicide resistance may be responsible for the poor performance with atrazine observed in some growers fields. Several new herbicides effectively managed TR common lambsquarters including mesotrione and isoxaflutole at low or reduced rates.
Impacts
In summary, after four years of glyphosate or ALS-based herbicides in corn-soybean or soybean-corn rotation, only minor weed shifts have occurred. The weed seedbank and annual weed management tactics will determine the trajectory of present and future weed problems. If problem weed species exist, monitoring and altering management tactics will be important to preclude the development of future weed problems.
Publications
- Bravo, M.A. and Curran, W.S. 2001. A survey of triazine-resistant common lambsquarters on Pennsylvania farms. Proc. NEWSS 55:18
- Lingenfelter, D.D. and Curran, W.S. 2001. ALS-resistant pigweed in Pennsylvania - is it finally here? Proc. NEWSS 55:20.
- Messersmith, D.T., Curran, W.S., Lingenfelter, D.D. and Stout, R.C. 2001. Triazine-resistant common ragweed: fact or fiction in Pennsylvania? Proc. NEWSS 55:21.
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