RESEARCH INTERESTS:

The objective of my research program is to develop weed control strategies based on a multidisciplinary approach that builds bridges among scientific disciplines, especially between weed/crop ecology and herbicide technology. A single weed control measure is not feasible due to the number of different weed species and their highly variable life cycles. My program, therefore, advocates a combination of weed control methods (the use of many "little hammers").

My interests include, but are not limited to, weed ecology, crop-weed interactions as affected by cropping practices and nutrient management, herbicide technology and systems simulation.

COURSES TAUGHT:

• AGRON 896- Integrated Weed Management

MAJOR PROJECT ACTIVITIES:

Current program activities (Year 2004):
I. Herbicide screening: 22 herbicide trials in corn, soybean and pasture.
II. Soybean and corn variety trials: A total entry of about 120 soybean and 80corn varieties
III. Current research projects:

1. Critical Time for Weed Removal in Soybean as Influenced by Early Season Insect Defoliation. The damage caused by the bean leaf beetle [Cerotoma trifurcata (Forster)], painted lady caterpillar, and the imported longhorned weevil (Calomycterus setarius Roelofs) has been on the increase in recent years. Early season defoliation reduces the plant height which delays the canopy closure and allows weeds to gain an advantage early on in the growth of the soybean. Therefore, insect defoliation could very well have an impact on weed growth and management tactics. This is the second year of the study that will examine the effects of 3 defoliation levels and weed removal on soybean yield. This study is funded by the Soybean Marketing Board. MS student Travis Gustafson.

2. Weed control in riparian buffer area . This is the third year of the study that examines the effects of several cultural, mechanical and chemical control methods on weed control in newly plated grass-type buffer crop. This study is part of larger project in collaboration with Dave Shelton. PhD thesis for Janyce Woodard.

3. Individual weed species competitiveness as influenced by soybean row spacing. This is second year of the study that examines the effects of two soybean row spacing (7.5" vs 30") on individual competitiveness of 12 most common weeds in Nebraska. We are examining 8 broadleaf weeds and 4 grasses. The data collected will be used for testing competitive indices of weed species in the WeedSOFT program. MS thesis for Shawn Hock.

4. Long spine sandbur control in irrigated corn. MS student Katie Wrede

5. Hoary vervain and western ragweed control in marginal rangeland. MS student Jim Schoenberg.

6. Multi-study project on problematic weeds in Roundup-Ready soybeans. To determine: (1) Biologically effective rates of Glyphosate used alone, (2) tank mixes of glyphosate and other POST herbicides and (3) soil applied (PRE) herbicides for problem weeds in soybean. The list of weed species includes: morninglory, bindweed, buckwheat, Pennsylvania smartweed, Venice mallow, sweet clover, velvetleaf, lamb's-quarters, and nightshade. Funded by the Nebraska Soybean Board.

7. Integrated management of Purple loosestrife. Purple loosestrife is a new noxious weed for Nebraska. It has a devastating impact on wetland by out-competing native plants and creating habitat that is not suitable for wildlife. We are testing various control methods including herbicides, repeated disking, repeated mowing, planting replacement species and burning. Herbicide control studies are at 4 locations along the Missouri, Niobrara and Platte rivers.

EXTENSION INTERESTS:

• To keep crop producers up to date with the current weed control issues.
• To respond promptly and accurately to the regional needs and requests related to weed control and crop production.
• To utilize various distance education tools in order to disseminate information to county educators, crop consultants, growers, and the public in general.

SELECTED PUBLICATIONS:

• Evans S. P., S. Z. Knezevic, C. Shapiro and J. L. Lindquist. 2003. Nitrogen level affects critical period for weed control in corn. Weed Sci. 51: 408-417.
  
  
• Evans S. P., S. Z. Knezevic, C. Shapiro and J. L. Lindquist. 2003. Influence of nitrogen level and duration of weed interference on corn growth and development. Weed Sci.51 546-556.
  
  
• Knezevic, Z. S., S. Evans and M. Mainz. 2003. Yield Penalty Due to Delayed Weed Control in Corn and Soybean. Crop Management Journal online: http://www.plantmanagementnetwork.org/pub/cm/research/2003/delay/
  
  
• Knezevic, Z. S., S. Evans and M. Mainz. 2003. Row spacing influences critical time of weed removal in soybean. Weed Tech. 17:666-673.
  
  
• Knezevic, Z. S. and. K. Cassman. 2003. Use of herbicide tolerant crops as a component of an int. weed management. Crop Management. J. online: http://www.plantmanagementnetwork.org/pub/cm/management/2003/htc/
  
  
• Blankenship E. , W. Stroup, Evans S. P., and S. Z. Knezevic. 2003. Statistical Inference for Calibration Points in Nonlinear Mixed Effects Models. Journal of Agricultural, Biological and Environmental Statistics. Accepted
  
  
• Knezevic, Z. S., A. Kantrovich, and B. Masters. 2003. Eastern Red Cedar Control in Pasture. Crop Management Journal. http://www.plantmanagementnetwork.org/pub/cm/management/2003
  
  
• Shrestha, A., S. Z. Knezevic, R. C. Roy, B. Ball-Coelho, and C. J. Swanton. 2002. Effect of tillage, cover crop and crop rotation on the composition of weed flora in a sandy soil. Weed Research 42:76-87.
  
  
• Knezevic Z. S., S. P. Evans, E. Blankenship,R. VanAcker and J. L. Lindquist. 2002. Critical period of weed control: The concept and data analysis. Weed Sci. 50(6)773-786.
  
  
• Elmore, R. W. , F. W. Roeth, L. A. Nelson, C. A. Shapiro, R. N. Klein, S. Z. Knezevic, and A. Martin. 2001. Glyphosate-resistant soybean cultivar yields compared to sister lines. Agron. Journal.93,2:408-412
  
  
• Elmore, R. W., F. W. Roeth, R. N. Klein, S. Z. Knezevic, A. Martin, L. A. Nelson, and C. A. Shapiro. 2001. Glyphosate-resistant soybean cultivar response to glyphosate. Agron. 93, 2:404-407
  
  
• Knezevic, Z. S., M. J. Horak and R. L. Vanderlip. 2001. Relative time of Amaranthus retroflexus affects partitioning of dry matter. Weed Science. 49:617-621.
  
  
• Swanton, C. J., A. Shrestha, R. C. Roy and S. Z. Knezevic, 2000. Vertical seed bank distribution changes with tillage practice in sandy soils. Canadian Journal of Plant Science 80:455-457
  
  
• Hamill, A., S. Z. Knezevic, K. Chandler, P. Sikkema, F. Tardif, and C. J, Swanton. 2000. Weed control in glufosinate tolerant corn (Zea mays L.). Weed Tech. 14: 578-585
  
  
• Knezevic, Z. S., M. J. Horak and R. L. Vanderlip. 1999. Estimates of physiological determinants for redroot pigweed.Weed Sci: 47:291-296.
  
  
• Sikkema, P., S. Z. Knezevic, F. Tardif, A. Hamill, and C. J. Swanton. 1999. Biologically effective dose and selectivity of SAN1269H for weed control in no-till corn (Zea mays L.). Weed Tech. 13:283-289.
  
  
• Swanton, C. J., A. Shrestha, , B. Ball-Coelho, R. C. Roy, and S. Z. Knezevic. 1999. Effect of tillage systems, N, and cover crop on the composition of weed flora. Weed Sci: 47:454-461.
  
  
• Knezevic, Z. S., and M. J. Horak. 1998. Influence of emergence time and density on redroot pigweed. Weed Sci 46:665-672.
  
  
• Knezevic, Z. S., P. H. Sikkema, F. Tardif, A. S. Hamill, K. Chandler, and C. J. Swanton. 1998. Biologically effective dose and selectivity of RPA 201772 (isoxaflutole) for Preemergence Weed Control in Corn. Weed Tech. 12:670-676.
  
  
• Knezevic, Z. S., M. J. Horak and R. L. Vanderlip. 1997. Relative time of redroot pigweed (Amaranthus retroflexusL.) emergence is critical in pigweed - sorghum (Sorghum bicolor L.) competition. Weed Sci. 45: 502 - 508.
  
  
• Knezevic, Z. S., S. F. Weise and C. J. Swanton. 1995. Comparison of empirical models depicting density of maranthus retroflexus L. and relative leaf area as predictors of yield loss in maize (Zea mays L.). Weed Research. 35: 207 - 214.
  
  
• Knezevic, Z. S., S. F. Weise & C. J. Swanton. 1994. Interference of redroot pigweed in corn. Weed Science 42: 568 -573.

BOOK CHAPTER:

• Lindquist L. J. and S. Z. Knezevic. 1999. Quantifying crop yield response to weed population: Applications and Limitations in Biotic Stress and Yield Loss, edited by Robert K. D. Peterson and Leon Hidley . The book will be published by CRC Press with an expected release date January, 2000.