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Biology and Ecology of Palmer Amaranth (Amaranthus Palmeri) Prashant Jha Clemson University, [email protected]

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Biology and Ecology of Palmer Amaranth (Amaranthus Palmeri) Prashant Jha Clemson University, Jpacific10@Gmail.Com Clemson University TigerPrints All Dissertations Dissertations 12-2008 Biology and Ecology of Palmer Amaranth (Amaranthus palmeri) Prashant Jha Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/all_dissertations Part of the Agronomy and Crop Sciences Commons Recommended Citation Jha, Prashant, "Biology and Ecology of Palmer Amaranth (Amaranthus palmeri)" (2008). All Dissertations. 296. https://tigerprints.clemson.edu/all_dissertations/296 This Dissertation is brought to you for free and open access by the Dissertations at TigerPrints. It has been accepted for inclusion in All Dissertations by an authorized administrator of TigerPrints. For more information, please contact [email protected]. BIOLOGY AND ECOLOGY OF PALMER AMARANTH (AMARANTHUS PALMERI) A Dissertation Presented to the Graduate School of Clemson University In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Plant and Environmental Sciences by Prashant Jha December 2008 Accepted by: Dr. Melissa B. Riley, Committee Chair Dr. Jason K. Norsworthy Dr. Krishna N. Reddy Dr. Douglas G. Bielenberg Dr. Nyal D. Camper ABSTRACT Palmer amaranth (Amaranthus palmeri S. Wats.) is a troublesome weed of crops in southeastern United States. This research highlights studies on the biology and ecology of Palmer amaranth. Following dispersal in fall, Palmer amaranth seeds require high mean temperatures of 25 to 40 C for germination, which is not likely to occur in South Carolina until the following spring. With dormancy reduction over winter, seeds can germinate at high temperatures ($25 C) and thermal amplitudes of 15 C during late spring (May) in the presence of light. A majority (>90%) of the non-dormant population in the soil seedbank emerge from early May through mid-July, with two to three peak emergence periods which often follow rainfall events. No difference in emergence was observed between no-tillage and shallow spring tillage situations. Early canopy closure in drill-seeded soybean (18-cm row width) had a suppressive effect on the emergence of Palmer amaranth cohorts following early July. This is attributed to the decrease in photosynthetic active radiation (PAR) and red:far-red (R:FR) ratio experienced by seeds lying on the soil surface beneath the canopy in no-tillage systems. Seed germination during fall (August to November) is phytochrome-regulated, with germination stimulation by R light and inhibition by FR light. Burial of seeds to a 10-cm depth for 3 to 6 months induced dormancy with a R or natural light requirement for germination. Palmer amaranth seeds developing under shade conditions (87% reduction in PAR) showed increased dormancy, a survival mechanism in low-light environment. In ii addition, seeds maturing in the bottom-third of a mother plant exhibited increased dormancy, partially explaining variability in timing and extent of germination within a single seed population. Besides exhibiting increased seed dormancy, Palmer amaranth showed photosynthetic and morphological acclimation to 87% shading. These characteristics make Palmer amaranth a troublesome weed in crop-production systems. Based on this research, an early-season glyphosate application preferably at the V3 stage of glyphosate-resistant soybean in conjunction with early planting dates (April) with narrow row (18-cm wide) spacing can be a promising strategy to reduce Palmer amaranth interference and seed production and improve soybean yields. iii DEDICATION From the core of my heart, I dedicate all the hard work and sincere efforts it took to complete my Ph.D. to my father Mr. Santosh Kumar Ojha, my mother Mrs. Narayani Ojha, my brother Mr. Sushant Jha, and my beloved wife Mrs. Anjani Jha. My father has been a positive force and motivation behind my successful achievement of this endeavor. I am indebted to my wife, mother, and brother for all their love, affection, sacrifice, and incessant encouragement. I am thankful to the almighty for giving me strength and blessings. iv ACKNOWLEDGMENTS I wish to express my sincere appreciation and regards to my advisory committee for their guidance in successful completion of my Ph.D. program. I like to give my heartfelt thanks to my major advisor, Dr. Melissa Riley, for her countless hours spent on the achievement of my research objectives and writing this dissertation. She is an excellent teacher and one of the best persons I know for teaching analytical techniques used in plant science research. I really appreciate her mentorship and extended support. I started my Ph.D. program in weed science with Dr. Jason Norsworthy. I am grateful to him for providing me the opportunity to gain diversified knowledge and research experience in weed science discipline. Besides teaching the basic and applied principles of weed science, he taught me the skills needed to achieve success in a competitive environment. He is one of the best mentors I know. I can never think of completing my research without his support and guidance and could never thank him enough for his time and efforts in making my dissertation research worth publishing in high quality journals. I want to thank Dr. Douglas Bielenberg for his guidance in successfully completion of a major objective of my research. I also thank Dr. Krishna Reddy and Dr. Dwight Camper for their valuable suggestions in improving this dissertation. I have no words to express my gratitude to my best friend, Mr. Mayank Malik, for his moral support, untiring help, and whole hearted cooperation. The technical assistance of Mr. Rex Blanton, Mrs. Fran Harper, and Mrs. Rachel Rowe will always be appreciated. v TABLE OF CONTENTS Page TITLE PAGE. ........................................................ i ABSTRACT..........................................................ii DEDICATION ....................................................... iv ACKNOWLEDGMENTS ...............................................v LIST OF TABLES ................................................... viii LIST OF FIGURES ....................................................x CHAPTER 1. LITERATURE REVIEW..........................................1 Palmer amaranth ............................................... 1 Weed Seedbank Dynamics and Seedling Emergence . 1 Seed Dormancy and Germination ...................................3 Effect of Maternal Environment .................................4 Effect of Burial Depth .........................................5 Effect of Temperature .........................................7 Effect of Light ...............................................8 Effect of Hormones ...........................................8 Effect of Stratification .........................................9 Effect of Scarification ........................................10 Physiological Effects of Shading on Survival and Growth . 10 Weed Control..................................................11 Effect of Glyphosate Timing ...................................11 Effect of Row Spacing........................................12 Literature Cited ................................................14 2. SOYBEAN CANOPY AND TILLAGE EFFECTS ON EMERGENCE OF PALMER AMARANTH FROM A NATURAL SEEDBANK . 21 Abstract ......................................................21 Introduction ...................................................22 Materials and Methods...........................................24 Results and Discussion ..........................................27 vi Literature Cited ................................................34 3. TEMPERATURE AND LIGHT REQUIREMENTS FOR PALMER AMARANTH SEED GERMINATION OVER A 12-MONTH PERIOD ............................................48 Abstract ......................................................48 Introduction ...................................................50 Materials and Methods...........................................54 Results and Discussion ..........................................58 Literature Cited ................................................67 4. SEED DORMANCY OF PALMER AMARANTH AFFECTED BY MATERNAL SHADING AND SEED LOCATION ON THE MOTHER PLANT.................................................78 Abstract ......................................................78 Introduction ...................................................80 Materials and Methods...........................................84 Results and Discussion ..........................................89 Literature Cited ................................................98 5. ACCLIMATION OF PALMER AMARANTH TO SHADING . 105 Abstract .....................................................105 Introduction ..................................................106 Materials and Methods..........................................109 Results and Discussion .........................................114 Literature Cited ...............................................121 6. INFLUENCE OF GLYPHOSATE TIMING AND ROW WIDTH ON PALMER AMARANTH AND PUSLEY DEMOGRAPHICS IN GLYPHOSATE-RESISTANT SOYBEAN.............................130 Abstract .....................................................130 Introduction ..................................................132 Materials and Methods..........................................136 Results and Discussion .........................................140 Literature Cited ...............................................155 7. CONCLUSIONS .................................................166 vii LIST OF TABLES Table Page 3.1 Two-way ANOVA for determining the main effects
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