EVALUATION OF HERBICIDES FOR NO-TILL CORN ESTABLISHMENT by Paul Hi 11 Davis Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of MASTER OF WEED SCIENCE in Plant Pathology, Physiology and Weed Science APPROVED: E. S. Hagood, Jr., Chairman D. E. Brann J. F. Derr D. M. Orcutt May, 1986 Blacksburg, Virginia EVALUATION OF HERBICIDES FOR NO-TILL CORN ESTABLISHMENT by Pa u1 Hi 11 Dav i s Committee Chairman: E. Scott Hagood, Jr. Plant Pathology, Physiology and Weed Science (ABSTRACT) Field experiments were conducted in 1984 and 1985 in Fluvanna and Montgomery Counties in Virginia, to evaluate HOE-O661 (glufosinate) [ammoni um-(3-ami no-3-carboxypropyl )-methyl phosphi nate], cyanazi ne ( 2- [[ 4-chl oro-6-( ethyl amino )-s-tri azi n-2-yl ]ami no]-2-methyl propi oni tri le)), glyphosate [N-(phosphonomethyl)glycine] and paraquat (l,1'-dimethyl- 4,4'-bipyridinium ion) for the control of vegetation existing at the time of no-till corn establishment. These herbicides were applied alone or in combination with 2,4-D [(2,4-dichlorophenoxy)acetic acid] or dicamba (3,6-dichloro-2-methoxybenzoic acid) at three timings of appli- cation. Both locations were heavily infested with annual, biennial, and perennial broadleaf weeds, including horseweed (Conyza canadensis), buckhorn plantain (Plantago lanceolata), field bindweed (Convolvulus arvensis), curly dock (Rumex crispus) and wild mustard (Sinapis arvensis). All four non-selective herbicides provided good overall weed control. The addition of 2,4-D or dicamba generally improved the control of broadleaf weeds in all four experiments. Control of horse- weed with paraquat was variable, but improved significantly when dicamba was applied in combination with paraquat. Glyphosate, cyanazine and HOE-O661 alone or in combination with 2,4-D or dicamba provided excel- lent horseweed control. Wild mustard control with glyphosate was dependent on the weed size and growth stage of development. Contra l with paraquat, cyanazine and HOE-0661 was not affected by differences in wild mustard size or growth stage. Glyphosate and HOE-0661 provided acceptable field bindweed control alone, and all herbicides gave excel- lent field bindweed control when applied in combination with 2,4-D or dicamba. Cyanazine and HOE-0661 showed better control of shoot growth on the more difficult-to-control weeds than paraquat and glyphosate when applied alone. With the addition of either 2,4-D or dicamba, cyanazine and HOE-0661 provided better overall weed control, in most cases, than corresponding paraquat and glyphosate combinations. Timing of applica- tion and weed size did not significantly affect herbicide activity, even at later application timings when weeds were well established and exceeded 60 cm in height. ACKNOWLEDGEMENTS I sincerely thank Or. Scott Hagood, my major professor and close friend, for the extra time and consideration he shared with me. A special thanks also to the members of my committee, Ors. Dan Brann, Jeff Derr and David Orcutt. I also extend appreciation to Mr. Claude Kenley for help with field work and his friendship throughout the project. Mrs. Ruth Pennington donated invaluable time and secretari a 1 skills in all phases of the project. The faculty, staff and fellow graduate students of PPWS provided encouragement and assistance with both my courses and research. I would like to thank Mr. Hollis Black and Mr. Roger Black, of Blackgate Farms, for their time and support in allowing me to conduct research on their farm. A very special thanks goes to my parents, Mr. and Mrs. Clifton W. Davis, who have provided endless support and encouragement, not only in this project but in every decision I have ever made. My deepest thanks and appreciation go to my wife, Marian E. Davis, for her patience, encouragement, support and especially for her belief in my ability to complete this project. I also thank my daughter, Trudy Lynn Davis, for being a daily reminder that there is a lot more to life than studying. Finally, I want to thank God for my given talents and the desire to acquire new ones. - iv - TABLE OF CONTENTS Page ABSTRACT ii ACKNOWLEDGEMENTS iv LI ST OF TABLES vi INTRODUCTION 1 LITERATURE REVIEW 4 MATERIALS AND METHODS 13 RESULTS AND DISCUSSION 17 CONCLUSIONS 51 LITERATURE C!TED 52 VITA 60 V LIST OF TABLES Table 1. Timing of application (planting dates) for the four experiments ............................................. 14 Table 2. Rates of application for herbicide treatments .......•... 16 Table 3. Weed species present in 1984 Fluvanna County, Va. experiment as percent of total sample dry weight from check plots and as frequency of occurrence in check plots ........................................................ 18 Table 4. Weed species present in 1984 Montgomery County, Va. experiment as percent of total sample dry weight from check plots and as frequency of occurrence in check plots ........................................................ 19 Table 5. Weed species present in 1985 Fluvanna County, Va. experiment as percent of total sample dry weight from check plots and as frequency of occurrence in check plots ........................................................ 20 Table 6. Weed species present in 1985 Montgomery County, Va. experiment as percent of total sample dry weight from check plots and as frequency of occurrence in check plots ........................................................ 21 Table 7. Effect of herbicide treatment and timing of appli- cation on overall weed control in Fluvanna County, Va., 1984 . 23 Table 8. Total weed dry weight, expressed as the percent of untreated at each timing, as affected by herbicide treatment in Fluvanna County, Va., 1984 ••......•.........•............. 25 Table 9. Effect of herbicide treatments and timing of appli- cation on overall weed control in Montgomery County, Va., 1984 . 26 Table 10. Total weed dry weight, expressed as the percent of untreated at each timing, as affected by herbicide treatment in Montgomery County, Va., 1984 ...•••....•.•..•.....•••...... 28 Table 11. Effect of herbicide treatment and timing of appli- cation on overall weed control in Fluvanna County, Va., 1985 ......................................................... 29 Table 12. Total weed dry weight, expressed as the percent of untreated at each timing, as affected by herbicide treatment in Fluvanna County, Va., 1985 .....••.•.....•••....•........•. 31 vi Table 13. Effect of herbicide treatment and timing of application on overall weed control in Montgomery County, Va. , 1985 . 32 Table 14. Total weed dry weight, expressed as the percent of untreated at each timing, as affected by herbicide treatment in Montgomery County, Va., 1985 ............•................. 34 Table 15. Effect of herbicide treatment and timing of application on horseweed control in Montgomery County, Va., 1984 .................................................... 36 Table 16. Effect of herbicide treatment and timing of application on horseweed control in Montgomery County, Va., 1985 .................................................... 37 Table 17. Effect of herbicide treatment and timing of application on field bindweed control in Fluvanna County, Va., 1984 .................................................... 39 Table 18. Effect of herbicide treatment and timing of application on curly dock control in Montgomery County, Va . , 1984 . • . • • . • . • . • . • . • . • . • . • . • • . 40 Table 19. Effect of herbicide treatment and timing of application on prickly lettuce control in Montgomery County, Va., 1984 .................................................... 41 Table 20. Effect of herbicide treatment and timing of application on wild mustard control in Fluvanna County, Va., 1984 .................................................... 43 Table 21. Effect of herbicide treatment and timing of application on wild mustard control in Fluvanna County, Va. , 1985 . 44 Table 22. Effect of herbicide treatment and timing of application on buckhorn plantain control in Montgomery County, Va., 1984 ............................................ 46 Table 23. Effect of herbicide treatment and timing of application on ragweed control in Fluvanna County, Va . , 19 84 . 48 Table 24. Effect of herbicide treatment and timing of application on ragweed control in Fluvanna County, Va., 1985 .................................................... 50 vii INTRODUCTION No-till corn production has increased steadily over the past ten years as an alternative to conventionally tilled corn (64, 65). The success and benefits associated with no-till corn production have been the primary impetus for its adoption. Since its introduction, no-till corn has produced yields comparable to those achieved with conventional tillage while reducing soil erosion and operating costs (63, 69). Associated with this increase in no-till corn acreage has been the development of annual, biennial, and perennial weed species that have not typically been associated with conventional tillage (52). The success or failure of no-till corn depends upon control of the vegeta- tion existing at planting as well as residual control of weeds during the growing season. In conventional tillage, moldboard plowing provides a means for disrupting and destroying root systems of perennial weed species (52). In addition to the lack of weed suppression via tillage, the development of weed problems in no-till systems are due to the lack of effective control of many species with standard