SURFACTANT FORMULATIONS TO ENHANCE TRICLOPYR AMINE EFFICACY: EFFECTS ON ADHESION, RETENTION AND CONTACT PHYTOTOXICITY ON THREE HARDWOOD SPECIES

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1 SURFACTANT FORMULATIONS TO ENHANCE TRICLOPYR AMINE EFFICACY: EFFECTS ON ADHESION, RETENTION AND CONTACT PHYTOTOXICITY ON THREE HARDWOOD SPECIES W. Alison Forster Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements of the degree of MASTER OF SCIENCE IN FORESTRY APPROVED: Shephard M. Zedaker, Chair John R. Seiler Jerzy A. Zabkiewicz 8/22/98 Blacksburg, Virginia Keywords: Adhesion, Retention, Triclopyr, Organosilicone Copyright 1998, W. Alison Forster

2 SURFACTANT FORMULATIONS TO ENHANCE TRICLOPYR AMINE EFFICACY: EFFECTS ON ADHESION, RETENTION AND CONTACT PHYTOTOXICITY ON THREE HARDWOOD SPECIES W. Alison Forster Abstract Loblolly pine (Pinus taeda L) is the leading Southern (USA) pine, in terms of acres planted (Fortson et al.,1996). Since commercial forest acreage is predicted to remain fairly constant over the next 50 years, productivity must be increased if the South is going to meet a larger share of the nation s timber supply needs (Gjerstad and Barber, 1987). Hardwoods have been shown to have a consistent negative growth impact on pines, and uncontrolled hardwoods continue to compete aggressively with pines throughout a rotation, especially when hardwoods remain in the pine canopy. Competing vegetation can be efficiently controlled by herbicides, which need to be formulated either in-can or in-tank to allow them to perform optimally. Adjuvants have proven essential to increasing the efficacy of herbicides, due to their ability to consistently improve the performance of the basic pesticide product. There are, broadly speaking, two routes by which adjuvants can do this. The first is the minimization of off target deposition and second, by the maximization of the herbicidal effect once it is placed on the target ( Reeves, 1989). The major contributors to offtarget deposition and retention are drift, in-flight volatilization, droplet shatter, bounce or runoff, washoff, and removal by wind. These losses result in pesticides never reaching the target or achieving only transitory deposition. There are two basic methods of maximizing the effect of the pesticide once it is on the target. The first is to improve coverage by the spray solution, which can be accomplished by lowering the surface tension of the spray with surfactant materials. The second is by improving the penetration or uptake into the target. Organosilicone surfactants can reduce the surface tension of aqueous pesticides far below that which is possible with nonsilicone surfactants, resulting in efficient wetting of even the most hydrophobic leaf surfaces. Additionally, ii

3 by virtue of their low surface tension, these adjuvants can significantly increase the uptake of active chemicals directly into the plant via stomatal infiltration ( Stevens et al., 1991). Triclopyr ([(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid) has been found to be an effective herbicide for hardwood control. Its two commercial formulations, a triethylamine (TEA) salt (Garlon 3A) and a butoxyethyl ester ( Garlon 4 ), vary considerably in their acceptability. The current ester formulation has two undesirable characteristics. One is that all ester formulations, regardless of chain length, have some volatility which is usually more than that of water-soluble salts. The second is that the current ester formulation utilizes a kerosene solvent which is known to cause rapid foliar necrosis (possibly inhibiting herbicide translocation) and is a suspected carcinogen ( Zedaker et al., 1995). In most applications, the ester formulation has been more efficacious than the amine formulation on both an equal active ingredient basis and on an equal cost basis. Research had demonstrated a potential to enhance the uptake of triclopyr through the use of organosilicones; however, significant problems still existed. It was found that the commercial TEA formulation of triclopyr (Garlon 3A) was "antagonistic" to the organosilicone surfactant Silwet L-77. To take full advantage of the properties of organosilicones, the antagonistic co-formulants of Garlon 3A needed to be removed or replaced, the best surfactant formulation identified, and a cost-effective concentration of the surfactant(s) needed to be found. To do this adequately required that both physico-chemical processes and biological processes be studied. The relevant physico-chemical processes involved in a formulation's effect on spray impaction on the target plant include adhesion, reflection, retention and run-off. The important biological processes include the uptake and translocation of the herbicide into the plant The objectives of this study were: to evaluate the influence of formulation, active ingredient concentration, droplet size and leaf surface (adaxial vs. abaxial) on contact phytotoxicity, adhesion and retention to Acer rubrum, Liquidambar styraciflua and Quercus rubra by triclopyr formulations containing organosilicone surfactants and mixtures of silicone plus conventional surfactants. The adhesion and retention studies also evaluated the influence of leaf angle. Further objectives were to evaluate the influence of formulation and active ingredient concentration on iii

4 spray retention by the adaxial and abaxial leaf surface of the selected species under field and tracksprayer conditions and to determine whether leaf characteristics (wax character and leaf angle ) could explain adhesion / retention. Garlon 4, Garlon 3A and Triclopyr TEA + sequestrant (each at 0.32%, 1.6% and 3.2% ae) plus various concentrations of the surfactants Polyglycol 26-2, Rhodasurf DA-630, Surfadone LP-100, Silwet L-77 and Silwet 408, were tested for contact phytotoxicity, adhesion and retention on the adaxial and abaxial leaf surfaces of sweetgum, red oak and red maple. Little or no contact phytotoxicity was observed with any formulation applied to the adaxial surface within 6 hours; some phytotoxicity was noted within 24 hours. Abaxial surface treatments showed much greater contact phytotoxicity. Contact phytotoxicity was caused by (1) increasing concentrations of stock triclopyr products, and (2) the influence of the organosilicone surfactants. However, these results were very species dependent. Conclusions made from the contact phytotoxicity study were: if the droplet size becomes too big, then efficacy will be reduced; increasing the concentration of active ingredient above a certain limit will not increase efficacy, and may in fact reduce it; the addition of the organosilicone surfactants Silwet L-77 and Silwet 408 delayed and reduced phytotoxicity in red oak ( the most susceptible species to contact phytotoxicity), and to a lesser extent in red maple, but increased the rate in sweetgum. Major influences on adhesion were: droplet size ( increasing droplet size decreased adhesion); adaxial/abaxial leaf surface (abaxial adhesion less than adaxial); product concentration (increasing product concentration increased adhesion); leaf angle (increasing leaf angle decreased adhesion); and addition of surfactants (variable adhesion). All new formulations gave greater adhesion than the commercial formulations, with Triclopyr TEA plus sequestrant plus n-octyl pyrrolidone plus Silwet 408 giving, overall, the greatest adhesion. Increasing product concentration gave greater adhesion. Increasing droplet size and angle of impact reduced adhesion. The adaxial leaf surface showed higher adhesion than the iv

5 abaxial leaf surface. Adhesion was higher on sweetgum, followed by red oak, with red maple being the most difficult species to get formulations to adhere to. Whereas increasing product concentration improves adhesion, the lowest contact phytotoxicity result would be from lowering product concentration. Looking at both sets of results, the best product concentration of those studied would then be 1.6% ae as this can provide high adhesion, while still enabling us to choose a formulation which gives minimal contact phytotoxicity. In the laboratory, formulation had no significant effect on retention. However, there are other considerations which affect retention that need to be kept in mind. It was observed that droplets containing organosilicone could impact an already wetted surface and still adhere or be retained, whereas those droplets not containing any organosilicone surfactant would bounce quite a distance on impact with a pre-wetted surface. Impaction with an already wetted surface was not part of this study, and therefore was not studied quantitatively. Also, formulations containing organosilicone surfactants provide greater wrap-around to the lower surface ( Forster and Zabkiewicz, 1998), which is of great benefit when stomata are only on the abaxial surface, as is the case with these species. Concentration and leaf angle also had no significant effect on retention. Droplet size was significant, with retention decreasing with increasing droplet size. Retention by the adaxial surface was significantly higher than retention by the abaxial surface. There was no significant difference overall between sweetgum and red oak, but retention by red maple was significantly lower. Spray retention by the adaxial and abaxial leaf surfaces of the three tree species was also characterized in a field experiment conducted on a right of way site in North Anna, Virginia, USA. Amine ( Garlon 3A) formulations of triclopyr combined with Silwet 408, and the commercial triclopyr ester formulation, Garlon 4, were applied using a Radiarc sprayer equipped with mm nozzles (approx Œm droplets) applying 140 l/ha. The addition of the organosilicone surfactant Silwet 408 to the amine formulation gave the same total deposition as the commercial ester formulation, Garlon 4, while enhancing the abaxial retention as a percentage v

6 of total deposition. Thus the addition of organosilicone surfactant may have the ability to enhance herbicide uptake via the abaxial leaf surface, and therefore enhance efficacy. Field trial results showed that the alcohol ethoxylate, DA6, is not an essential component of the triclopyr amine / Silwet 408 formulation, in terms of retention. The field trial application was also simulated on sweetgum, using a track-sprayer at the NZ Forest Research Institute Ltd. As in the field trial, the addition of Silwet 408 to triclopyr amine greatly enhanced abaxial retention as a percentage of total deposition, compared to that of Garlon 4. However, the track-sprayer results were very different from the field results, with amounts of adaxial and abaxial retention and total deposition much lower. In agreement with published literature, it was found that the micro-roughness of the leaf surface can be used as a guide to explain adhesion results. The difference among trees in terms of leaf angles appeared to be much less important in explaining retention. vi

7 ACKNOWLEDGEMENTS The author is grateful to Dr. Jerzy Zabkiewicz for the encouragement to do an MS., for making it possible, for his moral support and guidance throughout, for his considerable help with the field trial and for reviewing the Thesis. Thanks go to Dr. Shepard Zedaker for making this MS. possible, for his help with the field trial and for reviewing the Thesis. Appreciation is also extended to Dr. John Seilar for his help with the field trial and for reviewing the Thesis. The author would like to thank her employer, the New Zealand Forest Research Institute, for making this MS possible. Appreciation is also extended to Pat Burch, Meral Jackson, Jason Heinz, Mathew Nespeca and Robert Farrell for their considerable help with the Field trial, and to Dr. Clint Coakley for helping the author through Applied Statistics, and for giving her an enthusiasm for statistics. The author would like to thank the staff of PPC for their support, in particular, thanks go to Kevin Steele for setting up the instrument used to produce the 2000 µm droplets, Rachel Murray for her help with the contact phytotoxicity study, Arthur Vanner for his help with the Track-Sprayer study and Robyn Gaskin for her review of the draft Thesis. The author thanks Mark Kimberley for his advice and help with the statistical analysis. Appreciation goes to Witco Corporation, OrganoSilicones Group, USA and DowElanco, USA for their financial support and for supplying the chemicals used. Funding was also supplied from the New Zealand Public Good Science Fund. Last, but not least, I would like to thank my parents for their encouragement and support. vii

8 ACKNOWLEDGEMENTS TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES CONTENTS Page vii viii xi xiv CHAPTER 1: INTRODUCTION AND JUSTIFICATION 1 CHAPTER 2: LITERATURE REVIEW 5 Forestry in the Southern United States 5 Chemical Weed Control in Conifer Plantations 7 Factors Affecting Herbicide Efficacy 10 Transport to Target 10 Wetting / Adhesion 12 Retention 13 Spreading 13 Drying 14 Organosilicone & Conventional Surfactants used 15 Characteristics of Adhesion and Retention 16 Adhesion-Plant Interactions 17 Spray Retention 18 Application Technologies 19 Microfoil Boom Sprayer 20 Radiarc Sprayer 20 Contact Phytotoxicity 21 Summary 21 CHAPTER 3: HYPOTHESES 23 Contact Phytotoxicity Study 24 Adhesion and Retention Study 25 Spray Retention: Field and Track-Sprayer Conditions 26 Leaf Characteristics 26 CHAPTER 4: METHODS AND MATERIALS 27 Contact Phytotoxicity Study 27 Formulations 27 Plant material 27 Contact phytotoxicity 28 Experimental design and statistical analysis 29 Adhesion & Retention Study 29 Formulations 29 Plant material 29 Adhesion and retention 29 Experimental design and statistical analysis 31 viii

9 Spray Retention under Field & Track-Sprayer Conditions 31 Spray Retention under Field Conditions 31 Formulations 31 Field site and plant material 32 spray retention 32 Experimental design and statistical analysis 33 Spray Retention using a Track-Sprayer 35 Formulations 35 Plant material 35 Spray retention 35 Experimental design and statistical analysis 36 Leaf Characteristics (Wax Character and Leaf Angle) 37 Plant material 37 Scanning electron microscopy (SEM) 37 Leaf angle determinations 37 CHAPTER 5: RESULTS AND DISCUSSION 38 Contact Phytotoxicity Study 38 Statistics 38 Red maple, 0.24 µl 41 Red maple, 4.0 µl 42 Sweetgum, 0.24 µl 46 Sweetgum, 4.0 µl 46 Red oak, 0.24 µl 50 Red oak, 4.0 µl 50 Overall results 54 Adhesion & Retention Study 56 Adhesion 56 Overall comparison of formulations 56 Specific adhesion results 59 Sweetgum 60 Red oak 60 Red maple 60 Main effects 68 Formulation effects 70 Retention 71 Overall comparison of formulations 71 Spray Retention under Field & Track-Sprayer Conditions 74 Spray Retention under Field Conditions 74 Spray retention by the adaxial leaf surface 75 Spray retention by the abaxial leaf surface 76 Abaxial retention as a percentage of total deposition 76 Total and theoretical spray deposition 77 Spray Retention under Track-Sprayer Conditions 79 Spray retention by the adaxial and abaxial leaf surface 79 ix

10 Abaxial retention as a percentage of total deposition & total deposition 79 Leaf Characteristics (Wax Character and Leaf Angle) 83 CHAPTER 6: CONCLUSIONS 86 Contact phytotoxicity 86 Adhesion and retention study 87 Spray retention under field and track-sprayer conditions 89 Leaf characteristics (wax character and leaf angle) 89 LITERATURE CITED 91 APPENDIX A: Contact phytotoxicity results 99 APPENDIX B: Adhesion and retention results 105 VITA 116 x

11 LIST OF TABLES Table 1: Surfactants and products used showing their active ingredient and function 27 Table 2: Concentration (% product) of solutions used for contact phytotoxicity, adhesion and retention studies 28 Table 3: Concentration of solutions used for spray retention study 32 Table 4: Concentration of solutions used for track sprayer study 35 Table 5: ANOVA table for complete phytotoxicity data 39 Table 6: Contact phytotoxicity (mean of observations made at 2, 4, 6, 8 and 24 hours) 41 caused by 4.0 µl droplets of adjuvant alone onto adaxial and abaxial leaf surfaces of red maple, sweetgum and red oak Table 7: Regression analysis of percentage droplet adhesion to the adaxial and abaxial 56 leaf surfaces of sweetgum, red oak and red maple Table 8: Standard errors and LSD comparisons for adhesion obtained from logistic 58 regression model Table 9: Adhesion of droplets ( 650 µm) of triclopyr (at 0.32, 1.6 and 3.2 % a.e.) 61 and alternative formulations onto abaxial and adaxial leaf surfaces of sweetgum Table 10: Adhesion of droplets ( 1000 µm) of triclopyr (at 0.32, 1.6 and 3.2 % a.e.) 62 and alternative formulations onto abaxial and adaxial leaf surfaces of sweetgum Table 11: Adhesion of droplets ( 2000 µm) of triclopyr (at 0.32, 1.6 and 3.2 % a.e.) 63 and alternative formulations onto abaxial and adaxial leaf surfaces of sweetgum Table 12: Adhesion of droplets ( 650 µm) of triclopyr (at 0.32, 1.6 and 3.2 % a.e.) 64 and alternative formulations onto abaxial and adaxial leaf surfaces of red oak Table 13: Adhesion of droplets ( 1000 µm) of triclopyr (at 0.32, 1.6 and 3.2 % a.e.) 65 and alternative formulations onto abaxial and adaxial leaf surfaces of red oak Table 14: Adhesion of droplets ( 650 µm) of triclopyr (at 0.32, 1.6 and 3.2 % a.e.) 66 and alternative formulations onto abaxial and adaxial leaf surfaces of red maple Table 15: Adhesion of droplets ( 1000 µm) of triclopyr (at 0.32, 1.6 and 3.2 % a.e.) 67 and alternative formulations onto abaxial and adaxial leaf surfaces of red maple Table 16: Regression analysis of percentage droplet retention 71 Table 17: Standard errors and LSD comparisons for retention obtained from logistic 72 regression model Table 18: Retention (µl/100 cm 2 ) of triclopyr formulations by the adaxial and abaxial 75 surfaces of sweetgum, red maple and red oak Table 19: Abaxial retention as a percentage of total deposition (µl/100 cm 2 ) of 77 triclopyr formulations by sweetgum, red maple and red oak xi

12 Table 20: Total deposition (µl/100 cm 2, taking the leaf area to be that of one side of 78 the leaf surface only) and % of total theoretical spray deposit available, of triclopyr formulations to three plant species Table 21: Retention (µl/100 cm 2 ) of triclopyr formulations by the adaxial and 80 abaxial surfaces of sweetgum using 650 µm and 1000 µm droplets Table 22: Abaxial retention as a percentage of total deposition, together with total 81 deposition (µl/100 cm 2 ) Table 23: Field and track sprayer spray retention by adaxial and abaxial leaf 82 surfaces using 1000 µm spray droplets Table 24: Percentage abaxial retention as a percentage of total deposition, along with 82 total deposition (µl/100 cm 2 ) for both field and track-sprayer results using 1000 µm spray droplets Table 25: Contact phytotoxicity caused by 0.24 µl of triclopyr product 99 (at 0.32, 1.6 and 3.2 % a.e.) and alternative formulations onto abaxial and adaxial leaf surfaces of red maple Table 26: Contact phytotoxicity caused by 4.0 µl of triclopyr product 100 (at 0.32, 1.6 and 3.2 % a.e.) and alternative formulations onto abaxial and adaxial leaf surfaces of red maple Table 27: Contact phytotoxicity caused by 0.24 µl of triclopyr product 101 (at 0.32, 1.6 and 3.2 % a.e.) and alternative formulations onto abaxial and adaxial leaf surfaces of sweetgum Table 28: Contact phytotoxicity caused by 4.0 µl of triclopyr product 102 (at 0.32, 1.6 and 3.2 % a.e.) and alternative formulations onto abaxial and adaxial leaf surfaces of sweetgum Table 29: Contact phytotoxicity caused by 0.24 µl of triclopyr product 103 (at 0.32, 1.6 and 3.2 % a.e.) and alternative formulations onto abaxial and adaxial leaf surfaces of red oak Table 30: Contact phytotoxicity caused by 4.0 µl of triclopyr product 104 (at 0.32, 1.6 and 3.2 % a.e.) and alternative formulations onto abaxial and adaxial leaf surfaces of red oak Table 31: Adhesion and Retention using 0.72% Garlon Table 32: Adhesion and Retention using 3.59% Garlon Table 33: Adhesion and Retention using 7.18% Garlon Table 34: Adhesion and Retention using 1% Garlon 3A 106 Table 35: Adhesion and Retention using 5% Garlon 3A 106 Table 36: Adhesion and Retention using 10% Garlon 3A 106 Table 37: Adhesion and Retention using 1% Triclopyr TEA + sequestrant 107 Table 38: Adhesion and Retention using 5% Triclopyr TEA + sequestrant 107 Table 39: Adhesion and Retention using 10% Triclopyr TEA + sequestrant 107 Table 40: Adhesion and Retention using 1% Triclopyr TEA + seq % Silwet % n-octyl pyrrolidone Table 41: Adhesion and Retention using 5% Triclopyr TEA + seq % Silwet % n-octyl pyrrolidone Table 42: Adhesion and Retention using 1% Triclopyr TEA + seq % Silwet L % n-octyl pyrrolidone xii

13 Table 43: Adhesion and Retention using 5% Triclopyr TEA + seq % Silwet L % n-octyl pyrrolidone Table 44 : Adhesion and Retention using 1% Triclopyr TEA + seq % Silwet % alcohol ethoxylate Table 45: Adhesion and Retention using 5% Triclopyr TEA + seq % Silwet % alcohol ethoxylate Table 46: Adhesion and Retention using 1% Triclopyr TEA + seq % Silwet L % alcohol ethoxylate Table 47: Adhesion and Retention using 5% Triclopyr TEA + seq % Silwet L % alcohol ethoxylate Table 48: Adhesion and Retention using 1% Triclopyr TEA + seq % Silwet % alkyl phenolic glycol ether Table 49: Adhesion and Retention using 5% Triclopyr TEA + seq % Silwet % alkyl phenolic glycol ether Table 50: Adhesion and Retention using 1% Triclopyr TEA + seq % Silwet L % alkyl phenolic glycol ether Table 51: Adhesion and Retention using 5% Triclopyr TEA + seq % Silwet L % alkyl phenolic glycol ether Table 52: Adhesion and Retention using 1% Triclopyr TEA + seq % Silwet 408 Table 53: Adhesion and Retention using5% Triclopyr TEA + seq % Silwet 408 Table 54: Adhesion and Retention using 1% Triclopyr TEA + seq % Silwet L-77 Table 55: Adhesion and Retention using 5% Triclopyr TEA + seq % Silwet L-77 xiii

14 LIST OF FIGURES Figure 1: The structural and chemical formulae of triclopyr acid (A), Triclopyr 9 butoxyethyl ester (B) and Triclopyr triethylamine salt (C) Figure 2: Factors affecting herbicide efficacy 11 Figure 3: Structures of the organosilicone surfactants Silwet L-77 and Silwet Figure 4: Photos taken at the field site in North Anna, Virginia, USA 34 Figure 5: NZ Forest Research Institute Track-Sprayer 36 Figure 6: Comparison of contact phytotoxicity caused by 0.24 µl droplets of formulations at 3 concentrations to adaxial and abaxial surfaces of red maple Figure 7: Examples of contact phytotoxicity on red maple 44 Figure 8: Comparison of contact phytotoxicity caused by 4.0 µl droplets of formulations at 3 concentrations to adaxial and abaxial surfaces of red maple Figure 9: Comparison of contact phytotoxicity caused by 0.24 µl droplets of formulations at 3 concentrations to adaxial and abaxial surfaces of sweetgum Figure 10: Examples of contact phytotoxicity on sweetgum 48 Figure 11: Comparison of contact phytotoxicity caused by 4.0 µl droplets of formulations at 3 concentrations to adaxial and abaxial surfaces of sweetgum Figure 12: Comparison of contact phytotoxicity caused by 0.24 µl droplets of formulations at 3 concentrations to adaxial and abaxial surfaces of red oak Figure 13: Examples of contact phytotoxicity on red oak 52 Figure 14: Comparison of contact phytotoxicity caused by 4.0 µl droplets of formulations at 3 concentrations to adaxial and abaxial surfaces of red maple Figure 15: Comparison of the adhesion of Garlon 4 (3.59 % product, 1.6 % a.e.) 69 droplets (676, 951 and 1930 µm vmd droplet size) onto sweetgum leaves at 0, 22.5 and 45 degree orientation from horizontal Figure 16: Comparison of the adhesion of Garlon 4 (at 0.72, 3.59, and 7.18 % product) 69 droplets (951µm vmd droplet size) onto red oak leaves at 0, 22.5 and 45 degree orientation from horizontal Figure 17: Comparison of the adhesion of Garlon 4 and Garlon 3A (at 1.6% a.e.) 70 droplets (681 µm vmd droplet size) onto the abaxial surface of red maple leaves at 0, 22.5 and 45 degree orientation from horizontal. F1 series: triclopyr TEA + n-octyl pyrrolidone + Silwet 408 Figure 18: SEM views of the adaxial and abaxial leaf surfaces of red oak (a,b), sweetgum (c,d) and red maple (e,f) 84 xiv