EFFECT OF SULFENTRAZONE RATE AND APPLICATION METHOD ON WEED CONTROL AND STUNTING IN FLUE-CURED TOBACCO

Transcription

1 EFFECT OF SULFENTRAZONE RATE AND APPLICATION METHOD ON WEED CONTROL AND STUNTING IN FLUE-CURED TOBACCO L. R. Fisher, W. D. Smith, and J. W. Wilcut 1 Research was conducted at five locations in 1998 and three locations in 1999 to evaluate the effects of labeled and below-label rates of sulfentrazone on weed control and phytotoxicity in flue-cured tobacco. s ranged from 0.14 to 0.42 kg ai ha -1. Labeled rates varied based upon soil texture and percent organic matter at each location. All rates were applied preplant incorporated (PPI) and pre-transplant to the soil surface (PRE-T). Additionally, at two locations in 1998 and 1999, all rates of sulfentrazone were tank-mixed with clomazone at 0.84 kg ai ha -1 and applied PPI and PRE- T. Tobacco stunting was observed at four of eight locations. No significant differences in stunting or control of Palmer amaranth, pitted morningglory, redroot pigweed, and yellow nutsedge were observed between the 0.5X and 1X rates. Large crabgrass control was similar with 0.75X and 1X rates. Stunting from PPI applications of sulfentrazone was significantly greater than PRE-T applications at three of the four locations where stunting was observed. At two of the four locations where stunting was observed, stunting was significantly reduced by the use of a tank-mix of clomazone and sulfentrazone. PRE-T applications were less effective than PPI applications at only one location for each weed species rated probably as a result of below normal rainfall during the test. s of sulfentrazone can be reduced to X without reducing weed control. However, rate reduction did not reduce the phytotoxicity of sulfentrazone when applied PPI. Based on our results, PRE-T applications offer the greatest opportunity to reduce tobacco stunting due to applications of sulfentrazone. INTRODUCTION is a member of the aryl triazolinone family of herbicides and inhibits protoporphyrinogen oxidase, an enzyme in the chlorophyll biosynthesis pathway (1). It controls many broadleaf weeds and sedges, and provides suppression of some annual grasses. was first labeled in burley and flue-cured tobacco (Nicotiana tabacum) in North Carolina in It provides excellent control of morningglory (Ipomoea spp.) and yellow and purple nutsedges (Cyperus esculentus and C. rotundus) (> 90%), which are three of the most troublesome weeds in tobacco production in North Carolina. is the only herbicide labeled for use in North Carolina tobacco that controls morningglory. Morningglory is problematic for both growers and leaf processors because it interferes with mechanical harvesters and is a potential source of foreign matter contamination in cured leaves. While sulfentrazone has provided excellent weed control, significant levels of tobacco stunting also have been observed (2). Labeled rates of sulfentrazone in tobacco range from 0.28 to 0.42 kg ai ha -1 and, as specified on the label, are based on soil texture and percent organic matter (Spartan, FMC Corporation, Philadelphia, PA). Fine textured soils and soils with greater than 2% organic matter receive the highest labeled rate. can be applied pre-plant incorporated (PPI) or pre-transplant (PRE-T) to the soil surface (2). A range of sulfentrazone rates have been evaluated for weed control and crop injury in soybean. Oliver (7) evaluated soil applied (PPI) and pre-plant (PRE) rates of sulfentrazone from to 0.56 kg ha -1 on soybean in a Taloka silt loam soil with 1% organic matter. Greater than 90% control of most broadleaf weeds evaluated was achieved with 0.14 kg ha -1 or less. An acceptable level of control of grasses (80% or greater) and some broadleaf weeds required rates up to 0.42 kg ha -1. method was significant only in the control of pitted morningglory, where PRE applications were superior to PPI applications at rates below 0.28 kg ha -1. No injury to soybean from soil applications of sulfentrazone was reported. Greenhouse experiments conducted by Wehtje et al. (10), showed that 0.14 kg ha -1 was effective for control of several broadleaf weeds and sedges on sandy soils, but comparable control on a clay loam required 0.28 kg ha -1. The majority of research with sulfentrazone in tobacco has been conducted within the range of labeled rates (0.28, 0.35, and 0.42 kg ha -1 ) (4,6,9). Stunting from sulfentrazone has been observed, primarily with PPI applications (2,9). However, weed control from PRE-T applications can be inadequate without timely precipitation for activation (2,5). Tobacco growers who plant on a raised bed prefer to incorporate preemergence herbicides because it does not require an additional trip across the field to knock down the row ridge before application, or modification of the transplanter to prevent soil movement after herbicide application. The use of lower than labeled rates of sulfentrazone in tobacco could reduce stunting without affecting control of most weeds and allow for sulfentrazone to be applied PPI with a greater margin of safety. Therefore, the objectives of this research were to evaluate weed control and stunting from sulfentrazone, applied PPI and PRE-T, at labeled and below-label rates. 1 Assistant Professor and Professors, Department of Crop Science, North Carolina State University, Raleigh, North Carolina Corresponding author: L. R. Fisher; loren_fisher@ncsu.edu 12

2 MATERIALS AND METHODS Research was conducted at 5 locations in 1998 and 3 locations in 1999 to evaluate weed control and injury to flue-cured tobacco from sulfentrazone (N-[2,4-dichloro-5- [4-difluoromethyl)-4,5-dihydro-3-methyl-5oxo-1H-1,2,4- triazol-1-yl]phenyl]methanesulfonamide). The treatments included above- and below-label rates of sulfentrazone (Table 1). Label rates vary with soil texture and percent organic matter (Table 2). All rates were applied as PPI and Table 1. rates used at the five locations in this study. CCRS 1 Duplin Co. LCPRS Randolph Co. UPRS kg ai ha (0.5X) (0.5X) (0.75X) 0.21 (0.75X) 0.21 (0.75X) 0.21 (0.5X) 0.21 (0.5X) 0.28 (1X) 0.28 (1X) 0.28 (1X) 0.28 (0.67X) 0.28 (0.67X) 0.35 (1.25X) 0.35 (1.25X) 0.35 (1.25X) 0.35 (0.83X) 0.35 (0.83X) (1X) 0.42 (1X) 1 UPRS = Upper Piedmont Research Station; CCRS = Central Crops Research Station; LCPRS = Lower Coastal Plain Research Station Table 2. Soil characteristics and labeled rates of sulfentrazone in 1998 and Labeled of...%... kg ai ha -1 Location Year ph O.M. Sand Silt Clay Texture Duplin sand 0.28 Randolph scl 0.42 UPRS scl 0.42 CCRS ls 0.28 LCPRS sl 0.28 UPRS scl 0.42 Duplin sand 0.28 Randolph scl UPRS = Upper Piedmont; CCRS = Central Crops; and LCPRS = Lower Coastal Plain Research Station Table 3. Effect of sulfentrazone rate and application method on stunting of flue-cured tobacco at four locations in 1998 and Method Duplin Randolph Duplin Randolph 0.21 PPI 11 bc 46 b 4 bc 6 ab 0.28 PPI 23 ab 35 bc 18 b 11 a 0.35 PPI 25 a 43 bc 44 a 3 ab 0.42 PPI a -- 8 ab 0.21 PRE-T 0 d 4 d 0 c 8 ab 0.28 PRE-T 0 d 0 d 0 c 5 ab 0.35 PRE-T 6 c 4 d 0 c 0 b 0.42 PRE-T cd -- 0 b Means b 23 a na 7 a ab 18 a na 8 a a 31 a na 1 a a -- 4 a PPI 20 a 50 a na 7 a PRE-T 2 b 6 b na 3 a X App. Pr > F Means within a column followed by the same letter for overall treatment, rate, and application are not different according to Fisher=s Protected LSD test at P = PRE-T. Treatments were arranged in a rate by application method factorial with a nontreated, cultivated check used to determine percent weed control (but not included in the statistical analyses). At the Duplin and Randolph Co. locations in 1998 and 1999, clomazone at 0.84 kg ha -1 was included with all sulfentrazone rates and application methods in a rate by application method by clomazone factorial. The experimental design at each location was a randomized complete block with four replications. Herbicide treatments were applied using a CO 2 pressurized sprayer mounted on a tractor for on-farm tests, or a backpack sprayer for research station tests. Delivery volume was 225 L ha -1 applied at 138 kpa. Incorporation of PPI treatments was performed using a field cultivator at the Duplin and Randolph Co. sites, and by a power driven, rotary tiller at the three sites at research stations. All plots were then bedded and knocked down (tops removed) to a similar height by the mechanical transplanter. PRE-T treatments were applied to the soil surface of knocked-down beds in specified plots. Transplanting was performed with minimal soil movement. Tobacco cultivars used were >NC 71' at the Duplin, Randolph, and Central Crops Research Station (CCRS) locations, and >K 326' at the Lower Coastal Plain Researach Station (LCPRS) and Upper Piedmont Research Station (UPRS) locations. Plants were spaced 56 cm within rows and 122 cm between rows. Plots were 4 rows by 15.2 m on farms and 3 rows by 12.2 m on research stations. Fertilization, cultivation, insect control, sucker control, and irrigation (at CCRS, UPRS, and Randolph) were conducted based on normal practices and extension recommendations for the region. Weed control and crop injury were visually rated on a scale of 0-100%, with 0 = no weed control or no crop injury, and 100 = complete weed control or crop death (3). First cultivations were delayed until early-season weed and injury ratings were made, typically three weeks after transplanting. All plots were cultivated two or three times during the season. Additional ratings were made at mid-season (after the last cultivation) and after final harvest. Data were subjected to an arcsine square root transformation prior to analysis of variance. Means were separated using Fisher=s Protected LSD Test at P = Nontransformed data are presented, with statistical analysis based upon transformed data. Yield and quality data were collected for all locations except Duplin Co. No differences in yield or quality were observed at any of the locations and therefore are not shown. 13

3 RESULTS AND DISCUSSION Table 4. Stunting. Early season stunting from sulfentrazone was -1 kg ai ha 0.14 PPI a a 0.21 PPI 86 a 100 a 69 a 90 a 0.28 PPI 70 a 97 a 91 a 95 a 0.35 PPI 98 a 99 a 81 a 91 a 0.42 PPI a PRE-T a b 0.21 PRE-T 98 a 99 a 74 a 49 b 0.28 PRE-T 98 a 100 a 71 a 71 ab 0.35 PRE-T 86 a 93 a 69 a 49 b 0.42 PRE-T a -- Means a a a 99 a 71 a 69 a a 98 a 81 a 83 a a 96 a 75 a 70 a a -- PPI 85 a 96 a 81 a 91 a PRE-T 94 a 97 a 72 a 51 b X App. Pr > F UPRS = Upper Piedmont Research Station; LCPRS = Lower Coastal Plain Research 2 Station. Means within a column followed by the same letter for overall treatment, rate, and application are not different according to Fisher=s Protected LSD test at P = Table 5. Effect of sulfentrazone rate and application method on crabgrass control at five locations in 1998 and Method 1 CCRS observed at four of eight locations across the two years of the study (Table 3). Stunting was observed three weeks after transplanting (WAT) at the Duplin and Randolph locations in 1998 and Because of a significant rate by LCPRS Randolph LCPRS Randolph kg ai ha -1 % PPI 25 c 65 b c PPI 56 abc 86 ab 96 ab 59 abc 31 bc 0.28 PPI 71 abc 90 ab 97 ab 88 a 60 ab 0.35 PPI 79 abc 85 ab 94 ab 79 ab 84 a 0.42 PPI a a 0.14 PRE-T 38 bc 73 ab bc PRE-T 66 abc 74 ab 89 ab 76 ab 0 c 0.28 PRE-T 86 a 95 a 73 b 83 ab 70 a 0.35 PRE-T 70 abc 90 ab 95 ab 91 a 48 ab 0.42 PRE-T ab bc Means b 69 b b ab 80 ab 92 a 68 a 16 b a 93 a 85 a 81 a 65 a a 88 ab 94 a 85 a 66 a a a Effect of sulfentrazone rate and application method on control of yellow nutsedge at four locations in 1998 and Method Duplin 1 LCPRS UPRS LCPRS PPI 58 a 83 a 97 a 63 a 66 a PRE-T 65 a 82 a 89 a 77 a 35 b X App. Pr > F CCRS = Central Crops Research Stat ion; LCPRS = Lower Coastal Plain Research Station 2 Means within a column followed by the same letter for overall treatment, rate, and application are not different according to Fisher=s Protected LSD test at P = % application method interaction, main affect means are not reported for the 1999 Duplin location. There were no differences in stunting between the 1X and lower rates at either location in 1998 or Significant stunting was observed only when a 1.25X rate of sulfentrazone was included at the Duplin location (Table 2). In 1998, greater stunting was observed with PPI compared to PRE-T applications at both locations. Stunting averaged 20% and 50% for PPI applications and only 2% and 6% for PRE-T applications at the Duplin and Randolph locations, respectively. Differences between application method means were not significant at the Randolph location in 1999, likely because stunting only ranged from 0 to 11%. At the Duplin location, stunting ranged from 4 to 44% with increasing sulfentrazone rates applied PPI, whereas, no stunting was observed in PRE-T applications. The reduced stunting observed with PRE-T applications compared to PPI applications of sulfentrazone may be attributed to the limited availability of sulfentrazone in the root zone of the tobacco transplants with PRE-T applications. Similarly, differences in stunting between locations may be related to the type of incorporation equipment used. A field cultivator was used to incorporate sulfentrazone at both onfarm locations where stunting was observed. At all other locations, a power driven, rotary tiller was used to incorporate sulfentrazone treatments. It is possible that incorporation with the field cultivator was not as uniform or thorough as incorporation with the rotary tiller, which in turn could have resulted in concentrated areas of sulfentrazone in the root zone after plots were bedded to prepare for transplanting (8). Recovery from stunting was rapid and no growth differences were observed six WAT at all locations except for the Randolph location in At this location, stunting from sulfentrazone was apparent until eight WAT. Yield data were collected at all locations, except Duplin, and no differences in yield were observed (data not shown). 14

4 Stunting from sulfentrazone was reduced by the addition of clomazone at both locations in A significant clomazone X application method interaction was observed and main affects of clomazone are not reported. At the Duplin location, stunting in the PPI applications was 7% with the tankmix and 20% with sulfentrazone alone. Table 6. Effect of sulfentrazone rate and application method on control of redroot pigweed at three locations in Method CCRS 1 Randolph UPRS kg ai ha -1 % PPI 98 a a 0.21 PPI 98 a 99 a 100 a 0.28 PPI 99 a 89 a 99 ab 0.35 PPI 100 a 96 a 96 ab 0.42 PPI a PRE-T 100 a ab 0.21 PRE-T 100 a 100 a 85 c 0.28 PRE-T 100 a 100 a 86 ab 0.35 PRE-T 99 a 98 a 100 a 0.42 PRE-T a -- Means a a a 99 a 93 a a 94 a 93 a a 97 a 98 a a -- PPI 99 a 96 a 99 a PRE-T 100 a 98 a 90 b X App. Pr > F UPRS = Upper Piedmont Research Station; CCRS = Central Crops Research Station. 2 Means within a column followed by the same letter for overall treatment, rate, and application are not different according to Fisher=s Protected LSD test at P = Table 7. Effect of sulfentrazone rate and application method on control of Palmer amaranth at two locations in 1998 and Method Duplin Duplin 0.21 PPI 45 b 86 ab 0.28 PPI 65 ab 91 a 0.35 PPI 95 a 86 ab 0.21 PRE-T 99 a 83 ab 0.28 PRE-T 83 ab 68 b 0.35 PRE-T 100 a 66 b Means a 84 a a 81 a a 79 a PPI 68 a 91 a PRE-T 94 a 72 b X App. Pr > F Means within a column followed by the same letter for overall treatment, rate, and application are not different according to Fisher=s Protected LSD test at P = Similarly, at the Randolph location, stunting was 15% with the tank mix and 50% with sulfentrazone alone. Stunting with the PRE-T applications was always 7% or less and was not significantly affected by the addition of clomazone. In 1999, stunting was always less than 18% with label rates and was not altered by the addition of clomazone. Weed Control. There were no affects of rate on control of yellow nutsedge, pitted morningglory (Ipomoea lacunosa), redroot pigweed (Amaranthus retroflexus) or Palmer amaranth (Amaranthus palmeri). Large crabgrass (Digitaria sanguinalis) control with the 0.5X rate was significantly less than with the 1X and higher rates at four of five locations. only provides suppression of large crabgrass, therefore reduced control at lower than labeled rates would be expected. The addition of clomazone at 0.84 kg ha -1 at the Duplin and Randolph location in 1998 and 1999 improved control of large crabgrass to greater than 90% with all rates of sulfentrazone (data not shown). The addition of clomazone had no effect on control of other weeds rated. typically provides excellent control of all other weeds rated in this study and no effect of clomazone was expected (2). At one location for each weed rated, PPI applications of sulfentrazone provided greater weed control than PRE-T applications. Soil moisture was low early in the 1999 season and weed control from PRE-T compared to PPI applications of sulfentrazone was reduced because the herbicide was not activated (5). CONCLUSIONS Early season stunting of tobacco was not reduced by the use of lower than labeled rates of sulfentrazone. However, injury was reduced by applying sulfentrazone PRE-T. Stunting was consistently greater from PPI applications than from PRE-T applications and therefore may be related to factors such as placement and/or concentration of the herbicide in the root zone. Recovery from early-season stunting was typically very rapid, especially under good growing conditions. Even with the high levels of crop injury observed at the Randolph location in 1998, no yield loss was recorded. Further research on the interaction of clomazone and sulfentrazone is needed to determine if this is consistent across environments and locations and to determine the physiological basis for the observed response. Weed control from sulfentrazone was not reduced at lower than label rates (down to 0.5X), but was reduced with PRE-T applications compared to PPI due to poor activation of the herbicide when soil moisture was low. ACKNOWLEDGMENTS The authors wish to thank Sherwood Wood, agricultural research technician, The North Carolina Tobacco Research Commission, and R. J. Reynolds Tobacco Co. for support of this project. 15

5 Table 8. Effect of sulfentrazone rate and application method on control of pitted morningglory at two locations in 1998 and Wehtje, G. R., R. H. Walker, T. L. Grey, and C. E. Spratlin Soil effects of sulfentrazone. Proc. South. Weed Sci. Soc. 48:224. Method Randolph Randolph 0.21 PPI 99 a 96 ab 0.28 PPI 98 ab 98 a 0.35 PPI 99 a 99 a 0.42 PPI 100 a 99 a 0.21 PRE-T 90 cd 59 c 0.28 PRE-T 88 d 80 abc 0.35 PRE-T 96 bc 66 bc 0.42 PRE-T 92 cd 65 c Means a 77 a a 89 a a 83 a a 82 a PPI 99 a 98 a PRE-T 91 b 68 b X App. Pr > F Means within a column followed by the same letter for overall treatment, rate, and application are not different according to Fisher=s Protected LSD test at P = LITERATURE CITED 1. Dayan, F. E. and S. O. Duke Phytotoxicity of protoporphyrinogen oxidase inhibitors: phenomology, mode of action and mechanism of resistance. Pages 11-35, in: Herbicide activity: Toxicology, Biochemistry and Molecular Biology. R. M. Roe et. al., eds. IOS Press. 2. Fisher, L. R. and W. D. Smith Weed Management. Pages 51-69, in: 2001 Tobacco Information. N. C. Coop. Ext. Serv. Bull. AG 187 (revised). 3. Frans, R., R. Talbert, D. Marx, and H. Crowley Experimental design techniques for measuring and analyzing plant responses to weed control practices. Page 37 in: Research Methods in Weed Science 3 rd Ed., N.D. Camper, ed. South. Weed Sci. Soc., Champaign, IL. 4. Hancock, H. G Spartan DF performance in tobacco. Proc. South. Weed Sci. Soc. 51: Hancock, H. G : a broad spectrum herbicide for soybeans. Proc. South. Weed Sci. Soc. 48: Moore, J. M., J. W. Wilcut, D. C. Bridges and J. S. Richburg, III Tobacco and weed response to F Proc. South. Weed Sci. Soc. 48: Oliver, L. R., R. W. Costello, and C. A. King Weed control programs with sulfentrazone in soybeans. Proc. South. Weed Sci. Soc. 48: Thompson, L. Jr., W. A. Skroch, and E. O. Beasley Pesticide incorporation, distribution of dye by tillage implements. N. C. Coop. Ext. Serv. Bull. AG Walker, E. R., T. C. Mueller, G. N. Rhodes, Jr., and R. M. Hayes Spartan for weed control in tobacco. Proc. South. Weed Sci. Soc. 51:32. 16