EVALUATION OF HERBICIDE SYSTEMS FOR DARK FIRE-CURED TOBACCO

Transcription

1 EVALUATION OF HERBICIDE SYSTEMS FOR DARK FIRE-CURED TOBACCO William A. Bailey 1 *, Timothy W. Lax 1, Robert A. Hill 1, and Mitchell D. Richmond 1 Field experiments were conducted at Murray, KY in 2005, 2006, and 2007 to compare dark tobacco tolerance and weed control from various herbicide systems applied prior to transplanting. Herbicide treatments included sulfentrazone at 0.42 kg ai/ha applied pretransplant (PRETR), clomazone at 1.12 kg ai/ha PRETR, sulfentrazone at 0.42 kg ai/ha plus clomazone at 1.12 kg ai/ha PRETR, pendimethalin at 1.66 kg ai/ha applied pretransplant incorporated (PTI), pendimethalin at 1.66 kg ai/ha PTI followed by sulfentrazone at 0.42 kg ai/ha PRETR, pebulate at 4.48 kg ai/ha PTI, napropamide at 2.24 kg ai/ha PTI, pebulate at 4.48 kg ai/ha plus napropamide at 2.24 kg ai/ha PTI, and a nontreated control. Injury to dark tobacco (Nicotiana tabacum L. Narrowleaf Madole ) from any herbicide system was considered minor and did not exceed 11% at 3 weeks after application, and was not apparent by 6 weeks after application in any year. Weed species evaluated included annual grasses (primarily large crabgrass and goosegrass), yellow nutsedge (Cyperus esculentus L.), common ragweed (Ambrosia artemisiifolia L.), and entireleaf morningglory (Ipomoea hederacea var. integruiscula). Herbicide systems that included pendimethalin or clomazone were most effective against annual grasses evaluated, herbicide systems that included sulfentrazone were most effective against yellow nutsedge, and those that contained clomazone were most effective against common ragweed. Sulfentrazone was most effective against entireleaf morningglory, but control was improved with the addition of clomazone or pendimethalin. Total dark-fired tobacco yield where herbicides were applied ranged from 2,765 to 3,051 kg/ha, although lowest total yield, quality grade index, and gross revenue was from tobacco that received pendimethalin only, most likely because of poor control of yellow nutsedge and common ragweed. Additional key words: Gross revenue, quality grade index, tobacco injury, tobacco yield INTRODUCTION Dark fire-cured tobacco (Nicotiana tabacum L. Narrowleaf Madole ) is grown on approximately 6,600 ha in the United States in the areas of western Kentucky, northwestern Tennessee, and central Virginia, and is used primarily for the production of moist snuff products. The majority of the crop is grown in western Kentucky and northwestern Tennessee, where the average yield is 3,695 kg/ha and the average market price is $5.91/kg. Total annual revenues for dark firecured tobacco are in excess of $138 million (16). Weeds compete with tobacco for moisture, light, and nutrients, and this competition can adversely affect tobacco growth and yield (5). Weeds also contribute to disease and insect transmittal to tobacco, interfere with tobacco harvesting and curing operations, and increase foreign-matter contamination in harvested tobacco (10). Hauser and Miles (9) observed that uncontrolled weeds reduced flue-cured tobacco yields by 26%, reduced price index, and caused substantial changes in grade distribution and chemical composition of flue-cured tobacco. In Kentucky, monetary losses in burley and dark tobacco due to weeds were estimated at $22.2 million in 2001 (17). Losses included reduction in yield and quality, extra land preparation and cultivation, and increased cost of harvesting. Although dark tobacco is a very high value crop, it is grown on a relatively small area compared to major agronomic crops and, as a result, there are a limited number of pesticides that are registered for use. Dark *Corresponding author: William A. Bailey; abailey@uky.edu 1 Department of Plant and Soil Sciences, University of Kentucky, Research and Education Center, Princeton, KY tobacco is also grown at relatively low plant populations compared to other tobacco types, which limits its ability to compete with weeds (2). Herbicides currently registered for use in dark tobacco include sulfentrazone, clomazone, carfentrazone, pendimethalin, napropamide, and sethoxydim. Sulfentrazone controls or suppresses several annual broadleaf weeds, nutsedges, and grasses (7,13). However, it does not control common ragweed (Ambrosia artemisiifolia L.) and giant ragweed (Ambrosia trifida L.), which are presently 2 of the most common and troublesome weeds in dark tobacco. Clomazone controls common ragweed and several annual broadleaf weeds and grasses, but does not control pigweed species (Amaranthus sp.) (3). Carfentrazone is registered for use in dark tobacco as a nonselective herbicide for pretransplant burndown applications in conservation tillage tobacco, and as a directed spray application after transplanting. However, carfentrazone has no soil activity and its effectiveness is very limited depending on weed species and size. Carfentrazone has also shown potential to cause significant injury in dark tobacco from directed spray applications (4). Because of limited weed control activity and potential for crop injury, carfentrazone is generally not recommended for use in dark tobacco. Pendimethalin and napropamide are primarily grass herbicides that provide limited control of broadleaf weeds. Sulfentrazone and pendimethalin are registered for use prior to tobacco transplanting, whereas clomazone and napropamide can be applied prior to or just after transplanting. Sethoxydim is the only true postemergence herbicide currently registered for use in dark tobacco. Weed control from sethoxydim is limited to grasses only. Pebulate was registered for use in dark tobacco until it was discontinued in Tobacco Science (2013) 50:34 38

2 Pebulate was the only herbicide other than sulfentrazone that provided control of yellow nutsedge, but control of other weed species was limited. Dark tobacco growers commonly ask which herbicide system has the least potential for crop injury and/or yield reduction and provides the most effective control of the weed spectrum typically encountered in western Kentucky and northwestern Tennessee tobacco fields. Because of the high value of dark tobacco, many growers use reduced rates of herbicides because of crop injury concerns, and often observe reduced weed control as a result. The objective of these experiments was to evaluate dark tobacco response and weed control where full rates of all available residual herbicide systems were used. MATERIALS AND METHODS Field experiments were conducted in 2005, 2006, and 2007 at the West Farm of Murray State University near Murray, KY. Soil type was a Grenada silt loam (fine silty, mixed, thermic Glossic Fragiudalfs) with 1.8% organic matter. Soil ph was 6.1 in 2005, 6.4 in 2006, and 6.5 in These soils are representative of the western district dark-fired tobacco production region of western Kentucky. Test sites were moldboard plowed and disked 1 month before tobacco transplanting. Fertilizer was broadcast applied and incorporated prior to transplanting according to soil test recommendations. Mefenoxam (Ridomil Gold EC, 4 lb./gallon, Syngenta Crop Protection, Greensboro, NC) and chlorpyrifos (Lorsban-4E, 4 lb./gallon, Dow AgroSciences, Indianapolis, IN) were broadcast applied and incorporated at 0.48 and 0.96 kg ai/ha, respectively, prior to transplanting to control soilborne diseases and insects. Final field preparation was done with a field cultivator. The same field cultivator was also used to incorporate, to a shallow (#5 cm) depth, all herbicide treatments that were applied pretransplant incorporated (PTI). Plants of dark tobacco cultivar Narrowleaf Madole were produced in a greenhouse float system with the use of standard practices in each of the 3 years of the experiment. Experiments were transplanted into the field on June 9, 2005, June 1, 2006, and June 6, Tobacco was transplanted on 1-m row spacing with 81-cm plant spacing within rows. Plots were 4 rows wide and 12 m in length. The experimental design was a randomized complete block with treatments replicated 4 times. Herbicides were applied at the highest rates allowed on product labels. Treatments included sulfentrazone (Spartan 4F, 4 lb./gallon, FMC Corporation, Philadelphia, PA) at 0.42 kg ai/ha applied pretransplant (PRETR), clomazone (Command 3ME, 3 lb./gallon, FMC Corporation) at 1.12 kg ai/ha PRETR, sulfentrazone at 0.42 kg ai/ha plus clomazone at 1.12 kg ai/ha PRETR, pendimethalin (Prowl 3.3EC, 3.3 lb./gallon, BASF Corporation, Research Triangle Park, NC) at 1.66 kg ai/ha applied PTI, pendimethalin at 1.66 kg ai/ha PTI followed by sulfentrazone at 0.42 kg ai/ha PRETR, pebulate (Tillam 6-E, 6 lb./gallon, Syngenta Crop Protection) at 4.48 kg ai/ha PTI, napropamide (Devrinol 50DF, 50% napropamide, United Phosphorus, Inc., King of Prussia, PA) at 2.24 kg ai/ha PTI, and pebulate at 4.48 kg ai/ha plus napropamide at 2.24 kg ai/ha PTI. A nontreated control was included that did not receive any herbicide treatment. All other production practices were standard according to University Extension Services guidelines (14). All herbicide applications were made with the use of CO 2 -pressurized sprayers calibrated to deliver 140 L/ha at 152 kpa with standard flat-fan spray tips (Teejet 8002VS flat fan spray tip, Spraying Systems Co., Wheaton, IL). 8 All treatments were applied on June 8, 2005, May 31, 2006, and June 5, Crop injury and weed control was evaluated with the use of a 0 100% scale where 0 5 no plant injury and plant death (8). Crop injury was evaluated at 1 and 3 weeks after herbicide applications. Weed control was evaluated early season at 4 5 weeks following herbicide applications and late season at 4 5 weeks prior to tobacco harvest. Tobacco was cultivated once with a standard 2-row sweep and harrow cultivator following the early-season weed control evaluation. Thirty tobacco plants per plot were manually stalk harvested at 6 weeks after flower removal, impaled on sticks, and hung in a conventional fire-curing barn. Standard firecuring practices were used with the crop being exposed to 4 firings with hardwood slabs and sawdust to achieve an acceptable leaf color and texture for current marketing conditions. Following curing, tobacco leaves were removed from the stalks, separated into 3 stalk positions (lower stalk [lug], midstalk [second], and upper stalk [leaf]), and weighed. Tobacco was then graded according to United States Department of Agriculture standards for Type 22 dark fire-cured tobacco (15) and grades were assigned an index value of as described by Miller and Legg (12). Grade index data are a weighted average of grades across stalk positions. Gross revenue was determined with the use of loan values based on grades for Type 22 dark fire-cured tobacco (1). Gross revenue values are the sum of loan values for the grade of each stalk position multiplied by the yield of each stalk position. All data were subjected to analysis of variance, and means were separated with the use of Fisher s Protected LSD test at P with the use of statistical analysis software (SAS Institute, Inc., Cary, NC). Tobacco injury data and weed control data were arcsine squareroot transformed prior to analysis, but only nontransformed data are presented, as transformation did not affect results of data analysis. RESULTS AND DISCUSSION Data for tobacco injury and weed control are presented by year, as there were significant year by treatment interactions for injury and all weed species evaluated. Data for dark-fired tobacco yield by stalk position, total yield, quality grade index, and gross Tobacco Science (2013) 50:

3 Table 1. Dark tobacco injury from herbicide treatments. Herbicide Treatment Timing Rate Tobacco Injury a kg ai/ha % Sulfentrazone PRETR bc 3 bc 0 b Clomazone PRETR bc 0 c 0 b Sulfentrazone + clomazone PRETR bc 4 b 0 b Pendimethalin PTI b 5 b 2 a Pendimethalin fb b sulfentrazone PTI fb PRETR a 11 a 2 a Pebulate PTI bc 3 bc 0 b Napropamide PTI bc 2 bc 0 b Pebulate + napropamide PTI bc 5 b 0 b Untreated control 0 bc 0 c 0 b a Means within a column followed by the same letter are not significantly different according to Fisher s Protected LSD as P50.05 b Abbreviations: fb 5 followed by; PRETR 5 pretransplant; PTI 5 pretransplant incorporated. revenue were pooled across years, as there were no significant year by treatment interactions. Tobacco Injury. Tobacco injury from herbicide treatments was seen as relatively minor stunting in each year, and was most prevalent at 3 weeks after transplanting. This injury was transient and was not apparent by 6 weeks following transplanting (data not shown). Tobacco injury ranged from 1 to 10% in herbicide-treated plots in 2005 (Table 1), with the highest injury noted from pendimethalin followed by sulfentrazone (10%). Injury from other treatments ranged from 1 to 5%. Similar levels of tobacco injury were seen in 2006, with injury ranging from 0 to 11% in herbicide-treated plots and greatest injury occurring from pendimethalin followed by sulfentrazone (11%). Injury from other treatments ranged from 0 to 5%. Significantly less injury occurred in 2007 and did not exceed 2% from any herbicide treatment. Differences in tobacco injury between years may be explained by differences in rainfall received soon after herbicide application. Both 2005 and 2006 were considered above normal for rainfall, with 7.4 and 6.3 cm rainfall occurring in the first 2 weeks following herbicide application and transplanting. Conversely, 2007 was considered a dry season, with only 0.8 cm of rainfall occurring in the first 2 weeks following herbicide application and transplanting. Weed Control. All weed control data are from lateseason evaluations taken at 4 5 weeks prior to tobacco harvest. Annual grasses were evaluated in 2005 and 2007, and species composition was primarily large crabgrass (Digitaria sanguinalis L.) and goosegrass (Eleusine indica L.). Annual grass control in both years was generally highest in treatments that contained pendimethalin (Table 2). In 2007, treatments that included clomazone provided annual grass control equivalent to pendimethalin treatments. Annual grass control from treatments that contained pendimethalin or clomazone ranged from 89 to 97%, and annual grass control from other treatments ranged from 45 to 88%. Addition of sulfentrazone to pendimethalin or clomazone did not improve control of annual grasses. Yellow nutsedge was evaluated in 2006 and 2007 and treatments that contained sulfentrazone provided the highest level of yellow nutsedge control (91 97%). Treatments containing pebulate also provided good yellow nutsedge control, but results were not as consistent between the 2 years (77 78% control in 2006 and 90 91% control in 2007). The addition of clomazone Table 2. Weed control from herbicide treatments. Herbicide Treatment Timing Rate Annual Grass a,b Yellow Nutsedge Common Ragweed Entireleaf Morningglory kg ai/ha % Sulfentrazone PRETR d 77 c 91 a 97 a 30 d 31 e 90 b 89 b Clomazone PRETR bc 96 a 17 c 23 d 78 ab 87 a 62 d 51 d Sulfentrazone + clomazone PRETR ab 97 a 96 a 97 a 83 a 86 a 97 a 97 a Pendimethalin PTI a 96 a 23 c 24 d 33 cd 50 d 73 c 44 e Pendimethalin fb c sulfentrazone PTI fb PRETR 1.66 fb a 96 a 93 a 97 a 44 c 63 bc 94 ab 96 a Pebulate PTI d 80 c 77 b 91 b 41 cd 64 bc 35 ef 48 d Napropamide PTI c 76 c 22 c 36 c 74 ab 61 c 31 f 60 c Pebulate + napropamide PTI c 88 b 78 b 90 b 69 b 72 b 39 e 62 c Untreated control 0 e 0 d 0 d 0 e 0 e 0 f 0 g 0 f a Predominant annual grass species were large crabgrass (Digitaria sanguinalis L.) and goosegrass (Eleusine indica L.). b Means within a column followed by the same letter are not significantly different according to Fisher s Protected LSD as P c Abbreviations: fb 5 followed by; PRETR 5 pretransplant; PTI 5 pretransplant incorporated. 36 Tobacco Science (2013) 50:34 38

4 Table 3. Effect of herbicide treatment on dark-fired tobacco yield, quality grade index, and gross revenue. a Herbicide Treatment Timing Rate Stalk Position b,c Total Quality Grade Lug Second Leaf Index d Gross Revenue e kg ai/ha kg/ha $/ha Sulfentrazone PRETR a 580 ab 1,992 a 2,977 ab 64.9 ab 12,497 a Clomazone PRETR ab 579 ab 2,010 a 2,944 ab 70.1 a 12,911 a Sulfentrazone + clomazone PRETR a 595 a 2,028 a 3,017 ab 64.4 ab 12,598 a Pendimethalin PTI ab 565 ab 1,843 a 2,759 b 61.9 b 11,163 ab Pendimethalin fb f PTI fb PRETR ab 617 a 2,059 a 3,051 a 63.4 ab 11,883 a sulfentrazone Pebulate PTI ab 569 ab 1,958 a 2,878 ab 63.6 ab 11,779 a Napropamide PTI ab 594 a 1,879 a 2,828 ab 66.7 ab 12,067 a Pebulate + napropamide PTI ab 603 a 2,031 a 3,004 ab 65.9 ab 12,430 a Untreated control 314 b 499 b 1,592 a 2,405 c 66.2 ab 9,377 b a Data pooled across years, b Means within a column followed by the same letter are not significantly different according to Fisher s Protected LSD as P c Tobacco leaves removed by stalk position following fire curing. Lug corresponds to lower stalk leaves, second from midstalk, and leaf from upper stalk. d Quality grade index is a numerical representation of federal quality grade received for tobacco and is a weighted average of grade index for all stalk positions. e Gross revenue is the total gross value of tobacco based on federal grade and price support values. f Abbreviations: fb 5 followed by; PRETR 5 pretransplant; PTI 5 pretransplant incorporated. or pendimethalin to sulfentrazone, or the addition of napropamide to pebulate, did not improve yellow nutsedge control compared to sulfentrazone or pebulate alone. Common ragweed is 1 of the more troublesome weeds encountered in dark tobacco production and is also an alternate host to bacterial wilt and tobacco ringspot virus (6,11). Common ragweed was evaluated in 2005 and 2006, and treatments that contained clomazone generally provided the highest level of control in both years. Napropamide-containing treatments provided some control of common ragweed, but were not as effective or as consistent between the 2 years as clomazone-containing treatments. Entireleaf morningglory was evaluated in 2005 and Treatments containing sulfentrazone were most effective in controlling entireleaf morningglory in both years. Sulfentrazone alone controlled entireleaf morningglory 90% in 2005 and 89% in The addition of clomazone to sulfentrazone improved entireleaf morningglory control to 97% in both years. The addition of pendimethalin PTI prior to sulfentrazone PRETR also improved entireleaf morningglory control to 94% in 2005 and 96% in Tobacco Yield, Quality Grade Index, and Gross Revenue. Yields of lug, second, and leaf stalk positions were generally similar between herbicide treatments (Table 3). Total yield in herbicide-treated plots ranged from 2,759 to 3,051 kg/ha, compared to 2,405 kg/ha in nontreated control plots that received no herbicide treatment. Within herbicide-treated plots, highest total yield was from tobacco that received pendimethalin PTI followed by sulfentrazone PRETR (3,051 kg/ha), and lowest total yield was from tobacco that received pendimethalin PTI only. Differences in these 2 treatments are most likely associated with differences seen in yellow nutsedge and entireleaf morningglory control. Quality grade index ranged from 61.9 to 70.1, with highest quality grade index in tobacco that received clomazone PRETR only and lowest quality grade index in tobacco that received pendimethalin PTI only. Gross revenue in herbicide-treated plots ranged from $11,163/ ha in tobacco that received pendimethalin PTI only, to $12,911/ha in tobacco that received clomazone PRETR only. Gross revenue in untreated tobacco was $9,377/ha. CONCLUSION These data suggest that herbicide systems that include sulfentrazone are critical in controlling the weed species typically seen in dark tobacco fields of Kentucky and Tennessee. Clomazone should also be included in fields where common ragweed is expected, and addition of clomazone or pendimethalin can improve annual grass and morningglory control compared to sulfentrazone alone. Although slightly higher early-season injury was seen with pendimethalin followed by sulfentrazone, particularly in years where substantial rainfall occurred in the first 2 weeks following herbicide application and transplanting, this injury was minor and did not translate to reductions in dark fire-cured tobacco yield, quality grade index, or gross revenue. ACKNOWLEDGMENTS The authors would like to thank students and faculty at Murray State University for technical assistance in this research. Appreciation is also extended to U.S. Smokeless Tobacco Manufacturing Co. for financial support. LITERATURE CITED 1. Anonymous Official Schedule of Loan Values for Type 22 Dark Fire-Cured Tobacco. Eastern Tobacco Science (2013) 50:

5 Dark-Fired Growers Association, in cooperation with Tobacco Division, Farm Service Agency, U.S. Department of Agriculture, Springfield, TN. 2. Bailey WA Basic principles of dark tobacco production in Kentucky and Tennessee. Pages 23 24, in: Proceedings of the of 41st Tobacco Worker s Conference. 3. Bailey WA Dark tobacco (Nicotiana tabacum) tolerance to trifloxysulfuron and halosulfuron. Weed Technol 21: Bailey WA, Pearce RC Experimental herbicide systems for no-tillage dark tobacco. In: Proceedings of 2007 CORESTA Joint Meeting of Agro-Phyto Study Groups. Paper AP Chaudhry GA, Chaudhry MH, Fareed M Weed competition and its effects on the yield components in a tobacco crop. Pak Tob 2: Daub ME, Echandi E, Gooding GV Jr, Jones KJ, Lucas GB, Main CE, Powell NT, Schneider SM, Shew HD, Shoemaker PB, Spurr HW Jr In: Compendium of tobacco diseases, H.D. Shew and G.B. Lucas, editors. American Phytopathological Society, St. Paul, MN. 7. Fisher LR, Smith WD, Wilcut JW Effect of sulfentrazone rate and application method on weed control and stunting in flue-cured tobacco. Tob Sci 46: Frans R, Talbert R, Marx D, Crowley H Experimental design and techniques for measuring and analyzing plant responses to weed control practices. Pages 29 46, in: Research methods in weed science. 3rd ed. N.D. Camper, ed. Southern Weed Science Society, Champaign, IL. Pp Hauser EW, Miles JD Flue-cured tobacco yield and quality as affected by weed control methods. Weed Res 15: Hawks SN Jr., Collins WK Principles of flue-cured tobacco production. 1st ed. North Carolina State University, Raleigh, NC. Pp Lucas GB Diseases of tobacco. Biological Consulting Associates, Raleigh, NC. 12. Miller RD, Legg PD A grade index for type 22 and 23 fire-cured tobacco. Tob Sci 34: Ritter RL, Menbere H, Momen B Tolerance of Maryland-type tobacco (Nicotiana tabacum) to sulfentrazone. Weed Technol 19: Seebold KW, Pearce RC, eds Kentucky & Tennessee tobacco production guide. University of Kentucky, Cooperative Extension Service, Lexington, KY. 15. [USDA] U.S. Department of Agriculture Official standard grades, Kentucky and Tennessee fire-cured tobacco U.S. Types 22, 23, and Foreign Type 96. U.S. Department of Agriculture, Tobacco Division, Agricultural Marketing Service, Washington, DC. 16. [USDA-NASS] United States Department of Agriculture, National Agricultural Statistics Service Accessed 2013 May Webster EP Economic losses due to weeds in southern states. Proc South Weed Sci Soc 54: Tobacco Science (2013) 50:34 38