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© 2007 Plant Management Network. Use of Methoxyfenozide (Intrepid) and Bifenthrin (Capture) for Management of Southwestern and European Corn Borers in Conventional Field Corn in Arkansas Paul McLeod, Professor, Department of Entomology, Agri 321, University of Arkansas, Fayetteville 72701; and Justin B. Hensley, County Agent, Andy Vangilder, Staff Chariman, and Jason Kelley, Agronomist, Cooperative Extension Service, University of Arkansas, Little Rock 72203 Corresponding author: Paul McLeod. pjmcleod@uark.edu McLeod, P., Hensley, J. B., Vangilder, A., and Kelley, J. 2007. Use of methoxyfenozide (Intrepid) and bifenthrin (Capture) for management of southwestern and European corn borers in conventional field corn in Arkansas. Online. Crop Management doi:10.1094/CM-2007-0419-02-RS. Abstract In order to conserve the gene pool of insects susceptible to Bacillus thuringiensis (Bt) protein in transgenic plants, 50% of field corn produced in Arkansas is required to be non-Bt or conventional. In conventional corn, farmers generally apply either bifenthrin (Capture) or methoxyfenozide (Intrepid) during early July to manage second generation southwestern corn borers, Diatraea grandiosella Dyar, and European corn borers, Ostrinia nubilalis (Hubner). The study reported herein sought to establish the effectiveness of the insecticide sprays on reducing corn borer feeding and increasing yield. When corn borer populations were high, as in 2003 and 2004, both Capture and Intrepid were often effective in reducing damage from tunneling larvae. In 2005, however, when corn borer population levels were lower, insecticide application failed to produce significant reductions in corn borer tunneling. Yield increases were not detected when feeding reductions were observed. Of the nine fields sampled throughout the three-year study, no significant increases in yield were detected in plots receiving insecticides when compared to non-sprayed plots. The lack of yield increase may be due to the advanced maturity of Arkansas field corn when attacked by second generation corn borers. Ears on field corn that is planted during March and early April are generally at or near dent stage (R5) by mid-July, the time of attack by second generation corn borers in Arkansas. Of the nine fields sampled, the application of the foliar insecticides significantly reduced stalk lodging in five. Thus, foliar insecticide application may offer the Arkansas field corn producer a method of reducing plant lodging. Introduction The availability of transgenic field corn has been a major factor responsible for the increased acreage of field corn produced in Arkansas during the past decade. This corn possesses the Bacillus thuringiensis (Bt) protein gene that imparts resistance to both southwestern corn borers (SWCB), Diatraea grandiosella Dyar, and European corn borers (ECB), Ostrinia nubilalis (Hubner). Both insects are major pests of field corn produced in Arkansas and, prior to the use of Bt corn, yield losses in Arkansas were significant (1,4,5). One of the major concerns with the use of Bt field corn is the development of insects resistant to the Bt protein (2). Insects of concern include both corn borers along with the corn earworm [ Helicoverpa zea (Boddie), a pest of field corn], cotton, and many other crops. Because of this, the Environmental Protection Agency requires that 50% of field corn planted in the Cotton Belt, which includes all of Arkansas, be non-Bt or conventional. The susceptibility of the insects to Bt should be prolonged in corn borer populations that develop on conventional field corn. Farmers, particularly in eastern Arkansas, generally apply insecticides to foliage of conventional field corn to reduce damage from corn borers and to reduce yield losses. During the last few years two insecticides have been regularly applied for corn borer management. These are bifenthrin (Capture) and methoxyfenozide (Intrepid) (6). Although most conventional field corn produced in Arkansas now receives one or two foliar applications of insecticide, little information is currently available documenting the benefits of these management tactics. The objective of the study described herein was to evaluate the effectiveness of bifenthrin and methoxyfenozide against corn borers attacking conventional field corn in eastern Arkansas. Test Sites Three fields planted in conventional field corn were selected in eastern Arkansas during June 2003 and were designated HA (at Haynes, Lee Co.), PI (8 miles south of Piggott, Clay Co.), and FC (6 miles south of Forrest City, St. Francis Co.). In 2004, the PI and FC fields were located on the same farms as in 2003. The HA field was unavailable and was replaced with a field designated CL (9 miles west of Clarendon, Monroe Co.). The study was repeated in 2005 with fields located on the same farms as 2004 (Table 1). Soil type in all fields was sandy loam and all fields were irrigated as needed with the use of center pivot irrigation. No insecticide treatments were applied post-planting to any of the fields prior to the application of the study treatments. Additional information on cultivar, planting and application dates, and insecticides are listed in Table 1. Table 1. Field corn plot and insecticide application descriptions in eastern Arkansas, 2003-2005.
Insecticide Application Insecticide timing was based on the presence of emerging corn borer moths from pupae within field corn stalks. Within each field, stalks were searched for corn borer damage during late June of each year. When damage was observed, the stalk was split to find larvae and pupae. The first dark (mature) pupae were generally detected from 23 June (in 2005) to 7 July (in 2003). Insecticides were applied approximately 1 week later (Table 1). At application, developmental stage of the corn ranged from VT (tasseling) to R1 (Silking) growth stage (3). Insecticides included Intrepid 2 SC at 8 fl oz/acre and Capture 2 EC at 6.4 fl oz/acre. Sprays were applied with an Air Tractor 802 fixed wing aircraft callibrated to deliver 10 GPA with an 70-ft-wide spray. The adjuvant CS-7 was also used with each treatment at a rate of 0.25% by volume. Plots ran the length of each field and included two adjacent passes of the aircraft. Individual plot size ranged from 1.8 to 4.2 acres (Table 1). Experimental design was randomized complete block with 3 or 4 replications which varied due to field size. Data Collection Sampling was initiated on 13 August 2003. In subsequent years, samples were taken between 12 and 20 August. Ten plants from each plot were randomly selected and cut at the soil level. Stalks were split with a band saw and corn borer damage was assessed for each stalk area between plant nodes. This area was designated "internode." Any stalk with a single damaged internode was considered infested. Ear shanks were dissected and assessed for the presence or absence of tunneling. Although it was not possible to distinguish between damage resulting from first and second generation corn borers in the August sample, almost all of the detected damage appeared recent and was considered to be the result of second generation feeding. Data were analyzed with ANOVA and means were seperated with LSD (SAS Instituted Inc., Cary, NC). Lodging data were collected from all fields just prior to harvest in mid-August. Within each plot a row within the center 10 rows was randomly selected. After walking about 100 ft into the field, a 13-ft, 9-inch (1000th acre) length of the selected row was marked and the number of plants were counted. Each plant was categorized as lodged (broken stalk below the first ear) or not lodged. Data were converted to percentage lodged plants and analyzed as described above. At harvest, grain yield was determined for each plot by harvesting two 8-row-wide sections of corn with the farmer’s combine. The harvested section ran the length of the field and was generally taken from the center most rows of each plot. Harvest dates varied from 26 August to 8 September. The grain from each sample area was weighed with a University of Arkansas Cooperative Extension Service weigh wagon. The weights were corrected to 15.5% moisture, converted to bu/acre and analyzed as described above. 2003 Summary of Findings Delaying the sampling date until just prior to harvest provided the best indication of total corn borer feeding but prevented corn borer species identification as most insects had reached the adult stage and left the plant. From previous samples however, both ECB and SWCB occur at approximately equal frequencies at the PI, HA, and FC sites. ECB is more predominant at the CL site. Damage for corn borers was high in eastern Arkansas during 2003 and ranged from 55.0% (untreated plots at the HA location) to 70.0% (untreated plots at FC) of the sampled plants infested with corn borers (Table 2). At the HA site, no significant differences were detected among the insecticide treatments in percent infested plants (F = 1.16, P = 0.3256), percent of internodes damaged (F = 1.25, P = 0.2943), or percent shank damage (F = 1.43, P = 0.3265). Yield (F = 2.21, P = 0.2109) and percent of lodged plants (F = 0.20, P = 0.6779) also did not significantly differ among the treatments. The application of Intrepid at the PI site significantly reduced percent of infested plants (F = 6.49, P = 0.0128) and percent of internodes damaged (F = 13.58, P = 0.0004) (Table 2). Shank damage (F = 1.84, P = 0.1789), yield (F = 2.79, P = 0.1699), and lodged plants (F = 0.30, P = 0.6130), however, were not significantly reduced. Results were somewhat similar at the FC site during 2003. Both insecticides significantly reduced the percent of infested plants (F = 16.38, P < 0.0001) and percent of internodes damaged (F = 21.34, P < 0.0001). Again, yield was not increased in the plots receiving the insecticides. The FC site was the only field in which the insecticides significantly reduced plant lodging (F = 8.25, P = 0.0454). In plots receiving Intrepid or Capture, the percent of lodged plants was 1.5 and 2.0, respectively. Lodging in untreated plots was 11.7%. Table 2. Evaluation of foliar insecticides for corn borer management in field corn, 2003.
Column means within a location (HA, PI, or FC) followed by the same letter are not significantly different (P = 0.05, LSD). 2004 Summary of Findings Damage from corn borers was again high in eastern Arkansas during the 2004 season. In non-treated plots at the FC location, 90.0% of the plants were infested with corn borers as indicated by stalk tunneling (Table 3). The percent of damaged internodes in non-treated plots ranged from 6.3 at the CL location to 17.7 at FC. At the CL location, Intrepid application resulted in significant reductions in percent infested plants (F = 4.48, P = 0.0365) and percent damaged internodes (F = 7.22, P = 0.0082). However, no additional significant differences were detected among the other measured variables. The application of Intrepid at the PI location resulted in significant reductions in percent infested plants (F = 11.68, P = 0.0009), percent damaged internodes (F = 13.31, P = 0.0004), percent shank damage (F = 6.90, P = 0.0098), and lodging (F = 30.77, P = 0.0052). No significant differences were detected in yield (F = 5.13, P = 0.0861). At the FC location, no significant differences due to application of Capture were detected (Table 3). Table 3. Evaluation of foliar insecticides for corn borer management in field corn, 2004.
Column means within a location (CL, PI, or FC) followed by the same letter are not significantly different (P = 0.05, LSD). 2005 Summary of Findings During the 2005 season, corn borer population levels were much lower throughout the state than in the previous two years. The highest percent of infested plants (38.3) was detected in non-treated plots at the PI location (Table 4). No significant differences in percent infestation, percent damaged internodes, percent shank damage or yield were detected between treatments at any of the three locations. Each treatment, however, significantly reduced lodging, i.e., CL location F=2.89, P = 0.0245; PI location F=2.45, P = 0.0476; FC location F=3.15, P = 0.0165. Table 4. Evaluation of foliar insecticides for corn borer management in field corn, 2005.
Column means within a location (CL, PI, or FC) followed by the same letter are not significantly different (P = 0.05, LSD). Discussion When corn borer populations were high, as in 2003 and 2004, both Capture and Intrepid were often effective in reducing damage from tunneling larvae. These reductions were observed at the PI and FC locations during 2003 and at the CL and PI locations during 2004. In 2005 when corn borer population levels were lower, insecticide application failed to produce significant reductions in corn borer tunneling. Yield increases, however, were not detected when feeding reductions were observed. Of the nine fields sampled throughout the study, no significant increases in yield due to insecticide application were detected. The lack of yield increase may be due to the maturity of Arkansas field corn when attacked by second generation corn borers. Ears on field corn that is planted during March and early April are generally well formed (R5-R6) by mid-July, the time of attack by second generation corn borers in Arkansas (3). Small plot studies on later (May) planted field corn in eastern Arkansas have at times shown yield increases following July insecticide application for corn borer management (P. McLeod, unpublished data). When conventional field corn planting is delayed, the application of foliar insecticides may prove beneficial in reducing yield losses in Arkansas. Although yield is likely the greatest issue regarding the use of foliar insecticides in field corn, growers are continually faced with lodging problems at harvest. This greatly slows the harvest operations and many field corn growers consider lodging a major problem. Of the nine fields sampled the application of the foliar insecticides significantly reduced stalk lodging in five. Thus, foliar insecticide application may offer the Arkansas field corn producer a method of reducing lodging. Literature Cited 1. McLeod, P., and Studebaker, G. 2003. Major insect pests of field corn in Arkansas and their management. Pages 29-44 in: Corn Production Handbook. L. Espinoza and J. Ross, eds. Coop. Ext. Serv. MP 437, Univ. of Arkansas, Fayetteville, AR. 2. Onstad, D. W., Guse, C. A., Porter, P., Buschman, L. L., Higgins, R. A., Sloderbeck, P. E., Peairs, F. B., and Cronholm G. B. 2002. Modeling the development of resistance by stalk-boring Lepidopteran insects (Crambidae) in areas with transgenic corn and frequent insecticide use. J. Econ. Entomol. 95:1033-1043. 3. Ritchie, S. W., Hanway, J. J., and Benson, G. 1993. How a corn plant develops. Iowa Ext. Serv. Spec. Rep. No. 48. Iowa State Univ., Ames, IA. 4. Rolston, L. H. 1955. The southwestern corn borer in Arkansas. Ark. Agric. Exp. Stn. Bull. 553. Coll. of Agric., Food, and Life Sci., Univ. of Arkansas, Fayetteville, AR. 5. Studebaker, G., Johnson, D. R., and Jones, B. F. 1996. Control of Insects in Corn (Rev. Ed.). Coop. Ext. Serv. Fact Sheet FSA 7021, Univ. of Arkansas, Fayetteville, AR. 6. Thomson, W. T. 2000. Agricultural Chemicals - Book I: Insecticides, Acaracides, and Ovicides. Thomson Publications, Fresno, CA. |
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