Seasonality may be the single greatest constraint to the expansion of local vegetable production (Offner, 2011). The impact is especially critical for certain vegetables that might contribute to farm-to-school marketing programs. Such programs connect schools with local farms to improve the nutrition of school meals, increase agricultural literacy, and support local producers (Kish, 2008). For example, seasonal availability was the main perceived obstacle to increasing local food usage in a survey of Maryland schools (Dimitri et al., 2012).
Oklahoma is representative of the south-central United States, where fresh sweet corn primarily is a summer crop. Historically, production of a fall sweet corn crop in this region (that would be available during the typical September to December fall semester of a school year) has been constrained by insect pressure. The primary pests are Lepidoptera larvae, chiefly fall armyworm (Spodoptera frugiperda) and corn earworm (Helicoverpa zea) (Brandenberger et al., 2014). Transgenic sweet corn cultivars that express the CryIA(b) toxin from the bacterium Bt have been available since about 1998 (Lynch et al., 1999a). These Bt sweet corn cultivars have provided excellent control of Lepidoptera larvae (Burkness et al., 2002; Lynch et al., 1999b; Musser and Shelton, 2003), thereby increasing the chances of a successful fall crop. While larval densities typically are reduced on transgenic sweet corn compared with non-Bt corn, damage is not completely eliminated (Burkness et al., 2002; Farrar et al., 2009). Therefore, programs that combine transgenic cultivars and chemical insecticides have been tested to further reduce insect damage (Farrar et al., 2009; Lynch et al., 1999b; Musser and Shelton, 2003; Speese et al., 2005). However, these tests have not occurred under the combination of hot weather and high pest densities typical of the fall production season for sweet corn in the south-central United States. Further, investigators have focused on insect damage and have not considered other marketability factors, particularly cob fill and the degree of kernel development, which may be adversely affected by high temperatures.
A transgenic yellow sweet corn cultivar, GSS-0966, that expresses the CryIA(b) toxin (Nuessly et al., 2007) has been shown to be well adapted to Oklahoma conditions during the traditional (April to July) growing season. More information is needed on stand establishment and crop development of this cultivar during the hot summer months. Some potential customers for fall sweet corn may be concerned about the use of a genetically engineered cultivar. Therefore, we included ‘Garrison’, a nontransgenic near-isoline of ‘GSS-0966’, in one of our experiments. Customers, particularly schools, also may desire corn grown using insecticides with relatively low mammalian toxicity, or those listed by the Organic Materials Review Institute (OMRI). OMRI-listed insecticides include botanicals, microbials, insecticidal soaps, and semiochemicals (Balusu and Fadamiro, 2012). Therefore, we included some less toxic insecticides in two of our experiments. Insecticides and fungicides used across the 3-year study are given in Table 1.
Insecticides and fungicides used in research on fall sweet corn from 2010 to 2012 at Bixby and Stillwater, OK.
The overall objectives of this study were to 1) manipulate seeding rates and planting dates so as to achieve successful stand establishment of sweet corn in the summer and an extended harvest period during the fall, and 2) study the use of a transgenic cultivar and various insecticides with the goal of producing fall sweet corn ears that will meet fresh market standards.
Balusu, R.R. & Fadamiro, H.Y. 2012 Evaluation of organically acceptable insecticides as stand-alone treatments and in rotation for managing yellowmargined leaf beetle, Microtheca ochroloma (Coleoptera: Chrysomelidae), in organic crucifer production Pest Mgt. Sci. 68 573 579
Borror, D.J., DeLong, D.M. & Triplehorn, C.A. 1976 An introduction to the study of insects. 4th ed. Holt Rinehart Winston, New York, NY
Brandenberger, L., Kahn, B. & Rebek, E. 2014 Sweet corn production. Coop. Ext. Serv., Oklahoma State Univ., Stillwater, OK, HLA-6021
Brooking, I.R. & McPherson, H.G. 1989 The impact of weather on the scheduling of sweet corn for processing. 1. Quantifying the link between rate of development and the environment N. Z. J. Crop Hort. Sci. 17 19 26
Burkness, E.C., Hutchison, W.D., Weinzierl, R.A., Wedberg, J.L., Wold, S.J. & Shaw, J.T. 2002 Efficacy and risk efficiency of sweet corn hybrids expressing a Bacillus thuringiensis toxin for Lepidopteran pest management in the midwestern US Crop Prot. 21 157 169
Dimitri, C., Hanson, J.C. & Oberholtzer, L. 2012 Local food in Maryland schools: A real possibility or a wishful dream? J. Food Distrib. Res. 43 112 128
Farrar, R.R. Jr, Shepard, B.M., Shapiro, M., Hassell, R.L., Schaffer, M.L. & Smith, C.M. 2009 Supplemental control of lepidopterous pests on Bt transgenic sweet corn with biologically-based spray treatments J. Insect Sci. 9 1 8
Garcia y Garcia, A., Guerra, L.C. & Hoogenboom, G. 2009 Impact of planting date and hybrid on early growth of sweet corn Agron. J. 101 193 200
Kish, S. 2008 From farm to school: Improving small farm viability and school meals. NRI Res. Highlights 2008. 19 Apr. 2016. <http://naldc.nal.usda.gov/catalog/15377>
Lynch, R.E., Wiseman, B.R., Plaisted, D. & Warnick, D. 1999a Evaluation of transgenic sweet corn hybrids expressing CryIA (b) toxin for resistance to corn earworm and fall armyworm (Lepidoptera: Noctuidae) J. Econ. Entomol. 92 246 252
Lynch, R.E., Wiseman, B.R., Sumner, H.R., Plaisted, D. & Warnick, D. 1999b Management of corn earworm and fall armyworm (Lepidoptera: Noctuidae) injury on a sweet corn hybrid expressing a cryIA (b) gene J. Econ. Entomol. 92 1217 1222
Malvar, R.A., Revilla, P., Velasco, P., Cartea, M.E. & Ordás, A. 2002 Insect damage to sweet corn hybrids in the south Atlantic European coast J. Amer. Soc. Hort. Sci. 127 693 696
Nuessly, G.S., Scully, B.T., Hentz, M.G., Beiriger, R., Snook, M.E. & Widstrom, N.W. 2007 Resistance to Spodoptera frugiperda (Lepidoptera: Noctuidae) and Euxesta stigmatias (Diptera: Ulidiidae) in sweet corn derived from exogenous and endogenous genetic systems J. Econ. Entomol. 100 1887 1895
Speese, J. III, Kuhar, T.P., Bratsch, A.D., Nault, B.A., Barlow, V.M., Cordero, R.J. & Shen, Z-X. 2005 Efficacy and economics of fresh-market Bt transgenic sweet corn in Virginia Crop Protection 24 57 64
Williams, M.M. II 2008 Sweet corn growth and yield responses to planting dates of the north central United States HortScience 43 1775 1779