Submitted to: Aflatoxin Elimination Workshop Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/25/2002
Publication Date: 5/1/2004
Citation: Dowd, P.F., Barnett, J., Bartelt, R.J., Beck, J.J., Berhow, M.A., Duvick, J.P., Kendra, D.F., Molid, G.A., White, G.A. 2004. Insect management for reduction of mycotoxins in Midwest corn. FY 2002 Report [abstract]. Proceedings of the Aflatoxin and Fungal Genomics Workshop/Mycopathologia 157(5):474.
Technical Abstract: Mycotoxin management studies: The computer program developed at USDA-ARS, NCAUR, to predict mycotoxin levels in Midwest corn has been well validated for fumonisin levels in three commercial fields in 2000 and seven fields in 2001 (most fields were planted with two hybrids) using the generalized values (a version using customized values is under development). In 2000, rainfall was relatively common and insect damage was limited. A predicted level of ca. 1.5 ppm compared well to actual field means of 0.8, 1.3, and 1.6 ppm for previously studied hybrids. In 2001, the climate was drier during the summer, and insect damage varied according to planting date, with later planted corn being more heavily damaged by European corn borers. For "early" plantings, predicted fumonisin levels (ca. 0.5 ppm) were close to actual means in fields (0.2, 0.3, 0.4, 0.4, 0.6 ppm) except for one field, which ran well below the predicted value. We have a tentative explanation for the lower values of this one field, which was restudied in 2002. Later planted corn encountered more insect damage, but predicted values of near 2.0 ppm compared well with actual values of 2.2, 2.2, and 4.2 ppm. No aflatoxin was predicted for 2000, and none was found. In 2001, predicted aflatoxin values of circa 10 ppm were higher than mean values found in some fields, although some individual samples had 2 to 10 ppm. Initially, equations used for aflatoxin prediction in the program were based on published values from 1983 and 1987; but we knew this data was probably not detailed enough (no insect damage levels available) to predict values very well (although predictions of negative occurrences have all been correct for years from 1992 through 2000 in the area monitored). The new data has allowed for adjustment in the program which will be checked against data collected in 2002, another year that the program has predicted aflatoxin may be present. The program is currently being converted from DOS Basic to a format that will run in Windows, with the intent of producing a version that is commercial quality. Seven commercial corn fields were intensively monitored for insects, mold inoculum, ear damage, and mycotoxins in 2002; nearly all fields had two hybrids. Fields had considerable variation in distribution of Fusarium subglutinans, F. proliferatum, and F. verticilliodes, as indicated by PCR analysis of material collected from leaf axils 7-10 days after pollination. However, all fields had at least some of each species present. Both corn earworms and European corn borers were common, but earlier planted fields escaped most of the corn borer damage in milk stage (which was above 80% in the late planted fields). Bt hybrids had less insect damage and symptomatic mold, and one Bt hybrid had significantly (10X) lower incidence of corn earworms than the corresponding nonBt hybrid. Symptomatic Fusarium mold was mostly associated with insect damage, except for one hybrid. Mycotoxin analyses are pending. Commercially available traps were again found to be suitable for monitoring sap beetles when tested in sweet corn. Commercially available dusky sap beetle pheromone (based on the patent of Bartelt and Dowd) was available this year for the first time, and was found to be essentially equivalent in attractancy to dusky sap beetles monitored in sweet corn as the pheromone synthesized in-house at NCAUR. Plant resistance: continued studies of functionally effective combinations of resistance mechanisms have produced significant increases in caterpillar mortality (increasing mortality 0 to 55%) when a digestive enzyme inhibiting protein was combined with a protein toxin. Compounds involved in Tex6 silk resistance to caterpillars were purified to near homogeneity, but insufficient quantities were available for NMR. Greater quantities of Tex6 silk were produced in 2002 for