|TOEWS, MICHAEL - University Of Georgia|
|BUNTIN, G. DAVID - University Of Georgia|
Submitted to: Corn Performance Tests
Publication Type: Experiment Station
Publication Acceptance Date: 10/15/2012
Publication Date: 11/29/2012
Citation: Ni, X., Toews, M.D., Buntin, G. 2012. Resistance of multiple ear-feeding insect resistance in 79 commercial corn hybrids in 2012. Corn Performance Tests. 101-4:35-39. Available: http://www.swvt.uga.edu/2012/cn12/AP101-4-insect.pdf.
Interpretive Summary: not required
Technical Abstract: Commercial corn hybrids were screened for ear and kernel feeding resistance to insect damage in the field at Tifton, GA. Nine of the top performing 23 hybrids (rated as VG in 2012) were developed utilizing YieldGard VecTran Triple technology (abbreviated as VT3 or VT3P). The hybrids with VT3 contain two Bt genes, while the hybrids with VT3PRO contain a stack of three Bt genes. Insect damage was moderate in the 2012 trial; the six groups of ear- and/or kernel-feeding insects in the order of infestation severity are: corn earworm and fall armyworm, stink bugs, sap beetles, pink scavenger caterpillar, and maize weevil. Multiple species of sap beetles were recorded in 2012. Corn earworm and fall armyworm feeding penetration in corn ears was between 0 and 2.7 cm, which was higher than in 2011 (0 - 1.7 cm), and lower than in 2010 (0.1 - 3.2 cm). Corn earworm and fall armyworm damage was combined because the damage was difficult to separate. Stink bug damage in 2012 was relatively high, ranging from 0 to 5.4% of the kernels per ear. The highest percentage of stink bug-discolored kernels in the previous five years ranged between 0.8 and 5.6%. Sap beetle damage was 0 - 0.3%, and pink scavenger caterpillar damage was 0 - 0.5% of the kernels in 2012. Losses to pink scavenger caterpillar and sap beetles were based on damage by possibly multiple generations of these insects as the crop matures in the field. Maize weevil infestation at harvest with 18% kernel moisture was low at 0 - 3 weevils per ear. The moderate insect damage might be related to relatively normal weather conditions in 2012 in comparison with the previous years. Because husk tightness and husk extension are considered important traits for ear- and kernel-feeding insect resistance, the husk features of the sampled ears were also examined in 2012. Husk tightness was assigned using a scale of 1 to 5, in which 1 = very loose and 5 = very tight. Because average rating for husk tightness was between 2.9 and 4.2, only medium (M = 2.9 - 3.9), and tight (T > 4) ratings are given in the table. Husk extension was between 0.5 and 5.7 cm. Corn earworm damage was negatively correlated to both husk tightness and husk extension in the 2012 data. The combined insect resistance ratings shown in the following table reflected cob damage by both corn earworm and fall armyworm. Multiple insect resistance was categorized in four groups according to the insect damage ratings on corn cobs and kernels; they are very good (VG), good (G), fair (F), and poor (P). VG represents the lowest amount of insect damage, while P represents the greatest amount of insect damage in 2012. The rankings of the 79 hybrids for multiple insect resistance in the table was based on the results of the principal components analysis using corn husk extension and tightness, and damage caused by corn earworm and fall armyworm, stink bugs, sap beetles, pink scavenger caterpillar, and maize weevil. The lettered ratings in the table refer only to relative resistance to insects and are not indicative of yield. Please refer to other reports for yield data. Hybrids resistant to multiple insects are highly recommended for planting and are the most economical means, especially in late plantings, for reducing insect related yield loss, as well as quality loss related to aflatoxin contamination. Consult with your county agent and/or extension entomologists for additional control recommendations for a specific pest in your area. The trial was planted on the University of Georgia Gibbs Research Farm near Tifton, GA on April 6, 2012, and harvested between August 27 and 30, 2012. Kernel moisture was approximately 18% at harvest. The experimental plots were thinned to 20,000 plants per acre and maintained using local Extension recommended agronomic practices by Penny Tapp and Trevor Perla (USDA-ARS, Tifton, GA).