Submitted to: Corn Performance Tests
Publication Type: Experiment Station
Publication Acceptance Date: 10/30/2007
Publication Date: 1/22/2008
Citation: Ni, X., Krakowsky, M.D., Buntin, G., Brown, S.L. 2007. Evaluation of insect resistance among 47 commercial corn hybrids - 2007. Georgia 2007 Corn Performance Tests, Research Report 712, Georgia Agricultural Experiment Stations. Interpretive Summary: not required
Technical Abstract: During the growing season of 2007, the dry environmental conditions in Tifton, Georgia were favorable for the rapid buildup of all insect populations in the irrigated experimental plots, providing the potential for considerable damage to the corn crop. Seven ear-feeding insects recorded in the order of infestation severity were: the corn earworm and the fall armyworm, the pink scavenger caterpillar and the sap beetles, the southern green and brown stink bugs, and the maize weevil. Total insect damage ratings were based on corn earworm and fall armyworm damage ratings and added kernel damage by the maize weevil, the stink bugs, the pink scavenger caterpillar, and the sap beetles. Overall insect resistance ratings were grouped into five categories; they were very good (VG), good (G), fair (F), poor (P), and very poor (VP) as shown in the table. While VG represents the lowest amount of insect damage, VP represents the greatest amount of insect damage. Losses to maize weevil, pink scavenger caterpillar and sap beetles were based on damage by multiple generations of these insects as the crop matures in the field. Corn earworm and fall armyworm damage was combined because the damage was hard to separate, so was pink scavenger and sap beetle damage. Corn earworm and fall armyworm feeding penetration in corn ears on the 47 hybrids was between 0.7 and 3.7 cm, which was lower than what we observed in 2006 (2.6 - 6.7 cm). Stink bug damage in 2007 (0.02-2% of discolored kernels) was similar to the data recorded in 2006 (0-1.5%). Other insect damage was similar between 2006 and 2007. Pink scavenger and sap beetle damage was 0.1-2.6% of the total number of kernels in 2007, and 0.1-3.2% in 2006, and maize weevil damage was 0.1-0.8% in 2007, and 0-0.6% in 2006. The most important insects were the corn earworm and the fall armyworm, which caused the greatest kernel loss among all ear-feeding insects examined. Some of the transgenic Bt hybrids showed poor insect resistance ratings (with deep ear penetration), which could be caused by the fact that transgenic events in these hybrids might confer resistance to one species or the other but not to both species. Timely harvest can substantially reduce losses caused by these two insects. Rankings of the 47 hybrids for their resistance to the major ear-feeding insects (i.e., corn earworm and fall armyworm, pink scavenger caterpillar and sap beetles, maize weevil, and stink bugs) are given in the following table. The lettered ratings in the table refer only to relative resistance to insects and are not indicative of yield. Please refer to the yield data in other tests for specific information. During the damage evaluation in 2007, two physical features (i.e., husk tightness and husk extension) of corn ears were examined. 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 is between 3.8 and 4.7, only loose (L), medium (M), and tight (T) ratings are given in the table. Husk extension was between 2.7 and 8.2 cm. The insect damage was not correlated to husk features according to the data collected in 2007. Hybrids resistant to insects are highly recommended for planting and are presently the most economical means, especially in late plantings, for the reduction of ear-feeding insect damage. Consult your local county agent and/or extension entomologists for additional control recommendations for a specific insect pest in your region. All entries were planted on April 11, 2007 and harvested on September 10, 2007. Plots were thinned to 20,000 plants per acre. Data for this section were collected by J. C. Mullis (USDA-ARS, Tifton, GA), Wesley Pope, Nathan Hill, and Kristoffer Wright (University of Georgia, Tifton, Georgia).