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United States Department of Agriculture

Agricultural Research Service

Title: Insect Screening Results: Assessment of Corn Hybrids for Insect Resistance

Authors
item Ni, Xinzhi
item Krakowsky, Matthew
item Gunawan, Gunawanti - UNIV OF GA
item Buntin, David - UNIV OF GA
item Brown, Steve - UNIV OF GA

Submitted to: Corn Performance Tests
Publication Type: Experiment Station
Publication Acceptance Date: October 18, 2006
Publication Date: November 1, 2006
Citation: Ni, X., Krakowsky, M.D., Gunawan, G., Buntin, D., Brown, S. 2006. Insect Screening Results: Assessment of Corn Hybrids for Insect Resistance. Georgia 2006 Corn Performance Tests, Research Report 707, Georgia Agricultural Experiment Stations. p. 36-37.

Interpretive Summary: not required

Technical Abstract: During the growing season of 2006, the relatively dry environmental conditions in Tifton, Georgia were favorable for the rapid buildup of corn earworms, providing the potential for considerable damage to the corn crop. Six ear-feeding insects recorded in the order of infestation severity were: the corn earworm and the fall armyworm, the pink scavenger caterpillar, the maize weevil, the sap beetles, and the southern green and brown stink bugs. In contrast to 2005, stink bug damage was very low (only 0-1.5% of discolored kernels) in 2006. The most important insect was the corn earworm, which caused the greatest kernel loss among all ear-feeding insects examined. The corn earworm and fall armyworm feeding penetration in corn ears on the 58 hybrids was between 2.6 and 6.7 cm. Because the ear-feeding damage caused by the corn earworm and the fall armyworm was hard to separate, the penetration measurement included the feeding damage by both species. Some of the transgenic Bt hybrids showed poor insect resistance ratings (with deep ear penetration), which could be caused by the fact that these hybrids might only be resistant to either species but not to both species. The maize weevil damage was between 0 and 0.5%, while pink scavenger damage was between 0.1 and 3% of the total number of kernels. Insect resistance was rated by amount of total insect damage using 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 least amount of insect damage, VP represents the most amount of insect damage. Losses to the pink scavenger caterpillar and the maize weevil were based on damage by multiple generations of these insects as the crop dries in the field. Timely harvest can substantially reduce losses caused by these two insects. Rankings of the 58 hybrids for their resistance to the five main ear-feeding insects (i.e., the corn earworm and the fall armyworm, the pink scavenger caterpillar, the maize weevil and the stink bugs) are given in the following table. The lettered ratings in the tables 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 process, husk tightness ratings were 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 3.6 and 4.5, only loose (L), medium (M), and tight (T) ratings are given in the table. 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 7, 2006 and harvested on September 1, 2005. Plots were thinned to 20,000 plants per acre. Data for this section were compiled by J. C. Mullis, M. McDaniel, and H. Hilton working at the University of Georgia, Tifton, Georgia.

Last Modified: 7/10/2014
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