Multiple insect resistance in 53 commmercial corn hybrids - 2015

Authors: Ni, Xinzhi; TOEWS, MICHAEL - University Of Georgia; BUNTIN, G - University Of Georgia

Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 10/26/2015
Publication Date: 10/30/2015
Citation: Ni, X., Toews, M.D., Buntin, G.D. 2015. Multiple insect resistance in 53 commmercial corn hybrids - 2015. Georgia 2015 Corn Performance Tests, Georgia Agricultural Experiment Stations, Annual Publication 101-7, pp. 33-36. Athens, GA, October 2015. http://www.swvt.uga.edu/2015/cn15/AP101-7insect.pdf

Interpretive Summary: not required

Technical Abstract: Commercial corn hybrids were screened for ear- and kernel-feeding insect resistance under field conditions at Tifton, GA. Fifteen hybrids were rated Very Good (VG), the highest rating for multiple insect resistance in 2015 (Table 1). Sixteen were Good (G), 9 were Fair (F), and 13 were Poor (P). Two hybrids included a blend of 80% transgenic and 20% non-transgenic seeds, known as refuge in a bag (RIB). Six hybrids were developed utilizing YHR traits (also known as Optimum® Intrasect™), 9 hybrids have Genuity VT Double PRO (VT2P) traits, and 3 hybrids have VT Triple PRO (VT3P) traits. The Optimum® Intrasect™ insect protection traits (or YHR) include a combination of two insect protection traits – Herculex® I and YieldGard® Corn Borer, while the VT2P or VT3P traits contain a stack of two or three Bt genes. VT2P hybrids targeted foliar- and ear-feeding lepidopteran pests, while VT3P hybrids have an additional Bt gene for rootworms. Overall insect damage was moderate in the 2015 trial. The six types of ear- and/or kernel-feeding insects in the order of damage severity were: corn earworm and fall armyworm, stink bugs, sap beetles, pink scavenger caterpillar, and maize weevil. Corn earworm and fall armyworm damage was combined because the damage is difficult to separate. Feeding penetration by these caterpillar pests of natural infestations in corn ears was between 0.1 and 2.1 cm, which was less than the damage observed in 2014 (0.2-4.3 cm). Multiple species of sap beetles were recorded in 2015. Stink bug damage in 2015 was relatively low, ranging from 0.1 to 1.4% of the kernels per ear. Percentage of stink bug-discolored kernels in previous years ranged between 0.8 and 5.6%. Sap beetle damage was 0.3-2%, which is greater than 0.4-1.1% in 2014, and pink scavenger caterpillar damage was about 0-0.5% in 2015, which was less than 2014 (0-1% of the kernels). Maize weevil infestation at harvest with 18% kernel moisture was also seldomly observed in 2015. The high level of sap beetle damage, as well as relatively low level of the stink bug damage, may have been influenced by both planting time and weather conditions in 2015. In addition, flowering time of all entries were similar (between 53 and 55 days after planting), irrespective of categorization of Short (S) or Medium (M) maturity as shown in Table 1. The phenomenon observed in 2015 could be the result of relatively late planting date (April 23, 2015) in combination with high temperature during the first 51 day after planting. In 2015,730 degree days were recorded from April 23 to June 13 (using 60°F as base temperature), while in 2014, 595 degree days were recorded from April 17 to June 7. 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 examined. Husk tightness was assigned using a scale of 1 to 5, in which 1 = very loose and 5 = very tight. Average ratings for husk tightness were between 3.4 and 4, which were all considered medium for husk tightness. Husk extension ranged between 0.25 and 1.5 cm, and was negatively correlated to worm penetration and percentage of sap beetle-damaged kernels in corn ears, but not to husk tightness. 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 least amount of insect damage, while P represents the greatest amount of insect damage. The rankings of the 53 hybrids for multiple insect resistance in the table was based on the results of the principal component analysis using corn husk extension and tightness along with 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 rel