Multiple insect resistance in 53 commercial corn hybrids, 2018

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

Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 11/15/2018
Publication Date: 11/26/2018
Citation: Ni, X., Toews, M.D., Buntin, G. 2018. Multiple insect resistance in 53 commercial corn hybrids, 2018. In: D.J. Mailhot, D. Dunn, H. Jordan Jr., and J.L. Day (eds.). Georgia 2018 Corn Performance Tests, Georgia Agricultural Experiment Station Publication 101-10, pp. 32-35.

Interpretive Summary: not required.

Technical Abstract: Commercial corn hybrids were screened for ear- and kernel-feeding insect resistance under field conditions at Tifton, Georgia, and the results are summarized in the following table. Of the 33 mid-season hybrids, nine were rated very good (VG), the highest rating for multiple insect resistance in 2018; 11 were good (G); seven were fair (F), and six were poor (P). Among the 20 short-season hybrids, five entries each were rated as VG, G, F, and P, respectively. Two hybrids were developed utilizing SmartStax™ technology; five hybrids have YHR traits (also known as Optimum® Intrasect™); 15 hybrids have Genuity VT Double PRO (VT2P) traits; and four 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. Corn rootworms and corn borers were not present at Tifton during these tests in 2018. Overall insect damage on corn ears was relatively high in the 2018 trial, compared to observed damage in 2016 and 2017. The six types of ear- and/or kernel-feeding insects in 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 as symptoms between these two pests are very similar. Feeding penetration by these caterpillar pests of natural infestations in corn ears was between 0 and 5.6 cm per experimental plot, which was greater than the damage observed in 2017 (0.2-2.8 cm). Stink bug damage at the plot level in 2018 was also high, ranging from 0 to 22.6% of the kernels per ear, which was greater than that in 2017 (0.1 to 1.6%). Multiple species of sap beetles were recorded in 2018. Sap beetle damaged kernels were 0-40% per plot, which is much greater than 0.7-4.1% in 2017. Kernel damage by the pink scavenger caterpillar and maize weevil was relatively low in 2018, which was 0-5.8% and 0-2.8%, respectively. In addition, flowering time among all entries was similar (between 63 and 69 days after planting), irrespective of categorization of mid- (M) or short- (S)season maturity as shown in the table. The late flowering in 2018 in comparison to 2017 (50-57 days after planting) reflects the relatively cool and wet weather conditions before pollination at the Tifton location in 2018. Because corn husk tightness and 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 and 5, which were all considered medium for husk tightness. Husk extension ranged from 0 to 4.8 cm. Both husk tightness and extension were negatively correlated to overall insect damage ratings in 2018. 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 all hybrids for multiple insect resistance in the table was based on the results of the principal component analysis using corn husk tightness and extension along with ear damage (by corn earworm and fall armyworm penetration listed in table) and kernel damage (by stink bugs, sap beetles, pink scavenger caterpillar, and maize weevil). Although kernel feeding insect damage data are not listed in the table, the results were included in data analysis and overall rankings. The data in this report are not indica