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Insect Management & Insecticide Evaluations, Illinois 1996
Field, Forage, & Vegetable Crops

The effectiveness of Bt-corn hybrids for control
of European corn borer in Illinois, 1996

John T. Shaw, Michael E. Gray, Kevin L. Steffey and James W. Finger

Summary

A trial was established at the University of Illinois, Champaign, Illinois, to compare the effectiveness of Bt-corn hybrids to non-Bt corn of the same hybrid for control of European corn borer. Statistical differences in grain weight between Bt hybrids and non-Bt of the same hybrid were not apparent. In all comparisons, the Bt hybrids had significantly fewer plants with cavities and fewer inches of tunneling per plant than their non-Bt isoline. Some statistical differences in percentage of plants damaged, ear, and shank damage were apparent among Bt hybrids.

Plot Information and Methods

Location	University of Illinois Cruse Farm, Champaign, Illinois.
Plot Size	Each plot (n=100) consisted of 4 rows 30-inches wide by 40 feet long with 35 plants per row after thinning. There were 10 foot wide alleys between each of the 5 replications.
Experimental Design	The experimental design was a split plot with type of infestation (natural or manual) of European corn borer (ECB) as the main plots and 5 different Bt-corn hybrids and their non-Bt isolines as the subplots. Treatments were replicated 5 times.
Planting Date and Agronomic Factors	See Table 9.1.
Weather Information	See Appendix A, Table A.3, Table A.4, Table A.5, Table A.6 and Table A.7
Soil Information	See Appendix B
Manual ECB Infestation	All manual infestations were made to all plants (70 total) in the middle 2 rows of each plot. Manual ECB infestations to simulate the first-generation were made on July 3 and 6 at the V7 corn leaf stage (Richie et al. 1993) by applying approximately 50 neonate larvae in corn grit to the whorls of corn plants using a "bazooka" applicator. Manual ECB infestations to simulate the second-generation were made at corn anthesis on August 7, by applying approximately 25 neonate larvae in corn grit to the leaf exiles above and below the ear node. On August 8, 25 neonate larvae were applied to the ear node and the second leaf axil above the ear node.
Post-Infestation Evaluations of Injury	ECB1: On July 31, 20 consecutive plants from 1 of the middle 2 rows of each plot were rated for leaf feeding caused by the first generation ECB larvae using the 1 to 9 Guthrie Scale (Table 9.2). Guthrie Scale: No visible leaf injury. Small amount of shot-hole injury on a few leaves. Shot-hole injury common on several leaves. Several leaves with shot-holes and elongated lesions. Several leaves with elongated lesions. Several leaves with elongated lesions about 2.5 cm long. Long lesions common on about one-half of the leaves. Long lesions common on about two-thirds of the leaves. Most leaves with long lesions. ECB2: On October 9 and 10, 15 consecutive corn plants from 1 of the middle 2 rows were split with a corn knife for evaluation The number of plants with cavities and the total length of cavities per plant were recorded. The number of live larvae per plant was also recorded. The mean percentage of plants with cavities, the mean length of stalk tunneling (in inches) per plant, and the mean number of live larvae were determined for each plot (Table 9.3). ECB damage to the ear and shank were analyzed separately from the stalk damage data. An ear rating scale of 1 to 3 was used, with 1 being tip damage only, 2 being side damage only, and a rating of 3 being tip and side damage on the same ear (Table 9.4).
Harvest	Hand-harvested yields were determined from the shelled grain weights taken from the ears of the 15 dissected plants and corrected to 15.5% moisture. These grain weights were then added to the machine harvested weights (moisture corrected) for the remaining plants of the middle 2 rows in each plot on November 6 (Table 9.5). A Gleaner K harvester with electronic scales mounted in the hopper was used for the mechanical harvesting.
Statistical Analysis	Data were analyzed with the Pesticide Research Manager version 5.0, from Gylling Data Management, Inc.(GDM).
Results and Discussion	The amount of leaf feeding recorded for the first generation European corn borer (natural and manual) infestation was minimal, but it was apparent that the Bt hybrids had less feeding damage than did the non-Bt hybrids (Table 9.2). In all comparisons, the Bt hybrids had significantly fewer plants with cavities and fewer inches of tunneling per plant than their non-Bt complement (Table 9.3). The mean number of live larvae per plant was also significantly less for the Bt hybrids than for the non-Bt hybrids. Some statistical differences in percentage of plants with ear (tip and side) and shank damage were apparent among Bt hybrids and between Bt and non-Bt of the same hybrid (Table 9.4). Statistical differences in grain weight for both hand harvest and machine harvest between Bt hybrids and non-Bt of the same hybrid were not apparent (Table 9.5). Table 9.6 was included to show the variations in yields between natural infestation and manual infestation for both the Bt and non-Bt hybrids for the 1996 growing season.
References Cited	How a Corn Plant Develops, Special Report, No. 48, Iowa State University of Science and Technology, Cooperative Extension Service, Ames, Iowa. Ritche et al. Reprinted June, 1993.

Table 9.1: Agronomic factors for the efficacy trial comparing Bt-corn hybrids and their non-Bt hybrid companion Urbana, Illinois, 1996

Variables	Urbana
Planting date	May 24
Hybrids Cargill Ciba Monsanto Mycogen Northrup King	non-Bt Bt X 7570 X 7570 BT CG 4494 MAX 454 Ezra Ezra + EXP 4705 NG 7059 BT N 6800 X 6534 CBR
Plant population	Hand planted every 8 inches
Row spacing	30-inch
Previous crop	Corn (95)
Soil insecticides	Lorsban 4E broadcast preplant
Herbicides	none (hand weeded)
Fertilizer	N 150 lb/A 28%nitrogen
Fall tillage	chisel
Spring tillage	disk (once) field cultivator (once)
Cultivation date	June 27
Infestation dates ECB1 ECB2	July 3, 25 neonate larvae per plant July 6, 25 neonate larvae per plant August 7, 25 neonate larvae per plant August 8, 25 neonate larvae per plant
Evaluation dates Guthrie ratings Stalk splitting Hand-harvest Machine-harvest	July 31 October 9-10 October 9-10 November 6

Table 9.2 Mean Guthrie scale rating for manual and natural infestation for first-generation European corn borer,Urbana, 1996.¹

Variety	Mean Guthrie rating per plant²
Ezra	1.69
Ezra +	1.00
N 6800	1.48
X 6534 CBR	1.00
EXP 4705	1.12
NG 7059 BT	1.00
CG 4494	1.53
MAX 454	1.00
X 7570	1.29
X 7570 BT LSD (0.05) SEM	1.00 0.20 0.0183
¹ Manual infestation of 50 neonate larvae per plant for first-generation ECB were applied on July 3 and 6. ² All data were analyzed using a factorial AOV. It was determined there was no significant differences between manual and natural infestations, therefore, it is reported with these 2 factors combined (P=0.05,LSD).

Table 9.3 Mean percentage of plants with cavities, mean cavity length per plant, and mean number of live larvae per plant for first- and second-generation European corn borer in Bt and non-Bt corn, Urbana, 1996.¹

Variety	Mean % plants with cavities²	Mean cavity length per plant (inches)²	Mean number of live larvae per plant²
Ezra	99.30	7.94	1.73
Ezra +	6.00	0.10	0.02
N 6800	96.00	5.52	1.41
X 6534 CBR	0.67	0.01	0.01
EXP 4705	92.00	4.10	0.95
NG 7059 BT	46.67	1.15	0.27
CG 4494	92.67	6.01	1.43
MAX 454	34.00	0.85	0.31
X 7570	91.33	5.55	1.35
X 7570 BT LSD (0.05) SEM	4.00 10.58 0.9659	0.07 1.51 0.1375	0.01 0.40 0.0369
¹ Manual infestation of 50 neonate larvae per plant were applied on July 3 and 6 for first-generation and 50 neonate larvae on August 7-8 for second-generation. Evaluation date was October 9 and 10, 1996. ² All data was analyzed using a factorial AOV; it was determined there were no significant dfferences between manual and natural infestations and therefore it is reported with these 2 factors combined (P=0.05,LSD)

Table 9.4 Mean cavity length per ear shank, ear injury scale, mean percentage of ear-tip damage, and mean percentage of ear- side damage for Bt corn and non-Bt corn for first- and second-generation European corn borer, Urbana, 1996.¹

Variety	Mean cavity length per ear shank (inches)²	Ear injury scale^2,3	Mean % tip damage per 15 ears²	Mean % side damage per 15 ears²
Ezra	0.88	1.19	45.33	36.67
Ezra +	0.01	0.23	8.00	6.67
N 6800	0.83	0.90	46.00	22.00
X 6534 CBR	0.02	0.04	3.33	0.00
EXP 4705	0.69	1.29	50.00	38.67
NG 7059 BT	0.35	1.04	45.33	29.33
CG 4494	0.75	1.13	42.67	35.33
MAX 454	0.19	0.60	30.00	14.67
X 7570	0.67	1.30	56.67	36.67
X 7570 BT LSD (0.05) SEM	0.01 0.21 0.0195	0.21 0.34 0.0307	8.67 14.00 1.8072	6.67 12.66 1.6339
¹ Manual infestation of 50 neonate larvae per plant were applied on July 3 and 6 for first-generation and 50 neonate larvae on August 7-8 for second-generation. Evaluation date was October 9 and 10, 1996. ² All data was analyzed using a factorial AOV; it was determined there were no significant differences between manual and natural infestations and therefore it is reported with these 2 factors combined (P=0.05,LSD) ³Ear injury scale 1=tip feeding only, 2=side feeding only, 3=tip and side feeding.

Table 9.5 Mean yield (bu/A) of hand-harvested and hand + machine-harvested Bt corn and non-Bt corn for first- and second-generation European corn borer, Urbana, 1996.¹

Variety	Mean yield hand-harvest bu/A²	Mean yield hand + machine-harvest bu/A²
Ezra	110.3	112.07
Ezra +	128.1	113.88
N 6800	144.2	133.87
X 6534 CBR	126.3	120.10
EXP 4705	138.3	119.85
NG 7059 BT	125.8	113.93
CG 4494	119.2	110.93
MAX 454	140.8	125.23
X 7570	127.2	112.95
X 7570 BT LSD (0.05) SEM	146.4 29.8 2.7241	128.15 19.53 1.1669
¹Hand-harvested yields were determined from the shelled grain weights taken from the ears of the 15 dissected plants on October 9 and 10. The hand-harvested grain weights were added to the machine-harvested weights of all remaining plants of the middle 2 rows of the 4 row plots (5 replications) on November 6. All yields were adjusted to 15.5% moisture. ² All data was analyzed using a factorial AOV.; it was determined there were no significant differences between manual and natural infestations and therefore it is reported with these 2 factors combined (P=0.05,LSD)

Table 9.6 Mean yield (bu/A) for manual and natural European corn borer infestation (both generations) of Bt and non-Bt corn at Urbana, 1996.

Variety	Infestation¹	Yield bu/A²
Ezra	Natural	112.85
Ezra	Manual	111.28
Ezra +	Natural	99.75
Ezra +	Manual	128.00
N 6800	Natural	146.52
N 6800	Manual	121.22
X 6534 CBR	Natural	125.88
X 6534 CBR	Manual	114.33
EXP 4705	Natural	122.40
EXP 4705	Manual	117.31
NG 7059 BT	Natural	121.76
NG 7059 BT	Manual	106.10
CG 4494	Natural	118.19
CG 4494	Manual	103.66
MAX 454	Natural	130.09
MAX 454	Manual	120.37
X 7570	Natural	115.99
X 7570	Manual	109.91
X 7570 BT	Natural	137.48
X 7570 BT	Manual	118.82
¹ Manual infestation of 50 neonate larvae per plant were applied on July 3 and 6 for first-generation and 50 neonate larvae on August 7-8 for second-generation. Evaluation date was October 9 and 10, 1996. ²The hand-harvested grain weights were added to the machine-harvested weights of all remaining plants of the middle 2 rows of the 4 row plots (5 replications) on November 6. All yields were adjusted to 15.5% moisture.

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Insect Management & Insecticide Evaluations, Illinois 1996 Field, Forage, & Vegetable Crops

The effectiveness of Bt-corn hybrids for control of European corn borer in Illinois, 1996

Insect Management & Insecticide Evaluations, Illinois 1996
Field, Forage, & Vegetable Crops

The effectiveness of Bt-corn hybrids for control
of European corn borer in Illinois, 1996