The Effectiveness of Bt-corn Varieties for the Control of European Corn Borer in Illinois, 2000
John T. Shaw, Kevin L. Steffey, and Michael E. Gray

Summary

Plot Information and Methods

Location

University of Illinois Cruse Farm, Champaign, Illinois.

Plot Size

Four rows ´ 25 ft for each treatment, with 30 plants per row after thinning. Between each of the replications was a 10-ft alley.

Experimental Design

Randomized complete block with four replications.

Planting Dates and Agronomic Factors

Refer to Table 6.1.

Manual Infestation of European Corn Borer Larvae

Manual infestations of European corn borer (ECB) larvae were made to all plants in each of the middle two rows of each four-row plot. Manual infestations to simulate the first-generation were made on July 11 and 12 by applying five egg masses (black-head stage) per plant whorl on each of the two days. Corn plants were in the V6 leaf stage (Ritchie et al. 1993). Manual infestations to simulate the second generation were made to the same plants in the same two rows, at corn anthesis (V18 - VT corn stage, Ritchie et al. 1993). Three egg masses (black-head stage) per plant per day were applied on August 16 and 18.

Post-Infestation Evaluations of Injury Caused by First- and Second-Generation ECB

Evaluation of first-generation corn borer injury:
On July 31, 10 plants in each of the center two rows that had been manually infested were evaluated using the 0-9 modified Guthrie scale:

0. No visible leaf feeding

1. Small amount of pin-hole or fine shot-hole injury on a few leaves

2. Small amount of shot-hole injury on a few leaves

3. Shot-hole injury common on several leaves

4. Several leaves with shot holes and elongated lesions

5. Several leaves with elongated lesions

6. Several leaves with elongated lesions about 2.5 cm long

7. Long lesions common on about one-half of the leaves

8. Long lesions common on about two-thirds of the leaves

9. Most leaves with long lesions

Evaluations of first- and second-generation corn borer injury:
On September 9 and 10, five corn plants from each of the middle two rows were split with a corn knife for evaluation. Evaluations of injury to the ear, ear shank, stalk above the ear, and stalk below the ear were recorded separately for each plant. The mean percentages of plants with cavities, mean numbers of cavities per plants, mean lengths of stalk tunneling (cm) per plant and mean numbers of live larvae per plant were recorded.

Weather Information

Refer to Appendix A, Table A.1, Table A.2 and Table A.3.

Statistical Analysis

Data were analyzed with Agriculture Research Manager (ARM) version 6.1.6, from Gylling Data Management, Inc. (GDM). Means were separated by Duncan's New Multiple Range Test (MRT) (P = 0.05).

Results and Discussion

All plots were examined periodically throughout the growing season for signs of infestation and/or injury caused by insects other than European corn borer. Nothing was found in sufficient quantity to analyze, so the data are not presented.

Results from evaluations of first-generation European corn borer injury are presented in Table 6.2. The mean Guthrie ratings for all Bt hybrids were significantly lower than the mean Guthrie ratings for the non-Bt isolines. There were no significant differences in Guthrie ratings among the Bt hybrids tested.

The percentages of plants injured by European corn borer larvae are presented in Table 6.3. The mean numbers of larvae, mean numbers of cavities, and mean cavity lengths (cm) per plant are presented in Table 6.3 (whole plant), Table 6.4 (plant below the ear), and Table 6.5 (plant above the ear). The mean numbers of larvae per shank and ear, mean numbers of cavities per shank, and mean percentage of ears injured are presented in Table 6.6.

The percentages of non-Bt plants with injury caused by European corn borer larvae indicated that the infestation in our trial was severe; 70 to 100 % of the non-Bt plants were injured (Table 6.3). The percentages of plants injured by corn borer larvae were significantly lower for all Bt hybrids than for all non-Bt isolines. One Bt hybrid (CBH-351) had a significantly higher percentage of injured plants than the other Bt hybrids. All Bt hybrids had significantly fewer cavities per plant than the non-Bt isolines. The mean numbers of larvae per plant were significantly lower in all Bt hybrids than in all but two non-Bt isolines (LEPOTD 11 and CBH-351 non-Bt). There were no significant differences in mean numbers of larvae per plant among the Bt hybrids. The mean cavity lengths per plant were significantly lower in all Bt hybrids than in all but one non-Bt isoline (LEPOTD 11). There were no significant differences in mean cavity length per plant among the Bt hybrids. Evaluations of the amount of injury below and above the ears are presented in Table 6.4 and Table 6.5, respectively. The mean numbers of larvae per plant and mean numbers of cavities per plant below the ear for all Bt hybrids were significantly lower than in all but one non-Bt isoline (Y non-Bt-larvae; CBH-351 non-Bt-cavities) (Table 6.4). There were no significant differences in numbers of larvae or numbers of cavities per plant below the ear among the Bt hybrids. The mean cavity lengths per plant below the ear for all Bt hybrids were significantly lower than in all but two non-Bt isolines (LEPOTD 11 and CBH-351 non-Bt) (Table 6.4). There were no significant differences in mean cavity lengths per plant below the ear among the Bt hybrids.

The mean numbers of larvae per plant above the ear for all Bt hybrids were significantly lower than in all but two non-Bt isolines (Y non-Bt and CBH-351 non-Bt) (Table 6.5). There were no significant differences in numbers of larvae per plant above the ear among the Bt hybrids. The mean numbers of cavities per plant above the ear for all Bt hybrids were significantly lower than in all but one non-Bt isoline (CBH-351 non-Bt) (Table 6.5). There were no significant differences in numbers of cavities per plant above the ear among the Bt hybrids. The mean cavity lengths per plant above the ear for all Bt hybrids were significantly lower than for all non-Bt isolines (Table 6.5). There were no significant differences in mean cavity lengths per plant above the ear among the Bt hybrids.

Evaluations for numbers of European corn borer larvae and amount of injury to shanks and ears are shown in Table 6.6. There were no larvae, and consequently there was no injury in any of the shanks of the Bt hybrids. The numbers of larvae and numbers of cavities in the non-Bt isolines were very low. No corn borer larvae were found in any of the ears of the Bt hybrids. However, 2.5% of the ears of one Bt hybrid (CBH-351 Bt) have evidence of injury, although not significantly more than the amount of injury in the other Bt hybrids. There were no significant differences in the mean numbers of larvae and mean numbers of cavities per shank, the mean numbers of larvae per ear, and the mean percentages of ears injured among the Bt hybrids.

Few stalks were broken either above or below the ears, and no ears were found on the ground at evaluation time. Also, we observed no differences in the amount of stalk rot at the time of evaluation.

Similar to our results from Bt-corn efficacy trials in the past, the Bt-corn varieties in this year's trial were quite effective in reducing the numbers of European corn borer larvae and the amount of injury they caused to the stalks, shanks, and ears. However, CBH-351 Bt had a significantly higher percentage of plants injured (27.5%) than the other Bt hybrids.

References Cited

Ritche, S.W., J.J. Hanway, and G.O. Benson. 1993. How a corn plant develops. Special Report No. 48, Iowa State University of Science and Technology, Cooperative Extension Service, Ames.

Table 6.1: Agronomic factors and evaluation dates for the Bt-corn efficacy trial for control of European corn borer Champaign, Illinois, 2000

Variables

Urbana

Planting date

June 9, 2000

Hybrid

Various Bt and Non-Bt hybrids

Plant population

30 plants per 25 row feet after thinning

Row spacing

30 inches

Soil condition (top 2-3 inches)

Moist

Soil temperature (4-inch level)

68°F

Air temperature

79°F

Wind

0 - 5 mph

Previous crop

Soybeans

Soil insecticide

None

Herbicides

Dual + Atrazine

Infestation Dates

First Generation

July 11 and 12, 2000 (V6 plant stage)

5 egg masses per plant per date

Second Generation

August 16 and 18 (Anthesis)

3 egg masses per plant per date

Evaluation dates:

Guthrie Rating

July 31, 2000

Stalk splitting

September 9 and 10, 2000

Table 6.2 Guthrie ratings for the Bt-corn efficacy trial for control of first-generation European corn borer Champaign, Illinois, 2000

Treatment¹

Guthrie rating²

Cry 1F / TC1507 / M2722

0.01

c

M2722 non-Bt isoline

5.70

a

Y Bt

0.05

c

Y non-Bt isoline

5.60

a

LEPOTD 11 non-Bt

0.55

c

LEPOTD 12

0.00

c

LEPOTD 13

0.05

c

LEPOTD 14

0.00

c

LEPOTD 18

0.15

c

LEPOTD 19 non-Bt

5.95

a

CBH-351 Bt

0.10

c

CBH-351 non-Bt isoline

3.80

b

¹ Cry 1F and its isoline was supplied by Dow AgroSciences;
all LEPOTD hybrids were supplied by Monsanto;
and the CBH-351 hybrids were supplied by Aventis.

² The modified Guthrie rating scale is explained in the text.
Means in a column followed by the same letter are not
significantly different (P=0.05; Duncan's New MRT).

Table 6.3 Mean numbers of larvae, cavities, and cavity length (cm) per plant for the Bt-corn efficacy trial for control of first and second-generation European corn borer Champaign, Illinois, 2000^1,2

Treatment

% Injured
plants

Mean no. of
larvae
per plant

Mean no. of
cavities
per plant

Mean cavity
length (cm)
per plant

Cry 1F / TC1507 / M2722

0.0

e

0.0

c

0.0

d

0.0

e

M2722 non-Bt isoline

92.5

ab

0.8

b

2.3

bc

8.2

bc

Y Bt

2.5

e

0.0

c

0.1

d

0.1

e

Y non-Bt isoline

100.0

a

1.2

b

2.8

b

10.5

b

LEPOTD 11 non-Bt

70.0

c

0.6

bc

1.7

c

3.3

de

LEPOTD 12

5.0

e

0.0

c

0.1

d

0.1

e

LEPOTD 13

2.5

e

0.0

c

0.0

d

0.0

e

LEPOTD 14

2.5

e

0.0

c

0.0

d

0.0

e

LEPOTD 18

0.0

e

0.0

c

0.0

d

0.0

e

LEPOTD 19 non-Bt

96.7

a

2.0

a

4.8

a

15.2

a

CBH-351 Bt

27.5

d

0.1

c

0.3

d

1.0

e

CBH-351 non-Bt isoline

80.0

bc

0.7

bc

1.7

c

5.5

cd

¹ Cry 1F and its isoline was supplied by Dow AgroSciences; all LEPOTD hybrids were supplied by Monsanto; and the CBH-351 hybrids were supplied by Aventis.
² Means in a column followed by the same letter are not significantly different (P=0.05; Duncan's New MRT).

Table 6.4 Mean numbers of, larvae, cavities, and cavity length (cm) per plant, below the ear for the Bt-corn efficacy trial for control of first and second-generation European corn borer Champaign, Illinois, 2000

Treatment²

Injury below the ear¹

Mean no. of
larvae per plant

Mean no. of
cavities per plant

Mean cavity
length (cm) per plant

Cry 1F / TC1507 / M2722

0.0

d

0.0

e

0.0

d

M2722 non-Bt isoline

0.5

bc

1.3

c

4.7

b

Y Bt

0.0

d

0.1

e

0.1

c

Y non-Bt isoline

0.9

b

2.1

b

8.0

a

LEPOTD 11 non-Bt

0.1

cd

0.5

de

0.9

c

LEPOTD 12

0.0

d

0.1

e

0.1

c

LEPOTD 13

0.0

d

0.0

e

0.0

c

LEPOTD 14

0.0

d

0.0

e

0.0

c

LEPOTD 18

0.0

d

0.0

e

0.0

c

LEPOTD 19 non-Bt

1.3

a

3.2

a

10.4

a

CBH-351 Bt

0.1

d

0.3

e

0.8

c

CBH-351 non-Bt isoline

0.4

bcd

1.1

cd

3.5

b

¹ Means in a column followed by the same letter are not significantly different (P=0.05; Duncan's New MRT).
² Cry 1F and its isoline was supplied by Dow AgroSciences; all LEPOTD hybrids were supplied by Monsanto; and the CBH-351 hybrids were supplied by Aventis.

Table 6.5 Mean numbers of larvae, cavities, and cavity length (cm) per plant above the ear for the Bt-corn efficacy trial for control of first and second-generation European corn borer Champaign, Illinois, 2000

Treatment²

Injury above the ear¹

Mean no. of
larvae per plant

Mean no. of
cavities per plant

Mean cavity
length (cm) per plant

Cry 1F / TC1507 / M2722

0.0

c

0.0

d

0.0

d

M2722 non-Bt isoline

0.3

bc

1.0

bc

3.5

ab

Y Bt

0.0

c

0.0

d

0.0

d

Y non-Bt isoline

0.4

bc

0.7

bc

2.4

bc

LEPOTD 11 non-Bt

0.4

ab

1.1

ab

2.3

bc

LEPOTD 12

0.0

c

0.0

d

0.0

d

LEPOTD 13

0.0

c

0.0

d

0.0

d

LEPOTD 14

0.0

c

0.0

d

0.0

d

LEPOTD 18

0.0

c

0.0

d

0.0

d

LEPOTD 19 non-Bt

0.7

a

1.6

a

4.7

a

CBH-351 Bt

0.0

c

0.1

d

0.1

d

CBH-351 non-Bt isoline

0.2

bc

0.5

cd

2.0

c

¹ Means in a column followed by the same letter are not significantly different (P=0.05; Duncan's New MRT).
² Cry 1F and its isoline was supplied by Dow AgroSciences; all LEPOTD hybrids were supplied by Monsanto; and the CBH-351 hybrids were supplied by Aventis.

Table 6.6 Mean numbers of larvae and cavities per shank, and mean numbers of larvae per ear and of ears injured percentage for the Bt-corn efficacy trial for control of first and second-generation European corn borer Champaign, Illinois, 2000¹

Treatment²

Mean no. of
larvae
per shank

Mean no. of
cavities
per shank

Mean cavity
length (cm)
per shank

% of ears
injured

Cry 1F / TC1507 / M2722

0.0

c

0.0

d

0.0

c

0.0

b

M2722 non-Bt isoline

0.2

a

0.3

bc

0.4

a

50.0

a

Y Bt

0.0

c

0.0

d

0.0

c

0.0

b

Y non-Bt isoline

0.3

a

0.5

a

0.3

ab

35.0

a

LEPOTD 11 non-Bt

0.0

bc

0.2

cd

0.2

bc

17.5

b

LEPOTD 12

0.0

c

0.0

d

0.0

c

0.0

b

LEPOTD 13

0.0

c

0.0

d

0.0

c

0.0

b

LEPOTD 14

0.0

c

0.0

d

0.0

c

0.0

b

LEPOTD 18

0.0

c

0.0

d

0.0

c

0.0

b

LEPOTD 19 non-Bt

0.2

a

0.4

ab

0.3

a

43.3

a

CBH-351 Bt

0.0

c

0.0

d

0.0

c

2.5

b

CBH-351 non-Bt isoline

0.2

ab

0.2

bcd

0.2

bc

13.3

b

¹ Means in a column followed by the same letter are not significantly different (P=0.05; Duncan's New MRT).
² Cry 1F and its isoline was supplied by Dow AgroSciences; all LEPOTD hybrids were supplied by Monsanto; and the CBH-351 hybrids were supplied by Aventis.

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