1997 European Corn Borer Survey and Evaluation of Bt Insect Resistant Corn in Eastern Virginia
Crop and Soil Environmental News, January 1998
Rod R. Youngman, Associate Professor and Extension Specialist
Curt A. Laub, Research Associate
Tom P. Kuhar, Graduate Research Assistant
Department of Entomology
The European corn borer is the most serious pest of corn grown for grain in Virginia. Although this pest occurs throughout the commonwealth, serious economic damage varies from one season to the next and tends to be sporadic across corn growing regions such as eastern Virginia. As many as three corn borer generations occur per year in Virginia; however, the second generation causes the most damage to grain corn in the state. Second generation corn borers damage corn by tunneling in the stalks and ear shanks. Stalk tunneling reduces nutrient uptake and leads to lodged or broken stalks and ear loss. According to a USDA bulletin, low corn borer infestations can cause up to 8 bu/acre in yield reductions. In North Carolina, a four-year study demonstrated that one corn borer tunnel per stalk causes about a 7% yield loss/acre. In recent years, the development and release of commercial Bt corn hybrids offers Virginia growers a powerful new tool for managing European corn borer. Scientists have successfully incorporated the Bt gene from a common soil bacterium into several commercial corn hybrids. In most cases, a corn borer larva stops feeding and dies after feeding for just a few minutes on a Bt corn hybrid.
1997 European Corn Borer Survey
Second generation corn borer damage was determined in August 1997 from a survey of 54 non-Bt cornfields in 14 eastern Virginia counties. The counties included three in the northern neck: Northumberland, Lancaster, and Richmond; three in the middle peninsula: Essex, Middlesex, and King and Queen; three in the lower peninsula: New Kent, Charles City, and James City; and five counties south of the James River: Surry, Sussex, Isle of Wight, Southampton, and Suffolk. In each field, 100 stalks were sampled for corn borer damage making up a total sample size of 5,400 plants.
The percentage of stalks with corn borer tunnels in 1997 ranged from very low in the northern counties to moderate in the southern counties (Table 1). Infestation levels averaged only 0.6% in the northern neck and middle peninsula counties, and 3.5% in the lower peninsula counties. The highest percentage (13.2%) of infested stalks occurred in those counties surveyed south of the James River. Overall, most of the cornfields in this survey had below-threshold infestation levels of corn borer; however, at least one field in New Kent Co., and as many as six fields in counties south of the James River had infestation levels that probably would have benefited from the Bt corn hybrid technology. The field in our survey with the highest percentage of infested stalks (77%) was located in Isle of Wight Co.
Evaluation of Selected Bt Corn Hybrids in Eastern Virginia
Six Bt corn hybrids and a non-Bt standard were planted in April 1997 at the Virginia Crop Improvement Farm in Mt. Holly and the Eastern Virginia Agricultural Research and Extension Center in Holland. The Bt hybrids evaluated were: Pioneer 35N05, Pioneer 33V08, Mycogen 7059, Mycogen 7559, Novartis N7639-Bt(11), and Novartis N6800-Bt(11). The non-Bt hybrid used as a standard at both sites was Pioneer 3394. At the Mt. Holly test site, corn was planted on 30-inch rows, thinned to 26,000 plants/acre, and grown under irrigation, whereas at Holland, corn was planted on 36-inch rows, thinned to 22,000 plants/acre, and grown under dryland conditions. All corn hybrids were replicated 4 times in a randomized complete block design. Damage caused by second generation corn borers was determined in all plots at both locations in mid-August 1997. Twenty cornstalks per plot were first thoroughly inspected for evidence of feeding and tunneling activity. When feeding damage was detected, a plant was destructively sampled, with records made on the number of damaged leaves and the numbers of ear and shank tunnels. To characterize the intensity of tunneling activity in infested stalks and tassels, seven tunnel length categories, ranging from 0-0.5 inches to over 3 inches, were used. Records also were made on the numbers of corn borer egg masses, larvae, and pupae associated with each stalk. In addition, grain yields were determined on the remaining cornstalks from the center two rows of each plot.
Pressure from second generation corn borers was very low at both locations in 1997. Of the 480 cornstalks sampled at Mt. Holly, a total of only 2 (0.4%) corn borer tunnels were found. Likewise, only 12 (2.5%) corn borer tunnels were found at the Holland site. It is worth noting that no tunnels were detected in Pioneer 3394 stalks at Holland. The lack of pest pressure in both locations precluded an evaluation of the different Bt hybrids' ability to withstand late-season damage from European corn borer. Despite this lack of pest pressure, however, there were significant differences in yield among hybrids at the Mt. Holly site (Table 2). Grain yields ranged from a high of 249.7 bu/acre for Novartis N7639-Bt(11) to a low of 213.0 bu/acre for Pioneer 35N05. Other top yielding varieties included the Bt-hybrid: Pioneer 33V08 (241.5 bu/acre), and the non-Bt standard: Pioneer 3394 (243.3 bu/acre). Novartis N6800-Bt(11) gave an intermediate yield of 232.0 bu/acre, which was followed by the two Mycogen Bt hybrids: 7059 (222.3 bu/acre) and 7559 (222.0 bu/acre). Under the conditions of this test, these results indicate that at least two Bt hybrids: Novartis N7639-Bt(11) and Pioneer 33V08 are competitive with the non-Bt hybrid, Pioneer 3394, for eastern Virginia. Grain yields were dramatically lower among all corn hybrids evaluated at the Holland site (Table 3). The lack of sufficient moisture during critical times for corn growth at Holland, contributed substantially to the low hybrid grain yields experiment-wide.
This research was supported by a 1997 grant from the Virginia Corn Board.
Table 1. 1997 county survey of European corn borer levels in eastern Virginia.
|County||Percent of stalks affected|
|Total stalk tunnels||Tunnel lengths||Shank tunnels||ECB larvae||ECB pupae|
|0 - 2.5 cm||> 2.5 - 5.1 cm||>5.1 cm|
|King and Queen||1.7||0.5||0.7||0.5||0.0||0.5||0.0|
|Isle of Wight||29.3||13.3||11.3||4.8||5.0||11.8||5.3|
Table 2. Bt Corn Hybrid Evaluations; Mt. Holly, Virginia, 1997
@ 15% moist.
|Percent moisture||Test Wt (lb/bu)|
|Novartis||N7639-Bt(11)||249.7 a||23.2 a||52.9 d|
|Pioneer||3394||243.3 a||20.6 d||54.2 b|
|Pioneer||33V08||241.5 ab||21.3 c||54.4 b|
|Novartis||N6800-Bt(11)||232.0 bc||22.1 b||53.4 c|
|Mycogen||7059||222.3 cd||22.0 b||52.2 e|
|Mycogen||7559||222.0 cd||23.0 a||53.5 c|
|Pioneer||35N05||213.0 d||18.2 e||56.2 a|
Table 3. Bt Corn Hybrid Evaluations; Holland, Virginia, 1997
@ 15% moist.
|Percent moisture||Test Wt (lb/bu)|
|Pioneer||33V08||115.8||23.4 ab||54.4 b|
|Novartis||N7639-Bt(11)||102.3||22.9 ab||52.6 c|
|Novartis||N6800-Bt(11)||100.0||23.8 a||52.8 c|
|Mycogen||7059||96.8||21.9 bc||52.4 c|
|Mycogen||7559||90.3||22.4 ab||53.2 bc|
|Pioneer||35N05||87.0||20.2 c||56.0 a|
|Pioneer||3394||81.5||21.5 bc||54.1 b|