Evaluation of Transgenic Bt corn for Rootworm Control on Pennsylvania Farms During 2003

Conducted by: Ron Hoover, On-Farm Research Coordinator, Dennis Calvin, Professor, Dept. of Entomology, Greg Roth, Professor, Dept. of Crop and Soil Sciences, Craig Altemose, Centre/Clinton Counties Extension Educator, David Johnson, Senior Research Associate, Mark Madden, Bradford/Sullivan Counties Extension Educator, Thomas Murphy, Lycoming County Extension Educator, John Rowehl, Capital Region Extension Educator, Pennsylvania State University

Location: Seven locations in Pennsylvania

Collaborators: Jim Haldeman, Monsanto Company, Technology Development Manager

Research Objective: To evaluate the performance of a corn hybrid containing the MON 863 Bt event in continuous corn fields where there is a risk of injury from western corn rootworm larva.

Background: Recently transgenic Bt corn, resistant to larval damage from the corn rootworm, has become available to Pennsylvania corn producers. This product is derived from the MON 863 Bt event and is commercial marketed as YieldGard TM Rootworm Corn. With the commercial registration of YieldGard CRW, corn producers were offered a new technology for protecting their crop against corn rootworm root injury. Since the 1960, soil insecticides in the classes organophosphates, carbamates, synthetic pyrethroids and fipronil have been the backbone of corn rootworm management in non or long-term crop rotation systems. The objective of this research was to assess the agronomic performance of a YieldGard Rootworm corn hybrid compared to its isoline (same genetics without the Bt event) planted with and without a soil applied rootworm insecticide in on-farm trials.

Study Description: Seven field trials were conducted on six private farms and at the Penn State University’s Southeast Research and Education Center in Landisville. The trials were located within a corridor near the center of the state that stretches between the Maryland and New York borders. Fields were selected based on a field history that would increase the likelihood of a high population of overwintering corn rootworm eggs. All fields were in corn during 2002 with several having a history of more than one year of corn. At each location, standard corn production practices were employed: corn starter fertilizer were applied through the planter when soil test results warranted its usage, planting populations between 28,000 and 30,000, weed control with herbicide, etc. Special inputs and practices are noted below for each location.

A 110-day relative maturity Asgrow Bt rootworm transgenic hybrid, RX 708 YGRW, was evaluated in all studies except that at the MacAfee farm. This hybrid was compared to two treatments with its non-transgenic isoline, RX 708. One isoline treatment received the soil-applied insecticide, tefluthrin (Force 3G), applied at 5 oz/1000 feet of row through the planter. The other isoline treatment received no insecticide (control). The hybrid used at the MacAfee farm was Dekalb DKC46-23 (93 days relative maturity), and the trial there did not include the Force soil insecticide treatment. Only two replications were harvested for yield at this location.

Fifteen corn roots were randomly selected and dug from the center two rows of each plot. Roots were transported to a washing facility where all soil was removed and root-feeding injury was quantified. Root injury ratings are presented on a zero to three-point scale. Rootworm feeding usually begins on the outer, older node of the three nodes that collectively make up a corn root system. A zero score indicates that no feeding was observed on any roots, while a 1.2 score indicates that an entire node of roots is missing and 20 percent of the second node is also severely damaged. A score of 3.0 indicates that all roots had suffered damage and the plant had senesced.

Grain was harvested using a combine provided by each host farm. After each plot was shelled, grain was transferred into a self-unloading weigh cart. Grain moisture was measured with on a sub-sample using an electronic grain moisture meter. Grain yields were corrected to 15.5 % moisture. The corn at the Hartle Farm (Centre Co.) was harvested as silage by a custom operator and weighed on truck scales in the field. Corn forage samples were collected from each plot for moisture determinations. Silage yields were corrected to 65 % moisture. Additional subsamples were frozen prior to quality analyses by a forage testing laboratory

Results:

Corn root injury from feeding by corn rootworm was variable across locations (Table 1). The damage at the Bishop, MacAfee, and Miller farms was minimal, as indicated by the amount of damage on the unprotected (control) roots. The damage on the late-planted fields (Hartle Farm and Landisville research center) was much greater than that of the early and mid-season plantings.

Average corn growth across the seven locations during 2003 ranged from good to excellent. Rainfall was plentiful to excessive and the corn crop at no test site suffered from moisture stress. Planting dates should have been earlier at many sites, but were delayed by as much as three weeks by the excessive spring rains.

Corn at all sites experienced some rootworm larval feeding on the roots, Root ratings were conducted during mid to late July (Table 1). At two sites, Landisville and the Hartle Farm, corn suffered severe feeding damage on roots in the control plots. As many as two or more nodes of roots were damaged. Damage at the Landisville site was exacerbated by furrow-wall smearing that resulted when the planting into moist soil. Root growth through the furrow wall was limited; roots developed primarily in only two dimensions. Several locations (Miller, Bishop, and MacAfee farms) had surprisingly low corn rootworm pressure as indicated by the lack of root feeding on unprotected roots. Two of these locations, the Bishop and MacAfee fields, are located on floodplains near the Susquehanna River. The Bishop field is usually rotated with soybean, but the MacAfee field has been in corn continuously for at least 25 years. This confirms our previous observations that not all fields need protection from corn rootworm feeding, as some have low populations of the pest.

Grain yields overall were good, but may have been limited due to excessive precipitation in some locations. Nitrogen loss due to leaching, runoff, or denitrification was likely considerable. Grain yield differences were significant at only at the Landisville location, where the MON863 hybrid yields were greater than the Force treatment, which had higher yields that the control. The yield response to rootworm control was likely limited by the wet season, since corn plants have the capability to recover from rootworm injury when moisture is not limiting. Generally, yield responses will begin to occur when root damage ratings exceed 0.25, but in our trials we did not measure significant differences in yield even at root damage levels of 1.88 at the Hartle farm. Analyses of pre-ensiled forage quality revealed no differences between treatments for crude protein, neutral detergent fiber, digestibility of neutral detergent fiber, or starch.

Table 1. Summary of Mon863 corn hybrids performance compared to their isoline treated with Force insecticide and an untreated isoline control.
Location
Farm: Brenneman Swift MS Landisville Miller Bishop MacAfee Hartle
County: Lancaster Lancaster Lancaster York Lycoming Bradford Centre
Planting Date 2 May 15 May 30 May 12 May 22 May 7 May 12 June
Harvest Date 22 Oct 22 Oct 30 Oct 11 Nov 4 Nov 16 Nov 30 Sept
Treatment Root injury ratings (0 to 3 scale)
Mon863 0.02 0.08 0.30 0.01 0.02 0.02 0.42
Force 0.38 0.19 0.20 0.06 0.02 0.24
control 0.90 0.66 2.39 0.17 0.05 0.21 1.89
signif. P<.05? Yes Yes Yes No No Yes Yes
LSD (0.05) 0.22 0.21 0.22 - - 0.14 0.54
Treatment Grain or Silage Yields
---------- bu/ac @ 15.5 % moisture ---------- tons/ac
Mon863 191.8 156.4 79.8 131.4 136.4 134.7 15.2
Force 194.1 158.4 55.5 131.0 142.4 14.9
control 185.4 152.4 42.7 128.9 129.3 132.8 14.5
signif. P<.05? No (0.07) No Yes No No No No
LSD (0.05) 7.6 (0.05) 12.3
Treatment Relative Yields
(expressed as % of control yields at a location)
Mon 863 103.4 102.6 186.7 101.8 105.5 101.4 104.8
Force 104.7 103.9 129.9 101.7 110.2 - 102.5
control 100 100 100 100 100 100 100
Treatment Grain Moisture (%)
Mon 863 18.2 19.7 16.3 16.8 25.5 15.9 71.5
Force 18.0 19.6 16.2 16.8 26.2 71.5
control 18.0 19.4 16.2 16.8 26.5 15.9 71.4
signif. P<.05? NO NO NO NO NO NO NO
LSD (0.05) - - - - - - -

Averaged over all six sites where we had all three treatments, relative yields of the Mon863 and Force treatments averaged 117 and 109% of the control. This suggests an advantage of the Mon 863 product over the isoline with the Force treatment. Much of this difference, however, was due to the large relative response that occurred at the Landisville location. Without that location included relative yields of the Mon863 and Force treatments averaged 104 and 105% of the control, respectively.

In this trial, there was no indication of a difference in grain or plant moisture due to differences in rootworm feeding (Table 1). This effect has been observed in some trials with the Bt corn used for control of the European corn borer.

Conclusions:

These studies demonstrated that injury from the corn rootworm is variable and that sometimes corn has significant ability to recover from the injury without reducing yield. In a drier year we likely would have observed more yield reductions in the control plots. The MON 863 hybrid provided good control of the corn rootworm larva. Root ratings were similar or lower with the MON 863 hybrid relative to the Force treatment. The relative yield of the MON 863 corn relative to the Force treatment was variable with similar yields at most locations and superior yields at another location. Additional research is necessary to determine how often the MON 863 hybrid produces yields superior to the isoline treated with Force and under what conditions this occurs. Averaged over all environments there was approximately a 4% benefit from control of the corn rootworm with either Force or the transgenic hybrid. There did not appear to be any evidence of a consistent yield reduction (yield drag) with the Mon 863 hybrid compared to its isoline.

We appreciate the assistance of the producers and others who provided assistance to conduct this project:

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