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2-Plants: Bt-cotton only pays off under heavy ECB infestation



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TITLE:  Yield Comparisons of Bt and Non-Bt Corn Hybrids in
        Missouri in 1999
SOURCE: Integrated Pest & Crop Management Newsletter Vol. 9, No.
        22, University of Missouri-Columbia, USA
        http://ipm.missouri.edu/ipcm/archives/v9n22/ipmltr2.htm
DATE:   December 17, 1999

----------------- archive: http://www.gene.ch/ ------------------


"It is clear that there is a return on the Bt corn seed premium
or technology fee when most non-Bt hybrids are heavily infested
with European corn borer."

For more critical informations on Bt-corn see:
http://www.btinternet.com/~nlpwessex/Documents/gmagric.htm

                          *****

Yield Comparisons of Bt and Non-Bt Corn Hybrids in Missouri in
1999

Full-season corn hybrids were evaluated in nine non-irrigated and
six irrigated trials in the University of Missouri Variety
Testing Program in 1999. Seed corn companies had two options for
assessing the performance of Bt hybrids:
Fifteen standard corn hybrid trials, averaging 75 hybrid entries
per trial. Separate Bt corn trials, embedded by replication
within the standard trials. These smaller trials were comprised
of eight and four Bt corn hybrids in the non-irrigated and
irrigated trials, respectively, and three productive non-Bt
hybrids. These three were selected on the basis of high yield
performance in the MU Variety Testing Program over a wide range
of environmental conditions. In three of the 15 separate Bt
trials, the non-Bt hybrids were artificially infested with
European corn borer.


Objectives

- Evaluate yield performance of Bt and non-Bt corn hybrids under
  conditions of natural (endemic) European corn borer infestation
  in 15 standard corn trials.
- Evaluate the yield performance of non-Bt corn hybrids (under
  two levels of European corn borer infestation) relative to that
  of Bt hybrids in three artificially infested trials.
- Monitor natural levels of first and second generation European
  corn borer infestation in 15 standard trials located in 14
  counties of Missouri.
- Assess the economic benefits of the Bt technology; i.e.,
  determine the level of European corn borer infestation that
  offsets the higher seed costs associated with Bt corn seed.


Experimental procedures

Field plot design.All trials were arranged in lattice or
randomized complete block designs with three replications. All
plots were four rows wide and 25 feet long with a between-row
spacing of 30 inches. Agronomic practices such as planting date,
seeding rate, fertility and weed control were selected and
applied to optimize yields at each trial site. The center two
rows of each plot were harvested with a plot combine for yield
comparisons among the corn hybrids. Yields were adjusted to a
uniform moisture of 15.5% and reported in bushels per acre.
European corn borer survey. In each of the 15 standard trials,
natural levels of European corn borer infestation were surveyed
by dissection of 60 cornstalks of the same non-Bt hybrid (Pioneer
brand 33G26) at both the late vegetative and dent stages of corn
growth. Dent stage was selected for the last survey because
research indicates that stalk tunneling after the grain-filling
period does not reduce physiological yield. Artificial
infestation of European corn borer. The three non-Bt "check"
hybrids were artificially infested with European corn borer in
two non-irrigated trials (Marshall and Columbia) and one
irrigated trial (Columbia). The center rows were infested with
approximately 250 neonate larvae/plant using the Davis (bazooka)
technique. The larvae were applied to each plant in the leaf axil
of the primary ear and in the leaf axil above and below the
primary ear at the R1 (silking) stage to simulate second
generation infestation.

Fifteen stalks from the center two rows of each non-Bt plot were
split lengthwise to measure the following:
- Number of tunnels per plant
- Tunnel length per plant, rounded to the nearest centimeter
- Percent of tunneled plants per plot

Plants were counted as tunneled if there was an entry hole with a
tunnel length of one centimeter or more in the shank of a
harvestable ear or in the stalk. The top four internodes were not
dissected because researchers have found no relationship between
yield and level of infestation in the top three to six internodes
regardless of corn growth stage infested. Natural levels of
infestation were assessed in the same three non-Bt hybrids in the
adjacent standard trials by the same method, except that 10
cornstalks from the center two rows of each plot were split
instead of 15 stalks.


Results and discussion - Natural infestation

European corn borer survey.
Natural infestation levels of the pest were low at the 15 trial
locations, ranging from fewer than 10% tunneled plants at six
trial locations to 37% tunneled plants at the non-irrigated
trials at Columbia and Chillicothe (Figure 1, see web-page). When
yield comparisons were made between the top 10 Bt and non-Bt
hybrids, the level of infestation did not appear to have a
consistent effect on performance (Figures 1-2, see web-page).

Yield comparisons in standard trials.
Averaged over the 15 standard trials, the top 10 Bt hybrids and
top 10 non-Bt hybrids were within 1.0 Bu/A of each other (Figure
2, see web-page). On a regional basis, there were larger
differences in yield performance when the Bt and non-Bt hybrids
were compared in the four irrigated trials in the southern half
of the state. Overall, the Bt hybrids yielded higher in the
southwestern Missouri trials and lower in the southeastern
Missouri trials than the non-Bt hybrids (Figure 2, see web-page).

Yield comparisons in separate Bt trials.
Eight Bt hybrids were entered at each of the nine non-irrigated
trial sites, and four Bt hybrids were entered at each of the six
irrigated trial sites. The results of the 12 naturally infested
Bt trials closely followed those obtained in the standard trials,
with the exception of the irrigated trials in southeast Missouri.
The three top-yielding Bt hybrids yielded only 3.0 Bu/A more than
the three non-Bt "check" hybrids when the yields of the two
"Bootheel" trials were averaged (Table 1, see web-page).

No evidence of "yield lag" in Bt hybrids. There was no "yield
drag" or "yield lag" associated with the performance of Bt
hybrids in the 15 standard trials. Although 33.9% of all corn
hybrids tested possessed the Bt trait, the Bt hybrids comprised
42.3% of the hybrids that were the highest yielding or that did
not yield significantly less than the top performer. The Bt
hybrids accounted for 39.7% of all hybrids that yielded above the
average (Figure 3, see web-page).


Results and discussion ­ Artificial infestation

European corn borer infestation levels.
When non-Bt hybrids were averaged across the three artificially
infested trials, 100% of dissected stalks were tunneled, with an
average of 5.2 tunnels per plant and a mean tunnel length of 24
centimeters per plant (Tables 2-4, see web-page). In comparison,
only 34% of those cornstalks from the naturally infested non-Bt
hybrids were tunneled, with an average of 0.5 tunnels per plant
and a mean tunnel length of 2 centimeters per plant. In the
naturally infested non-Bt hybrid plots, approximately 70% of the
tunnels were initiated after the tassel stage (by second or third
generation corn borers). In the artificially infested non-Bt
hybrid plots, over 95% of the stalk tunneling began at the
blister stage (i.e., approximately one week after the neonates
were applied).

Impact of infestation levels on yields.
In the artificially infested trials, Burrus BX86, Mycogen
2888IMI, and Pioneer brand 33G26 yielded an average of 19.4 Bu/A
or 12% less relative to the average yield of their naturally
infested counterparts at the same three trial sites. Based on
this comparison, the yield loss in the three artificially
infested hybrids corresponded to an average of 2.5% per tunnel;
however, there were notable differences in hybrid tolera
ce to stalk tunneling (Tables 2-4, see web-page). Burrus BX86,
heavily infested with an average of 5.8 tunnels per plant at the
two non-irrigated trial sites, yielded only 0.4% or 3.6 Bu/A less
than the naturally infested Burrus BX86 with 0.4 tunnels per
plant (Tables 2-3, see web-page). Burrus BX86 did not yield
significantly less than the highest yielding Bt hybrid in two of
the three artificially infested Bt trials.

When yields of the three top-ranked Bt hybrids were compared to
the non-Bt "check" hybrids, the Bt hybrids averaged 22.2 Bu/A
more than the artificially infested non-Bt hybrids and 3.9 Bu/A
more than the naturally infested non-Bt hybrids (Tables 2-4, see
web-page). The non-irrigated trial at Columbia, the most highly
infested and moisture stressed of the three sites, accounted for
the greatest difference (7.0 Bu/A) between the top three Bt
hybrids and naturally infested non-Bt hybrids (Table 3, see web
page).

Economics of Bt corn.
It is clear that there is a return on the Bt corn seed premium or
technology fee when most non-Bt hybrids are heavily infested with
European corn borer. However, what level of European corn borer
infestation offsets the higher seed costs associated with Bt
corn? Corn infested at the blister stage averages 3%
physiological yield loss per borer (i.e., per tunnel) according
to best estimates provided by North Central Region entomologists.
Assuming the infestation began at the blister stage, the economic
injury level would be one larva (tunnel) per plant based on an
expected yield of 140 Bu/A, a market price of $2.00/Bu, and a
technology fee of $8.50/A (Figure 4, see web-page). The break
even point would be one larva per plant, and yield protection in
excess of 4.2 Bu/A would provide a net return on the Bt
technology.

This report is based on performance trials in:
Corn: 1999 Missouri Crop Performance.
University of Missouri-Columbia Special Report 521.
October, 1999, by H.C. Minor, C.G. Morris, H.L. Mason, D.R.
Knerr, R.W. Hasty, G.K. Stafford, and T.G. Fritts.
The performance trials are also available at http:/
agebb.missouri.edu.cropperf/corn/.
The full 10-page Bt corn report is available from Maureen O¹Day
at odaym@missouri.edu. (Harry Minor, 573-882-2001 and Maureen
O¹Day, 573-882-3786)


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