Golden Valley, Minnesota
March 24, 2008
 |
|
Untreated roots
(left) vs. hybrids with the Agrisure® RW trait. |
|
Source:
Syngenta
Root ratings are the best way to
measure feeding damage from hungry northern and western corn
rootworms, but are they the best way to evaluate the performance
of rootworm-resistant Bt corn?
It’s a question that’s being raised by Kevin Steffey and his
colleagues within the University
of Illinois Department of Crop Sciences. And it’s the focus
of an article available for viewing at
www.ipm.uiuc.edu/bulletin.
“The root ratings system introduced back in 1971 and revised in
2000 was basically developed to compare soil insecticides,” says
Steffey. He adds that the system had been the gold standard for
almost four decades, providing valuable insight when evaluating
the performance of a host of soil insecticides, from carbamates
and organophosphates through the newer pyrethroid products.
But does the same rating scale for rootworm damage in plots
treated with soil insecticides apply in equal measure to
rootworm damage to corn with transgenic rootworm traits?
The current 0 – 3 root rating scale developed by
Iowa State University is
based on nodal feeding. “A node is simply a circle of roots,”
explains Marlin Rice, entomologist with Iowa State University. A
root rating of one means that one node or its equivalent has
been completely eaten. A root rating of two means two nodes have
been eaten, and so forth. Feeding that falls under one full node
is conveyed as a percentage. For example, a root rating of 1.5
means that one and a half nodes, or the equivalent of one and a
half nodes, have been eaten.
According to Larry Bledsoe, entomologist at Purdue University,
root mass and even node size can vary from hybrid to hybrid. As
a result, a root rating of 0.5 for one Bt corn hybrid may look
more like a 0.75 on another Bt corn hybrid.
“It’s completely different from soil insecticide trials, where
we’re planting the same hybrid and sometimes even the same lot
numbers,” explains Bledsoe.
In addition to root mass and node size, root architecture also
varies from hybrid to hybrid. “In some hybrids, the distance
between nodes is longer and roots tend to branch out as they
grow,” says Bledsoe. “In other hybrids – or where there’s
drought – the internodal distance is shorter and roots tend to
be packed together.”
Root regeneration may also vary from one hybrid to the next.
“Some regenerate roots slowly, so when they are pruned, these
hybrids suffer the whole season and you see the response in lost
yield,” notes Bledsoe. “Other hybrids regenerate roots very
rapidly.”
So how can growers compare one rootworm trait to another? Von
Kaster, entomologist with Syngenta Seeds, suggests that results
from multiple rootworm control trials are more telling than
results from just one or two.
“When you look at rootworm results from multiple trials at
multiple sites, you’re getting a broad view of insect control
over a range of hybrids and genetics, as well as weather, soil
and cultural conditions,” he explains. “For example, results
from 2004 through 2007 Syngenta and university trials
representing 57 locations show that hybrids with the Agrisure®
RW trait generated root ratings averaging just 0.22.”
Entomologists agree that it’s important to look at a variety of
results when evaluating any corn rootworm control method.
“Here at Purdue, we have two seasons worth of efficacy data for
Agrisure RW and a few years on top of that for YieldGard® and
Herculex®, which have been around longer,” says Bledsoe. “Our
results and other data from the eastern Corn Belt demonstrate
that all three traits provide good control of rootworms. They
further demonstrate that all of the transgenics are definitely
an improvement over the granular and liquid soil insecticides
that we’ve been using for the last 40 years.”
Syngenta is a
world-leading agribusiness committed to sustainable agriculture
through innovative research and technology. The company is a
leader in crop protection, and ranks third in the high-value
commercial seeds market. Sales in 2007 were approximately $9.2
billion. Syngenta employs over 21,000 people in more than 90
countries. Syngenta is listed on the Swiss stock exchange (SYNN)
and in New York (SYT).
Agrisure® is a registered trademark of a Syngenta Group Company.
YieldGard® is a registered trademark of Monsanto.
Herculex® is a registered trademark of Dow AgroSciences LLC. |
|
