October 14, 2005
University of Nebraska, Lincoln
The U.S. Environmental Protection
Agency has registered two new Bt corn hybrids with the Bt
proteins, Cry34Ab1 and Cry35Ab1, for use against corn rootworm
larvae. They will be sold under the trade name Herculex RW by
Pioneer Hi-Bred International, Inc. and Mycogen
Seeds/DowAgroSciences LLC, which jointly developed the genetic
different Bt proteins than those used in YieldGard Rootworm
hybrids or any other Bt corn to date. Company and university
research indicates that they effectively protect roots from
rootworm feeding injury.
previous Bt corn hybrids, EPA has required registrants to
implement a resistance management plan as a condition of
registration. The resistance management plan for Herculex RW
hybrids is similar to that for YieldGard Rootworm hybrids:
than 80% of the acreage on a farm can be planted to Herculex
of 20% of the acreage on a farm must be planted to a hybrid
not containing a Bt protein active against rootworms, and
refuge must be within or adjacent to the Herculex RW field.
refuge details are outlined below.
another source of Bt corn with a different type of Bt protein
for rootworm management will provide growers another option to
increase the diversity of controls available for this important
agreements (also known as stewardship agreements) will specify
that growers must adhere to the refuge requirements as described
in the grower guide/product use guide and/or in supplements to
the grower guide/product use guide.
Refuge size. The use of Cry34/35
corn from event DAS 59122-7 requires an accompanying 20%
Refuge location. The rootworm
refuge is required to be planted within or adjacent (e.g.
across the road) to the Cry34/35 corn field.
Refuge management options. The
rootworm refuge may be managed in such a way that there is
little or no yield loss to rootworms, but must be managed in
a way that it is sufficiently productive of susceptible
rootworm adults. The in-field refuge options may be planted
as a single block or as a series of strips measuring at
least four crop rows wide.
mixtures of Cry34/35 and refuge corn are not permitted.
refuge is planted on rotated ground, then Cry34/35 corn also
must be planted on rotated ground.
refuge is planted in continuous corn, the Cry34/35 field may
be planted on either continuous or rotated land (option
encouraged where western corn rootworm rotation-resistant
biotype [soybean variant] may be present).
Application of soil insecticide is permitted in the refuge.
treatment is permitted in the refuge, either for rootworm
protection or for controlling secondary soil pests.
insecticides are applied to the refuge for control of CRW
adults, the same treatment also must be applied in the same
time-frame to Cry34/35 corn.
other than adult corn rootworms can only be treated with
CRW-labeled insecticide on the refuge acres without treating
the Cry34/35 acres if treatment occurs when adult corn
rootworms are not present. Pests on the Cry34/35 acres can
be treated as needed without having to treat the refuge.
rootworm refuge can be planted to any corn hybrid that does
not express Bt proteins for rootworm control (e.g.
lepidopteran-protected Bt corn, herbicide-tolerant corn, or
refuge and Cry34/35 corn should be sown on the same date, or
with the shortest window possible between planting dates, to
ensure that corn root development is similar among
are encouraged to plant the rootworm refuge in the same
location each year, as it allows the rootworm population to
remain high and the durability of the trait is extended.
This option may be preferable to growers who wish to only
think of their refuge design once and for those who grow
continuous corn. However, for those growers who need to
employ crop rotation, a fixed refuge would be impractical.
Bacillus thuringiensis Cry34Ab1 and Cry35Ab1 proteins and the
genetic material necessary for their production (plasmid insert
PHP 17662) in Event DAS-59122-7 corn,
Fact Sheet, published by the U.S. Environmental Protection
Tom Doerge and Steve Butzen. 2005. Pioneer® Brand Hybrids
with the Herculex® RW Trait, Crop Insights Vol. 15, No. 13.
Mycogen Seeds Announces New Herculex® RW Grain Corn Hybrids:,