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PLANTS: GE corn helps U.S. farmers to grow corn after corn

------------------------------- GENET-news -------------------------------
TITLE:  Managing rootworms in continuous corn
SOURCE: South Dakota State University Extension
AUTHOR: Farm & Ranch Guide, USA
DATE:   18.03.2007

Managing rootworms in continuous corn

BROOKINGS, S.D. - The current high demand and market value of corn makes
continuous corn attractive to producers, but it will also attract more
rootworm pressure than usual, a South Dakota State University specialist
warned. SDSU Extension Entomologist Mike Catangui said in fields seeded
to continuous corn, rootworms have a continuous food supply, resulting
in the buildup of rootworm infestations of cornfields over several
years. "Roots of corn are the exclusive food of rootworm larvae; they
cannot normally survive on roots of soybean, wheat, sunflower, and
alfalfa," Catangui said. "It is this almost complete dependence on corn
that makes rootworm larvae vulnerable to crop rotation. Remove corn from
the field and rootworm larvae will starve to death due to lack of
suitable food for survival." Growing corn continuously on the same field
is not yet very common in the region. However, Catangui said that he
knows of a few growers who have been planting corn continuously for up
to 40 years. Continuous corn planting also has been made easier to
accomplish by the recent introductions of genetically engineered (Bt)
corn hybrids that produce proteins in their roots that are toxic to
rootworm larvae.

Rootworm eggs are laid in the soil from late summer until the female
rootworm beetle adults are killed off by the first killing frost in the
fall. In the Dakotas, rootworm eggs are still laid mainly in cornfields.
Eggs of rootworms overwinter in the soil. Fields planted with corn the
previous season will most likely already have rootworm eggs waiting for
corn. Eggs hatch as soon as roots start growing from the planted corn
seeds. Most injuries by rootworm larvae occur in June and July during
the very active root growth phase of the corn plants. Larvae transform
into pupae in mid July; adult rootworm beetles emerge from the soil
starting from late July through August while the corn is silking and

Adult beetles feed on corn pollen, silk, and leaves. They also feed on
the pollen, flower, and leaves of many other plants including soybeans,
sunflowers, and garden flowers. Corn growers who wish to grow corn
continuously will have to manage corn rootworms to improve yield and
facilitate harvest, Catangui said. Root pruning by the rootworm larvae
can result in reduced water and nutrient intake by the injured plants
resulting in severe loss of yield. Partial and complete lodging of corn
plants can also result because of reduced root support. Lodged corn is
also very difficult to harvest and likely results in increased fuel cost
at harvest. SDSU research in 2006 conducted by entomologists Billy
Fuller and Brad McManus on 15th-year continuous corn near Garretson,
S.D., showed that corn protected from rootworms yielded between 19.3 to
46.9 bushels per acre more than unprotected conventional corn. The
rootworm control tactics investigated were genetically engineered corn,
granular soil insecticides, and seed treatments. In Bryant, S.D., on
third-year continuous corn, the yield advantages were from 3.2 to 39.2
bushels per acre. Catangui and SDSU graduate student Jon Kieckhefer have
also been conducting an inventory of all corn insects (from the roots to
the ears) of conventional and genetically engineered corn hybrids since
1996. Results last season of their rootworm research indicated up to
39.7 bushels per acre yield advantage in fields where rootworm larvae
were controlled using a liquid soil insecticide, genetically engineered
corn, and seed treatments. That research is funded in part by the South
Dakota Corn Utilization Council. In continuous corn, the main control
tactics available to growers are genetically engineered corn hybrids,
granular or liquid soil insecticides, and systemic insecticidal seed
treatments. Genetically engineered corn hybrids containing the YieldGard
Rootworm, YieldGard Plus, Herculex RW, Herculex XTRA, and Agrisure RW
genes are resistant to feeding by rootworm larvae. Insecticidal proteins
toxic to rootworm larvae are produced in the roots by these Bt-corn
plants. Which Bt genes to utilize in the corn plant is decided upon by
the seed brand or company. All corn hybrids containing the Bt genes
effective against rootworm larvae are also automatically treated with a
low rate of an insecticidal seed treatment. Insecticidal seed treatments
available to corn growers are clothianidin (Poncho), imidacloprid
(Gaucho, Prescribe) or thiamethoxam (Cruiser). These systemic
insecticides are coated onto the seeds before the seeds are bagged and
sold to growers. Granular or liquid rootworm insecticides are applied in-
furrow or very close to the seed furrow during the planting process.
Corn planting in South Dakota usually occurs from late April through
early June. Soil insecticides labeled for rootworm larvae are bifenthrin
(Capture LFR, Discipline), carbofuran (Furadan 4F), chlorethoxyfos
(Fortress), Chlorpyrifos (Lorsban, Nufos), ethoprop (Mocap), fipronil
(Regent), Phorate (Phorate, Thimet), tebupirimfos + cyfluthrin (Aztec),
tefluthrin (Force), and terbufos (Counter). Always read and follow label

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