Wooster, Ohio
October 19, 2007
Populations of Western corn
rootworm and its variant counterpart continue to increase in
fields throughout western and northwestern Ohio, and are even
beginning to spread east, according to Ohio State University
Extension sampling.
Ron Hammond, an Ohio State
University (OSU) Extension entomologist with the Ohio
Agricultural Research and Development Center, said in
preliminary data of the first year Western corn rootworm
variant, 26 of 93 fields reported have reached or come close to
the threshold of five adult corn rootworm beetles per trap per
day.
“This year we have seen populations similar, if not slightly
more, to what we saw last year with regards to the variant. Most
of these fields are still in the northwest and west central
portions of the state, from Fulton County down to Darke County,
and as far east as Crawford County,” said Hammond. “In terms of
the normal Western corn rootworm, we are seeing higher
populations throughout the area as well. Unlike five years ago,
when the pest was something we had to just simply be aware of,
now it’s getting to be a concern.”
Entomologists are also continuing to see high levels of corn
rootworm injury this past summer, both in corn following corn
and in first-year corn following soybeans.
“As in 2006, we saw rootworm feeding injury ratings well over 1,
at least one node missing, in many fields,” said Hammond.
Larvae hatching in cornfields following corn, or, in the case of
the variant, hatching into cornfields that had been in soybeans
the previous season, cause the most significant damage by
feeding on corn roots. In severe cases, corn lodging can occur
and reduce yields.
Hammond said that fields reaching threshold numbers will need a
preventive treatment for rootworm if corn is planted into those
fields next spring. There are many management options available
to growers to help control populations and reduce feeding
injury. They include:
- Granular insecticides
Several granular insecticides are available, and all do
a good job against corn rootworm populations. “The most
important thing about using granules is to make sure the
granular equipment is properly calibrated and the granules
are applied properly at planting,” said Hammond.
- Liquid insecticides
Like granule insecticides, these products are effective
in controlling rootworm larvae.
- Seed treatments
Currently there are two seed treatments that are
effective against the corn rootworm: Cruiser and Poncho.
“They do a good job against low to moderate populations, but
they may not do a good job against high populations,” said
Hammond. “If populations are severe, then we don’t recommend
using the products.”
- Crop rotation
In areas not impacted by the Western corn rootworm
variant, crop rotation is the best management practice.
“Crop rotation still does the job in breaking the cycle,”
said Hammond. Continuous cornfields are most at risk for
corn rootworm problems since most adults lay eggs in
cornfields for larvae emergence in the following year’s corn
crop.
- Transgenics
Corn hybrids with single or stacked traits can be used,
especially in fields impacted by the corn rootworm variant.
"There are several Bt-rootworm transgenic hybrids that can
be used to control the rootworm,” said Hammond. “If using a
transgenic hybrid, a grower must plant a 20 percent refuge
within or adjacent to the transgenic corn.” The refuge
prevents the corn crop from losing its resistance to corn
rootworm.
Hammond said that sampling is the
first step in determining the level of corn rootworm populations
in a given field.
“Unless you have sampled your field, you don’t know for sure if
you will have a problem with corn rootworm,” said Hammond. “If
growers haven’t sampled their fields for next season’s
management, then they should check with their Extension office
to see where the county is at in terms of populations. It will
at least give growers an idea as to whether or not they should
treat.”
Extension specialists have been tracking corn rootworm
populations in Ohio for the past decade. For more information on
corn rootworm, refer to the OSU Extension Agronomic Crops Team
Web site at
http://agcrops.osu.edu.
Additional information on corn
rootworm management can be found at
http://ohioline.osu.edu/ent-fact/0016.html. |
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