—Lancaster Fannins, Saturday, February 17,1979
134
Effective rootworm control safeguards
BLOOMINGTON, HI. -
“In terms of economic
damage over a wide
geographic area, corn
rootworm is probably the
number one insect problem
in com,” according to Dr.
Mike Turner, manager of
entomology and pathology
research for Funk Seeds
International. Studies have
repeatedly shown that one
rootworm per com plant can
cost a grower eight-tenths of
a bushel in yield loss per
acre.
Dr. Turner says root
worms are a perennial pest
throughout the Com Belt,
There are three species: the
western, norther •> and
sourthem. Althougn one
species usually
predominates in a field, Dr.
Turner notes that two and
sometimes all three species
may be present, depending
on the geographic location.
The adult beetles of the
western rootworm are
yellowish with a dark stripe
on each wing cover. Nor
thern rootworm adults are
pale yellow as they emerge
from the ground in mid
summer, later turning a
uniform green. Adults of the
southern species are
yellowish green with 12
black dots.
The western rootworm
interbreeds with the other
two species, and the larvae
and adults of the mating
closely resemble the western
rootworm parent. The
western rootworm has been
expanding its range in
recent years, moving in a
northeasterly direction
across the Com Belt.
Rootworms can reduce
com yields in several ways.
Dr. Turner says. Larvae of
the northern and western
species eat on the surface of
the soil. They gouge out
holes and tunnel lengthwise
into the roots. Southern
rootworm larvae also feed
on the roots, but do not
tunnel lengthwise. They
feed on the growing points of
young com plants while they
are near the soil line, and
may cause seedlings to wilt
and die. Such root pruning
weakens the plant’s root
system and reduces yields,
Dr. Turner explains, adding
that lodging may also result.
In addition to reducing
anchorage and the plant’s
ability to take the nutrients
and water required for good
yields from the soil, the
Funk scientist says the
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adults of all three rootworm
species feed on com silks.
When this occurs befoi e
pollination, this too can
reduce yields. Dr. Turner
says. The western rootworm
is especially damaging in
this respect.
Several factors determine
the capacity of com to
tolerate rootworm damage.
Dr. Turner says these in
clude the strength of the root
system, the number of roots
the plant produces and its
ability to regenerate roots,
the stage of growth when
attacked and how favorable
growing conditions are after
the rootworm larvae have
attacked.
According to Dr. Turner,
Funk Seeds evaluates its
mbred lines, present hybrids
and those under develop
ment for their ability to
tolerate rootworm damage
at all Funk research stations
where com rootworms are a
problem.
“We continue to test
hybrids that have already
attained the G-Hyhnd rating
to evaluate how tolerant they
are to rootworm damage,”
he says. “We’re taking
materials that are new to
develop tolerance as we
develop the hybrids. We’ll
throw things out very early
m the program that are not
tolerant, and this will allow
us to carry greater tolerance
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Tatamy, Pa. 18085
Phone 215-258-2871
right along with our high
yielding capacity.
“When we talk about
tolerance, we’re talking
about two thines One is the
number of roots that a plant
produces and the second is
that plant’s ability to
regenerate roots if some of
its roots are destroyed by the
com rootworm. The better
adapted a plant is at
regenerating roots or the
more roots it may have to
begin with, the less damage
is apt to occur from root
worm larvae damage. ”
Dr. Turner says a root
pulling technique developed
by Funk is being used to
evaluate each hybrid’s
tolerance to rootworm
damage under heavy in
festion. The physical
resistance to being uprotted
by the special mechanical
device that is employed is a
function of the number and
size of healthy roots each
plant has near the end of the
growing season, he explains.
Visual observations are also
made, such as whether or
not the feeding of the root
worm larvae has caused
lodging'.
Ray Sullivan, a Funk
agronomist, says some
growers think there’s little
danger of rootworm damage
in first-year com following
soybeans because the beans
are not a good host crop for a
build-up of rootworm
populations.
While this is true, he points
out that a soybean field can
be a good place for root
worms to multiply to
economically damaging
levels if it is weedy.
“If there’s a weedy
soybean field, whether it’s
grasses, broadleaf weeds or
volunteer com, the weeds
will furnish the rootworm
beetles with a food supply
while they are mobile and
ucpositmg eggs for the next
generation, from mid
Summer on,” he says.
“When flowering, these
weeds serve as hosts for the
beetles, which feed on the
pollen.
“In a clean soybean field,
the problem is less likely to
occur, but rootworm beetles
will migrate to a soybean
field, particularly if it is
close to a com field or if it is
dry and the soybeans are
lusher than the surrounding
vegetation ”
Sullivan encourages
growers to apply a soil in
secticide when planting com
is-a field that had hpqn jp
soybeans the previous year
especially if the field was
weedy or had volunteer com,
Several soil insecticides,
including Amaze, Counter,
Dyfonate, Furadan, Lor
sban, Mocap and Thrmet,
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Phone 284-4464
f - _
give good rootworm control,
the agronomist says.
He continues: “I’ve seen
situations where there’s
been a 25- to 30-bushel yield
loss in first-year com from
com rootworm because the
grower didn’t treat for the
insect.”
While some attempts have
been made recently to
control rootworms by
aerially spraying fields with
a Sevin oil formulation while
the adult beetles are mobile,
Sullivan says this would
work only if large areas of
com were sprayed as needed
throughout the egg-laying
period, which lasts until
frost. Field scouting by a
yields
past management con
sultant is a must in such an
approach to rootworm
control, he adds.
For further information,
contact Sam Brungardt,
Bader Rutter and
Associates, Inc., 733 N. Van
Buren, Milwaukee, Wis.
53202, (414) 276-7303 or
Kenneth Rinkenberger,
Public Relations Manager,’
Funk Seeds International, P.
O. Box 2911, Bloomington,
Illinois 61701, (309) 829-9461.
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