The Rural Voice, 1982-02, Page 11congregate on the corn silks where they feed. (In Ontario, most
corn is pollinated by this time so damage at this point is not
extensive).
The females lay clusters of eggs in the soil, at depths of up to
two inches among the brace roots of corn plants. Egg laying occurs
in late August to October and the adults die with the first frost. If
it's any consolation, there is only one generation a year.
So how do you get rid of the corn rootworm? Or at least, control
it? Farmers have heard it all before. The right corn hybrid? One
that is tolerant to rootworm? Some hybrids are more tolerant than
others, says Pat Lynch, but that means they are more effectively
feeding the rootworm and so help build up the population. So,
breeding for resistance is for the short term. A stop gap measure?
A survival tactic, says Lynch.
Crop rotation? Red Clover plowdown? One year rotation out of
corn will break the cycle. But that's still hard to do in corn county.
Lynch says plant your worst field for infestation last. Because of
that the plant will have a smaller root system but the insecticide
applied will not have broken down by that time so the application
will be at its peak. Lynch says there is so much conflicting
information and data on the rootworm; he has piles of papers and
reports to prove it. He has been fighting for more rootworm
research for the last nine years.
Cliff R. Ellis of the University of Guelph. is working on a
research project "Threshold Limits in Pest Control" funded by
the provincial Lottery Research Awards Program. This project
deals with applying chemicals to control pests. Two factors are
involved -the accurate costs of control programs and a reliable
estimate of crop losses with given numbers of pest insects. From
the data collected, he hopes to determine the "level of infestation
that can be tolerated before losses from the absence of chemical
control are greater than the costs of treatment."
Ellis, on the telephone, says he is currently working on
insecticide applications for best results and these results will be
released shortly.
Ridgetown presently is involved in the screening of insecticides
and Bob Forrest, at Central College of Agricultural Technology
reports they have an application in the works for funds to study
Northern Corn Rootworm
corn rootworm and are patiently waiting to hear if their application
has been accepted.
"The college depends on OMAF for funds," he says.
"Universities have other sources and federal money is available to
them. The economic situation being what it is, we can't add new
people for research without dropping other staff."
Forrest feels more research is needed in genetic resistance and
chemicals which are systematic or degradable.
Henry Olechowski, soil and crop specialist, OMAF Extension
Dept. in Newmarket, has studied the rootworm problem
extensively. "Growing hybrids for resistance is one possible
control method," he says. "One hybrid will stand while ten others
will not."
Olechowski says insecticide application rates can vary
tremendously and the calibration of planters can be different;
even a small breeze can make a big difference. "What we need,"
he says, ",is better insecticides and better application. Even with
the best, there'll only be a certain percentage "kill". The best we
can hope for is some control."
For eight years, Bernie Smith at the Harrow Research Station,
has studied the problem of rootworm infestation and has made
some interesting observations. He says rotation is one of the best
methods of control but he puts a lot of stock in insecticide
applications. Insecticides, he says are about 60 per cent effective,
depending on the methods and conditions in application.
Smith is experienced in this area and is a world authority on
Western Corn Rootworm
insects. particularly ladybug predators. insects are a real
indicator of conditions, he says.
Smith's work involves monitoring the adult rootworms. He says
the larvae affects the roots but the adult beetle can still cause yield
loss, even if the corn is still standing tall. He uses the "sticky
trap" method; he counts the adult rootworm population to
determine adult density and if the infestation is great, works out a
control program for the next year.
"With insects, you have to work on integrated control," he
says. "we have to be aware of non -target insects. We have to
make sure we don't harm beneficial insects as we try to minimize
rootworm damage."
Another angle is the insecticide/herbicide mix. "The female
western rootworm was known to always go for first year corn,
"sink corn" as we call it," he says. "But then we were seeing the
western rootworm not going to first year corn from second year
corn. Work has been done at Purdue (Indiana) trying to identify
this and the herbicide used seemed to be a factor. Right now,
additional work is being done on this.
"Small populations of intinerant rootworm adults can feed on
foxtail, a well known and prevalent weed and, volunteer corn in a
bean field can also harbour rootworm adults," he says. .
The research dollar is scarce, he says, and he would like to do
research on the corn rootworm. He would like to propagate
rootworm eggs in large numbers, then seed the eggs in the soil.
He then would like to test different varieties of corn and chemicals
in a controlled situation to get valid information and maybe, just
maybe in the future, control the rootworm problem.
Damage by the corn rootworm is still growing. Northern adult
rootworm, says Smith, has caused a reduction in honey production
in the Tiverton area because the adults feed on the same flowers
that bees do. Corn growing is just now moving into the Bruce area,
so the problem there is just beginning.
Smith says what we really need is a more balanced and
diversified practise of cropping.
As long as this is corn country, then we'll probably be corn
rootworm country. Only a little more time and a lot of research can
change that.
THE RURAL VOICE/FEBRUARY 1982 PG. 9