MICE, INSECTS ULTIMATE BIOLOGICAL CONTROL?

By TOM BUTTON

No-till farmers can cut their spray costs if they
can keep their cats out of the fields, new research
from the University of Guelph suggests.
Professors Clarence Swanton and Stephen Murphy are
finding that mice and small insects eat up to 95
per cent of the weed seeds produced in no-till
crops.
Swanton thinks it could be a key reason why
conservation farmers find it gets easier and less
expensive to keep weeds under control the longer
they're in the system.
"It's a real-life example of biological control at
work on the farm," Swanton says. "It's free, it's
broad spectrum, and it just happens to come along
with the change in tillage. You don't have to do
anything special or anything different to make it
happen."
The Guelph team tested the theory by putting dishes
of lamb's-quarters, ragweed and foxtail seeds in
no-till fields, covering them with cages with
different mesh screens so they could control which
animals could get access to the free meal.
So far, the researchers have one year's data, and
they say they'll repeat the tests for two more
years to make sure the preliminary results aren't a
fluke.
Those early results have raised eyebrows. In corn
tests, for instance, 95 per cent of the seeds were
eaten between harvest and planting, mainly by mice.
In soybean plots with smaller-mesh cages, ants ate
70 per cent of the seeds.
Swanton thinks that in plowed fields, more seeds
would survive because they'd be buried out of the
reach of many seed eaters.
He also thinks that life is tougher for no-till
seeds than it is for seeds that are turned under.
Seeds left on the surface are exposed to a harsh
environment, with no layer of soil to shield them
from extreme temperatures, making it likely they'd
have a lower germination rate than seeds that are
buried.
And since the seeds are concentrated at the soil
surface in no-till, those that do survive tend to
sprout all at the same time, making it easier to
use a non-residual post-emerge spray to keep the
field clean.
Swanton thinks these studies may encourage more
conservation tillage farmers to adopt the new
theories of critical periods of weed control.
Research at Guelph and elsewhere shows that corn
growers need only worry about weeds that emerge
with, or shortly after their crops. Weeds that
emerge four to six weeks after the crop is up
rarely cut yields enough to make spraying economic.
In soybeans, farmers need weed control only until
the field reaches the second to third trifoliate
stage, about 30 days after planting. 
Many farmers have told Swanton they can't use these
findings, because they're worried about adding
seeds to their seedbank.
"The argument we always hear is - I have to use
lots and lots of herbicide to be sure my fields are
clean or else I'll end up with a serious long term
problem," Swanton says. "Our work shows it's a
non-issue. You don't have to worry about weed seeds
if they aren't going to survive."
Over the next two years, the Guelph team will take
a look at which predators are attracted to which
seeds, and at ways farmers can boost their
biological weed control.
There are already strong indications that more
seeds get eaten in fields with high residue cover.
Early studies show, for instance, more seed eating
in corn residue than in soybeans.
"There may be ways we can manage our residues to
encourage more seed predation," Swanton says. "It's
one year's data. It needs more research. But if the
numbers hold up, this could become one of the most
important factors in our weed control strategies."   

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