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New Hampshire vegetable
grower Eero Ruuttila uses a mix of hairy vetch and rye cover
crop mulch to crowd out weeds in his valuable tomato plots.
Top: Living rye and vetch; bottom: killed and shredded as mulch.
Photos by Eero Ruuttila |
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Producers from as far away as Georgia and Oregon say they want
to emulate Groff’s system. Groff, whose combination of no-till,
cover crops and rotations has eliminated many pest problems, manages
the farm as a whole rather than as individual fields.
“Mother Nature has given us incredibly powerful tools,” says Fred
Magdoff, a soils professor in the Department of Plant and Soil Science
at the University of Vermont, who likes to repeat entomologist Joe
Lewis’ strong and simple message: “Let’s learn how to use them.”
Across the country, researchers are finding that whole-farm, ecological
systems work.
 In Pennsylvania,
80 percent of apple growers now rely on the black ladybird beetle
to control European red mites. Using chemicals very judiciously
and applying only those that the beetle can tolerate, producers
have saved millions of pounds of pesticide.
Cotton,
when attacked by beet armyworm larvae, releases volatile chemical
cues that attract the parasitoid Cotesia marginiventris,
a natural enemy of the armyworm. Leaving habitat for the parasitoid
aids the natural system.
Along
ditch banks in Michigan, three times more ground beetles are harbored
by native switchgrass filter strips than by soybean fields. These
beneficial insects can remove up to 4,000 cutworms an acre and
as many as 40 weed seeds per square foot per day. A single female
field cricket sheltered by a grassy strip can eat more than 240
pigweed seeds in 24 hours.
In Oregon,
an integrated cover crop and strip tillage system is reducing
tractor trips in vegetable crops from eight to one and confining
herbicide application to 12-inch bands. Among the results: 60
percent less herbicide use, 95 percent weed control in the untreated
areas between rows and higher yields.
For the past 50
years, most farmers have relied on pesticides as their main tool to protect
their crops from pests. Wielding pesticides like a big hammer, they pounded
back menacing insects, nematodes, weeds and diseases. Then they watched
the pests return — braced by pesticide resistance and paired with serious
outbreaks of what were once minor pests.
“It’s picked up so much speed that we can’t sustain it anymore,” says
Lewis, an entomologist with USDA’s Agricultural Research Service.
“Relying on high inputs has become unprofitable. When you just can’t
make a living or a profit anymore, you have to take a serious look
at redesigning the farming system so you can work with its built-in,
renewable strengths.”
A Growing Problem
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Corn grown in hairy vetch
mulch allowed 83 percent fewer annual grass weeds than corn
grown in unmulched soil, according to research conducted at
USDA’s Agricultural Research Service in Beltsville, Md. Photo
by John Teasdale. |
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The key weakness
of “big hammer” management is a philosophy that ignores basic ecological
principles. Reacting to complex pest problems with one tool eventually
fails because it does not consider problems as symptoms of a system whose
intricate natural controls have collapsed.
“No matter whether
that single tactic is chemical, biological or physical, if it kills 99
percent of a pest population, the few surviving pests will find a way
to avoid it or resist it,” says Doug Landis of Michigan State University’s
Department of Entomology and Center for Integrated Plant Systems. “That’s
what natural selection is all about.”
Organisms find
ways to adapt to new environments or toxic materials. Over the years,
a succession of chemical “big hammers” has reaped unintended environmental
impacts, unnecessary human safety risks, unwanted expense, unwelcome problems
with secondary pests and unnerving surges in pest problems.
From 1965 to 1990,
as conventional pest control intensified, estimated crop losses from insects,
diseases and weeds increased from about 35 percent to 42 percent worldwide.
That suggests conventional approaches are not effective in many situations.
In Eastern states,
corn and soybean growers have watched at least 10 species of annual weeds
become resistant to triazine herbicides. Now, in no-till systems, producers
use four to five different herbicides to control the weeds once stopped
by atrazine. Similarly, the costly Colorado potato beetle has become resistant
to many pesticides.
In the South,
growers battling boll weevils soon needed about 20 insecticide applications
a year to control both the weevils and all of the secondary pests —including
bollworms, aphids and spider mites — that arose after the pesticides killed
beneficial insects.
“As managers of
cotton production, we hadn’t made all of those connections until we took
the primary pest — the boll weevil — out of the picture,” says Lewis.
“The boll weevil was like a little, yapping terrier: It only took a couple
of dollars an acre to treat it. The problem was that when we treated the
boll weevil, the little dog woke up the big one.”
In the Midwest,
growers have watched corn rootworm develop resistance to [organochlorine]
soil insecticides. Even the more environmentally friendly single-tactic
of rotating corn with other crops has produced corn rootworm populations
that can over-winter for two or more years or lay eggs to avoid control
by rotation.
Resistance to
sulfonylurea herbicides in Russian thistle and to diclofop in Italian
ryegrass has left wheat growers in the West struggling to find alternatives
— only five or 10 years after the herbicides were first used.
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