Ecologically Based Systems
|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
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
|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.|
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.