Reducing Pest Pressure, Page 3
|Hana Newcomb stands by the vegetables produced by her 30-acre organic farm in northern Virginia. She and her mother, Hiu, rely on mulches to control weeds - from onion plants blanketed by composted leaves, to blueberry bushes rising through mounds of sawdust, to cucumber plants pushing protective sheets of white polyester. Photo by Valerie Berton.|
Reduce tillage for healthy soils. Many people consider tillage necessary for crop production. However, this seasonal practice can destroy some vital processes by depleting organic matter, intensifying the loss of topsoil to erosion and destroying soil tilth. Damaged soils are less able to provide nutrients, hold water and support biological activity. The net result: less diversity in crucial soil organisms.
'In my opinion, there's no single greater catastrophic event in the life of the soil than to have some big piece of tillage equipment run across it,' says Luna. 'Worms and bugs are killed, fungi are broken up and destroyed, and you end up with a much more simplified biological system.'
To plant and establish vigorous crops, you need to clear vegetation and residues from at least a portion of your field. Some equipment, however, minimizes soil disturbance. No-till planters, which cut a slot just wide enough to insert seed, disturb soil the least. Strip-tillage disrupts only a band of soil along the crop row, leaving untilled areas between rows. Ridge-till systems produce only shallow soil disturbances. Chisel plows do disturb soil structure, but, unlike moldboard plows, they do not invert or pulverize soils. No-till, zone-till and ridge-till also leave accumulations of plant residues covering the soil.
In a 1997 vegetable trial, Oregon State University researchers found a Willamette Valley farmer improved corn yields after strip-tilling into a winter cover of oats, vetch and Austrian winter peas. The farmer planted in eight-inch strips cut into the cover crop residue. The new system returned $100 per acre more than the standard tillage system.
Surface plant-residue mulches supply organic matter that reverses many of the detrimental effects of tillage. They take the edge off soil temperature extremes and keep soil moisture more consistent, thereby favoring a wide group of organisms. These factors combine to improve biological activity, soil tilth and nutrient- and water-holding capacity.
In Lancaster County, Pa., Groff says his cover crops - along with his 'full time, 100-percent commitment to no-till' - have increased his soil organic matter from 2.7 to 4 percent in the last decade. Although he farms on slopes as steep as 17 percent, his annual erosion losses are only a fraction of the county's average.
When putting in underground irrigation lines, Groff found 'roots of my rye cover crop 40 inches deep and earthworm holes 36 inches deep. By not tilling the soil, by leaving all of that structure intact, over several years I have a soil that begins to open up.'
Maintain surface residues. More diverse biological and physical environments at the soil surface spark more bountiful opportunities for regulating pests. The living and dead plant materials linked with no-till management readily establish biological activity, which can contribute to natural suppression of pests. The soil organic matter and fertility generated by cover cropping and reduced tillage also lessen pest damage simply by improving the growth and vigor of crops.
Cover crops supply generous amounts of surface vegetation and residue that can be customized for specific needs. Live, they furnish excellent habitat and food for beneficial insects. Strip-tilling a cash crop into a winter annual cover crop or overseeding the cash crop with a cover crop after the last cultivation allows bands of live covers to flourish between rows without over-competing.
In some systems, cover crops eliminate the need for pre-plant herbicides and reduce the need for post-emergence herbicides. (See Resources for information about the comprehensive book, Managing Cover Crops Profitably.) Winter annual cover crops continue to yield crop benefits even after they have withered. Along with residue from previous crops, they can interfere with pest populations by:
hindering weeds or other soil pests by physically obstructing their growth, tampering with soil temperature or moisture, or unleashing plant-inhibiting allelopathic chemicals,
preventing fungal spores from being dispersed by water or wind, thereby curbing foliar diseases, and
enhancing populations of predatory insects such as ground beetles and spiders.
'We see it over and over in our research,' says weed specialist Teasdale: 'The tomatoes in the vetch cover crop system stay green and healthier longer than tomatoes grown on a black plastic mulch.' Indeed, the tomatoes maintain healthy green foliage about 50 percent longer.
Other practices for building healthy soils. Good management of soil organic matter - reducing tillage, applying animal manures and composts, and rotating with such soil-building crops as sod-forming grass and legume forages - forms the basis for healthy soils. Develop strategies to encourage on-farm nutrient cycling and help organic matter accumulate. Take care to avoid compacting soils. You may need to keep heavy equipment off wet soils, maintain controlled traffic zones on soils susceptible to compaction, or use some tillage to break up compacted layers. Many of the soil-building practices discussed above help reduce soil erosion. On soils that are prone to erosion damage, consider strip cropping, grassed waterways to conduct runoff off fields, and soil terracing to help keep topsoil in place.