Newsletter of ATTRA - National Sustainable Agricultural Information Service: A project of the National Center for Appropriate Technology (NCAT). This issue of ATTRAnews is available online.
Healthy Soils Can Help Manage Pests
Healthy soils are complex, dynamic ecosystems that interact with many other organisms—both above and below ground—through an incredible web of life. Researchers are just beginning to understand the interactions within these diverse underground communities. One thing is clear: it pays to nurture the soil by following nature’s lead. Keep disturbance (both physical and chemical) to a minimum. Keep the soil covered. Add organic matter. In this issue we look at some of the interactions and relationships between insects, fungi and other micro-organisms that work together to keep plants productive.
In this issue:
Healthy soils provide many invisible services that support the production of healthy crops and livestock. Orrsop’s Fable, as retold by NCAT Specialist Rex Dufour with thanks to David Orr, entomologist at North Carolina State University, presents a tiny slice of that picture which, even if multiplied by a million, would still underestimate the complexity of these systems.
Once upon a time in Michigan, there was a fellow researching onion maggots. His laboratory insects died out due to pesticide residues in the onions, so a graduate student suggested they use organic onions. That solved the problem, but raised a question in the researcher’s mind. He’d been told that you couldn’t grow onions in Michigan without pesticides, but clearly someone was doing it. (This was in the days before national distribution of vegetables was common.)
So he and some students went to visit the organic onion farmer. They found a small farm next to a pasture. The farmer was able to grow onions profitably. When they looked closely at the farm, they found a wasp parasite that attacked the fly larvae living in the cow patties in the pasture next door. That wasp also parasitized the onion maggots.
Some weeds were growing between the beds of onions. The researchers found adult onion maggot flies on the tips of the weeds. The flies were dead, killed by a fungus that was now spreading spores from the dead flies, to the farmer’s benefit.
The researchers also found a high population of robber flies preying on the onion maggot flies. Robber flies are generally larger flies that capture their prey “on the wing” and then pierce the soft membrane between the head and thorax of their prey and suck out the juices...but I digress. An interesting fact of robber fly life is that their larvae are parasites of earthworms. So in order to have a high population of robber flies, you need a high population of earthworms. Earthworms require healthy soil with a good amount of organic matter.
Moral of the Story
ATTRA’s online search tool helps you find the least toxic ways to manage pest problems. It provides details on biorational pesticides and prevention techniques to manage hundreds of insect pests, weeds, plant diseases, and nematodes as well as snails, slugs and vertebrate pests.
One major downfall of conventional pesticides is that they can damage a wide spectrum of living creatures—not just the target pest.
Ecological systems are highly complex, with many checks and balances. Elements of these systems can be unintentionally destroyed by over-reliance on “hard” chemical pesticides. If the natural controls are eliminated, then the pests take over. ATTRA’s ecological pest management database provides softer pest management options that help avoid harm to non-target organisms.
You can use the database to search for materials and ways to control a specific pest. Or you can use it to find information about pesticide trade names and labels, active ingredients, beneficial organisms, and the manufacturers of all these materials. See the database on ATTRA’s website.
What are Biorational Pesticides?
Plants depend on their roots to bring them nutrients for vigorous growth. But in healthy soils, the roots don’t operate on their own. They attract other organisms to help them perform their work.
The soil surrounding a plant root can be dense with bacteria and fungi. This is not surprising, since roots exude carbon compounds that the fungi and bacteria need. Using these sugars and acids as fuel, these organisms can give the plant access to the minerals in the soil.
Mycorrhizal networks can “mine” a much larger volume of soil than plant roots could reach by themselves. It seems to be a fair trade. The plant gets access to an extensive supply of water and minerals, and the fungi and bacteria get carbon compounds to help them grow.
In another beneficial interaction, mycorrhizae trigger systemic acquired resistance (SAR) in plants, inducing the plant to produce special compounds that protect it against pest organisms in the soil. There is evidence that the SAR response “primes the pump” for plant defenses against above-ground insect attacks, too.
(Reference: Induced pathogen and insect resistance in Arabidopsis. Vivian R. Van Oosten. Wageningen University, Netherlands. 2007.)
But that’s the situation in healthy soils...
The struggle to produce extra large amounts of carbon compounds may stress the plant, making it more attractive to insect pests. The effort may also reduce the carbon the plant can use for crop production, reducing yields.
(Soil-Root Interface: Biological and Biochemical Processes by H. Marchner. Soil Chemistry & Ecosystem Health, Soil Science Society of America, 1998.)
Recent research shows the complex interactions taking place in the soil and the unintended side effects of over-reliance on “silver bullet” pest management strategies. If combined with poor soil management, some of the issues discussed here could seriously impact farm profitability and sustainability.
The researchers found that glyphosate (a broad-spectrum herbicide that kills weeds) can significantly increase the severity of various plant diseases, impair plant defenses against pathogens, and immobilize soil and plant nutrients, making them unavailable for plant use. Their research found that glyphosate reduces manganese in plants. This element is essential to many defense reactions that protect plants from disease and environmental stress.
In addition to manganese, glyphosate can immobilize other plant nutrients such as copper, potassium, iron, magnesium, calcium, and zinc so they are no longer nutritionally functional. Keep in mind that glyphosate is systemic. So when it is sprayed on a plant, it is absorbed and transported throughout the plant. It accumulates in the roots and is exuded into the root zone.
Many studies have shown that glyphosate is not entirely and immediately immobilized by soil colloids because a portion is available for metabolism by soil and root zone micro-organisms. However, glyphosate is also toxic to some bacteria and fungi, so the net effect is a disruption of soil ecology—some soil and root zone microbes are stimulated, while others are suppressed.
Some other findings of recent research on glyphosate include the following:
(Reference: Glyphosate interactions with physiology, nutrition, and diseases of plants: Threat to agricultural sustainability? D. Huber & G.S. Johal. European Journal of Agronomy, 2009.)
Vineyards infested with phylloxera, a serious root pest, do better with organic management than in a conventional system. Researchers at UC Davis found equal numbers of phylloxera in the roots of conventional and organic vines. But the conventional vines suffered significantly more damage from secondary fungal infections as a result of the phylloxera feeding on them.
Root samples of conventionally managed vines showed 31 percent losses, while organically managed vines lost only 9 percent of their roots. The soil types of the two systems were quite similar, except for increased soil organic matter in the organic vineyards. The roots of the organic vines also had higher numbers of the beneficial fungus Trichoderma and lower levels of the disease-causing Fusarium oxysporum and Cylindrocarpon species.
(Reference: Grape phylloxera-related root damage in organically and conventionally managed vineyards. Don Lotter, et al. HortScience, 1999.)
Building Soils for Better Crops by Fred Magdoff and Harold Van Es. USDA-SARE, 3rd edition 2009. The complex interactions within the soil are explained here in practical, easy-to-understand terms. This 3rd edition has been refined, revised and expanded. Download free: www.sare.org/publications/soils.htm
Rhizosphere and Symbiosis is an online collection of illustrations and explanations about life in the root zone. This is just one section of Morning Earth, a website linking ecology and art.
Sustainable Soils: The Place of Organic Matter in Sustaining Soils and Their Productivity by Benjamin Wolf and George H. Snyder. Haworth Press, 2003. This book explains the vital importance of soil organic matter, and how and why to protect and increase it in farm soils.
ATTRA Soils and Pest Management Resources
See ATTRA’s pest management publications for information about various specific pest problems. Most ATTRA publications about specific crops have sections on pest management.
ATTRAnews is the bi-monthly newsletter of The National Sustainable Agriculture Information Service - ATTRA - which was developed and is managed by the National Center for Appropriate Technology (NCAT). The project is funded through a cooperative agreement with the United States Department of Agriculture's Rural Business-Cooperative Service. Visit the NCAT Web site for more information on our other sustainable agriculture and energy projects.
Teresa Maurer, Project Manager
Comments? Questions? Email the Weekly Harvest Newsletter editor Karen Van Epen at firstname.lastname@example.org.
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