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Insects and Diseases
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Vegetable growers like Steve
Mong of Stow,
Mass., have controlled corn earworms, a
significant pest for organic farmers, by
using a new device designed by SARE-
funded researchers that dispenses corn
oil and Bacillus thuringiensis (Bt).
– Photo by Ruth Hazzard |
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"Organic farming requires more intensive management than conventional
methods," said Joe Rude, the poultry farmer from Colo, Iowa,
"because without access to a broad spectrum of pesticides and
antibiotics, you have to understand the life cycle of the pests
that are attacking your crops and animals. You have to understand
the biological and chemical processes and work with the environment."
For organic farmers, this means employing strategies such as crop
rotations, enhancing biodiversity, determining threshold levels
of pest populations, introducing natural enemies and using good
sanitation practices. Although certain sprays such as Bacillus
thuringiensis (Bt) and rotenone are permitted, many organic
farmers do not rely upon them exclusively. Rather, the key focus
of organic pest control is prevention.
In California, where dry summers make it less challenging to grow organic fruit,
a SARE-funded on-farm study comparing organic and conventional apples found
that synthetic pheromones, biological control agents and sanitation successfully
controlled codling moth mating in most locations. Disease control with sulfur
and copper, when timed right, was as effective in scab control as the synthetic
fungicides used in conventional systems.
In New York, where the wet humid summers pose enormous challenges for organic
fruit production, Robert Pool, a Cornell University viticulture professor, found
that organic grapes could be managed to be as pest-and disease-free as conventional
ones. During a three-year, SARE-funded experiment, which compared organic and
conventional grape production on three varieties, pheromone disruption and insect
scouting allowed researchers to eliminate regular insecticide use.
"Going in, we thought the main problem would be diseases," said Pool.
But instead, researchers applied, on average, less than one spray per year and
found that the powdery mildew commonly observed on Concord grapes was far less
destructive than predicted. The researchers also learned that pheromones successfully
controlled grape berry moth and that scouting allowed them to control insects
that emerged when the regular spraying was eliminated. They avoided an expected
huge spike in grape leafhopper by releasing predatory wasps.
Other SARE-funded research has shown similar control:
 In
a study of potatoes in Idaho, researchers were able to control
Colorado potato beetle with mineral and biological compounds.
In the
Northeast, where sweet corn can be devastated by caterpillar pests,
Bt and corn oil were used effectively to control corn earworm.
Eight farmers from Vermont to Connecticut found that the oil controlled
ear damage in 83 percent of their trial plots in 2000.
Many organic farmers have observed that, over time, pest populations seem to
decrease. Results from a California on-farm organic tomato experiment showed
the presence of 46 percent more predators and parasitoids and 43 percent more
natural enemies on the organic farms, which could provide one possible explanation
for reductions in pest populations. A SARE-funded study in Washington testing
mowing frequency in pear orchards found that mowing only once a month rather
than more frequently as done on conventional farms, creates alluring habitats,
attracting beneficial insects that control pests.
"By reducing the frequency to once a month, we see a dramatic increase
in natural enemies moving into the ground cover without a big increase in pests
that feed on fruit," said David Horton, the ARS researcher testing mowing
regimens.
Stone fruit grower Marilynn Lynn of Bridgeport, Wash., relies on living mulches
to attract beneficial insects that prey on potential pests before they can harm
her peaches, apricots and nectarines. "We mulch extensively," Lynn
said during a satellite broadcast about organic production aired by Washington
State University in spring 2003.
Calling their orchard grass, yarrow and clover covers a "bed and breakfast"
for beneficial insects, she added: "They give a nice diversity to the floor
of our orchard, providing food and water in the spring when they wake up."
For soil borne-disease control in organic systems, many growers use composts,
long known as effective plant pathogen suppressants. Rotations also
are important for decreasing pathogen populations, as most pathogens
are plant specific. In general, rotating the crop, planting resistant
varieties, and adding organic matter have all been shown to reduce
the incidence of soil-borne diseases: In the SAFS project in California,
a four-year organic rotation had lower incidence of corky root and
red root rot than a two-year conventional rotation; an on-farm tomato
study in the Central Valley of California showed that organically
managed soils may be suppressive to the organism that causes corky
root; and in North Carolina, another SARE-funded study showed disease
was significantly reduced by organic soil fertility amendments and
on organic versus conventional farms.
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