Alternatives to pesticides - what are they and are they really effective in agriculture and the home?
I. Biological
controls: a. Use of larger natural
predators includes the use of birds and other insects -
we see here an approximate 40% success rate only.
Why? Introduction of foreign predators has lead
to problems as they move out into natural systems and outcompete similar
native species. They themselves have been known to become pests eventually.
However, times are
changing...... In a small town in Michigan,
cockroaches became so plentiful that they were coming home
in students' lunch boxes. Poisons had been used in the
past but simply weren't killing the pests because the
cockroaches had grown pesticide resistant. Additionally,
Michigan state passed laws requiring schools to seek
alternatives to chemical pesticides. The long-standing problem
became so severe five or six years ago that the Allegan
school district had nearly halted the school's lunch program
when Praxis, a local company that sells biological pest
controls, stepped in to, as Praxis co-owner Sam DeFazio puts
it, "create an artificial ecosystem indoors." According to
DeFazio, Allegan's school system became the first in the
country to eliminate pesticides in favor of biological
controls. Now the cockroaches in
Allegan school district are dined on by tiny wasp
parasitoids and attacked by nematodes, placed in strategic
locations throughout the school. "When you start to talk about
bringing in wasps, people start to panic," says Doug McCall,
Allegan School Superintendent. "But these wasps are the size
of a pinhead. And we've found that when we consistently
apply and manage the biological controls, they
work." The little predators may go
hungry soon; the cockroaches have all but disappeared. And
other methods have also replaced poisons for control of
yellow jackets, ants, termites and mice. Results of the biological
control have been entirely positive, says
DeFazio:
b. Bacterial predators; one of the most commonly used bacterial species is Bt or Bacillus thurigensis.
- At sporulation, the bacterium produces a spore and a protein crystal which releases powerful toxins when degraded by the gut fluids in larvae consuming it; death can occur in 30 minutes- to 3 days.
- Timing has to be right - larvae must be feeding on leaves treated with spores.Doesn't work with adults not feeding on leaves.
c. Viruses; 1600 virus isolates which can cause disease in 1100 species of insects. So far not a commercial success since virus is specific to insect so limited sales. However some real advances are emerging:
i.e. A peptide hormone was isolated and incorporated into a baculovirus. The peptide was active in preventing larval feeding and causing mortality among corn earworm larvae.
d. Fungi; One example of fungi control involves the use of another nonpathogenic fungus below taken from:http://www.ars.usda.gov/is/pr/fusarium0897.htm
"Unchecked, wilt fungi waste little time invading a plant through its roots and xylem, or vascular water supply system. The pathogens use the xylem as a conduit to spread and grow in the plant, causing blockages and stealing vital nutrients. Such assaults can exact a heavy toll on yield.
But casting certain strains of the benign Fusarium fungi onto the scene evens the score, the researchers found. For one, the protectant microbes colonize the root system better than their pathogenic brethren.
"They live on and in the vicinity of the roots, as well as just inside the roots' epidermis, or outer cell layer," Larkin explains. There, they crowd out the competing pathogens for sugars, amino acids, and other nutrients both need in order to flourish.
But the good fungi don't cause disease, and they're not fungal freeloaders. In fact, five of the strains the scientists examined play a very important role: they jump-start plants' natural chemical defense system against the pathogens.
Helping Plants To Help Themselves
Scientists named the phenomenon "induced systemic resistance." In greenhouse studies, Fravel and Larkin observed the response in tomatoes, muskmelons, and watermelons.
Induced systemic resistance might be likened to the immune response of a child vaccinated against a germ-caused disease. As part of treatment, a doctor administers a weakened form or strain of the germ to the young patient. This stimulates the child's immune system to make antibodies or other defensive cells that destroy the virulent forms.
Plants don't have immune systems, so they can't make antibodies against microbes that attack them. But they can defend themselves with natural antifungal compounds called phytoalexins and other antimicrobial substances.
The trick is to ensure that plants muster their defenses ahead of time--and that's where the benign Fusarium strains play a role. In this sense, the microbes serve as a kind of vaccine for the plant."
Another example :
Evaluation of novel biocontrol fungi. Strains of three novel fungi of the genera Stilbella, Cladorrhinum, and Laetisaria were isolated from soil, grown in liquid and semi-solid fermentation, and evaluated for their ability to reduce disease caused by Rhizoctonia solani. Selected isolates of these antagonists significantly reduced growth of the pathogen in soil and soilless mix and also reduced damping-off of eggplant, pepper, zinnia, and sugar beet seedlings under greenhouse conditions. These data indicate the presence of a wide diversity of microflora in natural ecosystems, which could be isolated, investigated, and exploited for their biocontrol capabilities.
e. Nematodes can work on soil pests.
Nematodes are simple worms consisting of an elongate stomach and reproduction system inside a resistant outer cuticle. Most nematodes are so small, between 400 micrometers to 5 mm long. Their small size, resistant cuticle, and ability to adapt to severe and changing environments have made nematodes one of the most abundant types of animals on earth;
Most nematodes feed on bacteria, fungi, and other soil organisms. Others are parasitic, obtaining their food from animals (such as the dog heartworm), humans (such as the pinworm), and plants. Agricultural cultivation encourages an increase in parasitic nematodes that feed on the crops being grown. = from:http://www.ars-grin.gov:80/ars/Beltsville/barc/psi/nem/what-nem.htm
Nematodes are considered one of the most abundant groups of living animals, and although morphological they are very simple, they have exploited a wide range of diverse habitats including invertebrates (Poinar, 1979). Nematodes can parasitize spiders, leeches, annelids, crustaceans, molluscs, and insects. If the entomopathogenic (insect-parasitic) nematode attacks insect pest; kills or hampers the development of the insect host; and is capable of mass production it can be used as an effective biological control agent (Joiner 1979).
g. Pheromones: 436 available on the market. These synthesized chemicals act to attract the opposite sex into bags or traps.
from: http://www.coopermill.com/intro.htm
Insects of the same species can communicate with one another by releasing small quantities of chemical substances from their bodies into the air. These distinct 'scents', which are called pheromones, will attract others to the source of that attraction.
Since the chemical composition of the pheromones differs from species to species, the attraction of an insect's pheromone is specific to that species alone.
Over the years, researchers have been able to chemically identify many of these individual pheromones and in a number of cases have also been able to synthesize them. As a result, it is now possible to communicate with certain insects by using these synthesized pheromones, enabling us to attract them, or disrupt them from their normal behaviour.
The key component of Integrated Pest Management for insect pests, is to have a greater knowledge of their behaviorOnly by being aware of when and where insects are present, and at what stage of their life cycle they are at, can timely decisions be made on the need for any control treatment. Pheromone monitoring provides this important tool.
Another use of pheromones is to create insect mating disruption. This is a control method which is proving itself to be a successful pest management tool in many different crops around the world and can lead to significant pesticide reduction..
A new method of insect control now in the experimental stage is to attract adults to a trap where they are infected with a pathogen before exiting. Researchers in England have developed special traps that allow diamondback moths to enter the trap, pick up the fungal pathogen Zoophthora radicans and then exit the trap. The moth then carries the pathogen to the crop where it can infect both moth larvae and other adults.
h. Juvenile hormones anti-juvenile and juvenile hormones mess up the molting cycles of insects. Very species specific and timing is critical. For more information or background on insect cycles and juvenile hormones see here:http://www.ent.orst.edu/berryr/ENT311/LECTURE5/index.htm
from:http://www.ent.orst.edu/berryr/ENT311/LECTURE5/sld012.htm
II. Genetic controls
a. Sterile male: Screw worm history: 62-71 a success; 72' strain ejected; 77' strain sexy 81' strain not sexy- consistency is a problem, though when it works can be a wonderful means of control. Still get damage by that years pest.b. Introduction of naturally resistant host strains; wild species are naturally resistant to insects via alkaloids and other chemical defense systems. These have been bred out over time due to taste or unintentionally. Aggies go back to find wild types and breed in naturally by crossing or insert gene directly to get plant to produce its own defenses.
c. Bioengineered resistance: the alpha-endotoxin gene of Bt has been inserted into tobacco and other species so no longer need the bacterium itself. Problem if bug becomes resistant to this product. In plants they naturally evolve different forms of their chemicals via selection. Can this happen if the gene involved is not 'natural to the plant'?
III. Integrated Pest Management (IPM) includes the use of cultural, biological (see above) and chemicals (pesticides at low doses). They use any technique at the appropriate time. Idea is not to completely kill off the pest but to control at an economically sustainable injury level.
Boll Weevil, common name for a
destructive beetle that infests cotton plants. The adult
insect has a long snout, is grayish in color, and is usually
less than 6 mm (less than 0.24 in) long. Feeding only on the
cotton plant, it begins in early spring to puncture the buds
and bolls and lay its eggs in them. The eggs hatch into
larvae in three to five days. The life cycle of the boll
weevil from egg to egg-laying adult is about three weeks.
Four or five generations may breed in one season. The larva, a fat, white
maggot, does the most damage. It lives on the internal
tissues of the buds and bolls. An infested bud usually
drops, but most of the damaged bolls remain on the plant and
become stunted or dwarfed. Adult weevils that emerge in the
autumn hibernate in grass, old bolls, or other vegetation or
in the seeds around the cotton gins. They reappear in
spring. The insect was first known in
Central America, Mexico, and Cuba. In 1863 its ravages
stopped the cultivation of cotton in Mexico. About 1892 it
spread across the Río Grande to Brownsville, Texas.
From this focal point it moved outward at a rate of about
113 km (about 70 mi) a year, eventually infiltrating into
every cotton-growing district in the United States east of
the Rocky Mountains. The boll weevil has been the target
of intensive pesticide spray programs. Today, however, it is
increasingly treated using nonchemical means of pest
control, including pheromone-baited traps and so-called
clean culture, the careful removal of old cotton stalks to
deprive the beetle of its overwintering
refuge.
a. Cultural methods:
These techniques require more knowledge, more labor ( some difficult to use large equipment)
Can Sustainable Farming work? yes and yet the movement in this
direction is very slow:
The American Farmland Trust found about three fourths of the 150 farms participating in its sustainable agriculture demonstration project maintained or increased crop yields while reducing their chemical use.
Slow support and too many restrictions by the government:
Myth versus Reality: Views of
Various Forms of Farming conventional
farmers vs.
low-input farmers
Yields: 70.9% think yields
will fail if they cut chemicals vs. 35.3%
say yields fell: 17.6% say they rose. Profits: 63.8% say fear of
lost profits is 1 of 3 barriers to low-input
farming. vs 76% say
lower costs increased profits. * Campbell Soup Company
reduced pesticide application by more than 50 percent in
four years without sacrificing yields or quality. Campbell
farmers in Ohio lowered the number of pesticide applications
by 80 percent and saved $26 per acre * Illinois soybean producers
saved an estimated $23 million in 1992 by using innovative
crop rotations and planting pest-resistant crops * a collaborative effort
between governments, academic institutions, growers and
processors reduced pesticide spraying on potato fields in
Wisconsin and saved almost $6 million on pesticides and
irrigation. 38% Worry that increases in
pests will decrease yield xvs.
43.4%
say pests were a problem at first ; just 33.3% say they
remained a problem after a few years of farming with fewer
chemicals Labor needs 28.3% expect
low-input farming to increase their labor
needs vs 63.6%
say labors needs increased. Information on 18.2% say
lack of good information would keep them from trying new
methods. vs. 71%
said finding good information was a problem in the
beginning Crop base 13. 1% expect
cutbacks in crop base acres if they use fewer
chemicals vs. 25.6%
say base acres fell when they cut back on
chemicals. Source: The New Farm,
May/June 1989,
The 1985 Farm Bill attempted to encourage sustainable agriculture by creating a program to study it. It never actually received any money to do the study until 1988, when $4 million was put aside.-just 1 percent of the USDA's research budget. Then in 1990, Congress broadened the program by funding $40 million to study alternative agriculture.The 1990 Farm Bill created a new program called Integrated Farm Management, which was intended to promote crop rotations without penalizing farmers. But the USDA scaled back and delayed the program; few farmers have enrolled, in part because of the way the rules have been drafted and enforced.
Farmers today produce roughly twice as much per acre due to technological innovations which have more than halved the labor required on the farm, while doubling chemical use. To many farmers these changes reflect significant progress. Farmers who want to change face many obstacles as they believe that alternative agriculture takes more time, skills, and labor, which has become increasingly hard to supply as greater numbers of young men and women leave rural areas.
In a 1990 GAO survey, 75 percent of farmers responding said they would consider growing other crops if the farm programs did not penalize them for doing so. Several farmers indicated that the federal farm programs should give them more flexibility.
The end!!!
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