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?

  • Need to set up an appropriate home for the predator - nesting habitat etc. not to common in corn fields.
  • If the the predator is too good, it consumes up all the pest and then migrates out- must be alternate prey.
  • Need to have handy a good taxonomist who knows how to id the pest and appropriate predator.

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:

  • *The school is now pest free
  • *Use of pesticides has been discontinued
  • *The school system is spending up to 80 percent less on pest control than it did when it relied on conventional methods of control.

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:

"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:

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.


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:


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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