CHEMICAL CONTROLS

IPM systems can, and often do, use various chemical controls as part of the overall pest control strategy. Key, however, is that the reliance on chemicals is lessened by comparison with conventional approaches to pest control. behavioral and hormonal chemicals to control pests. Chemicals used as part of IPM systems include pesticides as well as other, less conventional chemicals.

PHEROMONES

One less conventional chemical approach to pest control involves the use of pheromones. Pheromones are chemicals produced and released by insects that modify the behavior of the recipients. Most commonly used are sex atractants, which are emitted by females to attract males. Many of these have been successfully synthesized, and they are effective in extraordinarily small concentrations.

They are deployed in several ways:

One example of successful use of "confusers" involves a peach grower in CA who has used sex attractants dispersed in his peach orchards to disrupt the mating of the oriental fruit moth -- a serious peach pest. His use of confusers allowed him to reduce his use of chemical insecticides by 75% over four years!

Pheromones are now being used successfully to control many insect species.

The advantages of pheromone use include the facts that they:

Hazards or difficulties associated with their use include the facts that:

CHEMICALS PRODUCED BY PLANTS

You may have heard of "Neem" a biopesticide obtained from oils from seeds of the neem tree, which is native to portions of Africa and Asia. The plant and its effects were discovered through following up anecdotal reports about this tree that seemed to be free of insect pests. It turns out that chemicals from its seed ward off over 200 insect species, including the gypsy moth and med fly, and, fortunately, it has low toxicity to mammals, as far as is known at present. compounds from the oils interfere with many insect functions -- molting (it blocks ecdysone, a hormone needed for molting, so that the insect can't molt), reproducing, and digesting. It is safer than many synthetic insecticides, many of which poison nerve cell functions, and it doesn't seem to hurt predators of pests -- for example, aphids die, but the ladybugs that prey on them are just fine. This seems to be the case because when it is sprayed on plants, they take it in through their leaves, so only insects that eat the plant tissue seem to be affected. A neem-based product is marketed now for nonagricultural use (nursery, forest, home, greenhouse) and a license to use it on food crops has been applied for (and perhaps approved by now).

However, is this compound really benign ecologically? For example, maybe the ladybugs aren't killed directly by the compound, but they lose their food ... Again we may interfere with natural controls, as by decreasing availability of their food, and we risk also killing nontarget herbivore species that may serve some useful ecological function....

We also know that some plants (maybe many) produce volatile organic chemicals when they are attacked by herbivores. In some cases, these chemicals deter further attack (or egg-laying) by additional herbivores and/or attract predators of the herbivores. That is, some of these chemicals repel herbivores and attract their predators. I don't know of attempts to produce these compounds for commercial use, but they may be on-going. (See article in Science 291 (2001): 2104 - 2105.)

MORE PRUDENT USE OF PESTICIDES

While people often think that IPM means "pesticide free," that isn't necessarily the case. IPM systems, and sustainable agriculture, can involve use of pesticides, but much more judicious use than is common. Some general components of this more prudent use are listed below, with elaboration and examples of some to follow.

An example of successful decrease in pesticide use, partially through a combination of the tactics listed above, involves Sweden. In 1985, Sweden set a national goal of reducing pesticide use in agriculture 50% by 1990 (measured as pounds of active ingredient). They accomplished this, and set an additional goal of decreasing it again by another 50% over the following few yrs. The Netherlands, Norway, and Ontario followed suit. The Swedes have accomplished about 2/3 of the reduction by:

About 1/3 of the reduction is attributable to the use of new relatively low dose compounds, such as sulfonylurea herbicides, as well as to the fact that growers rely on pest forecast and warning services, which guide them about when spraying will be most effective; they spray when warned of impending problems, rather than on a fixed schedule. In addition, Sweden has imposed a charge on using pesticides (essentially a tax on their purchase), which encourages conservative use. Farmer acceptance of this charge has been high because revenues from the tax are used to support surplus crop exports. Growers also have increased their use of crop rotation, cultural controls and resistant crop varieties. All of these techniques also delay the development of resistance to pesticides because pesticides are less heavily used! Sweden has also established a program that gives 3-yr grants to farmers who convert to organic farming. This program has quadrupled the acreage farmed organically, which, as of the mid-1990's represents 1.3% of the agricultural land in Sweden.

Analyses for the US conflict in their perspectives on how well we could accomplish a similar reduction in pesticide use (see articles in your readings packet for examples of this conflict, with additional examples in the supplementary readings list.) Some analyses predict devastation (major crop losses if pesticide use was reduced, with accompanying increases in food prices). Some estimate that yields in the US would decrease 24-78%, depending on the crop, if farmers immediatdly substituted currently available alternatives, and that too few of those are available. Others, such as Pimental et al's analysis (1991, BioScience article on supplementary readings list), suggested that the US could reduce pesticide use in agriculture by 50%, using then-currently available biological and environmental control technologies, with only a 0.6% increase in food prices. The price increases would be incurrend because of increased farmer costs of about $1 bill/yr, or a 25% increase in pest control costs. This analysis assumed that food supplies wouldn't shrink much because of increased losses to pests -- i.e. yields would be about the same -- so that consumer prices woulnd't be driven up by increased losses. This increase in food prices should, according to Pimentel et al., be judged against an estimated $ 4-10 bill savings per yr in decreased damage to fish and water supplies, costs of pesticide regulation, health care costs for those poisoned by pesticides, monitoring of groundwater for pesticides, and destruction of beneficial organisms (including honey bees).

According to Pimentel et al.'s analysis, pesticides at then-current use rates appeared to be cost effective, but weren't really. There were direct yield benefits of about $3-5 for every $1 invested in pesticides. But those cost figures don't reflect the indirect costs of chemical use -- poisoning, fish and wildlife effects, pesticide resistance, honeybee damages, etc . In addition, these benefits are calculated based on current agricultural practices, which can actually increase pest problems (click on crop diversity or pesticides for some reminders about this). Their analysis (based on US production of cotton, corn, soybeans, apples, and potatoes) included use of such pesticide reduction techniques as:

They point out that, since 1966, insecticide use on cotton in Texas has decreased by about 90% through increased use of pest monitoring, biological control, sanitation, rotation, clean seeds, and changed planting dates. They also claim that, for US corn production, combining rotation with use of varieties resistant to insects could avoid 80% of current insecticide use and concurrently decrease insect losses. These changes would, however, increase the cost of corn production by about $10/acre above that associated with growing corn continuously.

Consumer effects of reducing pesticide use depend on how the reduction is accomplished. Pesticide bans (particularly when no effective substitute pesticides are available -- or when the substitute is much more expensive) tend to cost consumers more than do pesticide-use fees (as imposed in Sweden). This is because the supplies of produce may drop dramatically when no substitue pesticide is available, or because the main areas of production shift (avoiding geographically-restricted pest problems), causing economic hardships to growers. However, most of these changes are suggested to be short term, so that over the long term, consumer hardships do not result. Thus, pesticide use fees are generally considered more efficient than outright bans as a mechanism for obtaining environmental goals. Such fees encourage farmers to be more selective in their choices of chemicals, and to switch to other options, as they become more cost effective by comparison with the fees. With fees, growers in areas where the pest that the pesticide is used against isn't a problem may begin to grow that crop if its price increases because of the pesticide fees, or because of decreased supply when farmers in other areas quit growing it because the fees are too expensive, and then the supply would increase again and the price to the consumer would return to normal. The fees can then be used for research on and development of safer pesticides or pesticide alternatives, to subsidize their adoption, and to address negative side effects from pesticide use

In fact, cancellation of some pesticide registrations can actually increase the use of chemsicals! For example, apple farmers used phosphamidon which controls aphids without killing natural predators of mites, so that they didn't also need to use miticides. When the registration of phosphamidon was withdrawn, farmers began using other chemicals to control the aphids, but these also killed beneficial predators and mite outbreaks increased, so farmers resumed use of miticides. Here a pesticide cancellation actually disrupted an IPM program.

In the US, mainstream farmers are switching more and more from chemical insecticides to biological and environmental control agents, owing to a mix of social, scientific, and economic considerations. They are concerned about the environmental and health risks of the chemicals, are concerned about the problem of pests developing resistance, prefer the relative lack of paperwork, and don't like the rising insurance premiums associated with the use of chemicals. Many have learned that there are alternatives that they can use while still making the desired income. Conventional modern agriculture is at one extreme, "organic" farming is at another, and a sustainable middle ground may be found between.

However, the government's committment to research and development on alternatives must increase if we are to be really successful at decreasing pesticide use on a wide scale.

To return to the list of topics for this discussion on sustainable agriculture, click on sustainable. To return to the master Table of Contents for this BI 301 home page, click "Contents" at the bottom of the page.

This page is maintained by Patricia Muir at Oregon State University. Page last updated (partially!) November 28, 2012.

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