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Volume 87 Issue 7 | pp. 13-20
Issue Date: February 16, 2009

Cover Stories

Greening The Farm

Safer and environmentally friendlier pesticides and agricultural practices gain traction on U.S. farms
Department: Science & Technology | Collection: Climate Change, Green Chemistry, Sustainability
News Channels: Environmental SCENE
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In season
Tomato growers have a variety of pest-management options: plastic for weed control, fumigation under the plastic before planting to eradicate fungi and nematodes, and pesticides to protect the growing plants and fruit.
Credit: Courtesy of Pam Marrone
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In season
Tomato growers have a variety of pest-management options: plastic for weed control, fumigation under the plastic before planting to eradicate fungi and nematodes, and pesticides to protect the growing plants and fruit.
Credit: Courtesy of Pam Marrone

AD HOC efforts by an impressive array of federal and state agencies, farmer alliances, chemical companies, and nonprofit advocacy groups are dramatically shifting the way pesticides are made and used. As a result, pesticide use in the U.S. has dropped. Data from the Environmental Protection Agency show that conventional pesticide use, which includes agricultural and home and garden applications, peaked at 1.46 billion lb in 1979 and fell to 1.23 billion lb in 2001, the last year for which comprehensive data are available. Since then, pesticide use in the U.S. appears to have remained flat, according to limited government data and market research reports.

The drop in pesticide use is due to a host of factors, including better pesticides that not only are more selective and applied at lower rates, but also have lower inherent toxicity and thus a lower impact on human health and the environment. Another factor is the set of farming strategies called integrated pest management (IPM), which relies on the life cycles of pests and crops to control pests economically and withholds use of pesticides until potential damage reaches a certain threshold.

A third factor is organic farming, which shuns synthetic pesticides altogether. But when organic farmers need help, they can turn to approved nonsynthetic pesticides and so-called biopesticides, which have emerged as a viable alternative pest-control agent for safety- and environment-conscious farmers and consumers.

Christmas trees provide an unexpected example of how these changes in pesticide use have come about. U.S. tree farmers produced nearly 17.5 million Christmas trees on some 343,000 acres in 2007, according to the Department of Agriculture's Census of Agriculture. By comparison, potatoes were grown on about 1.13 million acres, field tomatoes on 442,000 acres, and green peas on 214,000 acres.

"There definitely has been a decrease in the amount of pesticides used per acre on Christmas trees," says Jill R. Sidebottom, an extension forestry specialist at the Mountain Horticultural Crops Research & Extension Center, in Mills River, N.C. The center is operated by North Carolina State University and the North Carolina Cooperative Extension Service.

Three pest-management surveys of North Carolina Christmas tree farmers conducted by Sidebottom and colleagues found that the average amount of active herbicide ingredient used to grow trees decreased by 15% to 1.45 lb per acre between 2001 and 2007. During the same period, application rates of insecticides dropped by 50% to 2.1 lb of active ingredient per acre. On average, it now takes only about 0.25 fluid oz of active pesticide ingredient to produce a Christmas tree over eight years.

The reductions have come about in part because older, potentially more toxic pesticides are being phased out under the Food Quality Protection Act of 1996, says Dale Kemery, an EPA spokesman. The law enables EPA to expedite the review of reduced-risk synthetic pesticides and biopesticides to help them reach the market sooner.

"THESE PESTICIDES reduce risks to human health, reduce pesticide risks to nontarget organisms, reduce the potential for contamination of valued environmental resources, and broaden adoption of IPM or make it more effective," Kemery points out. So the act "is helping transition pesticide use in the U.S. to safer pesticide use," he says.

Spurred on by EPA's reduced-risk initiative, Syngenta has "significantly intensified its product development program across all types of agricultural chemistry," says Sherry D. Ford, head of communications for crop protection at Syngenta. Since 1993, when EPA launched its reduced-risk program, Syngenta has introduced 16 reduced-risk pesticides—many that can replace problematic methyl bromide and organophosphates. That's more than any other company, Ford notes.

For example, the synthetic herbicide (S)-metolachlor, a chloroacetamide-based plant enzyme inhibitor, is the most successful reduced-risk registered pesticide, Ford says. It accounts for a 17 million-lb annual reduction in herbicide use over the original metolachlor product, which contained a mixture of enantiomers.

Better implementation of IPM has also affected pesticide use, Sidebottom notes. She has been working with Christmas tree farmers for the past 20 years to improve IPM and select more effective pesticides.

IPM employs information on the life cycles of pests and crops to manage pest damage by the most economical means and with the least possible hazard to people and the environment, Sidebottom explains. Farmers monitor and identify pests—not all insects or weeds require control—and wait for established thresholds before using pesticides.

Farmers who practice IPM also prioritize strategies. First, they try the least risky pest controls, such as natural pheromones, parasitic predators, and diseases that afflict pests. Next, they apply limited spraying at the lowest possible rate with selective pesticides. Spraying a whole field with a broad-spectrum pesticide is a last resort. IPM thresholds are set so that farmers don't use pesticides until the potential cost of pest damage to the crop outweighs the cost of applying the pesticide.

Weed Control
The environmentally persistent herbicide simazine is being replaced by greener options, such as glyphosate.
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Weed Control
The environmentally persistent herbicide simazine is being replaced by greener options, such as glyphosate.

"IPM has provided farmers the ability to continue using many of the same materials to treat their fields that they have always used, but use them in a more environmentally responsible way," Sidebottom emphasizes. "Plus, it's a way farmers can cut costs."

The big change in herbicide use on Christmas trees over the years has been a shift away from products such as simazine, which is sprayed on fields before weeds emerge, to glyphosate, a reduced-risk chemical that is sprayed on growing weeds and grass, Sidebottom says. Simazine is a triazine-based herbicide that disrupts photosynthesis. It has been associated with a number of potential human health problems and is persistent in the environment. Because of those concerns, EPA has set a maximum contaminant level of 4 ppb of simazine in drinking water.

Glyphosate, one of the most widely used herbicides in the world, is an aminophosphonate analog of the amino acid glycine and interferes with plant biosynthesis of amino acids. It is less persistent in the environment than simazine and has a drinking water limit of 700 ppb. According to data from lethal-dose testing in animals, glyphosate is less toxic than caffeine, aspirin, and table salt.

TREE FARMERS have gotten away from trying to eradicate weeds in favor of applying just enough herbicide to stunt their growth, a technique known as "chemical mowing," Sidebottom says. They typically apply herbicide around the base of trees and, when necessary, use tractors to mow between rows.

"With this approach, farmers can maintain a living ground cover free of weeds that is habitat for wildlife, including natural predators for certain pests," she says. "The ground cover also reduces erosion and helps protect the roots of trees."

Greener Acres
Biopesticides such as the fungicide Regalia, which contains physcion, and the reduced-risk synthetic herbicide (S)-metolachlor are cutting down the risks of pesticide use.
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Greener Acres
Biopesticides such as the fungicide Regalia, which contains physcion, and the reduced-risk synthetic herbicide (S)-metolachlor are cutting down the risks of pesticide use.

Meanwhile, the big change in insecticide use on trees is that lindane (hexachlorocyclohexane) is no longer available. This neurotoxin had been widely used to control the tiny balsam woolly adelgid, an insect that feeds on the bark of the Fraser fir—the most common species of Christmas tree grown in North Carolina—and releases toxins that can kill the trees.

EPA tests dating back to the 1970s show lindane to be more persistent in the environment than other pesticides. Lindane was phased out for agricultural use in 2006, to the dismay of farmers who note that it was the most effective insecticide on trees, Sidebottom says.

Several new products have replaced lindane. One is the pyrethroid compound bifenthrin, which also is an insect neurotoxin but is about 10 times less toxic to rats and has a lower application rate than lindane. Pyrethroids are synthetic analogs of natural insecticidal pyrethrin compounds produced by plants. They are less toxic to birds and mammals than traditional synthetic insecticides, Sidebottom says, but they can be toxic to fish.

Quantifying the environmental and health impacts of lower pesticide use is not easy, Sidebottom says, but she has compiled some data. Wells and public water samples near North Carolina tree farms have been tested for pesticides for more than 10 years. Fewer than 10% of the samples tested contain simazine or lindane, she says, and none of the samples has exceeded the EPA action levels. In addition, cancer rates in North Carolina counties that grow Christmas trees are on par with or lower than in other parts of the state, even for prostate cancer, which has been associated with pesticide use among farmers, Sidebottom notes.

The links between the proper use of pesticides and health problems are not conclusive, Sidebottom says. "It should still be everyone's goal to reduce their exposure to pesticides."

Because of consumer concerns about pesticide use and residues, Sidebottom has been thinking about some new approaches to tree farming. The growing interest in organic agriculture is influencing her ideas.

Organic farming incorporates the basic tenets of IPM, but it relies more heavily on composts, cover crops, crop rotation, and hand labor to control pests. Foods and agricultural products that are certified organic by USDA's National Organic Program are grown without synthetic pesticides, chemical fertilizers, irradiation to kill pathogenic bacteria, or bioengineered plants. Farmers must meet the criteria for three years before their products earn the USDA certified organic label.

THE COMMON BELIEF that organic farms don't use pesticides is untrue, however. Sulfur, copper sulfate, pyrethrins, and products based on compounds produced by the soil bacterium Bacillus thuringiensis are approved for organic use. In fact, elemental sulfur and copper sulfate are the most widely used fungicides on all types of crops—both organic and conventional—but in particular on grapes, melons, and berries.

Organic tree farms are few and tend to be small, Sidebottom says. The problem with organic production of Christmas trees is establishing the seedlings: The little trees can't tolerate high grass or weeds, she explains. Farmers have experimented with putting fabric or plastic on the ground around the trees, which is highly successful in controlling weeds and improving drip irrigation for crops such as tomatoes. But for Christmas trees it's too labor-intensive, she says.

One idea for tree farmers is to refrain from using pesticides during the last year before harvest, so that when the trees are sold they should be pesticide-free, Sidebottom says. "Late organic" is another strategy that she is researching. "It takes six or more years to grow a Christmas tree, and to be certified organic, a farmer can't use pesticides for three years," she notes. "So farmers can grow trees the conventional way, using herbicides and insecticides until the trees are several years old, then stop using chemicals." These approaches can also be used on citrus and tree nut crops.

Organic farming advocates are pinning their hopes for environmentally friendlier agriculture on such innovations. The U.S. organic industry is already enjoying brisk growth, nearly 20% annually during the past decade, according to the Organic Trade Association. But as the sector matures during the next few years, growth is projected to slow to about 10% annually. The U.S. organic food and beverage sector reached $16.7 billion in sales in 2006, or 2.8% of the overall food and beverage market, up from 0.8% of the market in 1997.

Although organic farming techniques cut down pesticide use and pesticide residues on foods, it's uncertain by how much. In the U.S., organic crops are currently grown on only 1.5 million acres of the approximately 220 million acres of planted cropland, notes Leonard Gianessi, director of the Crop Protection Research Institute, a research organization supported by the pesticide-manufacturer trade association CropLife America. He concludes that organic farming is having little impact on overall pesticide use so far.

Although there are effective nonsynthetic insecticides and fungicides approved for spraying by organic growers, Gianessi says, there are no highly effective nonsynthetic herbicides that can be used by organic growers. Thus, weed control problems remain the biggest barrier to expansion of organic farming, he adds. For example, synthetic herbicides cost fruit and vegetable growers about $50 per acre compared with $1,000 per acre that weeding by hand can cost the organic grower, Gianessi says.

Using natural product chemistry to develop a bioherbicide that can be used on conventional and organic crops would be a godsend. And that's exactly what entomologist Pamela G. Marrone has in her sights.

"The growth of biopesticides is outpacing the growth of the chemical pesticide market, and that is going to continue," observes Marrone, who is chief executive officer and founder of Marrone Organic Innovations (MOI), a biopesticide company in Davis, Calif. In fact, more than half of the new pesticides being registered by EPA are biopesticides, she says.

Before chemists came along, nature evolved its own mechanisms for protection in the form of pheromones that disrupt the reproductive cycle of insects and proteins that work by various mechanisms to ward off pests. These compounds, derived from plants, bacteria, fungi, and insects, are collectively known as biopesticides. They tend to not be harmful to most beneficial insects such as honeybees and ladybugs; have low toxicity to mammals, birds, earthworms, and aquatic life; and break down quickly to compounds that are innocuous in the environment.

Sales of synthetic pesticides dominate the $30 billion global pesticide market, Marrone notes. But she estimates that global biopesticide sales are growing at 10% per year and will hit $1 billion by next year.

Besides helping reduce the use of synthetic pesticides, biopesticides are in demand for their novel and complex modes of action that can work around pest resistance, which is starting to occur with synthetic gold standards such as glyphosate, Marrone says. And as the food market becomes increasingly global, the maximum residue levels of pesticides allowed on fruits and vegetables become more critical. Conventional pesticides can prevent U.S. farmers from exporting their products to Europe, which has more stringent requirements than the U.S., she notes.

FURTHERMORE, the number of new pesticides coming out of large company research labs is at an all-time low, Marrone adds. Pesticide manufacturers are starting to realize there are huge opportunities to develop new products by mixing and matching existing synthetic pesticides and even by sharing active ingredients to make collaborative products.

"There's no reason biopesticides can't be in that mix," Marrone says. "We could combine a biopesticide with a traditional pesticide to potentially get a boost in efficacy and delay resistance."

Sprucing Up Firs
Environmentally problematic insecticide lindane, used on Christmas trees, has been replaced by greener products, such as bifenthrin,a synthetic analog of natural pyrethrins.

One of the pioneers in the field, Marrone started working on biopesticides at Novo Nordisk in the 1990s. In 1995, she started her own company, AgraQuest, which at first focused on developing biofungicides. AgraQuest took off and achieved great success, receiving a 2003 Presidential Green Chemistry Challenge Award for its first commercial product, Serenade, the first broad-spectrum biofungicide.

Serenade's antifungal properties stem from the activity of a suite of more than 30 lipopeptides produced by a strain of Bacillus subtilis that one of Marrone's colleagues discovered in a soil sample from a California orchard. The lipopeptides form micelles that destroy fungal cells and spores to prevent the plant pathogens from reproducing. Serenade is now being used on commercial fruit, nut, and vegetable crops and for home and garden use.

Two years ago, with AgraQuest well established, Marrone started MOI to create a new line of products to move beyond biofungicides. "It is easier to find a fungicide than it is to find something to kill insects, nematodes, and weeds," she says. "We set a very lofty goal that we are going to find microorganisms that produce interesting compounds that work systemically in plants." Systemic agents are absorbed by plants and tend to be more selective and last longer than pesticides that work on contact, she explains. "That would really change the game for biopesticides," Marrone says.

MOI already has two winners on the market and a handful of prospects in the pipeline. One of the products is Regalia, an extract of the giant knotweed plant, so named for the jointed swollen nodes on its 12-foot-long stem. Its active ingredient includes two anthraquinones, emodin and physcion. These chemicals induce plants to boost production of proteins and phytochemicals that are active against bacterial and fungal invaders, such as the Botrytis fungi that cause fuzzy gray mold on fruits and vegetables.

MOI's other product, GreenMatch EX, is a herbicide that contains citral, a terpene derived from lemongrass oil, as the active ingredient. The nonsystemic herbicide strips away the waxy cuticle of leaves, causing them to quickly wilt. Because lemongrass oil and the inert ingredients in GreenMatch EX are food-grade natural components, the herbicide is certified organic and does not require EPA registration as a pesticide, Marrone points out.

GreenMatch EX is an interim product for what Marrone is really after: a systemic bioherbicide that works as well as the systemic synthetic herbicide glyphosate. Marrone and her team are developing several possible candidates derived from bacteria and fungi. She's keeping details of these potential bioherbicides a secret for now, but MOI is aiming to commercialize one by the end of next year.

"GROWERS TODAY are becoming more interested in these new types of solutions," says Janice L. Person, Monsanto's public affairs director. Monsanto is best known for its genetically modified Roundup Ready crops, which are resistant to damage from its Roundup brand of glyphosate. One of the company's newer offerings is Bollgard cotton, a variety modified with B. thuringiensis genes to resist worms that damage cotton bolls. When Bollgard is "stacked" with Roundup Ready technology, the combination of insect and herbicide resistance is a powerful new tool for farmers, she says.

Another Monsanto R&D effort still being tested is the first "three-way stack" of herbicide-tolerant technologies. It incorporates resistance to glyphosate, to the related aminophosphate glufosinate, and to dicamba (3,6-dichloro-2-methoxybenzoic acid) into one variety of cotton to provide farmers with greater flexibility in weed management.

"These types of products really help growers control pests without having to use chemicals or significantly reducing the amount of pesticides they have to spray," Person says. "These are the kinds of ideas that keep us excited."

Any reduction in the use of agricultural chemicals inherently enhances the safety of farming and its products and protects the farm and its surrounding environment. The ability of farmers, consumers, chemical companies, and government agencies to work together toward the judicious use of pesticides will be important in that effort.

 
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