February 16, 2009
Volume 87,
Number 07
pp. 13-20
Greening The Farm
Safer and environmentally friendlier pesticides and
agricultural practices gain traction on U.S. farms
Stephen K. Ritter
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 environmentconscious 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 chloroacetamidebased 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.
"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."
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 pesticidemanufacturer 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."
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 herbicidetolerant 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.
Original online posting:
http://pubs.acs.org/cen/coverstory/87/8707cover.html