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Whitewashing Agriculture
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An Empire apple protected with a kaolin coating.
See K9133-1—showing
an Empire apple treated with conventional pesticides.
(K9134-1)
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Last year, Michael Glenn held the Big
Apple in the palm of his hand . . . and he was far from New York City.
In the orchards of ARS' Appalachian
Fruit Research Station in Kearneysville, West Virginia, the severe drought of
1999 revealed another advantage of covering apple and pear trees with a white,
reflective film of specially processed kaolin, a type of clay. Empire apples
harvested from treated trees were an average of 17 percent larger than fruit
from trees left naked to withstand the heat—even from trees that were
irrigated. And there was no decline in the number of apples.
Sekel pears reacted a little differently. The protected trees yielded twice as
many pears as the naked trees—with no loss in fruit size, says Glenn, a
soil scientist and plant physiologist. |
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An Empire apple treated with conventional pesticides.
See K9134-1—showing
an apple protected with a kaolin coating.
(K9133-1)
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On the West Coast, the stark-white
particle film, now sold under the trade name Surround WP, prevents sunburn on
apples and walnuts, he adds.
Yes, fruit can suffer sunburn too, and the damaged areas are perfect places for
rot organisms to multiply. So packers pay bottom dollar for produce with
blemished skin or shells, or they reject it altogether. In studies here and in
South America, South Africa, Australia, and New Zealand "the kaolin-based
product has cut sunburn damage on apples in half," Glenn says.
That reduction gives growers an economic advantage, says Jim McFerson, manager
of the Washington Tree Fruit Research Commission. He notes that several
Washington apple growers are using kaolin to prevent sunburn alone. In his
collaborative studies with Glenn, the coating has not increased tree vigor or
yield nor improved the color of the state's apples as it has in the East. |
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Soil scientist Michael Glenn (left), entomologist
Gary Puterka (center), and Engelhard Corporation marketing director
John Mosko evaluate the particle film coverage and the color of
Empire apples.
(K9130-1)
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Cooler Crops
As nomads crossing the desert wear white robes to reflect the sun's rays, trees
wearing the specially processed kaolin coat reflect the heat-producing infrared
wavelengths, as well as the burning ultraviolet rays. In fact, it's the ability
to keep the tree cooler under a blazing sun that increases yield.
"The reflective kaolin helps to improve the tree's environment by reducing
leaf temperature and heat stress," explains Glenn. As a result, the leaves
keep their tiny portals—stomates—open, allowing more carbon dioxide
to enter. This gives the leaves more raw material to photosynthesize into food
for the tree.
"The tree doesn't have to abort as much fruit, and there's more carbon for
its own growth and maintenance," explains Glenn. The result: a healthier,
happier tree that can support higher yields year after year. |
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Technician Wilbur Hershberger uses infrared thermography
to evaluate the ability of water-repellent particle films to block
ice formation in frost-sensitive plants.
(K9132-1)
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In the Kearneysville orchards last
summer, kaolin-coated trees photosynthesized up to 30 percent faster than
uncoated trees, says Glenn. He measures the rate of photosynthesis by covering
the whole tree with a clear balloon through which he forces air with a fan. His
instruments read how much carbon dioxide enters the balloon at the bottom and
how much exits the top. The difference is a measure of photosynthesis.
A multiyear drought ongoing in Israel has parched farmland, forcing the country
to import fresh water from Turkey for irrigation. So Israeli horticulturist
Amnon Erez, who recently retired from the Volcani Center in Bet-Dagan, spent 4
months in Kearneysville last year learning about the film's stress-reducing
potential. Now back in Israel, Erez is overseeing a wide range of crop studies
to demonstrate Surround's ability to help plants and trees thrive under extreme
heat and water stress.
"He had never seen anything that affects a tree's microclimate as much as
Surround does," says Peter Barrows, project manager with Surround's
producer, Engelhard Corporation of Iselin, New Jersey. Robin Matson, western
field representative for Engelhard, says Surround improves color and raises the
sugar content of Arizona-grown lemons, while preventing the trees from shutting
down under the hot temperatures common in the Southwest. And Surround-coated
grapes reach the desirable sugar content—known as brix—a little
sooner than those left bare. |
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Under drought conditions, kaolin-coated trees
often photosynthesize faster than uncoated trees. In preparation
to measure photosynthesis rate of a whole tree, support scientist
Patty Gundrum and Glenn anchor a whole-canopy photosynthesis chamber.
(K9127-1)
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It All Began . . .
About 8 years ago, while looking for a way to reduce the use of synthetic
chemicals in orchards, Glenn conceived of using kaolin particles as a physical
barrier that would repel insects and prevent disease organisms from digging in.
He approached Engelhard, one of the largest producers of kaolin, about doing
cooperative research.
Among its many uses, kaolin gives paper its whiteness and is used in paint,
pottery, and cosmetics. And it's safe to ingest. A tiny bit of kaolin is
already in aspirin and some other tablets. (See "Particle Films:
A New Kind of Plant Protectant," Agricultural Research,
November 1998, pp. 16-19.)
But agricultural uses were uncharted waters. Early studies by Glenn and ARS
entomologist Gary J. Puterka showed that the physical barrier controlled insect
damage well. The type of kaolin Glenn had selected for the studies transmitted
visible light and gases necessary for photosynthesis while reflecting
ultraviolet and infrared bands. But the film was difficult to spray on the
trees because it didn't suspend in water. So Engelhard, under a cooperative
research and development agreement with ARS, removed the waterproofing
additive, improving kaolin's ability to mix with water. What's more, leaving
out the additive dramatically cut the cost of the product.
That started what may prove to be one of the most versatile agricultural
products ever to hit the market (see box on page 17). Surround Crop Protectant
went commercial in 1999. This year it was upgraded to a wettable powder
formulation called Surround WP Crop Protectant.
Barrows says Engelhard priced the product to compete with insecticides. Since
it is a physical barrier, it must be reapplied to cover new growth or after a
heavy rain, he says. The cost of three to four applications of Surround is
about equal to one application of the insecticide pear growers use against pear
psylla.
It was this tiny but devastating insect that boosted Surround commercially last
year. "We had intended to have a year of trial usage," says Barrows.
But entomologists found pockets of insecticide resistance. "When it became
known that Surround controlled pear psylla as well as it does, we had to make
and ship a lot more than we anticipated."
Glenn stresses that "specially formulated kaolin has the potential to
greatly reduce pesticide use on conventionally grown crops. The Organic
Materials Review Institute has listed Surround WP for organic food
production."
Insects Don't Like Biting the Dust
After several years of testing, the product is proving its prowess against all
shapes and sizes of insects. The white leaves keep insects from recognizing
their favorite hosts, and the tiny particles ensure a lack of hospitality. Just
as people don't like climbing into a bed full of sand, insects don't like
crawling on a plant or tree covered with kaolin. It sticks to their wings,
legs, and mouth parts, so they quickly leave to find a more comfortable place
to feed and lay eggs.
In studies around the country, codling moths, apple maggots, plum curculio,
leafhoppers, Japanese beetles, rose chafer, thrips, and rust mites—not to
mention pear psylla—have fled whitewashed crops in search of greener
pastures. Even glassy-winged sharpshooters—the transmitter of Pierce's
disease, which threatens to devastate southern California's grape
vineyards—avoid kaolin-treated lemon trees. And early results suggest
they'll stay away from treated grapevines too.
ARS' Puterka says the specially formulated kaolin particles "have the
potential to work against almost any insect. The key is getting good coverage
of the crop. If you can get it to stick and stay, it will control most
insects." One crop that has failed the stick test is cabbage, so Surround
doesn't control cabbage loopers and other worms. And because it's eventually
washed off all crops by rain, areas of low rainfall are most adaptable to this
technology, Puterka adds.
Don Gallagher of Gallagher Vineyards in Manteca, California, was pleased with
the early results of Surround on 12 of his 57 rows of grapes. "When I put
it on, there were a lot of mealybugs on the vines. But I can't find one of them
now. I don't know where they've gone." Gallagher did, however, find a
couple of mealybugs on insecticide-treated vines, he says, noting that he's
finding a similar pattern for leafhoppers on the crop.
Jay Brunner, professor of entomology at Washington State University in
Wenatchee, is looking at Surround's clout against insect pests of the state's
apple orchards. His results have been mixed. "It's as good as many
selective insecticides for controlling Lacanobia fruit worms and
leafrollers," he says. But it proved only fair for codling moths and
variable for stinkbugs. Plus, it seems to interfere with helpful parasitic
insects that hang around the orchard and keep leafminers under control, Brunner
adds.
In insect control, as in comedy, timing is everything. So Brunner and other
entomologists are working to determine the optimum timing and application rates
to control specific pests without disrupting the biological control of others.
"I think Surround will have a place in certain pest-management programs
where growers are trying to avoid pesticides," says Brunner.
Todd DeKryger, agricultural research specialist with Gerber Products Company in
Fremont, Michigan, sees potential for Surround to fit in with conventional
methods to control specific pests on specific crops. "It eliminates
residues of conventional pesticides and helps us maintain a stable supply of
produce," says DeKryger.
This year, Gerber growers are trying it on pears, apples, peaches, and carrots.
DeKryger says it appears to work better in the dry West because more of the
film stays on the foliage. "The jury's still out on its feasibility east
of the Rockies," he says, noting that May 2000 was the wettest May on
record in Michigan.
Fungi Dodge It, Too
While the potential for insect control got brighter, the outlook for
controlling orchard diseases didn't look very promising . . . until last
summer. After some trial and error, Glenn believes he has hit on the right
formula by adding other minerals to Surround. The minerals make the film more
alkaline (raise the pH), he says, and that seems to prevent fungi from taking
hold.
In the middle of July, Glenn's untreated apple leaves were contorted under the
stress of powdery mildew infection. Not so with the treated trees. Leaves lay
flat and looked healthy. And 90 to 95 percent of the fruit were disease free.
The mixture also controlled apple scab.
"We still get the same insect control," says Glenn. "The mineral
combination adds a new dimension."
And That's Only the Beginning
Uses for kaolin films don't end here. Glenn and Puterka also see kaolin's
potential as a carrier for just about any chemical used on the
farm—pesticide, fungicide, herbicide, pheromone—you name it. "It
can be used as a matrix to hold chemicals on the plant or soil and get more
even distribution," Puterka says. Such improved delivery would benefit the
environment, farm workers, and consumers. "You may be able to reduce the
active ingredient by 50 percent or more," he says. The latest patent
application jointly filed by ARS and Engelhard covers this use of kaolin.
A water-repelling kaolin formula may have other applications. Tests show that
this hydrophobic film protects tender plants and trees from frost damage.
Normally, when the temperature drops below freezing, ice crystals forming on a
wet leaf penetrate the surface and freeze the leaf tissue. Frost damage can
cost U.S. growers hundreds of millions of dollars annually.
But the waterproof kaolin keeps water from direct contact with the leaf
surface. And it makes water bead up, which further reduces the surface area of
the droplet resting on the leaf, says ARS' Michael E. Wisniewski, a plant
physiologist at Kearneysville. In his tests in environmental chambers,
kaolin-treated tomato and bean plants have withstood temperatures as low as
21°F (-6°C). They normally die when the thermometer drops to
28°F (-2°C).
Wisniewski says Mick Fuller, professor of horticulture at the University of
Plymouth in England, is getting similar results on citrus, potato, and grape
plants in his environmental chambers. "His findings are particularly
impressive for citrus," he adds.
In addition, other researchers are beginning to look at the potential of
kaolin-based products to address several other needs—agricultural and
otherwise. Kaolin's agricultural uses "have opened a whole new area of
science," says Puterka. So far, they have spawned four patents jointly
owned by ARS and Engelhard Corporation, and five more patent applications are
either pending or being prepared.—By Judy McBride, Agricultural
Research Service Information Staff.
This research is part of Crop Protection and Quarantine, an ARS National
Program (#304) described on the World Wide Web at
http://www.nps.ars.usda.gov.
D. Michael Glenn,
Gary J. Puterka, and
Michael E. Wisniewski are at
the USDA-ARS Appalachian Fruit Research
Station, 45 Wiltshire Rd., Kearneysville, WV 25430-9423; phone (304)
725-3451, ext. 321 [Glenn], ext. 361 [Puterka], ext. 320 [Wisniewski], fax
(304) 728-2340.
The Versatile Horticultural Coating:
Proven and Potential Uses:
Field tests show that kaolin can:
- control insect pests.
- prevent sunburn on fruit and nuts.
- prevent heat stress, thereby increasing yields.
- increase photosynthesis.
Some potential uses for kaolin in early stages of testing:
- control fungal diseases.
- prevent frost damage.
- serve as a delivery system, allowing growers to reduce the amount of
chemicals applied.
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"Whitewashing Agriculture" was published
in the November
2000 issue of Agricultural Research magazine.
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