Particle Films . . . A New Kind of Plant
After a season-long spray program using a particle film, soil scientist Michael
Glenn (left) and entomologist Gary Puterka note that this Sekel pear tree is
healthy and insect-free.
Microscopic mineral particles may help promote environmental stewardship
around the world. Agricultural Research Service and Engelhard Corporation
scientists have discovered that films made from these particles repel pests and
may deter disease attack when sprayed on plants.
These particles have been specially sized and shaped. Prototypes of this
particle film technology called HPF have been successfully field-tested in
North America, Europe, and South America.
Products, which will be commercially available in 1999 in parts of the
United States for use on apples and pears, will be cost-competitive with
conventionally used chemicals.
"Not only can agricultural products made from these particles cut the
amount of pesticides needed, they may also boost plant health, aid fruit
quality, and over time, improve the condition of the soil," says ARS soil
scientist D. Michael Glenn. He heads the project, assisted by entomologist Gary
J. Puterka, at the Agricultural Research
ServiceAppalachian Fruit Research Station in Kearneysville, West Virginia.
"We've successfully tested HPF technology on several insects and mites
and on disease-causing fungi and bacteria," Glenn reports. "It works
not only on tree fruit crops, but has potential to work on vegetable and field
crops as well."
ARS has signed a cooperative research and development agreement with
Engelhard Corporation of Iselin, New Jersey, to develop and commercialize the
new technology. The company has filed patents, including foreign patent rights,
on the particle technology, with ARS as co-owner. More patents may be
This research shows why USDA joined with the U.S. Environmental Protection
Agency (EPA) and Food and Drug Administration (FDA) in 1994 to establish a
voluntary partnership with industry to protect human health and preserve the
environment by reducing pesticide use and risk.
In this case, industry became involved early on, for it was a particle
provided by Engelhard Corporation--one of the largest producers of specialized
particles in the world--that first aroused Glenn's interest. As a leader in
surface chemistry, Engelhard can modify the size and shape of particles and
control the way they are distributed on a particular surface, making it
possible to engineer them for specific purposes.
"The films are made of microscopic mineral particles of low
toxicity," Glenn says. "Current prototype films are made by modifying
kaolin, a naturally occurring mineral that is generally regarded as safe."
In fact, kaolin is approved by the Food and Drug Administration as an
indirect food additive. It doesn't harm earthworms or beneficial insects like
ladybugs and doesn't affect crop pollination. HPF products made from kaolin
should reduce the amount of conventional pesticides needed for crop production.
Engelhard produces kaolin commercially for use in many products, including
pharmaceuticals, electrical insulators, cosmetics, plastic extenders, paint,
and paper. The product is sprayed on as a liquid, which evaporates, leaving a
film on the plant or crop surface. Coating plants completely with the liquid is
very important. Since the particles are sprayed on crops in a water-based
slurry, the material sticks to plant leaves, stems, and fruit, forming a white
powdery film. No special equipment is needed for application; traditional
spraying equipment can be used.
Does this coating interfere with photosynthesis?
Untreated Sekel pears (left) show insect and disease symptoms while those
exposed to the same growing conditions, but treated with a particle film,
exhibit undamaged, healthy fruit.
"Just the opposite," Glenn explains. "The properties of the
particles are such that sunlight diffuses into leaves, resulting in little
reduction of light."
What's more, the reflective nature of the particles reduces heat stress on
leaves and lowers the temperature in a tree or plant canopy. As a result, fruit
will often have better color, higher soluble solids, reduced internal
breakdown, and increased weight.
The particle application may also indirectly enrich the soil. While some
pesticides reduce earthworm populations, this material allows them to move
freely through soil, funneling organic matter down from the surface and making
tunnels that increase water infiltration and aeration. Improved soil structure
created by earthworms aids plant growth and productivity.
According to Puterka, particle technology works to deter insects and mites
in several ways. "The particle film coats the plant, forming a protective
barrier," he says. "When insects come in contact with film-coated
plants, tiny particles from the coating attach to their bodies, agitating and
"Even if the particles don't attach to their bodies, the insects still
find the environment unsuitable," Puterka reports. "Nonflying insects
that are unable to leave the plant thus become confused and disoriented when
the particles attach to them. The pests are unable to feed or lay eggs."
Another deterrent for insects, he says, is that the white, highly reflective
particle coating makes the plant unrecognizable as a host. This may be similar
to the concept of whitewashes, which have been shown to repel certain insects,
such as aphids.
Which Pests and Diseases Are Thwarted?
For several growing seasons, Glenn and Puterka have tested the particles on
a broad range of insect pests and diseases on apple and pear trees. The
treatment was effective against leafhoppers, leafminers, spirea aphids, thrips,
European red mites, two-spotted spider mites, and late-season apple diseases
such as sooty blotch and flyspeck.
"We also had high suppression rates for the plum curculio and codling
moth but haven't yet reached economic levels of control," Puterka says.
"Our most spectacular success with the particle films to date has been
controlling arthropod pests and diseases of pears. We've been able to fully
control pear psylla and pear rust mite and to suppress fabrea leaf spot--major
problems for pear growers."
According to Puterka, the particles may be most applicable on crops that
will end up being washed and waxed, like tree fruits, peppers, and cucumbers;
or on root crops like peanuts, potatoes, and sweetpotatoes. This, he says, is
because the white film left on leaf, stem, and fruit can be either allowed to
weather off or removed after harvest. Conventional packinghouse equipment
removes the film.
ARS and Engelhard field-tested particle films in 1997 and 1998 on apples,
peaches, and pears in Chile. "We did the tests in Chile while it was
winter here in the United States. Results were very successful," says
In one trial, several sections of an abandoned pear orchard were selected
for particle film spraying. "At the end of the season, we went back to
check progress and were amazed. Treated groups of trees stood out in the
orchard like tiny oases in a desert," says Glenn.
"Trees in treated areas were green and flourishing, while those in
untreated areas were starkly different: sparse foliage, small leaves, and
little new growth. And the pears we gathered from the treated areas were the
first harvested from that orchard in 7 years. There was no fruit on the trees
that had not been sprayed with the particle mixture."
In other Chilean studies, treated peach trees yielded 50 percent more fruit,
while treated apple trees maintained their yield.
Technicians Adam Finkelstein and Sharon Jones apply particle film to
blackberries using a handgun sprayer. Results with blackberries indicate a
broad insect suppression.
In tests on tree crops in Italy, particle spray increased color in pears.
But it didn't completely stop aphids in apples, peaches, or pears, nor the
third generation of codling moths. Nevertheless, Glenn says, the Italian tests
were successful, overall. Fine tuning the spray timings could improve control.
Treatment on apples in Kearneysville orchards increased tree vigor, which
allowed trees to support more fruit and increased production. When applied to a
newly established peach orchard, the treatment even controlled Japanese
beetles. Glenn says this is an indication that the particle film would work
well for the nursery industry, giving young trees a chance to get a head start
on growth by preventing insect attack, while reducing water stress.
Results were confirmed in collaborative studies at ARS' Yakima Fruit and
Vegetable Research Station horticulture research station at Wapato, Washington.
There, particle-sprayed apple and pear orchards showed increased fruit size,
red color, and leaf photosynthesis, along with cooler canopy temperatures.
These research results were confirmed at six different fruit-growing regions
in 1998. Fine tuning the spray program increased efficacy and reduced the
number of sprayings needed.
Growers Try It and Like It
Both conventional and organic growers are excited about their field-test
results with the particle films.
Grower Eric Rice of Middletown, Maryland, says, "The particle film
worked better than the crop protection methods we were using. Although I'm
impressed with what the particle film did on my crops, one of the major
advantages this technology has over conventional chemicals is the aspect of
"A farmer is exposed to whatever he applies to his crops. This particle
film comes from inert mineral deposits, and we know that the FDA regards it as
safe. This means a lot to growers," he says.
Rice's acreage includes apples, pears, berries, vegetables, flowers, and a
"I sprayed my apple trees with the mixture, and it suppressed the
codling moth and plum curculio, which are major pests, and worked on
leafrollers," says Rice. "We don't have much trouble with mites,
aphids, and other insects, probably because we use beneficial predatory
Results were more variable for disease control, he says.
"The spray was completely effective for fire blight, although 1997
might have been a year of low incidence. Under organic guidelines, we can spray
streptomycin on fire blight, but even then, we always get a little infection.
With the particles, we didn't have a single incident of fire blight."
However, the new treatment didn't work as well with apple scab the first
year. Trees not susceptible--or with average susceptibility--to scab, fared
well. But for gala apple, which is highly susceptible to the disease, the
particles didn't provide protection.
"I must say that our spray schedule in 1997 for the galas was probably
not properly targeted. We didn't spray until after full bloom, and we got
infection on the fruit. But since there was no infection on the leaves, we know
that the material must have provided some measure of control," Rice
reports. Adjusting the spray schedule in 1998 brought excellent results.
The Washington Tree Fruit Research Commission--a grower-funded organization
that is a research partner in the venture--is testing the products in
commercial apple orchards.
"We are interested in these products for their insect- and
disease-control potential, but primarily for their horticultural
benefits," says James McFerson, a scientist with the Commission.
"We're evaluating the products, which we applied with typical airblast
sprayers, on three 1-acre, replicated test plots."
Ray Schmitten grows pears on 120 acres in the Wenatchee River Valley of
"We sprayed our orchards with kaolin products this spring and got
complete control of pear psylla, our biggest pest problem," he says.
"We used no other products for this pest."
Pear psylla deposit honeydew on leaves. But in areas where the new products
were used, there was no evidence of this sticky substance. For pear psylla, the
products worked better than conventional pesticides.
Schmitten says the products also completely controlled rust mite and were
effective on codling moth, although it was still early in the season for this
pest. Another unexpected benefit, he says, was that the kaolin products reduced
the effect of a fine fuzz that pear leaves produce, which causes field workers
EPA Exempts Particle Film
In 1997, EPA granted an experimental use permit for Engelhard and ARS to
field-test the material with 50 collaborators--including other ARS and
university scientists, as well as growers--throughout the United States. The
mineral particles have been approved for use on organic farms in Virginia,
Maryland, and Washington. Because the product is chemically inert and low in
toxicity, EPA exempted the particle film technology from pesticide tolerance
regulations and on March 17, 1998, registered three prototype products for use.
"It takes about 8 years for a new pesticide to go through the EPA
registration process," says John Mosko, marketing manager for Engelhard.
"But with help from USDA, we dramatically stepped up the trial program for
these products after we saw such promising early results. This will help us
launch particle film products commercially in 1999.
"We're not touting these particle films as a replacement for chemical
use. But we realize that growers need alternatives to chemicals, especially
those that may have difficulty in getting re-registered by EPA," he says.
Minor Crops Have a Major Need
The new Food Quality Protection Act of 1996 sets a higher standard for
conventional pesticides, encouraging development of reduced-risk products. Many
so-called minor-use pesticides may soon no longer be available to growers.
Potential registrants will not seek re-registration if there is insufficient
economic incentive to justify data requirements or if new regulations require
them to cut back some uses. Minor-use pesticides are applied to such crops as
fruits, vegetables, nuts, ornamentals, and nursery products.
Grown on 8 million acres in the United States, minor crops are valued at
around $24 billion annually. This is about 40 percent of all agricultural crop
sales. "Growers of these crops are going to be hurting for alternatives to
chemicals that may not be available in a few years," Mosko says. "Our
new particle technology can help fill this void."
"We're fortunate that Engelhard is our partner in this venture to
further develop new technologies from these mineral particles," says
Glenn. "This technology can help us realize our goal of having 75 percent
of U.S. agricultural acreage under integrated pest management programs by the
year 2000."--By Doris
Stanley, Agricultural Research Service Information Staff.
D. Michael Glenn and
Gary J. Puterka are at the
USDA-ARS Appalachian Fruit
Research Station, 45 Wiltshire Rd., Kearneysville, WV 25430-9423; fax (304)
728-2340. [Glenn] phone (304) 725-3451, ext. 321, and [Puterka] phone (304)
725-3451, ext. 361.
"Particle Films . . . A New Kind of Plant Protectant" was
published in the November 1998 issue of Agricultural Research magazine.
to see this issue's table of contents.