Natural Plant Extracts Might Sub for
Technician Brian Otto evaluates plant essential oils for potential use as
antifungal soil fumigants.
Essence of peach sounds like a perfume or flavoring.
It is, actually. But the scientific name for this colorless, nontoxic,
aromatic liquid found in essential oils of peach seeds is
"benzaldehyde." Many such volatile oils, like lemon, cinnamon, and
peppermint, are extracted and distilled from plants. Naturally occurring
benzaldehyde is used commercially in perfumes, flavorings, pharmaceuticals, and
But Charles L. Wilson, a plant pathologist at the
ARS Appalachian Fruit Research Station in
Kearneysville, West Virginia, has found a potential new use for this compound.
He has been testing benzaldehyde and other natural plant volatiles as possible
alternatives to methyl bromide fumigation.
The research is collaborative with scientists from the Volcani Center in Bet
Dagan, Israel, and the INFRUTEC Center for Fruit Technology at the Fruit, Vine,
and Wine Research Institute of the Agricultural Research Council in
Stellenbosch, South Africa.
Methyl bromide is critical to agriculture worldwide as a soil fumigant,
postharvest storage protectant, and quarantine treatment to control many pests
on various crops. The primary use for this chemical is to fumigate soil to
destroy soilborne pests. However, the escape of some of the fumigant from the
soil into the atmosphere has led to its being declared an ozone depletor. So,
under the U.S. Clean Air Act, production and importation of methyl bromide will
be banned in the United States in 2005.
"For several years now, we've been diligently searching for practical
and effective alternatives to methyl bromide," says ARS administrator
Floyd P. Horn. "This fumigant is used on more than 100 crops. And
differences in soil types, weather, importing country requirements, and many
other factors complicate the issue."
"Our collaboration with industry, universities, state agencies, and
international organizations is vitally important to our search," Horn
says. "This joint work with Israel and South Africa could lead not only to
viable alternatives to methyl bromide, but to jointly patented commercial
products as well."
In lab studies at Kearneysville, Wilson and colleagues have found several
natural plant volatiles that have fungicidal properties.
"We protected fruit against postharvest decay with these
compounds," says Wilson. "We found onebenzaldehydeto be
particularly effective. Then we went a step further and used benzaldehyde to
fumigate soil and found it very effective against several soil pathogens."
This work is collaborative with Deborah R. Fravel, a plant pathologist with
the ARS Biocontrol of Plant Diseases Laboratory in Beltsville, Maryland. Wilson
and another associate, Jose Solar, have applied for a patent on a time-release
formula of benzaldehyde to fumigate fruit, grain, and soil.
"Since it is inexpensive, easily biodegradable, and breaks down into
products that aren't harmful to humans, animals, or the environment,
benzaldehyde would be a desirable alternative to methyl bromide as a soil
fumigant," Wilson says.
He and Fravel found that soil fumigated with benzaldehyde initially had
significantly lower pH values. However, within 2 weeks, the pH returned to
previous, nonfumigated, levels. Says Wilson, "This showed that the changes
in soil pH are readily reversed and should not interfere with crop
Wilson and colleagues have found several natural plant volatiles that are
effective against soilborne pathogens such as Fusarium oxysporum,
Rhizoctonia solani, Pythium aphanidermatum, and Sclerotinia
To find potential alternatives to methyl bromide, more research is needed on
the destructive, or biocidal, activity of natural plant compounds against a
wide range of pathogens, insects, and weeds.
A Quick, Easy Test for Fumigants
In addition to comparing the efficacy of natural fumigants in different soil
types and different applications, scientists will need to evaluate delivery
systems, Wilson says.
"The first order of business is to find, in the lab, the compound or
combination of compounds that will control soilborne pests and diseases,"
he explains. "Then, we'll need to test these in soil and eventually begin
field tests to complete the research. We already have several interested
It is difficult to evaluate the effectiveness of fumigants on soil in
planting beds or greenhouse containers.
To test a fumigant's effectiveness, large volumes of soil must be fumigated,
and elaborate evaluation procedures need to be devised. With the help of
Fravel, Wilson built an apparatus to quickly and easily test soil fumigants
against soil pathogens.
"Simple to use, this equipment allows the soil to retain uniform
amounts of a fumigant for a definite period. Once the soil is fumigated, it can
be tested for pathogen activity," Wilson reports.
Wilson and Fravel successfully used it to evaluate the effectiveness of
benzaldehyde and nitrogen against soil pathogens.
Partnering Up To Find Alternatives
Plant pathologist Charles Wilson transfers soil fumigated with natural plant
volatiles into a beaker for examination.
Eli Shaaya, who is with the Department of Stored Products at the Volcani
Center, works closely with Wilson on the search for natural compounds that
might replace methyl bromide.
He and colleagues have identified several essential oils extracted from herb
and spice plants that have proven effective as fumigants. They have used these
extracts to control the most common stored-product insectsthe rice
weevil, lesser grain borer, sawtoothed grain beetle, and red flour beetle.
Shaaya also found that several of the essential oils were active against
cut-flower insects, including the whitefly.
Wilson has also been working with Johan Combrink of INFRUTEC. Essential oils
from indigenous South African plants are now being marketed as flavor and
"These oils could also provide a rich source of new compounds that may
fumigate soil, agricultural commodities, and physical structures," Wilson
Combrink and colleagues are seeking natural plant compounds that fight
Botrytis cinerea, Penicillium expansum, Mucor piriformis,
and Rhizopus nigricanspathogens that attack pome fruit, such as
apples. They are now controlled with chemicals.
When the research project gets in full swing in South Africa, Combrink and
colleagues plan to test natural compounds on controlling weevils, the dried
fruit moth, and mites on dried fruit. They'll also investigate controlling the
root-knot nematodea worldwide pest and one of the most significant
nematode pestson a wide range of crops, including stone fruits and
vegetables. They will also test natural compounds on the ring nematode, a
serious pest of stone fruit and peach orchards not only in South Africa, but in
Georgia and South Carolina as well.
In addition, they will fumigate with new natural compounds to control
Fusarium wilt on melons, root rot on strawberries, Phytophthora root rot on
citrus, replant syndrome on apples, clubroot on cabbage, and damping-off on
Two South African companies, Ulimocor and the Ciskei Agricultural
Corporation, are interested in this research, as is the Maktishim Chemical
Company in Israel. Wilson has also been talking with a couple of U.S. companies
about research results.
A Reprieve for Methyl Bromide
Legislation passed with the FY 1999 Agriculture Appropriations Bill delays
the ban on methyl bromide because U.S. growers have very few viable
alternatives to this heavily relied-on chemical. The new legislation ensures
that regulations governing U.S. use, production, import, or export of methyl
bromide are no more stringent or restrictive than those required by the
Montreal Protocol. Instead of the earlier January 1, 2001, target cutoff date,
U.S. growers may now use methyl bromide until 2005.
"This reprieve makes our research even more critical, Wilson says. It
gives us a little more time to find and test more natural compounds that may
replace methyl bromide." By Doris Stanley Lowe, Agricultural
Research Service Information Staff.
This research is part of Methyl Bromide Alternatives, an ARS National
Program described on the World Wide Web at
Charles L. Wilson is at the
USDA-ARS Appalachian Fruit
Research Station, 45 Wiltshire Rd., Kearneysville, WV 25430-9425; phone
(304) 725-3451, X330, fax (304) 728-2340.
"Natural Plant Extracts Might Sub for Methyl Bromide" was
published in the March 1999 issue of
Agricultural Research magazine.