Diane Relf
Virginia Cooperative Extension
Natural
pesticidal products, also called botanical pesticides, are
available as alternatives to synthetic chemical formulations.
Although thought of by some as "natural," and therefore assumed
to be harmless, safety clothing must be worn when spraying
these, even though their toxicity is low to warm-blooded animals.
Some botanical pesticides are toxic to fish and other cold-blooded
creatures and should be treated with care.
The
botanical insecticides break down readily in soil and are
not stored in plant or animal tissue. Often their effects
are not as long-lasting as those of synthetic pesticides.
INSECTICIDE |
USE
AGAINST |
Pyrethrum |
Pickleworms, aphids, leafhoppers, spider mites, harlequin
bugs, cabbageworms, Mexican bean beetles, flea beetles,
flies, squash bugs |
Rotenone |
Colorado potato beetle, Mexican bean beetle, Japanese
beetle, flea beetles, fleas, cucumber beetles, spittlebugs,
aphids, potato beetles, mites, carpenter ants, cabbage
worms, loopers |
Ryania |
codling moths, corn earworm, oriental fruit moth, potato
aphids, onion, thrips, corn earworms |
Sabadilla |
armyworms, harlequin bugs, stink bugs, cucumber beetles,
leafhoppers, cabbage loopers, blister beetles |
In addition
to botanical insecticides, other biological products can help
in the battle against insects. However, some of these compounds
may be difficult to find.
Bacillus
thuringiensis (B.t.) is an effective product commonly used
against moth larvae. B.t. is a bacteria that produces a toxin
quite lethal to caterpillars, but nontoxic to beneficial insects
and mammals. B.t. is most effective on young larvae. New strains
of B.t. have been developed to work against other types of
insect larvae.
Another
biocontrol product available to gardeners is grasshopper spore.
It is not proven for small-scale use, but may help gardeners
reduce damage by grasshoppers.
Commercial
insecticidal soap, a special formulation of fatty acids, has
proved effective against aphids, leafhoppers, mealybugs, mites,
pear psylla, thrips and whiteflies. Homemade, soap sprays
also work to some extent. They can be formulated by combining
three tablespoons of soap flakes (not detergent) per gallon
of water. Spray on plants till dripping.
Repellent
sprays, such as garlic sprays and bug sprays (made from a
puree of bugs), have been reported as useful by some gardeners,
but their effectiveness is questionable. Some researchers
believe that bug sprays may work if a disease is present in
the insect macerated and that disease is spread through the
spray to other insects.
Apply
all insecticides locally, to take care of a specific pest
problem, instead of blanketing the entire garden. Call your
local Extension office for specific recommendations.
Disclaimer
and Reproduction Information: Information in NASD does not represent
NIOSH policy. Information included in NASD appears by permission
of the author and/or copyright holder. More
NASD Review: 04/2002
(Originally
published as "Minimum Chemical Gardening" by Diane Relf, Extension
Horticulture Specialist, and John Luna, Extension Entomology
Specialist in The Virginia Gardener Newsletter, Volume 6, Number
7. For more information)
Diane Relf, Extension Specialist, Environmental Horticulture
November
1997
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