Pesticides in the
Summer of 2003
By Lee Oliphant, Ed.D., Master Gardener
No Master Gardeners worth their salt are going to recommend that you
indiscriminately spray insecticides as a means of pest control. There are numerous proven strategies
available for the home gardener that will create a natural balance in the
environment and manage pests, while minimizing damage to plants and wildlife -
all without the use of chemical substances.
But let's face it; there are times when the home gardener feels the need to
rely on technical support through the use of biochemical warfare. Before doing so, thoughtfully evaluate your
reasons for this action. Are pests
causing unacceptable losses in your garden beyond your tolerance? Do you completely understand what is causing
the damage? Are you treating the
offender(s) at the proper time in their life cycles? Do you know how to read the pesticide label
and use the appropriate dilution formula?
Know Your Enemy
The
By identifying the culprit that is causing the damage in your garden, you will
have completed the first step in selecting the appropriate pesticide and
applying it effectively. There are some
excellent resources available that will help you identify the insect or mite,
for example, which may be causing damage in your garden. Pests of Landscape trees and Shrubs, and
Pests of the Garden and Small Farm are published and available from the
While the mere presence of an insect on a plant does not necessarily mean that
it is the offending critter, finding and capturing the insect is the best way
to get help with its identification.
Some pests are elusive and this may not always be possible. To help you identify the damaging insect,
note whether or not the leaf has been chewed, or is discolored or withered from
the sucking mouthparts of insects such as mites, scales or aphids. Identify the kind of plant that is
affected. Some plants are prone to
particular insect infestations. Know the
lifecycle of local insects. Some go
through complete metamorphosis (beetles and butterflies) while others, like
aphids, change little as they mature.
Identifying and understanding the offending insect, its growth and its habits,
will help you select the appropriate control measure and apply it at the proper
time in the life cycle of the insect.
Subsequent articles on types of pesticide and formulations, and reading
pesticide labels will follow, as well as information on the use of pesticides
for maximum results.
Pesticides
are often grouped by the type of pests they control. Notice that all of the pesticides end in –cide
(a suffix meaning killer or killing).
There are insecticides to control insects, miticides to control mites,
molluscicides to control slugs and snails, nematicides to control nematodes,
and rodenticides to control rodents.
There are fungicides to control fungal diseases and bactericides to
control bacterial diseases.
Understanding what you need and what is involved in using pesticides is
essential before purchasing.
Pesticide Formulations
Pesticides are mixtures of active ingredients and other materials, know as
inert ingredients, combined into what is called the pesticide formulation. The formulations are symbolized by a letter
or letters that are printed on the pesticide label. It is helpful to become familiar with these
symbols when choosing the pesticide you need.
Emulsifiable Concentrate (EC or E) is a common formulation. Its active ingredient is mixed with an oil
base (usually a petroleum derivative) that is diluted with water. Agitation is required to keep the oil and
water mixed. Solutions (S) are
pesticide formulations that, once dissolved in water, require little agitation. Flowables (F or L) are also liquids
mixed with water but require constant agitation or will settle in the spray
tank. Aerosols (A) are applied as
a fine spray from a container (convenient but expensive) and wettable powders (WP
or W) are a combination of the active ingredients with fine powder and
mixed with water. Soluble powders (SP)
dissolve with water and constant agitation is not needed for suspension. Pesticides also come in bait formulation (B),
granules (G) and dusts (D), and are applied directly from the
package.
The Label
The label and any brochures accompanying the product are required reading for
the responsible home gardener. The label
is easy to read and follows a specific format.
It will include the brand name as well as the chemical name. You will find the formulation along with
active ingredients in percentages by weight.
The inert ingredients may not be named if the label shows the percentage
contained. The U.S. EPA labels
pesticides as unclassified or restricted-use depending on their effect on
people and the environment. The home
gardener should avoid restricted-use pesticides.
The pesticide product label will contain a “signal word” from “Caution” to
“Danger-Poison” depending on its toxicity, and a “Keep Out of Reach of
Children” warning. A Precautionary
Statement tells the gardener how to avoid exposure and lists protective
equipment required
The Directions for Use section lists target pests plus plant species where
pesticide may be used. It tells how to
mix and apply the product, how often, and where to use it. It is extremely important for the consumer to
read the Precautionary Statement as well as the Directions For Use.
The rest of this article provides home gardeners with information on choosing
the appropriate pesticide for controlling garden pests. As noted in previous articles, before you
consider using pesticides in your garden, be sure you have correctly identified
the pest to be controlled and have explored other cultural and mechanical
controls.
Some insecticides can control insects only at particular stages in their
development. For instance, for a moth
whose larvae eat leaves, the insecticide must be administered when the insect
is in the larval stage and is actually eating.
Stomach poisons for the larvae will not affect the insect in the egg,
pupae, or moth stage. The location of
the pest is important. Some insects live
inside the fruit and are not affected by foliar spraying after the fruit is
formed. Certain pesticides must be
applied at particular times. Dormant
sprays help control overwintering insects and mites with minimal impact on
natural enemies. Information on the
pest’s life cycle, location on the plant and timing of applications for many
common garden pests are presented in
Understanding how a pesticide works, or its mode of action, helps determine its
effectiveness because pesticides are only effective when used at the correct
time, in the correct manner. Is the
active ingredient carried in the tissues of treated plants (systemic) or does
it need to contact the pest? Does it
selectively kill only certain kinds of insects?
Does it kill by contact or does the poison need to be eaten?
The following types of pesticides, which break down rapidly in the environment,
are best suited for the home garden.
Horticultural oil has low or no toxicity to humans or wildlife and is
effective in controlling mites and insects by suffocating them. It is also effective against eggs, immature
forms and soft-bodied adults, scale, mealy-bugs, aphids and whiteflies. Horticultural oil, applied to deciduous fruit
trees during the dormant season, is effective in controlling eggs of western
tussock moth, green fruitworm, aphid and leafroller eggs, scale, mealy bugs and
mites. Insecticidal soaps help to
control mites and aphids and can also reduce populations of whiteflies,
immature scale insects, thrips and leafhoppers.
Pyrethrums are derived from the flowers of a Chrysanthemum species. It causes paralysis in mosquitoes, flies,
aphids, beetles, moth larvae, thrips and mealy bugs. Bacillus thuringiensis is a microbial
insecticide and causes a disease in specific groups of insects (larvae of some
butterflies, moths, beetles and mosquitoes), yet is harmless to warm-blooded
organisms.
Always begin with the least toxic pesticide.
Choose one based on its ability to break down quickly and selectively
control pests. According to the
To simplify information, trade names of products may have been used. No endorsement of named products is intended,
nor is criticism implied of similar products which are not mentioned.