Pests & Diseases
Despite our best efforts, nonchemical methods sometimes fail to
prevent excessive insect damage in the garden. At such times,
the use of insecticides may be the only alternative left to save
the crop. When damage becomes great enough to warrant emergency
measures, organic gardeners often will want to use natural
insecticides and various homemade botanical sprays, instead of
synthetic organic chemicals.
The insecticide used should have low toxicity to man and to other
warm-blooded animals. Insecticides should be used only when needed
and in strict accordance with label directions. A good understanding
of insecticides allows these materials to be used effectively without
harming you or the environment.
The following information may help New Mexico gardeners select a
natural insecticide for their specific needs.
Pyrethrum -- Botanical insecticide. This slightly toxic
insecticide is derived from the flowers of a species of chrysanthemum
imported mainly from Kenya and Ecuador. The material causes rapid
paralysis of most insects, but the insects usually recover unless the
pyrethrum is combined with a synergist or other poison. Pyrethrum
mixed with synergists such as piperonyl butoxide or piperonyl cyclonene,
which increase toxicity and produce longer residual action is used
extensively in space sprays, household sprays, crop sprays and dusts.
This chemical is registered for use on most vegetables and fruits at
any time during the growing season.
Nicotine -- Botanical insecticide. Pure nicotine is a tobacco
extract highly toxic to warm-blooded animals. The insecticide usually
is marketed as a 40% liquid concentrate of nicotine sulfate, which is
diluted in water and applied as a spray. Dusts can irritate the skin
and are not normally available for garden use. Nicotine is used primarily
for piercing-sucking insects such as aphids, whiteflies, leafhoppers
and thrips. Nicotine is more effective when applied during warm weather.
It degrades quickly, so can be used on many food plants nearing harvest.
It is registered for use on a wide range of vegetable and fruit crops.
Sabadilla -- Botanical insecticide. Sabadilla is obtained
from the seeds of a lily-like plant and acts as both a contact and
stomach poison for insects. It is not particularly toxic to mammals,
but does cause irritation of the eyes and respiratory tract. A mask
should be worn when working with this insecticide. This material
deteriorates when rapidly when exposed to light and can be used
safely on food crops shortly before harvest. Sabadilla generally is
used as a 5 to 20% dust or as a spray.
Rotenone -- Botanical insecticide. Rotenone is extracted from
the roots of derris plants in Asia and cube plants in South America.
This general garden insecticide is harmless to plants, highly toxic
to fish and many insects, moderately toxic to mammals, and leaves no
harmful residue on vegetable crops. It acts as both a contact and
stomach poison to insects. It is slow acting and, in the presence of
sun and air, its effectiveness is lost within a week after application.
Wear a mask during application because rotenone can irritate the
respiratory tract. Rotenone dusts and sprays have been used for years
to control aphids, certain beetles and caterpillars on plants, as
well as fleas and lice on animals.
Gardeners have been using soap to control insects since the early
1800s. During the first half of the 19th century, whale oil soap and,
more commonly, fish oil soaps were an important part of insect control.
Recent tests indicate Ivory Liquid dishwashing detergent, diluted
with water to a 1 to 2% solution, provides the most consistent control
and is easy to mix. There are also soaps available that are specifically
formulated to control insects on plants. Thorough coverage of the
plant and repeated applications may be necessary to bring insect
populations under control. High rates of soaps and detergents may
damage some varieties of plants. The most effective soaps have carbon
chains of C-12 or C-18. Laurate (C-12) is the main component of most
dishwashing liquids and various other products in common usage. The
richest natural source of this is coconut oil.
Organic gardeners have been using a spray mixture containing onions,
garlic and pepper mixed together to control insects for many years.
Recent scientific research indicates the use of the combination of
these materials has been erratic and, in many cases, ineffective for
insect control. Sprays of food-derived substances do not appear to
be good choices as a pesticide. However, some success may be achieved
with them, but is likely to be sporadic. Spraying several times a
week might help to bring infestations under control. Control with
one application should not be expected.
Safe Use of Pesticides
When it is necessary to use insecticides to protect the garden,
use them wisely and safely. The following tips will help you
make better use of insecticides.
In most situations it is helpful to use several control techniques
to reduce insect pest populations to low enough levels that insecticides
are not required, or are needed only sparingly. With reduced insecticide
use, biological control agents can become more effective, insecticide
costs will be saved, and you will have the satisfaction of knowing that
few, if any, poisons were applied to edible crops.
- Inspect the entire garden at least weekly to monitor insect
numbers and activity. Pay particular attention to underside of
leaves where mites, whiteflies, aphids and insect eggs occur. If
treatments are applied when an infestation first starts, insect
numbers can be maintained at lower levels much more easily, and
with smaller amounts of chemicals.
- Apply insecticides to all plants surfaces so an insect anywhere
on the plant will be exposed to a lethal amount of the chemical.
Do not apply insecticides to wilted plants or during the hottest
part of the day. Apply dusts only when the wind is calm and plants
are dry. Sprays should be applied when the wind is no more than 5
to 10 miles per hour. Retreatment may be necessary after a rain.
- Apply insecticides only at recommended dosages. Increased amounts
can be dangerous, cause plant damage and leave harmful residues
without improving insect control.
- The length of effective control with insecticides varies widely.
The longevity of toxic properties varies primarily with the product,
formulation, water, pH and environmental conditions. Temperature,
humidity, wind and sunlight affect insecticides. The greater the
extremes, the sooner the insecticides are detoxified.
- The time interval required by the Environmental Protection
Agency between treating a crop and harvesting that crop varies
with the insecticide and the crop. This information is printed
on the pesticide label to ensure that any residues will be within
established tolerances at harvest time.
- Always read and follow mixing and application instructions on
the insecticide label for safe and effective insect control.
- Some synthetic organic materials are actually less toxic and
more efficient than some natural insecticides. Because a material
is a natural pesticide, it does not necessarily follow that it is
not toxic to man or harmful to the environment if improperly used.