Pesticides vary in their toxicity and in their potential to cause undesirable
ecological impacts. Pest control materials that are relatively non-toxic
with few ecological side-effects are sometimes called ‘bio-rational' pesticides,
although there is no official definition of this term. Some, but not all,
biorationals qualify for use on organic farms. The major categories
of bio-rational pesticides include botanicals, microbials, minerals, and
Botanicals are plant-derived materials such as rotenone, pyrethrum,
sabadilla, ryania, etc. Nicotine products, although natural, are not considered
bio-rational due to their high mammalian toxicity. Botanicals are generally
short-lived in the environment, as they are broken down rapidly in the
presence of light and air, thus they do not provide pest control for very
long, perhaps a day or several. Most botanicals are broad spectrum, so
they kill beneficial insects, too. They tend to be moderately toxic to
people and wildlife; many are irritating to mucous membranes.
Some newer botanical insecticides have low mammalian toxicity. These
include products made from extracts of Neem tree seeds, such as 'Azatin'
and 'Align' which are labeled for many vegetable crops. Azadirachtin is
the active ingredient. It works by inhibiting development of immature stages
of many insects, and by deterring feeding by adults. Garlic and hot pepper-based
materials are other low-toxicity botanicals used by some growers, although
their efficacy is uncertain.
Microbial pesticides, formulated from micro-organisms or their by-products,
tend to have advantages over the botanicals in that they are safer to use,
and are more selective in what they kill, so beneficials are not harmed.
Bt, or Bacillus thuringiensis, is the most widely-used microbial
insecticide. There are many different Bt products which contain various
crystals made by a bacterium that are toxic to specific insect pests such
as caterpillars ('Dipel', 'Xentari') and Colorado potato beetle larvae
('Novodor', M-Trak). To be effective, Bt must be applied to foliage when
small larvae are actively feeding.
Some microbial insecticides are entomopathogenic fungi which can infect
insects and kill them. Products containing live spores of Beauvaria bassiana
are available, such as 'Mycotrol', which work best when applied at the
onset of an infestation of soft-bodied insects such as whitleflies or aphids.
It takes a week or more after spraying for the spores that came in contact
with the pest to germinate, penetrate, and grow throughout the insect thus
Other microbials are available that work as fungicides, such as 'Mycostop',
a soil drench derived from Streptomyces fungus, and 'Gliogard', derived
from Gliocladium fungus. Both these products are labeled to control some
root-rotting organisms that cause damping off and similar problems in greenhouse
and seedling crops. Products containing Trichoderma are labeled for control
of pathogens in greenhouse soils and potting mixes ('Root Shield')
as well as on seeds and seed pieces as a planter box treatment ('T-22').
Foliar applications of this organism will soon be registered for control
of powdery mildew, botrytis, etc.('Topshield').
Some biorational pesticides are minerals, such as sulfur for control
of foliar diseases and in some cases, mites. Kaolin, or white clay-based
products such as 'Surround' have been developed and will eventually be
registered for crop use to suppress a variety of insects and foliar diseases.
Low-toxic synthetics include soaps, or fatty acids of potassium salts,
which are formulated to be both insecticides ('M-Pede') and herbicides
('Scythe'). Soaps work by suffocating soft-bodied insects and by burning
the leaves of weeds. Application directly onto exposed insects is critical
to good control. Soaps can be phytotoxic to some crops, and harmful to
some beneficials. Horticultural oils are petroleum-based but organically-allowed
means of smothering scale and other insects, and have been used to suppress
aphid feeding, too.
Potassium bicarbonate is a recently registered material ('Armicarb-100','Kaligreen')
for prevention of powdery mildew and other diseases on crops like cucurbits,
and ornamentals. Just like more conventional fungicides, it must be applied
to healthy tissue in advance of infection in order to be effective.
Copper compounds are fungicides and bactericides available in different
formulations, including Bordeaux mixture, tri-basic copper, copper hydroxide
('Kocide'), cupric oxide, copper sulfate, elemental sulfur, calcium polysulfide
(lime sulfur) and copper/zinc. Although for most foliar diseases these
are not as effective as other synthetic fungicides, with a good spray program
and cultural practices that maximize leaf drying, they can provide effective
prevention. Caution must be used because of potential phytotoxicity, especially
with temperatures over 80 degrees.
The so-called "beneficial" insects include predators and parasitoids
such as lady beetles and various wasps, as well as certain nematodes that
are used for insect control. These are classified by regulatory agencies
as biological controls, not as pesticides. Most suppliers of these organisms
provide good information on how to best use them.
With bio-rational pesticides, as with all others, read the label carefully
to be sure it applies to the crop and pest in question, and to learn the
most effective means of application. Remember that labels may change from
year to year as crops and pests are added or withdrawn, or new application
(Mention of brand names is for information purposes only; no endorsement
is implied nor is discrimination intended against products not mentioned).