Use of Mineral for Pest Management in Organic Gardening


Insecticides developed from elemental (mineral) sources mined from the  earth are classified as natural products and often cost  less than other processed or harvested insecticides. The toxicity of mineral-based insecticides depends on  the  chemical properties of the  mined ele- ments. Some  mineral insecticides such as sulfur are regis- tered for organic use and have relatively low toxic effects on  people and nontarget organisms. In contrast, lead arsenate is a natural mineral product that was cancelled as a pesticide in 1988  due  to its toxicity and persistence in the  environment.

Diatomaceous earth is a fine particle  dust comprised of fossilized diatoms that is effective against slugs and soil-dwelling insects. Diatoms are small, usually single-celled phytoplankton commonly found in aquatic or moist environments. Diatoms are encased in- side a cell wall made of silica,  the  same  compound used  to make glass. Diatomaceous earth works  as a fine abrasive that disrupts the  exoskeleton cuticle of a slug or insect and causes  it to desiccate (dry out).

Insecticides developed from elemental (mineral) sources mined from the  earth are classified as natural products and often cost  less than other processed or harvested insecticides.

Use diatomaceous earth only in landscape areas  that do not contain edible plants (e.g., ornamental gardens) ;To create an effective barrier for slugs,  apply diatomaceous earth in a 3-inch wide,1-inch thick band around the  habitats that slugs use. Repeat applications after  periods of rain. Note, however, that diatomaceous earth can  also be toxic to beneficial insects such as predatory ground beetles and is highly toxic to bees if applied to blooms.

Elemental sulfur is a finely ground powder that can  be applied either as a dust or a spray. This mineral is one  of the  oldest pesticides known, and reported pest  resistance is rare.  Sulfur  acts as a metabolic disruptor (interferes with a chemical reaction, digestion, or the  transport of substances into or between cells) to in- sects such as aphids, thrips, and spider mites. Most  sulfur formulations have low toxicity to people but  can  be an eye and skin  irritant. Sulfur  is highly toxic to fish, so it is important to keep  it away  from water (ExToxNet n.d.).

Do not use sulfur on  a
crop  just  before harvest if you plan to preserve it;
sulfur can  produce off-flavors in canned
products, and sulfur dioxide can  form,
which may  cause  containers to explode. In addition, sulfur is
phytotoxic to most crops if applied two 
weeks  before or after  the 
application of a horticultural oil.

Iron phosphate is very effective at managing slugs and snails
when combined with bait. Baited  iron
phosphate usually comes in pellet form. Scatter the  product around the  crop 
in need of protection and areas 
where slugs seek refuge, such as garden bed  borders and rocks.  Liquid formulations are also available.
Follow  label  suggestions for subsequent applications.

Insecticidal soaps  are very effec- tive  for managing soft-bodied insects like aphids, scales, whitefly, mealybugs, thrips, and spider mites.

Slugs that feed on  iron
phosphate will stop  eating, usu- ally
seek a hiding place, and then die of starvation. Iron phosphate is considered
relatively nontoxic and does not affect 
insects, birds, or mammals when applied in the recommended amount.
Avoid  over-application, as there is some
evidence that iron phosphate baits  can
negatively affect  earthworms (Edwards et
al. 2009). Because  iron phosphate is
nontoxic only in the  labeled ap- plication
amounts, be sure  to store  it in a safe place  away from pets  and children. Most  brands of iron phosphate are approved for
organic production by the  National
Organic Program.

Kaolin is a fine  clay that is sprayed on  plant foliage or fruit  to deter feeding and egg laying of insect pests  such as apple maggot, codling moth, and leafhop- pers.  It can  also have some repellant properties that cause  irritation to insects upon contact (Stanley 1998).

The effectiveness only lasts as long as the  clay film cov- ers the  fruit  or foliage to mask  its chemical, visual, and tactile cues.  Reapplication is necessary if rain  washes the  product off. Kaolin’s  toxicity to pests  is additionally dependent on  the  insect being on  the  fruit  or foliage during the  entire time of pest  susceptibility. You will need to monitor insect activity to be sure  that plants are protected during the  required times. Kaolin is an  organi- cally-approved material.

Natural soaps  are derived
from plants (coconut, olive, palm, cotton) or animal fat (whale oil, fish oil,
or lard) and have been used  since  the 
1700s to control certain soft-bodied insects such as aphids (Olkowski et
al. 1993). Soaps  are fatty acids  that can 
degrade or dissolve the protective layers  of the 
insect cuticle, causing the 
insect to desiccate. Insecticidal soaps 
are considered nontoxic to humans and many beneficial insects, but  selectively kill certain pest  insects. Some 
soaps  are approved for use in
organic agriculture.

Insecticidal soaps  are
very effec- tive  for managing
soft-bodied insects like aphids, scales, whitefly, mealybugs, thrips, and
spider mites. The soap must contact the 
insect’s outer skeleton to be effective. Leaf-feeding insects are often
found on  the  undersides of leaves, so be sure  to fully 
cover  plant foliage. Results from
the  application of soap  are usually seen  in 1–3 days. Multiple applications are often
needed to be effective. Insecticidal soaps 
are usually diluted with water before applying.

Do not use household soaps 
as insecticides. Household soaps 
vary  tremendously in composition,
purity, and effectiveness, and thus have the 
potential to harm crops.

For example, household soaps 
can  be phytotoxic to some plants,
resulting in leaf burn. Only use soaps 
that are specifically registered and sold  for use as insecticides. Be sure  to read 
the product label  for known
phytotoxic effects  and always test  the 
product on  a small portion of the  plant to see if leaf burn occurs. Leaf burn
symptoms usually develop within two 
days.



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