Despite more than 100 years of use, there is still some uncertainty
about how soaps kill insects. For many years the reason was given as a
disruption of the insect cuticle (the wetting agent effect) and death
occurring as a result of the loss of water from the insect's body.
While this may in fact take place, there is additional evidence that
the soaps may enter the insect's respiratory system and cause internal
cell damage (the sodium and potassium component of soaps and detergents
are often attributed to causing such cellular damage.)
There is good evidence that both true soaps, those made from animal
fats, and detergents have insecticidal properties. The original
product "Safer's Soap" was derived from fatty acids in soap,
specifically potassium salt of oleic acid. There is ongoing research
in the use of non soap detergents for insect control. There are two
major problems with the use of soaps and detergents for insect
control. One is the lack of a residual period and the other is the
potential phytotoxicity. Slight increases in soap and detergent
concentration, as well as increases in frequency of application, have
caused reduction in the yields of various vegetable crops and reduction
in the appearance of various ornamental crops.
We are seeing an increased use of soaps and detergents as pest control
materials by commerical hort companies here in Maryland but I am also
seeing an increase in complaints of plant damage, especially when these
materials are used during the summer.
----------------------
Bob (who frequently uses soap) Stewart
Southern Maryland (USDA Zone 7)
Rs72@umail.umd.edu
