From: klier@cobra.uni.edu
Newsgroups: rec.gardens
Subject: To Spray or Not to Spray?
Date: 16 Jul 94 07:44:54 -0500

We've talked a lot on this group this year about use of various controls
for plant pests... everything from Bacillus thuringensis, to soap and water,
to malathion, nicotine, sevin, and arsenic.... what I've not seen discussed
is *what level* of damage is needed before you start applying some of these
controls (esp. insect controls).

My point of view is that there should be no controls (except cultural
controls like mixed plantings, and the proper soils, water, light
and fertilization) until you have good evidence that the problem will be
reaching "crisis", and you really need to do something.  Until you've
reached this threshhold, don't do anything... so what if you have a
few holes in your bean leaves, or a squash borer... if you've planted
enough to allow for some crop damage, why create a surplus?  Chances 
are, if there hasn't been a great deal of spraying in your neighborhood,
that natural enemies of the pests are going to move in and feast when
the pest population gets big enough.

If, however, things are getting out of hand, try some hand picking, 
high pressure water sprays, pruning, or other "basics" as a first
resort in reducing pest populations.  Don't get out the "big guns"
until you really know you need them.

Why?  
1) Most pesticides, unless applied in a very targeted way, are not
   specific; thus, you get the good guys along with the bad guys.

2) Insects and other short-lived critters have a tremendous capacity
   to adapt their populations in response to a selection pressure: like
   malathion or Bacillus thuringensis.  When a population with a few
   individuals that aren't susceptible to the pesticide is subjected
   to pesticide treatment, the susceptible ones die, and the resistant
   ones reproduce.  Thus, by using a pesticide, you run the risk of
   helping create a resistant strain of pest.  (and the shorter the
   life cycle of the pest, the more likely we are to see resistant
   pest populations, soon!) 

3) Developing new strains of BT and other microbial pesticides isn't
   easy; ditto developing pesticides that are targeted to specific
   pests.  If we "wear out" the "environmentally desireable" pesticides
   with overuse, we're stuck with the "bad pesticides" when we really
   need controls. :-(  (this is rather like the new antibiotic resistant
   strains of bacteria that have been developing in response to increased
   antibiotic use-- e.g., multi-drug resistant tuberculosis, multi-drug
   resistant Staphylococcus aureus.)


Kay Klier  Biology Dept  UNI


