In my opinion, one should NEVER use insecticides as a preventive treatment.
If I may "borrow" Eric's example, a killing dose of imidicloprid (via that
specific product, according to the manufacturer*) is to use 1 ounce per
gallon, applied 2 or 3 times at weekly intervals.
By using 1/2 tsp per 24 oz, the application concentration is less than half,
meaning it is less toxic and might leave some survivors that having been
exposed, may build some resistance to it. Likewise, the 4- to 8 weeks
between applications is well beyond the complete life cycle of a lot of
critters, so if they were exposed and began to develop immunity, they will
have had the opportunity to mature, reproduce, and potentially pass that
Preventive treatments with s-kinoprene (Enstar II) on the other had, is
safe, and definitely the way to go, as the chemical is an insect growth
regulator that prevents the maturation of all stages of the insects' life.
No maturation = no reproduction = no population and more importantly, no way
to develop and pass on immunity to offspring, which is how a resistant
Even better, Enstar II apparently has no effect on bees, which cannot be
said for most insecticides.
If one absolutely insists on doing "preventive" insecticidal treatments, the
very least that should be done is to switch insecticides - or more
specifically, the killing mechanism - at each treatment. By doing so, even
though you are not affecting a complete kill, the likelihood of a bug being
resistant to two different chemicals is much lower than to repeated doses of
a singe one.
* The asterisk next to the "according to the manufacturer" comment was to
remind me to state that in a phone call, it was recommended that I purchase
a different (more dilute and more expensive) Bayer product for use in the
greenhouse, but after some prodding about a comparison of the concentration
of the active ingredient, the CSR acknowledged that the Tree & Shrub stuff
Ray Barkalow - First Rays Orchids - www.firstrays.com
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"Eric Hunt" wrote in message
We've been using Bayer Advanced Tree and Shrub in the OrchidMania
greenhouses for about 8 months now - applying every 4-8 weeks as our GH
manager has the time - diluted and put into a hand sprayer. We dilute to
the rate of 1/2 tsp per 24 oz water.
Scale and aphids are dramatically down - only have spot infestations now
whereas before whole sections were getting engulfed by scale and every new
bud covered in aphids.
We're starting to think about switching - I am sure the buggers are
developing resistance as we speak. We're looking at starting prophylactic
Enstar II as the next thing.
-Eric in SF
wrote in message
Observations from a landscape (not greenhouse) gardener regarding
imidocloprid best use and best effect in zone 5a Maine.