Indoor Orchid Pest Control with
Bayer's "Merit" Insecticide

BAYER Advanced Garden          Orchid growers are constantly on the lookout for infestations of various
orchid pests such as scale and mealybugs.  There are ways of eliminating these insects such as
physically removing them (mostly scale) and topical/contact treatments with Neem Oil, alcohol, or other
common insecticides (e.g. pyrethrums). This is usually only partially effective since the pests in various
stages of development are well hidden and continue to multiply. Pesticides are also available that are
systemic where the chemical used becomes incorporated into the stems and leaves of the plant and
eventually kill the pests.   
Orthene in its wettable powder WP form (dissolved in water) is commonly used, but it and similar
products such as Orthenex which is supposed to control certain diseases as well have very penetrating
foul odor and must be used outdoors.  There is a granular  material with systemic action called DiSyston
sold by Bonide that has been used by some of our members.    

The point of this article is to mention that the systemic insecticide imidacloprid, trade name Merit (also
known as Marathon), is a broad-spectrum systemic insecticide that has been used on orchids. It is an
odorless analog of nicotine, a chemical used in the past for controlling aphids.  Imidacloprid is of low
toxicity (used in flea collars) and is classified by Consumers Union as a "reduced risk alternative
pesticide."  It is expensive and the minimum amount for purchase is larger than most people need ($300
for 100 g from E.C. Geiger).  Several recent orchid bulletin board postings have pointed out that while
Merit alone is expensive, it is found as the sole active ingredient in the Bayer Advanced Garden - Tree
and Shrub Insect Control product (see above label).  This is readily available at Garden Centers
including Home Depot or Lowes for about $19 for a 32 fl.oz. bottle and thus is a reasonably priced
source for this pesticide. Merit is very effective at very low use rates and according to the label remains
effective for 12 months.  It is not sprayed on the plants but is used only as a soil drench where the
chemical is taken up by the roots and moved upward into stems and foliage.

This is NOT an endorsement for the product.  The label does not say anything about its use on orchids.  
Bayer apparently told someone that it was not worth the expense of getting it approved for orchids, but
that it probably could be used safely.  I have used this product (recommended rate one tsp/gal) on some
orchids this spring but have not made any definite conclusions.  I still prefer to clean any infested plant
with an alcohol rub prior to any systemic treatment and my trials should be more organized.  The growth
of the treated plants did not seem to be affected.  As with most systemic treatments, you can not expect
a severely infested or weak plant to be cleared of insects overnight, if at all.  If you decide to try it,
please follow all instructions.

For an interesting case study of using Merit on orchids, see

www.njorchids.org/articles/Mealybug/Mealybug.htm

As an unsubstantiated followup, a note recently has been posted on a bboard mentioning that there is a
Bayer product available that contains both a systemic and contact insect killer that possibly can be used
on orchids.  The label on Bayer Rose and Flower Insect Killer indicates that it contains the systemic
acting imidacloprid (Merit) and contact acting insecticide cyfluthrin.   I have not been able to find this
product to test.  Please let me know if you find it somewhere or have used it.

Of course the best way to keep pests out of your orchid collection is to purchase bug-free plants in the
beginning.  However, the little rascals are adept at hiding, multiplying and spreading quickly. A good
practice is to isolate and inspect all new plants for awhile and watch for any infestations.

Chuck VanDyke (cvandyke@andrew.cmu.edu)