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 Indoor
control of orchid mealy bug by imidacloprid (Merit®, Marathon®)
by
Jean Kahan
My
orchid collection is grown under lights in our basement. Orchid
mealy bugs infected some of my orchids quite suddenly, and it didn’t
take long before all my basement plants – including a large
collection of non-orchids – were infested. Topical approaches
such as Neem Oil or the old Isopropanol / Q-Tip routine were only
partially effective, as juvenile insects were unreachable and
well-hidden. Meanwhile, scale started to appear on numerous
plants. Insecticides applied outdoors, such as Malathion, were
unsuitable for domestic indoor use. I truly contemplated tossing
everything out and turning my time and attention to other
interests!
An
internet search for alternatives revealed a report from the
Connecticut Agricultural Experimental Station on the efficacy of
the systemic agent imidacloprid (with brand names Merit® and
Marathon®) against orchid mealy bug, Pseudococcus microcirculans.
They believe this pest was introduced from the Southern US.
Imidacloprid
(an odorless analog of nicotine, that time-honored aphid
treatment) is absorbed by the roots and translocated to the stems
and leaves and is relatively stable. Importantly, imidacloprid is
of low toxicity, e.g. it is classified by Consumers Union as a “reduced
risk alternative pesticide” and is used in pet flea collars. My
reservations about this product is that it does not break down
quickly when discarded and is toxic to bees and certain fish.
Nevertheless it is widely used in sensitive outdoor environments
like golf courses.
In
its most economically available form, imidacloprid is adsorbed at
0.5% on clay particles supplied in 10lb bags (minimum size found)
for broadcast use against turf pests. However, use with orchids
required a tedious extraction of the active principal from a gooey
gumbo of clay. I strongly discourage anyone from going this route!
Pure
imidacloprid as a wettable powder can be purchased as Marathon
60WP from EC Geiger, Harleysville, Route 63, Box 285,
Harleysville, PA 19438, (215-256-6511) or www.hortnet.com. The
price (hold your hat!!!) is about $300 for 100g, enough powder to
treat my two 4-tiered light-stand collection plus new
introductions, intensively for 1 year.* Geiger delivers free any
order over $100.00 to the central NJ area.
I
used imidacloprid at a rate of 300 mg (500 mg of 60WP) per gallon
of either water or fertilizer solution. The final concentration
(75 ppm) is midway between the recommended levels for ornamentals
and one quoted for scale eradication in cycads. I treated
everything with imidacloprid regardless of whether or not insect
pests were noticed, and I used it both as a drench and as a foliar
spray. It was probably over-kill, but I applied it every time I
watered or fertilized my plants for a period of three months.
I
had wonderful success with imidacloprid, and all but one of my
plants (a non-orchid) not only survived treatment but responded
with shoots, buds, flowers, and new growth. Amazingly, I was able
to spray orchid blooms without visible damage! However, a few
orchid plants that were in bud produced distorted flowers that
fortunately reverted to form the next time they bloomed. The
numbers of visible mealy bugs dropped rapidly, and there were no
signs of them after a few weeks. All forms of scale dried up and
were easily removed. If I have problems with susceptible insects
in the future, I would be inclined to treat with imidacloprid
every two weeks or so for a period of a month rather than each
time I watered or fertilized.
*
The powder form is sold already subdivided into 5 20g pouches,
lending itself to easy cost sharing.
Here
is a site showing various forms of scale and mealy bugs. If you
can’t stand the site of these pests, don’t look here! -Max
http://www.geocities.com/hibiscusred/bug/suckers2.htm
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