Whiteflies on Cymbidium

[orchid doctor]

Hi Dennis:

I have a cymbidium that is infested with white fly. How
do I treat these pests? The only pesticides I have in my arsenal are
Rose Defense and a light horticultural oil. Would either of these
be
appropriate to use?

Thank you taking the time to answer my question,

Jean

**********************************************************************
Dear Jean:

I don't usually think of Cymbidiums as preferred hosts for whitefly,
so the first thing you need to do is look around your garden (and look
as carefully as you can at the adjoining yards as well) to determine
the source of the infestation. Whiteflies prefer thin leafed plants,
and are particularly attracted to pale green and yellowish leaves.
They like Fuchsias, Abutilons, Bamboo, Roses, Marigolds,
Impatiens, Thunbergias, Euphorbias and such. They will infest irises,
Columbines, Oreganum, vegetables and a host of other things.

Horticultural oil, and Neem oil are not of much use against them.
Adults will scatter as soon as you begin to spray, so most of them
will not be killed, plus they have a powdery bloom on their bodies
which will keep the spray from suffocating them (which is what oil
sprays do). If you are thorough and coat both sides of every leaf, you
will be able to kill many of the nymphs present on leaves and so
reduce the infestation. Neither spray has any residual action so
anything that is not hit and wet by the spray will not be killed.

Whiteflies have also developed resistance in some areas to commonly
used insecticides with chemical action (as opposed to the mechanical
action of oil or soap). The best tactic then is to use several (or at
least two) different products. Four or five applications must be made
at five or seven day intervals to eradicate them. I would recommend
trying an insecticidal soap spray at five day intervals, making sure
to thoroughly get the undersides of all the leaves as well as the
tops. If they reappear, then you will need to try again with products
containing one of the following: acephate, imidacloprid, resmethrin,
permethrin, malathion or diazinon. Imidacloprid and acephate are
systemic, and so provide longer protection and a more thorough kill of
existing insects. The reason for five sprays is to make sure all eggs
have hatched so there is no reservoir of potential reinfestation. Eggs
take about a week to hatch, nymphs take about four weeks to become
adults (and begin laying eggs).

Left untreated, whiteflies will severely weaken plants by feeding on
their sap. Even though they have many natural predators they are
prolific enough that it is hard for the predators to eliminate
populations.

Hope this helps, and good luck. Thankfully they will naturally be
reduced in numbers and vigor by the cold weather.

Sincerely,
Dennis