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Orchids/Dendrobrium with ??


A dendrobrium that I received from a grower had a white granular coating on the bottom of the leaf stalk, where they meet the roots.  I thought that perhaps the grower had over fertilized by accident.  It lost all flowers shortly after arriving, which was unusual as other orchids received from this grower lasted easily a month.  I soaked it in water and repotted it.  It is dying.  Another orchid that was sitting near it now is showing the same white granular coating and has lost on leaf stalk.  What can this be (I can not find anything in my books or online) and what else can I do to treat it?

Amy, without seeing it, it sounds like a scale insect.  There are many types of these. As a start, wet several q-tips in isopropyl alcohol and rub these over the tissue where you suspect the insects are present. If they come off on the q-tip, that is a pretty good indication of an infestation.  Be sure to isolate any infested plants. If your plant is infested with scale, they are likely not only to be on the plant but in the pot as well.  If that is the case, remove the plant from its pot and discard the pot and all of its contents.  Repot in fresh orchid potting mix and new pot and treat the pot and its contents with an insecticide that can be absorbed into the plant tissue to kill any insects that hatch from eggs (called a systemic insecticide).  The latter may be a spray, granules, or powder.  I prefer the granules which will dissolve over time.  Many of these are quite pungent so you may want to enclose the plant in a plastic bag for a couple of weeks after treatment.  Another approach is to insert the entire plant (after removal from its pot) in an insecticidal solution for an hour. Be sure the label on the insecticide specifies for treatment of scale. Follow the directions on the label for safe handling.


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Wayne King


Any question about orchid culture. I have thirty+ yrs of growing experience,president 2x of our local Orchid Growers Guild,held a position in most all other offices associated with the Guild at one time or another. Head of Orchid judging team for local club meetings and some shows. Member of two Orchid Socities and local Rep.for Mid America Orchid Congress for several yrs.I have in my collection about 800 Orchid plants of all types.


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