Alberto Castillo
Sat, 11 Dec 2010 11:08:58 PST
Dennis, those are not thrips. Thrips are so tiny that one normally see the damage they cause before actually seeing any. Their droppings, like small black powder particles, can be seen near or on the lesions. 
Imidacloprid is very effective against thrips as are pyrethroids. Thrips can become resistant to insecticides rapidly. Give your plants a spraying with a well diluted solution of the mentioned drugs and cover overnight the plants with a plastic to make a gas chamber. Pyrethroids are not harsh chemicals, their persistence is low.
> Date: Sat, 11 Dec 2010 11:59:37 -0500
> From:
> To:
> Subject: [pbs] thrips?
> I'm battling what I believe to be a thrips infestation on my gesneriads.
> Today I noticed a couple plants dying back in my terrarium which is located
> in another room. Lo & behold there's a huge quantity of the same beasties
> on those plants. I only occasionally see flying bugs, but what I frequently
> find are these orange worm-like organisms crawling on the leaves, they are
> incredibly small, flexible, and relatively fast. In my terrarium they were
> on my Hippeastrum seedling in huge quantities... more than I've seen on any
> other plant.
> So first of all, does this sound like thrips to you? And second of all, how
> would you battle them? I never use harsh chemicals, so if that's my only
> choice I will just give up growing those plants. I've been trying to do
> immersions in hot soapy water and then isolating the plants. But it is not
> totally effective. (I started this treatment when I thought the problem was
> foliar nematodes.) Clearly I need to improve my tactics.
> Plants affected the worst: Hippeastrum, Gesneriads (all except Chirita (so
> far)), Rex Begonia.
> Plants apparently not affected: Orchids, Irids, Passiflora, Eucharis.
> Interesting that the Hippeastrum was affected but not (yet) the Eucharis.
> It could simply be the humidity & warmth of the terrarium vs the dryness and
> coldness of the windowsill with the Eucharis.
> I can't pinpoint when the problem started, but I am suspecting it was a
> loooong time ago, and I wasn't alert enough to see the initial signs. Now
> I'm upset it seems to be in 3-out-of-4 of my grow rooms.
> On the Hippeastrum they created dark red streaks on the leaves. On the
> Gesneriads and Begonias the leaves basically turned necrotic (black)
> wherever they were feasting... from edges outward, or anywhere really. It
> seems to take them a long time to cause lethal damage.
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