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  insect problem
From: David Thornton <dave at dave-aroid.demon.co.uk> on 1999.02.06 at 16:08:46(3006)
Dear all,

I wonder if anyone can identify an insect problem that has wiped out my
Colcasia esculenta and is now spreading over Xanthosoma.

It appears on the leaf surface and underside as small black
flecks,rounded bodies, on closer look they appear as small grains of
sand, some sand colour others black. I can see the odd one physically
moving about. Eventually more and more of these flecks appear and
strands of web like thread stretch between them.

The bodies are soft and easily crushed.

So far they have proved quite resistant to insecticide

Advice Please !

+More
From: "Julius Boos" <ju-bo at email.msn.com> on 1999.02.06 at 18:05:37(3007)
>>Dear all,

I wonder if anyone can identify an insect problem that has wiped out my
Colcasia esculenta and is now spreading over Xanthosoma.

It appears on the leaf surface and underside as small black
flecks,rounded bodies, on closer look they appear as small grains of
sand, some sand colour others black. I can see the odd one physically
moving about. Eventually more and more of these flecks appear and
strands of web like thread stretch between them.

The bodies are soft and easily crushed.

So far they have proved quite resistant to insecticide

Advice Please !

+More
From: Jonathan Ertelt <jonathan.ertelt at vanderbilt.edu> on 1999.02.06 at 18:11:33(3008)
At 6:11 PM -0600 2/6/99, David Thornton wrote:
>Dear all,
>
>I wonder if anyone can identify an insect problem that has wiped out my
>Colcasia esculenta and is now spreading over Xanthosoma.
>
>It appears on the leaf surface and underside as small black
>flecks,rounded bodies, on closer look they appear as small grains of
>sand, some sand colour others black. I can see the odd one physically
>moving about. Eventually more and more of these flecks appear and
>strands of web like thread stretch between them.
David - This sounds very much like an infestation of spider mites, of which
there are several species. The description is quite good for this pest.
Word is that they drown in seven seconds, and they actually can be washed
off pretty easily, but with persistance, as they will return and repopulate
quickly from a few individuals or from eggs. Not being a big advocate of
heavy duty pesticides, I generally use a combination of 70% rubbing alcohol
with a mild soap, which proves quite effective. Test this on a small bit
of leaf first, however, because I have seen some cell damage result from
this. This does need to be applied several times at 7 to 10 day intervals.
Good Growing.
- Jonathan

From: dave-poole at ilsham.demon.co.uk on 1999.02.07 at 08:33:24(3010)
One point worth noting is that spider mites, whether of the black or
'red' form, rarely thrive in humid, moist atmospheres, tending to
prefer the dry, warm air of the average, centrally heated home. They
can also reach epidemic proportions in glasshouses that are allowed to
become searingly hot and dry in summer. If you do not wish to use
malathion based insecticides, washing the leaves in a weak, soft soap
solution and then rinsing with clean water will remove most if not all
of the adults. However, the eggs are not so easily dealt with, being
immune to insecticides and often deposited at some distance from the
plant. In the home, this can mean eggs are laid on curtains, the wall
or even just the outside of the pot. They are so tiny as to be
Virtually invisible. The worst thing about them is, that they can
remain dormant for weeks or months, not hatching until air
temperatures and aridity have reached the right levels.

Keeping the leaves of your plants regularly misted - at least once,
preferably twice a day, will go a long way towards deterring
re-infection.

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From: Greggy6392 at aol.com on 1999.02.07 at 17:16:36(3011)
Dear all,
As regards the red spider mite problem, if you do not like using pesticides
you could try the natural predator Phytoseilius persimillus which is effective
if infestation is not too great.

Alan Gregg

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From: Krzysztof Kozminski <kk at netgate.net> on 1999.02.08 at 15:30:21(3018)
On Sat, 6 Feb 1999, David Thornton wrote:
> It appears on the leaf surface and underside as small black
> flecks,rounded bodies, on closer look they appear as small grains of
> sand, some sand colour others black. I can see the odd one physically
> moving about. Eventually more and more of these flecks appear and
> strands of web like thread stretch between them.

As an addendum to other messages identifying this pest as spider mites, my
favorite method to kill'em is to use one of the horticultural oil sprays.
Just be sure it is not one of the heavy duty dormant oils, but rather one
of the ultra-fine varieties using a fine emultion of parafinnic oil. In
the US, I think one brand is "Sunspray" (Gardens Alive has their own
brand which is the same thing, as far as I could tell.).

I tested these oils on many aroids, and they all seem to tolerate it very
well. The oils also kill scale, and should be able to take out mite eggs
as well - just spray the surface of the soil and the pot. They work by
suffocating the critters, so generally they do not harm any beneficials if
you scare them away by shaking the plant. The treatment may need to be
repeated weekly for a couple of weeks.

The best prevention is to keep the humidity high. I never saw a spider
mite in North Carolina, and am fighting them on a regular basis in
California...

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