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Re: [aroid-l] Amorph Blues

  • Subject: Re: [aroid-l] Amorph Blues
  • From: Dan Levin <levin@pixar.com>
  • Date: Sun, 04 Jul 2004 02:38:40 -0700


I knew exactly what pest you'd found even before I clicked on
the link to view your image.  Sadly, I find these all too often in
the rotting tubers/ corms of many aroids; Amorphophallus and
Alocasia especially.  The pest you discovered is the larval or maggot
stage of (enter sinister organ music...) the ubiquitous Fungus Gnat.

Thing is- and this is important- it is my firm belief based upon
years of rotting more aroid tubers/ corms than I'd ever admit to
in a public forum, that these fungus gnat larvae are more akin
to a nasty secondary infection and are rarely if ever the primary
causal agent.

Not to diminish their impact; I'm sure the larvae -greatly- accelerate
the demise of any tuber/ corm they infect, but there always seems to have
been an initial case of rot or decay in said plant parts which has preceded
the invasion.  Even if it's only a matter of hours or one day... i.e. I've never
observed fungus gnat larvae laying siege to a healthy tuber- though they are
reputed to eat root parts and consequently stunt plant growth.
Once fungus gnat larvae are discovered inside a tuber or corm, the
problem is most certainly compound and not quite as simple as
"eliminate the pest and all will be well... "  You will have some fungal or
bacterial rot to contend with and by implication, sour compost or media.

If you google "fungus gnat" you'll find pages & pages of info; most
Universities with an Ag school offer info on this pest & potential controls.
A few such sites hosted here in the states:
 http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7448.html  (UC Davis)
 http://www.ipm.ucdavis.edu/PMG/B/I-DP-BRAD-LV.004.html  (a Larvae image)
 http://ohioline.osu.edu/hyg-fact/2000/2114.html   (Ohio State)
 http://insects.tamu.edu/extension/bulletins/uc/uc-028.html  (Texas A&M)

My advice for hatching Wilbert's micro mail-order Amorpho tubercles:
- Never overpot, stick to a suitably sized container
- Keep moist but never wet, unless growing in very high heat
in a media/ pot with great drainage and much air movement
- Check/ lift the little tikes every other day; scrupulously check for rot
or desiccation... it's a fine line!  Checking them daily is not too often.
- If you have fungus gnats in your growing area, by all means: drench
the soil in all of your pots with an appropriate insecticide on a preventative
basis.  By the time your application needs to be curative, you're too late.
I'd be happy to offer info/ personal data on effective pesticidal chemistries,
but will refrain from doing so unless asked.

Hope this is of some help, I wish for you much success.

Neil Gordon wrote:

> So i broke it in half and what was inside? One of these little buggers.
> http://www.ng23.abelgratis.co.uk/bug/damn_bug.jpg
> It was (past tense intended!) about 5mm long.
> Does anyone recognise what it may be? Is it contagious? Should I spray
> the soil of my other amorphs with insecticide?

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