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market-farming - Re: Fungus gnats

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  • From: Sandra Beerman <sbeerman AT ucinet.com>
  • To: market farming <market-farming AT franklin.oit.unc.edu>
  • Subject: Re: Fungus gnats
  • Date: Mon, 17 Apr 2000 19:19:47 -0700


Here is something I copied a while back . Hope it will be of some use to
you.
Think I'd be more worried about what the Fungus gnats left
behind...larva


USING POTATO WEDGES TO DETECT FUNGUS GNAT LARVAE --
March 11, 1999
by Richard K. Lindquist, The Ohio Sate University

Wondering what to do with those extra potatoes? Martha Stewart
might have
other suggestions, but we suggest using them to sample for fungus
gnat larvae
and other growing media-inhabiting creatures. This will help you know
more
about what is happening in your crops – which is what crop management
is all
about. Potato pieces pressed into the media are very useful for
detecting fungus
gnat larvae, and probably other potential pests such as bulb mites.
Fungus gnat larvae are especially harmful to plants in
propagation beds,
cuttings just after sticking, and seedlings – any plant with a
limited root system.
Fungus gnat adults are attracted to fresh potting media to lay their
eggs. The
larvae hatching from these eggs can be feeding on roots in a matter
of days
after potting plants. But that's not all. Recent research at Michigan
State and
Purdue Universities demonstrated the presence of fungus gnat larvae
and bulb
mites in some potting media before the presence of any plants. In
other words,
fungus gnat larvae could be waiting for plants to be added! Placing a
cutting into
media already infested with larvae is asking for trouble. Using the
potato
sampling method is useful as a kind of early warning system.
There are at least two ways to use this sampling method: 1. Cut
potatoes into
pieces about 1-inch thick (to prevent them from drying) and about
1-inch in
diameter. Press the pieces slightly into the potting media surface
and leave in
place for 48-72 hours. Some cut the potato piece into a wedge, making
it easier
to push into the media. After the 48-72 hour period, lift the pieces
and look for
larvae, either on the potato piece or in the media where the potato
was. 2. Cut
the potato into "French fry" pieces and push them deeper into the
media (1-2
inches), because fungus gnat larvae may be well below the surface.
The number of potato pieces to use in a sampling plan is a kind
of educated
guess at the moment. One suggested sampling plan is to use one potato
piece
per 100 square feet of bench area. You will need to use the number
that can be
examined within 48-72 hours of placing them in pots or flats. Much
longer than
that and the pieces either dry out or rot. It's not necessary to use
potato pieces
everywhere in the greenhouse, but only on those young plants on which
fungus
gnats are known to be problems. Should you give up the yellow traps
for
sampling adults? No. Yellow sticky traps should be used in addition
to potatoes.
The two methods together will give a pretty good picture of the
fungus gnat
situation.
Sandie OR.








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