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Re:Fungus gnats...long...

Greetings from Sweden,

We all have in one way or the other have had experience with the sciara fly
or more commonly known as the fungus gnat. The trouble with this fly began
when "we" started to use peat in our composts, previously this was only a
problem for mushroom growers.
Most books say and people believe that these flies are harmless, however
that is not so!!!! Read this!!!

The larvae stage of this fly is up to 5.5 mm long, clear and has a black head.
It can cause severe damage by burrowing into roots, graze on young feeder
roots, or just tunneling into the body/stem of a plant, thus opening up for
other fungi and molds to enter, like Fusarium and Botrytis. Sometimes
seedlings can wilt for no reason, found lying on their sides with no roots,
leaf yellowing, leaf distortion are other symptoms.

These infestations occur mainly when you use socalled "soilless" media like
peat. It attracts the fly and they lay their eggs. Also, most commercial
potting mixes that you buy are already infected, probably as early as from
the bog!!!!

When you water your seedlings, the eggs hatch and the larvae feed for two
weeks on your plants, then go into a pupal stage, and then after a while (
about three days) the fly emerges, and lives for another week. And the
cycles continues...
There are several ways of battling these pests, I'll state most I know of,
with my personal experiences;

1. Sticky traps. Catches some of the adults, but does not deal with the
problem in the long run, and not with the larvae stage where the real
damage is done. In no way will the traps catch all adults.

2. Avoid the use of peat. Good if you are able too, but most can't. Try
sowing in vermiculite might be a good solution.

3. Cover the top of pots with a layer of grit/sand and pebbles, 2
centimeters or more. Good, since the gnat does not lay eggs in sand,
however somehow they manage to do multiply anyway.

4. Repot all new acquisitions, most likely when you buy plants grown in
greenhouses, they are already severely infested...see next point;

5. Sterilise soil. If you add water to a measure of soil and microwave it,
the eggs are destroyed. There are currently discussions if you don't
destroy the beneficial micro organsims by doing so, but in my experience,
the seeds germinate fine anyway. Some sow their seeds in pure vermiculite
and report fine results.
This is smelly if you don't have a microwave, and messy in bulk.

6. Pyrethrum based drenches. The adults aren't too fond of this, but you
need to do this on such a frequent rate as the pyrethrum degrades so
rapidly that it isn't effective.

7. Pesticides. Not effective against the eggs or pupae, are also harmful in
the long run.

8. Shaking pots. This is something some people swear by, saying that the
larvae "fall out". Most of the time the larvae live in the upper strata in
the pot, so not effective, nor is stirring up the soil.

9. Checking your greenhouse and growing area...they might also live on any
decaying organic matter you might have about, fruit bowls, ( then often
called fruit flies) etc.

10. Purchasing a number of carnivorous plants. Deals only with the adult
fly, and the damage done by the larvae is unchecked.

11. Bacillus thuringensis var israelensis. This is a biological pesticide,
and it attacks the larvae stage of the fungus gnat's life cycle.

This product can be found under a variety of brand names, mine is called
Gnatrol but you can buy any product which lists B.t.i as active ingredient.
It is a pathogen, not a poison, repeat not a poison, it is harmless to
humans, also if you should happen to get some in your eyes, harmless to
breathe in.

However, you might wish to repeat the treatment as it only deals with the
larvae stage, not the adult. It might be desirable to combine it with some
of the methods described above.

A good side effect of Gnatrol or B. t. i is that it also deals with wine
weevils, mealy bugs, springtails and a lot of other pests. Often pest
control firms neglect to mention this, but in my opinion, this is an added
bonus.

However, B. t. i. cannot be used as a preventive measure or combined with
pesticides, and it requires a minimum temperature of 60 F to be really
effective, and the soil musn't be allowed to dry out.

Good Luck!

Ingrid ( Spring at last! )
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