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Re: Brussels Sprouts and "Maggots"

Stephen Griffiths wrote:
> 
> These "maggots" sound like Cabbage Root Fly larvae.

They are indeed.

> The female lays eggs at the junction of the soil and the stem of young
> Brassicas. They aren't fussy about which type.
> Brussels Sprouts, Cabbage, Cauliflower, Broccoli, Swede can all be
> affected.

Add radish, turnip, mustard, kohlrabi...  and BTW, for the U.S.'ers on
the list, a Swede is a rutabaga.

> Larger plants can tolerate some infestation but seedlings and small
> transplants are very vulnerable to attack.

I get such huge populations of these things that even very large plants
are done in.  Many times I've seen three or four flies lay eggs at the
base of a newly transplanted seedling within seconds of me taking my
hand away from pressing the soil down.  Some of my Bai Cai plants
(Chinese cabbage -- my true joy) look ready to harvest, then they
collapse into a pile of rotten mush, completely full of the cabbage fly
maggot.  Others are less damaged but they all get infested.  (But I
still get several of the most beautiful 3lb Bai Cai you've ever seen. 
Sorry, just had to brag.)

> 
> Using Diazinon will help, but it is not nice stuff to use and I wouldn't
> fancy eating anything exposed to it. Not knowingly anyway.

If you buy brassicas from the grocery, you may be exposed to lorsban and
dursban which are even nastier than the (relatively) milder diazanon. 
(Not that I would ever recommend the use of diazanon.)

> There are other soil insecticides but another way, does not require use of
> any chemicals, is a physical barrier.
> 
> Take pieces of old rubber or felt carpet underlay or roofing felt, even
> cardboard will do, and cut them into  approx. 10 to 15cm squares. Cut a
> slit from one edge to the centre of each square. When you plant out your
> brassicas slide a square around the stem of each using the slit.
> When the fly comes to lay her eggs, as she will, the eggs are exposed to
> the air rather than the moist soil and  will dry out before hatching.
> 
> This *does* work. I use it. I lose very few plants to root fly.
> If you want 100% success you will have to use chemicals and use a lot of
> them.

I've tried this with both my spring and autumn brassicas.  The roofing
felt I used was too heavy and damaged the stems of some the
transplants.  I would make certain that the material I used was more
flexible if I did this again.  Stephen metioned rubber, which is a good
idea.  But the roofing felt did seem to reduce the infestation or at
least delay it somewhat.  But eventually the plants were infested and my
losses were only somewhat less than normal.  (Although the surviving
plants may have had better yields.  I had no controls so I couldn't
measure that sort of thing.)  I think the flies were laying in the gap
in the material as the growing stem widened it.

> If you are prepared to accept a few, maybe no, loses then try the barrier
> method.

Another barrier I've has some limited success with is a thick layer of
sawdust banded around the plant.  Someone mentioned coffee grounds as a
deterrent to carrot fly, so some of the list members have suggested they
will try the same for cabbage fly.

As for me, I've given up on individual barriers for my spring crop. I
typically experience 40-80% losses depending on variety -- brocolli
suffers the least damage and cauli the most.  Since my spring crop is
relatively small I have purchased a 50'x67" piece of Reemay fabric which
I shall use to cover my spring brassica beds.  That won't work for my
autumn crop which covers an area of some 800-1000 square feet  (each row
is widely spaced with a drainage swale between).  So I'm still
interested in methods designed to deter, confuse or kill the dreaded
cabbage fly and her maggot. 

Steve

> 
> Regards
> Stephen
> 
> <><><><><><><><><><><><><><><><><><><><><>
> Stephen Griffiths
> Barfield Allotment Association
> Whetstone, London. England.
> stephen.griffiths@dial.pipex.com.
>  http://dspace.dial.pipex.com/town/close/xpz05/
> <><><><><><><><><><><><><><><><><><><><><>
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