I have a persistent problem with red spider in the greenhouse. I know
that people do use biological controls successfully (Sacha's husband has
for years and was one of the pioneers), and I've had success with the
red spider predator in previous years.

However, in my but of W Yorkshire, we have had three rotten summers on
the trot. The last two years the red spider predator seemed to have no
effect, and I came to the conclusion it wasn't very happy unless the
weather was warm.

This year, the early part of summer was shaping up a bit better, so I
bought the predator. And then the weather went downhill and once again
the predator seemed to fail. I gave it about 6 weeks (when successful,
there has been about 3 weeks of apparently no effect, then after that
I've suddenly realised there don't seem to be any red spider around any
more) and since then I've operated on a combination of spraying with
soapy solution rather than water and removing the worst affected leaves,
and this has kept it to a level where the plants have been cropping
reasonably well.

Has anyone else noticed this? Is it a known problem that biological
controls work better in the warm south of the country? Or am I imagining
it?


--
Kay

On 2009-10-02 11:37:11 +0100, K said:

I have a persistent problem with red spider in the greenhouse. I know
that people do use biological controls successfully (Sacha's husband
has for years and was one of the pioneers), and I've had success with
the red spider predator in previous years.

However, in my but of W Yorkshire, we have had three rotten summers on
the trot. The last two years the red spider predator seemed to have no
effect, and I came to the conclusion it wasn't very happy unless the
weather was warm.

This year, the early part of summer was shaping up a bit better, so I
bought the predator. And then the weather went downhill and once again
the predator seemed to fail. I gave it about 6 weeks (when successful,
there has been about 3 weeks of apparently no effect, then after that
I've suddenly realised there don't seem to be any red spider around any
more) and since then I've operated on a combination of spraying with
soapy solution rather than water and removing the worst affected
leaves, and this has kept it to a level where the plants have been
cropping reasonably well.

Has anyone else noticed this? Is it a known problem that biological
controls work better in the warm south of the country? Or am I
imagining it?

Kay, I asked Ray about this and he'd had identical experiences many
years ago when using a compost which contained something that killed
off vine weevil but unfortunately, it also killed off the predators.
He can't remember the name atm but I'll post it if and when he does!
For quite a long time the makers denied this but in the end, so many
people remarked upon it that they had to admit it should not be used
where biological control predators were being used. So he wonders if
you've been using something similar. The other possibility is the
residue of old pesticides in the greenhouse killing off the predator.
If the effects of pesticides have now passed, the predator will be
fine.
OTOH and to cover all bases, Phytoseiulus persimilis which feeds on the
eggs and on the active spider mite needs good light levels and daytime
temps of around 21C so as to breed faster than the mite. HTH in one way
or another.
--
Sacha
www.hillhousenursery.com
Shrubs & perennials. Tender & exotics.
South Devon

Sacha writes


Kay, I asked Ray about this and he'd had identical experiences many
years ago when using a compost which contained something that killed
off vine weevil but unfortunately, it also killed off the predators.
He can't remember the name atm but I'll post it if and when he does!
For quite a long time the makers denied this but in the end, so many
people remarked upon it that they had to admit it should not be used
where biological control predators were being used. So he wonders if
you've been using something similar.

I haven't changed my compost between .3 years ago when I got good
control and the last three years. I use New Horizon.

The other possibility is the residue of old pesticides in the
greenhouse killing off the predator.

Possible, but I use pesticide in the autumn, then not through winter or
spring because I'm keeping the cacti dry.

If the effects of pesticides have now passed, the predator will be
fine.
OTOH and to cover all bases, Phytoseiulus persimilis which feeds on the
eggs and on the active spider mite needs good light levels and daytime
temps of around 21C so as to breed faster than the mite.

I think this is the most likely. Our air temperatures have been in the
teens most of the summer, and it takes a bit of sun to get the
greenhouse higher than this, which we haven't had. How good is 'good
light levels'? - do I need some serious glass cleaning? ;-)

I still have a few predators - the odd cocoon type thing here and there,
so slow breeding seems the most likely.

--
Kay

On 2009-10-02 16:07:15 +0100, K said:

Sacha writes


Kay, I asked Ray about this and he'd had identical experiences many
years ago when using a compost which contained something that killed
off vine weevil but unfortunately, it also killed off the predators. He
can't remember the name atm but I'll post it if and when he does! For
quite a long time the makers denied this but in the end, so many people
remarked upon it that they had to admit it should not be used where
biological control predators were being used. So he wonders if you've
been using something similar.

I haven't changed my compost between .3 years ago when I got good
control and the last three years. I use New Horizon.

And it does have anything added to it to control vine weevil -
something Green, IIRC. It's one of those names that just will not stay
in my head!

The other possibility is the residue of old pesticides in the
greenhouse killing off the predator.

Possible, but I use pesticide in the autumn, then not through winter or
spring because I'm keeping the cacti dry.

However, the pesticides get onto e.g. plastic pots and that holds a
residue for rather a long time. I have at the back of my mind some
experiment or other that Ray carried out - or found out about - I'll
try to remember to ask him about it.

If the effects of pesticides have now passed, the predator will be fine.
OTOH and to cover all bases, Phytoseiulus persimilis which feeds on the
eggs and on the active spider mite needs good light levels and daytime
temps of around 21C so as to breed faster than the mite.

I think this is the most likely. Our air temperatures have been in the
teens most of the summer, and it takes a bit of sun to get the
greenhouse higher than this, which we haven't had. How good is 'good
light levels'? - do I need some serious glass cleaning? ;-)

In sunny Leeds - perish the thought. ;-) i.e. Probably!

I still have a few predators - the odd cocoon type thing here and
there, so slow breeding seems the most likely.

Of course, once the predators have eaten all the nasties, they, too,
will die off so you may have to start again next year.
--
Sacha

Sacha writes
On 2009-10-02 16:07:15 +0100, K said:

Sacha writes
Kay, I asked Ray about this and he'd had identical experiences
many years ago when using a compost which contained something that
killed off vine weevil but unfortunately, it also killed off the
predators. He can't remember the name atm but I'll post it if and
when he does! For quite a long time the makers denied this but in
the end, so many people remarked upon it that they had to admit it
should not be used where biological control predators were being
used. So he wonders if you've been using something similar.
I haven't changed my compost between .3 years ago when I got good
control and the last three years. I use New Horizon.

And it does have anything added to it to control vine weevil -
something Green, IIRC. It's one of those names that just will not stay
in my head!

No mention in the data sheet of added pest control. Are you sure that it
does? If so, I'll have to ask the manufacturer about it. I'm inclined to
think not, else I wouldn't have had success with the predator in better
years.



However, the pesticides get onto e.g. plastic pots and that holds a
residue for rather a long time. I have at the back of my mind some
experiment or other that Ray carried out - or found out about - I'll
try to remember to ask him about it.

Again, that's something I'd expect to happen every year, but it is worth
investigating.


In sunny Leeds - perish the thought. ;-) i.e. Probably!
I still have a few predators - the odd cocoon type thing here and
there, so slow breeding seems the most likely.

Of course, once the predators have eaten all the nasties, they, too,
will die off so you may have to start again next year.

That's not a problem that I've had in the last three years ;-)
--
Kay

On 2009-10-04 12:42:24 +0100, K said:

Sacha writes
On 2009-10-02 16:07:15 +0100, K said:

Sacha writes
Kay, I asked Ray about this and he'd had identical experiences many
years ago when using a compost which contained something that killed
off vine weevil but unfortunately, it also killed off the predators. He
can't remember the name atm but I'll post it if and when he does! For
quite a long time the makers denied this but in the end, so many people
remarked upon it that they had to admit it should not be used where
biological control predators were being used. So he wonders if you've
been using something similar.
I haven't changed my compost between .3 years ago when I got good
control and the last three years. I use New Horizon.

And it does have anything added to it to control vine weevil -
something Green, IIRC. It's one of those names that just will not stay
in my head!

No mention in the data sheet of added pest control. Are you sure that
it does? If so, I'll have to ask the manufacturer about it. I'm
inclined to think not, else I wouldn't have had success with the
predator in better years.

No, I made a typo there. I meant to say "does it", not "it does". Sorry!



However, the pesticides get onto e.g. plastic pots and that holds a
residue for rather a long time. I have at the back of my mind some
experiment or other that Ray carried out - or found out about - I'll
try to remember to ask him about it.

Again, that's something I'd expect to happen every year, but it is
worth investigating.

I'll get him onto it when he comes in from the RAIN!


In sunny Leeds - perish the thought. ;-) i.e. Probably!
I still have a few predators - the odd cocoon type thing here and
there, so slow breeding seems the most likely.

Of course, once the predators have eaten all the nasties, they, too,
will die off so you may have to start again next year.

That's not a problem that I've had in the last three years ;-)

I almost wish you had. ;-)
--
Sacha
www.hillhousenursery.com
Shrubs & perennials. Tender & exotics.
South Devon