mealy bug control

Johannes-Ulrich Urban
Thu, 08 Dec 2011 16:59:00 PST
Dear All,

Fortunately I do not have mealy bugs in my collection except the odd new
plant that brings them with itself, in these cases I use Imidacloprid
(not always effective) or dimethoat (very effective) If the plant is not
valuable I would throw it away.

But I think if a whole greenhouse is infested with mealy bugs spraying
is of no use: In this case I highly recommend biological pest control
which works very well for me with spider mite and scale insects. The
approach is different: predating insects would be killed by pesticides
or the remains or breakdown products of them. Companies supplying
predators have lists for how long you need to wait after chemical
treatment according to the chemical and the predator.

When biological control is used it is important to start it at the very
fist sign of infestation. The predators need time to multiply, to find
the pest and most of them also need a certain minimum temperature to act
and/or survive.

The best results I had with spider mite, with one or two releases of
predating mites I am clear of that horrible pest, nothing else worked
before I discovered this method. And it works better the longer I use
it, it feels as if there is a certain permanent population of predators
present now. Less sucessful was a predator against whitefly, it took
very long to eradicate it and now they are almost gone but I still see
the odd white bit flying or sitting somewhere. But chemical treatment
nowadays has become virtually impossible.

On the other hand some pests cannot be delt with with biological
control, for example root mealy bugs. The company I get my predators
from has an excellent service. I can send them an infested leaf, they
would identify the pest and recommend a specific predator (in some rare
cases no predator was known) 

It gives me a much better feeling to use this totally harmless method
rather than using more and more poison as I did in the past, also
because I  grow edible plants in my greenhouse like grape, fig and

One word about Imidacloprid. It is a good insecticide and so far I have
never had any plant damage using it. BUT: it is VERY long acting. This
seems to be an advantage at first glance but in reality this is its
biggest risk and disadvantage. Because long acting agents take a long
time to disappear from plant tissue the active level in the plant tissue
will decline very slowly. During this slow and prolongued decline
resistance develops because pests can get used to low levels of the
agent that just does not kill them. The same applies to long acting
antibiotics in medicine by the way.
This problem of Imidacloprid was known from the beginning on and it was
always recommended not to use it as the only product but use it
intermittently with other, non related substances.

A good alternative in between Imidacloprid sprayings is neem oil or
pyrethrum or a mixture of both. Neem and pyrethrum are much less
dangerous for biological predators than Imidacloprid and using the bio
method now I only use Imidacloprid in very precise exceptions on a small

bye for today,   Uli

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