Iris Cohen wrote:

Much to my horror I discoverd cobweb like "sacs" of caterpillars and their
small black eggs in my apple tree.

You have tent caterpillars. Spray with an insecticide which is listed for fruit
trees. You will probably have to spray several times. Wait until evening when
they are in their web and spray it heavily. You can also kill them if you have
a blowtorch with a very narrow flame, so you can aim it right at the web
without damaging the tree.

The occurence of tent caterpillars is very cyclical in nature - some years there
are few, if any, tents visble while in other years (like this one), the population
seems to be huge and very widespread. Many folks panic at the appearance of these
creatures, but they are short-lived and with the exception of very young and
vulnerable trees, seldom do any significant damage. Any defoliation will not be
permanent - trees releaf very easily. Tent caterpillars do not feed on anything but
foliage - your fruit will be unaffected.

Recommended treatment is to remove and destroy the nests before the caterpillars
emerge or while they are still very young. This is best done very early in the day
or late evening, when they regroup at their nests. When mature, they do not return
to the nests and control (if required) is done by application of a bio-control, Bt
(Bacillus thuringiensis), which affects only caterpillars. If they are mature
enough, they stop feeding and Bt is no longer effective, however their damage stage
is also over. Birds will take care of a good many, anyway. :-)

You DO NOT need to spray with a toxic insecticide. The damage does not warrant it
and it will destroy more beneficials than the target species, not to mention
mucking up the rest of the environment and rendering your fruit inedible. If your
tree is small enough, try hosing them out with a sharp stream of water. It will
kill many and the others you can pick and destroy.

I have given out this same information so often to clients and nursery customers
this season, I should have a recording made - it seems to be the number one topic!

pam - gardengal