Are you sure you have gypsy moths? Their populations crashed a few years ago (here in SE Mass) as part of their normal decadal boom and bust cycle. But the winter moth is still wreaking havoc.

I think rockman50 is correct, it was Winter Moths that ruined my spring last season and decimated our yard.
I found some info on the UMASS Extension site. I have attached it here for you to check out.

I plan on spraying with BT in early April, or as soon as I see evidence of them! Not only did they eat my trees but they ate my prized roses and it was devistating.

Good luck. I too plan on prevention this year!

Here is a link that might be useful: Winter Moth Fact Sheet

BT works on either type of moth, and can be applied by the homeowner to all but the tops of big trees. It's preferable to other treatments because it doesn't cause collateral damage, not even to butterfly larva, since it has to be ingested to kill (and caterpillars are selective in what kinds of leaves they eat).

You just spray it on with a pressure sprayer. Those are available from the hardware store and are not expensive. Don't let a tree guy talk you out of BT; they don't like it because it has to be applied during a short time window when the larva start eating and damage is noticed. This is easy for the homeowner, but difficult for a commercial applicator who needs to treat many houses for the same pest, presumably all at the same time in any neighborhood.

Treating the caterpillars on the foliage is much more effective than treating the moths themselves, since moths can fly in from all over.

I've noticed that the caterpillars are still there, and look unaffected after spraying, but apparently they stop eating as soon as they've had a bite of treated foliage; it takes them up to 3 days to die, but they're not doing damage during that time.

I'm not gonna let them get me this year!

I tried using BT last year, but that didnt work. All of my 30 rose bushes were eaten by these darn moths.

This year, I have purchase Dormant Oil, in an effort to kill the eggs, rather than the caterpillar.

So, question is: Can anyone tell me when I should start applying the Dormant Oil?

Also, does anyone out there have past experience with Dormant Oil and winter moths?

As always, thanks for any info. It's much appreciated.

I don't think dormant oil will accomplish what you want it to do. Even if you manage to kill any egg masses on the rose bushes, caterpillars will still find them as they travel in the wind on silk threads from any larger trees in the area. So your best bet is to spray with BT. I did last year and it was very effective. You may have to reapply a few times during caterpillar season as heavy rain may wash it off, and then more caterpillars flying in may start munching again.