Get your horticultural oil out NOW (Dormant Oil) and get some spraying done before your shrub breaks buds. Horticultural oils (I don't mean neem) are the number one recommendation for scale insects, especially during the dormant season.

I assume that you have a small pump sprayer? Hopefully one with a fan spray head. That would make short work of applying product to your dormant shrub.

Could you take pictures of the scale so that we can see what kind they are?

Sorry, I forgot to add the attached link for you.

Here is a link that might be useful: Hort. Oils are useful

Does you Lilac actually have scale or are the branches covered with lichens, as mine are? If that is lichens there is nothing you need do since they do nothing to harm the Lilac.
Many people think the presence of lichens is scale and they are not.

Here is a link that might be useful: lichens

EXCELLENT point! Though I'm pretty sure that Amy probably knows scale from lichen (judging from her past posts), it's always good to make sure of an identification.

Amy, by the way, you shouldn't be using strong chemicals of ANY kind with your illness. Not even household products. The horticultural oils are not likely to be a problem, however.

Rhizo,
It's scale... DEFINITELY...

I can't figure out how to do photos at moment, confusion is pretty bad. Even if I had step by step, right now I can't learn well...temporary?

As for hort. oils, I read your link and tried to figure out something and had my mom stop and get something called "Ortho Volck Oil Spray" that's a dormant insect killer. She just came to visit today so she brought it... it's too rainy today to think about using (plus tired today). It reportedly kills scale.

Though reading back it says easy to apply with ortho Dian N spray applicator, hose-end (not doing that), or tank sprayer (don't have, don't want to buy)... If it's okay to use, I'll use one of my sprayers in basement.

Yeah, I'm limited by chemicals (never liked in past, now is different)..

Tomorrow maybe i'll figure it out..

amu

Aw, you need to get yourself a little two or three gallon plastic pump sprayer! They can very useful for small jobs. You can just fill it a gallon at a time and be much more accurate than your dial-n-spray hose end.

I've used Volck Oil many times. You'll see that there are at least two mixing rates on the label...some are for dormant spraying on bare woody plants and other rates are suitable for growing season plants. So your Volck oil can be used all year round...just pay attention to temperatures. Read the directions before each use.

You can send me pictures, if you want to. Just use my email address found in 'My Page'.

You are aware that this lilac has numerous and pronounced lenticels? Verify that this is indeed scale. Now is the time to treat with dormant oil if that is the case.

get a tank sprayer.. small ones are under $10 ... this is not a hose end deal ...

precise timing is of the essence.. and the only real issue ...

what you see today is momma ... and she is basically dead.. and has her progeny in egg form underneath.. and her carcass is impermeable to oil ...

you need to spray.. at the moment the little chuckers come out [they are seen with a jewelers loop] ... and if you spray then.. the oil will suffocate them .. before they can develop the hard shell ...

i would also look into rejuvenation pruning of the entire shrub.. and i might even consider going way past the 1/3 per year for 3 year cycle ...

with an intense infestation ... i might be tempted to forego this years bloom .. and simply cut the whole down to 3 inches .. and then spray that part at the right time .... with no insult to the root system.. it will probably be 5 foot tall by fall ... but again.. you would lose this years show ... and that is how you get rid of 99.9% of them w/o any chemicals ... or oils ...

all that said .. i personally would go with bayer systemic ... but i am not in chemo.. and i think.. in this case.. you ought to go with pruning or rhiz's thoughts ...

and i bet.. the plant came with it.. if you buy new stock .. now that you know what a scale is.. always ... always ... check ... and if one is infected at the store.. presume they all are ...

ken

ps: actually the babes are known as crawlers.. but i like chuckers ...

strobiculate has a good point, too, about the lenticels. It's been a looooooooooong time since I saw a lilac, so I don't remember what they look like. I know that on many plants, lenticels can look mighty suspicious.