No I wouldnt apply a dormant oil because the pest is on the underside of the leaf the oil will only coat the top layer of leaf and stem and staulk. I have applied material at high pressure and was able disturb the leaves enough to get some material on the underside or you can use a special wand to apply to the underside. I think the Orthene is your best bet. You'll have them controlled in no time if you
Toddpp note that oils should be only applied when air temperatures are above freezing (daytime) and the material
has ample time to dry before night time freezing temps.