Imidacloprid can still be used by certified pesticide applicators, just not the general public. You can hire someone to purchase an apply a product containing a neonicotinoid ingredient (which includes imidacloprid) when it is needed to manage a pest.

Horticultural oil or insecticidal soap can help, but might not eliminate a population of adelgids. We do not collect information on which sprayer models or brands work best, nor do we make specific product recommendations. Ideally, the entire tree should be treated in case adelgids (or mites or scale, the other two major pests of hemlock) are present in undetected numbers further up into the canopy. Refer to our Hemlock Woolly Adelgid page for information about treatment, which mentions that oil or soap sprays can be made around early summer to kill crawlers (the juvenile and most-vulnerable life stage of adelgids). It's too late now to apply dormant oil, which might damage the hemlock's foliage.

Miri