We sprayed our hemlock hedge a month ago with dormant oil. There is quite a heavy infestation visible. Is there anything more we can do now?
Montgomery County Maryland
To be most effective, a dormant oil is best used from November to early March.
They are hardest to control when they are the most fluffy.
Oncwe the eggs under the fluff hatch, they are called crawlers and are most susceptible to control. You can look closely, perhaps with a magnifier, to see these as they feed on needles, and use an insecticidal soap or summer rate of oil spray to kill immatures from now through June. This could also happen in September, though the spring generation is usually much larger than the fall generation.