Hemlocks have long been one of my favorite evergreens. They are native to our area, thrive in sun or shade and make great natural hedges or green screens. Up until recently I had hoped that Hemlocks in our area of Massachusetts would be immune to an insect called Wooly Adelgid. These tiny insects attack, weaken and can potentially kill Hemlocks, but up until this past winter the adelgids had only been found south of us.

It began with a hemlock branch covered with white puffy snow type “stuff” stuck to the undersides of the needles that a customer brought into my store in Mid June. I’m sure my surprised reaction did not go unnoticed – and my repeatedly questioning where they’d found the branch was a dead give away that I was surprised. The customer was from Fitchburg and they assured me that the branch was too. It was my first official sighting of Wooly Adelgid here in the Tri-town area. Within a week several customers had called or stopped in with descriptions of what could be nothing other than adelgid

Adelgids are near microscopic in size so it is difficult to spot them. Fortunately, the sacs that protect the eggs are woolly and white, looking something like tiny cotton balls attached to the base of the needles on the underside of the twig. This “wool,” is noticeable in early summer to late fall and is a sure sign that the adelgids are making a home in your hemlock. Once the infestation has affected the general health of the tree, you also will notice that the tree produces no new growth on certain limbs and die-back of full limbs can also occur.

If you’ve found adelgid on your Hemlocks, there are two types of treatments available. They are oil sprays and systemic treatments. Selecting the appropriate treatment method for your hemlocks depends on factors such as the trees’ accessibility (can you get to it easily), whether it is near water or in rocky soil, and the expense of the treatment. Each treatment option has benefits and drawbacks relating to cost and effectiveness at killing the adelgids.

For most landscapes, an application of horticultural oil is one of the most effect treatment methods and has the least potential for negative environmental consequences. The spray bottles that attach to hoses and mix automatically are the easiest to use. Once you’ve got your spray ready, thoroughly drench the tops and bottoms of needles, covering the entire tree and thoroughly coating the insects. Application will be most effective in late March through April when adelgids have hatched from their eggs, and in late August to October before the nymphs produce their woolly covering.

The most effective treatments of adelgid-infested hemlocks is accomplished with the systemic chemical imidacloprid. The product is applied either to the soil and tree’s root zone by drenching or injection, or to the tree itself with a thorough spray application. Systemic sprays can be used in spring or fall when the tree is taking up water and nutrients. Most systemic sprays for trees can be effective for a full growing season – with just one application!

Maintaining the general health of your hemlocks will help in their survival. In

summers like this with very hot, dry weather you should water your trees to give them one inch of water per week. You can also prune out any dead or dying limbs. I generally don’t recommend fertilizing an adelgid infested hemlock because fertilizer will help improve the adelgids survival rate and reproduction levels.

Keep a vigilant eye out this late summer and fall for those little white “flecks” on the back of your hemlock branches. If you find them, use either option, but do spray to control them. I’m not optimistic that this winter will be harsh enough to kill off the entire adelgid population here, so they are most likely to be a problem for us to contend with in our yards for the immediate future. Michelle Harvey is a Massachusetts Certified Horticulturist. She can be contacted at Lakeview Nurseries in Lunenburg or Winchendon or at michelle@lakeviewnurseries.com