Tracy from Federal Way, WA writes:
“Our Mountain Hemlock has an Adelgid infestation. It is all over the middle tree but will probably spread to the others.
What do you suggest for treatment?
I have Neem oil and “Safer” insect killing soap. I also have some Fertilome products – Fungicide ornamental and evergreen spray though I don’t like what the warnings are on the label.
I am also thinking I should treat the other like trees in the back just in case.”
Katy took this question on and answers:
Interesting.
When I first moved to Seattle in 1997 I worked at the Seattle Arboretum, and there was an employee who was always on about monitoring the Wooly adelgid and who was convinced it was bringing down the native Hemlock (Tsuga heterophylla) population. Since that time I actually haven’t seen much of it around Bainbridge Island or Seattle.
I called Randall Hitchen, curator at the Arboretum to discuss this case. He was surprised to hear of the adelgid hitting the Mountain Hemlock enough that it was making a problem and so was I. Although we may have lost a bit of the touch for smaller urban gardens where you might only have that one tree, stare at it all the time and it actually makes a significant difference to the landscape whether it thrives or not (he works in a 214 acre garden, and I live on an acre of wooded land) both he and I agreed that adelgids usually don’t usually bring down this kind of Hemlock.
It led us muse about a couple things: How old are the trees? Is it causing severe defoliation or foliar problems or are they at an acceptable level for the client? Is there anything else stressing the trees out to make them more susceptible to an adelgid attack? Is the client ok with spraying? It might be that they actually need a one-time “good hygiene” spray. I was also interested to hear that other kinds of Hemlock (some other cultivars and ornamental type) really don’t tend to succumb to the adelgid.
Both he and I agreed that we wouldn’t go so far as recommending any kind of spray product. Not only do products often change names, we aren’t licensed applicators. Also one shouldn’t ever treat other nearby trees “just in case”. Not only is random spraying a waste of money, there is no sense introducing more pesticides or herbicides into your landscape (and neighborhood and drains and to the Puget Sound) if your trees really don’t need it. Just-in-case spraying is not like a human taking Airborne before taking a flight.
Finally, ask your applicator when you are supposed to spray for the problem you have. If the bug is dormant or at a stage in its lifecycle that won’t be affected by spray there is, again, no sense in spraying.
So that’s a lot of “don’ts” but do call a CPH, certified Arborist or someone identify if your other trees have a problem or not. Be an informed and savvy client who doesn’t knee-jerk into spending money on a spray that might not work. And finally, don’t worry! If your tree does succumb, you have other hemlock species options that you could put in its place if you just need that look in your garden. Good luck! Katy
(As Katy notes in her message above, for-fee pesticide applications and pesticide recommendations made in the state of Washington may only be made by licensed, registered pesticide applicators with active licenses. Yes, a homeowner can go buy anything off the shelf and do basically whatever s/he wants with it, but professionals can’t provide any such service legally without a license. Sure, we may know better even without a license, but we’re more regulated than homeowners who may try to apply a fungicide where a pesticide makes more sense or where nothing at all is required. But, that’s a post for another day. -Robin)
