Regarding the woolly adelgid problem on Hemlock trees:
Live outside of Boston.
Very confused over when the "best" time to spray is.
Spoke to a few arborists that do this, but i have the feeling they have a
stock answer that
the best time seems to be whenever one calls them.
Might someone please summarize for me when I should have spraying done, and
what treatment (oil, soap, type, etc. ), when in the year ?
Is the above answer different if one sees no problem, but wants to prevent
the belief that there is already a problem.
The insect has 2 or three generations per year, and has the semi-odd habit
of going into a summer estivation (sleep-mode). Thus it seems to be better
to spray (if using a high-quality horticultural oil) at least twice per
annum, maybe thrice.
Late summer / early Fall and early Spring seem to be the most effective IMO.
It is possible to have great effect with oil so I do not recommend going to
more aggressive chemicals such as imidacloprid (Merit). Tree companies push
the Merit because they can charge more for it.
This is an easy bug to control as long as it is possible to really drench
the tree with sprays - trees too tall (over 50') or too close to
obstructions need other treatments.
Mike LaMana, MS
Heartwood Consulting Services, LLC
My Eastern Hemlocks were treated successfully w/ horticultural oil - applied
in May in Zone 6b. I used an arborist with a specialized boom sparyer
system to reach 60'+. I think he was going after them in the egg laying
stage. In my case, I took action late - maybe 2 or 3 years after first
noticing the "white stuff." I'm no expert, but preventative spraying
probably isn't necessary as the "white stuff" is easy to spot. If you've
already had a W.A. infestation, be sure to watch out for a secondary
infestation of spider mites (oils & soap will work, but proper timing is
everything). They are opportunistic and attack already weakend trees. The
arborist also suggested using soak hose irrigation during dry spells as
Hemlocks often grow near water. He also recommended root zone fertilization
to help them recover. It all worked out well and there has been no
re-infestation 3 years later. I suggest you consult someone w/ specific W.A.
Other Hemlock & W.A. observations and factoids:
1) There are experimental programs using a predatory Asian lady bug (I
think) to control the W.A.
2) In my area, native Hemlocks, which are in bad shape, line many pristine
trout streams. It is predicted that the trout (& the entire stream
ecosystem) will be seriously harmed - even wiped out in some streams, b/c
when the shade cover is gone, water temp rises, reducing dissolved oxygen,
thus killing the fish. Since they're near water, our state DNR won't spray
anything on them.
3) I have a friend who has a lone hemlock in a 10 year old sub-division that
has never been infected or treated. It seems that they attack in areas of
high population and can "skip" isolated specimens.
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