why is it still such a huge problem? Spray the hemlocks. Isn't it just as simple as that?

==>> i thought there were forests of them east of the Appalachian mountains?? .. if so.. therein lies thee rub ....

https://en.wikipedia.org/wiki/Appalachian_hemlock%E2%80%93northern_hardwood_forest

so many questions.. so little time.. keep up Gods work ...

ken

Spraying a large hemlock or treating it with an injectable systemic is either impractical or expensive. You do that only for your most cherished trees. That says nothing about the millions of mature Hemlock growing in forests in eastern North America.

Treat small cultivars and special trees and the rest are left to die.

Is it even worth it to buy Hemlocks on the east coast? I have 3 hemlocks which have HWA now. One of my hemlocks that have HWA is a small tree and it's been with us since we've been living in the house which is at least 30 years. So I'd say it's a pretty big problem on the east coast. The reason that HWA is such a big problem here is because it has no predators on the east coast that kill them. I don't like using Insecticides because their toxic. I would prefer to use these beetles that kill them. If everyone released these beetles eventually their population will grow and HWA will not be a problem anymore. Does anyone know if these beetles that kill HWA are for sale?

Neither of the beetles which feed on the hemlock wooly adelgid is available for purchase by home gardeners, as far as I know. Applied at the correct time, both dormant oil spray and insecticidal soap provide effective control and neither is "toxic". Both are, in fact, approved for use in organic farming and gardening. Is it worth planting hemlocks on the east coast? It depends. If you're in an area with heavy existing HWA infestation, probably not. Warm zones such as Z7b are stressful environments for hemlocks even without the HWA threat. Hemlocks grow best in cool northern climates or cool mountain environments further south. Prolonged cold and deep cold limit HWA populations. Trees already stressed by a marginal environment are more prone to infection. I wouldn't hesitate to plant hemlocks on the east coast in Z6 and colder, but I would not plant them in warmer areas.

Some of the larger hemlocks (100 ft tall or more) in a section of the Buchanan St Forest in PA (z6) were treated w/an injected, systemic insecticide (documented by tags on the trunks). What happened was that some of those survived the initial adelgid onslaught and later the adelgids diminished. So that treatment saved some of those large ones (so far). For homeowners this may be possible, but perhaps not practical for most because of the expense.

The beetles actually can be bought, though they are very expensive. I have considered buying some for a few areas near me with a high hemlock density. More in an aim to protect the younger trees than to save the more mature ones, though I wish I could save them all.

Here's where you can buy them: http://www.tree-savers.com

So I planted a few Canadian hemlock in my zone 7a in Virginia.I am hoping I can keep mine clean until those beetles are more available I am using the soil drench mentioned above once a year as per instructions. they are only 3 to 4 feet tall so easy to manage. I also started some Chinese hemlocks which are supposedly resistant to Hwa. is it true that the western hemlocks are Hwa resistant? If so, is there any reason to not try them on East coast?

I'm pretty sure all hemlocks except for the canadensis is resistant to wooly adelgid. Though they can still get them if you don't properly care for them. But I've heard the western hemlocks don't do too well in the east coast environment and are more suited only to their native area.

I would not include z6. There is a clear line at the New Hampshire border where the eastern hemlock still thrives. Maybe z5 in western MA is Ok as well, but they have been absolutely decimated in z6. Of 1900 hemlocks at the Arnold arboretum, they have had to remove 500, and 100% are infected. This is just since 1997, and with some of the best plantsman and horticulturalists in the world monitoring and treating them.

The good news is that the Chinese hemlocks planted almost 20 years ago at the Arnold look fantastic, and have proved to be fully immune to HWA. The Adelgids do not even live on the trees, unlike the western hemlock, which has a high tolerance, but is not immune. The western hemlock still gets HWA, it just doesn't impact the tree the same way it does on the Eastern hemlock. Also, as mentioned, Western hemlock was ruled out as a replacement option on the east coast because they do not survive/thrive here long term.

The beetle may make an impact in the long term, but I wouldn't bank on it. It's been 20 years and that idea has yet to show real promise. For z6 plus, go with Tsuga chinensis. For colder climates Tsuga diversifolia is an option down to Z4-Z6, but they seem do suffer in anything beyond Z6. Chinensis on the other hand, has been reported to do well as far south as Georgia

Also, in addition to Tsuga canadensis, Tsuga caroliniana is also very vulnerable to HWA. Caroliniana forests have been totally destroyed. This was considered the hemlock for the south, hopefully Chinensis can prove a reasonable replacement.

Interesting, sc77. When the adelgid first appeared in west MD, there were some hemlocks affected at a friend's house, and adjacent Douglas firs had the adelgids too!

I read a report from the Dawes Arb in Ohio that was growing Chinese hemlocks. The report said they were healthy enough, but were slow-growing, bushy, spreading specimens, unlike the native eastern hemlock.

That sounds more like the description of the other asian hemlock Tsuga diversifolia. I've probably posted this here before, but here are the links to 2 papers done by the Arnold arboretum. They compare growth rates, immunity, shade tolerance, ect. This was early in their search for a replacement to the eastern hemlock. I've been to hemlock hill a number of times, and without checking the tags, I wouldn't be able to tell the difference between chinese hemlock and a healthy eastern hemlock.

http://www.arnoldia.arboretum.harvard.edu/pdf/articles/2010-68-2-chinese-hemlock-tsuga-chinesis.pdf

http://arnoldia.arboretum.harvard.edu/pdf/articles/658.pdf

Well my Thorsen's Hemlock has Hemlock Wooly Adelgid. This is it's fourth year in the ground and it was doing well until this year when all of the needles on the front of the tree fell off. It wasn't until my dad noticed the little white sacks all over the front of the tree that I researched what this was. I had never heard of Hemlock Wooly Adelgid before the tree got it so I never knew to look for it. Unfortunately my Thorsen's Hemlock will always be baron in the front of the tree so I might remove it. I don't know if new needles could regrow in the front. My Tsuga Canadensis 'Pendula' has the begining stages of HWA. I bought the horticultural oil which I will be applying on my hemlocks next year.

Thanks for the pdf files, sc77.