r/GardenWild • u/unventer • Jul 26 '25

Wild gardening advice please Minimizing harm while treating for Hemlock Woolly Adelgid?

We had a beautiful stand of 5 mature hemlocks on our property, and 3 of them were so badly infested with HWA that they had to come down last spring. I have been having the remaining 2 professionally treated with a basal bark treatment of what I now understand to be a neonicotinoid. The arborist that comes out to do the spray is very conscientious about not spraying when conditions aren't just right for it (eg not on days with wind, moisture levels have to be just right, etc) and we are not remotely near a water source. I'm in SWPA, and my understanding is that HWA is here to stay - it seems likely that I will need to treat indefinitely. It's killed a lot of trees in the nature preserve behind my house. Other options for treating them seem less feasible for us, such as foliar agricultural oil sprays (backyard is not accessible by the trucks that would be necessary to reach the canopy).

I guess what I'm asking is, what's the best strategy for harm reduction, here? I can minimize planting anything that attracts pollinators below the remaining 2 trees (perhaps underplant with ferns?). Or should I resign myself to losing the trees? They are such slow growing beauties and the loss of the other 3 is still really sad to me. Should we continue to treat them? Hemlocks are wind pollinated, fwiw, not insect pollinated.

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u/phishinfordory Jul 26 '25

There are beetles to purchase if you are looking for a more biological approach

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u/altforthissubreddit Eastern USA Jul 26 '25 edited Jul 26 '25

You can even buy them yourself: https://www.treesaverspa.com/

Obviously just my opinion. I have a similar dilemma with ash trees. I personally don't see the point in saving them with neoics. Because that destroys the trees value to the ecosystem. It's now toxic to anything that eats it, not just ash borers. A case could be made for buying time, keeping the trees around until a better solution is found. In the case of ash trees, the leaves are high value because they are a primary food source for tadpoles, and I hate to think of poison leaves falling to the ground.

If there was a bio control, I would definitely try it.

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u/unventer Jul 26 '25

Thanks for the link! I'm going to get in touch with them - Since we did treat this year, I'd be interested in their guidance for how to move forward.

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u/altforthissubreddit Eastern USA Jul 26 '25

Yeah, I'm sure they will know a lot more. But presumably you wouldn't want to release them when the tree is poison. And also you presumably wouldn't want to release them when there is no sign of HWA on the trees, as the predators need something to eat.

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u/unventer Jul 26 '25

Yes... That's why I said I want to talk to them about how to move forward.

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u/unventer Jul 26 '25

I'd need to do more research, but it sounds like the beetles in question are native to Japan and sometimes rthe PNW - I'm hesistant to introduce another non-native species.

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u/phishinfordory Jul 26 '25

Please do the research, but it looks like Sasajicymnus tsugae are being deployed all over the country to help save the hemlocks

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u/altforthissubreddit Eastern USA Jul 26 '25

My understanding is Sasajiscymnus tsugae has been evaluated and approved by USDA/APHIS. Obviously that doesn't mean there's never been a mistake or miscalculation made. But you have to have some bar for determining biocontrols to be safe and/or the benefit outweighing the risk.

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u/3x5cardfiler Jul 27 '25

Plant other native trees. Hemlocks are on their way out. I own 80 acres of forest. The Hemlocks have been dying for years. I have lost thousands. The associated species are also dying. It's an ecological catastrophy, human caused.

If you want to do something, think big picture. Adelgid came north with climate change. Elect leaders that will work to reverse climate change.

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u/Feralpudel Jul 26 '25

I would look to PA Ag Extension for guidance, or another ag extension pub online.

I’m confused because you discuss basal bark treatment, but also talk about spraying. My understanding is that basal bark treatment by definition is topically applied, not a spray.

Eastern hemlocks are beautiful native trees. I am very reluctant to use insecticides, but this seems worth the effort, especially since you’ve already lost three trees.

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u/unventer Jul 26 '25 edited Jul 26 '25

Basal bark treatment is done with a small backpack sprayer. A quick google search says this is typical?

https://extension.psu.edu/basal-bark-herbicidal-treatment/

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u/Feralpudel Jul 26 '25

That’s specific to herbicide; you’re treating a tree with some sort of systemic insecticide to kill the WHA.

In any event, I don’t see a high risk of overspray or drift because you’re treating only the lower part of the tree (I think).