Hemlock Woolly Adelgid Treatment for Private Landowners

Hemlock Woolly Adelgid Treatment for Private Landowners:

A private landowner seeking treatment options for hemlocks with hemlock woolly adelgid (HWA) infestations faces a clear choice – between chemical and biological control options. And despite the patter about the “expensive” predator beetles, the cost of chemical treatments will always be greater and the coverage always less complete than enlisting an effective biological agent to manage your “HWA invaders”. Among other important considerations for the choice of treatment strategy are your time horizon for hemlock preservation (short-term or long-term), the scope of protection required (individual trees or entire areas) and your tolerance for introducing synthetic, neurotoxic chemicals into your  residential environment.

The Basic Choice in Hemlock Woolly Adelgid Control boils down to:

 Short-Term, Chemical Insecticide Treatments for Selected Individual Hemlocks


Long-Term, Natural, Biological Treatments for all Hemlocks in an Area

To many of us, this wouldn’t seem like a difficult choice! What rational person would elect for repeated expensive applications of the synthetic neurotoxic chemicals used to protect hemlocks from Hemlock Woolly Adelgid damage? Perhaps you only have one or two “yard trees” to protect. But even then, anyone living in a neighborhood would have to consider the visual impact of not protecting hemlocks on surrounding properties. (For more on combining short-term chemical and long-term biological treatments, go to IPM.)

Does it make sense to invest in chemical treatments for your property while allowing all the other hemlocks visible in your neighborhood to be destroyed or removed? And what if you own a large woodland or riparian hemlock area. Do you chemically treat some hemlocks and let the others die? Or do you pay to have all the hemlocks removed and then face the problem (and expense) of how to repopulate your woodland areas so as to support the hemlock-dependent natural ecosystems ?

On the other side of the decision-tree, we have a natural treatment solution – biocontrol of hemlock woolly adelgid – that will last for the natural life-span of your hemlocks. Once established, it will protect all hemlocks in an area and will allow HWA-damaged hemlocks to restore their foliage. It has no toxic properties, immediate or residual. And the recommended HWA predator is a specialist insect which requires adelgids and reproduction. So it represents no threat to other native native insects or plants. Plus for most properties, one-time applications to establish biological control of HWA will cost less than the alternative first (of many) chemical applications.

Here are some sources of information on other topics concerning hemlocks, HWA and its biological predators:

How does biological control of HWA work?

How can you mobilize individuals and community groups to protect and restore hemlocks?

What is a commercial source for HWA predator beetles ?

How can a tiny beetle protect giant hemlocks from hemlock woolly adelgid?

Biological control is a simple numbers game, which in this case involves a Hemlock Woolly Adelgid (Adelges tsugae) organism accidentally introduced from Southern Japan – and its native predator beetle from southern Japan Sasajiscymnus tsugae (Sasi or St for short) which was intentionally introduced by USDA for HWA control purposes. Sasi predators respond to a large HWA (food) supply by eating and laying lots of eggs. And the larvae that emerge from these eggs consume many more adelgids as they grow and mature. Then they pupate into adult beetles and begin another round of feeding and reproduction. These consecutive predator reproductive cycles, which encompass both Spring and Summer HWA cycles, produce an exponential increase in Sasi predator beetle populations and a corresponding dramatic decrease in HWA population densities.


Above are a group of Sasi beetles that have been introduced to a HWA-infested site in the Smokies. Each hemlock woolly adelgid ovisac contains an adult (female) and an accumulation of eggs. As shown, these voracious little predator beetles will tear open an HWA ovisac and consume all the contents  before moving on to the next. But some ovisacs may be left for the beetle larvae hatching from eggs that the beetles deposit wherever HWA is found. These larvae are even more voracious than their parents and need an HWA food supply to develop and mature. This is why HWA ovisacs in beetle release areas should not be poisoned with neurotoxic chemicals.

Despite the widespread destruction of wild hemlocks that we can see around us, the hemlock woolly adelgid is not a particularly dangerous biological organism. The damage that we see today is due to prior human mismanagement of an “introduced insect”. The failure to control HWA for over an 80 year period, (40 of which were under direct USDA “management”) has resulted in a biological avalanche that has swept over our native hemlocks. The key to solving the HWA problem is not eradication, which would require destroying all the rest of earth’s inhabitants as well. Instead the key is simple HWA population control using a biological agent whose purpose in life is to consume hemlock woolly adelgid.

How can you contribute to biological control of Hemlock Woolly Adelgid?

Those who own property in areas with HWA-infested hemlocks have the option of purchasing HWA predator beetles to establish self-sustaining predator colonies on their own property. Unlike chemical treatments, biological treatments with Sasi predator beetles are not restricted to individual trees. They will spread to adjoining trees and areas, establishing protection for an entire hemlock area. So release the beetles where there is a good HWA food supply, and the beetles will take care of the rest. Property owner groups are an option for funding biological control efforts in larger residential areas. And land trusts and other conservation groups are likely partners for wild area preservation efforts. See Community-based control page.

But even if you don’t have hemlocks on your own property, there are many ways that you can contribute to saving our native hemlocks and hemlock-dependent ecosystems. Think of all the local parks and wild places that have at-risk hemlocks. Think of all the groups that should care about the preservation of hemlock ecosystems: birders, anglers, hikers, kids … And think of all the good that could be done if you could encourage just one group in your area to initiate a biological control project!

Imagine the feeling of passing through an area with recovering hemlocks and knowing that you had contributed to their recovery – Talk about a rewarding environmental investment! Here is one of my 8 year release areas near Gorges State Park in North Carolina, showing the bursts of “exuberant” foliage growth that are characteristic of beetle-assisted hemlock restoration of previously damaged trees.


What can YOU do?

You can’t begin biological control of HWA without access to predator beetles. And the Sasi beetle responds well to conditions in insect rearing laboratories. So these beetles are readily available for purchase from a predator beetle rearing lab that supports private property releases. (Disclosure: I have no ownership or other financial ties with any predator beetle rearing lab!).

None of the USDA-supported rearing labs for HWA predator beetles are allowed to provide beetles to private landowners or other groups. But there is one private predator beetle rearing lab that will be in operation for 2018 – that is Tree-Savers in PA. They have an experienced manager, a very informative website (http://tree-savers.com/) and 2018 will be their 6th year of production.

They will have a good supply of beetles available for the March – June release season. You can order as few as 100 beetles (at a cost of $2.50@), but unit costs go down with larger orders. So consider talking to neighbors and friends about sharing an order with you. But place your order ASAP to ensure getting beetles for the coming 2018 “growing season”.

HWA Predator Beetle Sources for 2018

Tree-Savers         Website:  http://tree-savers.com/   Phone: 570-871-0088

Manager:  Jayme Boniewicz    

Jayme has been successfully been rearing Sasajiscymnus tsugae predator beetles since 2008, first for Eco-Scientific Solutions, then with her own Forever Green lab, and now for Tree-Savers in northeastern PA. She will be happy to offer free consultation for planning your predator beetle release.

My guide for planning and implementing a low-density beetle release is also available for your use (see paper on low density release methodology). Typically a release of ~200 beetles should be sufficient to establish biological control over a 1-3 acre residential hemlock area. Releasing more beetles should speed up the coverage time.

But for wild areas, I typically use a strategy of multiple small releases to establish coverage over as large an area as possible. Remember, the purpose of predator beetle releases is not to match the quantities of HWA present, it is to establish breeding colonies of these specialized beetles whose natural reproduction will produce exponential population growth. And this expanding predator beetle presence will get the HWA population under control – over a 2-3 year period.

Hemlock Restoration

The recovery of hemlocks from HWA defoliation can be a slow process. First, the beetles have to build up their numbers in order to bring the adelgids in the area under control (1-3 years). And this will allow the hemlocks to begin the slow process of producing new foliage to replace their lost and HWA-damaged foliage (3-5 years). But as shown above, once it starts hemlock recovery can be breathtaking!

With severely defoliated hemlocks, you won’t see instant recovery but you should see new crown foliage growth production in the release area during the first year. (See paper on measuring hemlock crown density.) Hemlocks in early stages of HWA infestation (or trees with prior chemical treatment) should see a much more rapid recovery and return to normal hemlock foliage production.

Large HWA-damaged hemlocks face another threat from the Hemlock Borer, a native insect that is normally benign, but can be very destructive in the presence of numerous large damaged hemlocks. Unfortunately, this insect is not affected by either chemical or biological controls for HWA. And once a hemlock borer infestation gets started in an area, most of the large hemlocks will be destroyed. So hemlock restoration in such areas will focus on the smaller surviving trees.

After your beetle release treatment the adelgids will not disappear, but they will begin to decline in number. New foliage produced at the crowns and upper branches of beetle-assisted hemlocks will usually be clear of adelgids. But branches closer to the ground (up to 10′ up the trunk) may show concentrated patches of adelgids on new growth. Just think of these as “beetle nurseries”, which will be used by the beetles to increase their population during the year. And no one would poison nurseries, would they?

Unfortunately, in some neighborhoods with chemically dependent residents, the answer is “Yes, they would poison predator beetle nurseries where HWA are present!” But never fear, the exponential growth capabilities of the predator beetles will never be overcome by neighborhood dispenser(s) of neurotoxic chemicals.

New hemlock foliage growth has a distinctive golden-green color. So when you see this golden-green “frosting” appearing on your hemlocks in May-June, you will recognize the progress that is underway. Just look at the trees to observe how the Sasi beetles are contributing to the health of your hemlocks!