Hemlock owners beware! Few tree pests are as destructive as the hemlock woolly adelgid, and they are a serious problem across Connecticut. The small pests may appear insignificant in the beginning, but in just one or two years they can destroy a full-grown hemlock tree.
If you have healthy Canadian hemlocks in your yard you’re lucky, but to keep your trees healthy you must know how to quickly identify and manage hemlock woolly adelgids so you can immediately treat and save your trees.
What are Hemlock Woolly Adelgids?
First identified in Connecticut in 1985, the hemlock woolly adelgid (Adelges tsugae) is an invasive species from Japan that is most destructive to the native Canadian hemlock (Tsuga canadensis), while hemlocks from Asia are resistant.
Adelgids are sucking insects that look a bit like aphids and siphon the juices from hemlock needles. The sucking damage quickly kills foliage and branches.
The small bugs multiply and spread with lightning speed. In a single season, they can become so numerous that whole trees are consumed, dry up, and die.
How Can I Identify These Pests?
Check the branches on your hemlock trees early in the season. Late winter or spring is the best time to look for them and stop them from overcoming your trees.
Start with branches that have dying needles and look for branches with small, white woolly masses on the undersides of the needles. The white masses contain woolly adelgid eggs. Just one egg mass can contain as many as 300 eggs, which is why quick management is essential!
How Do Hemlock Woolly Adelgids Spread?
Woolly adelgid egg masses open between April and June, releasing hundreds of tiny, reddish brown, juvenile adelgids called “crawlers”. The tiny crawlers are nearly microscopic, so they’re impossible to see.
Not only do they crawl across the tree looking for new needles to damage, but they can be picked up by birds, squirrels, or the wind and spread to other hemlocks nearby. Once they find fresh needles, they will feed, grow, and become big enough to reproduce in just a few weeks.
When they reach adulthood, some adelgids develop wings and fly away to find new trees to attack. The ones without wings stay on the tree to reproduce and keep feeding.
How Do I Manage Hemlock Wooly Adelgid?
Chemical management is the most effective method of managing hemlock woolly adelgids, although some methods are safer than others.
Spraying non-toxic horticultural oils and insecticidal soaps before bud break and intermittently throughout the growing season can effectively smother adelgids—stopping their spread. We recommend spraying dormant oil before new needles emerge in spring and using more lightweight horticultural oils and insecticidal soaps during the growing season.
If possible, prune off badly infested branches. Pruned branches should be bagged in plastic or burned – never put them in the compost or use them as mulch!
If you have dwarf Canadian hemlocks, you may be able to manage this yourself but be sure to get 100% coverage on all surfaces of the tree when spraying, including the tops and bottoms of all needles.
For larger trees, you’ll need more intensive controls that must be professionally applied.
Commercial insecticides and injections are effective in controlling woolly adelgid in mature trees. The key to success is proper timing and thorough application, so it’s essential to choose a company like Green Environs that’s experienced in woolly adelgid maintenance.
Removing stresses from infested hemlocks will also help them stay healthier for longer. Be sure to keep them well watered during times of drought, keep their roots protected, and refrain from feeding them until the adelgids have been eradicated (fertilizers high in nitrogen have actually be shown to encourage adelgid damage).
If you discover hemlock woolly adelgids on your favorite specimen Canadian hemlocks, don’t panic. Follow these management steps or contact us to get your trees the help they need.