From the beaches in Cape Cod to lush, dense, green forests, Massachusetts is known for its picturesque landscapes. Located in the Northeastern region of the U.S., Massachusetts is home to many native plant species, including Eastern and Carolina hemlocks.
Since the 1980s, Massachusetts landscapes have been affected by the invasive hemlock woolly adelgid (HWA), an aphid-like pest that can cause severe damage to hemlock trees.
Hemlock Woolly Adelgid Overview & Identification
How did the hemlock woolly adelgid get to America? The pest is native to Japan and came to the Eastern U.S. in the 1950s. It was first detected in Massachusetts in 1988 from an existing infestation in Connecticut. The insects severely weaken and kill hemlock trees through feeding. While more mature trees may take longer, stressed plants can die in 3-5 years after infestation.
Hemlock woolly adelgids produce woolly masses resembling a cotton swab's tip. They can be found on the underside of hemlock branches and at the base of needles. Unlike other insects, HWA is much more noticeable in winter than in the growing season. The insects are hard to spot, but their wooly masses are large.
Life Cycle Of Hemlock Woolly Adelgid
HWA has three life stages: egg, nymph, and adult. Nymphs are smaller than adults, black in color, and sometimes ringed with a fringe of white waxy material. Adults can be found feeding at the base of needles covered in a white, fluffy wax. HWA has two generations per year, and feeding is almost constant at differing levels outside of late summer. The winter generation is the most prolonged with nymphs feeding, but a second generation is also around in late spring.
Hemlock Woolly Adelgid Tree Damage
HWA feeds on hemlock trees by piercing the tree’s branches and drinking its contents. Because the hemlock woolly adelgid reduces the tree’s store of carbohydrates while feeding, the bug weakens the tree and increases its susceptibility to drought, hemlock scale, and other stressors.
If left untreated, hemlock tree needles will dry out, turn grey or yellow, and drop early. There will be signs of dieback or reduced new growth, and major limbs will begin to die within a few years. Homeowners may not a tree or shrub taking on a gray appearance as well. The hemlock may die completely in as little as two years, although healthy trees usually take 10 to 12 years.
Hemlock Woolly Adelgid Threats
While HWA mainly affects hemlocks in the northeastern part of the country, it can spread to other hemlock species as well, including:
- Mountain hemlock
- Western hemlock
- Eastern hemlock
- Carolina hemlock
HWA can also infect forested trees and ornamental plantings.
Hemlock Woolly Adelgid: Management & Control
Management for WHA is centered around chemical treatments and regular monitoring. If the only pest present on your trees is HWA, imidacloprid soil drenches or basal bark sprays will control it for several years. If Elongate Hemlock Scale or spider mites are present, this isn’t recommended as a treatment. The most common systemic treatment is a basal bark spray of Dinotefuran around once a year, which will take care of the Elongate Hemlock Scale as well. Treatments can be spaced out further with regular monitoring. Horticultural oil sprays are recommended alongside systemic treatments and are generally applied in the fall and spring. The spring treatment will control the first generation, and the fall treatments will also help control spider mites.
How you want to mix up these treatments depends on budget, the tree’s condition, and location. For severe infestations, Dinotefuran followed up with oil sprays tends to work best. Larger trees may use Imidacloprid as it’s more budget-friendly.
Hemlock Woolly Adelgid Treatment
If using a chemical treatment for hemlock woolly adelgid, applying an insecticidal soap to the hemlock during the growing season targets HWA during its early life cycle. Certain insecticides can protect trees from HWA for 3 to 4 years, although it may take a few weeks for the chemical to take effect.
Hemlock Woolly Adelgid Frequently Asked Questions
Hemlock woolly adelgid moves to new host trees through wind, animals, and humans moving nursery plants and equipment.
Yes! Chemical, mechanical, biological, and cultural treatment options can help save hemlock trees from infestation.
Japanese hemlocks are relatively unaffected by HWA because of its natural resistance to the insect.
Yes! Continued monitoring and early detection can help stop an infestation before it causes severe damage.
At Hartney Greymont, we have local arborists in Needham, Concord, Danvers, Cape Cod, and the surrounding areas to help control and prevent hemlock woolly adelgid infestations.
Not Sure If Your Tree Is A Victim Of Hemlock Woolly Adelgid? Contact Your Local Hartney Greymont Arborist For A Free Tree Inspection!
