Introduction. Hemlock woolly adelgid

(HWA), Adelges tsugae (Annand), is an

insect native to Japan, China, and the Pacific

Northwest. The first population detected in

can cause death of even large and healthy

trees. Worldwide, there are nine Tsuga

species, however, HWA has only been

problematic with eastern hemlock and

ecosystems in the Blue Ridge Mountains,

VA, and the severity of HWA’s outbreak

intensified. Once HWA was introduced into

native stands of hemlocks, it was able to

spread more quickly. Native hemlock

species exhibited severe stress and mortality

in forest ecosystems as the insect spread.

Spread of HWA is aided by wind, including

extreme weather events, such as hurricanes,

Columbia, Georgia, Kentucky, Maine,

Maryland, Massachusetts, New Hampshire,

New Jersey, New York, North Carolina,

Ohio, Pennsylvania, Rhode Island, South

Carolina, Tennessee, Vermont, and West

Virginia (Fig. 1).

HWA Lifecycle. Hemlock woolly adelgids

produce two generations per year: a short-

lived progrediens generation and a longer-

lived sistens

125 eggs. The sistens generation hatches in

late spring, remains dormant until late fall,

lives approximately nine months, and each

nymph produce 50-175 eggs. The first-

instar HWA nymphs, also called crawlers,

are the only mobile phase (Fig. 2a). While

crawlers do not move far on their own, they

can be passively dispersed by wind, wildlife,

and movement of infested nursery plants.

Crawlers seek feeding sites at the base of

their straw-like mouthparts into the hemlock

and begin feeding on carbohydrate-rich

fluids near the xylem. As HWA grow they

progress through four larval instars, and

produce "wool," which is a wax-like

protective material. Hemlocks begin to

decline once HWA nymphs deplete

carbohydrate reserves. HWA feeding causes

decreased growth, reduced ability to move

the southern US die more rapidly because

winter temperatures are not cold enough to

reduce HWA populations.

Scouting for HWA. Scouting for egg sacs

and crawlers to treat early in an infestation

can improve management success. In

Tennessee, scouting should begin in winter

and continue through early spring. HWA

infestations are easily recognizable by their

white, woolly egg sacs and crawlers on

branch tips (Fig. 3). Branches with graying

foliage may indicate an infestation and if

present, HWA crawlers will be feeding at

needle cushions at the base of needles in

early spring. Management of HWA in

Nurseries. In nursery production, treatment

vulnerable. Systemic insecticide drench

applications are another option for season-

long control.

Localized infestations may be removed with

pruning before treating the entire plant.

Insecticides suitable for treatment of

hemlock under nursery conditions include

the active ingredients acetamiprid,

imidacloprid, dinotefuran, bifenthrin,

spirotetramat and horticultural oil (Table 1).

Additionally, all of these products and

application methods prevent second

generation HWA establishment, with the

exception of bifenthrin and horticultural oil.

The longevity of many of these season long

products permits growers to manage HWA

with a single application in the spring when

first generation HWA are most vulnerable.

Dormant applications of horticultural oil are

foliar applications of spirotetramat or

dinotefuran are options for growers wanting

to treat and ship plants quickly.

Several other products are labeled

for adelgid control in nursery crops but have

not been tested on HWA (Table 2). These

products include additional neonicotinoids

(thiamethoxam), pyrethroids (tau-

fluvalinate), neonicotinoid-pyrethroid

combination products, the anthranilic

diamide chlorantraniliprole, abamectin,

azadirachtin, various carbamates,

organophosphates and insecticidal soaps.

More research is necessary to evaluate the

effectiveness of these other products on

HWA.

shipment. Rotation of products with

different modes of action (different IRAC

code numbers) and the use of horticultural

oil are recommended to slow pesticide

resistance development in HWA. Proper

irrigation of hemlock trees will aid in uptake

of systemic treatments and mitigate water

stress caused by HWA infestations allowing

for faster tree recovery.

HWA Quarantine Regulations. All

States and Canada have quarantines that

restrict the movement of hemlock plants

from infested areas. States with quarantines

include Maine, Michigan, New Hampshire,

Ohio, Vermont, Wisconsin and all of

Canada (Table 3). Areas of the country that

these states will reject shipments of hemlock

from include all or parts of Alaska,

California, Connecticut, Delaware, Georgia,

Columbia in Canada. Regulated items may

include live HWA insects, propagated

materials of Tsuga spp. (hemlock), Picea

jezoensis (Yeddo spruce), and Picea polita

(Tiger-tail spruce); Christmas trees; fresh

wreaths, foliage and branches; forest

products with bark attached (logs and

lumber); bark chips; wood mulch with bark;

firewood; and dried branches. Non-regulated

items may include seeds, cones, debarked

wood or lumber, processed wood material

(banisters, flooring, furniture, etc.), railway

ties, wood mulch without bark, composted

wood mulch with bark, wood shingles and

shakes, wood shavings or wood chips

without bark and wood packaging material.

from infested to infested areas, infested to

non-infested areas, and non-infested to non-

or infested areas. Some states prohibit all

hemlock material or restrict only materials

from infested counties or some infested and

adjacent counties. Some states require

phytosanitary certificates whether or not the

products were produced in an infested

county. Rules for using insecticides on live

quarantine guidelines. Additional

restrictions may apply to how hemlock is

shipped through infested areas. For example,

states may require the trees to be shipped in

a closed box trailer. Additionally, shipments

of hemlock may require a second inspection

upon arrival to ensure no HWA arrived on

the shipment. If HWA is observed on

received materials, single plants or entire

shipments may be destroyed. Additional

regulations may be placed on the sale of

hemlocks by nurseries and landscapers,

including Record of Sale requirements.

The quarantine summary provided here is

only a guide, because the actual quarantine

regulations are the law and supersede any

information provided in this publication. For

the most up-to-date information on

quarantines and shipment certification,

contact your state department of agriculture

inspection service.

Table 1. Product information and efficacy data following a single treatment application to

nursery grown 7-gallon hemlock

Talstar® F

3A

bifenthrin

Safari® 2G

4A

dinotefuran.

Safari® 20

SG

4A

dinotefuran

1% G

Publication AR-ENT-01-2018 WSFNR-18-46 November 2018

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