Hemlock Woolly Adelgid (2024)

FAQs

Can hemlocks recover from wooly adelgid? ›

The recovery of hemlocks from HWA defoliation can be a slow process. First, the beetles have to ramp up their numbers to bring the adelgids in the area under control (1-3 years). And this will allow the hemlocks to begin the process of producing new foliage to replace their lost and HWA-damaged foliage (3-5 years).

Homeowners and private landowners have two treatment options: 1) spray foliage with insecticidal soap or horticultural oil at the proper times during the HWA life cycle, or 2) use a systemic insecticide that moves with the tree sap and is consumed by the adelgids as they feed.

HWA use sucking mouthparts to pierce through the base of the hemlock needles into the parenchyma cells (nutrient transport cells). Large infestations can quickly deplete trees of their vital nutrients. Early impacts on trees infested with HWA include loss of needles and reduction to growth of new needles and branches.

Adelgids are best controlled by continual applications of systemic insecticides such as Supreme IT and pruning of leaves and stems. Spray the top and bottom of foliage leaves and branches until wet, but not to the point of run-off.

Solutions: Many of our remaining mature eastern hemlock trees are only alive today because they have received chemical pesticide treatments that have acted as an immediate life-support system. Chemical treatment is still the only completely reliable way to save an individual tree from mortality due to HWA.

Hemlock trees will grow new branches from the needle whorls, and pruning just above them will ensure that the new branches come in properly. If damage to the hemlock tree is extensive, severe pruning may be needed. Hemlock trees can withstand severe pruning and will recover from losing as much as 50% of its branches.

Commercial pesticide applicators can successfully manage Hemlock Woolly Adelgids with imidacloprid (Merit®). Merit controls Hemlock Woolly Adelgid by contact (foliar application) and ingestion (soil application). Foliar applications are made between mid-May and mid-June, and again between late-July and mid-October.

The imidacloprid suspension should be applied to the soil within 18 inches of the hemlock trunk. Using the included measuring cup, measure the correct amount of suspension. Pour the suspension evenly around the base of the tree.

Hemlock woolly adelgids are all female in northeastern North America. They develop parthenogenetically (asexually) and have six stages of development: egg, four nymphal instars and adult.

Apply horticultural oil in spring, summer, and fall to help control large infestations. Additionally, soil injections of appropriate insecticides can provide protection throughout the season. Applications of the proper insecticide can help the tree rebound from hemlock woolly adelgid damage.

What temperature kills woolly adelgid? ›

Hemlock woolly adelgid (HWA) vary in their susceptibility to temperatures considerably below freezing. Many individuals may die by -20°C (-4°F), but more cold-tolerant individuals will allow populations to persist.

In its native range, the hemlock woolly adelgid lifecycle includes winged males and females that fly off hemlocks to spruce trees to mate and reproduce. We lack a suitable spruce species in North America, so sexual reproduction is unsuccessful. (Winged individuals fly off and die.)

Ladybugs do eat the hemlock woolly adelgid, but there are two main reasons why they don't have any impact on controlling the HWA population.

Two beetles that are native to North America, Laricobius nigrinus and Laricobius rubidus, are predators of adelgids in the western and eastern United States, respectively.

Native to Asia, the hemlock woolly adelgid, or HWA, is an invasive, aphid-like insect that attacks North American hemlocks. HWA are very small (1.5 mm) and often hard to see, but they can be easily identified by the white woolly masses they form on the underside of branches at the base of the needles.

Chemical treatment is still the only completely reliable way to save an individual tree from mortality due to HWA (trees can still die due to other factors).

Life Cycle

Hemlock woolly adelgids are all female in northeastern North America. They develop parthenogenetically (asexually) and have six stages of development: egg, four nymphal instars and adult. There are two overlapping generations per year.

There are three main tools used to mitigate HWA and its impacts. These include insecticide treatments, biological control agents such as predatory insects, and cultural prac- tices such as breeding hemlock for resistance and regener- ating other desired tree species where hemlocks have died.