Hemlock Woolly Adelgid

Adelges tsugae

DESCRIPTION

Appearance: 2mm long, aphid-like insect with a black, oval shaped soft body. Eggs: Very small, brownish-orange, laid in white, woolly masses of wax Nymphs: Also called crawlers, they attach specialized mouthparts to underside of hemlock needles Adults: HWA reproduce in two ways: Some adults are wingless and remain on host tree, feeding and reproducing. Other winged adults must seek out a suitable spruce tree to complete their life cycle. The spruce trees in our area are not suitable for this purpose and the winged adults die soon after without producing offspring. This may contribute to reductions in total HWA population.

 

THREATS/DAMAGE

HWA threatens hemlock trees, genus Tsuga. It feeds on the tree’s needles, attacking the food storage cells. The hemlock “walls off” the area where the HWA is feeding, causing a disruption in nutrient flow and, eventually, killing the needle. Needles will dry out, gray, and fall off. Over several years, whole limbs will die back, killing the host tree from the bottom up.

CONTROL/MANANGEMENT

MANUAL

Stress on infested hemlocks can be reduced by pruning dead or dying branches and watering trees during dry periods.

CHEMICAL

Materials Application

Individual trees can be treated with a systemic insecticide, applied as soil drench or basil bark spray. Once applied, the treatment can provide years of protection for the tree.

Hemlock foliage may also be treated with horticultural oils and insecticidal soaps as long as the trees are small enough to be saturated, ensuring that the HWA has been exposed.

Note: Avoid fertilizing hemlocks with a nitrogen fertilizer as it will encourage HWA reproduction and survival.

BIOLOGICAL

Several HWA predators, including beetles and fungal pathogens, are being tested for effectiveness in treating infested hemlocks on a large scale. While more research is needed to assess long term feasibility, studies have shown this to be a promising method of controlling HWA.