Managing Hemlock Pests

Managing The Hemlock wooly adelgid

Hemlock wooly adelgid (HWA) is an invasive insect pest that attacks hemlock trees and causes decline and eventual death over the course of some years. It is easily recognizable if infected branches are turned over. At the base of the needles are small, fuzzy white masses that HWA produces to protect its eggs.

There are a number of things you can do to reduce the chance of your hemlock trees being affected by the wooly adelgid. If your tree has already been infected, there are also a number of options to lessen the impact of HWA and maintain its health.

Maintain overall tree vigor with these tips: 1) Add mulch around the base of the tree where appropriate and water it in extremely hot, dry weather. 2) Don’t fertilize your hemlock if it has HWA; studies have shown that nitrogen fertilizer will increase pest activity and needle damage. 3) Take down bird feeders between April and August as birds are a primary way HWA is spread.

There are several treatments for hemlocks with wooly adelgid. Trees of modest size can be sprayed with horticultural oil, which suffocates the insects. Larger trees can be treated with systemic products that the tree absorbs and brings to the needles, where HWA feeds. Systemic treatments can be applied directly to the bark near the trunk of the tree, or injected into the soil around the base of the tree.

Managing Elongate Hemlock Scale

Elongate hemlock scale (EHS) is a more recent arrival to Vermont. It is an insect that sucks nutrients from the undersides of hemlock needles and several other conifers. Although more rare than the wooly adelgid, EHS can deliver an additional blow to hemlocks with HWA. Fortunately, EHS is also treatable.