West Michigan's Nature Needs Your Help

Without action, the future is uncertain. Together, we can change that.

Effective action requires an approach which is both scientific and pragmatic.

Integrated Pest Management

Integrated Pest Management (IPM) is an approach to invasive species which combines chemical, biological, mechanical, cultural and or other management methods into a comprehensive, overall strategy.

IPM is a proven, effective approach to managing invasives while maximizing efficiency and minimizing risk to the environment and community.

Chemical

Biological

Mechanical

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Horticultural Oil

Insecticidal Soap

Imidacloprid

Dinotefuran

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HWA IPM in Residential Settings

The number, condition and location of hemlock trees determines the IPM strategy for HWA.

For most residential landowners, chemical treatment is the most practical option. If the hemlock tree is no longer creating new growth, it is at high risk of dying and should be treated with insecticides ASAP. This publication by Penn State explains various insecticide options and application instructions in great detail. When applying insecticide, be sure to follow all instructions on the label: with pesticides the label is the law.

If the HWA infestation is light, or if there is a large number of hemlock trees, biological control is an option. The following companies sell S. tsugae and L. nigrinus. After release, hemlocks should continue to be monitored, ensuring HWA is still controlled in following years. If HWA does not significantly decrease the following year, more beetles should be released (multiple releases are sometimes required for a population to become self-sustaining) or insecticides should be applied instead.

HWA predator beetles and insecticides should not be utilized on the same property simultaneously, as the insecticides can kill the predator beetles as well.

HWA IPM in Forest Settings

In the long term, the survival of our hemlocks depends on us establishing a self-sustaining population HWA predator beetles in the wild. However, in park settings or when when high-value hemlocks (ones providing shade for body of water, growing near a structure, providing particular aesthetic value etc) are damaged and are at risk of dying, chemical treatments are usually the most reliable and cost-effective approach.

Biological Options

S. tsugae is currently the cheapest and easiest HWA predator to obtain commercially. If successfully established, S. tsugae acts as a stand-alone solution to HWA, as it is well synchronized with HWA's lifecycle and controls HWA effectively in their native environment. Studies show that relasing S. tsugae during warmer temperatures and releasing them over multiple years in the same location increases the chances of a self-sustaining population being established.

L. nigrinus is more expensive and may longer to acquire due to lower commercial production, but studies show that it is more reliable in establishing self-sustaining populations, and the bulk of HWA biological control research has been put into L. nigrinus in recent years. L. nigriunus only feeds on HWA in colder months (as opposed to year-round with S. tsugae), which means that while L. nigrinus can significantly reduce the density of HWA, it will not entirely eliminate it. Consequently, the most recent research centers around pairing L. nigrinus with new potential HWA predators such as silver flies, through this research is still in its preliminary stages.

S. tsugae and L. nigrinus can coexist and even act complimentary to one another in the same environment, so releasing one species in an area does not preclude the possibility of releasing the other species in the future.

The West Michigan Wildlife Conservancy has several S. tsugae releases planned in 2025, the results of which will help inform future IPM strategies in West Michigan.

Chemical Options

In limited areas such as a park or nature preserve, chemical treatments by certified applicators are often the most cost effective solution. These treatments include basal trunk sprays and trunk injections. Ottawa County Parks has used chemical applications to great effect in saving affected hemlocks in their parks system.