Landscape Trees and Their Susceptibility to Invasive Insects

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In recent years several exotic insects have either entered NH or are nearby on our doorsteps 

Native plants have no natural defenses against exotic insects, which makes these invasive pests so devastating and able to spread so rapidly once they are introduced. These invaders include the Asian longhorned beetle (ALB), emerald ash borer (EAB), hemlock woolly adelgid (HWA), and elongate hemlock scale (EHS). All four insects are pests of forest and landscape trees, and they will have economic impacts on the landscape and economy of New Hampshire.

New Hampshire is more than 80% forested. The New Hampshire forest, tourist, maple syrup, landscape, and nursery industries are valued at more than $2 billion a year and provide 15,000 jobs. Additionally, invasive insects may severely impact native and natural forest areas, interrupting natural succession, opening areas up to non-native invasive plants, and subsequently disrupting the ecology and food web. We must do our best to prevent the invasion of the harmful exotic insects that aren't yet here, like the ALB, and manage those that are, including the EAB, HWA and EHS.












The ALB isn't currently known to be in New Hampshire, but it has been detected as close by as Worcester, MA, and in the Boston metropolitan area. In an attempt to eradicate ALB in Worcester, thousands of host trees were removed and chipped. The eradication process is ongoing.

The EAB attacks all species of ash (Fraxinus spp.) trees. Since its initial detection in Michigan in 2002, it has spread across the Midwest, killing millions of trees. The EAB was first found in New Hampshire in March 2013 and it continues to spread within the state. Unlike the ALB, the EAB isn't a pest targeted for eradication, but it can be managed to slow its spread, reducing the economic burden associated with this insect.

The HWA and EHS are two insects that have begun to spread in New Hampshire. The HWA was fi rst detected in 2000 and is spreading throughout southern and central New Hampshire. The EHS was first detected in 2008 and is mostly located in a few a

Both pests can be transported by birds, and infestation with either pest can cause tree mortality. Neither the HWA nor the EHS can be eradicated. However, you shouldn't be discouraged reas in south central NH. from buying hemlocks since HWA or EHS might not infest your tree. If your tree is infested, there are management options available and biological controls may be developed in the future.

This publication isn't meant to discourage the purchase of susceptible trees, but to inform the consumer of the relative risks. In addition to the four invasive insects already mentioned, this publication also lists other key pests and diseases that may significantly affect the health and aesthetic quality of these plants if they become infested. With this knowledge, consumers can weigh the many benefits of trees against the risk of damage or loss due to these insects and diseases. Promoting biodiversity through planting and maintaining mixed species is our best defense against widespread pest epidemics.

This fact sheet lists some native and adapted recommended trees for New Hampshire and rates their susceptibility to attack by the ALB, EAB, HWA, and EHS as well as other pests and diseases.



Nursery & Landscape Horticulture State Specialist Emeritus
Office: Cooperative Extension, Spaulding Hall Rm G36, Durham, NH 03824