Pests and Diseases

Invasive pests and diseases can cause damage to native plants and ecosystems. There are several invasive species that residents should be on the lookout for in Watertown.

Spotted Lanternfly

The Massachusetts Department of Agricultural Resources (MDAR) recently confirmed an infestation of the invasive insect known as spotted lanternfly (SLF) in Watertown. A survey team followed up on a report that came in from Mount Auburn Cemetery and confirmed that the insects were present. The full extent of the infestation is not known yet, only a preliminary survey has been done so far.

Spotted lanternfly is a pest that attacks tree-of-heaven, grapevines, maple trees, hops vines, and many other types of plants. This pest is known to impact grape/wine producers and other agricultural commodities and can also interfere with outdoor recreation if infestations reach high levels due to the swarming behavior of adult SLF in late summer and fall. That said, the insects themselves do not bite or sting. They are a nuisance because they gather in large numbers in areas where people are, and they cover anything they are on with a sticky, sugary waste product known as honeydew.

Asian Longhorned Beetle

The Asian longhorned beetle (ALB) is a destructive is a destructive invasive insect that is native Japan, China, and Korea, and was first detected in the United States in 1996. Like many invasive pests, it was likely introduced unintentionally via the packing material for imported goods. Since its introduction, ALB has destroyed tens of thousands of trees of various species, including birch, maple, poplar, willow, and elm trees.

The beetle—which can be up to 1.5 inches in length with large antennae and irregular black and white spots—damages trees by burrowing into them to lay eggs. As larvae are developing, they eat outer sapwood that is below a tree’s bark, causing hollowing of the tree. The mature beetle exits through bore holes, often leaving behind sap-oozing wounds in the tree and a sawdust-like substance (called “frass”) at the base of the tree or on branches. Heavily infested trees become so hollowed out that they die and/or need to be removed.

In Massachusetts, ALB has had the largest impact in and near Worcester, where 27,000 infested trees had to be removed in 2008. Since then, state and local initiatives have mostly eradicated ALB and several towns have been removed from the regulated quarantine zone. Regardless, residents are encouraged to report suspected sightings of ALB.

Emerald Ash Borer

Emerald ash borer (EAB) is an invasive insect that was first discovered in the United States in 2002. As the name suggests, EAB uses ash trees (Fraxinus spp.) as their primary hosts. In Massachusetts, they mostly affect white, black, red, and green ash trees. EAB has not yet been reported in Watertown but has been reported in all towns surrounding Watertown.

Adult EAB are approximately 1/2 inches in length and a brassy green color. They harm trees when their larvae feed beneath the bark of ash trees, leaving distinct S-shaped tunnels under the bark. When the larvae mature and adults emerge from the tree, they leave D-shaped exit holes. Ash trees that are affected by EAB will show signs such as vertical splits in the bark, increased inner bark showing from woodpecker activity (sometimes called "blonding"), tree dieback, and growth of new shoots below the dead portion of the trunk as the tree attempts to fight the pest. Eventually, EAB infestation will lead to the death of the tree, resulting in biodiversity loss and potential safety and property damage risks.

General landscape pests/diseases

To learn more about invasive pests and diseases that might impact the landscape in Watertown, as well as your personal garden, visit the Massachusetts Department of Agricultural Resources website or the UMass Extension website. Both of these sites provide information on identifying, reporting, and managing invasive insects, plants, and fungi.