Invasive (Exotic) Pest Watch
There are some very destructive insects closing in on the Northern New England area. These insect pests are called exotic because they are not native to our country and they have no natural enemies. These three are currently considered to be the most threatening:
1) Emerald Ash Borer (EAB)
The Emerald Ash Borer (EAB) is an invasive beetle that has killed hundreds of millions of ash trees in North America since its discovery Michigan in 2005. As a non-native insect, EAB lacks predators to keep it in check. The larvae of the beetle attack ash trees and the infested trees die within three to five years.
EAB is in NH
EAB was first detected in NH (in Concord) in 2013 and has spread to Hillsborough, Merrimack, Belknap and Rockingham counties. A quarantine of all hardwood firewood, ash wood-products and all ash nursery stock is in effect for these four counties. For more specific locations for both NH’s infested and alert areas, click on this PDF. Ash trees make up about six percent of New Hampshire’s northern hardwood forests, and it’s a commonly used landscape tree.
Just a Matter of Time for VT
So far, EAB has not been detected in Vermont, but has been detected in all states and Canadian provinces surrounding Vermont; clearly it is coming. “Ash was widely used to replace the stately elms that graced our communities and were decimated by Dutch elm disease in the middle of the 20th century and have historically been a favorite choice for street trees in Vermont due to fast growth and salt tolerance.” (not sure how to identify the source of this last sentence, it was from Steven Sinclair, director of forest for the state Department of Forests, Parks and Recreation, Rutland Herald, May 4, 2014.)
Emerging females mate and lay eggs individually in bark crevices on the trunk and major branches. The eggs hatch in about a week with the small larvae boring through the bark into the cambium area where they feed on the phloem and create long, serpentine galleries. Larvae continue development through the late summer and into the fall when they begin the pupae stage and emerge as adults in the spring, leaving 3-4mm wide D-shaped holes. EAB can be present in a tree for two years without signs of decline. Eradication is difficult and painful, requiring the removal of thousands of trees in the quarantined areas.
Individual high-value trees can be saved by treating them with insecticides, but it is best to treat preventatively, before the tree is attacked. Products are applied to the soil or bark, early or throughout the growing season. Curative, cambial treatments may be effective if caught early enough. In terms of controlling the spread of EAB, the NH Division of Forests and Lands has recently discovered some positive results using parasitic wasps as biocontrol. This process requires wasp larvae to be injected into the ash trees where they can actually develop inside EAB larvae. The wasp larvae will then eat their way out of the EAB larvae to become adult wasps that will continue to feed on the EAB larvae as well as their eggs. This could prove to be very successful because the parasitic wasps will reproduce aggressively and only face minimal food competition from woodpeckers. While early findings offer hope for a solution it will require a good deal of additional testing and could prove to be very expensive.
2) Asian Longhorned Beetle (ALB)
Native to China and other parts of eastern Asia, this insect hitched a ride to the US in crating material shipped to NYC in the 1980s. It has affected areas in New York, New Jersey and Chicago, IL. More recently, and of greatest concern to New England, was the discovery of ALB in Worcester, MA, during the summer of 2008. Removal of 6,000 infested trees began in January of 2009. Host species include all of the maples, horse chestnut, poplar, willow, birch and elm.
The ALB will travel up to 400 yards in search of host trees but is more likely to make it to our area in firewood. Its lifecycle begins when a mated adult ALB chews individual depressions into the host tree's bark where it lays its eggs. Within a few weeks the larvae emerge and tunnel into the tree, eventually endeing up in the heartwood where they pupate, become adults and exit the tree leaving perfectly round one inch holes, usually in the spring and summer. Eradication is difficult and painful, requiring the removal of thousands of trees in a quarantined area.
3) Hemlock Woolly Adelgid (HWA)
This insect pest appears to have originated in southern Japan and was introduced to the Pacific Northwest in 1924. Its introduction to the northeast was probably in 1951, first reported near Richmond, VA. To date it has affected more than 16 states from Maine to Georgia. HWA is dispersed by wind, birds and other forest-dwelling mammals as well as by the transport of infested nursery stock.
HWA threatens the health and sustainability of the Canadian and Carolina hemlock species. Hemlock decline and mortality typically occur within four to 10 years of infestation in our northern range. These parthenogenetic insects (all females reproducing asexuallly) develop through six stages, completing two generations per year on hemlocks.
It is during the heat of the summer the nymph enters a period of dormancy, feeding as temperatures cool in the fall and throughout the winter. HWA feed on stored starches critical to the trees' growth and long-term survival. The 'wool' (ovisacs) can be seen from late fall to early summer on the underside of the outermost branch tips of hemlock trees. Control is possible in the urban landscape utilizing various chemcial pesticides along with horticultural oil and insecticidal soap. Unfortunately, our forests face the greatest risks.
To report an invasive pest in Vermont or New Hampshire, contact:
State Plant Health Director
617 Comstock Road, Suite 2
Berlin, NH 05602-8927
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