Invasive Species of Concern in Maryland

redbay damage Beginning in 2003, reports surfaced of dying redbay trees (Persea borbonia) in coastal areas of Georgia and South Carolina; in 2005 the problem was also found in northeast Florida. Further study confirmed that the cause was a previously unknown fungus in the same genus as Dutch elm disease, Ophiostoma. The pathogen is transported by a recently introduced ambrosia beetle from Asia, Xyleborus glabratus, which first was detected in the U.S. in 2002 near Port Wentworth, Georgia. Currently, infestations have been detected in more than 30 counties in coastal Florida, Georgia and South Carolina. Because redbay is an endangered plant in Maryland and this pathogenic fungus and its vector beetle are red alert species for us, the Maryland Invasive Species Council has chosen them as the December Invader of the Month.

Redbay is a common understory tree in the coastal plain, distributed primarily from Virginia’s far southeast corner to the Mississippi-Louisiana border. In Maryland, redbay is present in small numbers on the Eastern shore. It is related to sassafras (Sassafras albidum), another recorded host, and one that is much more widespread in Maryland forests. Its range includes most of the eastern deciduous forest from central Florida to Massachusetts, across Pennsylvania into Michigan, and then southwest across central Illinois to Missouri and eastern Oklahoma and Texas. Both species are important to wildlife - the fruits are eaten by wild turkey, bobwhite quail and several species of song birds. Deer also consume the fruits and leaves. The most vulnerable wildlife species are two butterflies which depend on redbay and sassafras as larval food supplies; these butterflies are the Palamedes swallowtail butterfly (Papilio palamedes) and the spicebush swallowtail (Papilio troilus).

Native to India, Japan, Myanmar and Taiwan, the redbay ambrosia beetle is thought to have arrived in the U.S. in wood packing material like pallets and crates. Like many ambrosia beetles, it is tiny, about 2 mm long. It is shiny black, and almost smooth on top. The beetle’s hind end drops off very abruptly to a blunt point. Ambrosia beetles do not feed on the wood of their tree hosts, but on colonies of fungus introduced into galleries in the wood. The wilt fungus associated with redbay ambrosia beetle spreads through the vascular tissue of the tree from the shot hole bored by the beetle, staining the tree’s tissue and causing the plant’s leaves to wilt and turn reddish or purplish. This discoloration and eventual browning may occur in only one section of the tree’s crown or simultaneously all over the crown. Mortality is high and occurs quickly after symptoms become apparent.

Laboratory tests indicate that many additional plants in the same plant family (Lauraceae) might become infected, including spicebush (Lindera benzoin), a common understory shrub. In addition to the spreading ecological impacts of the disease complex, there are economic costs. Park managers and municipalities face rising costs for the removal of dead and dying trees that pose a hazard to the public. Disposal of the trees presents its own challenges, since moving the wood could spread the disease whereas leaving significant amounts of woody debris on site could be a fire hazard.

The rate of spread of the beetle is estimated at about 20 miles per year. The ambrosia beetle and fungus complex has been found as far north as Charleston, South Carolina, which means that under natural conditions, it would reach Maryland in two decades. It could reach us much sooner, however, if unsuspecting humans inadvertently transport it in firewood or infested plants. MISC defines a “red alert” species as one “not yet established in Maryland but considered to be of high risk.” Based on the experience of our neighbors in the southeastern U.S. the redbay ambrosia beetle and its associated fungus threaten an entire plant family within Maryland forests.

For more information about other Invasive Species of Concern, visit www.mdinvasivesp.org or call the Maryland Department of Agriculture at 410-841-5920.

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