What Happened to our Red Bay Trees? | Gardening

Large brown patches of the dead trees blight the beautiful landscape along the coastal plain. In the woodlands from southern Virginia to Florida and on to eastern Texas, for centuries red bay trees have been a major understory tree. They have thrived in parks and back yards. Suddenly the red bays are dead, dying and at risk of extinction.

Laurel wilt is the cause. It is a relatively new plant disease carried by an exotic beetle. This is yet another case of a non-native species invading our forests, parks and backyards. The disease is caused by a fungus carried by the red bay ambrosia beetle (Xyleborus glabratus) which is native to parts of Asia.

The beetle was first detected in Georgia in 2002. It made its way from Asia to the U.S. embedded in wooden shipping materials that came into Port Wentworth near Savannah. Since its identification the beetle has already moved into the red bay tree population in eight coastal states.

Scientists believe the beetle, unaided, moves at a rate of about 20 miles per year. However, just as the beetle was assisted by humans in its jump from Asia to the southeastern US, it is likely the beetle has had human help with its local journey too. Dying red bay trees reflect the beetles track northward as far as southeastern North Carolina. A trail of dead and dying trees leads southward through the entire state of Florida and west across the Gulf States to Texas. That’s more than 20 miles per year.

Laurel wilt is a fungus disease that affects certain trees in the laurel family, particularly red bay (Persea borbonia) and swamp bay. Other susceptible plants include sassafras, avocado, spicebush, pond spice and camphor. Loblolly bay and sweet bay (magnolias) have not been susceptible to the disease.

Female ambrosia beetles carry laurel wilt fungus in their mouth parts. The female beetle deposits the fungus as she bores into a tree to lay her eggs. The fungus grows in the tunnels she has hollowed out and feeds the developing larvae. The disease disrupts a tree’s circulatory system, blocking the movement of water from its roots to the rest of the tree. As a result, the tree wilts and dies.

The first symptom of laurel wilt appears as toothpick-like tubes of sawdust that jut out from bore holes in the trunk or branches of a tree. Boring dust around the base of a tree indicates a major invasion, but wind and water can easily carry away this fragile evidence. The tree’s leaves droop and turn red, purple and brown. A peeling away of the bark on the trunk reveals black streaking on the sapwood. Trees typically die within six months of infection.

Red bays are significant for ecological reasons. Deer and black bear browse on their evergreen foliage. Songbirds, quail and wild turkeys feed on the trees’ blue berries. Palamedes swallowtail butterflies depend on the dark green leaves to lay their eggs and nourish their larvae.

The rapid demise the once plentiful tree has already changed the species make up in affected areas where other types of trees are replacing the red bays.

The avocado, also in the laurel family, is economically valuable in Florida where avocado production is an important industry. Laurel wilt has already been identified in isolated cases among avocado trees.

Laurel wilt is established. Forestry and environmental professionals warn that, tragically, we may lose all of our red bay trees. We are unable stop the spread of the beetle and associated fungus, but we can slow its movement.

Sanitation is a critical part of management. The South Carolina Forestry Commission urges homeowners to keep infected wood on site where it may be cut, chipped and burned. (Remember to comply with local ordinances relating to an outdoor burn.) They advise that diseased wood should not be transported unless it is to the local landfill.

Homeowners, campers, fishermen, second home owners and vacationers should not transport firewood. Instead, it should be bought where it will be burned.

If you suspect you have a diseased red bay tree on your property call your local extension office.

This story was originally published July 22, 2016 at 11:09 AM with the headline "What Happened to our Red Bay Trees? | Gardening."