“If laurel wilt kills off all the Persea, then it will very likely take the Palamedes swallowtail [butterfly] with it,” Hall explains.
Joni Mitchell once wrote “You don’t know what you got ‘til it’s gone.” People who are familiar with the coastal plain forests of North Carolina may soon find out how true that is – thanks to laurel wilt, which just reached the state and is likely to wipe out a substantial part of the forest midstory.
Laurel wilt was identified in Bladen County this spring. It is caused by a fungus (Raffaelea lauricola), which is spread by the ambrosia beetle (Xyleborus glabratus) that is native to Asia. It obliterates redbay trees (Persea bobonia), which are widespread along streams, springs and swamps in the coastal plain.
Ryan Blaedow, a plant pathologist with the N.C. Division of Forest Resources (DFR), discovered the disease in North Carolina. DFR had been monitoring for laurel wilt since it was identified in Horry County, South Carolina in the fall of 2009. He had set up a grid system that monitored red bays that were on points approximately 10 miles apart. He and a coworker were driving from one point to the other in March when they noticed dying redbays along the road. At first, he thought the dead trees were the result of herbicide sprayed along a road right-of-way. “Then, we noticed that redbay was dying further back in the woods as well. We stopped the car on the side of the road and peeled back the bark on one of the trees and we saw a vascular streak.” That streaking is one of the signs of the wilt. Subsequent lab tests confirmed their finding.
Blaedow had seen what laurel wilt can do to a forest from visiting Florida where the disease has decimated redbays. “You don’t realize how many redbay trees there are until they start to die. The forest just turns brown.”
Although the redbay isn’t a particularly charismatic tree, the Palamedes swallowtail butterfly (Papilio palamedes) is a showy species. “It is one of the most conspicuous species in the coastal plain,” says Steve Hall, an Invertebrate Zoologist with the North Carolina Natural Heritage Program. “Much more conspicuous than redbay, unless you are a botanist.”
But, Palamedes swallowtail’s fate is intertwined with the redbay. In its larval stage, Palamedes feeds almost exclusively on redbay. “If laurel wilt kills off all the Persea, then it will very likely take the Palamedes swallowtail with it,” Hall explains.
The redbay is a forest workhorse, an important source of wildlife food and a vital part of the ecosystem. While Palamedes swallowtail could become extinct because of the disease, other plants and animals will be affected as well.
So far, nothing has stopped the spread of laurel wilt. Since 2002, the disease has marched through coastal plains forest from Florida to South Carolina. The ambrosia beetle likely entered the United States as a stowaway in packing material. The beetle introduces the fungus into the tree’s vascular system. The fungus spreads rapidly throughout the tree. In an effort to save itself, the tree plugs its own vascular system. Eventually, the tree dies from thirst.
Other plants in the laurel family, including sassafras, avocado swamp bay, pondberry, pondspice and spicebush, are also susceptible to the fungus. Pondberry is on the federal endangered species list. There are only two remaining populations left in North Carolina, one of them at Pondberry Bay in Sampson County, which was protected by the Conservancy in 2001.
Under its own steam, the ambrosia beetle would move through coastal plain forest at a rate of about 20 miles annually. But, man has helped the beetle find new hosts more rapidly. Researchers suspect that moving infected firewood has led to its rapid infestation along the southeast coastal plain. That’s almost certainly the case in North Carolina – the Bladen county infestation is not contiguous to any other infected areas.
Rob Trickel, who heads DFR’s Pest Control Branch, says the state will focus its efforts on education – convincing the public that moving infected firewood from place to place is likely to expedite the redbay die off in North Carolina. “As far as control goes, there is no silver bullet,” Trickle says. “If we can slow the spread down, then if a silver bullet does appear we will have resource left to work with.”