Southern pine beetles loom as potential threat to South Carolina’s stressed trees
CLEMSON — For about 15 years, the state’s most destructive forest insect has been lying low in South Carolina. But damage caused by recent droughts, storms and fires raises the specter of a resurgence.
Sizable infestations of southern pine beetles have been few and far between since the last major outbreak in 2000-2002, when the tiny but voracious creatures caused about $1.5 billion in damage in the southeastern United States to loblolly, shortleaf, longleaf, pitch, pond and Virginia pines. But with most of South Carolina’s current crop of pine trees now stressed by weather-related catastrophes in recent years, the potential for statewide infestation has taken a step in the wrong direction.
Though the risk of a major outbreak in the state remains unlikely due to low numbers of southern pine beetles overall, the possibility is viable enough to at least spur a need for vigilance. As always, when it comes to the health of trees, it’s better to be safe than sorry.
“The populations of southern pine beetles tend to be cyclical and vary by region,” said Carolyn Dawson, a Clemson Cooperative Extension area forestry agent based in the Upstate. “When stress conditions are widespread, the potential for these populations to increase becomes a legitimate concern. By no means am I saying that it’s panic time. But for anyone who owns stands of pine, it would be wise to be on the lookout for signs of (beetle) activity, especially when the weather warms up in 2017.”
There are more than 13 million acres of timberland in South Carolina comprising about 67 percent of the state’s total land area. South Carolina’s trees are split about 50-50 between pine and hardwood types. But pines are the region’s most valuable to grow and harvest, with pine plantations — defined as stands of pine that are intensely managed, harvested and replanted — representing 25 percent of the state’s timberland but producing 50 percent of the timber cut each year. With these figures in mind, it’s easy to recognize how a major infestation of southern pine beetles, which only attack pines and a few other softwoods, could inflict significant economic damage.
“The past two years, our state has been battered by a superstorm and a hurricane that caused major flooding and wind damage. We’ve also had months-long stretches of high heat and severe drought,” said Dawson, who is a member of Clemson’s forestry and wildlife management team. “To further complicate matters, too many of our pine forests aren’t properly managed, which makes those trees even more vulnerable to southern pine beetle activity. Though not much of consequence has occurred recently in South Carolina, outbreaks have occurred in Georgia and Florida in 2016 that could be early signals of an eventual threat to our state.”
More than 220 spots covering 1,200 acres were reported by Florida Forest Service personnel. Georgia’s numbers have been smaller – about 100 spots covering 500 acres – according to Georgia Forestry Commission officials.
“This past year, Florida and Georgia had southern pine beetle outbreaks that reached as far north as Savannah,” said David Coyle, director of the Southern Regional Extension Forestry’s Forest Health Program, which serves the 13-state southeastern region. “South Carolina has not yet had issues, but that doesn’t mean it won’t happen in the future. I think the conditions are there in South Carolina for a rise in southern pine beetle activity, especially considering its neighbors to the south have already had them. Regardless of the severity of the risk, it would behoove everyone to spread the word to landowners to keep an eye out.”
Southern pine beetles, which are each about the size of a grain of rice, tend to hunker down during winter. But when temperatures rise, the beetles can spring into action. Adult females begin the attack sequence by finding a suitable tree – usually a stressed or overly mature pine – and then releasing pheromones that attract males and additional females. If the beetles gather in large enough numbers – often thousands per tree – they will begin to colonize. The females mine into the tree’s vascular cambium, a thin layer of tissue between the bark and wood that is crucial to a plant’s growth and healing mechanisms. Once inside the bark, females construct S-shaped galleries in the cambium to house their eggs. Newly hatched larvae then bore into the inner bark. Older larvae move to the outer bark, where they feed and then pupate. Finally, new adults chew their way out, leaving small holes on the bark surface.
This activity girdles trees and leads to death. And that’s not even the worst of it. Southern pine beetles harbor a fungus called “blue stain” that separates from its host once inside the tree and then replicates, eventually blocking the flow of water from the roots to the crown. The combination of burrowing and feeding along with the introduction of the fungal infection kills virtually every tree that’s been colonized. The first symptoms are needles that turn from green to faint yellow and finally to rust. Death occurs in as little as two weeks after the initial assault.
However, healthy trees are not defenseless. They fight back by oozing resin that envelops, flushes out and drowns the beetles before they can do much harm. The resin eventually dries into white or reddish globs that are visible on the trunk, which is another good indicator of infestation. But stressed trees tend to have less resin, rendering them more vulnerable.
The best way for landowners to protect their pines is to properly manage their stands. This involves thinning, prescribed burns and various other methods that reduce stand density while also enhancing the quality of the soil and understory. Because the pheromones released by female beetles only travel a limited distance, thinned stands – where the trees are farther apart – are less likely to suffer widespread infestations. Statistics show that properly managed pine forests are more resistant to southern pine beetle infestations than those left untended.
Another effective tool for landowners is called “cut-and-remove” – or in more remote areas, “cut-and-leave.” These suppression treatments involve felling the infested trees, and also an outer buffer of healthy trees, toward the center of the infestation. In cut-and-remove, the trees are salvage-harvested. In cut-and-leave, they are left on the ground. Either way, the beetles perish.
Southern pine beetles also have natural foes. Predatory clerid beetles are their arch enemy, feasting on adult and larval southern pine beetles. Woodpeckers eat them, too. Finally, extremely hot or cold temperatures can kill them.
The S.C. Forestry Commission searches for southern pine beetle activity on an annual basis. In 2016, 32 counties were monitored over a 28-day stretch in early spring. Based on the results, the commission correctly predicted that no counties would experience significant southern pine beetle damage throughout the rest of the year. However, the 2016 traps did record a slight increase in activity from the previous year. If there is a further increase in 2017, it could indicate that a new cycle of infestation might be on the horizon.
“Over the long term, South Carolina southern pine beetle populations have mostly declined since the 2000-02 outbreak,” said Chisolm Beckham, the southern pine beetle prevention coordinator for the S.C. Forestry Commission. “But even though current southern pine beetle populations are lower than they were in previous decades, we still encourage landowners to manage their forests, which includes distributing their pine acreage evenly among age classes, thinning on a timely basis and harvesting high-risk stands as soon as possible.”
If landowners suspect that they might have a southern pine beetle infestation on their property, they should contact Clemson Cooperative Extension, the S.C. Forestry Commission or an S.C. Registered Forester.
“It’s always best to be prepared and informed. When it comes to the health of your trees, knowledge is power,” Dawson concluded. “Early detection of any threat to your timberland makes it easier to manage and eradicate. If it turns out that the next southern pine beetle infestation doesn’t occur for several more years, this will give landowners the time they’ll need to properly manage their woodlands. Doing this will not only benefit the landowners themselves, but South Carolina as a whole.”