The southern pine beetle (Dendroctonus frontalis) is the most impactful pest of southern pines in the eastern U.S. A new article in the Journal of Integrated Pest Management reviews SPB suppression methods, which generally involve removing the infested (and some uninfested) trees to halt the spread of the outbreak. (Photo by Matt Bertone, Ph.D.)

By David Coyle, Ph.D.

David Coyle, Ph.D.

If you’ve ever driven through the southeastern U.S., you’ve probably seen miles and miles of roads lined with pine trees. Some of these forests are planted in rows (“pines in lines”) while others are grown using natural regeneration (“let the seeds fall and grow where they may”). Forestry is a major economic driver in the region, and scientists have been researching how to grow and care for pine trees for decades. Coming from the Midwest, it sort of reminds me of corn—fields of it planted in neat, tidy rows, operations done with equipment, and lots and lots of research and grower education on how to optimize productivity. Part of this productivity optimization involves managing pests, and for southern pines the most impactful pest in the region is the southern pine beetle (Dendroctonus frontalis).

Southern pine beetle (SPB) is a bark beetle that can impact commercial and non-commercial southern pines—pretty much any pine tree in the southern U.S. is susceptible (though longleaf is the least susceptible). Both adults and larvae feed on phloem, and this feeding usually kills the tree. SPB is an eruptive herbivore, meaning populations can be endemic (low and difficult to detect) then increase quickly to eruptive, or outbreak, populations. It is these outbreak populations that are a management challenge for southern foresters, as beetle-damaged areas (or spots, as they’re called) can grow rapidly.

A new article in the open-access Journal of Integrated Pest Management reviews suppression methods for SPB outbreaks, with an emphasis on “what’s next?” In the past, cut-and-leave or cut-and-remove were standard methods to stop SPB populations and outbreaks, but changes in management and expansion of the natural range of SPB have prompted scientists to reexamine SPB management strategies.

Cut-and-leave treatments are as you might expect—infested trees are cut and left on the ground—while cut-and-remove treatments end with the removal of the cut trees. The most common factor that determines if C&L or C&R treatments will be used is the markets; if it’s economically worthwhile to send the logs to the mill, foresters will, but if the landowner would lose money (due to transportation costs, product value, etc.), then trees may be left on the ground.

Trees attacked by the southern pine beetle (Dendroctonus frontalis) typically exhibit numerous masses of resin, known as pitch tubes, a defense mechanism of the tree. (Photo by Dave Coyle, Ph.D.)

One option for managing southern pine beetle (Dendroctonus frontalis) infestations is the cut-and-leave approach, in which infested trees are felled and left in place. The most common factor that determines if cut trees are left or removed is the markets; if it’s economically worthwhile to send the logs to the mill, foresters will, but if the landowner would lose money (due to transportation costs, product value, etc.), then trees may be left on the ground. (Photo by Dave Coyle, Ph.D.)

Bark removed from a pine tree reveals the gallery, or path followed as a larva feeds on phloem, of a southern pine beetle (Dendroctonus frontalis). (Photo by Dave Coyle, Ph.D.)

A major challenge with SPB populations is where they occur. On private land, management is fairly straightforward once the outbreak is identified, as management activities can occur as soon as the landowner makes the call and crews get on site. On publicly owned land, however, it’s much more difficult and time consuming. Permits need to be issued, a call for contracts made, bids evaluated, and so on. It’s not that the needed activities are different but rather that it’s so much more difficult to get treatments in place. And this delay in management means SPB populations have that much more time to increase and kill trees.

Any forest health professional in the South will tell you that SPB is our number-one pest of concern. For decades, SPB management strategies have been consistent and very effective. With new forest management strategies, flexibility has to be exercised when it comes to forest pest management. We know how to manage for SPB, but we also can’t be afraid to make some tweaks to the system.

David Coyle, Ph.D., is an assistant professor in the Department of Forestry and Environmental Conservation at Clemson University. Twitter/Instagram/TikTok: @drdavecoyle. Email: dcoyle@clemson.edu.