Southern Pine Beetle
The Southern Pine Beetle (SPB), Dendroctonus frontalis, is the most destructive of the bark beetles that attack pine trees in the southern U.S. Pine engravers and the black turpentine beetle are common, but less aggressive than SPB. The preferred host trees for SPB are loblolly pines, although all pine species can be attacked. Outbreaks of the southern pine beetle occur periodically in the southern United States, killing millions of dollars worth of pine timber and landscape pines. Good forest management, or cultural care in the case of landscape pines, can minimize the risk of southern pine beetle attacks. However, knowledge of the beetle life cycle and symptoms of infested trees is necessary to properly deal with southern pine beetle attacks when they occur.
SPB populations can rapidly build to epidemic proportions under certain environmental conditions. Periods of drought and other factors that cause stress to pine trees are believed to contribute to SPB outbreaks. Pine trees in Lee County have suffered stress from the tornado. These conditions were followed by the current drought. We are seeing symptoms of SPB all over the county.
The most obvious symptom of a southern pine beetle infestation is the discoloration of the needles in the tree crown. Needles fade from green to dull green, yellow, and finally reddish-brown before falling. Small, light yellow to white pitch tubes usually form where the beetles enter the tree along the entire trunk length. These masses of pitch are about the shape and color of popcorn, and can be the same size or slightly smaller. Especially weak trees may not produce pitch tubes, but reddish boring dust in bark crevices or cobwebs at the base of the tree is evidence of infestation. The SPB is smaller than a grain of rice, measuring only 1/8 inch long.
The life cycle of SPB from egg to adult is about one month. New generations of SPB continue the cycle, typically emerging between April and September. The adult SPB invade pine trees by boring through the bark to lay their eggs. The winding S-shaped galleries that are developed eventually girdle the host tree resulting in its death. Galleries house tiny white eggs of SPB that hatch into larva, then the larva develop into pupa. Once pupation is complete, newly formed adults chew exit holes through the tree bark, take flight and repeat the cycle of reproduction and infestation of pines.
The key to SPB control is early detection of nearby SPB infestations. High value residential and commercial trees in urban or rural areas should be protected with OnyxTM insecticide in late winter prior to adult flight or when the threat of SPB attack is imminent.
Two types of treatment methods to control southern pine beetle are used for forest:
1). Cut and Leave – Infested pine trees are cut and left where they fall. A buffer zone of non-infested pine trees is cut in some areas where the direction of spread could be determined. The buffer zone can go up to 200 feet.
2). Cut and Remove – Infested pine trees and non-infested pine trees in the buffer zone are cut and removed from the site. This method reduces the number of adult and maturing beetles that would likely emerge to attack more trees.
No other control methods are an option for SPB infestation on such a large scale. Spraying thousands of pine trees with pesticide over thousands of acres is not practical or environmentally sound. Burning infested areas hot enough to kill infested pine trees would kill other trees in the area and possibly create air quality problems.
The NCDMAC advises all water users in the counties that are indicated on the US Drought Monitor Map as suffering from Moderate Drought (D1) conditions to enact the following precautions in addition to previous advisories until further notice:
- Adhere to local water use restrictions.
- Participate, as appropriate, in regional and local coordination for the management of water resources.
- Stay informed on drought conditions and advisories (www.ncdrought.org).
- Project water needs and available water supply for a ninety day period from the issuance of this advisory.
- Assess your vulnerability to the drought conditions and adjust water usage to prolong available supply.
- Inspect water delivery system components (e.g. irrigation lines, fixtures, processing equipment, water system lines, etc.), repair leaks and ensure that existing equipment is operating as efficiently as possible.
- Minimize nonessential uses of water.
- Implement available public awareness and educational outreach programs emphasizing the need to conserve water.
Want more pertinent horticulture information delivered directly to your home computer? Subscribe to the new Lee County home horticulture e-mail list. Simply send an e-mail to firstname.lastname@example.org with subscribe leehomehort in the body of the message. You will then be a member of email@example.com.
Brenda Gwynn is the Horticulture Agent for North Carolina Cooperative Extension in Lee County