Forest Health

The greatest threat to the future health of southern forests is the introduction and spread of non-native invasive plants, insects and diseases. Once these pests are established, a lack of natural controls permits them to become extremely destructive and almost impossible to eliminate.

Forest insects account for 20 percent of the total negative growth impact on forest trees, while diseases account for 45 percent of it (Tainter and Baker 1996). Among significant non-native insects and diseases established in the South are the hemlock woolly adelgid, European gypsy moth, Formosan termite, beech bark disease, and dogwood anthracnose. Monitoring and suppression are important tools for preventing and managing these pests.

The following links contain descriptions for identification and management of the South's most important insects and diseases from the Southern Forest Resource Assessment, U.S. Forest Service, 2002.

Damaging Insect and Disease Pests in the Southern United States

Native Diseases of Conifers

Native Diseases of Hardwoods

Native Insect Pests of Conifers

Native Insect Pests of Hardwoods

Non-native Diseases of Conifers

Non-native Diseases of Hardwoods

Non-native Insects

Non-native Insects of Hardwoods

Invasive Species

Many invasive plants affect forest health, productivity, access and use, forest management costs, and limit species diversity on millions of acres of forests. These plants displace native plants and associated wildlife, and can alter natural processes such as fire regimes and hydrology.

For list and maps of invasive plants of the southern states, visit Maps of Occupation and Estimates of Acres Covered by Non-native Invasive Plants in Southern Forests.

Top Southern Forest Heath Issues

Firewood Movement

Truck with LogsWhy is moving firewood a problem?

Moving firewood has been linked to the spread of destructive, non-native insects and diseases to forest ecosystems. While these pests can’t move far on their own, they can travel hundreds of miles when people move firewood, logs, chips, and mulch. Forest pests can kill our native trees and be very expensive, if not impossible, to control.

Many species of hardwood and pine trees serve as potential hosts for these destructive pests, so no firewood is considered safe to be moved long distances. Non-native organisms can wreak havoc on the environment. They are often resistant to natural controls and can spread unchecked, resulting in much greater harm to our forests than is experienced with native pests. Tiny, non-native insects and their larvae, and even microscopic fungus spores can hide in firewood that is transported by visitors into campsites and parks. They can fall unnoticed to the ground on a small chip of bark, or washed off the firewood from a sudden rainstorm.

What pests are threatening the South’s forests?

A non-native insect known as the redbay ambrosia beetle that is spread by the movement of firewood has killed millions of native redbay trees, and is also killing native sassafras. Other non-native threats to southern forests include the Asian longhorned beetle, emerald ash borer, gypsy moth and sirex woodwasp. These pests are already established in the northeastern United States and could spread into the South through the movement of firewood.

What can you do?

To combat the threat and spread of non-native pests and diseases, campers are asked to leave their firewood at home and purchase local wood. If wood has been inadvertently brought into camp, it should be burned on-site or turned over to park officials. For more information, visit Don't Move Firewood.


Why is cogongrass a problem?

Cogongrass is considered the seventh worst weed in the world and listed as a federal noxious weed by USDA Animal and Plant Health Inspection Service – Plant Protection and Quarantine. It has become widespread throughout Alabama, Mississippi, and Florida and is moving into Georgia and South Carolina. This weed suppresses and eliminates natural vegetation thereby significantly reducing tree and plant regeneration, wildlife habitat, forage, and ecological diversity. Cogongrass grows in most soil types with the exception of saturated soils and is highly adaptable from full sunlight to shade. It invades forests, pastures, old fields, roadsides, utility rights-of-ways, and ditches and spreads by way of rhizomes and seed production. Forming dense mats, it is extremely flammable and creates hazardous prescribed burning and wildfire conditions. Cogongrass is difficult to eradicate once it has become established due to the dense root system.

What can you do?

The first step in eradicating cogongrass is to learn how to identify the grass. Fluffy, white seed heads produced in the spring are the most recognizable feature of cogongrass. When not in the flowering stage, inspection of the roots is the most identifiable feature. Cogongrass has sharp-pointed, scaly rhizomes with a very dense root system that usually grows in a circular-shaped pattern. Although not a sole identification feature, the grass also has an off-centered midrib on long leaf blades. Report suspected infestations to your state forestry agency.

Hemlock Wooly Adelgid (HWA)

Hemlock Wooly AdelgidWhy is HWA a problem?

All eastern and Carolina hemlocks, except for treated trees and geographically isolated populations, could be killed by a non-native insect, the hemlock woolly adelgid. HWA was accidentally introduced in Virginia in the 1950’s from Japan. The adelgid is dispersed by wind, birds, and human activity and is spreading at an alarming rate. In the absence of natural control elements in eastern North America, this introduced insect pest attacks both eastern (Canadian) and Carolina hemlock which are often damaged and killed within a few years of becoming infested. HWA is now established from northeastern Georgia to southeastern Maine and as far west as eastern Kentucky and Tennessee.

What does HWA look like?

HWA is a tiny insect measuring around 1/16 of an inch long. As the adelgid matures, it produces and covers itself with a white, waxy filament used to protect the adelgid and its eggs from drying out and natural enemies. Adelgids can be found on the underside of the branch, on the newest growth in the winter months. Needles on infested branches to dry, turn a grayish-green color, and then drop from the tree, sometimes within a few months. Most buds are also killed, so little if any new growth is produced on infested branches. Dieback of major limbs can occur within two years and progresses from the bottom of the tree upward, even though the infestation may be evenly distributed throughout the tree.

What can you do?

Hemlocks infested with HWA can be kept healthy in a landscaped setting by using an integrated management approach that includes the following:

  • Take care when moving plants, logs, firewood, or bark chips from infested to uninfested areas, especially from March through June when adelgid eggs and crawlers are abundant.
  • Water hemlocks during periods of drought and soak the roots thoroughly. Also, prune dead and dying branches and limbs from hemlock to reduce the likelihood of attack by insect pests and diseases, by allowing the formation of cellulose tissue to “close off ” the stub wounds more rapidly. HWA infests and kills eastern and Carolina hemlocks of all sizes and ages, even in habitats with seemingly optimal growing conditions. However, trees that are growing off site or experiencing stress from drought and other agents succumb to adelgid attack more quickly.
  • Fertilize a tree after adelgids have been controlled to encourage growth and stimulate recovery. Fertilizing infested hemlocks with nitrogen enhances survival and reproduction of HWA. Therefore, nitrogen fertilizer should not be applied to an infested hemlock.
  • Application of chemical insecticides is an essential component of any integrated approach to managing populations of HWA. Even though the measures described above can help maintain and improve overall tree health, infested trees are usually unable to survive for more than a few years without chemical insecticides. Contact your state forestry agency for technical assistance.

Source: McClure, Salom, and Shields, 2001.

Pest Management

Generally, the more diverse and vigorous a stand, the less likely it is to suffer significant insect or disease damage. As diversity decreases or vigor declines susceptibility to catastrophic pest damage increases.

The four main pest management strategies are: (1) prevention, making the forest more resistant to the invasion of pests or more resilient if attacked; (2) suppression, lowering unacceptably high pest populations to acceptable levels; (3) eradication, eliminating the pest from the ecosystem; and (4) exclusion, preventing the movement of non-native pests into a new area. Ideally, managers will scientifically select the most effective, most environmentally friendly method (Thatcher and others 1986). Source: Southern Forest Resource Assessment, U.S. Forest Service, 2002.

SGSF professionals provide technical assistance in the prevention, detection, evaluation, and suppression of forest pests. Contact your State Forester's office for assistance.

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