Campbell Vaughn: Look out for stressed pine trees

Last year’s drought and heat equals tough times ahead for trees. Be on the lookout for stressed pine trees. Pine bark beetles are on the move and can really cause big problems in forests as well as your own neighborhoods.

 

According to UGA’s Forest Health Specialist Dr. Elizabeth Benton, drought stresses and weakens trees, making them more likely to be attacked by bark beetles. Under drought, trees don’t receive enough water to perform their normal life processes, like converting sunlight to energy. Tree drought responses include leaf wilting, early leaf fall, dying tissue, shutting down roots, and changing chemical process within the tree.

Many of these changes occur to conserve water and keep the tree from dying. Even as rainfall conditions return to normal, trees require time to fully recover from their drought response. So there can be a time-lag between increased rainfall and full tree health recovery. Unfortunately, this time-lag and milder winter temperatures gives bark beetles more time to attack pine trees.

In Georgia, we have three types of beetles that feast on pine trees, the Southern Pine Beetle (Dendroctonus frontalis), Ips Engraver Beetle (Ips spp.) and Black Turpentine Beetle (Dendroctonus terebrans). All bark beetles have similar life histories. Usually, the adult beetles are attracted to trees under stress. They bore into the bark and hollow out areas where females lay eggs. After about a week, the larvae hatch and start feeding on the cambium layer. Simply speaking, the cambium is a thin layer of a tree that produces the vein system that moves water and nutrients up and down the plant. When the beetles mature, they pupate in cells constructed in the bark. When the adults emerge, a small exit hole is cut in the bark and the beetles fly to another tree. Several generations are produced each year. Infested green trees are attractive to adult beetles.

The southern pine beetle is the most destructive forest insect in the southern U.S., and can also cause damage in urban settings. This year in Georgia, the Ips engraver beetle is wreaking havoc with over 200 infestations being reported in excess of five acres. Many infestations have been 25-50 acres in size.

These type of infestations can be catastrophic to timber growers. Foresters have to remove huge quantities of timber to keep from losing stands of trees. This supply saturation leads to drastically reduced lumber prices. These infestations also can really hurt the pocket book of homeowners when these infected trees have to be removed from nearby structures. Pine engravers can complete their lifecycle in as little as 30 days, with up to six generations per year in Georgia.

That rapid breeding can lead to a lot of dead trees in a hurry.

Southern pine beetles usually enter the trees from 6 to 30 feet above the base, where the Ips beetle will attack any part of the tree. This means that spraying insecticides is almost completely ineffective. Once these two types of beetle are in the tree, the tree is going to die. To tell the difference between these beetles, southern pine beetles chew “S” patterns under the bark; which is different from the Ips beetle that which has a pattern like an I, H or Y shape. Both SPB and Ips can also infect the trees with a blue stain fungi that affects water flow and hastens tree mortality. Southern pine beetle and Ips may be present in the same tree.

The other beetle is the black turpentine beetle and is not a major problem, only attacking a few stressed trees in the forest. The turpentine beetles enter from the base of the tree up to about five feet. If you hear a crunching sound in your tree, it is likely a black turpentine beetle.

The best control is to keep trees in vigorous, healthy condition. This will usually prevent the initial attack by adult beetles. Healthy trees have a heavy flow of pitch and can “drown” the beetles as they bore through the bark. It is not possible to prevent natural weakening factors such as old age, prolonged floods, fire, drought and lightning strikes. However, homeowners should know that water and fertilization go a long way towards keeping trees healthy. Also, avoid injuring trees with riding lawnmowers.

Reach Campbell Vaughn, the agriculture and natural resources cooperative extension agent for Richmond County, by e-mailing augusta@uga.edu.

 

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