These past few months, there has been an increase in the typical number of homeowners contacting me at the Collier County University Extension office about their slash pines being attacked by bark beetles. They described popcorn size masses of reddish-orange resin, and or small holes with sawdust along the lower ten feet of the trunk and canopy thinning and yellowing-browning.
Construction, root disturbance, drought, disease, flooding, or lightning can predispose slash pines to ips beetle infestations. The ips beetles are related to the southern pine bark beetle, Dendroctonus frontalis, which fortunately does not tend to attack our native south Florida slash pine, Pinus elliottii var. elliotti. The southern pine bark beetle range extends to central and northern Florida, and it primarily attacks loblolly and shortleaf pines. Lucky for us, as the southern pine bark beetles will swarm trees and can kill a relatively healthy pine tree in a matter of days. Thousands of southern pine bark beetle adults can overwhelm a tree and bore through the bark and deposit their eggs where the larvae feed.
The most common pine bark beetle attacking slash pines in our area, is the sixspined ips pine bark beetle, Ips calligraphus. Symptoms of bark beetle attack mimic root damage or chlorosis (nutrient deficiency) symptoms.
Needles of infested trees turn from green to yellow then red to brown accompanied by small, reddish-orange colored masses of resin on tree stems and branches. The beetles leave 1/16- to 1/8-inch round holes in the outer bark. Reddish-orange boring dust collects in the bark crevices or underneath the tree. Adult beetles are small, about 3/16 inch long and are dark brown to black in color and have minute spine-like projections at the end of their wing covers (front wings).
When females find a host tree they bore in and deposit eggs and several days later the eggs hatch. The larvae (white, no legs, orange-brown head) eat the inner bark of the host tree. Trees are damaged from the excavation of galleries in the phloem (food-conducting cells of the plant). These galleries cut the flow of the phloem and essentially girdle the tree internally. In addition, the adults carry a blue stain fungus into the tree. This fungus eventually plugs the xylem (water-conducting cells of the plant) as well. These beetle have many generations each year, so trees can be attacked almost all year.
Calls about bark beetle attacks are often from new homeowners who didn't insist that their builders design a construction site that was "tree safe." Heavy construction equipment running over the root zone; long-term storage of building materials on top of the tree's root system; and burying or excavating the roots with more than 2 inches of soil can put the tree on its death bed.
That is when the beetles move in. There are reports that the beetles key in on a weak tree by the chemicals that volatilize from wound and stress reactions and some scientists even speculate that the beetles are drawn to trees when they "hear" (antennae pick up the vibrations) the shrinking, creaking wood fibers as the trees start to dry out internally. The sixspined ips beetles don't tend to attack healthy trees, rather they cull the sickly pines. It is almost impossible to know when beetles may attack a particular tree as it is difficult for us to tell when a pine is stressed. So if what appears to be a healthy pine in your eyes is under attack, rest assured it is a tree that was already on its way out, the beetles just hastened its demise.
What stresses the trees, so that they become beetle fodder? Slash pines are pretty tough and not too easily stressed by environmental fluctuations. Natural pine stands occur in both areas that are under water for months at a time as well as exist quite satisfactorily in very dry hilly areas.
However, if they are into the final years of their life, around 70 years, weather or human-caused events can trigger their demise. Lawn Irrigation and fertilization can adversely affect the mycorrhizal fungi that are associated with the roots and required by the pines to assimilate the nutrients they require.
What to do: Avoid construction damage to trees that you would like to save when building. Use fencing to keep heavy equipment away from tree trunks and just as importantly, do not disturb the root zones during construction. If a pine has a distance of 10 feet from the trunk to the dripline (where the rain drips from the outermost branches), place fencing at least 15 to 20 feet away from the trunk. See: "Trees and Home Construction Minimizing the Impact of Construction Activity on Trees" at this Web site:
Keep the turf away from pine tree root zones. Inspect trees often, at least weekly. When trees have died on a neighbor's property, start scouting your trees closely. Removal of infested or brood trees is essential to help reduce beetle spread. Insecticide applications using a product with permethrin may stall the invaders. This insecticide will provide about three months of protection, so at least three applications would be needed each year. However, the dose used is an environmental assault concentration and costs about $17 per 10 gallons of diluted spray solution.
The sixspined ips beetle tends to attack at the 15 foot height and lower on the main trunk, so canopy sprays above 15 feet would not be necessary. There are other borer species that may attack higher on the trunk bole that one would have to keep an eye out for. Spraying the trunk with insecticides is usually discouraged as results with insecticides are unreliable, as an attacked tree is already under stress and is probably on its deathbed anyway.
For this reason, a community-based approach (scouting and removal of infested trees) is highly recommended.
Doug Caldwell is a certified arborist and the commercial landscape horticulture extension educator and landscape entomologist with the Collier County University of Florida Extension Service. E-mail firstname.lastname@example.org;call 353-4244. For more landscape maintenance information, see this Web site: collier.ifas.ufl.edu.