Three types of pine bark beetles (Ips grandicollis, calligraphus and avulsus) are frequent pests of stressed pines in the southern United States, especially the Southwest. These bark beetles feed just underneath the bark of infested trees, girdling them and leading to their death. In addition to feeding in the phloem, bark beetles can introduce blue stain fungi which will colonize the sapwood and cause further dieback. Although Ips beetles primarily focus on dead and dying trees, when populations reach sufficient levels they will infest neighboring healthy trees.
Trees at Risk
All three Ips species can infest any pine species within their range, and occasionally other conifers such as spruce, hemlock, and fir. Common hosts in Georgia include loblolly pine, longleaf pine, pond pine, sand pine, shortleaf pine, slash pine, and spruce pine.
Signs of Damage
- The first visible symptoms are typically needles turning yellow or red.
- Dry reddish-brown boring dust is visible in bark crevices.
- Pitch tubes are 1/8”-3/8”. They are white to reddish-brown and are often found in bark crevices.
- Massive numbers of tiny holes in the bark.
Most attacks are initiated by male bark beetles, tunneling through the outer bark and excavating a small chamber in which to mate. Mating occurs and females then construct egg galleries, laying eggs in niches chewed on either side of the gallery. Eggs hatch and begin feeding outward from the gallery, each larvae creating its own tunnel. Larvae pupate at the end of their tunnel, emerging as adults who continue feeding, creating winding tunnels in the inner bark before maturing and exiting through the bark. One generation generally is completed in about 21-40 days depending on weather. Development is much quicker during the hot summer months, but ceases below about 59 degrees.
Treatment for Ips beetles is really only necessary for stressed trees or those that are near infested trees; therefore, the most effective treatment strategy involves both supporting the tree’s natural defense system and controlling the insects in the tree. Soil applied systemic insecticides typically do not work on bark beetles because these insects feed in the phloem. Instead, insecticides sprayed on the bark and major branches are more effective. Two products, Tengard™ and Carbaryl™, are sprayed on the bark of pine trees and provide approximately three months of control. Applications should begin in the spring once temperatures reach 60 degrees or when neighboring trees are showing symptoms. In some cases, follow-up treatments will be necessary every 3 months until temperatures cool below 60 degrees.
Products to Use:
When applied at the correct time, trunk sprays can be very effective. Supporting tree health with proper watering practices will also help trees handle bark beetle attacks. Emamectin benzoate, because of its long residual, is a great choice for suboptimal application times. Carbaryl™ can cause mite outbreaks by affecting mite predators.