Landscape - Red Oak Death

I have noticed many trees in landscape that have died this year. One species that is being reported as having more death than usual is Red Oak. The following is some information from the University of Maryland.

Several arborists and landscape managers are reporting to us that red oaks have major dieback and sometimes death of the trees is occurring in Maryland landscapes. It is mainly trees that were transplanted in the last 3 years or older trees that are being reported with dieback. Three years of summer droughts is taking a toll on these trees. Red oak is often attacked by two-lined chestnut borer, Agrilus bilineatus. Adult beetles have been out since July and are just finishing up flight activity. Eggs are laid on the bark and larvae bore into the bark disrupting movement of moisture and nutrients through the phloem and xylem as they make mines in the trunk and larger branches. The larvae usually have a one year life cycle but may require two years in some trees. You may notice wet spots on the trunk in August and September of infested trees as the trees try to expel the tunneling larvae. You can use a chisel to open the area and see if a larva is present. The larvae are long, cream colored, and appear legless. The two-lined chestnut borer attacks stressed trees and we have plenty of stressed trees.

Control: Dinotefuron (Safari) applied as soil injection, soil drench or trunk injections are reported to give pretty good control of emerald ash borer, which is another Agrilus species. This might have potential against the two-lined chestnut borer. Susceptible trees can have the trunk treated with Onyx or Astro in June to kill larvae before the get under the bark. Examine for new “D”- shaped exit holes in June next year to determine when adults start to emerge.

Reprinted from the September 5, 2008 edition of the TPM/IPM Weekly Report for Arborists, Landscape Managers & Nursery Managers from the University of Maryland Cooperative Extension.