Nursery growers have been struggling with ambrosia beetles for decades. In the southeast it is
Scopes-eye view of camphore shot borer fresh from a trap mixed in with granulate and other ambrosia beetle species. Photo: Andrew Ernst, NCSU.
primarily the granulate ambrosia beetle, Xylosandrus crassiusculus. In the Northeast and Midwest the predominate species is Xylosandrus germanus. These are tiny beetles that make tiny albeit lethal holes in trees.
In the past several years a new species has been detected in several states including Florida, Tennessee, North Carolina, and just last month Virginia. This is the camphor shot borer, Cnestus (used to be Xylosandrus) mutilatus, and it is BIG. At least by ambrosia beetle standards this one makes holes as big as a pencil instead of then tiny 2mm holes made by other species. You can find out all about it in a thorough publication from University of Tennessee.
We trap at 5 -10 nurseries every year around Johnston County, North Carolina. In 2011-2013 we captured 1 or 2 camphor shot borers each year. This year we captured about a dozen from at least 3 different nurseries. So it is here to stay and will probably become more of a problem over time.
Camphor shot borer in a twig photographed by Matt Bertone, NCSU.
This time of year arborvitae plants may get a little shabby. Many branches get short brown
Damaged tip from arborvitae leaf miner. Photo: SD Frank
tips. Other branches may turn brown and just hang on the plant. Arborvitae leaf miners, Argyresthia spp., are tiny moths responsible for brown tips. Moths lay eggs on new growth which is why the tips of plants are damaged. Larvae burrow into leaf scales and mine foliage as they feed and develop.
Larvae overwinter in the mines and resume feeding in spring. Damage is most evident in winter and early spring so the damage you see now is likely from mines initiated last year. Mines can be differentiated from other damage by looking for exit holes and by opening damaged tips to look for larvae.
If you have larger brown branches that are hanging, barely attached to the tree, you
Flagging branch from bark beetle feeding. Photo: SD Frank
probably have damage from Phloeosinus spp. bark beetles. Commonly called cypress bark beetles, eastern species attack arborvitae. These beetles chew branches 15-30 cm from the tip making a groove or short tunnel that weakens the branch. The branch then breaks easily in the wind and turns brown, a condition called flagging. You can look for the hollowed end of branches you suspect were damaged by these beetles.
Sadly, thousand cankers disease has been confirmed in the Great Smoky Mountains National Park in Haywood County. This disease has been present in Tennessee since 2010 so it was only a matter of time. This disease is caused by a fungus carried by walnut twig beetles. It is native to the southwest US and Mexico where it feeds on a different walnut species. Infected trees die in just a few years. You can read more on the NCFS alert. There has been a quarantine on the movement of walnut into North Carolina from infested areas. Now there is an additional interior quarantine limiting movement of walnut wood out of Haywood Co. I will post more later on the biology and damage of this disease.