black pine (Pinus thunbergii) has long been a favorite in
coastal plantings because of its excellent salt spray and soil salt
tolerance and its function as a wind screen and 'backbone' evergreen.
But in the last few years, it has been showing up in plant clinics
across the region far too frequently to be considered a sustainable
plant. In this fact sheet we examine the pests responsible for the
decline of the Japanese black pine and explore more sustainable
main pest causing Japanese black pine to die in large numbers is
the turpentine beetle (Dendroctonus terebrans) which frequently
carries with it the bluestain fungus (Leptographium spp.).
These beetles typically feed on the inner bark of the lower four
feet of the trunk and may even girdle the tree. Characteristic signs
of turpentine beetle injury include long clumps of hardened sap
around the lower trunk and reddish sawdust around the very small
entry holes. In addition, the introduction of the bluestain fungi
can destroy cambial tissue and compound the injury caused by the
beetles. A pine affected by this pest complex will show a yellowing
or rusty browning throughout the entire tree before the foliage
begins to die and needles begin to drop, often within the year.
The small black beetle (about 3/8 inch long), primarily attacks
Japanese black pine, but also attacks Austrian pine (Pinus nigra
var. austriaca), pitch pine (Pinus rigida), Scots
pine (Pinus sylvestris) and even the occasional spruce. They
lay their eggs in galleries under the bark and larvae feed gregariously
on the inner bark. Old, slow growing or weakened trees are most
susceptible to invasion, as beetles are attracted to volatile chemicals
released by these hosts. All sorts of stresses including grade changes,
soil compaction, mower damage, and moisture stress can predispose
individual trees to attack.
Another pest equally capable of killing these pines is the pinewood
nematode (Bursaphelenchus xylophilus). This nematode is transmitted
by certain beetles of the long-horned borer family (Cerambycidae)
which feed on healthy trees and breed in dying trees or logs.
The nematodes enter through feeding wounds, reproduce quite rapidly,
feed on the tree from the inside out, and cause localized foliage
dieback before the tree quickly begins to yellow, wilt and die.
Trees can often die within months of initial nematode infestation.
Again, stressed trees seem to be more susceptible to attack than
Once trees are attacked, it is quite difficult to control these
pests. If you catch the beginnings of beetle injury early enough
and before the introduction of bluestain fungi, well-timed insecticides
may be effective. As this often involves fairly toxic chemicals
and direct injection into the tree, we recommend this option only
for trained and licensed arborists. You may enhance the survival
potential of your Japanese black pines by watering them deeply during
dry periods, fertilizing correctly once a year, and avoiding unnecessary
pruning/wounding of the trees.
now, we recommend caution in planting Japanese black or Austrian
pines. If you live away from the coast, you could save yourself
maintenance headaches by planting any of a number of other more
sustainable evergreens. If you live on the coast, your choices for
salt-tolerant wind screens are limited. For coastal areas, you could
also plant Eastern Red Cedar (Juniperus virginiana), though
its texture and form are quite different from pine. Landscapers
are experimenting with Leyland cypress (x Cupressocyparis leylandii),
Southwestern white pine (Pinus strobus) and Bosnian pine
(Pinus heldrechii var leucodermis) The greatest attraction
to Japanese black pine in the northeast is its salt-tolerance. Yet
it seems to be more susceptible to disease in salty environments.
Finding a substitute for Japanese black pine in coastal areas is
a top priority in the URI Sustainable Landscapes Program. As we
develop new recommendations, they will be included in our updated
Sustainable Plant List, which is available from the URI Cooperative
Extension, accessible on the web at http://www.uri.edu/research/sustland/
or available in PDF format through the GreenShare
Factsheet on Sustainable Trees & Shubs.