Japanese 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 alternatives.

Black Turpentine Beetle

The 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.

Pinewood Nematode:

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 healthy ones.

Managing These Pests:

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.

Alternative Trees:

For 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.