Japanese Black Pine--Problems

Since the 1940's the Japanese black pine, Pinus thunbergii, has been one of the most widely planted trees in seashore landscapes on Long Island. This evergreen tree has been valued for its ability to withstand salt spray and its usefulness as a windbreak and/or screen. Although it is so widely planted that it seems a natural feature of the landscape, the Japanese black pine is actually an exotic ornamental on Long Island, introduced from Japan and Korea where it is native.

For about the last 10 years, Japanese black pines on Long Island have been dying in relatively large numbers, particularly on the North and South Forks. The trees most susceptible to problems seem to be 15 to 20 or more years in age. Initially the trees which were most often seen dying were those exposed to the harshest growing conditions. Usually they were receiving little maintenance and they were growing in very sandy soils, often exposed to the rigors of a seashore location. There seemed to be a correlation between trees growing in stressful conditions and those that were dying.

BLACK TURPENTINE BEETLE

In the late 1970's, the black turpentine beetle, Dendroctonus terebrans, was discovered attacking Japanese black pines on the South Fork of Long Island. At that time personnel from Cornell Cooperative Extension - Suffolk County and the Long Island Horticultural Research Laboratory in Riverhead developed information and control suggestions for this pest. In more recent years, these beetles have been frequently observed in Japanese black pine on the North Fork of Long Island and further west, at least to the SUNY @ Stony Brook campus. These insects have also been reported on Pinus rigida, the native pitch pine, in a few isolated cases.

The boring of the black turpentine beetles causes resin to flow, harden and produce the characteristic pitch tubes, which are usually seen on the lower 4 to 5 feet of the trunk. The larvae, which feed on the inner bark, may completely girdle the tree.

Although pitch tubes are a good indication of black turpentine beetle attack, they will not be apparent if the beetles have attacked below the soil line, as is occasionally the case. Recently the beetles were found in the major roots of a Japanese black pine on the SUNY @ Stony Brook campus, even though no pitch tubes were visible on the main trunk above ground.

Often a blue-stain fungus, Leptographium sp., is carried by the beetles and introduced into the tree. The killing of cambium by this fungus often magnifies the injury from the black turpentine beetle. Up until recently these two factors have been looked upon as the primary cause for the death of Japanese black pine which were at least 15 to 20 years of age and situated in the often stressful sites of the seashore landscapes. Affected trees would turn a lighter green color, eventually turning brown and dying. This symptom progression would often take place within a few months.

PINEWOOD NEMATODE

The pinewood nematode, which is thought to be native to this country, has recently been identified as another major factor in the death of the Japanese black pine on Long Island. Samples of pine taken from New Suffolk, Springs (East Hampton), Muttontown, Jones Beach and Orient State Park have been found to contain this nematode.

Pinewood nematodes are microscopically tiny, unsegmented worms, which are carried to healthy pines by an insect vector, a long-horned beetle called a pine sawyer. While the beetle feeds on branches at the top of the tree, nematodes gain entry through the feeding wounds and proceed to multiply and feed within the resin canals of the pine. The population buildup of the parasitic nematodes within the tree results in yellowing and death of foliage of perhaps at first just a single branch. Ultimately the entire tree succumbs. The pine sawyers are attracted to dying (including nematode-killed) trees to lay their eggs. Two years after egg- laying, adult beetles bore out from the dead trunks, leaving 1/4 inch round holes. Their bodies may be contaminated with pinewood nematodes, which will hasten the demise of healthy pines that the beetles feed upon. Note that the presence of pinewood nematodes in a dying tree does not necessarily mean that they caused its death: pine sawyers will also introduce the nematodes as they lay eggs in trees that are already dying from some other agent.

The New York State Department of Environmental Conservation has now stopped growing and shipping Japanese black pine seedlings from the state nursery largely due to the trees' vulnerability to pinewood nematode. At this point they are offering no plant substitute with the characteristics or adaptability of the Japanese black pine. It has been suggested that white pine, Pinus strobus, or European larch, Larix decidua, be shipped to Long Island instead. The white pine, however, does not tolerate salt in soil or salt spray and the larch has been reported susceptible to pinewood nematode.

The real question now is, are pinewood nematodes the real cause of death in the majority of Japanese black pine on Long Island? The importance of this question is due to the fact that there are no known controls for the nematode. On the other hand, arborists have been able to reduce losses of the Japanese black pine to the black turpentine beetles with a combination of timely insecticide sprays and increased maintenance, including quick removal of dying trees and their stumps. Successful control is most likely when an infestation is identified early and when the blue-stain fungus has not been introduced.

Recently we have gone to Orient State Park to look at the Japanese black pine situation in that location. On the majority of pines which had been cut down or were showing symptoms of decline, pitch tubes from the black turpentine beetles were found at the trunk base. Some of the tubes were freshly made this spring, and some were from previous years. At the entrance to the park, many very large trees showing no symptoms are next to trees with fresh pitch tubes. These are showing the classic symptoms of decline and/or dying which have been associated with black turpentine beetle and/or blue-stain fungus. Other trees in the park which show no pitch tubes above ground do have branch-by-branch foliar yellowing symptoms that are typical of pinewood nematode, which has been found in several pine samples taken in the Park. In the Orient State Park site it appears that pinewood nematode and black turpentine beetle are sharing responsibility for death of pines and it would be difficult to determine which has the more significant role.

PINE VOLE

Although probably not the most common cause of Japanese black pine death on Long Island, injury from pine voles, Microtus pinetorum, has also been seen in many landscapes. These rodents feed on the bark of roots and the lower trunk of the trees. This injury can at least weaken and may in some cases cause the death of the tree. Deep mulches or needle litter under trees can hide the network of tunnels and exit/entering holes of these rodents.

CENANGIUM CANKER

In some sites, especially on Shelter Island and Amagansett on the South Shore of Long Island, the Japanese black pine has succumbed to a fungus disease called Cenangium canker. The opportunistic fungus enters branches through wounds and causes at times a significant amount of dieback. Stresses that may make a tree susceptible to infection include drought, wounding, extremely cold weather or hurricane injury. Infection takes place any time between mid-July and mid-September. Clusters of small, brown, cup-like fruiting structures can be seen on branches, in the scars where needle bundles were attached years before.

CONCLUSION

It is obviously wise to start to look for acceptable replacements for the Japanese black pine for Long Island's seashore landscapes. In the meantime it may still be one of the most useful trees for true seashore conditions, where a windbreak is needed. Eventual replacement cost should be anticipated, as older trees appear to be more susceptible to all the known pests. Also, when planting these trees it would be wise to incorporate a maintenance plan that would include deep irrigation during periods of prolonged hot, dry weather. Proper fertilization could also help trees to maintain good health. Avoid unnecessary pruning - let the trees grow to their natural form. Use discretion when recommending or requesting the use of Japanese black pine in the landscape. Unless a true seashore condition exists, it would be wiser to use other plants that will accomplish the same or similar results. Another choice could be Juniperus virginiana, the eastern red- cedar. This tree is native to Long Island and is often found growing in the sandy soils near the seashore. If a tall plant is not needed in a seashore landscape, consider some of the smaller plants that grow well in these sites. Some of these are Myrica pennsylvanica, the bayberry; Prunus maritima, the beach plum; Rosa rugosa, the rugosa rose; or Ilex glabra, the inkberry. Also, encourage native plants to develop in these sensitive areas. They are naturally adapted to these particular sites.

In conclusion, it may not be wise to totally disregard the Japanese black pine when planting a Long Island landscape, but its high susceptibility to fatal insect and disease problems should be taken into account. Landscape designers and architects, horticulturists, as well as the homeowner are all responsible for seeing that the Japanese black pine is not overused in the landscapes that are not in seashore locations.

Prepared by: Margery Daughtrey, Extension Associate-Plant Pathology, Long Island Horticultural Research Laboratory, Riverhead, New York and Thomas Kowalsick, Extension Educator, Cornell Cooperative Extension-Suffolk County.