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White Pine Decline
Martha Maletta, RCE Hunterdon County

Lots of white pine samples arrive at the Rutgers Cooperative Extension Garden Information Center every year. Is there one particular problem with white pines in Hunterdon County? No. White pines have been turning up with a variety of problems. Some, such as pine needle scale, pine sawfly, spittlebug, pine bark adelgid, white pine weevil can either be controlled or are not serious problems. But, when people report, as has been the case in recent years, that white pines are dead or dying, it's another matter. The possible causes are many and can be complex.

In 1988, researchers at Virginia Polytechnic Institute reported on their investigation of white pine decline, the slow or rapid white pine death that had been observed and investigated for many decades. They suspected and confirmed through their study that the decline was associated with a number of tree stress factors. Trees of various ages on "human-altered" sites exhibited dramatically poorer health than trees in a "natural" habitat.

Specific conditions accounting for poor health were: competition from turf and detrimental effects of standard turf management practices - liming, mowing, fertilization; heavy soil texture and disturbed soil conditions; pH averaging almost 7 and, in many

cases, much higher; compacted soil both above and below root zones; physical limitations on root growth due to site conditions and/or planting methods. Poor soil conditions were due mainly to construction activities, which brought subsoil to the surface or removed top layers and/or mixed them with subsoil. Mechanical and chemical damage to the top portion of trees were also cited. Once the trees' decline was underway, a number of pests were identified as compounding the problem.

Over the years, white pines have suffered various other stresses in New Jersey. In the early to mid-eighties, Rutgers Specialists attributed many white pine problems to moisture extremes. In 1986 problems were attributed to several stress factors including drought, poor site, soil compaction, recent construction and transplant shock. In 1988, heat and drought related problems predominated. The 90's have seen several seasons of moisture extremes and 1999 looks to be a continuation of the recent dry weather pattern. Site-related and environmental stresses likely account for much of white pine decline and death in our area. In many cases the trees finally succumb to boring insects that attack declining trees.

Declining white pines typically exhibit a number of symptoms, which, in early stages, may not attract attention. These include: pale and/or yellow color compared to healthy trees; shoot length and needles shorter than normal; needle tips may brown; needle drop, normal in fall, occurs earlier than usual; sparse tree canopy; needles droop (winter, especially); shoot bark wrinkled. Direct evidence of borer infestation includes resin - fresh or dry - on trunk associated with holes that may be as small as pin head size; tunneling patterns in wood under the bark; oval cavities filled with wood fiber under bark; white larvae present under bark; tiny red-brown, brown to black beetles present under bark

While boring pests tend to attack trees under stress and declining due to conditions such as those mentioned above, newly transplanted trees may also be damaged. Apparently healthy trees may also be attacked when pest populations build up in a planting. If boring pests are found in recently dead or dying white pines and other white pines are nearby, some steps can be taken to prevent decline and borer damage.

Clearly the best approach is to avoid the problems in the first place by planting white pine on suitable sites: deep, well drained, moderately acid soil that is in good health; full sun; plenty of space for root and top growth. Proper care after planting and beyond is also important in preventing decline and borer damage: water; fertilize; mulch; avoid physical damage.

For trees already in decline, identifying the probable cause or causes is an important first step. If unsuitable conditions, such as poor soil drainage, exist, the condition will need to be corrected. When this is not possible or practical, then choosing different tree species may be the only solution. Some conditions contributing to decline - soil pH, soil fertility - can be corrected. Drought should be avoided. In a year like this one, that can be difficult, even impossible.

When trees are infested with borers, it is important to identify the borer. The white pine weevil that kills the leaders of trees does not pose the same hazard as other boring pests that attack the trunk and branches of white pine in New Jersey. These other beetles, many of which are very tiny (less than 1/16 inch), feed under the tree bark destroying critical tissue. Unfortunately, these borers in trees are not susceptible to insecticide treatments. Trees killed or heavily damaged by these borers should be removed and destroyed.

Insecticides are useful, however, in preventing borers from invading trees, but they must be applied at the right times to be effective. The right time depends on the particular borer being controlled. This is why identification of the pest is important. The presence of holes, even very tiny ones, in the bark is a clear sign of borers. The culprit may be apprehended by carefully removing bark in the vicinity of the holes.

Residents can submit insects collected from recently dead or dying pines to the Rutgers Cooperative Extension Garden Information Center in the Extension Center on Route 31 for initial evaluation. Then, if a definitive identification is needed, they will be referred to the Rutgers Plant Diagnostics Lab. Once the pest is identified, control recommendations can be made.

In cases where a number of trees are involved or at risk, an on-site evaluation by professionals is probably warranted and strongly suggested. Many New Jersey Certified Tree Experts offer insect and disease inspection and diagnostic services. As a public service, a list of New Jersey Certified Tree Experts covering Hunterdon County is available from Rutgers Cooperative Extension of Hunterdon County. Send a SASE to 4 Gauntt Place, Flemington, NJ 08822.

 

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