|It's not always easy to tell why trees start to decline|
White pines are native to western North Carolina so you'd think they'd have fewer pest problems. A fast growing tree, most people view white pines as being a lot 'tougher' than Fraser fir. After all you can plant white pines where Frasers have died from Phytophthora root rot and they will most likely survive, even though they are also susceptible to the disease. But white pines do have pest problems and are sensitive to poor sites which, unfortunately, are often associated with loading yards.
Recently, Brian Heath, Forest Health Specialist with the NC Forest Service, helped me walk through a local loading yard that utilized white pines for shade. We discussed some of the pest issues that face these important trees and what a grower can -- and more often cannot -- do about them.
|White pine aphids|
|Tree with pine bark adelgid|
White pines grown for Christmas trees or nursery can suffer from several pests such as pine needle scale, introduced pine sawfly, rust mites, white pine aphids (a species of Cinara aphid), weevils including white pine weevil and Pales weevil, and needle blights including ozone injury, but these problems are primarily cosmetic and will not affect trees being grown for shade.
|Introduced pine sawfly|
STRESS THE MAJOR ISSUE: When it comes to loading yards, it is stress that is the primary cause for concern. Stressed trees attract pests like bark beetles and are more likely to succumb to other pests that usually aren't a problem. The stress, however, is the underlying factor.
White pines in the mountains typically grow on stream banks in areas that are well drained. They grow well on poorer. sandier soils where they can out-compete hardwoods. They do best when planted in undisturbed forest soils. But most loading yards are on level ground that used to be a field or are near a building site. This past soil disturbance affects white pine growth. They may grow well for 20 years, but then often start to decline for no apparent reason. If planted on forested land, those same trees would live as long as 200 years.
Stress continues in the loading yard. Soils are compacted with equipment movement, and trees may be injured by equipment or deicing salt. If the ground is watered to keep cut Christmas trees moist, the white pine roots may stand in water.
Cutting pines adjacent to white pines in a loading yard can also bring in a host of problems such as more bark beetles and weevils. In addition, Annosum root rot will infect cut stumps and grow along the roots into adjacent, living trees -- even Fraser fir.
|Bark beetles attacked this tree because|
it was under stress.
In the loading yard that Brian and I visited, we found black turpentine, Ips and sawyer beetles, pine bark adelgid, and evidence of injury from road construction and/or salt injury. But many symptoms of decline couldn't be pinned down to a specific problem. Procera root rot is also a common disease found on white pines growing in fields, but was not observed at this particular site.
KEEPING WHITE PINES HAPPY: The best possible set up for a loading yard is to put it to the south of a bank planted in white pines. Setting the white pines on undisturbed soil and allowing no traffic on the roots will greatly reduce stress to these trees.
Tree spacing is another issue. You might want to initially plant trees every 6 feet, but they should be thinned to 12 or more feet apart as they get larger. If you are planting two or more rows on a bank, they should be thinned to around 20 feet apart.
|Trees growing too close together will experience more stress|
Setting up two loading areas that you could rotate between every 10 years would be the ideal situation but replanting in an existing loading yard is the only option most people have. Just realize that survival may be low. Plant more trees than necessary to replace declining trees, but thin out trees as they get older to 12 or more feet apart.
And don't become too concerned if trees start to decline. That is to be expected. There really isn't any need to treat the trees for incoming pests, the best thing to do is keep them as stress-free as possible.
READ MORE ABOUT IT:
US Forest Service -- Eastern White Pine
White Pines for Windbreaks
Procera Root Rot of White Pine
Pine Bark Beetles