Wednesday, July 2, 2008

Landscape - White Pine Decline

I recently had a call from a landscaper about loss of white pines in the landscape. This is a common occurrence in Kent County. The following is an article that explains why we lose white pines.

White pine (Pinus strobus) is a native forest species with many cultural problems because it is not generally well adapted to landscape use outside its native range with Southern Delaware being out of that range.

White pine decline refers to a combination of environmental stress factors and soil pathogens. White pines are sensitive to heat, soil pH and the compacted soil common in landscapes. White pine is also one of the tree species most sensitive to air pollution damage. Low levels of sulfur dioxide, ozone, and fluorides will lead to needle chlorosis and tipburn. The older needles (two to three years old) will often fall off prematurely.

The white pines available from nurseries have been grown originally from seeds. Due to the natural genetic variability found in seed grown trees, individual white pines will differ greatly in their adaptability to landscape conditions. In other words, a planting of white pines, all from the same nursery, will frequently have some trees declining and the rest doing well.

White pine decline in landscapes has been the subject of several recent research projects. It has been determined that summer temperatures above 75° F, salt spray, and disturbed soil profiles (poor drainage) are serious stresses on white pine. In addition, white pine is subject to a greater array of diseases than any other North American tree species. White pine root decline, caused by the Verticicladiella procera fungus, is often associated in the death of weakened pines. This disease in its later stages produces an obvious canker at the trees base covered with bleeding white sap.

Mulching around white pines and watering deeply once a week during hot spells is recommended. A fertilization and pest control program should also be established. Soil pH should be maintained between 5.2 and 5.6 and micronutrient deficiencies (such as iron) should be corrected. Soil compaction can be mitigated with a variety of soil aerification procedures.

Declining white pines will frequently die, even with the best of care. When this happens the following is recommended: I. Do not replant white pine in the same location. II. Replant with a tree species known to have tolerance to landscape conditions in your area.

Conifers (evergreens) adapted to replace declining white pines include:

Pitch pine (Pinus rigida) or Virginia pine (Pinus virginiana)
Cedar of Lebanon (Cedrus libani)
Deodar Cedar (Cedrus deodara)
Japanese cryptomeria (Cryptomeria japonica)
Norway Spruce
Eastern Red Cedar

If white pine must be used in the same location, select a locally grown tree (this will be better adapted to your conditions). Plant in the fall or early spring, avoid late spring and summer planting.

Adapted from "Cultural Problems of Eastern White Pine" by Bruce R. Fraedrich, Ph. D., Plant Pathologist, Bartlett Tree Research Laboratories, Charlotte, NC

No comments: