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White Pine Decline

May 26, 2004

Did your white pine suddenly turn brown and die? Was it an established tree? Do other white pines nearby appear healthy? You are not alone. This condition, dubbed white pine decline, usually becomes evident each year following a period of hot weather. With the early-season high temperatures in Illinois already this year, white pine decline has become evident.

Symptoms vary but generally include some pattern of needle yellowing or browning, shriveled bark on branches or trunk, sap exudate on branches, and, in some cases, death of the tree. Affected trees have ranged in size from 2 feet to more than 20 feet. Keep in mind, however, that this is a problem on established trees rather than new transplants.

The Plant Clinic staff has assayed samples for the presence of pinewood nematodes; cultured for fungal pathogens of needles, stems, and roots; and inspected for insect infestations or injuries. The common factor seems to be root decline. Few live white roots have been found, but fungal pathogens cannot be correlated with poor rooting. It appears that roots are on the decline for other reasons. Some possibilities include heat, drought, flooding, deep planting, and sudden extremes in temperature and moisture.

White pines are understory trees that thrive in the cool, moist, well-drained soils of Wisconsin although they grow with intermittent success in Illinois. Many problem trees we have seen in Illinois have been situated on clay sites or exposed to the elements (planted in new housing developments or used as windbreaks). It is also likely that site stress has contributed to their decline. Excessive rains of recent springs may have contributed to root injury and decline by saturating the soil and reducing soil oxygen.

Look for more white pine problems this year. If roots were injured as we are suggesting, they will not be able to absorb enough water in drought-stress situations. Watering helps, as does the use of natural mulch over the root system; but without adequate root mass, plants are not able to use the available water quickly enough to replace what the foliage uses. The result is sudden browning or off-color needles and death of branches.

Because these problems in white pine are not usually the result of an infectious disease, immediate removal of the tree is not necessary. Instead, try to keep the tree watered and see how it responds. Also, try digging into a bit of the root system for a better picture of the situation. If roots are brown in cross section and the outer layer easily pulls off or is not present, then root injury has occurred. If the roots are white and healthy, then the problem is above ground and our theory is wrong, at least in your case. Check the base of the tree for injury. Dig a few inches below ground around the trunk to be certain the first major root is near the soil surface: This indicates the tree was planted at the correct depth. Make certain there are no girdling roots or mechanical barriers to trunk growth.

Another factor that may be involved in Illinois is soil pH. Our soils have a fairly high pH level, whereas pines prefer more acidic soils. Have the soil pH level tested by a soil-testing lab. It may be helpful to fertilize with an acidic fertilizer specifically packaged for pines or acid-loving plants. Follow the directions so as not to burn the roots by applying too much fertilizer. Fertilization is usually recommended in early spring or late fall.

Author: Nancy Pataky


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