We are seeing a resurgence of white pine problems at the Plant Clinic and in the field. This is not a new situation but one aggravated by the long drought this summer. It all goes back to root damage, so we see increases in white pine decline after heavy rains or after a long drought. Because we had both this spring and summer, I suspect we will all see more white pines dying, seemingly all at once. In fact, roots have probably been declining for many months. The trees reach a point of no return (permanent wilting), and symptoms appear to happen overnight.
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 range in size from 2 feet to more than 20 feet. The Plant Clinic 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 only 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, 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 of the problem trees we have seen have been situated on clay sites or exposed to the elements (planted in new housing developments or used as windbreaks). The excessive rains of the past several springs also may have contributed to root injury and decline by saturating the soil and causing a lack of soil oxygen.
What can we do to help these trees? If roots were injured as we are suggesting, they will not be able to absorb enough water if drought-stressed. Watering helps, as does the use of a natural mulch over the root system; but without adequate root mass, plants will not be 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 it watered and see how it responds. Also, try digging into a bit of the root system for a better picture. If the 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.
Another factor that may be involved in Illinois is the soil pH. Our soils have a fairly high pH level, whereas pines prefer more acidic soils. 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. It may be helpful to test the soil pH (use a soil-testing lab) to determine the starting level before you apply an acidic fertilizer. Fertilization is usually recommended in early spring or late fall.