Illinois plant specialists, nurserymen, landscapers, and home owners have been reporting stressed white pines in our landscapes for many years. The drought experi-enced over the last 6 to 9 months has aggravated the situation. In fact, we are now seeing stress on a number of other evergreen species, in addition to white pine. We have seen similar problems on spruce, pine, and arborvitae trees.
Symptoms vary but generally include some pattern of needle yellowing or browning; shriveled bark on branches or trunk; sap exudate on branches or trunk; and, in some cases, death of the tree. The most severe injuries continue to be reported on white pines. Af-fected trees have ranged in size from 2 feet to more than 20 feet. On pines tested in the last few years at the Plant Clinic, few live white roots have been found. Although roots are dead, laboratory cultures have not implicated fungal pathogens as the cause of poor root growth. It appears that roots are on the decline for other reasons. Some possibilities include heat, drought, flooding, and sudden extremes in temperature and moisture. 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). It is likely that site stress has contributed to the decline of these trees. The excessive rains of the last several springs also may have contributed to root injury and decline by saturating the soil, causing a lack of soil oxygen and root death. Soils with high pH levels are also known to be stressful for pines; and Illinois soils typically test high in that regard.
Evergreen needles continue to lose moisture all winter, so they are more susceptible to winter drought stress than are deciduous trees. Because of this winter drought stress, we can expect to see more pine problems this year. If roots were injured as we are suggesting, watering will help but will not provide immediate relief. Without an adequate root mass, plants are not able to use the available water quickly enough to supply demands by the foliage. Use of a natural mulch over the root zone may help to maintain a more uniform soil moisture and temperature. Still, if enough root damage has occurred, the plants will continue to decline despite your best efforts.
Because these pine problems are not usually the result of an infectious disease, immediate removal of the tree is not necessary. Instead, keep the tree watered and see how it responds. Also, dig 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.
There are a few other problems that can mimic root injury and drought stress on pines. The one-sided burn seen on evergreens along roadways is often the result of salt injury from the mist created by traffic over salted roadways. A scattered browning of branches could be due to a fungal canker disease, fungal tip blight, insect damage, or mechanical injuries. Sudden death of entire Scotch or Austrian pine might indicate infection by the pinewood nematode. As with all diagnoses, it is important to look at the overall pattern of injury in the neighborhood or field as well as the pattern on the individual tree.