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Why Are My White Pines Dying?

April 28, 1999
We continue to see decline of white pines in Illinois, and I imagine this trend will continue as long as the tree exists in this state. No, this is not an epidemic. It is not even an infectious disease problem. It is a problem directly related to soil type, pH, water, and the white pine species requirements. 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. Over the past 10 years or so, the Plant Clinic has assayed various white pine samples for the presence of pinewood nematodes; has 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 thrive as understory trees 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 (for example, planted in new housing developments or used as windbreaks). It is also likely that site stress has contributed to the decline of these trees. The excessive rains of the past several springs may have contributed to root injury and decline by saturating the soil and causing a lack of soil oxygen. 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 in drought stress 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, the problem is above ground and our theory is wrong, at least in your case. There are two root pathogens that are sometimes associated with this decline, but they are thought to follow the other problems mentioned. Both Phytophthora and Verticicladiella (Procera) have been found on occasion. Fungicides are not recommended because these root pathogens are not the cause of the decline. Another factor that may be involved in Illinois is the pH of the soil. Our soils have a fairly high pH level, whereas pines prefer more acid soils. Start with a soil test to determine the pH level of the soil around your trees. It may be helpful to fertilize with an acid fertilizer specifically packaged for pines or acid-loving plants. Follow the directions so you donít burn the roots by applying too much fertilizer. (Nancy Pataky)
Author: Nancy Pataky


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