Extension Educator, Horticulture
It's an old storyline. We exchange mass plantings of one tree for mass plantings of another. We never seem to learn that diversity is important. Over the last years Scotch pines have been dying from pine wilt disease so people started planting white pines since they are reportedly resistant (although not immune) to pine wilt. Mass plantings of white pine may be catching up with us.
Over the last few years, I have had more calls about dying white pines. As Nancy Pataky, director of the Plant Clinic, reported in the May 16 issue of the University of Illinois Extension Home, Yard and Garden Pest Newsletter she also spends a great deal of time diagnosing white pines.
So is there now some dreaded infectious disease or insect ravaging white pines? It appears not.
Unlike other pines, white pines don't seem to get needle blights. Although white pines can get the fungal disease white pine blister rust, it is rare in Illinois. So if white pines don't get the usual pine problems then why are so many white pines in Illinois dying or growing poorly?
Reported symptoms include pale needles, an apparently sudden decline of the tree, death of trees in the midst of other healthy white pines, spongy bark, and no signs of any pathogens or insects. In fact, many homeowners report that nothing has changed in their established landscape that might cause tree decline.
In all cases where Pataky has been able to get to the roots of struggling trees, she finds no new white root tips, few root hairs, and an outer cortex that easily pulls off the roots. The trees are dying because the roots are dying. However, as far as Pataky has been able to determine in the lab, this is not a primary root rot disease problem. The vast majority of white pines that she sees in the Plant Clinic are not infected with a root rot pathogen.
As Pataky reports, much of the white pine problem appears to involve the site, the environment, and species requirements. 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. If roots were injured, they will not be able to absorb enough water in drought-stress situations.
Because these problems in white pine are not usually the result of an infectious disease, immediate removal of the still struggling tree is not necessary. Here are suggestions for caring for white pines. Watering during dry periods can help along with mulching with 3–4 inches of a natural mulch over the root system. However keep in mind in unhealthy trees without adequate root mass, plants will not be able to use the available water quickly enough to replace what is used by the foliage. The result will be sudden browning of foliage or off-color needles and death of branches. Fertilizing with an acidic fertilizer specifically packaged for pines or acid-loving plants may also help.
For some great looking plants, check out the U of I Extension Master Gardener Garden Walk on June 17. Contact the Extension office at 801 North Country Fair Drive in Champaign, 333-7672 or area garden centers for tickets.