Many of us fight this chronic fungal disease of pines. Sphaeropsis causes tips of branches to die. The needles in the terminal 8 inches or so of the stem are entirely brown. Often, there are large, sappy cankers on the stems that may girdle and kill tissue beyond the canker. The canker phase can be particularly damaging to plant growth and to tree aesthetics. We discussed the disease in issue no. 1 of this newsletter. At that time, we were looking at last year’s infection and damage visible in the spring. The fungus infects new needles in the spring and early summer, so recommendations were made in issue no. 1 to help prevent problems again this year.
Now we are seeing this year’s new infections on the current season’s growth. Look for brown needles at the tips of branches. At the base of these needles, you will see black, pinhead-sized fruiting bodies of the fungus. Pull needles out of the basal sheath and look for fruiting bodies at the base of the needles. If the weather has been particularly dry, the fruiting bodies may not be seen easily. Place some needles in a plastic bag with a wet paper towel, seal it up with a twist-tie, and examine the needles the next day. The fruiting bodies should be visible after 24 hours in this humidity chamber. The needle blight phase of this disease is most intense in years with a lengthy cool, wet spring.
As with any fungal canker, Sphaeropsis canker infections are related to stress. In fact, drought-stressed trees have been shown to be more susceptible to this disease. Watering your pines in times of extended drought stress is one of the most critical actions you can take to avoid this disease. Most cankers are problems on injured trees as well. The sudden temperature drop last December caused some plant injury and may have predisposed pines to this canker disease. In Illinois, Sphaeropsis blight is found most frequently on Scotch and Austrian pines. It may also occur on red pine, mugo pine, Ponderosa pine, eastern white pine, Douglas-fir, true fir, or spruce. Refer to issue no. 1 for management options, and mark your calendar now to remember when to treat.
For more on Sphaeropsis blight, consult Report on Plant Disease(RPD) no. 625, “Sphaeropsis Blight or Diplodia Tipblight of Pines,” available on the VISTA Web site at http://www.ag.uiuc.edu/~vista/horticul.htm or in your local Extension offices.