Sphaeropsis tip blight and canker is a disease of Austrian and Scotch pine that has been around for many years in Illinois. The most common symptoms of this disease are blighting of the branch tips and death of lower branches. It tends to be more of a problem in years when we have lengthy, cool, and wet spring weather. Under these conditions, the fungus (Sphaeropsis sapinea) infects immature candle and needle tissues, which is why we see the typical blighting of branch tips. To diagnose the tip-blight phase, collect several brown needle clusters from several shoots that died last spring, then use a hand lens to examine the basal 1/2 inch or so of the needles. Look for tiny, black, pinhead-sized fruiting bodies of the fungus. You can often “trick” the fungus into producing these fruiting bodies by placing diseased shoots in a plastic bag for 24 to 48 hours with a damp paper towel. Keep in mind that these fruiting bodies may not show up in freshly killed shoots. The combination of tip blighting and these fruiting bodies is enough evidence to implicate Sphaeropsis blight. If necessary, laboratory confirmation is quick and easy. For more details about this disease and how to iden-tify it, consult Report on Plant Disease No. 625.
With the dry weather so far this year across much of the state, experience tells us that it should be a fairly uneventful year in terms of foliar diseases. To some degree, this statement should hold true for Sphaeropsis tip blight and canker. While we may not see as much of the typical new shoot infections as we have in the past few years, a very dry summer may stress the trees to the point where we see more cankering than normal. Research and experience tells us that Sphaeropsis can be quite damaging to trees that are stressed by drought, compacted soils, root injury, and other factors. Under stressful conditions, Sphaeropsis has the ability to invade older branch tissue and cause girdling cankers. As a result, you may see twigs or entire branches dying rather than the typical tip blight. In the last 2 or 3 years, we have seen an increase in Sphaeropsis canker at the clinic. Similar to Cytospora canker on spruce, you should notice at least some white, caked resin associated with Sphaeropsis cankers. This resin can also indicate a wound caused by a variety of insects and animals, so investigate carefully.
Researchers consider the fungus Sphaeropsis sapinea to be somewhat of an opportunist. This means the fungus is kind of weak but can easily overcome the defenses of a stressed host plant. Furthermore, we now know that there are two distinct types of the same fungus—type A and type B. Type A is more aggressive and is reported to be far more common in Wisconsin and several other states. This all boils down to the fact that we have a complex fungus that can cause disease on healthy new shoots in wet springs and on older tissue during drought conditions. In Illinois, Austrian and Scotch pines are most commonly infected, although almost any stressed conifer should be considered susceptible to infection.
Short-Term Management. As of May 3, many of the Austrian pines in Champaign, Illinois, have new candles that are 2 to 3 inches in length. At this point, you can see the succulent green candle tissue with needles that are just about to break through the papery fascicle sheath. For trees plagued by Sphaeropsis from previous years, making the first fungicide application of the year at this point would be ideal, particularly since we’ve had some rain already and the forecast calls for a bit more. Warmer weather to the south and in other parts of the state has certainly pushed growth along much further. For those who have already made the first or second application, you may be wondering if a second or third application is needed. The answer largely depends on the weather in your area. Keep in mind that the fungus is most damaging to new shoots under moist conditions and that new candles and needles are most susceptible during a 3-week period following bud break. Reports from researchers and practitioners in Illinois and neighboring states indicate that thiophanate-methyl (active ingredient) is an effective systemic fungicide and that chlorothalonil is acceptable as a contact-type fungicide. Registered fungicide options are listed in the Illinois Commercial Landscape and Turfgrass Pest Management Handbook 2000. Homeowners can check the listings in the Illinois Homeowner’s Guide to Pest Management.
Long-Term Management. There is no research to support the use of a fungicide beyond springtime to protect a stressed tree from Sphaeropsis cankers. Similarly, we don’t recommend any sprays to manage Cytospora canker of spruce. Your best option is to do what you can to reduce the local inoculum (spores) and prevent excessive stress on the tree.
Diseased branches, branch tips, and cones all contribute to future infections. Prune diseased branches 6 to 8 inches below the point where they are obviously infected. This is best done in the dormant season but can be done at other times when the fo-liage is dry. Dip your shears in a 10% bleach or 70% ethanol solution between cuts to reduce the chances of infecting healthy tissue. Cones are the next target for control. Take a close look at some fallen cones or older cones still attached to the tree, and you’ll probably find that they are loaded with the same fruiting bodies described above; this is a major source of spores for new infections. Pick up the fallen cones and, where practical, remove them from the tree.
Doris Taylor of The Morton Arboretum recently provided some advice about establishing effective watering habits (“Drought Stress,” The Plant Health Care Report: The Morton Arboretum, April 1-7, 2000, Issue 2000.02). This, and the above advice, should go a long way toward reducing disease potential and eventually improving the look of your pines:
- Because root systems of established plants are wide spreading and deep, it is vital that enough moisture be applied to reach them. Established trees and shrubs should be watered deeply every 10 to 14 days during dry periods.
- Irrigate slowly so water percolates down into the soil. Know your soil. Observe how quickly soil dries out after a rain or watering.
- During late fall, water trees and shrubs well, especially evergreens, when soil moisture is low.
- Mulch plants with a 3- to 4-inch layer of organic mulch (wood chips, shredded bark) to reduce soil evaporation and temperature fluctuations and to conserve moisture.
- Do not fertilize unless adequate irrigation is available.