We expect to see another banner year for Sphaeropsis blight of pine. The injury seen so far in 1998 is last year’s damage, but be ready for this perennial problem. This disease of pine has been quite devastating the last several years. The fungal pathogen thrives in cool, wet weather and often invades injured wood. We have experienced lengthy, cool, and wet spring weather for the past two years, and winter freeze-thaws have been common. Ideal weather conditions, plenty of fungal inoculum, and susceptible pines have set the stage for Sphaeropsis blight. We see most problems on Austrian and Scotch pines, but other pines are susceptible. The disease may even occur on some fir and spruce species.
The fungus (Sphaeropsis sapinea) infects young, healthy, unwounded needles of new candles (new growth), which is where we see the typical blighting of branch tips. All needles in the terminal six inches or so of growth turn brown and dry out. This phase of the disease is unsightly but does not cause branch death. Usually the tree develops new growth below the dead area and results in the crooked-looking branches so typical of Austrian pine. The fungus may, however, also infect the twigs of trees weakened by stress (such as drought, compacted soil, root injury, hail, or winter injury). Cankers develop on the twigs, usually causing noticeable sap exudate at the canker. When the canker girdles the twig, tissue beyond that point dies. In the last two or three years, we have seen an increase of Sphaeropsis twig blight at the clinic.
This disease is difficult to control. In fact, even the best efforts do not always give 100 percent satisfactory results. The first step is to recognize the disease. Look for black, pinhead-sized fruiting bodies of the fungus in the brown needles at the tips of branches. The combination of tip blighting and these fruiting bodies is probably enough evidence to implicate Sphaeropsis blight. If necessary, laboratory confirmation is quick and easy.
Next, remove all dead wood (or as much as possible) from the tree. This is best done in the dormant season but can be done at other times when the foliage is dry. Cones are the next target for control. You will find hundreds of the black fruiting bodies of this fungus on cones, which serve as a major overwintering site. Remove cones from the tree and the surrounding ground.
We don’t always advocate fungicide sprays for disease control, but in this case chemicals are necessary for near-complete control. Three sprays are recommended: one at budbreak, one at half-candle elongation (about 10 to 14 days after the first spray), and another at 10 to 14 days after the second spray. Chemical options are listed in the Illinois Commercial Landscape and Turfgrass Pest Management Handbook, 1998-1999. Homeowners can check the listings in the Illinois Homeowners’ Guide to Pest Management. For more details about this disease, consult Report on Plant Diseases No. 625.