In most cases, plant diseases cannot be managed with curative sprays. Rather, when fungicides are used, they are applied to protect new growth from infection. Management with fungicides is usually focused on preventing infection of new growth on hosts where there has been a chronic problem in the past. Such a disease is Sphaeropsis blight of pine. If you have seen this problem in the past and want to use a fungicide, get ready now because the first application should be made when pine buds begin to swell and elongate.
The disease infects buds and new needles, causing them to die each year. The newest growth in the spring is most susceptible, and growth in the summer often escapes infection. The result is death of branch tips. This perennial tip blight causes zigzag branch growth. Fungicides are applied to protect the new growth as it emerges. Applications are recommended when buds begin to elongate and swell, just before new needles emerge from the sheath, and 10 to 14 days later. These spray application times may also be described as budbreak, half candle, and full candle.
Sphaeropsis also causes a canker on stems. Cankers are caused by a pathotype of the same Sphaeropsis fungus that causes tip blight. We’ve been seeing the canker phase in Illinois for the past 7 or 8 years. The canker phase causes oozing sap on the stems. If the canker girdles the stem, all growth beyond that point dies. Fungicides have not been shown to be effective against the canker phase. I have not seen the disease kill a tree, but it can become very unsightly.
This is a tough disease to get under control. Management of Sphaeropsis blight should include removing dead branch tips now, before buds open. Preferably the pruning should occur in dry weather. Also, remove fallen cones and needles, which serve as overwintering sites for the fungus. Because drought-stressed trees are more susceptible to this disease, water your pines in times of extended drought. Fungicide options are listed in the Illinois Home-owners’ Guide to Pest Management (upcoming Home, Yard, and Garden Pest Guide) and the 2001 Commercial Landscape and Turfgrass Pest Management Handbook. Refer to the tables at the end of the disease chapters. Bruce Paulsrud (pathology pesticide applicator training specialist) has prepared information on trade names, common names, mobility, and producing companies for fungicides listed in the chapters. Reports from several Illinois applicators suggest that chloro-thalonil or thiophanate-methyl works well if three sprays are used. If you decide to use fungicides, all three applications are necessary with any of the product selections. Spraying only once is of little or no benefit. For details about Sphaeropsis blight and how to confirm disease presence, consult Report on Plant Disease (RPD) no. 625, “Sphaeropsis Blight or Diplodia Tipblight of Pines,” available in Extension offices or on the Web at http://www.ag.uiuc.edu/~vista/horticul.htm.