Pine Tip Blight
|April 14, 1999|
Although there is not much evidence of plant disease on the Illinois landscapes now, that scenario will change with a few weeks of warm, wet weather. One problem that is evident now is a fungal disease of landscape pines called Sphaeropsis blight (Diplodia blight). We won’t see new infections until the new needles emerge and become infected, but last year’s infection is easy to spot.|
Sphaeropsis affects mostly Scotch and Austrian pines. It infects buds and new needles, causing them to die each year. Needles turn brown, but spots and banding do not occur. The newest spring growth is most susceptible, and summer growth often escapes infection. This perennial tip blight causes dead tips on branches and the development of zigzag branch growth on pine species.
Sphaeropsis also causes a canker (a localized dead area) on stems. This canker is caused by a new pathotype of the same fungus that has developed or moved into central Illinois in the last several years (at least, that is when pathologists noticed it). This phase of the disease causes oozing sap on the stems where infection occurs. If the canker girdles the stem, all growth beyond that point dies. I have not seen the disease kill a tree, but it can make the tree very unsightly and certainly lowers tree vitality.
Although Sphaeropsis blight is most common on mature trees, it can sometimes infect nursery trees. Because shearing practices remove branch tips, the disease is manifested on small interior shoots, on older needles, or as cankers oozing sap on the trunk or major stems. It is extremely important to work with trees only when they are dry. Disinfect pruning tools regularly to prevent spread of the pathogen.
Report on Plant Disease No. 625 describes this disease in great detail. It is a difficult disease to manage. The first step is to prune out all dead wood when the foliage is dry. If you can do this before mid-April, you will reduce the fungal inoculum in the primary infection period. The second step is to rake and remove all fallen needles and cones. Because the fungus overwinters on the cones, remove cones from the tree, if at all possible. Water-stressed trees are thought to be more susceptible, so water the trees in periods of drought that last longer than two weeks. If the trees are large enough and budgets are tight enough, this may be all homeowners can do to manage the disease. There are fungicides that can be used as preventives, but three applications are required and they may have to be repeated annually. The first application is applied as buds first begin to open, and the second is applied when new growth (candles) are half-grown. The last application is made when needles are fully expanded. If you decide to use the sprays, all three applications are necessary. The fungicide will protect the new growth from infection. In central Illinois, the first application is usually made the last week in April or the first week in May. Registered fungicides are listed in the Illinois Homeowners' Guide to Pest Management and the Illinois Commercial Landscape & Turfgrass Pest Management Handbook. (Nancy Pataky)
||Nancy Pataky |