Two of the most common needle blights of pine are Dothistroma and brown spot. Both are caused by fungi that thrive in wet weather; and both prefer succulent new growth. Scout now for these diseases. You will definitely have some trouble telling the two apart, but the following should help.
In Illinois, Dothistroma needle blight occurs most often on Austrian pine. Scotch pine and red pine are resistant, making diagnosis much easier. Dothistroma causes reddish brown spots and bands on the needles, with infection most intense in the lower part of the tree. As the disease progresses, needle tips turn brown and drop, leaving the live, green needle base. Early defoliation may occur in spring and summer. Do not confuse these symptoms with salt burn or scorch, which causes needle tips to turn brown on the exposed side of the tree. Dothistroma is worse in more humid areas of the tree and shows definite spots and bands on the needles, not just brown tips.
Brown spot needle blight appears nearly identical to Dothistroma blight. Because chemical options differ depending on the disease, you need to distinguish between the two. Brown spot infects Scotch pine most readily in Illinois. Remember, Scotch pine is resistant to Dothistroma.
In both cases, cultural controls to promote more rapid drying of foliage may help. Suggestions are to prune overgrown plants in the area, control weeds, and use proper plant spacings at planting.
Fungicides may be used to prevent infection of new growth, especially on trees with a chronic needle blight problem. Choices are listed in the Illinois pest-management guides. Remember to look at the end of the disease chapters for information on mobility of the chemicals listed. Applications of fungicides are made when needles are half-grown and again 30 days later. First applications should be made now.
In the home landscape, some control may be at-tained by removing fallen needles and helping tree vitality with fertilization and watering. For both of these fungal needle blights, control measures are most suc-cessful when cultural controls are begun as soon as the disease is identified, with chemical controls started the following spring. For more information on pine needle blights, consult Report on Plant Disease (RPD) no. 624, available in Extension offices or on the Extension Vista Web site.