Pines are beginning to show some healthy new growth in Illinois. If you have seen spotting or blighting of older needles in the past, you might need to take action now to protect the healthy new growth. Here is some information on common Illinois pine needle diseases. You can get more from Report on Plant Disease, no. 624, “Needle Blights and Needle Casts of Pines.” This report is available on the Web at http://www.ag.uiuc.edu/%7Evista/horticul.htm or in your local Extension office. Needle cast usually refers to diseases that cause needles to drop early. Needle blights cause death of needles and stems and allow brown tissue to remain attached to the stem for at least part of the growing season, giving the blighted look.
Two of the most common look-alike 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.
Dothistroma needle blight occurs most often on Austrian pine in Illinois. The fact that Scotch pine and red pine are resistant makes 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 fall, 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. The pattern of infection helps considerably in diagnosis.
Brown spot needle blight appears nearly identical to Dothistroma blight. Because chemical options differ, you do need to distinguish between the two. Brown spot infects Scotch pine most readily in Illinois. 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 the time of planting.
Fungicides may be used to prevent infection of new growth, especially on trees with chronic needle blight. Choices are listed in the Illinois pest management guides. 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.
In the home landscape, some control may be attained by removing fallen needles and helping tree vitality through fertilization and watering practices. For both of these fungal needle blights, control measures are most successful 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, no. 624, available in Extension offices or on the Extension Vista Web site.
Sphaeropsis blight may be the most common pine blight in Illinois. The disease affects needles, stems, and cones, causing tip blight, branch death, and severe aesthetic decline of an infected tree. Sphaeropsis was discussed in issue no. 3 of this newsletter.
Two needle cast diseases we see in Illinois are Cyclaneusma needle cast and Lophodermium needle cast. The first is primarily a problem on Scotch pine. The latter infects Austrian, red, and Scotch pines. Neither is a big problem on landscape pines in Illinois but can be problems in Christmas tree plantations.