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Diplodia Tip Blight on Pines

POSTED May 11, 2018 12:56 p.m.

The last couple of weeks I have received a number of calls about pine trees having dead branches and/or an unusual amount of brown needles. Almost all of these calls were about Austrian pines (Pinus nigra). First, it is important to note that pines go through a healthy, normal process called natural needle drop. You will see this happen every year.
Still further, several pines like the Austrian, though adapted to Kansas conditions, can still suffer from environmental stresses. An example would be like the cold, dry winter we just had. Though the tree may be reacting to this stress, it will remedy itself in a few years if watered and fertilized properly.
However, many pines (and not just Austrian) are susceptible to several diseases, which can cause defoliation, dieback, and even death. One such common and serious fungal disease found here in Kansas is tip blight (Diplodia sapinea). Tip blight is a fungal disease that affects Austrian (P. nigra), Ponderosa (P. ponderosa), Scots (P. sylvestris), and Mugo (P. mugo) pines. The disease is most severe on mature trees (20 years or older). Repeated infections over many years can kill large sections of trees or even entire trees.
Tip blight infection period occurs when the buds start to expand, usually in late April. The symptoms usually start to appear in late May or early June. Wet spring weather increases disease severity. The newly developing shoots (candles) fail to grow. The shoots are stunted, and the emerging needles are stunted and turn yellow or tan. Dried sap (resin) is often found on the dead shoot tips. The damage usually starts in the lower part of the tree and works its way up over several years.
In trees that have been infected for many years, damage is distributed throughout the crown. The disease can also act as a canker, invading older tissues and causing extensive branch dieback. Severe tip blight is sometimes confused with the early stages of another pine disease called pine wilt. (Be sure to understand both diseases and consider submitting a sample for diagnosis if you are not sure which disease is affecting the tree.)
In late summer or fall, the tip blight fungus forms tiny black spore-producing structures (called pycnidia) on the scales of 2-year-old cones, as if black pepper has been shaken on them. The same black specks are also sometimes visible at the base of the infected needles later in the summer. The fungus survives from year to year in dead shoots, branches, and pine cones. The spores produced in the pycnidia are dispersed in splashing water. They require high humidity to germinate and to infect the host tissue. The fungus also can survive latently in tissue that appears to be healthy.

Mitigation:
Removal of dead branches can improve the appearance of diseased trees but will not prevent infection since many of the spores are produced on cones that remain attached to the tree. Trees with tip blight should be adequately watered and fertilized to maintain tree vigor.
The most important time for chemical management is when the new shoots (candles) are expanding in the spring. Fungicides applied at that time can prevent new disease. Fungicides need to be applied each year to protect new growth. Each year, the first application should be made when new shoots start to elongate, usually around the third week of April. The tree should be sprayed again 10 to 14 days later, and again 10 to 14 days after that if it is a wet year and the site has a history of disease. Spraying after this critical time will not be effective, as the infection has already occurred and cannot be cured.
Complete coverage is essential. A high-pressure sprayer may help in delivering the fungicide to the tops of tall trees. Homeowners should consider using a professional tree-care service, especially for large trees where getting good coverage is difficult. Several active ingredients available for control of tip blight are listed below.
Suggested fungicides include: Propiconazole, Thiophanate-methyl, Mancozeb, Copper, Mancozeb + copper, Thiophanate-methyl + chlorothanlonil

Rip Winkel is the horticulture agent in the Cottonwood Extension District for K-State Research and Extension. You can contact him by email at rwinkel@ksu.edu or call 785-682-9430 or 620-793-1910.

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