Landscape - Diplodia Tip Blight in Pines

This time of year, tip blight in some pines is very evident. The following is more information:

Austrian and Mugo pines growing in landscapes are showing the effects of infections by the Diplodia tip blight fungus, Diplodia pinea. The disease is noticeable in landscape pines now. Austrian, Mugo, and Scots pines are often planted in landscapes because of their dense, green foliage and symmetrical shape. When healthy, a grouping of Austrian pines can form an attractive year-round screen. Diplodia tip blight, also known as pine tip blight, or Sphaeropsis tip blight, is a devastating disease worldwide, but especially here on exotic two-needle pines such as Austrian pine (Pinus nigra), Mugo pine (P. mugo) and Scots pine (P. sylvestris) in landscape settings and Christmas tree plantations.

Tip blight symptoms on Austrian pines first appear on the newly elongating candles (shoots) in late April to early May. As its name indicates, the shoot tips are killed very quickly and by late May, the diseased tips are noticeably necrotic and stunted. Needles, even before they are out of the needle sheaths, start to turn a straw brown color and droplets of resin can be seen exuding from these dead needles. Some of the diseased needles may begin to break out of their sheaths, but often their growth is halted resulting in stunted, dead needles. Symptoms on Austrian pines are most characterized as progressing from the shoot tip inward. Over a few days to a week all of the needles on infected candles will turn brown and die and shoots will appear brown through late summer. The candle as a whole will be stunted, necrotic, and eventually brittle from resin exudation. The necrotic shoot and needles can sometimes give these dead tips a gray color.

As the fungus progresses from the tip back towards the trunk, older needles will turn straw color and die. This generally happens later in the year or the following year. Progression of the fungus can lead to branch dieback and eventually death of the tree. These symptoms typically start in lower branches of the tree and progress toward higher branches year after year until the tree dies or is so damaged it needs to be removed. On landscape Austrian pines disease symptoms generally begin to appear after trees reach cone-bearing age, typically 12-13 years old. Close examination of infected shoots will often reveal the presence of tiny black dots (pycnidia) on the base of infected needles. Pycnidia are black fungal structures embedded in and protruding through the host tissue, and in D. pinea are only produced on dead host tissue, such as cone scales and dead needles. Pycnidia are tiny but can be seen with the naked eye, resembling black pepper sprinkled on the dead cones and needles. It is not uncommon to see dead cones and needles from infected trees covered with pycnidia. The pycnidia release spores in warm, rainy spring and summer weather which we have had in abundance this year. These spores are dispersed by rain splash and windblown rain.

Pines are most susceptible to D. pinea infection in spring when shoots are just elongating and not yet lignified. As the fungus colonizes the host, it kills the host cells resulting in necrotic symptoms and sometimes resin production. An additional field symptom, canker disease, also is often accompanied by excess resin. After the fungus has killed the host tissue, it can produce pycnidia which can overwinter and be a source of inoculum the following spring.

Information from "Diplodia Tip Blight Is Causing Dead Shoots on Pines" By John Hartman in the current edition of the Kentucky Pest News. For the full article with pictures go to http://www.uky.edu/Ag/kpn/kpn_09/pn_090825.html#Landscape