Austrian pines are susceptible to several diseases

 
Posted8/28/2016 7:01 AM

Q. My Austrian pine is turning brown. Why?

A. The Austrian pine (Pinus nigra), an exceptionally hardy and attractive evergreen, is a true landscape favorite. Yet despite the name "evergreen," as pines and other conifers age, their needles become less effective in producing food and become shaded by the growth of newer needles. This causes the older needles to turn yellow, then brown, and to eventually fall off. Austrian pine needles typically last four to eight years, but drought can shorten their life span.

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If younger needles become brown, however, the cause may be disease or insects. Four possible culprits are:

• Diplodia tip blight, a fungal disease of stressed conifers, especially attacks the Austrian pine. Young seedlings and trees 30 years or older are most susceptible. Diplodia generally kills all the current year needles, which die several weeks after infection. If severe, diplodia can result in tree disfigurement or death. The fungus overwinters in pycnidia (fungal fruiting bodies) in infected shoots, bark and seed cones. Tiny spores (conidia) erupt from the pycnidia during the wet weather of spring and early summer, infecting the new needles (candles), which are expanding and susceptible. Starting at the lower half of the tree, the disease spreads upward from the brown needle tips to nearby stems, needles and cones.

• Pine wilt is caused by the pinewood nematode, an insect carried by the pine sawyer beetle from an already infected tree. Nematodes enter a healthy tree via the "feeding wounds" created by the beetle, thus allowing the nematodes to travel into the resin canals of the tree and disrupt its water supply. Symptoms are needles turning gray-green, then yellow, then reddish-brown; death of the tree follows within weeks or months. Laboratory tests are needed to confirm suspected pine wilt.

• Dothistroma is a fungal disease characterized by needles with yellow to tan spots that expand and form dark reddish bands, leaving the bases of the needle green; the tips of the needles die. Severe infection over the years can result in poor tree growth and eventual death. Confirm with laboratory testing.

• Lophodermium needlecast, also a fungal disease, spreads from August to October but only becomes apparent the following spring when last year's needles show brown spots or bands with yellow halos, which enlarge and turn the needles brown. Black fruiting bodies appear in late summer. Laboratory testing can confirm lophodermium.

                                                                                                                                                                                                                       
 

Two precautions: Don't prune in wet weather and keep trees mulched and watered during drought periods.

-- Arlene Swartzman

• Provided by Master Gardeners through the Master Gardener Answer Desk, Friendship Park Conservatory, Des Plaines. Call (847) 298-3502 or email northcookmg@gmail.com.

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