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Archive for Thursday, November 3, 2005

Falling pine needles on the increase

November 3, 2005

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The fall is a natural time for change. Green leaves turn to golden hues of yellow, orange and red. Flowers fade to dark green mounds of mush as the killing frost deals the final blow. But pine trees are supposed to be immune to this transition. Normally they stay green and beautiful the entire year. However, recently, many pines are turning brown and dropping needles - something usually reserved for the deciduous trees. Here is what you need to know about falling pine needles and what you can do to stop them:

Evergreen trees are very different from deciduous trees. Deciduous trees drop their leaves every year in the fall. Evergreens do not. They hold on to their needles for three and four years before letting go. This process is called natural needle cast. If the needles closer to the trunk are turning brown, yet the needles on the tips of the branches are still green, the tree is going through natural needle cast. This process does not harm the health of the tree and is normal. Environmental stress may increase the number of needles that fall, but there is nothing you need to do to stop or slow the process. White pine trees seem to be dropping a larger number of needles than normal this fall. White pines have needles that are 3 to 5 inches long, soft to the touch and grouped in bundles of five on the branches.

Natural needle cast is very different from branch dieback. In many cases, I'm seeing all the needles on a branch turn off-color. This is not good. There are two possible reasons why this is happening. In Scots pines, this may be due to pine wilt nematode, a non-controllable fatal disease. Scots pines have needles that are 1 to 4 inches long and are grouped in bundles of two along the branch. Pine wilt is caused by a parasitic nematode that infects the tree throughout the growing season. The only cure is to remove the dead tree and destroy the wood.

The other possible cause is environmental stress. Many times the environment is to blame for a failing tree. Heat and drought in the summer, excessive moisture in the spring and dry, cold conditions last winter all take their toll on locally grown pine trees. Here again, little can be done because the weather cannot be changed.

The final possibility is sphaeropsis tip blight, a fungal disease that attacks the tips of the branches in the spring. The fungus slowly kills the end of branches, causing the needles to be smaller, brown and dead. The disease then slowly works its way down the branch toward the trunk, killing needles as it progresses. The disease primarily attacks Austrian pines but will also get into Ponderosa and Scots. White pines are not normally infected with this disease. The cure for this malady is to have the tree sprayed the third week of April and again 14 days later. Use a copper-based fungicide, such as Bordeaux mixture. Dead branches can be pruned out to improve the overall look of the tree.

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