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Archive for Sunday, October 28, 2001

Natural needle drop no cause for concern

October 28, 2001

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The cool weather has made a wonderful backdrop for the fantastic fall display of leaves. Bright yellows, oranges and reds remind us that the warm days of summer are quickly fading into the cold days of winter.

Many watchful gardeners are concerned because their green pine trees are following after their deciduous counterparts and dropping yellow needles. For the most part, this is natural needle cast. But there are ways to tell the difference between natural and not-so-natural pine tree problems.

Pine trees are unique in that they do not shed all their needles, as deciduous trees do. They generally hold on to their needles for two and sometimes three years before they are dropped. Every year, needles are produced on the tips of the branches and the older ones, closer to the truck, are discarded.

Typically, needles are dropped in spring and again in the fall. This year, however, the fall drop has been more extreme than in years past. It seems that the trees are dropping all but current season's growth something that is a bit unusual. This could be a sign that the tree is stressed. It's either too wet or too dry, or it may be a delayed response to the drought stress of 2000.

In any case, there is nothing to do at this time to stop the process. Simply rake up the needles and add them to the compost pile.

This natural needle cast is vastly different from three potentially deadly diseases Sphaeropsis tip blight, Dothistroma needle blight and pine wilt nematodes.

Tip blight attacks new growth at the ends of the branches, resulting in needles that are tan to brown and stunted. These needles, which are less than half their original size, never mature.

Needle blight appears as dark spots or purple bands. The needles usually die from the infected point out, resulting in needles that are half green and half brown.

Pine wilt nematodes kill the entire tree, usually all at once. The needles turn uniformly brown and remain on the tree for several weeks before they fall off.

These three deadly diseases do require action. A spring application of a copper-based fungicide will help control the two needle diseases. However, applying the fungicide now will only waste time and money because the fungus is not active.

The only method of stopping the spread of pine wilt nematode is by removing and destroying the dead trees sometime before next spring. Failure to do so will allow the pine sawyer beetle to emerge and contaminate surrounding trees next year.

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