Garden Clippings

| October 2005


STATELY PINE TREE: Pine wilt was found in Kansas more than 25 years ago, and it is a growing problem that wreaks havoc on many of our pine trees.

From CAPPER'S photo library

I would bet that a large percentage of CAPPER'S readers lost an American elm in the last several decades, due to Dutch elm disease. There are still some old stalwarts scattered across the country that missed being infected or had a resistance to the disease, but what was once a tree for every garden has pretty much disappeared from the landscape.

Now is the time of year gardeners in the Midwest start to see the devastating effects of a similar problem that is wreaking havoc on many of our pine trees: Pine wilt.

Pine wilt was first found in Kansas more than 25 years ago, but as each year goes by, the problem spreads and larger numbers of pines are lost each year. The malady is severe among the Scotch pine species, but has also shown up in Austrian and White pines.

Like Dutch elm disease, insects spread pine wilt. A bark beetle, called the pine sawyer, infects the pine tree's system with microscopic nematodes, or for lack of a better term, tiny worms that rapidly reproduce. The rapidly growing population actually grows to a point that the organisms block off all of the conductive tissue of the tree, which causes the tree to die quickly.

Since there aren't any chemical measures available to control this problem, it's important to understand the life cycle of the insects involved, in order to do our best to decrease the crisis by cultural methods.

The pine sawyer lays its eggs on the pine trees, and the hatched larvae feed under the bark until they mature into the adult insect. In late spring, the adults emerge and fly off to feed on the shoots of other pines. If the pine sawyer emerges from a nematode-infected pine, the nematode will hitch a ride and enter a new tree via the wound and mouth parts of the sawyer feeding on the tree.

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