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Pine Saw Fly

Pine Saw Fly

What you’ll see… are pine trees that have been partially defoliated.  The needles will be brown and wilted and appear straw-like, when the larvae are young.  In heavily infested trees you will find that all the old needles are completely missing and only the current year’s needles remain, giving the tree a “pom-pom” look with fluffy tufts of new needles surrounding bare spots.  The sawfly prefers mugo pines, but will also readily attack Scotch pines.

The reason for the problem… is the larvae of the sawfly.  Usually only one generation occurs per year and then over winter as an egg.  The eggs will begin to hatch in April through mid-May and the larvae will feed until mid-June.  The mature larvae are grayish green with light and dark stripes, about ½ to 1 inch long, and look like caterpillars.  The larvae feed in tightly clustered groups, or colonies.  When the larvae are disturbed they will all move in unison raising their heads and tails in a threatening manner.  The larvae will drop to the ground and spin tough cocoons in the debris.  The adults emerge in late August through September to mate and lay eggs.  These eggs can be located after a hard frost turns the egg laying mass yellow.

You should… use some of the following mechanical methods of controls if only a few colonies are present:

  • If the needles containing over-wintered eggs can be found before they hatch, they can be pulled off the plants and destroyed. Do not simply throw on the ground since the eggs can still hatch.
  • Colonies of larvae can be easily removed by clipping off the infested branch. Place these branches in a plastic bag and destroy.
  • Colonies can also be knocked off by sharply striking the infested branch. Crush the larvae or knock into a pail of soapy water.

We can help by…thoroughly inspecting regularly and providing timely service with prudent advice.

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