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It's Alive! It's Alive!

Posted by Richard Hentschel -

Down the Garden Path

Richard Hentschel, Extension Educator

Master Gardeners have been handling the typical questions about gardening in recent weeks, but this week the calls have been about Mugo pines that appear to be alive when you walk by and later noting that the evergreen is disappearing right before your eyes. Every year there is an outbreak of the pine sawfly. European Pine Sawfly is an insignificant looking wasp like insect that is brownish black in color.

Sawfly larvae feed on older needles leaving the current year needles alone. They have a light stripe down the middle of their back, and a light stripe along each side followed by a dark green stripe running parallel down the length of their body. Newly hatched larvae are 1/8" long but measure one inch long when mature. The mature larvae have shiny black heads and are grayish-green. The larvae live and eat together and as a defense mechanism, they will all rise up together making the predator think twice about dining on them and making your Mugo pine"come alive".

Repeated feedings for several years in a row will stress and weaken the pines, making them more susceptible to disease. I have never seen this in the Midwest, yet reports from other parts of the country say that if the larvae run out of older needles, they will eat the current year needles too and that can lead to the death of the plant if this happens repeatedly.

As the name implies this is another of many insects imported into the United States. Mugo Pines seem to be its' favorite food, although it could feed on several other pine species too.

Overwintering eggs along the evergreen needles would typically hatch in May, but this year like so many other things in nature are already hatched and feeding. Once they have fed and reached their mature larval stage, the larvae drop to the ground below the pine where it creates a small brown cocoon. By late summer the adults emerge and mate. Eggs are laid on the needles to overwinter so the whole cycle can begin again. In Northern Illinois, there is only one generation a year.

Once you have sawfly in your yard, it can be there every year, so be sure to scout for it. Managing European Sawfly can be as simple as picking of the larvae is there is a limited number on your plants. If it is a bigger job than that, sawfly's respond to carbaryl, or permethrin based insecticides. If an organic approach is called for, neem oil or spinsad can be applied. Treatments should be done as soon as you see any feeding. One of our favorite biological controls, Bt (Bacillus thurengiensis) is not affective against the European Pine Sawfly.



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